we run a honda crf-450x and are considering going down to an 11 or 12 tooth front sprocket. we have been advised against this by the folks at sprocket specialists, who claim that they have sold their 12 tooth front sprocket to customers who have later complained about having troubles with keeping the chain from flying off...

my question for all of the single cylinder teams is whether or not you run a front sprocket which is smaller than 13 teeth.

thanks in advance.

Using a twin, we ran a 10 tooth sprocket on our jackshaft. We used a 428 chain and didn't have any problems. The tensioner was designed to be close to sprocket to make sure the chain wrapped well. Im pretty sure the singles use a 520 chain. You might be able to prevent the chain from falling off by downsizing to a 428 or adding a separate tensioner arm or an idler sprocket.

We run a 525 KTM single, a 12T front sprocket and a 428 chain.

So far we have had no issues with the chain leaving the sprocket.

As long as the chain tension is sufficient and front to rear sprocket alignment is correct, you shouldnt have an issue.

Cheers!

Brendan

FWIW we've been running an 11 tooth front sprocket on an F4i for the last two years. Never had any problems with wear, jumping chains, etc. I wouldn't expect to see any issues on a single.

thanks for the replies. i just wanted to make sure the single cyl didn't have some power pulse issue or something.

i figured it really comes down to how much less chain tension they run on dirt bikes compared to an FSAE car. also, i'm guessing those who went down to the 12T probably left their rear sprocket at whatever comes stock, resulting in even fewer teeth engaged on the front sprocket.

next question: does anyone know where to get an 11T front sprocket for a CRF-450x? i haven't seen any for sale, but i was thinking that there may be another bike with the same drive pattern that we could steal from. anything?

We also ran 12 thoot front on our F4i on a 428 chain, without problems... going to test the 11T sprocket this month

quote:

Originally posted by poweredbyvdub:
also, i'm guessing those who went down to the 12T probably left their rear sprocket at whatever comes stock, resulting in even fewer teeth engaged on the front sprocket.

Quite the opposite - our rear sprocket was 48 tooth, and we shortened the chain center distance to something ridiculously close, and still we had no problems. We had an idler tensioner that increased wrap a bit, so I think we had probably 5 or so teeth doing the work at any one time. Of course on a single you'd have a much smaller rear sprocket, but the front sprocket itself can be made to take a pounding.

Hey guys,

not sure I can contribute anything to answering the question I'm afraid,

but we are also looking for a source for 11T front sprockets. We are running a yammy R6, and we've been running 13T for the past two years because it was the smallest we could find.
If anyone knows of somewhere in the UK that supplies these, or somewhere else we can order one from and get it sent to the UK - or even, if someone can purchase one and send it to us (!) that would be awesome.

many thanks in advance!
B

Just remember there is a bit of a double-whammy when reducing the size of your front sprocket:
1. There are possibly less teeth engaging with the chain, and therefore more load per tooth
2. The lesser radius of the sprocket means greater chain tension force for a given torque being transmitted - so another amplification of load at the tooth.

We were running an 11 tooth front sprocket on the WR450 at FSUK in 04, and we were spitting off teeth all over the place. (One of the ones we kept as a souvenir had only one tooth left on it by the time we got to it). We had a stock of 11T sprockets and from memory we were putting on new ones each day just to be safe. I think the rapid take-up with the single adds a bit of impact load into the whole equation and things can get messy.

If you are going to do it, make sure you buy good quality sprockets.

Cheers,

while on the topic of singles, impact forces and sprockets, i was wondering if anyone had tried building a damped rear sprocket. I have been looking into it a little, but i need to go talk to some one that knows about polymers/rubber that can help do the calcs. any one have any experience with this?

I'm not sure how common they are on motor bikes, but the VFR750 has a rear damped sprocket. You could get one at the scrap yard and quickly measure elasticity and damping. Maybe use the entire unit :-)

Igor

Try Talon in the UK fro sprockets -

http://www.talon-eng.co.uk/

Sorted me out with some great alternatives for the Aprilia and also splined our Dyno flange at a great price.

Cheers

Dave