What Happens If a Bike Is Too Small or Big? – Problems & Solutions

Bicycles come in all sorts of shapes and sizes. When looking for a bike for you, this array of options can be confusing and intimidating. So what happens if you get it “wrong?” Here’s a comprehensive rundown on what happens when a bike is too small or too big, how to find a bike that fits you, and how to adjust the bikes you already own.

All About Bike Sizes

Bikes are made up of lots of different parts. Some parts, like the seat and the handlebars, are easy to adjust on your own. While you might need to replace your handlebars to make an extreme adjustment, you’re able to make modest tweaks to the position and height of these components with a few simple tools.

The frame, however, is not adjustable. When people discuss bike sizes, they’re almost always talking about the size of the frame. The frame controls how high the top tube is, how far away from the seat the handlebars are, and limits where you put your seat.

This means that it’s important to get a bike with a frame that’s close to the right size since it’ll let you adjust the other components and get your bike to fit you perfectly.

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In years past, bikes were often sized based on the size of the top tube, with the size of the bike corresponding directly to the length of the tube. These days, however, bike sizing is more nebulous. This means that a “50” from one manufacturer might be too big, while a “50” from another manufacturer might be too small.

Subjective sizes like “large” and “small” are equally inconsistent. If possible, you should always try to test-ride a bike before you buy it. Even if you can’t test-ride the bike itself, try to at least look at a similar bike from the same brand at a store and get a feel for what the manufacturer’s sizes are like.

While the raw size of a bike is subjective, numbers like “stack” and “reach” are objective measures between fixed points on a bike. If you can, look for these measurements and compare them to a bike that you feel comfortable on to take the guesswork out of the equation 

What Happens If My Bike Is Too Big?

People are tenacious. Even if your frame is way too big for you, you’ll probably be able to ride around and pretend that there’s nothing wrong. You might find that riding isn’t very fun, however.

If your bike is too big for you, you’ll probably have to have the seat all the way down, you might need to stretch to reach the handlebars, putting strain on your arms, neck, and back, and you’ll have difficulty mounting and dismounting, and the top tube may be pressing against your perineum or crotch, which is potentially even dangerous.

For a casual rider, these problems can easily fly under the radar. However, if you’re more serious, you’ll notice muscle fatigue and pain from the stretched-out riding position.

If you’re a mountain biker, you may injure yourself due to difficulty bailing smoothly from your bike. You might also have problems with your legs due to incorrect seat positions, causing muscle fatigue, pain, cramps, or even stress injuries.

What Happens If My Bike Is Too Small?

If your bike is too small, it will be hard to get the seat high enough without running out of seat tube, meaning that you might not be able to extend your legs as far as you like on each pedal stroke, which may lead to sore knees and to potential injury. The handlebars will be too close to your seat, giving you an awkward, uncomfortable riding position. 

In extreme cases, your body will interfere with the operation of the bike. This might mean that you’ll get your toes or knees in the way of the wheels while you steer the bike. This is a big safety hazard that you should avoid at all costs.

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I’m In Between Sizes – Should I Go Too Small Or Too Big?

If you’re a serious cyclist, bike fitting professionals often recommend a controversial recommendation to people between sizes – find a different brand.

There are a lot of very good bike manufacturers out there these days, and while some of them have big gaps in their lineup of sizes, others do not.

If you’re spending 100+ hours a month on your bike, it’s usually a good idea to get a bike that fits you perfectly and take the guesswork out of the equation. This might mean you have to get a slightly different bike than the one you’ve been eyeing, but it’s not a choice you’re likely to regret.

If you’re a more casual cyclist (or the smaller size is close enough that you’re willing to live with it), the answer is clear: go small.

A bike that’s a little bit too small will rarely give you problems. The bars will be a bit closer, and you’ll have to raise the seat a little bit more, but that’s it.

You can always adjust the handlebars to make your riding position more comfortable. It’s MUCH easier to get a longer stem than a shorter one. Similarly, it’s very easy to raise your seat, while lowering it past the minimum level is impossible.

This means that making a bike that’s just a little bit too small fit you is almost always an easier task than adjusting a bike that’s too big.

One final point here is that most riders adjust their saddles to be a little bit too high. You want a smidge less leg extension at the bottom of your pedal stroke than most cyclists assume, so you’ll often hear bike fit professionals recommend that you lower your saddle.

This is another point for going too small, as you’ll have plenty of room to experiment with this sort of adjustment.

How To Adjust a Bike To Fit You

Bike fitting is a complicated topic that requires a lot of trial and error.

In general, however, your goal is to put your pelvis above the pedals, give yourself a riding position that you can maintain over a long ride, and ensure that your weight is squarely on the seat, not your hands.

The easiest thing to adjust first is the saddle height. You can loosen your seat post and easily move it up or down to give you the right amount of leg extension.

  • To start, get your seat positioned so that with your leg fully extended, you can rest your heel on the bottom pedal.
  • Next, drop the seat about an inch.
  • From here, you’ll ideally raise the seat very slowly in 1/8th inch increments while going on boring test rides that allow you to pedal at a good cadence.
  • Once you start feeling like your pedal strokes are odd or choppy, drop your seat back down 1/8th of an inch and make fine adjustments as you see fit.

Most bike seats can also move forward and backward. To do this, there’s usually a nut or bolt at the bottom of your seat that you can loosen. You want your knee to be above the pedal at the front of your pedal stroke, but you also want to be able to comfortably reach the controls. If your bike’s frame is too big, you might have some problems here.

As far as handlebars go, some bikes have handlebars that are very easy to adjust, but many of them don’t. If you’ve got the less adjustable sort of handlebars, you’ll need some tools and parts to adjust things. A bike shop can help you add spacers to raise your handlebars, swap out your stem to move them forward or backward, or make other adjustments.

Alternately, if you’ve got experience working with bikes, these are definitely things that you can adjust on your own. Make sure you know where the closest bike shop is. It’s very common to find out that you need another spacer halfway through!

Happy Pedaling!

Sam Benkoczy

Hi, I'm Sam. I own and maintain 6 e-bikes, 15 regular bikes (road bikes, folding bikes, hybrid bikes, city bikes among others). I learned about bikes from my local bike mechanic as well as from bike maintenance courses. I love being out there in the saddle, and using my bike as a practical means of transportation. You can also find me on my YouTube channel at youtube.com/bikecommuterhero Say hi to me at sam@bikecommuterhero.com.

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