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Correct me if I am wrong, but changing the diff even if the ratio has changed wont make the speedo read incorrectly as it is measured off the output shaft from the gearbox.......

I might be wrong though :laugh:

Of course it's gunna be wrong if you change the final drive ratio. The speedo will read the same speed at the same rev-gear settings as it used to, but it wont correspond to the actual roadspeed

Shorter final drive ratio (i.e larger number after change, like 4.11 ---> 4.375) = Lower actual roadspeed than indicated on guage

Taller final drive ratio (i.e smaller number after change, like 4.11 ---> 3.57) = Higher actual roadspeed than indicated on guage

The ratio tells you how many times the pinion turns for each revolution of the crownwheel

Hope this helps :laugh:

Of course it's gunna be wrong if you change the final drive ratio. The speedo will read the same speed at the same rev-gear settings as it used to, but it wont correspond to the actual roadspeed

Shorter final drive ratio (i.e larger number after change, like 4.11 ---> 4.375) = Lower actual roadspeed than indicated on guage

Taller final drive ratio (i.e smaller number after change, like 4.11 ---> 3.57) = Higher actual roadspeed than indicated on guage

I stand corrected

Thanks

Of course it's gunna be wrong if you change the final drive ratio. The speedo will read the same speed at the same rev-gear settings as it used to, but it wont correspond to the actual roadspeed

Shorter final drive ratio (i.e larger number after change, like 4.11 ---> 4.375) = Lower actual roadspeed than indicated on guage

Taller final drive ratio (i.e smaller number after change, like 4.11 ---> 3.57) = Higher actual roadspeed than indicated on guage

The ratio tells you how many times the pinion turns for each revolution of the crownwheel

Hope this helps :laugh:

Thanks Shaun that helps alot, i raise this question because i suspect my diff is not stock. and the actual road speed is slower than what indicated on the gauge. (10km/h slower - was determined by Tom Tom GPS)

how do i know if my diff isnt stock?

cheers

A chassis dyno will be able to tell you what percentage speedo error you may have fairly accurately- get the operator to set the roller speed to 100km/h and see what your speedo reads, then again at 150 or so. You can then work out what % it reads over or under the actual speed.

Somewhere on this site, you should be able to find out various ratios, but some i know are-

R32 GT-R (GTS-t too?) - 4.11:1

GTS4 - 4.375.

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