sprocket size help please

[Agemax]

can anyone help me with a mathematical equation to work out sprocket sizes which will replicate the standard gearing ratio on a gs1000 when fitting a different size rear wheel? obviously it will have to involve the circumference of the new wheel compared to the original but i cant work it out!

[Mark M]

can anyone help me with a mathematical equation to work out sprocket sizes which will replicate the standard gearing ratio on a gs1000 when fitting a different size rear wheel? obviously it will have to involve the circumference of the new wheel compared to the original but i cant work it out!

To get the new overall ratio with the tire size factored in, simply multiply the chainset ratio by:

old tire circumference / new tire circumference

So if your final drive is 15/42 this is a ratio of 2.8:1 (42/15...)

Say your old tire was 60" circumference and the new one is 55" circumference. Your overall gearing will now be:

60/55 x 2.8 = 3.055

If you want to get back to the 2.8 ratio you had, you need to change your chainset ratio to:

2.8 x 55/60= 2.567 (which would be about a 15/39 combo)

You can also use the rolling radius for both tires as well, if you can get an accurate measurement. But I would say it is easier to simply roll the bike and measure the circumference that way with a couple of chalk marks on the driveway.

Clear as mud, right?

Mark

[Agemax]

i think i get it mark, will have a play with a tape measure and a calculator and see what results i get. cheers mate

[Agemax]

well after a play with a calculator and my brain frying i have worked out that to maintain the same ratio i would need an 18t front and a 51t rear sprocket to keep the same ratio of 2.8/1, i think! i need the larger front sprocket to clear the gsxr swingarm. at the moment i have a 48t rear sprocket which i believe is standard on a gsxr1100m which only gives me a ratio of 2.6/1. which i assume dosent sound a lot but might make a lot of difference on the road. maybe? i think! not sure!!!!!!!!!!?