robrob

Is the relationship to MPH (not RPM) linear? What I mean is when you lower the final drive 1st gear goes lower but you barely notice it but the effect on 6th gear is dramatic.

ZDan

The difference in speed between 4.10 and 4.77 gears in 1st gear at 9000rpm is exactly 4.10/4.77: 43mph with 4.10s, 37mph with 4.77s).
Difference in speed in 5th gear at 9000rpm is likewise dictated by the same factor, 139mph with 4.10s, 120mph with 4.77s.

Of course the difference in mph is much bigger at higher speeds, but that is exactly what a LINEAR relationship dictates!

And of course with either 4.10s or 4.77s, the rpm drop between gears is exactly the same, based on the differences in the transmission ratios. The difference is that the speeds at which you have to shift are much lower with 4.77s. But you don't end up at a higher rpm going to the next taller gear vs. stock diff gearing.

robrob

A difference of 6 mph in first and 19 mph in 6th isn't a linear relationship which is exactly what I've been describing. The relationship between gear selector and speed is not linear and this is what the driver experiences which is why it is important.

ZDan

43mph * 4.10/4.77 = 37mph. 139mph * 4.10/4.77 = 120mph. LINEAR relationship between speed and gearing, both in 1st gear and in 6th gear.

The relationship between adjacent gear ratios can of course be different for each upshift. Lower gears will be wider spaced and higher gears generally closer (except for cases with super-tall upper gears for cruise/highway, not the S). Fact remains that for a given set of transmission ratios, it doesn't matter what the secondary ratio or the diff ratio is, you have the SAME rpm drop between gears, determined by the relative difference in the trans ratios.

Going to AP2 secondary or 4.77 diff gears doesn't change the rpm drop going from 1-2 (9000-5875), 2-3 (9000-6518), 3-4 (9000-7055), 4-5 (9000-7519), 5-6 (9000-7515).

robrob

ZDan, I understand that the UNDERLYING function is linear, but the part the driver experiences (the important part) is nonlinear. I don't care that the RPM drop is the same between the gears, the speed of the shift points are what's important when changing the final drive.

For many tracks 1st and 6th gears are never used so we're basically saddled with a 4 speed tranny. By lowering the final drive we can compress the speed spread of the gears (not the RPM spread) and make 6th gear actually useful which adds another gear and flexibility to the transmission.

ZDan

Obviously if you have the option you'll want to gear for the specific track you're on (and in many instances, 4.10 will be "better" than 4.77 even if 4.10's don't allow use of 6th gear).

Why not just admit that you were wrong here in agreeing

JUSTINTHECOASTIE

MOAR SHIFTS?

when did say that

speedengineer

Yup, sorry ZDan, you are correct about same RPM drop regardless of final drive ratio.

ZDan

oopsie, quote failure!

JUSTINTHECOASTIE

^^^