Rm 250 sprocket sizing help

I've just recently bought a rm250 and for the most part I love it but I when ride the other weekend tackling some step fire breaks and found that I couldn't get up them.i was in first gear and was finding I was just getting heaps of wheel spin but as soon as a looked for second I found the bogging down and stalling. I'm just wondering if first gears to tall coz it seems it is. Current sprockets are 13 and 49 just wanna no if there is a better sprocket combo I could go with or if anyone recommends anything

Increasing the size of the rear sprocket can slow down the tire speed in 1st gear.  It can make it more like a 'granny gear' for crawling around.  Of course the trade off is, you loose some top speed, which dependent on the type of riding you're doing, it may not be a problem.  Step up to a 52 tooth sprocket, and you will notice a huge difference in 1st and 2nd gear climbing.


Another option is changing only first gear ratio.  That way you can have the climbing ability without affecting the other gears, and loss of top speed, but that's alot of work to do that.


Just a little sprocket trivia:

The amount of teeth on a sprocket has nothing to do with the gear ratio.  The diameter of the sprocket is what determines the ratio.  The amount of teeth is simply relevant to the diameter of the sprocket.  You can have 100 teeth or 50 teeth, the ratio will be the same as long as the diameter doesn't change.  Of course the chain would have to accomdate the different size teeth. 


Ok, carry on. 


yea im just looking to see what other people that have been in the same situation have done. not to concerned about losing top end speed i just get up some of these firebreaks my mates on 250f's make look way to easy , ive picked up a 12tooth front to try which i was told should work out to be the same as picking up 3 to 4 teeth (roughly) on the rear.

A 13-49 setup will give you a 3.76 final drive ratio.


A 13-52 setup will give you a 4.00 final drive ratio.


a 12-49 setup will give you a 4.08 final drive ratio.


The 12 tooth sprocket is may be what you're looking for.  Some of what you may be noticing with your freinds 4-strokes, is the low rpm grunt and stability.  If you get you gear ratio low enough, your 2-stroke can act very similar even off the pipe.


I just noticed your location. 


What time is it down in the land of Kiwis?

10:01 am Friday 30th August. Yea gain a bit more torque is wat on after gonna put the 12 on tonight and go for a ride tomorrow ill let ya no how I get on

Ok, test it out and be careful. :ride:


Does New Zealand have the Brown Snake? :jawdrop:

Nar that's Australia they have all the poisons animals we only see goats when we riding

Edited by BarnettN

I'm going to throw in my personal experience with sprocket sizing. I normally run the stock size sprockets for offroad and mx. I'm a big oem proponent....

2 weeks ago I was doing some maintenance and saw I needed a new rear sprocket badly.  I found some in my shed that I bought from RMMC last year, on sale.

They were all 47 tooth. The oem is 50. I figured I wasn't racing so what the heck and threw it on. My next track day was at a jumpy, elevation changing place. I was blown away by the amount of traction I was getting.  I could also hold the gears much longer than before. I didn't get the low end bogging that I was expecting. It was very 4 strokeish.  A buddy rode my bike today and he said the same thing.

Offroad may have different requirements, but it's working great at the track....

12 tooth works swell, it has made the bike act similar to a 4 stroke heaps better on the hill now. im able to hold her in 2nd and 3rd at ease and if i have a cock up and the back wheel goes astray and in to some loose slash i can just start chopping down gears and keep her going without bogging and stalling.

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