Transmission: Gear Ratios

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by Chris Wood

This section is a comprehensive listing of gearbox ratios for the four major USDM gearboxes offered (two AWD, two FWD), and the JDM version of the W6MG1 AWD gearbox that some users have exchanged gears in favor of. Wherever possible, the numbers have been taken from fractional gear ratios and only rounded to three decimal places after the last calculation to preserve their accuracy. Included also are methods of calculating vehicle speed at a particular engine speed and tire spec.

--Multiades 03:37, 20 March 2006 (EST)

Calculation

Formulas

Vehicle Speed

To calculate vehicle speed from engine speed, tire spec, and gear ratio:

(eng_rpm * 60 min/hr) / (overall_ratio * tire rev/mile) = vehicle_speed

Engine Speed

Alternate; to calculate engine speed from vehicle speed, tire spec, and gear ratio:

(vehicle_speed * overall_ratio * tire rev/mile) / 60 min/hr = engine_rpm

Explanation

Take engine RPM (rev/min) and divide by the overall gear ratio; this takes engine speed and gives you wheel speed in RPM. The overall gear ratio number signifies the number of engine revolutions per wheel revolution -- for example 12:1 would be twelve engine revolutions per one wheel revolution (first gear is approximately this).

Now that you have wheel revolutions per minute, you must convert to revolutions per hour; you will need to multiply by 60 (min/hr).

Finally, to convert wheel revs per hour to miles per hour, you will need to take the revs per mile spec of your size and model tire and divide the number you have obtained thus far by it. For example, you can look up this spec on tirerack.com -- they list specs on every brand/model tire they sell. If you don't feel like looking it up, a good ballpark for the stock tire sizes (turbo or non-turbo, 16s through 18s) is about 808-810 rev/mile. Looking up your exact tire rev/mile spec is probably unnecessary, but its quite easy if you are after precision.

Example Calculation

Example calculation @ redline in third (6-spd, 809 rev/mile tires)

(7000 * 60) / (4.803 * 809) = 108.1 mph

Simple and accurate. This is the factory spec for Yokohama AVS ES100, size 275/40/17. Tire specs can be found at Tirerack.

Factory Gear Ratios

Below are listed the ratios for the three major manual gearboxes. The column marked "overall" is the basic gear ratio multiplied by the final drive gear ratio. The final drive ratio and individual gear ratios are included for completeness; virtually anything useful that one might want to do can be determined with the "overall" number.

W5MG1 (ALL AWD 1991-1993)

Gear Overall Indiv.
1st 12.200 3.071
2nd 6.908 1.739
3rd 4.383 1.103
4th 3.271 0.824
5th 2.620 0.660
Reverse 12.212 3.076
Final n/a 3.97

W6MG1 (USDM AWD 1994-1999)

Gear Overall Indiv.
1st 12.674 3.266
2nd 7.377 1.904
3rd 4.806 1.241
4th 3.555 0.918
5th 2.838 0.733
6th 2.281 0.589
Reverse 12.209 3.153
Final n/a 3.872

F5M33 (M/T FWD 1991-1999)

DOHC and SOHC non-turbo models

Gear Overall Indiv.
1st 12.833 3.090
2nd 7.612 1.833
3rd 5.054 1.217
4th 3.688 0.888
5th 3.077 0.741
Reverse 13.148 3.166
Final n/a 4.153

W5M33 (M/T AWD NA GTO 1990-1999)

Gear Overall Indiv.
1st 14.391 2.917
2nd 8.308 1.684
3rd 5.501 1.115
4th 4.110 0.833
5th 3.291 0.667
Reverse 15.624 3.167
Final n/a 4.933

(thread reference)

F4A33 (A/T FWD 1991-1999)

DOHC and SOHC non-turbo models

Gear Overall Indiv.
1st 10.097 2.551
2nd 5.889 1.488
3rd 3.958 1.000
4th 2.711 0.685
Reverse 8.613 2.176
Final n/a 3.958

W6MG1 (JDM AWD 1994-1999)

Gear Overall Indiv.
1st 13.568 3.266
2nd 7.910 1.904
3rd 5.155 1.241
4th 3.814 0.918
5th 3.045 0.733
6th 2.447 0.589
Reverse 13.098 3.153
Final n/a 4.154

Comments

FWD limitations, improvements

For the FWD TT cars who actually have the possibility of running out of gear, the car would have an effective top-speed of 170mph with the stock tire size at the stock indicated redline.

Team Rip Engineering(TRE) used to sell taller top-gears in 8%, 16% and 25% flavors for the F5M33, which would yield 183mph, 196mph, and 212mph top speeds respectively, all at the stock indicated redline (7k). I really don't expect to see any FWD TTs (or any 3/S cars for that matter) running at Bonneville, but those gears would give a much better top-end pull through a certain speed range and better highway gas milage. For example, with the stock cams, the stock 5th ratio might give the best acceleration from 120mph to 145mph, with a severe drop-off after 155mph. The taller gears would move the optimum "window" further up (say 130-160mph, or 140-170mph, or 150-180mph for the taller TRE gears respectively).

Currently they only list a 10% taller fifth.

Overdrive

A word on the term "overdrive", which I belive to be very misleading:

This term refers to gear ratios less than 1:1, which does happen before the final drive gearing (4th & 5th on a 5-spd AWD; 4th, 5th, & 6th on a 6-spd AWD). Once the final drive gearing is taken into account you will never see less than about 2:1 (which is extremely tall already). Can you imagine the engine turning the wheels one or more full revolutions for every engine revolution? If a 3/S had a gear that was 1:1 overall, redline in this gear would be over five hundred miles per hour (or 74mph at 1000 rpm). As you can see, the gear would be unusable; the engine would have no leverage over the wheels whatsoever.

--Multiades 03:37, 20 March 2006 (EST)

This article originated from a thread or post on 3000GT/Stealth International. (1929)