Following on from my November blog post, where I set-out my plans to make a full-size model of a mountain bike girder / linkage suspension fork as well as listing some of the supposed benefits of this design, I’ve been spending a number of long nights in the shed trying to turn my CAD plan into a reality. Well, I've now finished it and thought that I'd present the results of my labour.
To try to help explain how the fork works I have colour coded the drawing below. Those parts shaded blue would be attached to the frame (steerer tube as well as top and bottom fork crowns), those in green are the girders that move with the front wheel, while those in orange are the linkages that control the movement of the green elements relative to the blue elements as well as drive the shock.
After trying to make the fork out of plywood (which kept ‘chipping’ around the pivots) I ended up making it out of MDF. My coping saw skills leave a lot to be desired, but this was never meant to be a thing of beauty. Rather, a practical test of an idea. For that it has been really helpful.
The fork is designed to work specifically with the headtube length of the Full-Moto frame that I will be making in February, but with some relatively simple alterations to the top shock mount and the girders / fork legs the fork can be adjusted relatively easily to fit any frame with a headtube length down to 125mm. Start playing around with the linkages and/or shock length and this could be reduced further. So, this general layout can be made to work with a wide range of frames, but, unlike a more conventional single crown telescopic fork, it will always need to be tailored for a bikes headtube length. There is some wiggle room if you are happy to accept a slightly altered axle path, but I suspect that this is a big reason why this type of fork has not had the commercial success of its telescopic cousins. Essentially, if you wanted one then it would need to be customised (to a greater or lesser extent) to your specific frame.
My fork pivots on four 12mm axles that rotate within eight nylon bushings. It has been made to accommodate a 110mm Boost front hub with a 15mm axle and uses a 28mm diameter wooden dowel as a proxy for a steerer tube (the closest that I could get to a 1-1/8’’ steerer). The nature of a linkage fork means that its offset varies through its travel with a minimum of 38mm and a maximum of 50mm. It has a little over 100mm of travel controlled by a 200 x 51mm RockShox Monarch RT air shock (that I bought second hand).
Just like many single pivot rear suspension layouts, the forks leverage ratio starts off being progressive (rising rate) for around the first two thirds of its travel, before going regressive (falling rate) at the end. Given the inherent tune-ability of an air shocks spring rate and the fact that they naturally ramp up towards the end of their travel I’m fairly confident that the fork and shock can perform happily together after some tuning to give a decent wheel rate.
Although I have no immediate plans to make a fully functioning version of the fork, I’m hoping that the brazing and fabricating skills that I will gain on my frame building course in February will at least make it a possibility. While I’m not aware of any other steel mountain bike full suspension fork, I still think that it can be made to work without being too heavy – think of a Jeff Jones truss fork with some pivots, linkages and a shock thrown in! Alternatively, I could try to find a friendly CNC machinist who can convert my CAD files into shiny pieces of aluminium. Or maybe even try to make the girders out of carbon fibre…
Anyhow, really I just wanted to prove to myself that it could be done and that there wasn't some practical reason (other than the aforementioned adjustments required to accommodate different headtube lengths) why this style of fork hasn't ever really challenged telescopics for sales. Plus it was pretty good fun making it! Let me know what you think.
To recap, I want to build a bike for having a blast in the woods. For relatively short, fast rides primarily along the North Downs and in the Surrey Hills. To achieve this, I want a bike whose limits are easy to approach and fun to reach. So, I’ve come up with a geometry for the frame with this in mind, something that I have discussed in previous blog posts. However, just as important are all of the components that will hang off it, so I thought that I’d explain some of the key choices that I’ve made (so far).
One of the most prominent selections is probably the handlebar. I spent a long time searching for the right one. I knew that my position on the bike would closely resemble that of a Motocross bike, so I was looking for a mountain bike handlebar with a similar shape to that of a Motocross ‘bar. Nothing seemed to fit the bill, and then it dawned on me – stop searching and just use a stock Motocross ‘bar. So, I did the decent thing and ordered a set of Renthal’s!
The next challenge was to workout how to connect the ‘bars to the bike. They have a constant diameter along their entire length of 22.2mm. So, fine for bolting on my shifter and brakes, but slightly less straight-forward when it comes to the stem. While a 22.2mm stem clamp may not sound familiar to many mountain bikers, it’s actually one of a few standard sizes for BMX ‘bars. But I wanted something that was just 35mm in length and I could only find one stem that fitted the bill – a Colony Exon Flatland. (I’ve actually had one on back order since March and it only turned up in November, so it doesn’t even appear to be particularly popular with the BMX crowd!)
Another important item is the fork. I wanted something relatively long to help me achieve the necessary stack height, something torsionally stiff for decent steering precision, but with a bit of fore-and-aft flex for some comfort. As it seems to have been with many of my component choices, the options available to me were pretty limited. I could only find one fork with a tapered steerer tube, 15mm axle and boost spacing, that was at least 480mm long and all for a decent price – an Identiti XCT ticked these boxes.
With the handlebars set much higher than normal there will be much more weight on my backside when seated than on a bike with more traditional geometry. As anyone who has ridden a Dutch-style town bike will know, this means that the Selle Italia Flight Titanium that I wanted so badly for my 1993 Diamondback Apex would probably just slice me in two on this bike. So something with a bit more width and padding is likely to be the order of the day. I’ve got a few options – a Fabric Scoop Radius and a Charge Spoon are both current favourites, but I don’t think I’ll really know what’s going to work until I’ve actually ridden the bike.
Tyres are the other big decision. To help achieve the type of bike that I want these need to provide consistent handling above all else. So, I wanted something with a repetitive tread pattern that extends from one side to the other, rather than something that’s lower profile in the centre with more aggressive shoulders. While this might blunt my straight-line speed and cornering grip respectively, it will hopefully mean a more predictable transition from grip to slip as I lean the bike into a turn. The tyre that I’ve gone for is a WTB Bridger.
The rest of the build will be pretty straight forward. In my opinion, a bicycle should be both elegant and economical. If people want to spend £8,000 on a bike then I won’t stand in their way, but when those new to the world of mountain biking are given the impression that they couldn’t possibly have anything other than a miserable time unless they spend upwards of £2,500 on a bike my heart sinks. So, some of the components will be bits that I have hanging around the shed after two and half decades of riding, together with some new stuff to plug the gaps. It should all be pretty workman like, but that’s no excuse for it looking like a dog’s dinner – who doesn’t love a bit of colour-coordinated anodizing!
I know that I’m getting way ahead of myself here and that it’s incredibly self-obsessed, but I’ve wanted to do this ever since I first thought about making my own bike. Yep, I’ve only gone and had some clothes made with the Davey Push Bikes logo emblazoned across them!
I’d had it all set-up on the printer’s website ages ago, but recently I had an e-mail from them telling me that they were doing some super-duper discount in an attempt to encourage people to place their orders before the Christmas rush. This was all the nudge that I needed. Next thing I know I’ve got a short sleeve and a long sleeve T-shirt, as well as a hoodie, winging their way over to me. This way I figure that I’ve got something to wear on the bike (either T-shirt depending on the weather) and something to throw on afterwards.
Watch this space for the Davey Push Bikes dressing gown and baby grow!
With the exception of a small minority of mountain bike suspension forks (Lauf being an obvious example), nearly everything on sale today relies on telescopic legs to enable the front wheel to travel up and down. But it hasn’t always been this way. One such alternative, known as a Girder Fork in the world of motorbikes, takes its name from the classic structural shape of the girder truss used primarily in bridge or roof construction, which was commonly used to create the fork legs. Back in the 1930s this was a popular choice for motorbike manufacturers, with some still continuing to develop variants of this approach, such as BMW's Duolever arrangement.
When adapted for use with mountain bikes these forks are more commonly referred to as linkage forks, which is probably a more useful description. The most famous example that I’m aware of was seen gracing the front of many Proflex bikes back in the 90’s, going under various names that included Noleen, Girvin and K2. This probably goes a long way to help explain my subsequent fascination with their design, having lusted after them as a teenager. But other examples have been produced by the likes of Amp Research, Look and Leonardi Racing.
Linkage forks have come in various different arrangements over the years. Some have both linkages below the head tube and the shock mounted somewhere between them (such as the Amp Research fork). While this arrangement improves frame compatibility (as the fork isn’t limited to a minimum headtube length), this layout generally has to rely on pretty high shock leverage ratios to achieve anything approaching a useful amount of travel on a mountain bike. However, forks like the Leonardi Racing Alike partly get around this by placing the shock above the linkages. Even so, having both upper and lower linkages below the head tube also limits the forks structural efficiency. For this reason, designs like those found gracing Proflexes all those years ago have the potential to be much stiffer (stiffer even than conventional, single crown telescopic suspension forks) by being supported both below and above the headtube.
Furthermore, linkage forks can be designed in such a way that dive under breaking is significantly reduced, enabling them to use their travel far more efficiently. This has further benefits, such as reducing the need for as much low speed compression damping, enhancing the forks potential sensitivity. Linkage forks also side step the issue of binding, something that becomes increasingly important for telescopic forks as head angles get slacker. This occurs when the entire fork tends to flex along its length rather compress due to friction between the forks lower and upper stanchions.
It is because a linkage fork pivots on bearings that they can be designed to be much more sensitive than a telescopic fork. As a slight segue, my perception is that most mountain bikers who have an opinion on the matter, would always view cartridge bearings as superior to bushings, regardless of the application on their bike. Somehow, cartridge bearings have simply become known as ‘the best’ with bushings normally thought of as something seen on cheaper bikes. But this over-simplifies the situation. While cartridge bearings have a number of positive attributes, these tend to only apply when they spin through full rotations, something that, for example, rear suspension pivots just don’t do. Instead, some rear suspension pivots would be lucky to rotate through just a handful of degrees under normal operation. It is not uncommon for the balls within a cartridge bearing to slide momentarily before they start to rotate within their races. In something like a hub this isn’t an issue, but in a rear suspension pivot these balls may never do anything other than slide backwards and forwards. Not only will this result in the balls ending up with flattened surfaces resulting in premature wear, they also introduce undue friction making suspension less sensitive. Bushings avoid these issues, but the mountain bikers blind lust for cartridge bearings seems unassailable.
Anyhow, given that I’m building my own frame in the New Year, I thought that it might be fun to see if I could design a linkage fork to fit it. Now, this is just me humouring myself at this stage – the bike will be fully rigid, but I like to have something to play around with in my head. I’ve designed the fork around a standard rear shock (200 x 51mm) to produce just over 100mm of travel. The drawing below illustrates what it might look like. My plan is to utilise the long, damp autumn evenings to build a full-size mock-up of the fork out of wood to see if it will actually fit the bike and cycle through its travel in reality. It’ll be pretty rough, but enough to hopefully prove that the idea is viable. Fingers crossed I’ll have something tangible to show for my efforts in the not-too-distant future.
Plans for my new bike, which I will be building early in the New Year
Early next year I'm going to build my dream mountain bike frame and it's time for me to start making some tough decisions about the specification. Whatever it ends up looking like, my number one goal is to build a bicycle that maximises my fun in the woods. The bike must give me the confidence to attack a trail and get loose, to be engaging and involving. To achieve this I believe that a bike must do two fundamental things: it must place the rider in a stable position, enabling them to maintain balance while descending; and it must give the rider the best chance of controlling the bike. Both sound pretty obvious, but I believe that these two attributes are compromised on many modern bikes. Firstly, I shall try to explain why before describing what this all means for the bike I will be building.
If the rider is struggling simply to maintain their balance on the bike or their control of its direction and speed then a rider cannot actively and purposefully push the limits, and it is when you can approach these limits with confidence that the fun really starts. This is not a binary situation – it is not simply a case of a bike providing its rider with stability and control or not. Rather, it is a sliding scale, with every combination of bike, rider and trail sitting somewhere along its length. However, I feel that I have always struggled to sufficiently achieve these two things with my previous bikes.
Fortunately, both rider stability and control are achieved in similar ways. Stability is achieved when a rider can maintain their balance despite external forces doing their best to disrupt them (such as those generated by riding a technical trail at speed). This has the best chance of happening when a rider is supporting all of their weight through their legs in what is known as an Athletic Stance (please see my previous Blog post for more on this).
For best control, a riders hands must be uncorrupted by the donkey work of having to support any significant proportion of their body weight, with the exception of the odd minor adjustment, leaving them free to focus on the relatively delicate job of steering and braking. So, both good stability and good control start when a rider is able to support their weight fully through their legs rather than also having to rely on their arms.
Importantly, this doesn’t mean that a bike that places a rider in a relatively unstable position cannot be ridden impressively quickly. I have a friend whose mountain bike has a 110mm stem, holding a ‘bar with no rise that’s slammed to the headset, about 150mm lower than his saddle. His bike handling skills are so good that he can compensate for the fact that, on pretty much any downhill, a large part of his effort will be given over to trying to maintain his balance on the bike. I’d love to see what he could do if he were freed from the need to constantly stop himself from falling over the ‘bars. If you need proof of the speed that can be achieved by a good rider, despite riding a bike that lacks inherent stability and control when ridden off-road, then just watch the business end of cyclocross race. What those riders can do is often mind-blowing.
Something that is often overlooked or confused is the difference between a stable bike and a stable rider. What the bulk of the mountain bike industry has been doing for the last few years (and probably longer) is creating ever more stable bikes at the expense of rider stability. Longer wheelbases have been achieved, at least in part, by steeper seat tube angles and a longer reach to the 'bars. This tips the rider forwards, requiring their hands to support an ever-increasing proportion of their body weight more of the time. The resulting shift in weight distribution towards the front of the bike also relies increasingly on the front suspension to absorb feedback from the trail in order for the rider to maintain sufficient levels of control. This has created bikes that can now steam-roller through some pretty rough stuff, meaning that bikes have got faster (good for racing and marketing departments), but also less involving. Essentially, so long as you can hold on to the thing, a modern mountain bike should get you to the bottom of a hill in record time. But the trade-off has been that a good deal of the fun, flow and finesse that comes from skilfully piloting a bike down a trail has been lost.
Interestingly, this runs counter to the geometry of a Motocross bike where, despite around 300mm of front suspension travel, the riders body position is more upright and centred over their feet with the fork doing less, relatively speaking, to isolate the rider. If anything, the closest that mountain bikes have ever got to placing a rider in a similar, stable position were the original Klunkers, repurposed from Schwinn beach cruisers in the 1970s.
Based on the thinking described above and covered in my previous Blog posts, the following is an explanation of how I have arrived at the geometry that I will adopt for the frame that I will be building in the New Year.
As a starting point, I suspect that a rider’s hands should be placed no lower than their hips if they want to have good stability and control while riding off-road on challenging terrain (a position that I have always struggled to achieve with stock frames). If a rider's hands get much lower than this, then these hands will have to start regularly supporting a significant amount of the rider's body weight. Because of my particularly long legs it just-so-happens that, for me, this results in a handlebar stack height that is the same as many Motocross bikes. It then seems reasonable to also look to Motocross bikes for the reach measurement. This then fixes my standing position on the bike, one which places me in a far more upright position than a standard mountain bike with my weight supported fully through my legs.
Having fixed the reach and stack measurements, I have simply used a seat tube angle that results in a stretch to the ‘bars when seated that is slightly shorter than my current mountain bike. My thinking is that a more upright riding position won’t require the same stretch to the ‘bars as something where your hands are lower and therefore required to support much more of your body weight more of the time. Rather reassuringly, this seat tube angle also happens to be similar to that used on the original Klunkers.
I’ve chosen a relatively slack head angle based, pretty much entirely, on my own experience, having had mountain bikes with everything from 64 to 70 degrees. I have tried to balance the need to keep things stable, helping to get my hands more ‘behind’ than ‘on-top-of’ the front wheel, whilst retaining some agility. This, combined with the rest of the frame geometry described above, gives me the bikes front-centre.
The chainstay length has been derived as a proportion of the overall wheelbase. Again, I have looked to the world of Motocross, adopting a rear-centre measurement that is the same proportion of the front-centre measurement as a Motocross bike. This should then provide a similar weight distribution. If you ask me, the marketing departments of the big mountain bike manufacturers have done a fantastic job of convincing us all that we need the same, short chainstays regardless of rider height. Quite why someone who is 5’ tall should be riding around with the same chainstay length as someone who is 6’6’’ is beyond me. The front centres on these two bikes will be massively different and so the weight distribution will also be completely different. Bonkers. But I digress.
For the sort of trails that I ride (primarily the Surrey Hills, Swinley Forest and the odd Welsh trail centre) I believe that a bike that provides me with good stability and control can be created without the need for suspension so long as the geometry is right. I’ve chosen 27.5+ wheels as the plus-sized tyres will provide some extra comfort over standard ones (important given the lack of suspension). And while they might still be lacking in this department when compared to 29+ wheels, I think that this is a worthwhile trade-off for the extra zip that they should bring. After all, this is a bike built for fun rather than mile munching. This is complimented by a relatively large bottom bracket drop that will keep the handling nimble at the expense of some ground clearance. But without the need to account for suspension travel constantly changing the effective bottom bracket height, this should be easier to accommodate.
A comparison of modern bike geometry (black - my XL Last Fast Forward) against my new bike (grey)
My current mountain bike is an extra-large Last Fast Forward 29er hardtail, with geometry numbers that are pretty typical of many modern mountain bikes (the black silhouette above). With a seat tube angle of 73.8 degrees and a reach of 475mm the rider is pushed further forwards than on bikes with more traditional geometry, increasing the frequency with which the rider will have to support their weight through their hands. As I've already discussed, while this might reduce the stability of the rider, it increases the stability of the bike as a result of a lengthened wheelbase (particularly when combined with this bikes slack, 64 degree head angle). But while outright speed may be easier to achieve with modern bike geometry, the confidence of the rider to control the bike from a stable body position will be diminished. So, I may not be setting any land speed records on my new bike (the grey silhouette above), but the inherent stability that the bikes geometry should give the rider (by enabling them to support more of their weight through their feet more of the time) should provide the confidence to really attack a trail and therefore have more fun.
The image at the beginning of this post has been pulled, poked and tweaked for more than a year, and is my current best guess at what the finished bike will look like. This will be an experiment in trying to build a bike that handles in a way that I have always wanted, but never found. Time will tell whether I am right or not. As always, I’d love to know what you think.
I may not play a lot of tennis, but the same theory applies - an Athletic Stance ensures great balance and stability
When riding a mountain bike fast downhill what is required, ultimately, is control. As the alternative – being out of control – is often quite painful. It is only once you have control that you can have the confidence to start playing with its limits, which tends to be where the fun really begins! This control is achieved when a rider has both balance and stability.
Although in casual conversation these two terms may be used relatively interchangeably, they actually have quite specific meanings. Balance refers to a person’s ability to remain in a steady state. While stability refers to the ability to maintain balance in the face of external forces. I find that the best way to understand this nuance is with an example where a person is displaying great balance, but not necessarily great stability, such as a person pulling a wheelie. In this example, the rider may be expertly managing the effects of accelerating, braking and gravity to maintain a state of equilibrium in order to remain on their rear wheel, but an external disturbance, such as rough terrain, is likely to destabilise this situation. So, someone pulling a wheelie could be described as displaying good balanced but, potentially, poor stability.
Athletic Stance is a term used to describe the position a person adopts whilst playing a sport – normally the starting position before accelerating or whilst waiting to react to an external factor (to hit or catch a ball, for example). For whatever reason, it tends to be a term more commonly used in America, with little traction here in the UK, but people adopt an Athletic Stance in sports that are played all over the globe. The stance can vary depending on what sport is being played, but a tennis player waiting to receive a serve, a cricket player preparing to catch a ball, a golfer about to tee-off or a weight-lifter preparing to snatch are all examples. It is a position that allows a person to maximise their strength, power or speed in any given direction. This is because an Athletic Stance begins with great inherent balance and stability.
Riding a bike off-road should be no different. If you are out of the saddle attacking a challenging trail then you need to adopt an effective Athletic Stance to enable you to react to the terrain. Where cycling differs from other sports is in the placement of the feet (which in cycling are governed by the pedals, while in other sports they tend to be placed slightly wider apart than the shoulders) and the placement of the hands (which are holding a handlebar rather than preparing to catch, block, hold a racket, etc.) However, like the examples given for other sports, all of a rider’s weight should be supported through their feet (as discussed in my previous two Blog posts).
Therefore, I believe that a good starting point for establishing the correct relationship between a bikes bottom bracket and the handlebars for a given rider is simply to ask them to adopt an Athletic Stance whilst holding their handlebar (no bike required!). It’s actually quite surprising how repeatable this position is. One advantage of adopting this position without the use of an actual bike (just the handlebars) is that it guarantees that there is no body weight being supported through the hands – lean forwards and you will simply topple over! Once the relationship between the bottom bracket and the handlebars has been established, all that remains is to decide upon the correct seat tube angle to provide sufficient length for a comfortable position whilst pedalling seated. A bike frame designed in this way should ensure that the rider is placed in the correct Athletic Stance whilst standing on the pedals, resulting in inherent balance and stability.
I’ll be using the approach described above to help confirm the geometry of my new bike that I will be building early in the New Year. Between now and then I’ll be deciding on the rest of the frame geometry and selecting all of the components that will hang off it. I’ll also be writing about the whole process here in the Blog. As always, I’d love to know what you think.
Your feet are fantastic at supporting your body weight and maintaining balance. While your hands excel at complex tasks that require a delicate touch. This is what they both do day-in, day-out and, respectively, they have evolved to become quite specialised. They certainly aren’t interchangeable. If you need further proof then try walking around on your hands while peeling a banana with your feet. You get the idea. But mountain bike manufacturers often seem to forget this.
If you’ve ever tried riding with as much of your weight supported through your arms as possible (perhaps whilst bored waiting for friends to put their bikes together at a trail centre car park or, more commonly for me, while trying to coax a bike home when it has a slow puncture in the rear tyre) then you will know how little finesse you have over steering inputs when in this position. The way that weight is distributed between your hands and your feet is critical to the level of control you have over a bicycle.
It helps me to use the following car-analogy when thinking about weight distribution on a bicycle… A front wheel drive car is asking these wheels to do a lot. The rear wheels are only really present to keep the back of the car off the ground. The steering and acceleration (and the majority of the braking) are all being done by the front wheels. Often this can mean that they become overloaded and start to spin or slide if driven hard with torque-steer being the bane of many high-powered front-wheel drive cars. Conversely, a rear wheel drive car is spreading the jobs around. The rear wheels are asked to cope with the tough but relatively simple job of driving the car forwards, while the front wheels are left to provide the more subtle but complex job of adjusting the cars direction. Each pair of wheels can be designed to do a specific job very well, much like the way our hands and feet have evolved.
So, a rear wheel drive car is similar to a rider in a neutral, balanced and stable position, with their weight supported through their feet. Their hands can focus on the steering, uncorrupted by the donkey work of supporting their body weight, other than for a little fine tuning. While a rider lent forwards with a significant amount of their weight being supported through their hands is like a front wheel drive car, trying to cope with both the manual labour of supporting their body weight whilst at the same time trying to execute the delicate job of picking the desired line.
Because of the above, it is my opinion that the position of your contact points, and therefore the shape of your bike frame, should be defined by the need to maintain a neutral, balanced and stable body position whilst allowing for your limbs to properly suspend your core. Just like any good suspension system, you want to start with your arms and legs part-way through their range of movement as having them slightly bent whilst riding provides far greater stability. This is something that most public transport commuters are all too aware of. Try to stand on a bus or train with your legs locked out straight and you will spend the journey shuffling around and bumping into people in order to stop yourself from falling over. However, bend your legs slightly and it becomes far easier to absorb these external forces, isolating your bodies core and keeping it stable.
Translating this to the bike, the most obvious scenario is when riding over something such as a rock or root, in which case you will want your limbs to compress to isolate your body from the impact. But equally, if your front wheel drops into a dip or off a ledge then you need your limbs to extend to maintain stability. A common problem is to see a rider knowingly approach a drop-off with their arms fully extended to allow them to get their weight as far back as they can based on the assumption that this will reduce their likelihood of being thrown over the handlebars. But at this point your arms will have lost any ability to react to the bike dropping away from you and therefore the ability to maintain a stable core. If anything, you will be more likely to topple over the front of the bike in this position as the handlebars will pull you forwards as the front end of the bike drops away. Partly, this situation is the result of poor technique, but often it is also because the geometry of so many bikes places too much of a riders weight on their hands and many of these riders, quite understandably, attempt to counteract this.
In many instances riders are having to reach forwards and down too much. This is particularly true for taller riders as most bike manufactures fail to increase their frames’ stack heights in proportion to either their reach or likely saddle height. Trek, for example, maintain exactly the same stack height across four different frame sizes on their 2017 Fuel EX, supposedly covering everyone from 5’1’’ (155cm) to 6’4’’ (193cm). The lines in the graph below should be horizontal if bike manufacturers increased a frames stack height in proportion to its reach. Instead, for all of these bikes the taller you are, the more you are expected to reach down to meet your handlebars.
Stack:Reach ratios across a range of frame sizes for some popular mountain bikes
My view is that current mountain bike geometry tends to place the handlebars too low and too far forwards relative to the bottom bracket, requiring riders to support a significant proportion of their body weight through their hands, reducing the ability to steer accurately or maintain a stable body position. Something that seems to only get worse as riders get taller. It’s time for a change! So, next month I’ll be suggesting what I believe to be the correct relationship between your bottom bracket and your handlebars to ensure that all of you weight is supported through your feet, leaving your hands to focus on steering and braking.
Two separate things have conspired to make me question the modern mountain bike: my slightly odd physical proportions and a nagging sense that bike geometry took a wrong turn sometime in the late 80s.
I have mentioned elsewhere that I have long legs relative to my height. At a little over 6 foot (184cm) I have the legs of someone closer to 6’ 4’’ (192cm). This means that I have a rather lofty saddle height of just over 32’’ (82cm). One of the practical ramifications of being at the extremity of the physical-proportions bell curve is that I have always struggled to achieve a comfortable handlebar height. This is compounded by my poor circulation (probably linked to my lanky limbs) that tends to leave me with numb hands if my handlebars are too low. Therefore, I’ve probably spent far more time thinking about my handlebars than most people.
Coupled with the above is a concern that mountain bike geometry, after a promising start, quickly looked to road bikes for inspiration. And despite subsequent refinements, I suspect that it has been constrained by this fundamental decision ever since. Essentially, it would appear that the mountain bike has charted the following evolutionary path:
So, after a strong start using bikes that just-so-happened to have pretty good geometry for having a laugh in the woods, we seemed to quickly replace these with bikes designed to excel at something that only a relatively small number of people have ever been interested in doing. The intervening years seem to have been spent trying to make comparatively superficial changes to overcome the inherent limitations of a bike designed for XC racing. There’s been plenty of other developments, like rear suspension, 29er’s and disc brakes, but I don’t believe that they are fundamental to this particular discussion. Essentially, I believe that we started with something fun, decided to junk that and instead created something for turning ourselves inside out and have been trying to fix the problem ever since. I would suggest that it might be worth pausing for a moment so that we might look out of the hole that we’ve been busy digging?
As I’ve pointed out before, the likes of Honda, Yamaha, KTM, et al. have far more money to invest in the development of their Motocross bikes than any mountain bike company does in the development of their own products. So maybe we should look over the fence at what they are doing? After all, they like to ride around in the mud just as much as we do, they just can’t be bothered to pedal. Fundamentally then, where does a Motocross bike place the riders contact points relative to the wheel axles and how does this differ from a MTB? Does a Motocross bike tip the rider forwards on to their hands and let the front suspension disguise the inherent issues with the resulting weight distribution as we appear to be doing in the world of mountain bikes?
The first thing to note about a Motocross bike is that its geometry is nothing like that of a road racing motorbike (see my previous blog, Assume the Position). The reach to the handlebars is only around 420mm while the stack height registers a mountainous 800mm or more. This gets the riders weight back and off their hands, despite having a fork with around a foot (300mm) of travel. The resulting position is a long way from that dictated by many current mountain bikes, with a seat angle of about 75 degrees and a handlebar height somewhere around the 660mm mark, a MTB rider is essentially preparing to do a forwards-roll by comparison.
Ah, but what about pedalling efficiency I hear you cry! Well firstly let’s be honest about why we ride mountain bikes. If you’re primarily interested in trying to claim every Strava KOM within a 20 mile radius of your house on you sub-20lb bike then this discussion probably isn’t for you. Stick with the bikes that have geometry perfected in the late 80’s and feel the burn – the best tool for the job is likely to be the equivalent of a road bike with knobbly tyres anyway. For everyone else I believe that there is real merit in finding out where the limits lie in terms of handlebar stack and reach.
This is where my genetic oddity comes into its own (like the worst X-Men ever). I suspect that for the vast majority of people, a handlebar height of 800mm will be too much once you’ve factored in that your pedals will, at some point, be around 170mm lower than the bottom bracket (resulting in a maximum vertical distance from the handlebars to pedals of almost a metre). However, as I’ve already mentioned, my saddle height is 82cm. Admittedly, this isn’t a vertical measurement, but even so, an 800mm stack height to the handlebars suddenly starts to seem quite reasonable.
This means that I can build a frame that puts me in exactly the same position as a Motocross bike safe in the knowledge that, for me at least, it won’t be completely beyond the realms of what is sensible. To borrow a saying from snooker, it would be a shot to nothing (for those not gifted in the ways of the green baize, this just means that I can give it a go without really risking anything). Then all I need to do is line up all of my mates in height order, ask them to throw the bike down some singletrack and find out at which point the inescapable magic starts to wear off! Simple.
Over the next couple of months I want to explore the fundamentals of achieving a good position on a bike – one that provides stability and control for the rider. As it is only once you have these that I believe you can then start to have fun playing with the bike on the limit.
When I got my first ‘proper’ job after graduating University there was a senior colleague who sort of became my Yoda. He wasn’t my boss, but he is someone of huge talent and integrity who, in hindsight, I probably pestered so much that it was easier for him to humour me than try to avoid me! We used to discuss all sorts of things, mainly work related, but plenty of other stuff as well. One such conversation got on to the subject of quality-of-life and a discussion about the things that we really value. He suggested that all we really have is time – it is the ultimate currency – and it is up to each of us to choose what we do with it. You can earn money, learn something new, watch your children grow up, spend time with friends, rest and recuperate or whatever else you fancy. But we only have so much time and so it’s probably best not to squander it. It was one of those conversations that sticks with you.
So, I was wondering the other day “Where does the humble bicycle fit into this?” Does riding my bike justify itself as a worthy use of my precious time? I suppose that there is the obvious stuff. I ride my bike to work, which saves me a chunk of money relative to owning a car or buying a train ticket (so I don’t need to spend so much time earning it or can spend it in other stuff). It keeps me fit, which, in the short term, makes me happier and healthier and, in the long term, actually provides me with a bit more of that ultimate currency if I’m lucky. And in its own small way, it helps everyone else out a bit by reducing pollution and congestion. All-in-all, probably not a bad way to spend my time?
But what about the really frivolous stuff – a quick blast along the North Downs after work or a weekend away to a Welsh trail centre? The indulgent, selfish sort of riding that’s just for cheap thrills rather than saving the planet or my bank balance. Does this stack-up in the ultimate cost-benefit calculation? For me it comes down to two different benefits that are almost polar opposites.
The first is time to think. This is especially true of a solo road ride, but is actually just as relevant to the mountain bike. While I would love to live at the epicentre of miles of exhilarating singletrack, the truth is that every ride from my house includes a bit of fire road climbing, some rather bland bridleways and a road connection or two. At first glance this may seem rather mundane, but over the years I’ve found that I do some of my best thinking whilst riding these sections. Mulling over ideas that haven’t fully fermented, making connections between seemingly unconnected topics, or working through a solution to a tricky problem. I suppose I’ve never really understood how some people can just drift off, clear their mind or meditate – I just don’t seem to be that way. I’m often most happy and excited when I’m on the cusp of fitting all the pieces together. And more often than not, this happens on the bike.
The second big reason for spending time on the bike is the chance to find that magic flow. Apparently, there is a point at which the cognitive load associated with an activity is just enough to fully engage you in the task at hand without overloading the senses. Where you immerse yourself in the here and now, fully focused. Not really thinking, but just doing. It’s these moments on the bike that I live for. For me it’s the combination of a flowing piece of singletrack combined with just enough bike to perfectly challenge your skills and fitness. And this little formula can have a very narrow window of operation. A few weeks off the bike can dull the fitness and skill levels or a few days of rain can slow the trails just enough to turn one week’s perfect ride into the next week’s inelegant staccato. And it’s this illusive nature that makes it all the more special when it does all fall into place.
So, on the one hand my mountain bike provides me with the opportunity to lose myself in my thoughts and on the other it becomes all consuming. Either way it is incredibly restorative and, for me at least, a very worthwhile use of my precious time. I hope that you’re using yours wisely!