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Joe's Corner

What about geometry?

August 18 — 2012

Something that every avid mountain biker knows a few things about, or at least pretends to...

Words by: Joe Graney, SCB Engineering

Mountain bike Geometry Diagram
Mountain bike Geometry Diagram

Many people skim geometry charts online and in catalogs, and make judgments on how something will ride based on a few numbers. Hey, I do the same thing, but that's kinda my job so I have an excuse.

So, how do we come up with this stuff anyway? Some bikes are pretty easy to understand, as they've been around for some time, and the type of terrain and handling expected is fairly consistent. As suspension travel has increased and riding styles have evolved, however, some of this stuff has had to get worked out along the way. We just finished the latest versions of our single pivot bikes. For the Heckler, it's the 4th complete frame overhaul in twelve years. The most common questions we get on the new bikes are about geometry and "what's different from the old one?" The simple answer is that it mostly boils down to the most common fork length used. The "axle-crown" heights on forks make a huge difference to how the bike handles. A huge difference. Huge and big.

Depending on the model, you can choose forks and headset configurations that can change the height of your headtube by 50mm or more. That's almost 2 inches, and it's the biggest factor that you should consider when building your new bike. We spend a lot of time tweaking the bikes so they work well for a certain use, and we pick forks to match the bike we've designed. The fork you choose changes almost every number for your bike on our geometry chart. Changing the fork travel changes the bike's effective top tube length, not to mention the bottom bracket height, seat tube angle, head tube angle, and chainstay length. With fork travel increasing by about an inch per year, the new single pivots really needed a complete frame overhaul to dial everything in for the latest travel in lightweight forks.

We strongly believe in choices, and the way we make and sell our bikes reflects that. One of the things we do in the time we spend developing a new model is trying out many different set-ups and adjusting as necessary. Here's an example: Our first two Bullit.3 prototypes got built in vastly different ways, with one ranging to the all-mountain side of things (Float R, Lyrik Solo Air 1.5, our AM kit wheels, 2.3 folding Nevegals, carbon bar, 135 QR rear wheel and a triple), and the other as a shuttle/lift specialist (DHX 5.0 coil, FR wheels, Totem Coil 1.5, DH bar/stem, Holzfeller DH cranks w/ an E13 chainguide, 150 thru axle DT rear wheel with a floating Avid Code brakes. 2.5 Kenda DH casing tires and tubes).

The bikes were totally different to ride, they handled differently and the suspension needed different set-ups to work the way we wanted. We brought both to Whistler, and, uh, we had fun. Both bikes worked well, but neither matched our geometry chart! An astute reader might ask why we don't publish different geometry lists for each fork size. We could, but it seems like we could spend our time working on something new that could be fun to ride rather than creating charts of something an 8th grade level of geometry could yield the truly inquisitive. We spend a lot of time, money and energy to make sure our bikes ride great. There are so many people involved who are bike junkies that just designing a bike we can all agree on is an achievement.

Maybe there are some companies that you can't trust with this sort of very personal decision about your new bike, and maybe you've been burned before. We're not geniuses here (I don't even know how to spell the plural of genius), and we make plenty of mistakes. Plenty. But we ride bikes, our friends ride bikes, our racers ride bikes, our bosses ride bikes, our receptionist rides, our salesguys ride, assemblers, the kit guys, QC freaks, web designer, engineers - you get the idea. We're pretty damn serious about making bikes that don't suck. So don't sweat the millimeters on the geometry charts. We already did, and it's cool.