Tremec gear ratios vs speed

[Mrzero]

Hey everyone, I found some Tremec gear ratio information on Car and Drivers website. I crunched some numbers and here are the maximum speeds for each gear at 7400 RPM.

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[Norm Peterson]

Hey everyone, I found some Tremec gear ratio information on Car and Drivers website. I crunched some numbers and here are the maximum speeds for each gear at 7400 RPM.

I'm afraid that tire calculator doesn't understand tire flexibilities any better than the rest. All those speeds are about 3% optimistic, so at 7400 rpm the speeds should be a lot closer to 46, 67, 93, 121, 150, and 239. This isn't too important in street driving, but it can be at autocross, road course driving (anywhere from HPDE up to W2W racing), and even drag racing.

Do yourselves a favor and divide the speeds from any of the online tire calculators by 1.03.

Wish they'd just round their answers off to the nearest whole mph, too.


Norm

 

[shogun32]

All those speeds are about 3% optimistic,

but at speed the centripetal force will counteract gravity and the tires will be at their perfectly round, unladen diameter.

 

[Norm Peterson]

but at speed the centripetal force will counteract gravity and the tires will be at their perfectly round, unladen diameter.

Ummmmm, no they won't. Steering feel would completely vanish if that could happen, as your contact patches would only be lines. Rear tires would be spinning rather than driving you forward.


Just for fun, go over to the Tire Rack's specs page for some tire. Any tire, doesn't really matter whether it's for an S550 or not. Calculate the tire revolutions per mile based on the listed tire OD. Compare that to the listed revs/mile.


Norm

 

[shogun32]

Ummmmm, no they won't. Steering feel would completely vanish if that could happen, as your contact patches would only be lines. Rear tires would be spinning rather than driving you forward.

damn it man, I was using spherical chickens in a vacuum for my equations.

 

[Mikepol2]

Assuming these ratios are correct, it means the Tremec puts down power to the pavement better than a stock PP2, or in some gears, even better than my PP1 with 4.09's and 305/35-19 rear tires. Which is what I thought I felt at times test driving a Mach.

Force applied to the road by each rear tire can be calculated as torque x transmission gear ratio x rear axle ratio x tire radius in feet / 2.

Here's what the pavement force at each wheel calculates to at 420 ft-lbs max torque for a stock PP2 and Mach, and my PP1 with 4.09's and 305/35-19 rear tires. Just for fun there's also a column for a Mach with 4.09's.

	PP2	My car	Mach 1	Mach 4.09
1st	2,324	2,436	2,296	2,517
2nd	1,506	1,579	1,585	1,738
3rd	1,019	1,067	1,144	1,255
4th	717	752	860	943
5th	581	609	711	779
6th	445	466	448	491

 

[shogun32]

my PP1 with 4.09's and 305/35-19 rear tires.

odd choice of tire size. 1st and 2nd look same. 4th in MT83 and 5th in Mach are the same, and top gear is the same. Maybe I'm missing something but all the Mach1 gives you an extra gear.

 

[Mikepol2]

odd choice of tire size. 1st and 2nd look same. 4th in MT83 and 5th in Mach are the same, and top gear is the same. Maybe I'm missing something but all the Mach1 gives you an extra gear.

Yep that was kind of what I was getting at, the M1 is similar to my MT82 with 4.09's. Tire size was because I had bought a set of GT350 wheels and tires, and swapped the tires onto the PP2 wheels.

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