box ratios.

[67worshipper]

is  a 1.21 4th gear with 3.88 ring and pinion gonna be to revvy for motorway use.im going to run 205/70/15 tyres to try and counteract it. whats the rpm at say 60mph or 90kph gonna be?

[Dougy Dee]

My calculator shows:
3000 rpm = 50 mph
3500 rpm = 58
4000 rpm = 67
4500 rpm = 75

Turn the radio up...

[67worshipper]

thats what i worked it out to be as well dougy. a bit steep need to keep the revs down. whats everyone elses cruising speed?

[Randy Jewell]

I have the same tyre size,ring and pinion and a 1.21 fourth gear and at 65mph is about 4000 revs

But acceleration is awesome

[67worshipper]

do you motorway drive it randy? lookin to drive to avon park and santa pod which is 80 and 160 miles away but unsure of driving it.

[Randy Jewell]

Yep, the bug see's regular motorway use like today as it was nice and sunny.

[67worshipper]

whats your cruising speed then randy?

[Peter Roberts]

Randy cruises at 60 mph , I followed him up to the Volksworld show in my Mercedes Sprinter van , that has a pretty acurate speedo .

He brought the car to work today , as the sun is shining , layed rubber right across the car park 

[67worshipper]

its not overly stressed then pete at that speed? nice pair there! n i wasnt even lookin down somebodys top!

[Peter Roberts]

No , 60 is about 3500 , seems fine , depends on how much lift you are running , Randy runs 0.585" , if you go over 0.600" I would probably keep it to 3000 RPM .

[67worshipper]

im running an fk8 with 1.4 ratio rockers.not sure what the lift is but not as lairy as randys.