I unconsciously bought a bike which's frame size is larger than recommended. (My height is 163cm bikes frame size is for people 174-190cm) (I dont have any problems with reaching ground with my feet when I stop) Bike is BMW M Cruise bike's large frame

My question is will this bigger bike cause orthopaedic problems and will it really differ my handling if I go for a proper sized bike?

Thanks beforehand

  • The main problem of having a different size is that it does not "feel" right. Think about it as using big shoes. It's not bad for you. The best way to check if the bike is not orthopedic is to ride it: if after 2 or 3 hours you feel pain in your back\shoulders\wrists etc than something is not right, independent of the bike size. Also, that does not mean you have to get rid of it: play with stem/handlebar position or buy a shorter stem/handlebar with more raise will probably solve it. – super Jul 1 '15 at 22:30
  • I had a slightly oversized (by perhaps 5cm) touring bike for 15 years. I had to change out the stem (to a taller one with less forward extension) to get my arms and shoulders comfortable. I don't recall any other serious problems. – Daniel R Hicks Jul 2 '15 at 0:56

Actually knowing if a bike frame is the correct size based on height is nearly impossible, they are best guesses. When looking at fitting a bike there are so many different things a fitter will look at.

First lets look at what changes on the bicycle when you change frame size:-

  • Top Tube (TT) - this is normally measured as a theoretical as this tube is not normally straight, see the below diagram. This determines how far you have to stretch on the frame
  • Head Tube (HT) - this determines how long the steerer is, this is how far down the stem could be mounted as a minimum, but also usually means that they can be mounted higher as well, simply the longer this is the higher the bars tend to be.
  • Seat Tube (ST) - this determines how low you can get your saddle, and how high - the longer the seat tube the higher your saddle can be as a minimum, and the higher as a maximum.

Bike Geometry Guide

So lets look at what all this means for you. If you happen to have short legs and a longer torso/arms, this could mean that a larger frame could be better, as the length of all the tubes increases. To break it down. The top tube length will help as the reach will increase, and usually no one has short enough legs to need seat post all the way into the frame.

If you happen to have very long legs and a short torso, its actually more difficult to size and then fit. This is because you have a short reach, which means you need a smaller frame size, but you need to have all of the seat tube out of the frame, this in conjunction with a short head tube means you will have a larger saddle to bar drop (great for the pros, horrific for those not flexible enough, or used to it!).

Having a frame too small and large also has an effect on handling, a larger frame is more cumbersome but much more forgiving and much less twitchy. A smaller frame the opposite is true, much "flickable" and maneuverable, but with the downside of being twitchy.

This is before we even get into the micro adjustments like stem length, angle and position; saddle position and angle etc etc. Which all again have an effect on handling and comfort e.g. a long low stem makes the bike feel great at high speed, but like a bus at slow speed.

The key points for you as a rider, are the points of contact with the bike and ensuring they are in the correct position. This will affect the overall comfort of the bike. i.e. while a stretched-out, super-low position might be fast, for a prolonged period it can be uncomfortable. And the converse is also true, an upright comfortable position may suit, but this can be slow. The aim here is to find the compromise of comfort, speed and handling.

(I dont have any problems with reaching ground with my feet when I stop)

This is only important in so much as ensuring when standing over the top tube you can put both feet flat on the floor.

  • There is also the concept of a "fit window." Some can ride in a variety of positions without experiencing discomfort (or even notice much difference), while others have a very narrow set of preferences which they find comfortable. – Rider_X Jul 2 '15 at 4:45

That frame really is considerably too large. If at all possible the best bet would be to ask to exchange for a smaller size. Many companies now offer 30 day return policies for bikes that have not been used beyond a short test ride.

In terms of fitting problems, the most likely areas to be effected will be the lower back, shoulders, neck, triceps and wrists as you will be in an excessively stretched out position causing additional weight to be taken on your upper body.

If returning the bike is not an option, you can mitigate the problem slightly by fitting a shorter stem. Whilst making the bike a better fit, this will also cause its handling characteristics to become more 'twitchy' (smaller movement to create same response from the bike).

The most important measurement is top tube length or how „stretched“ your position is. One can try to compensate with stem length.

(I dont have any problems with reaching ground with my feet when I stop)

That’s not necessary and actually often a sign for a too low saddle. Saddle height is usually not limited by frame size, unless you have very short or long legs. Saddle height is quite easily determined, just gradually raise the saddle until it’s too high (i.e. you (automatically) start tilting your hips left and right because your feet can’t reach the pedals). Fore and aft position is much harder to find.

Falling off the bicycle would be far more dangerous when the frame is too large. Especially if you ride on ice, cross-country, or use clipless pedals.

You posture also should be grossly wrong given the stated size difference.

Your Answer

By clicking "Post Your Answer", you acknowledge that you have read our updated terms of service, privacy policy and cookie policy, and that your continued use of the website is subject to these policies.

Not the answer you're looking for? Browse other questions tagged or ask your own question.