The counterpart to chainstay length in a bike’s design is what’s called front center. Unlike chainstay length, which relates to the length of the tube, there is no tube that corresponds to front center. So why is it a thing?
It’s a thing because builders find it a useful way to consider weight distribution and toe overlap.
What it is
Just as chainstay length is the distance from the center of the bottom bracket to the center of the rear dropout, front center is the distance from the center of the BB to the front dropout. Like chainstay length, this measurement is not parallel with the ground.
Traditionally, builders would massage top tube length, head tube angle, fork rake, wheelbase and chainstay length to arrive at a client’s ideal geometry. Front center, like wheelbase, isn’t a number a builder will generally build to, like BB drop, but they will always be aware of what it is. And while carbon fiber bikes will often feature identical length chainstays on every size of frame for simplicity of tooling, builders working in steel or ti, will manage the proportions between front center and chainstay length for weight distribution.
Why haven’t a mentioned mountain bikes? Because today’s mountain bike’s are built around such shallow head tube angles, toe overlap is as rare as a penguin in the desert.
For anyone considering the purchase of a new bike, front center is really only worth considering for one reason, and it’s not weight distribution. Builders (and bike companies) aren’t going to send bikes out in the world with questionable weight distribution, so it’s safe to assume that aspect of a bike’s design is dialed.
Where front center does matter for the buyer is in considering toe overlap. This is a concern for more diminutive riders (anyone riding a frame with a top tube shorter than 54cm) and basically anyone buying a gravel bike. When I first learned to fit frames to cyclists, I was taught to position the cleat directly beneath the ball of the foot. Working with that standard, only the tiniest riders ran into toe overlap issues.
A dozen years ago, or so, bike fitters began positioning cleats more toward the center of the foot. When I made the switch, I went from having no toe overlap issues on any of my bikes to having toe overlap on any road or gravel bike that ran a tire 28mm wide or larger.
How big a problem?
Toe overlap really isn’t a big problem. That may sound crazy, but in normal cornering—i.e., any time a rider is countersteering—the front wheel never turns enough to make contact with toe of the shoe. To actually make contact, a rider has to position the crank parallel to the ground and then steer through a turn. This can happen at low speeds, like when rolling away from a light, or if you’re a cyclocross racer, pedaling through a slow, tight turn.
And that’s really the key to understanding toe overlap and why it’s not a big deal: As long as someone is countersteering the front tire will never make contact with the toe of the rider’s shoe.
There’s no magic number to look for if someone wishes to avoid toe overlap. It’s a number that increases as bike size increases. I know that for myself, I need a front center of at least 59cm if I want to avoid overlap with 23mm tires. As tire size increases, front center has to go up as well. After about 32mm, it is impossible for me to avoid toe overlap in an appropriately sized frame.
And if for anyone racing cross or hitting singletrack on a gravel bike, the trick is to remember to keep that outside pedal down when steering. Problem solved … except that there is no coasting in ‘cross.