///MDex

This is kind of a question that spans multiple forums, so nobody crap on me for putting here.

Alright guys, I know LSDs have been discussed over and over and over again, but little has been written about the ratios and how the increased ratio of the RMM/Supra 3.76 unit will affect larger wheels & tires.

So here’s my question to the math / ratio / rotational gurus:

Now I know that MeanGene still hits rev limiter every once in a while with 18s / TC / & 3.76 LSD.

Obviously, I've now got 19s on my rear. How likely am I to still hit the rev limiter with them?

Here’s the math I’ve done so far……..

Factory 17s (235 45 17) with the factory open 3.23 (823 revolutions per mile)
Aftermarket 19s (275 35 19) with the 3.76 LSD (783 revolutions per mile)


Math:
These ODs are taken from here:
http://www.tirerack.com/tires/Spec.j...+Pole+Position

going from 3.23s to 3.76s is a 16.41% increase in ratio
[[[3.23-3.76]]/3.23]*100

going from Factory 17s with tires (235 45 17) (OD= 25.3") to 19s with tires (275 35 19) (OD=26.6")is a 5.14% increase in OD inches
[[[25.3-26.6]]/25.3]*100


So, if I read this correctly, the much higher gear ratio is being offset by my larger wheels and tires, but not by that much, so am I STILL looking at an approximate 11.27% higher ratio than stock even with my 19s?

I'm set on the 3.76 unit because I want to get the holeshot (huh huh, I like that term) back up to factory, and then some; heck, don’t forget about the weight of these 19s too.

Alright - lemme have it!

GS400_PUSHER

Hey, Dex you sound like you got it down to the dime! I agree with you , I wonder too. Also you sound pretty smart .....you NERD!!!!...lol

HI98GS

I have 19's and also am running the 3.76 gears. So far, I have hit it hard a few times and have not hit the rev limiter yet. I also have hit it hard on the freeway when I am coasting at 55 then accelerating as hard as possible. The car downshifts but does not hit the rev limiter. I have yet to try this with my 17's.

I also have the 3.23 and am waiting for the shop to call me because they are putting in the TRD LSD. We'll see what happens.

Mr Johnson

Hmmm.... Your wheels should offset it some but I've been wondering about this whole hit the rev-limiter shifting thing for a while.

My 2000 with the SC has the shifting issues in the first couple of gears. The RPMs rise too quickly and the goofy electronics don't react quickly enough. I had assumed that was the case with the taller gearing in the RMM too since it would get the revs up too quickly for the ECU to make up it's mind about whether it was time shift or not.

What seems weird is that the 98 GS SC cars don't seem to have the shifting issue as badly as mine does (or at all) or else the owners are lying So are the electronics in the 98s different from the 2000+?

If not that then are some engines just plain old stronger and fall more easily out of the "spec" that the tranny controller was designed for?!?

Just trying to bring a different angle to this,

Peter

itsallgood

Hey Peter,

This is happening to you also, and I thought I was the only one.
The shifting on my car is kind of funny too, now that I have the supercharger on.

Aloha,
Keone

Mean Gene

Peter - Your stronger engine theory seem valid as the shifting issues seem to creep on on those of us who have modded our cars. The electronics in the tranny must be designed for smooth shifting &, as U say, can't make up their minds when confronted by rapid acceleration. That's all the more reason to install Mo's valve body upgrade ( didn't U get one with your supercharger install? ) or at least hope they hurry up & perfect/release the tranny ECU. That way we can tailor our shifting points to allow for gearing changes or horsepower increases.

Mr Johnson

itsallgood: Yes, this is a known "weakness" in the Lexus transmission. When you produce a lot of power it doesn't like shifting. It should be happening to everyone at our power level but some folks supposedly don't have a problem. That's why I'm wondering about the electronics issue too.

Mean Gene: I got the valve body kit, a bit after the original SC install, but it doesn't help *my* shifting issue although the shifts are firmer under anything less than full throttle. Bring on the AATC (assuming that helps).

Peter