It doesn’t matter if you are shopping for a new complete bike or new frame to replace your old one. It is essential to understand the different specs on a bike and comprehend how each will affect your riding. With that being said, let’s talk about one of the most common BMX specs. The top tube.
Top Tube Spec Video
What is the top tube?
Why is it important?
The length of a top tube determines how far or how close the bars are to you. This dramatically affects your riding.
For example. A small top tube like a 20.25″ will make the bike more compact. While a bigger 21.25″ will make the bike bigger. (relative to size.) Size charts suggest a top tube and wheel size that will feel average to the rider of the chosen size.
I’m 6’4″ and it is suggested for me to ride a 21″ top tube. The 21″ top tube will feel average for me. But let’s say I want to have more power over my bike for triple tailwhips. Then I should go down a size to a 20.75″. However, if I wanted to ride more trails and have more stability and control I would want to go up to a 21.25″ -21.5″.
Common Top Tube Sizes
I have seen a number of odd top tube sizes. You could presumably find one in almost every size. Still, the common sizes are 20″, 20.25″, 20.5″, 20.75″ and 21″ with 21.25″ being a little harder to find. When you are shopping for a frame, its best to round up to the closest size. Especially if you are still growing.
Does it really matter?
I have seen a lot of speculation saying that top tube size doesn’t really matter. Let me tell you how wrong that is.
Maybe as a brand new rider who is just starting out it could be more important to just get on a bike and ride. But as you progress you will need a perfectly fitting top tube to help you progress. I went from a 21″ to a 20.7″ and while not much changed, the control was way off. I was now able to spin fast but I couldn’t handle high airs or gaps to save my life. I quickly went back to a 21″ and noticed the difference in my bike control. It felt so much better even though it was harder to spin.
Now imagine a kid getting his first bike. This kid is really short like 5’5″ and his bike is a 21″. No wonder he is having an incredibly hard time with learning hops and spins. Perfect bike = perfect progression.