Sprocket Guide

[chr155_d]

I am looking to tame my sherco 290cc a bit, I have purchased a 41- t rear sprocket, will a smaller or bigger front sprocket be more beneficial to go along with this? I have also bought a slow action throttle so hoping between these two things it will stop it from taking off low down! Any other suggestions welcomed!

[copemech]

I think you may be headed in the wrong direction with the 41 rear, as the stock is 42. This in itself may well not create a dramatic change from stock though.

If one wasnt to slow the reaction of the bike a bit, you could use a 9T, as compared to 10, front gear along with the 41 rear and it will yield a decent ratio still slowing the bike.

The larger the rear or the smaller the front, the slower the bike will go in a given gear.

There are other things to reduce the power and smooth delivery, yet that is another topic. Read through the old threads.

[tony27]

Personally I wouldn't go smaller on the front as it means the chain has to take a tighter turn which is not good for both chain & sprocket, always better to work on the rear-greater scope for incremental change

Some guys have been running around 44t here to slow them down, would possibly mean second gear is used more often & sounds to be what you're after

Only thing about lowering the gearing is that it can actually make the bike react quicker, think of how quickly the speed changes when in first compared to fourth

Edited December 2, 2009 by tony27

[copemech]

Personally I wouldn't go smaller on the front as it means the chain has to take a tighter turn which is not good for both chain & sprocket, always better to work on the rear-greater scope for incremental change

Some guys have been running around 44t here to slow them down, would possibly mean second gear is used more often & sounds to be what you're after

Only thing about lowering the gearing is that it can actually make the bike react quicker, think of how quickly the speed changes when in first compared to fourth

Tony makes a point, yet in the field they will still be quick reguardless, in any of the lower gears, and a gear change to a higher final drive ratio will simply propel you less for a given amount of throttle.

One can slow the motor itself a bit through changes in jetting of the carb and ignition timing. And also smooth the motor through a change in the reeds.

Any and all up to personal pref here. You can make a bit of a dog of it , yet it will never be a 125 or 250! A 2.9 still has lots of power!

[chr155_d]

Cheers guys was out yeserday bike felt good had a slow action throttle on my old 07 290 and does make a noticeable difference, I see what your saying about the sprockets, Im aware that a smaller rear reduces the initial bite i was just wondering what accompanied this on the front, It is always going to be a 290 which i like, I suppose its all down to amount of time out on bike! Tony27 As far as rear greater scope for incremental change that is way over my head!! Sounds good though and will read into it!!

[b40rt]

Cheers guys was out yeserday bike felt good had a slow action throttle on my old 07 290 and does make a noticeable difference, I see what your saying about the sprockets, Im aware that a smaller rear reduces the initial bite i was just wondering what accompanied this on the front, It is always going to be a 290 which i like, I suppose its all down to amount of time out on bike! Tony27 As far as rear greater scope for incremental change that is way over my head!! Sounds good though and will read into it!!

Re incremental

One tooth more on the front is more than a 10% increase, where 2 teeth on the back is approx 4%.

[tony27]

Re incremental

One tooth more on the front is more than a 10% increase, where 2 teeth on the back is approx 4%.

Well put.

One of the guys I was trailriding/tramping on 2 wheels had said about how he'd gone down 1 tooth on the front of his gasser & down 1 at the back which was too much. General consensus was that going up on the rear would have been less drastic

Using the gassers ratios as examples you'll see what we mean

Standard 11 front 42 rear =3.82/1 reduction

Present 10 front 41 rear =4.1/1 reduction

Suggested 11 front 43 rear=3.91 reduction

Common 10 front 42 rear =4.2 reduction this is standard for shercos & used by lots of gas gas riders

Another benefit of altering the rear is not needing to use a half link

Hope that makes sense

Edited December 8, 2009 by tony27