Bike sizing is not the most exciting topic to learn about, but it is one of the most crucial.
Having the right bike size is not just a matter of comfort -- it can prevent injury both short and long term, and allows you to have a much better riding experience as a result.
Many of us grew up using bikes inherited from our siblings, sharing with friends, or taking whatever we could get, with size being an afterthought.
This is fine for casual riders who barely get on the saddle, but if you are hoping to ride with any sort of regularity, the bike’s size needs to be your first priority after determining the type and model.
Sizing a bike correctly depends on a variety of factors that go well beyond just your height. If you’ve ever gone into a bike shop and had someone simply measure your height and point you towards a particular size, you’re likely to end up with the wrong one, even if it seems comfortable at first.
Yes, a little fine tuning can go a long way in regards to seatposts, handlebars, and stems, but getting the correct frame size is where it all needs to start.
This guide will discuss what the wrong bike size can do to you and your ride, and what you should do to ensure that you’re getting the right size for your riding needs and body.
Why You Should Care About The Correct Size of Your Bike
Bicycles aren’t very complicated. They operate off of pedal power, and are steered with handlebars. Pretty simple, right?
While the mechanics are indeed simple, the position of your body is dependent on the bike’s size, as well as your overall control of it.
Riding a bike that is too small or too big can result in a number of problems. Here are just a few of the main ones.
- Back Pain - Posture is important with any bike, whether you’re hitting high speeds on a road bike for tens of miles, or conquering a singletrack mountain bike trail. Riding a frame that is the wrong size will eventually lead to pain in your lower back, especially if you’re on a road bike. Adjusting a seatpost or handlebar won’t compensate for the frame.
- Fatigue - Pedal efficiency is a major reason for getting a bike that’s perfect for your size. When the bike is suitable to your size, you get the proper stance and leg positioning needed to get the most out of every pedal, without having to strain.
- Wrist Pain - If you spend a lot of time on a bike that is too big or small, your wrists will begin to take the brunt of the bad positioning. Your body’s stance will put more pressure on the wrists, which will naturally overcompensate. Frames that are too large will require you to reach further when controlling the bike with its handlebars, which is not ideal either.
- Higher Crash Risks - When you are on a bike that’s suitable for your size, you have much better control over the bike overall. Ride a bike that’s too big, and you’ll be sacrificing a large amount of control, which significantly ups the risk of a crash.
SO, WHAT SHOULD YOU DO?
The best way to make sure you end up with a proper bike size is to familiarize yourself with all of the aspects that are taken into account. Knowing how bikes are sized, and the standard measurements needed can help steer you towards the ideal size that will give you the best riding experience.
By informing yourself of how bike sizing works, you can always be sure that you are in the seat of the best bike size for your body and riding style.
Not all standard bikes are sized the same. The actual sizes themselves, and the sizing methods are all dependent on the bike’s type.
- Road bikes usually come in basic small, medium, and large sizes, as well as numerical sizes. No all numerical sizes are the same for all brands, however. For example, a size 48 in a Specialized bike may not be the same as a 48 from Trek. If you learn your size and stay within a brand, you'll be okay.
- Mountain bikes are a bit different. They also come in S, M, and L sizes, but differing brands are often very close to one another.
- Hybrid bikes are a sort of toss-up, and often include aspects of road and mountain bike sizing.
BIKE SIZE CHART
Size charts are a starting point when trying to hone in on the bike that’s best for your build. Everyone is shaped differently, and the length of your arms and legs play a major role as well. Use these charts to get an idea of your size.
Okay, now onto bike fitting.
Bike Frame Standover Height
Standover height refers to how tall the bike is in relation to your inseam, and the clearance in between. Standover height can be a bit tricky to calculate, depending on the shape of the frame. The bike’s actual standover height is the the middle of the top tube.
You will want at least one inch for a road bike, and two inches for a mountain bike.
Here’s how to measure. Stand over the frame in the center, with your feet flat on the floor. If you wear cycling shoes when riding, make sure you have them on. Measure the clearance in between your inseam and the top of the bike’s top tube.
- Road bikes: For a road bike with a top tube that is parallel with the ground, one inch of clearance is fine. If the tube slopes down, you’ll want two inches.
- Mountain bikes: Two inches of clearance is sufficient, and an extra inch doesn’t hurt. If you have a full-suspension bike that utilizes a Y-frame, you are probably not going to be able to figure out its standover height, although there are some exceptions.
- Hybrid bikes: Hybrids are a bit different. If the bike is more of a commuter road-style bike, use the same guidelines as a road bike. Cruisers and recreational bikes don’t require standover height, but you should be able to place your feet flat on the ground when seated.
So, to recap, you’ll first need to know your inseam. And then the bike’s listed standover height. So, if you have an inseam of 30 inches, you’ll want a road bike with a standover height of 31 inches, and a mountain bike with a standover height of either 32 or 33 inches.
Don’t know your inseam? It just takes a few seconds:
- Stand against a wall with your cycling shoes on (if applicable.)
- Take a book and place it under you and against the wall as if you’re sitting on it like a saddle, spine side facing up.
- Mark where the top of the book is.
- Now use a tape measure and measure up from the ground to the mark. This is your inseam.
Effective Top Tube Length
Standover height is a great way to get on the right track for ensuring a bike size that’s best for you, but there is one other measurement to account for.
Effective top tube length (ETT,) refers to the horizontal distance between the head tube and the seat tube.
This measurement does not require any certain shape of frame, or even a straight top tube, so it can be measured on any bike.
Buying a bike with the correct ETT for your body allows you to fine tune other parts of the bike later for a more perfect fit. Generally, the ETT is in sync with the bike’s standover height. If you have longer arms, you may need a bike with an added inch or two on the ETT.
This is where you can really dial in your bike to make sure you are in the best position for steering and pedaling. There are very few things you can actually adjust on a bike that are significant, but the two that you can are the saddle (seat) height, and the stem length.
Once you have the right sized frame using the criteria above, you are ready to fine-tune the fit with these two components.
Getting your bike saddle to the perfect height ensures that you get the most out of your pedaling, while also avoiding lower body issues over time. A proper height also puts you in the best stane to maneuver the bike with your body, and your arms.
Ride your bicycle for a few pedals while seated, and check the positioning of your leg.
When your foot is at the bottom of the pedaling cycle, your leg should be around 80 to 90% extended.
You don’t want a complete extension, as this will strain your leg and rob you of pedaling power.
If your leg is too bent, it means the saddle is too low. Adjust the saddle post by raising it a few notches, and then try it out again.
If your leg is too straight, the saddle is too high, and needs to be lowered a bit until you get the desired leg extension percentage.
Always be sure to not over tighten the saddle post, as you may break the lever, or even cause the post to crease and fold.
The saddle’s height isn’t the only thing that matters -- it’s slope and position above the seatpost are important as well. This is known as the saddle’s fore and aft.
The best way to tell if you have the saddle in the right position to to check the positioning of your foot as you pedal, in relation to where your knee rests above it.
When your right foot is at the 3 o’clock position of the pedal stroke, your knee should be aligned directly over your forefoot, with your shin tilted forward slightly.
If your knee is too far ahead of your forefoot, you need to slide the saddle back a little bit, and vice versa if your knee is behind your forefoot.
You can make slight adjustments by loosening the saddle binder bolt, and then sliding the saddle forward or backward as needed.
This adjustment and pedal position is the same for all bikes, although you may be able to tweak it a bit over time as your riding habits and strengths change.
The saddle’s tilt should be checked as well. If it’s not parallel with the ground, you’ll need to straighten it out. Loosen the saddle binder bolts at the top of your seatpost and adjust until it’s flat.
The stem is what connects the handlebar to the top of the fork. If your ETT is too short, you can purchase a stem that is a little longer, which will allow you to lean forward more comfortable as you steer, and allow your arms to relax more. It should be noted that your steering will not be as responsive, but this will not be an issue, most likely.
Fitting a bike for a woman may be different, but not always. Women tend to have narrower shoulders and longer legs when compared to men, which is why women’s bikes are sized differently.
Women’s bikes usually have narrower handlebars and a more compact frame as well. Some women may prefer men’s sizes depending on their body types, which is perfectly fine.
Now you know what to look for when shopping for a new bike that is fitted to your size. When looking online, pay special attention to the measurements, and check to make sure they are in line with your ideal size.
With just a little homework, you can be confident that you’re getting a bike you can use consistently without worrying about the issues that stem from an improper fit.