Advantage of 12t vs 13t?

[Lambkawi]

If the gear ratio comes out to be the same,then is there a difference in running a 12t or a 13t sprocket? I recently read on this site that a 13t puts more stress on the motor. Is this true? I am about to buy new sprockets and would like to get the right combo. I want to keep the low end sweetness, but I am also running with 250 2 strokes and don't want to lose want what little I have in 5th and 6th gears on fast fire roads. Any suggestions would be appreciated.

 

[Green Hornet]

12t will give you a more torque/better acceleration, allow you to run a gear higher in the woods. If the woods are tight that may benefit you.

 

[adam728]

Well running a 12 or 13 tooth front sprocket won't give the same gear ratio unless you change the rear sprocket as well. A 12/47 combo basically equals a 13/51 combo.

Benifits of running 12/47 instead of 13/51.
More chain guide clearance
Slightly less rotating mass (smaller sprockets, chain will be 4-6 links shorter)

Cons of running a 12/47 instead of 13/51
Greater chain wear - the chain needs to make a tighter turn around the front sprocket which has been said to reduce chain life and increase drag.

I think either one may sacrifice too much top end for your liking. Either way you will give up about 8% of your top speed, so if the bike pulls 70mph now you'll be limited to around 65mph. A 13/49 combo is just about "right" in my opinion. Closes up the gaps between gears nicely, but without too much top end loss. I found when running dry loose sand on the wider trails I really couldn't jump the gap from 5th to 6th gear. Once in the power in 6th it would go just fine, but getting over the little hump was difficult. 13/49 gearing cured that for me. If your bike is stock there is a lot you can do to help the 220 rev more which means you can run lower gearing and not sacrifice top speed.

Some guys will recommend really low gearing, like 12/52 or something. They usually ride all single track and don't care if their bike runs flat out in 6th at 50 mph.

 

[cr125freak]

get a +2 in the rear it wont be as low as a -1 in the front but still will be noticeably lower

 

[AZRickD]

I have 13/50 only my newly-purchased used 2003 KDX220. I'm not particularly experienced but I'll give you my input.

I've just intalled a Trail Tech "Vapor" speedo/tach/water-temp-etc unit and, assuming it's calibrated correctly, it does about 70 mph at around 9,000 RPM (at which point the motor loses the will to breath). I ride it on the road to get to some of my nearby trails so I have the jetting pretty rich (although I might lean it out in the mid-range some as it is very hot in Phoenix right now and splooging pretty severely).

I've been having the inkling that it's geared down a bit lower than I'd otherwise like it. First gear is a real granny gear, and of less utility than I would have expected -- accept for long rocky climbs (then I don't mind it so much).

I've considered gettingin a slightly smaller rear, or even a 14T in the front but I fear that it would take out some of the single-track usefulness of second gear.

I'll have to get a lot more seat/peg time before I can have a good clue what I want to do with the sprockets (or the suspension, for that matter).

Rick