I've got a 12 tooth now with a stock 40 tooth rear. I am buying a Renthal 42 tooth today and was wondering: will I need to lengthen my chain or get a new one in order to use the 13/42 combo? Thanks.

 

If your chain is worn replace it & the front sprocket along with the rear. It is always better to replace all sprockets & the chain at the same time. A worn sprocket will eat up a new chain in no time & a old chain will wear out a new sprocket & the new sprocket will wear out the old chain. Confused? If you look at your old sprocket next to your new one & can see a diffrence then your old parts will wear out your new ones at an abnormaly fast rate.
If your old chain has streached enough that you can install it over your 13/42 by just backing off the adjusters I would replace both sprockets & chain that would give you a much longer life on your parts.

 

Sounds good MOOSE. I've probably only got about 4 or 5 rides on the front 12 tooth and the 13 tooth doesn't have many more than that. I've also got a new chain in the stock length so I've probably got the longevity issue covered. I guess what I really was asking was: if I put my new chain on with my 13 tooth and 42 tooth, which is stock length, will it fit or will I have to add links? I know I didn't mention that I had a new chain in the first post. Sorry. Thanks for the help.

 

I've been running the 12/42 setup. Like it much better than stock. I'm guessing you could use the stock chain length. I just wanted to comment for you not to use an aluminum sprocket. I wore one out on one weekend. The power and conditions are to much for it. I'm going to get a stainless steel one for this season. Good luck.

 

Thanks for the info. Does anyone else think that a Renthal aluminum sprocket is not a good choice? It was sort of spendy so I'll just return it and get a different material for a little more dough if this one won't last. I'd rather spend a little more today than 2x shortly down the road. By the way, Renthal says that they have a special 7075(I think those are the numbers) aluminum alloy that is super durable on their rear sprockets. Any input is appreciated.

 

Stick to steel sprockets(weights not an issue), also running the 12 tooth front stucks a wee bit of power turning the tight radius. I run the 13 and 42 sprockets and that covers most riding conditions. I also replaced the chain as it required another link.

 

I was running the 12/42 and went to the 13/42 with a new R3 Renthal chain stock 92 link. It fit with the 13/42, there definitely isn't a ton of room for adjustment but it fits.