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Fine-tuning bike feel

| Buyers Guides, What Mountain Bike | 23/07/2010 09:15am

The properties and material structures of a bike’s frame and component parts play a far bigger role than many riders imagine in influencing ride feel.

From frame materials and tubing configurations to characteristics determined by tyre tread compounds, wheel build, fork stanchion/slider overlap, handlebar grip touch, suspension damping control, crank length and beyond, the finer points in a bike’s design and assembly can be just as crucial in dictating ride feel as the geometry itself.

Think of your frame, fork, wheels and tyres as a rolling chassis. It obviously takes a few more parts than that to get a bike up and running, but it’s the rolling chassis that dictates the main characteristics in the rolling feel of the bike. Obviously, the priorities and characteristics of ‘feel’ change radically as you add more suspension to a chassis.

First, a thought for those who shun suspension: every bike has suspension, and you need it. Air-filled tyres are suspension. First, choose your tyre size, then add or take away air depending on how much absorption of shock you want – just like other forms of suspension, really. Tyres with big air chambers run at about 40psi will compress by an inch or so over rocks and roots and, while an inch won’t affect geometry enough to radically change a bike’s handling, it will certainly affect feel. A rigid bike with skinny tyres pumped hard to avoid pinch punctures will roll faster over easy terrain, but the fact that it’s less comfy and harder to control over rough ground could make it slower overall than a rigid bike with fat tyres.

The character of a frame’s tubing material will make its presence felt in the ride of a rigid forked bike more than a bike with suspension. Everyone used to talk about the feel of steel. Well, it’s true – quality steel and titanium frames do have a certain zing to them that’s often missing in alu frames, and even alu frames vary a hell of a lot depending on thickness, shapes and qualities of tubes.

Tyre size and pressure is more relevant in shock absorption terms than frame material, but quality steel or titanium tubes noticeably make your chassis feel a little more sprightly, which is worthwhile if you ride a rigid fork and a minor plus if you ride a short travel suspension fork. A steel hardtail frame will weigh, on average, about a pound more than its alu performance counterpart. To put this into context, an average rigid fork weighs about two pounds less than an average suspension fork, but rigid forks need more skill and finesse to ride hard, fast and in control over rough terrain. In terms of feel, it’s a little like comparing hard skinny tyres with slightly softer bigger tyres – there are pros and cons either way.

In terms of feel, hardtail frames with suspension forks are constantly changing entities. The changes are dictated by what’s in the fork and by how it’s set up. The more suspension travel a fork offers, the more it’ll change the way the bike feels over different types of terrain. Obviously, the geometry changes as the fork compresses, but the main feel issue is how you tune the internals of your fork, assuming that they’re tunable – many budget forks are factory-set.

We won’t go into the fine points of suspension tuning here. It’s too big a subject. The main thing is to get compression and rebound damping feeling right. The way suspension works is a function of how strong the fork’s spring is (with an air fork, that means how much air is in it) and how the internal valves controlling the oil and/or air flow are set. On a quality fork, damping can be tuned by external knobs/dials. Compression damping controls how fast a fork compresses, while rebound damping controls how fast it rebounds. Bikes with well set up forks feel vastly superior to bikes with badly set up ones, and too much uncontrolled spring power on the rebound is as hard to control over the bumps as a rigid fork.

The more fork travel you have – within the geometric limits of the frame – the more you can sit forward on the bike over bumpy terrain and really work the fork. This effectively takes pressure off the back end of the bike, too. If you’re sitting forward, the back wheel follows through without being punished by your weight sitting right on top of it.

Shock and roll!
Everything we’ve said so far about suspension adjustment on forks applies to rear suspension too. A badly set up rear shock will detract considerably from the ride feel of a bike, while a well set up shock will considerably improve the ride. Maintenance – obviously an issue with forks – is an even bigger issue on a rear suspension chassis. As a rule, single-pivot frames involve less maintenance than linkage ones. But, whatever you ride, the main thing is to keep a check on all the bearings and bushings. If there’s any hint of ‘play’, replace the relevant bearing/bushings before the play produces major wear problems, either at that point or somewhere else.

As with suspension forks, we don’t have the space here to go into the fine-tuning aspects of all the different rear suspension systems or shocks. The main thing beyond common sense maintenance is to keep the front and rear shocks feeling well balanced. This has nothing to do with matching travel. It’s about setting up the fork and rear shock so that big and small bump responses don’t unduly mess up the ride feel of the bike and your body balance on it. For example, you don’t want to be sat so far back on the bike that a too-soft rear shock is doing all the work while an over-sprung fork is hardly compressing, or vice versa.

Finally, it’s probably worth stating the obvious here. Suspension will usually work at its best on a chassis that’s not flexing, twisting or fluttering under heavy braking. A stiff aluminium structure will usually perform best, with the ‘feel’ of the bike coming from the designs of the frame, shocks, wheels and tyres rather than coming from the materials. Obviously, you’ll still want to keep the weight sensible for the intended purpose, but there’s little point in making a full suspension frame that focuses on the ‘feel’ of steel, titanium or carbon unless the suspension travel is absolutely minimal, like on short travel soft tails. In all other cases, the formability and stiffness of alu is by far the best solution.

Componentry feel
The feel of componentry is dictated by an impossible-to-simplify blend of shape, weight, structure and materials. To complicate matters further, all these factors co-relate in different ways according to body shape, weight, structure, and materials. Think different size limbs, different muscle structures, different fat mass, different riding preferences and different attitudes.

The main thing to understand is that not all bike parts are created equal. A 24in carbon handlebar with soft compound grips will feel very different to a 24in aluminium handlebar with hard compound grips. It’s up to you to work out whether you want to pay a lot of extra cash for a bit of extra ‘give’ in the carbon bar and soft grips. If you’re on a budget, an alu bar with the soft grips would seem sensible. The point is to think carefully about what your priorities are.

The less chassis suspension you have, the more you should think about how to make a bike comfy and controllable in other ways. Tyres are the obvious focal point. As well as air chamber size, and how much air you choose to put in it, tread patterns and tread compounds will play a major role in how your bike feels.

As a rule, the round edged and/or shallower tread patterns (Hutchinson Pythons are a good example) feel faster and more predictable in terms of bike balance and steering feel, but their trail bite is a lot less aggressive than deeper knobbed and/or squarer-edged treads. Squarer-edged treads bite into the ground more aggressively when you’re cornering, but they also tend to be a bit slower in straight lines and less stable, because those big block edges are grabbing traction and affecting steering feel on every earthy edge that presents itself. Think about the sort of conditions you ride in and how much comfort and speed you want.

Saddles and seat posts can also have a major bearing on the feel of your bike. The bounciest saddles are rarely the comfiest, and all bums are shaped differently anyway. Experiment with saddle shapes and padding, but note that big plush saddles often become less comfy as a ride gets longer. Skinny saddles with generous surface padding are often the best compromise. Consider a suspension seat post, too. The decent telescopic ones add a little comfort, but it’s the longer travel parallel-linkage action of the Cane Creek Thudbuster that makes the biggest feel difference overall.

Weight for it
As with our own bodies, what actually matters in terms of performance is getting the right power-to-weight ratio balance. To put it simply, too much ‘dead weight’ means things get inefficient, too little ‘live weight’ means things get flimsy. A common sense approach – plus some trust in marketing descriptions of products – will usually guide you in deciding whether bulk and strength built into a product is overkill or just right for the sort of riding you do.

Feel-wise, more weight will usually make a bike go slower unless you’re going downhill, but it’s the weight at the spinning edges of wheels that make the biggest difference, slowing acceleration noticeably more than weight in a frame or other components. Lightweight tubeless tyres on lightweight rims will make an enormous feel difference to a bike. As always though, weigh up the pros and cons of lighter and flimsier versus heavier and stronger. If you ride with finesse and/or big tyres and lots of suspension, the lightweight parts on your bike are better protected than they would be if you rode clumsily and/or with skinny tyres and very little suspension. WMB

Trial and error tips
You’re fully entitled to experiment if your bike doesn’t feel comfortable…
A new bike, or someone else’s bike, often feels wrong simply because you’re so used to another one. Remember that it could be the bike you’re used to that’s wrong, as given time, you’ll get used to anything – so persevere for a while before you change anything major on a new bike.

Don’t automatically expect a bike that’s theoretically the right size to be right in every other way. Two riders of the same height are likely to have different length legs, arms and torsos. Even two riders of similar weight can have completely different weight distribution and this will definitely affect bike feel. Think about it. Skinny legs on a big upper body might demand a different bike set-up to big muscle-bound legs on a skinny upper body.

Tiny differences in componentry can make big differences in feel and ride confidence. Most MTB cranks are 175mm long, but if you’re 5ft 7in or less you’d probably be better off with 170mm ones. Think about all the bits on the bike that can be adjusted. Brake and gear levers can be swivelled on the bars or moved further inboard. Brake lever reach can be altered, handlebars can be swivelled to make a different wrist angle and stems can be raised or lowered. Different setting will suit different riders, so experiment. Try different tyre pressures from time to time and don’t get stuck in a rut as there are lots of different ways of tuning feel.

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This entry was posted on Friday, July 23rd, 2010 at 9:15 am and is filed under Buyers Guides, What Mountain Bike. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.

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