As title says. Converting from car engine to R1, current diff is 3.92. I assume this would not be suitable. Want to stick with sierra diff, what should I have?

Ben.

Austen posted a link to Speed Calc.

Its an excell spreadsheet that allows you to estimate / calculate max speed in each gear, with a specific engine, diff and wheel/tyre size.

Go here about half way down.

HTH

Mike

3.92 would give best acceleration in each gear but lowest top speed in each gear. For a 1998 R1 fitted with 195/50/15 tyres, you would get a rev limited top speed of 112 MPH.

A 3.62 diff (like mine) would give 120 MPH.
3.38 = 129
3.14 = 139

a 3.14 diff with 195/50/15s would give 63 MPH in 1st where as a 3.92 = 49 MPH.

low numbered diffs = better cruising but higher clutch wear.

Higher numbered diffs = better acceleration but noisier and lower top speed.

Best compromise for an R1 is a 3.38 in my opinion. Trouble is, if you want an LSD you can typically only find a 3.62. What I did on my R1 indy was to put the crown wheel and pinion from a 3.38 into a 3.62 LSD diff to get a 3.38 LSD. Worked very well but will obviously cost you extra 'cause you have to buy two diffs. Mine was a trackday car hence I wanted the LSD and the legs not to be bouncing off the rev limiter on the straights.

If you are not too fussy about top speed a 3.62 LSD is fine - the R1 is a bit higher geared than most bike engines.

Hope that helps

Paul