Mountain Biking - 29er sprocket sizing/gear ratios

I put a karate monkey together with some extra BMX parts so I put on some 180mm profiles and a 25t sprocket (25-17, maybe move to 28-17). Is there anything bad about using smaller gears? I notice most people run 32t, is this more of out of convenience since it's usually the middle ring in a triple?

Thanks

the only real downfall is that there will be less teeth engaged at one time, resulting in possible slippage (but I wouldn't be too concerned) and more wear on the chainring. Other than that, I wouldn't expect a problem. The issue is really when you get too small in the back, like smaller than 16.

I would say that you are probably correct in assuming that most people run 32-34 up front because it is the middle ring in a triple crank.

The thing i was worried about mostly was if there was too much stress on the chain from not being on enough teeth. On my bmx bike i have a 9t which probably results in 4 contact teeth which i suppose in theory makes chains break faster. I haven't had much problems.

The point that 16 and bigger are usually pretty good as far as teeth contact is a good one, I didn't think of that.

Thanks!

I just purchased an outcast 29er, nothing fancy so it won't hurt if it gets beat up during the winter. It comes with a 42t chainring and a 18t freewheel. Now, Ive ridden downhill before but never a 29er, to me this gear sounds too high. Should a 38t chainring be sufficient for should I go lower? a 34t or even a 32T??

32x18 is a very popular 29er gear. It's a very personal decision though.

42 x18 would be good for commuting and pavement

I used to ride a steelhead set up with 24"s and a 38/18, I was just thinking that maybe, since i was comfortable on that it would be similar with the 29er.

use sheldons gear inch calculator (http://www.sheldonbrown.com/gears/)to find a similiar gear