Quote:
Originally Posted by GuidoK
you can calculate it easily from your data:
3244 in 5th gear. 5th gear has 1:1 ratio.
With the 4,10 diff your wheels are turning 3244/1/4,10=791,22rpm
Your tire circumference is 80,36", which means 788,45 revs/mile (1 mile is 63360")
So in 1 min you travel 791,22/788,45 mile, so in 1 hour thats (791,22/788,45)*60=60,21mph if you have the 1:4,10 diff
But you're writing you were doing 70.
So 60.21/70*4,10=3.53
So calculated you have a 1:3,54 diff. Thats a heck more closer to the stock diff. (its not even inbetween the stock diff and the 4.10 diff)
Variations in the calculation are your measured speed (did you use gps? or speedo), and tire wear (tyre wear can go up to 8mm or so, so 16mm in diameter)
4th gear is 1,23:1 and 3rd is 1,67:1 so you can now calculate it for those gears.
But I think somethings fishy here, your rpm spacing is not correct I believe? Are you sure your data is correspondant to the gears you give?
If you do the calculations with 4th and 3rd gear you get different values, which is, of course, impossible.
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I like the math behind this, I was driving and trying to give readings to my son in the passenger seat for him to write down. My rear tires are at EOL as they have 2/32nd left on them with plans to replace in the spring so it appears that would affect the calculations to some extent. I was using a bluetooth odbII reader for speed and for RPMs so no I was not using the GPS which could have an effect on the calcs as well. Sounds like I will have to take her out for another spin, always looking for an excuse!!