Longer Cranks
 

Some time in the future I plan on getting a couple bikes running as my go-slow bikes, a touring bike (almost there) and road frame built as 1x5 or SS. When that happens I want to upgrade my fixed gear frame so it will be more of a go-fast bike rather than a general use bike. When I do this I would like go for something aggressive with less BB drop. I'm mostly curious how 175mm or even 180mm cranks will work out. Currently I am with an el cheapo Schwinn World Sport that has proximately 70mm of BB drop (and 170mm cranks). I'm guessing I'll be just fine but geometry isn't the side of bicycles I'm as familiar with. Will a typical track frame be suitable? I suppose I'll need 10mm less drop to get the same clearance with 180s as I have now or am I wrong?

This is all in an effort to get my bikes to be as user friendly for me as possible. Ideally I would have a frame with longer stays and larger diameter wheels, but what can I do.

You are correct that there is a direct relationship between BB drop and crank length vis-a-vis pedal strike clearance, but also other factors such as tire height, pedal width / height, Q-factor and even cornering technique. Given your leg length it makes sense to use longer cranks, although I'd still go about 5mm shorter on your FG cranks than on the geared / freewheel bikes. It may seem a little ridiculous, but in your case I'd consider 27" wheels, just as with me I'm better off with 650 c/b or 26" wheels, although I've yet to build a FG with 650c wheels or get cranks shorter than 165mm.

And I want to put 650b on my touring bike :P

It looks like my options for 180s is greatly limited (duh). Sram has some options while Shimano only has them in Dura Ace, other than that it's all MTB.

Being tall sucks. I should go for the full 200mm

What TT said, it's all intertwined.

But as for a go-fast bike, running a higher ratio, longer cranks will help out with torque, while sacrificing spin. But at your height, 175mm may very well be the spin-sweet spot. 180mm, maybe 185mm for torque. It's all personal fit.

Would recommend 27"s as well, if it weren't for the disparity of tire selection at that size. It would add some room for cornering at speed. Which would be the biggest concern when it comes to pedal strike.

The higher BB shell on any bike with track geo will help alleviate some issues of a longer crank. Still, this is cornering on flat ground, not the bank of a track.

I'd stick with shorter stays, in general, if possible. Helps keep the rear triangle stiff and typically leads to a more nimble, and solid---depending on the front end---tracking bike at speed.

There's bookoo DA track cranks on the ebay in big guy sizes. Not to mention the road cranks and Shimano 105. Q-factor, though.

just go 175mm. or change your gearing. the benefits of longer cranks can be simulated with different gearing

If you've been riding a 170, a 175 will be a noticeable improvement given your height. A typical track frame will have a 50-60mm BB drop, so with 175s you will have similar or perhaps even more clearance than before. Keep in mind that a higher BB is really only for clearance, and not for speed. I went the other way and got rid of my track geo bike to get a relaxed geo bike for commuting.

I'm not thinking about it for gearing reasons, just leg movement. I saw a ride video with a brief shot of me and I looked awkward with 175s

If you look at big bikes you'll see how the saddle ends up in line with the rear hub and I read a little that this takes away from the bike's handling :-/

honestly, for the cost of longer cranks and the very minute gains, it isnt worth the money.

Aye, but it does depend on the ST angle.

I prefer to have a bit of setback on the seatpost, to keep me close to on top of the rear axle, and within UCI guidelines.

I thought of you.