Well I just changed to the 12 th front sprocket, what a difference it's like a new machine , just wondered how many mph I lost on top end and can I still beat a stock 400ex? Awesome woods machine now!

 

kodiak2k,

do a search for this topic on this site. Going to the 12 in front is only a temporary fix. You should change your rear sprocket to a 42 or 43. The reasons for this will be found in the other posts.

 

i've had a sidewinder 12 tooth on my raptor for a few months. i can't imagine going back now. it makes 2nd gear totally functional now in the woods.

 

I agree, it makes a big performance difference. The problem is, when you go smaller in the front, you are causing the chain to change velocities a a much greater rate than with a larger front. That robs you of alot of hp, causes the chain to heat up too much and wears the smaller sprocket and chain much faster. The 12 is fine for a test but you really should spend the $$ and do it right with a rear sprocket.

 

Raptor720 said to check the 12 tooth postings, but that's like finding a needle in a haystack. After reading a couple dozen, all I could find was one or two statements that a 'friend of a friend' said a 12 tooth may be more stressful and this new robs horsepower thing that popped up in the past few weeks. What post was he refering to?

I can see using a 12 tooth adds more stress to the front sprocket, but I'd like to see someone back up this 'robs horsepower' statement with some facts. Like a Dyno run of equivalent gear ratios showing a measurable decrease in power. I can see the theory, but I haven't seen any facts.

IMHO, I can't see upping the rear sprocket because of the Raptor's inadequate ground clearance. The increase in rear sprocket diameter may be small (1/4"?), but I'll take the clearance.

 

I have changed the front and rear I was using just the rear sproket for a while and it had ALOT of bottom end It wanted to throw me off everytime I gunned it. I just recently put on the front 12 tooth sproket and it hasincreased my top end from stock a noticable change. This was tested on the street from the same place I ran it stock. Yes it DOES rob horse power just switching the front sproket to a lower tooth. It has been tested and is on the internet somewhere. If it that important to you you'll find it. *HINT* Renthal.com

 

Thanks for the tip on looking on the Renthal Site. It helps...some.
http://renthal.com/Resources/guide.htm

If I'm reading the site correctly,
"Gearing down reduces the speed at the rear wheel with a corresponding increase in torque"
Torque x RPM
Horsepower = ------------
5252

Baed on this, by gearing down you increase torque and a given RPM, which in turn calculates as MORE horsepower? At least, that's what it looks like it is telling me. Did I miss something?

They also don't really make a preference between changing the front or rear sprocket. They just state that changing the smaller sprocket results in larger gear ratio steps.

I went searching and found many other sites that talk about front vs rear as far as changing ratios, but with the exception of watching out for clearance issues - I found no articles saying a front sprocket change robs horsepower over changing the rear (same gear ratios).

If you have some more sites I can check out, let me know. I've been to dozens with no success - so I'm thinking urban myth.

 

When I was thinking of putting the 12 tooth sprocket on my Raptor, I asked my dirt bike mechanic about the issue of the chain overheating, loss of horse power, etc. He's a nationaly known race bike mechanic, and very respected. He told me that going to a 12 tooth wasn't a problem at all and that the effects that I was concerned about were very minimal. He said that it was not advisable to go to an 11 tooth for the reasons I mentioned, but that the only downside (for the 11 tooth) was slightly shorter chain life, and a slight decrease in horsepower because of the tighter turn the chain has to make. He said that these effects are very minor going from a 13 tooth to a 12 tooth. I even bought an 11 tooth for my Raptor for the very technical woods trails, but when I did the air box mods and installed the White Brothers slip on I decided that I then had plenty of low end with the 12 tooth.

Good luck,
Lorrin

 

Urban myth???

OK so, keep the 12.

I back up my knowledge with testing on the dyno, heat sensors, flow bench work, etc.