TRD final drive

[hare]

Anyone have one of these on their car?according to the graph,it should make the gear ratio less closer together,but how come TRD said it's better for 0-400m racing???anyone have some idea?

http://www.trdparts.jp/list_race-mis_ncp13.html

[kngrsll]

i thought about putting one in when i did my LSD, but man, looks hairy to install! you have to swap all your gears over to the other drive shaft.

[IllusionX]

error, longer final drive or shorter final drive does not make the gear ratio closer or less closer. The gear ratio are still the same. but a longer or shorter final drive will affect your top speed.

[hatchbackkid82]

Isn't the top speed determined by the ECU?

[Loren]

Originally Posted by IllusionX

error, longer final drive or shorter final drive does not make the gear ratio closer or less closer. The gear ratio are still the same. but a longer or shorter final drive will affect your top speed.

The transmission ratios don't change, but changing the final drive changes the overall gear ratio for each gear, as does changing the radius of the tire.

A taller (shorter numerically) final drive ratio will raise the potential top speed of the car (assuming you have enough power to get there and the ECU doesn't limit you), but it will ALSO raise the top speed in EACH gear of the transmission. You'll take longer to accelerate in each gear, and reach a higher top speed in each gear. The effect is exactly the same as if you put a slightly taller and more widely spaced set of gears in the transmission.

Taller gears are sometimes good for sprint races (1/4 mile, 400m, whatever) because they can eliminate a time-wasting shift right at the end. For instance, if you're timing 0-60 in some cars, you might need to shift to 3rd to get past 58 mph... where the same car with a slightly taller final drive (that should theoretically accelerate slower) can reach 60 at the top of 2nd gear up to about half a second quicker. In the 1/4, taller gears might get a Yaris through at the top of 3rd rather than shifting to 4th at the end.

[cali yaris]

In the 1/4, taller gears might get a Yaris through at the top of 3rd rather than shifting to 4th at the end.

4th in my case, and exactly right.

[Loren]

Just looked at the graphs on the linked page, they back up exactly what I said. The graph is a little short on detail, but if you look at 3rd gear top speed, it's clear enough:
Bottom graph is stock 4.3 ratio: top of 3rd = <120kph
Top left graph is TRD 4.0 ratio: top of 3rd = >125kph
Top right graph is TRD 3.7 ratio: top of 3rd = >135kph

For pure seat-of-the pants fun-factor acceleration, the shortest gear you can get is what you want. For higher top speed (pointless, you already have more gear than the speed limiter will allow) or for lower rpm cruising (better economy), you want the taller gear. Anything else is just playing games with shift points.

[ozmdd]

Garm, were you able to evaluate how your closer gear-ratios affected your autocross? I think I recall that you put in XB gears, right? Closer ratio? I have to shift to 3rd on long slaloms to stay off the rev limiter, so I'm curious how you felt about the gearing in that type of situation.



Loren - how much does running a 205/50/15 on a 15x7 wheel change the "effective final drive" of an 08 that came with the factory 15's?

[Loren]

Originally Posted by ozmdd

Loren - how much does running a 205/50/15 on a 15x7 wheel change the "effective final drive" of an 08 that came with the factory 15's?

Hell, Idunno. Do the math!

[cali yaris]

ozmdd, I have stock gearing still. I have access to the TRD gears from Japan, but haven't decided if I want to change yet.

My rev limiter is 7000, so on my Autocross outing I was in 2nd gear for the whole run, never made it to 3rd. Tight course, though, possible shift would be needed on a course with a longer straight in it.

And the stock gearing (with the extra power) works pretty well for drag racing.

[ozmdd]

Thx.