Wednesday, May 18, 2011

The Guadzilla guide to bike fit for beginners

The best of bikes is going to suck something fierce if it doesn't fit you properly.

Sadly, around here, bike fit seems to be consist of one of 2 strategies:   in more shops than you'd expect, the correct bike size for you is whatever the shop happens to have in stock.   Lucky you.   The more reputable shops make an effort:  they have you straddle the top tube and if there are 2-3 inches between your boys and the bar, you are good to go.  

Sadly, even the latter method - which is in widespread use the world over - is not a very reliable approach.   It has a good chance of putting you in approximately the right sized frame if you are of average proportions - that's about it.   It doesn't take into account personal factors like flexibility, the geometry of the bike or the fact that maybe you might not have "average proportions".

Let's take a step back and figure out what bike fitting is about - it is about putting 3 contact points of your body at the correct distance from each other:   the foot/pedal interface, the ass/seat interface and the hands/handlebar interface.  

The foot/pedal interface is pretty much fixed on a bike (you cannot really move the cranks around, they are where they are).  So good fit means putting the bicycle seat and the handlebars at the position that is comfortable, is biomechanically sound and which lets you generate a lot of power.

The "straddle the top tube" method is focused on one aspect of the bike only:  how high the top tube is from the ground.  It does nothing about actually fitting you on the bike - ie, putting the saddle and the bars at the correct point.   At best, it helps you get the correct bike size, but even the correctly-sized bike can be poorly set-up and lead to injuries.

Handlebars that are 2cm further than you'd like them, or 2cm lower than you'd like, can absolutely ruin your riding experience - because the moment you are not perfectly balanced on the bike, your body is straining to stay in position.   This affects your biomechanics. and can lead to all sorts of injuries.

There is good news, however - and it is that bike fit, while a relatively detailed topic, is not that complicated.   By following a methodical approach, you can adjust your bike just the way you want it.

Start by reading up on bike geometry (Google is your friend) and understand what the various terms seat tube length, top tube length & headtube length mean.   These are the 3 things that will affect your fit.

There are other terms - head tube angle, seat tube angle, fork rake and bottom bracket drop - which affect how a bike handles and also fit to some extent, but those are not so important right now.

Fitting is done in 2 steps:  first, you adjust your saddle position (up/down, front/back) to put your hips in the correct position relative to your pedals.   Second, you put the handlebars where your hands end up.  It really is that simple.

Saddle height can be set very easily by moving the seatpost up and down.   Barring any egregious fitting fuck-ups (ie, putting someone 6'5" on an XS frame), this part is easy and so the seat tube (ST) length is not so important.  

The challenge of a fit comes in making sure that once your saddle position is done, your handlebars are where you want them to be.    The main bike-related factors driving this are the effective top-tube (ETT) length (this affects the horizontal distance between you and the bars) and the head-tube (HT)  length (this affects how high the bars are).   Handlebar position can be tweaked by about 2-3cm up/down and 2-3 cm front/back by using different stems and spacers, but you need to get in the correct ballpark as far as ETT and HT are concerned.  

Note - the seat tube angle and head tube angle have a small effect in modifying the reach (so a 565mm effective top tube on one bike may give you the same reach at a 570mm effective top tube on another bike), but for now, we will ignore that.
    Ok, so hopefully by now you understand what we are trying to do with bike fitting and how the various measurements of a bike relate to fit.   If not, do some additional google research or ask a question on Bikeszone.   Do not go any further until you are completely clear on what we've talked about so far.

    Next, read the articles on this page, especially the Peter White article, to get a sense of how set saddle height and handlebar position:
    http://www.cyclemetrics.com/Pages/FitLi ... _links.htm

    Edit - the cyclemetrics website seems to be down, so here is a direct link to the Peter White article:
    http://www.peterwhitecycles.com/fitting.htm

    Now, if I know you, you are going "yeah, yeah, Guadz, that's very nice, but what do I do".

    Ok, so here's how you apply this information for your own bike fit:
    • If you are going to buy a frame, go to www.competitivcyclist.com and run their online fit calculator - it will give you a starting point as to what bike size you should be looking at.    Go to the website of the brand of bike you want, and find the frame that has same equivalent top tube length as the fit given to you by the CC website.   This is going to be your starting frame size.   Forget the traditional bike size (52, 54, 56, etc).   That is meaningless right now.  If you already have a bike, skip this bit.
    • Set the saddle height so that there is approximately a 20 degree bend in your knee when the pedal is at its lowest position.   Have a friend help you with this.  There are other methods you can also use, which are simpler (Google the Lemond formula, for example), but biomechanically, the 20 degree bend is achieving your saddle height via first principles and is probably the best method out there.     Again, this is just a starting point and you may find yourself moving the saddle up and down later.
    • Move your seat back and forth until the notch below your knee is directly over the pedal spindle when it is horizontal and forwards.   This is called "KOP neutral" - or knee-over-pedal neutral.    This is not necessarily where you will be, but is a good starting point.   Faster riders who ride in a more aggressive/bent position may prefer to be slightly further than KOP, while slower riders who ride with less weight on the pedals will often be slightly behind KOP.  For now, KOP-neutral is a good starting point.
    • Adjust your saddle height to make sure that you still have a 20 degree bend in your knee and adjust saddle forward/backwards.  Repeat these 2 steps till you have gotten it right.  
    • Make sure your saddle is flat.   Not pointing downwards.    Use a leveling app like Clinometer on the iPhone or something comparable on Android.
    • Now that you have your ass-pedal interface sorted, put the bike on a trainer, reach out and grab the handle bars (the hoods if you have a road bike - actually, my advice is geared towards road/hybrid riders - if you have an MTB, your fit will be different depending on the type of riding you do).   How do you feel?   You should feel pretty comfortable and well-balanced, and should have very minimal pressure on your hands.  If you feel that even some of your body weight is on your hands, your handlebars are too far forwards.  If you feel that you are bending too much, your handlebars are too low.   You can raise the handlebars by using spacers underneath the stem, or by choosing a different stem (one that is angled upwards more).   You can also adjust horizontal reach by using a shorter/longer stem.
    • It may also be that you are too comfortable - you are completely upright and there is no weight on your arms when in the riding position.  If so, you will need to lower your bar and maybe extend it further, to the point where you just start to feel a VERY slight amount of pressure on your hands:  ie, just the point where you go from not needing your hands to hold you in place to needing them very, very slightly.
    • If your initial bike size is correct, you shouldnt be too far off as far as handlebar positioning is concerned.   If the handlebar appears to be really further away, you need a smaller frame.  If your handlebar is way too close, you need a larger frame.   And if the handlebar is a lot lower than your saddlebar and this is uncomfortable, you need to consider a different bike geometry: one with a higher head-tube (for those of you with long legs/short torso, this is the main challenge - traditional road race bikes will put the bars way too low for comfort).
    This is your initial, static fit.     Now you start riding and adjust as needed.

    Some additional thoughts on fit:

    1/  If you already have your bike and are concerned whether it is the right size, take comfort in the fact that with any given bike frame, you can adjust the equivalent of one size up or one size down quite easily.   You can even make 2 sizes works, although that will be stretching it.  Of course, if you are way off in sizing, you may have to consider getting a new bike.

    2/ If you are in doubt about bike sizes, pick the smaller frame - it is easier to make a small frame fit bigger, but it is impossible to make a bigger frame fit smaller without affecting handling.

    3/ If you are riding and you feel pain in your hamstrings or hamstring ligaments, lower your seat

    4/ If you feel pain in the back of your knee, slide your saddle forwards by a mm or two at a time

    5/ If you are feeling pain in the front of your knee, slide your saddle back a mm at a time

    6/ If you are feeling pressure on your hands, your saddle is probably sloping downwards.  Level it.  If problems still continue, your handlebars are too far forwards or too low for you.

    7/ If your back hurts, your bars are probably too low.   But it could also be a matter of you having a weak core or poor riding position.   Try not to arch your lower back, but roll your pelvis forwards instead, flattening out your lower back.   This will require building some core strength.

    8/ If your saddle is causing your privates to go numb, make sure it isn't sloping upwards too much.  Typically, saddles are usually level or inclined upwards by 1-2 degrees max.    If your saddle is flat and it is still making you numb, you need a different saddle - dont angle it downwards or you will have all sort of hand/wrist pains.  Or try a recommendation I read on John Cobb's website - turn your saddle sideways by half the width of its nose.    John Cobb is an aerodynamic guru and makes excellent saddles to boot - he knows of what he speaks.  His advice is mainly for his own saddles, but you can try it as well.

    9/ If you have just bought a new bike and have also started to ride clipless - wait.   Stick to platform pedals and get your bike set up properly and then add clipless pedals.   Clipless pedals add their own complexity to fit, and it is best not to have too many variables to adjust at once.

    10/ Dont be afraid to experiment.  But experiment changing only one thing at a time, and in small increments.  Listen to your body and adjust accordingly, especially when it comes to your pedaling postion.

    Ride safe!

    4 comments:

    1. Brilliant article, helped me a lot.
      One problem though, the link to Peter White's article doesn't work

      ReplyDelete
    2. Gups - have put a direct link to the Peter White article. Thanks for pointing out the broken link.

      ReplyDelete
    3. Hello,
      Guru Fit
      well, this great provides me with lots of knowledge upon the topic on guru fit. So, keep writing.
      Thanks a lot!

      ReplyDelete