Tuesday, February 22, 2011

Typical road bike gearing

I'm curious what my companions will have on the ALC in terms of gearing. I'm reading that road bikes have something between 18-104GI's by utilizing a 11-34T cassette across a 22/32/44 chainring setup.

I did some further research and found a general idea of what different types of bikes can be expected to have:

Mountain Bike: 18-103GI's
Road Race Bike: 43-127GI's
All around: 20-90GI's

My KMX Tornado: 22-67.9GI's

Somehow I'm still a lot faster on the downhills than most DF bikes I've ridden with. They're not mashing down the hill though. I suspect my speed has something to do with my bent being more aerodynamic. I'm no physicist but theoretically, I would need less high end gear inches to achieve the same speed since I can take advantage of the momentum and aren't fighting as much resistance.

From experience, I think 2 extra gears up top would be ideal. Assuming there's a 15% increase in GI's per gear, that would put me at about 88GI's - far from the 100GI's that I original thought I may need/want.

This is good news. I can sacrifice quite a bit of high end gears to boost the low end. Calculating the same logic that I used for the high end gear to push the low end 2 gears down at 15%/each , I end up with around 15GI's on the low end.

A boom and chain ring setup from the old KMX X-Class satisfies the low end, but not the top end. The top end would pretty much remain unchanged whereas the low end is improved fairly drastically. My lowest gear inch will be 12.1 instead of 22.0. I'm certain I can climb any hill with that.

While the old KMX X-class gearing is supplied by a 42T chain ring, the newer setup from the KMX Cobra (mountain climbing version) is equipped with a 44T. I made this chart to decide whether it would be worth going for the newer Cobra setup or just stick with the available X-class one. I suspect the X-class one will be cheaper. It's priced at $250 shipped for the boom, derailleur, and chain rings.

I'm still considering the Schlumpf drive, an internal gearing system but that's priced at way over $250. It's more like $850-900 by the time it's completed. It involves not only acquiring the components, but customizing it and having it specially installed. The Schlumpf drive acts as a double or quadruple chain ring w/o a derailleur. It's typically used on geared unicycles. Who ever thought unicycles could be geared?? Well, they can and Schlumpfs technology makes it available....at a price - a steep one.

Looking at the numbers, this is pretty ideal! I would get virtually the same low end gears with high end topping out at 94.5GI's. If I got this setup, I wouldn't want to go further. I could commit to keeping it and not modding it any further.

The previous option of replacing the stock boom components with a new one from another KMX has an obvious price attraction, but I think I'd still have an urge to eventually increase the high end. With nothing else available, I'm topped out.

How practical would a higher top end be though? I think I've already gone 34mph. My goal had been 40mph, but I'm thinking that's just a ridiculous speed to go unless it's on a closed course, but even then it wouldn't be worth the extra cash it would cost to get there.

I'm still on the fence, but need to make a decision w/in the next month. I need time to get the components delivered, installed and tested before the ALC in June.


Post a Comment