Welcome to Netrider ... Connecting Riders!

Interested in talking motorbikes with a terrific community of riders?
Signup (it's quick and free) to join the discussions and access the full suite of tools and information that Netrider has to offer.

Playing around with sprockets

Discussion in 'Technical and Troubleshooting Torque' started by mattb, Feb 18, 2008.

  1. Hey Guys.

    I'm having an absolute hassle getting a standard rear sprocket for my SR500 (Peter Stevens, Yamaha City, Clipstone - after calling their various suppliers none can do it!), and I'm in a hurry cos the old chain's run out of adjustment and I've got the other new bits ready. Will no doubt find one, even if through a US supplier, but in the meantime the best I can do from shops in Melbourne is a 42 tooth rear (as opposed to the OEM 44 rear) which I've gone and ordered. The SR is grumpy on the freeway as it is so it's no good raising the revs, and as a tooth on the front equals about three on the back I figure I'll match this 42 with a 17 on the front (as opposed to the OEM 16 teeth sprocket) to keep it close to the standard ratio (so now 42/17 as opposed to OEM 44/16) albeit perhaps better on the freeway. My question is, fitting things aside, does it matter at this level where the gain and loss of teeth are? Does going down on the front and up on the rear differ in performance from going up on the front and down on the rear, if in both cases the ratios are basically the same?

    In future I'll go to an XT500 520 chain and sprockets (with spacers) - no supply problems there, but I've already bought the 530 chain and front sprocket (I intend to try 17/44 when I can eventually get the 44 rear, for the freeway's sake).

  2. Here I'll answer my own question (or rather Dan will):

    "When you get new sprockets, you might want to consider changing gear ratios. This can really help the bike be more enjoyable to ride. For example, if you want to lower your engine RPM at highway cruising speeds you can either get a bigger (more teeth) front sprocket or a smaller (fewer teeth) rear sprocket. If you need more power up through the gears on a dirt bike, you can get a bigger rear sprocket or a smaller front sprocket. Generally speaking, one tooth change on the front sprocket equals about a 3 1/2 tooth change on the rear sprocket. It's best to keep the front sprocket as big as possible to lessen chain velocity as the chain rounds the sprocket, however it is cheaper to change the front sprocket as opposed to changing the rear. Bottom line... if your bike has trouble climbing that hill, (not enough power) go one tooth smaller on the front (counter shaft) sprocket. If it revs too high in top gear... just won't go fast (MPH) enough... go up one tooth on the front sprocket."


    Settling on a 16/42 sprockets might just be the compromise that suits me between the OEM 16/44 and a change to 17/44!
  3. 17/42 as in your original post is a 10% decrease in revs, but the 16/42 sounds like a good enough compromise of 5% reduction in revs over the oem choice.

    Note that Dan's gearing conversion only works for sprockets with a 3.5:1 ratio, such as on dirt bikes. In your case the ratios are from 2.4:1 to 2.62:1 and 2.75:1. That means one tooth on the front is similar to 2.5 teeth on the back...but I haven't seen a half tooth in ages.


    Trevor G

    PS What's wrong when can you buy half links for chains, but you cannot get a half a tooth on a sprocket!??