shapelike

The latest and greatest commuter/urban assault/cx bike will be fixed and single speed. On my current fg bike (Pake) I'm running 165mm, but my road bike has 175mm cranks. I'm wondering if I should meet in the middle and run 170s on this new bike. I really miss single speed, so the bike will likely end up seeing 50/50 usage between fixed and ss. I'm just paranoid about pedal strike when I'm running the bike fixed and if I'll have enough leverage when I take the bike offroad.

The new bike is an On*One Il Pompino, the cranks will likely be the Sugino RD2 Messengers.

BB drop on the Pake is 58mm.
BB drop on the Pompino is 66mm.

trackstar10

keep the 165s, and just use a slightly lower gear. all longer cranks do is decrease the gear ratio by about 3%, and especially off road, pedal strikes suck.
ex: if you have a 42/16 with 170s, its about equivalent to a 40/16 with 165s.
the only reason people use 175s on road bikes is because they simply can, and because its easier to manufacture a longer crank arm than make a whole new set of bigger cogs and smaller chainrings.

stick with the 165s, especially because your new bike has almost a centimeter more bb drop.

trackstar10

also, if you ride the same gear ratio with 165s, youll build up leg muscle so you wont need extra leverage.

fatbat

with the high BB & fat tires of the cross bike, you should be able to run 170-175 cranks without problems. The added leverage is usefull when grinding the bike up steep hills. It's also easier to transfer spinning skills to the road bike with 175s.

marqueemoon

As long as you're running decently fat tires, 170mm sounds right for 50/50 fixed/ss use. Fat tires will raise your bottom bracket significantly.

The only reason I would go any shorter is if you're going to ride fixed off road.

shapelike

Thanks for the input, all. On the street I normally run 20mm tires (we've got some old stock at the shop that no one will ever buy so I've just been using them up). I'll run larger tires through the winter and offroad, obviously.

TimArchy

If there are hills where you're at I'd say go for 170's. I've had some on a bike without a super high BB and been ok. But I can really feel the difference when the road (dirt?) starts to go up. A bigger concern may be the pedals you're running and the Q-factor (a measurement of how far the crank arm sticks out from the frame) of the crank. If you have a crank with a low Q-factor and lower profile pedals (track style or better yet, clipless), you will be able to run a longer crank without increasing your chance of pedal strike, at least when turning. The best crank I've found was an old Gipiemme road set that cleared the chainstay by a mm or so. The sugino RD set looks to be pretty tight, especially with a 103mm BB.
All that said, my friend is building an il-pompino fixed with 165mm MTB cranks. Huge Q-factor but shorter length works for him.

shapelike

Time ATACs, so I'm not doing anything really stupid to increase the possibility of pedal strike.

mihlbach

I have 170s in my fixie and 175s on my roadie. The difference is slight but noticeable. I like the 170s better better and ride them most of the time. Whenever I get on my roadie, the longer 175mm cranks annoy me. I can't spin as fast and when I really crank it up, I start bouncing. Its not that 175s are bad, its just that I'm not used to them after thousands of miles on 170s. Stick with one crank length, adjust your gearing accordingly, and you'll be able to take advantage of your spinning skills on both bikes.

Jumbo

How come this sounds very unlogical to me?
You will travel further with longer pedal arms...