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What’s A Centimeter? It’s All In The Fit


February 2012

I had a comment the other day in which a person wrote that he’s had a hard time with cycling because anything longer than an hour’s ride required the application of an ice pack to his butt afterwards.   Whatever his problem, and there is definitely something very wrong there, I thought I’d take a minute to illustrate the need of a good fitting.  Now, it’s important to note, that one can get away with a smaller framed mountain bike – in many cases that is even desirable but that’s a post for another day.

It just so happens that I have two road bikes – one that is exactly the proper size (right down to the crank arm length) and one that is too small, but only by a matter of two centimeters and I can say for a fact, the difference in comfort between the two is astronomical.

It is important to note here, that I switched the stems – the stem that came with the Trek was too long (16 cm) so Matt put that one on the Cannondale and put the stem from the Cannondale (9.5 cm) on the Trek to get me in the proper position so while the bar/seat positions will look close with the two bikes side by side, this certainly wasn’t the case when I was riding the Cannondale – the bar was in another 6.5 cm.  I took the second photo from a higher angle to illustrate the seat heights which are identical.  That angle distorted, through an optical illusion, the stand-over height of the top tube.  The difference between the two is significant, 5.25 cm (C’dale 78.75 cm, Trek 84 cm) or about 2 inches.  Also, the top tube on the Trek is almost 5 cm longer 57.875 cm vs. 53 cm (center to center).  In any event with both bikes side by side you can see that there is a substantial difference.   When the fact that the stems were swapped is added to the equation, the differences are remarkable – and that’s just between a 56 and a 58 cm bike.

So what I ended up with was that I had to fit my body into a space that was too small to accommodate it.  I had to hunch here, rotate my hips awkwardly there etc.  This caused a lot of unnecessary pressure on my shoulders and kept me from breathing properly because my lungs and diaphragm were crammed into a small cockpit.  With the Trek, I’ve got 66 cm from the bar to the sweet spot on my saddle, on the Cannondale I had 58 cm.

So, to sum this up, there was only a 2 cm difference in the frame size but that translated into 8 cm where it counted.  This is why, without a doubt, one should consult a professional first and I can tell you from experience, the online bike measurement tools don’t count the same – the one I used says, by my stats, that I should have a 175 mm crank, but my fit up definitively showed 172.5.  As well, the online measurement tool suggested a 59 cm frame with possibles of 57, 58, 60 and 61…  I imagine when I checked that before I bought that Cannondale I said to myself, jeez, what’s a half-inch for crying out loud…  It’s a lot.

So long story short, don’t do what I did.


As a post script, if I just went by what the online do-hickey suggested, and I didn’t know that all manufacturers size bikes a little differently, I could end up picking the wrong bike.  In a purely hypothetical scenario, say I had my eye on a Scott Foil 20.  I walk in to the local Scott dealer and tell the saleswoman to order up an XL frame (based on my 59 cm measurement from the online thingamajig), because we all know that you want the exact size or one cm down…  First of all, I can’t imagine a shop out there that would let anyone walk in off the street and order a $3,500 bike without pulling out a tape measure, but let’s say that happened or you buy it online…you get your 58 cm Scott a few weeks later, you’re happy as a pig in poo…until your first century when you discover that the bike hurts.  You raise holy hell with the website and take your new steed to your local shop only to find out that Scott bikes run small (I don’t know if they do or not, this is hypothetical) and you should have ordered the 61 cm XXL frame.  The next time you get a chance, check out Craigslist and note how many posts for high end bikes start out with “I found out this bike is too small/big”.  It’s a lot.



  1. Being the bike nerd that I am, I’ve spent a lot of time studying bike geometry. You make a lot of great points in here that I’m glad you’ve gotten worked out. Millimeters and centimeters are huge distances on a bike!

    Luckily, there are a few ways to measure your fit independent of frame size. Check out this link:

    So, for example, if you got that righteous Scott Foil, you’d be able to dial everything in with those few simple measurements. The top tube on the Foil is 58cm, which seems right for you, given the size of your Trek. You would have to adjust your stem length, however, and you’d probably have a bit more seat post showing too, as the Foil has a slightly sloping top tube. With the measurements independent of frame size, you can literally copy the same position between bikes, so long as you have the right variable bits and pieces to accomodate for this (includes stem, bars, saddle, seat post, brake hoods, and spacers…). However, if flexibility is an issue, sizing up may be beneficial because you can avoid having a massive spacer tower (or super tall quill stem, as it looks like you’ve got).

    After a while you get to know your own body and generally you can pick out which frames will work best for you by just looking at the geometry chart. Once you get to that point, try not to drool 🙂

    • bgddyjim says:

      Oh man, you weren’t kidding about the drooling part – I almost shorted out my keyboard. They’ve got a great web site, though I must say, I’m glad Matt Assenmacher is a small town kind of guy – their pricing is double what I pay (though in line with what I’d expect, don’t mistake me on that). I’d have to move up a few notches for millimeters to matter.

      You’re absolutely right about copying the position from bike to bike which is shown to an extent in the photos I took… With the bars of both bikes stacked exactly in line, with the longer stem on the Cannondale, the saddles for both bikes are almost identical and I think any good bike guy would admit that with enough messing around you can fit a person to a smaller bike which would have been the case with the Cannondale (though one would wonder about the knee/pedal axle angle). The problem therein is cost. Once I figured the STI shifters, a new rear wheel, cassette, spreading the back end, new stem and crank (the C’dale arms are 170 mm), carbon fork – it was never ending and it still wouldn’t have been as good as the one I’m on now. Matt just set the C’dale up so I’d have a backup just in case.

      The tall quill stem is my one point of contention with Matt. It’s up at the limit line right now – I wanted it lower by about an inch (that was based on the idea that it looks cooler which is a little silly) but the current height is where the measurements came out based on the kind of riding I figured I’d be doing. So I deferred to his better judgment on that for comfortability. After I talked to him about doing the IM 70.3 he said that we have to go over everything again to get me in the best position possible so the stem will be coming down shortly methinks.

  2. I was lucky enough to be in a decent bike shop the first time I bought a bike for more than 250 bucks. I’m sure I could have thrown away a ton of money. Now if I could only get myself back on my bike things would be great. It’s coming!

    • bgddyjim says:

      I post things like that in hopes that I can save one noob the trouble of blowing his paycheck because he tried to do things on his own. If I had a dollar for every article and post I read before buying that Cannondale, well I could have bought a new Madone 5. I was sure it was going to work. I was very, very wrong.

      I have no doubt you’ll get there my friend. You’re doing everything right, you’ve got your plan, you started to implement it and now you’re building a support base of people who will help you through the tough spots.

  3. jerzak80 says:

    I’m having a few issues at the moment with sore heels of my hands probably from leaning too much on the bars. Probably the result of a minor tweak to the handlebar set up. A couple of cms does seem to make a big difference, although my wife says size doesn’t matter 😉

    • bgddyjim says:

      I just checked with my wife, she says it’s definitely the motion of the ocean… 😀 I’ve had that problem on my Cannondale – bad. It’s funny how just tweaking the bars by a couple of centimeters will throw a monkey wrench into the works. I’m more comfortable on my bike that I’ve ever been. I’ve got it so dialed in right now that I’m bummed out when my half our is up (I used to hate being on the trainer after about five minutes).

  4. need2run says:

    What is you are fat, short and squatty, all arse and no body, like me? How do I find the perfect fit?

    • bgddyjim says:

      We went looking at road bikes for my eight year old daughter tonight, Trek 1.2 46cm frame… As long as you’re taller than 4’10” you’re in. Also, if you are really heavy look into a mountain bike first – they’re tougher, a ton cheaper, you’ll burn more calories riding it (over a road bike) and you’ll be able to find out if biking is something you really like and want to invest in – because real cycling is anything but cheap (my bike is worth more than my truck). To ride in Olympic Tri, all you have to do is put some mtb road tires on it (abour $25 each) and you’ll be fine.

      I ride with a guy that’s 6’2″ and weighs 250 and he does just fine on his Specialized, though he did upgrade his wheels and tires to avoid flats.

  5. […] about the importance of how well my road bike fits to me (not the other way around), here, here, and here.  While I haven’t tinkered much with my setup of late, I did raise my saddle the […]

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