from Rookie’s keyboard,
Hello and welcome to the first Bike Geometry Lesson For Dummies(E01) on rookiejournal.com
Today, I’m going to educate you on the subject of chainstay length.
Don’t worry. You don’t have to be a physics professor to understand the info below. When I got into the cycling game, I didn’t know the difference between pedals and handlebars and developed the ability to explain complex subjects in ELI5 (explain it like I am five) fashion.
The chainstays, my friends, are the two parallel tubes originating at the bottom bracket (the tube out of which the crank arms stick) and going towards the back wheel.
The length of those two tubes is mega crucial to the performance of your bicycle because it determines two parameters:
- The position of the rear wheel in relation to the rider a.k.a. the heaviest element on a bicycle.
- The distance between the front and rear axle a.k.a. wheelbase.
Short chainstays bring the rear wheel closer to you and make it easier to lift the front wheel. Precisely for this reason, dirt jumpers, free-ride MTBs, and of course, BMXs have shorter chainstays.
– rookiejournal.com
To understand what’s happening, we have to back to the physics lesson about levers during which you couldn’t stop thinking about the new Call of Duty.
A lever is a tool used to amplify one’s effort. Think of a claw hammer used to take a nail out of a board.
The V-shaped claw grabs the nail. Then the carpenter exerts effort on the handle. The head of the hammer rotates around its curve. The curve is called a pivot point. This magnificent architectural genius makes it possible to take the nail out of the board with little effort.
(It will all make sense in a second, so don’t switch to Instagram just yet.)
Here’s how the above translates to the world of cycling:
- The axle of the rear wheel is the pivot point (the equivalent to the concave on the hammer’s head).
- The distance between the front axle (or the “nail”) and the rear axle is part of the lever arm.
The shorter the distance between the object that we want to lift and the pivot point around which we are using our lever, the easier it is to exert effort.
By moving the rear axle closer to the front wheel via shorter stays, we are shortening that distance.
To lift the front wheel, the rider has to shift their weight behind the rear wheel (pivot point).
The closer the rear wheel is to the front wheel, the easier it is for the rider to go behind the rear wheel.
So, ultimately, short chainstays not only reduce the distance between the pivot point and the object that we want to lift but also decrease the physical effort needed to apply force.
In this case, the rider’s body acts as the second part of the lever which is the equivalent to the hammer’s handle from the example above.
Pretty awesome, right?
Lifting the front wheel is fundamental to all basic bike tricks such as bunny hops (basic jump) and manual (riding on the rear wheel).
For that reason, BMX and dirt jumpers have some of the shortest chainstays in the game.
The average BMX frame comes with chainstays between 317mm and 368mm.
The chainstays of dirt jumpers are longer at about 343mm–419mm. The reason for that is that dirt jumpers use larger wheels (usually 26″) and frames.
The secondary benefits of short chainstays are:
- Better wheel traction because more of the rider’s weight is over the rear wheel.
- Less likely to experience lifting of the rear wheel when climbing and shifting your weight to the front.
- Lower weight and extra stiffness thanks to the shorter tubing requiring less material. By the way, when the chainstays are shorter, the seat stays have to reflect that. So, extra grams are saved.
And now it’s time to analyze longer chainstays.
If you want stability, you need longer chainstays.
The longer the wheelbase of a bike is, the more stable it becomes.
Bicycles designed primarily for comfortable long-distance pedaling often have very long chainstays so that they feel like a 1960s Cadillac gliding over the pavement. I’m referring to those old-school bikes that guys like Ultra Romance and his friends ride.
But some of you may be surprised to learn that downhill bikes have super long chainstays too (about 445mm). That’s because you’re associating downhill bikes with all kinds of MTB stunts some of which are done with a dirt jumper.
In practice, however, downhill bikes are well downhill bikes. They excel in overcoming brutally harsh terrain downhill. Chainstays as long as a broomstick add stability to the ride and eliminate unwanted lifts of the front wheel.
Don’t forget that during descents the rider positions a lot of his weight closer to the rear wheel to avoid flipping over the handlebars, falling on a rock, and cracking his skull open. Ok. I am slightly sorry for putting that imagery in your head.
But you’re a big boy. You’ll be alright.
If you want some distraction, check out the table below containing the chainstay length of popular bicycle types.
| Downhill | 445mm |
| Gravel | 430mm |
| Road | 405–415mm |
| Touring | 420-435mm |
The downhill controversy is already explained, but you may be wondering why road bikes have such short chainstays.
The reasons are:
- Maximal power transfer
Roadies are obsessed with keeping all their watts going straight into the rear wheel. The shorter chainstays result in a stiffer rear triangle and a shorter chain. Theoretically, this combo should result in a more direct output.
It probably does. But truth be told, it doesn’t matter unless you are one of the pros? Are you? If so, send me a message in the comment section 🙂
- Agility
Road bikes are not touring bikes designed for retired stock exchange gurus exploring the mountains of Thailand.
They are built for speed, agility, and competition. The bikes must be capable of changing direction in an instant. It’s a live-or-die type of situation during a pro race. You can’t be competitive on a bike designed for calm and romantic rides to the local park.
- Compact frame design
The pros like small frames because they’re light, stiffer, and as already mentioned more agile.
You’ve probably seen road bikes with rounded seat tubes. The goal is to bring the rear wheel even closer to the bottom bracket shell. This trick changes the effective chainstay length of the bike.
Bike Type > Chainstay Length
A lot of people in the bike community are suffering from paralysis by analysis a.k.a. thinking too much.
Yes, the length of your chainstay is important. Hence the name of this article. But before obsessing about chainstay measurements, remember that at the end of the day, chainstay length is only one part of the equation.
There are more important parameters that come first.
Those would be:
- Bike type (an XC bike with short chainstays is still an XC bike and can’t serve you well for street riding.)
- Quality
In other words, first, make sure that your bike corresponds to your goals and is of decent quality. Only then, analyze its chainstays.
But since I don’t like to sound like a snob, I will also tell you one eternal rule of cycling:
It’s not always about the bike. Sure, you can’t win a big road race on a folding bike, but you can certainly go out there and enjoy life.
So, take whatever you have and use it while you still have it because you never know what tomorrow might bring.
Until next time
– rookie
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