We recently received a great question from a customer asking how the reach on a 38cm 650b Straggler could be longer than on the 42cm model. They thought we had published incorrect numbers on our website, and although we are rarely perfect, the numbers were right. This got me thinking and it turns out they weren’t clued in on some of the nuances of bike fit.
Many riders know a bit about how to pick the right frame for their body by looking at numbers like effective toptube (ETT), standover height, stack, and reach. These numbers are great baselines for people with average builds, but some of us (me included) are shorter or taller than the average bear. Even more folks might have long torsos and short legs or vice-versa, so concessions need to be made on reach or standover. Luckily we are here to serve these people that fall outside of the norm, men and women alike. Although we don’t make women’s specific bikes, we offer a large range of sizes, and it just so happens many of the smaller ones are popular among female customers. I like to think of it as making great fitting bikes for people of all shapes and sizes.
The confusion starts to come in to play once we start looking at very small frames, like the 42cm and 38cm 650b Stragglers. The distance from the bottom bracket to the front axle (we will call that front center) has an absolute minimum with respect to toe clearance, so you can’t just keep shortening the front center in order to make a smaller bike.
By playing with the seat tube angle and headtube angle we can make a bike with a shorter ETT while still holding the front center constant. However, since reach is calculated from the BB center to the headtube, it is possible for a bike with a shorter ETT to have a longer reach than a bike with a longer ETT.
The bike shown in teal is the 42cm Straggler and the purple bike is the 38cm Straggler, by aligning the headtubes and overlaying the bikes, it is pretty clear to see the difference.
Whew! I’m tired after all of that. I could probably write a book on all the things that influence bike fit and frame geometry, trust me, you don't want to read it. Anyways, be on the lookout for some more frequent tech blogs from your favorite Surly nerds in the near future. Maybe this will become a thing...?