Technique: Perfect mountain bike fit
By Steve Worland, What Mountain Bike | Friday, March 18, 2011 1.00pm
Getting a bike to ﬁt you perfectly is something you need to work at. We know riders who’ve ridden for years on what they thought was their perfect bike, with perfect reach, perfect saddle height, perfect handlebar shape, a perfectly set up fork and perfectly inﬂated tyres.
Then circumstances put a ﬂy in the ointment and they discover that a basic change, perhaps even a few basic changes, to that setup seems to make them ride better. It'll often be something as simple as a different handlebar sweep, different tyre pressures or more suspension fork sag. It’s often minor details of bike setup that change the way you ride, and feel about, your bike.
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Tweak your ride setup from time to time, then give yourself a few rides to decide whether you like it or not. There are some things that feel wrong when you ﬁrst change them, but feel right after a few rides. In the following article we’ll lay down the basic guidelines of bike ﬁt, together with variations to consider and the reasoning behind them. Don’t think of bike ﬁt and setup as something that’s carved in stone. Use our guidelines as a starting point, then go out and experiment...
This images below show the key areas that should be adjusted for you to achieve optimum bike ﬁt. The first image shows the incorrect position, while the second image shows how the bike components should be positioned. Good bike position results in relaxed shoulders and slightly bent elbows
Arms: Good bike position results in relaxed shoulders and slightly bent elbows.
Saddle: Correct saddle position is essential for balance, control and pedalling efﬁciency.
Knees: Having very slightly bent knees at the bottom of each pedal stroke is perfect.
Frame: Getting the correct frame size is essential, but it’s only a starting point for perfect bike setup.
Shifters and brake levers: Don’t just leave them in one position. Experiment with setting them further in on the bars or tilting them.
Although everyone is different – some folks may have longer legs but a shorter torso, while others may have long arms but short legs – starting with the correct-sized frame allows you to further tune the position using stem, bar, seatpost and saddle tweaks.
Manufacturers’ listed frame sizes can be confusing. The traditional method is to list the seat tube length, but even that varies because some are measured to the top of the seat tube and some to the middle of where the top tube joins the seat tube. Many manufacturers simply list their bikes as S, M and L, perhaps with XS or XL at either end.
Either way, the measurement that matters more is top tube length. Together with seat position, stem length and handlebar position, top tube length dictates the comfort and efﬁciency of your body on the bike. To confuse matters further, the aspect of top tube length that matters is not the top tube itself, which often slopes, but a horizontal line from the middle top of the head tube to the middle of the seatpost.
So, where do you start to ﬁnd out what size frame you need? Like so many other things on a mountain bike, there's no one perfect solution, as within sensible limits you can adjust your saddle, stem and handlebar to help a slightly imperfect ﬁt feel ﬁne. Bear in mind that road, cyclo-cross and hybrid bike sizes tend to be 3-4in bigger for the same rider height. We mention this because a lot of riders are confused by it when ﬂicking through bike listings.
Here are some guidelines:
XS bike (13-14in): Generally for riders between 5ft and 5ft 4in
S (14-16in): Generally for riders between 5ft 4in and 5ft 7in
M (16-18in): Generally for riders between 5ft 7in and 5ft 10in
L (18-20in): Generally for riders between 5ft 10in and 6ft 1in
XL (20-22in): Generally for riders over 6ft 1in
What really matters is how the bike feels when you sit on it and ride. The ﬁrst thing you need to do, in the shop or on a demo ride, is set the saddle at the right height.
A rough approximation of saddle height for efﬁcient pedalling is your trouser leg measurement plus 5in from the centre top of the saddle to the centre top of the pedal. To work it out more accurately, with comfort and efﬁciency in mind, sit squarely on your saddle with the cranks in a straight up/straight down position. The saddle is at the right height when your heel just touches the top of the lower pedal with your leg straight; your crank should be right at the bottom of its stroke.
If you have to tilt to one side on the saddle to achieve this position then the saddle is too high. Place your foot on the pedal in the ready-to-pedal position. If your leg was straight with your heel on the pedal it should be slightly bent at the knee in a pedalling position. You should never feel as if you’re being forced to rock your hips from side to side on the saddle while pedalling.
You may need to make adjustments to this position according to conﬁdence and comfort preferences, and depending on what shoes you wear. And keep in mind that this is all based on efﬁcient pedalling for cross-country trail riding. Many riders will choose to set their saddles lower for difﬁcult descents, hence the growing popularity of dropper seatposts for big terrain riding.
As a rule, start with your saddle as level as possible on the top. This is an efﬁcient cross-country position but some riders will prefer a slightly tipped back saddle for tricks, stunts and/or steep downhill work, and a few who prefer the nose of the saddle slightly tipped down for climbing or a more forward-biased ride posture. But dead ﬂat is right for most riders.
Saddle rails have a lot of fore/aft slide adjustment, and not all seatposts are created equal. Some have set-back clamps, others have clamps in line with the top of the post. This has a bearing on the position you’re trying to achieve with your saddle. A saddle set too far back can make the bike feel back-heavy, possibly even too light at the front to achieve proper suspension fork compression. A saddle set too far forward can cramp your ride position and make you feel as though you’re putting too much body weight on the front of the bike.
In theory, if a bike has exactly the right reach for you and the fork is set up properly, you’ll probably end up with the saddle set dead centre on its rails. If you’ve got long arms for your height you may end up with the saddle set well back: short arms and you’ll be looking at inline seatposts and your saddle forward. You can use stem length and handlebar position to ﬁne-tune the way you sit over the bike too.
We’ve ridden a lot of bikes and discovered a few unusual aspects of bike setup that can help explain why a bike feels wrong for no obvious reason. One relates to saddle position. With your saddle at ‘perfect’ height, drop a plumb line from the centre of your saddle clamp to your frame’s chainstays. With everything set up for general trail riding, the plumb line should intercept the chainstays almost exactly halfway between the bottom bracket axle centre and wheel axle centre. If it’s further back you’re probably sat too far back. Put your saddle further forward for better balance, and to get the best out of your suspension forks.
If you have access to different stem lengths and different shaped handlebars, experiment with different ride positions, adjusting your saddle accordingly. Arm, leg and torso length will vary between riders of the same height and body weight distribution can have a major bearing on setup. A rider with a big belly will demand a different bike setup to a rider with a well distributed muscle mass or a heavy head – strange but true.
A guideline for saddle to handlebar reach is to put the tip of your elbow on the nose of the saddle and see how far your longest ﬁnger reaches along the stem; forearm length is generally a good indicator of full arm and torso length. Most riders looking for a fast and efﬁcient trail riding posture will discover that their longest ﬁnger reaches to almost exactly halfway between the steerer top and the handlebar centre.
You can ﬁne-tune ride feel from that point by adjusting your seat position, stem length and height, and handlebar type. Some handlebars have a more generous backsweep than others, and you can turn bars in the stem to tune your hold position/wrist angle. We know riders who like their bars straight and others who ﬁnd a 25-degree backsweep their ideal solution. Keep that elbow tip to ﬁnger tip measurement in mind when working out whether a test bike is the right size for you.
How high you have your bars is a function of steerer height (and the amount of adjustment washers on it), stem height and rise, and handlebar rise. Some riders feel relaxed with their bars at roughly saddle height, others (particularly cross-country racers) have them way below saddle height to achieve a ﬂat backed streamline posture on the bike.
Relative beginners might feel at ease with the bars set higher than the saddle. Bear in mind that you need enough body heft tipped towards the front of the bike to compress your suspension fork when you’re riding rough terrain. This becomes harder to achieve if your saddle is too low or your bars too high.
Brake levers and gear shifters can be put in different positions on the bar. On most brakes you can adjust lever reach too, and on some you can adjust the point of contact where the brakes compress the pads. We know riders who put up with their thumbs rubbing on their gear shifters for years before realising that setting them half an inch further inboard on the bars solves the problem without making them harder to use.
Bar width can be trimmed too: cutting an inch off either end of a 27in handlebar might make a difference to your ride comfort. Swivelling bars a few degrees back or forth in the stem can also make a difference. Don’t be afraid to try something different, but try it for a few rides in order to ﬁnd the pros and cons of a new setup.
The materials that your bike’s components are made from can have some bearing on setup and comfort. Materials, and the way they’re used, have the most effect at the major contact points (with the rider and the ground). We’re talking about your tyres, your grips, your saddle and your pedals.
Tyres: Tyre compounds, as well as pressures, will affect the way a bike feels on the trail. Cleverly treaded dual compound tyres with a high tpi (threads per inch) carcass construction will generally deform more over rough terrain, and so grip better, without any increase in rolling resistance. Cheaply made tyres tend to grip less and are more prone to losing traction when under pressure, especially in wet conditions.
Grips: Dual compound handlebar grips, or grips made from soft foam, might not be as hardwearing as others but they’re far more comfy, absorbing vibration and making you feel more at ease on the bike on rough terrain.
Saddle: The right sort of surface material and the right sort of padding on a saddle is obviously going to make a huge difference to the way you feel about your bike. As a rule, you should be able to move easily on the surface of a saddle; fancy embroidered graphics aren’t always conducive to this. And don’t assume that more padding is always better. Slimline saddles with minimal padding in just the right places are often more comfy than big bouncy affairs, which will often chafe after a while.
Pedals: The efﬁciency of your pedal/shoe interface has an impact on how you ride. Stiff soled shoes with inset cleats ﬁxed to clipless pedals will make you a more efﬁcient ‘full circles’ pedaller. But read instructions carefully when it comes to cleat position because poorly positioned cleats can cause problems, especially with knees. Most riders start with their cleats set dead centre in the shoe recess, but that doesn’t feel right for everyone, and some cleats/pedals offer more free ﬂoat movement than others.
Comfort and control variations
Your tyres, suspension fork and rear shock effectively provide an adjustable cushion between your bike and the ground. Setting them up properly is crucial to your overall control and comfort. Big volume tyres can be run at lower pressures than small volume ones, and big volume tyres with a low knob proﬁle will often roll just as fast as, and offer more comfort and control than, skinny tyres.
A good tyre pressure starting point for average weight riders on typical 2.1in tyres is about 35psi. Careful or lighter riders will often run under 30psi, especially on tubeless tyres where there’s no tube to pinch puncture. Heavier, clumsier or harder-hitting riders might prefer 40psi+.
Fork and shock pressures will vary according to make and model, but aim for between a third and a quarter of the available travel as initial sag when you sit on the bike. Also, take some time to learn about your compression and rebound damping controls.
Wrong fit ailments
Aches and pains can be caused by aspects of bike setup, but also by other things, so don’t take this list as gospel; it’s a rough guide. See your doctor if something is really hurting, especially if it continues to hurt after riding and it’s not solved by the adjustments mentioned here. Be aware that a lot of your aches and pains on a bike are simply caused by insufﬁcient muscle support. In other words, you may just need to ride more and do some core muscle training to work things out.
Here are some common ailments and their causes:
Knees: Knee pain when riding can be caused by your saddle being too high or too low, or your shoe cleats being poorly adjusted. Some riders ﬁnd that a pedal/cleat system with more free ﬂoat gets rid of knee pain.
Back: Back pain during/after riding will often be related to poor core muscle support so there may not be a quick and easy setup ﬁx. But try changing the position of your handlebars and/or your reach from the saddle to the bars. We know a lot of riders who’ve solved lower back pain simply by putting the stem up or down by half an inch, or getting a handlebar with more backsweep.
Shoulders/arms/neck: We're putting these three together because it’s often similar aspects of set-up that cause aches and pains in these areas, namely too much stress being placed on these bits of your body. This may be caused by being sat too far forward on the bike but it can also be down to sitting too far back, making you curl your shoulders and preventing you holding the bar properly. Experiment with stem height and saddle-to-bar reach. Try different bar shapes: a lot of riders ﬁnd that more backsweep or upsweep on a bar will make them feel far more comfortable. Also, try anatomically shaped grips, which support your hands better.
Hips: A lot of hip problems among cyclists are caused by the saddle being either too high, too low, tipped too far back or forward or not offering the right sort of padded support.
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