When considering buying a bike, the MOST important thing to keep in mind is bike fit. Anyone that tells you that anything else is important over bike fit, like the wheels or groupset, has never been on a bike for more than three hours. I would take a mediocre bike that fits me well over a spectacular bike any day. Even if you have the choice between an ugly looking one and a cool looking one, take the one that fits you best otherwise after an hour or so it’ll hurt so much you’ll hate the cool one anyway.

As a caveat, this discussion is mostly applicable to those of you that want to cycle for sport. If you are just putzing around town for 20 minutes or so, sure.. you’ll get away with an ill-fitting bike, just like it wouldn’t hurt you to run with shoes that were too big for you for a short period of time. However, if you plan on cycling for anything over 45 min, you’ll start to notice a difference in neck pain, lower back pain, knee pain, wrist pain, butt pain, and possibly even foot pain, if things are ‘off’ from what they should be, and hence the bike fit comes into play.

A true bike fit isn’t simply a ‘stand over the top tube’ sizeup that many chain stores do… it actually involves understanding any leg length discrepancies, torso length, flexibility issues, etc.  A decent bike fit can give you a generally ‘good enough’ fit, which is cheaper, and that will give you the saddle height, fore and aft adjustment, and stem length for your handlebars. A very good bike fit process will give you all the same things as the basic (or static fit), whilst you are pedaling on a turbo trainer (dynamic fit) plus your cleat adjustment and any kind of modifications to your shoes, such as length length discrepancy adjustments. Of course, you will pay extra for that, as those kinds of bike fits can costs in the hundreds of dollars or pounds. The cheaper ones, can be had for much less though or even free if you buy a bike from the store that did the fit (ask for this).

In the end, the objective is to get you as close a bike to your ideal fit as possible (unless you go down the custom bike route). Many people do find that stock bikes are ‘good enough’ for their use after they’ve been modified to fit them by altering crank length, stem, stack, and saddle height… but not all stores are friendly about helping you with changing these things. That’s why it’s worth it to shop in the stores that are better about accommodating these kinds of modifications. Also, keep in mind that you may not fit that beautiful bike you always wanted… as it may require more flexibility than you actually have.. I know I can’t fit some of the really short head tube race bikes without having to heavily modify them to the point that they look silly.. but I’d rather take one that is ‘less’ cool, and feel comfortable than take a cool one, modify it to the point it no longer looks cool, and then ride perhaps will some discomfort any way.

Below is the list of stores that I know (at least in London) that do bike fits and will be good about helping you out with buying a bike with that fit. For the ones where I know the guys in the store and trust them, I’ve listed their names… tell them Carlos sent you:

Prologue Bikes – Near Richmond park – Ask for Bruce or Tom
Condor Cycles – Greys Inn Road near Holborn – Ask for Greg
Mosquito Bikes – Near Angel – Ask for Roger, to read my experience getting fitted by Roger, go here.
Sigma Sport – Hampton Wick – Ask for Lee or Jeremy

Here are some others (but that I’ve never been to or used, so can’t assess them, but heard they are ok):

Cyclefit – Near Holborn
De Ver Cycles – SW163QL London
Bike & Run – East Finchley
ProFeet – Fulham

If you want to learn more about bike fittings, go to the bikefitting.com website where they have lots of good materials explaining the ins and outs. Also Retul a bike fitting tech provider has some additional info as well as directions for fitting centers.

Here is my recent experience with a bike fitting using the Retul system: https://faston2wheels.com/2010/11/06/a-bike-fitting-at-profeet/