Hi,

Is there a difference in a 12/48 front/rear sprocket combination versus 13/52?  Mathematically, the ratio of both is the same, 4.00.  Does one or the other have any advantages, or since they are the same overall ratio, do they have exactly the same characteristics?

I have a 2-Stroke 2003 CR250R with the 13/48 stock sprockets.  I live in Colorado and do mostly woods/technical riding.  Lots of tight turns, then oh crap, up some very steep rock sections.  I find myself feathering the clutch while trying to keep the front wheel down.

Yes, I know, 4-stokes are great for trail riding.  Most of my friends have 4-strokes and I'm sure I'll have one some day, but for now, I still like my squirlly 2 stroke.  I just need more low end.  Everything on the bike is stock.  I'll look at a FFW and pipe, etc at some point, but want to start with gearing.

Does anyone know if there are any differences in 12/48 vs. 13/52?  

Thanks!
Jeff

You will use a diferent length chain and your rear wheel will be in a different place. Some sprocket combinations will not work due to the limited amount of axle adjustment available.
A larger front sprocket is advantagious, but so is a smaller rear.

Edited by moto vita, 08 May 2012 - 03:29 PM.

Makes sense.  Thanks

how would your wheel be in a different place? just tale links out of the chain.. and i still dont see how you answered his ?, mathmaticly the ratio is the same, but does it still act the same?

LukeYZ426F, on 08 May 2012 - 06:32 PM, said:

Mathmatically, they are the same, but as moto vita stated, the larger diameter of both front and rear sprockets affects chain length and rear wheel locattion depending on how it all works out.  Personally, I prefer to run as large a front sprocket as I can.  The larger the sprocket, the less friction.  Now, is the difference between a 12 and a 13 big enough to notice?  I do not know, but why take the chance?  

I have always heard "drop a tooth in front on a 2 stroke to get more bottom end for trail riding".  If you're going to only change one sprocket without changing the other sprocket and the chain, buying a front sprocket is the cheaper way to go.  However, I need to upgrade from the stock sprockets and chain, so I'm going to buy a kit.  

As you guys have pointed out, I think it makes a lot more sense to go for the 13/52 over the 12/48.  Someone else told me about a situation where they were running too small of a front sprocket and it wore through the chain guide quickly, and started to cut into the swing arm.

The other side of the coin is that your rear chain guide has to be able to acommodate the bigger sprocket. I think (from memory) that 52 is about the biggest sprocket the stock chain guide can handle. If needed you can probably modify the guide to fit.
Also the bigger sprocket will be more likely to contact rocks etc,. thats why trials bikes use sprockets of 40-42 teeth.
There's no easy answer, but your doing the right thing by considering your options.

okay i just did this on my 450. i tried a 12t to see if i liked it, i did and rode with it awhile. now i put a new drive on it 13/52 with a 116 link chain. it shortened wheelbase maybe a 1/4".

still a little confusedd.. is the different combos with the same ratio EXACTLY the same gearing..

LukeYZ426F, on 09 May 2012 - 03:49 PM, said:

it is exactly the same final drive ratio as you originally stated.. maybe the TOP 5% of riders in the WORLD would feel the difference of the 13/52 vs. the 12/48 if you could get the axle position exactly the same. According to SOME there is a change in the way anti-squat works when you get on the gas and roll off the gas with the 2 different combos.. I usually say "yea-right" and roll my eyes to that. I highly doubt anyone reading this, me included, could ever tell. 13/52 and 12/48 are the same final drive ratio, you would need 116 links for the 13/52 where you could still use the stock 114 link chain with the 12/48 ..
axle position on the other hand IS something many better riders will feel. It changes a fair amount of things moving the axle significantly forward or back. But again, for 99% of us, don't worry too much about that. you will be pretty safe all teh way forward, or back.

Edited by MELK-MAN, 09 May 2012 - 04:08 PM.

yeah ratios are that, ratios, no mater. gearing makes a big difference power delivery and a flywheel weight would help also. te250 husaberg has a 36 carb.

ok, so just to clearify, no mater what the sprocket size if the ratio is the same it will perform exatly the same??? sorry im beating this to death its just had to type what i want to say lol and im getting ready to drop come coin on chain/sprockets but the bigger rear is eating my guide faster

LukeYZ426F, on 09 May 2012 - 05:28 PM, said:

but going to a 12 from a 13 in the front will wear the swingarm guide faster (the front sprocket is now smaller).. if your axle is way forward right now and your at 114 links.. go with 116 links. Moving the axle back will give you some additional clearance on the lower chain guide, and it won't get worn as fast.
Do sprocket combos that equate to the same drive ratio perform the same ? for the most part yes. that is a pretty big change (going up 3 at the rear, or down 1 in front). Why not go with say a 50 rear and stock 13 front.

Edited by MELK-MAN, 09 May 2012 - 05:36 PM.

MELK-MAN, on 09 May 2012 - 05:34 PM, said:

you can try a 12 and it's a fairly cheap experiment, but don't run it long.

yup.

I live in SW CO and have KX250, I've been playing around with gearing just like your talking about. Right now I have 12ft 50rear with a 11oz FWW. I lost top end but it rocks in the single track goat trails and I can now use more gears than 1st and 2nd.

I live near Denver, about 30 minutes from Rampart Range.  Also ride some of the mountain passes around the Continental Divide.

I bought a 13/52 kit, but haven't had a chance to try it out yet.  Going to Moab this weekend.

The gearing should make a big difference.  Did the 11oz FWW make a noticeable difference?

I really like the FWW it was very noticeable and allows you lug the engine down and tractor around. (i dont think I would go more than 11oz though)