Advice for a sprocket change needed

[wilko20]

I have a yzf R125 and my chain is reaching the end of it's life and will need replacing in the next few hundred miles I was planning in changing the rear sprocket at the same time.

My question is what sort of effect will I get from fitting a bigger or smaller sprocket I have read that you can increase speed or acceleration by doing this but you lose the other I wanted to know what sort of difference I could expect?

The bike hits the rev limiter in 6th gear at 84mph (down hill on a privet road ) I really need no more than 75 so to be honest I would look to increase acceleration and lose a lil of that unused top end!

How should I go about this and what effect will I see ( how much gains to acceleration and loos to top end to teeth added/ removed)

Thank you in advance

[Stu]

first of all replace the chain and ALL sprockets together as they wear together

lowering the teeth on the rear will give you more top end but will struggle to pull away

raising the number of teeth will give you more acceleration but less top end

also the same applies for the front sprocket but in reverse

lower teeth more acceleration less top end

more teeth less acceleration but more top end

If I was you I would look at around 2 -3 more on the rear

[Joeman]

If I was you I would look at around 2 -3 more on the rear

Or minus one tooth on the front will have similar results.

Front sprockets are cheaper so you could buy a standard front and a T-1 front and compare the results.

You will get better acceleration but reduced top speed.

[Stu]

This is true joeman

But I always advise against it as doing it on some bikes causes the chain to rub on the swingarm and cut through it