Which is harder on a transmission?

[asylummotorsports]

http://www.miata.net/garage/tirecalc.html

[IsaacHayes]

Tire diameter = ((2 * Width * Ratio) / 2540) + Rim-diameter
Example, L body 225/50r16. ((2 * 225 * 50) / 2540) + 16 = 24.85”

Or there is various ones online just search for "tire calc" and they do it automatically for you.

http://efi.moonwell.com/gears.php This will help too.

[carbon]

Is there a calculator somewhere for tire height? I have stock 215/60R-15 on a 7 inch wide rim, I believe. Also this is going into a Fiero, so it will be RWD.

[IsaacHayes]

Yes TDC was 3.43 with a 26.6" or so tall tire. On an L body, the shift points actually work out roughly the same when you compare the two (2.97 FDR with a 24.x" tire)

[carbon]

So I ask AGAIN!

What are you planning to do with this car? What tire are you wanting to use? The combinations are numerous combining tire size and FDR. I'm using a 24" tire and a 3.73 FDR on a pretty well purpose built race car.

I wouldn't consider it for a daily driver. 3500 RPM at 70 MPH can be a PITA

If you need more info PM me and I can send you the whole Diff to gear set ratios, however I'm pretty sure it's available here if you look around.

But you have 3T40/125C correct? So with about a 30% higher 4th on a 4T60 it would be around 2500 at 70MPH right? I am not looking to build a purpose built race car and I haven't even thought about tire size other than stock for now. I am not going to be making huge horsepower, so I am looking at gearing to make the most of it.

The stock Ws with automatics with 3.4 TDC motors came with a 3.43 final didn't they?

Model       TH125C      TH440/4T60
 1st         2.840        2.921
 2nd         1.600        1.568
 3rd         1.000        1.000
 4th         -----        0.705
 Rev         2.067        2.385

Chain Ratio | 33/37 35/35 37/33 38/32
-------------------------------------
Final Drive |   Overall Drive Ratio
   2.84     | 3.18  2.84  2.53  2.39
   3.06     | 3.43  3.06  2.73  2.58
   3.33     | 3.73  3.33  2.97  2.80

[robertisaar]

Yes, but isn't a higher ratio FDR easier on the clutches?

among other things, yes.

[asylummotorsports]

So I ask AGAIN!

what are you planning to do with this car.

What tire are you wanting to use.

The combinations are numerous combining tire size and FDR.

I'm using a 24" tire and a 3.73 FDR on a pretty well purpose built race car.

I wouldn't consider it for a daily driver. 3500 RPM at 70 MPH can be a PITA

If you need more info PM me and I can send you the whole Diff to gear set ratios, however I'm pretty sure it's available here if you look around.

[carbon]

I had always wondered about this due to the final drive actually still being 3.33 but the chain drive ratio makes it 3.73. Its two different sides of the transmission, so you have greater torque advantage against the axles than with, say, a 2.84, but you also give the engine a greater torque advantage against the tranny... Am I just thinking about this too hard?

[IsaacHayes]

Yes, but isn't a higher ratio FDR easier on the clutches?

[gpse3400]

Actually with this gear box, if you run a taller FDR the toque capacity increases as the FDR sun is larger. But if you set your transmission up to run the 3.73, get the SONNAX replacement FDR sun, It is a stronger gear.

[robertisaar]

I am looking at the 4T60 and trying to decide what to do with the ratios... it would not be a daily driver so the 3.73 looked interesting... this would be going behind a 3500 also, or at least a 3400/3500 hybrid...

How much work/cost is involved in doing a chain drive ratio change? Say 3.33 -> 3.73..

i think it's going to be hell trying to get traction with that combo since you're essentially running what Eric is, but Eric could probably answer the cost question.

[carbon]

I am looking at the 4T60 and trying to decide what to do with the ratios... it would not be a daily driver so the 3.73 looked interesting... this would be going behind a 3500 also, or at least a 3400/3500 hybrid...

How much work/cost is involved in doing a chain drive ratio change? Say 3.33 -> 3.73..

[robertisaar]

changing your FDR to a numerically higher gear removes stress on the tranny.

[asylummotorsports]

They all use the same chain. 70 teeth.

So what are you planning to do with this car?

I have had a 33/37 (3.73) in my 3500 Beretta 3t40 for about 1000 14-second runs with no problems.

A good trans cooler is your friend

[carbon]

What chain setup is harder on an auto transmission with a 3.33 final drive?

33/37 3.73
35/35 3.33
37/33 2.97
38/32 2.80