2000GT4.6

I am trying to decide weither I should go with a new 4.10 gear along with upcoming 31 spline install, or stick to the 3.73s or go 3.90s. I am not understanding the way a taller tire with more gear effects launch compared to a smaller tire with less gear.

ATM if I were to go with a 3.90 rear gear ratio, and a 26 inch tall tire according to http://www.f-body.org/gears/I would see about 119 MPH at 6000 RPM. With the 3.73 I would see 120+ mph easily, far more than I can trap. This would also get my street tires to around 117 MPH at 6000 RPM in 4th.

SO... am I better off going with a 4.10 and 28 (27.5 MT) tire, or would it not make a big difference compared to a 3.73 or 3.90 gear? The bad thing about a 4.10 is that on the street tires (315/35/R17) I loose ALOT of MPH in 4th gear, down to around 112 MPH. I would really hate to loose that 8-10 MPH on the street, not for the MPG savings but because generally speaking if I am in a close race, that last 105-120 MPH part of the race I can put em away (because of the centri power curve imo, not sure).117 would not be all that bad, but 112 seems afully low... maybe I am making a big deal of nothing.

To sum it all up: Explain to me how a taller tire + more gear means a better launch/run at the strip compared to a smaller tire/less gear setup, if the effective end ratio is the same? I am confused.

Quick Shot xMLx

Only thing I could see is with a taller tire you have more sidewall BUT you also have more rotational mass(and you loser top-end on the street).

I'd stick with 3.73s if I were you. When I pull my rear end out to throw 31 splines I'm probably going to switch to a 3.73(from 4.10). 4.10s are pretty lame for the street(I don't street race much but still). 28"s are huge(obviously I have some lol) and like I said earlier the extra rotational mass can't be good.

jjw88mustang

i have 4:10's and am running 26 inch slicks and 27 inch tires and my car can hit over 120(not in a trap)

Gene K

Both height and width effect traction. The tallest and widest tire you can fit will have the most traction.
It will allow you to run reduced pressure increasing footprint size.

The quickest tire will be the shortest and narrrowest tire you can consistently hook on.
This reduces rolling resistance and rotational mass.

The tallest gear (lowest number) will have the least frictional losses.

A 28" tire is around 743 rpm and a 26" tire around 800 rpm. That is with zero tire growth.
A 27.5" should be roughly 756 rpm.

You need to add roughly 2 mph to your trap speed when figuring rpm at the finish line.
This is because the trap speed is an average over the last 66' not the actual finish line mph.

4.10 x 743 / 60 = 50.77 rpm per mph

3.90 x 756 / 60 = 49.14 rpm per mph

3.73 x 800 / 60 = 49.73 rpm per mph

Assuming your trap speed is 117 mph.

(117+2) x 50.77 = 6042 rpm with 4.10 and 28's

(117+2) x 49.14 = 5848 rpm with 3.90 and 27.5's.

(117+2) x 49.73 = 5918 rpm with 3.73 and 26's.


If the car is hooking a larger tire with more gear and the samerpm per mph will be slower not faster.

code3GT

4.10's and 28" tire.

2000GT4.6

The only real problem with the 4.10s is its REALLY going to kill my streetracing IMO. Like it or not, there is simply no track avalible that I can go to more than about twice a year with my work and how far it is, but I can go streetracing once a week (were not talking about racing down the buisness loop either, but racing on abandoned areas where we setup and race for a few hours, aka no traffic). In other words, I hate to kill my streetracing for whats basically a bragging rights # (tired of hearing the mid 12s comments, even after whomping on 11 second cars).

I guess my question is, why is it that a 4.10 + 28 will be faster than a 3.90 and 26? the 26 + 3.90 should put me just at redline as I cross the trap assuming my MPH is about the same as it was before.

I'm just stuck at a bad point. I'm right on the edge between the gearsets/tires, and I can't really change my street tire height without going to a 15 inch rim etc... which I would hate to do (costs me lots of $$ and PITA).

JD1969

A 28 inch tall tire works better because of the increased sidewall AND a larger contact patch.

2000GT4.6

So, the gearing has nothing to do with it then correct? So long as the gearing ratio between gears and tires is the same final wise (say they both hit 120 MPH in 4th) its the same all the way thru the gear?

In other words, like the above poster said, if traction is not a problem then it doesn't matter right? Might as well go with the 26?

Magic_Man

I am running 26" tires & 3.73s in my C4 3 speed equipped car. I trap @119mph & I shift @ 6k. I'm almost out of gear at the end of the 1/4. I'll be going down to 3.27s eventually.