Calculating expected rpm/speed for 3.23 stick gears

[Bleep Bleep]

Is there a formula, or conversion chart, showing what speed should be for each gear at a designated RPM with stock 3.23 gears and 15” wheels?

Thanks.

 

[66 Sat]

Tremec have a calculator, go to their website.
I got a pen and paper and wrote down some figures for the 3 gearbox options for the TKX and my desired cruising rpm and max rpm, with different rear end ratios. It really helped my choice.

 

[VANDAN]

There are charts, but tire size is used, not wheel size.

 

[BSB67]

Is there a formula, or conversion chart, showing what speed should be for each gear at a designated RPM with stock 3.23 gears and 15” wheels?

Thanks.

Yes, there is a simple formula. Manual transmission or automatic?

Mph x 355 x final gear ratio x transmission gear ratio / tire diameter = rpm.

Use 336 if it is a manual transmission

 

[forphorty]

Calculate GEAR, RPM, MPH, TIRE DIAMETER

 

[Bleep Bleep]

Yes, there is a simple formula. Manual transmission or automatic?

Mph x 355 x final gear ratio x transmission gear ratio / tire diameter = rpm.

Use 336 if it is a manual transmission

Thanks! That’s perfect. Check my understanding here.
For an A-833 4-spd (primary gear ratios), 3.23:1 rear, at example speeds:

50mph, 4th gear - 336 x (1.0 gear ratio) x 3.23 / 26 = 2,087 rpm

40 mph, 3rd gear (1.39 ratio) =
2320 rpm

30 mph, 2nd gear (1.93 ratio) =
2416 rpm

20 mph, 1st gear (2.65 ratio) =
2212 rpm

One other factor. Actual rims are now 15” vs. stock 14”. Looks like Speedo reading accuracy mathematically appears pretty insignificant - around 1.5-2.0 mph under actual speed.

 

[66 Sat]

One other factor. Actual rims are now 15” vs. stock 14”. Looks like Speedo reading accuracy mathematically appears pretty insignificant - around 1.5-2.0 mph under actual speed.

Read Vandan's post #3 again, wheel size is irrelevant, it's tire diameter that's important.
A 14" wheel with a 215/70/R14 tire will have a larger diameter than a 15" wheel with a 215/60/R15 for example.

 

[Bleep Bleep]

I understand. Thanks. I didn’t look up the actual diameter for F70/14 stock vs P255/60/15 existing tires when I posted. I just plugged an assumption of rim size difference in the calc, which is to your and Vandan’s point incorrect.

The actual diameter difference 0.65 inches. So the speed differential is actually even less than estimated.

The exercise is just to prevent getting in trouble with the 5-O

 

[Bleep Bleep]

So bottom line virtually no difference at all in my circumstance.

 

[BSB67]

It’s not clear exactly what/how you are calculating and comparing. But the only way to know speedometer accuracy is measurement I.e. gps, not calculation.

 

[Bleep Bleep]

Your equation solved for rpm. I just modified the math to solve for speed given the same variables. The info you gave me was perfect to estimate how far off the Speedo would be with different tire sizes - replacing stock F14s with the 255/60 15s on it now.

The answer, not much difference at all. So for what I am doing it was what I was looking for. Unless I mis-interpreted what post #4 means. Thanks again.

 

[66 Sat]

I understand. Thanks. I didn’t look up the actual diameter for F70/14 stock vs P255/60/15 existing tires when I posted. I just plugged an assumption of rim size difference in the calc, which is to your and Vandan’s point incorrect.

The actual diameter difference 0.65 inches. So the speed differential is actually even less than estimated.

The exercise is just to prevent getting in trouble with the 5-O

There's nothing in mine or Vandan's points that are incorrect.
You can either do something properly or you can do something half-assed.

Good luck with whatever you are trying to achieve.

 

[Bleep Bleep]

There's nothing in mine or Vandan's points that are incorrect.
You can either do something properly or you can do something half-assed.

Good luck with whatever you are trying to achieve.

You misunderstood me. I agreed with you not the other way around. My bad if I wasn’t clear.

 

[66 Sat]

My apologies, I re-read your post and now understand.
Early in the morning here, not enough coffee...

 

[Bleep Bleep]

No worries at all my friend.

 

[71 Runner]

I used this simple calculator for choosing my S60 ratio with Tremec T56 6 speed conversion. I was able to play with wheel and tire size combinations till my brain hurt. I was replacing my 8 3/4 3.23 to the S60. With the combo and tire size I picked a 3.55 ratio Tire Size Calculator

 

[Bleep Bleep]

I used this simple calculator for choosing my S60 ratio with Tremec T56 6 speed conversion. I was able to play with wheel and tire size combinations till my brain hurt. I was replacing my 8 3/4 3.23 to the S60. With the combo and tire size I picked a 3.55 ratio Tire Size Calculator

View attachment 1740690

Thanks. Like you said, I’m about on the edge of ‘over-geeking’ it myself.
The calculator is helpful.

 

[71 Runner]

Thanks. Like you said, I’m about on the edge of ‘over-geeking’ it myself.
The calculator is helpful.

It really helped me work out the different Speed/RPM ratios for each gear. I wanted a descent RPM/speed combination in 6th gear for the freeway while not making 4th gear be a useless mess of to low speed at a higher rpm. It was an eye opener to how much effect tire size has on each gear ratio of the 6 speed trans. I went thru 3 pieces of paper on the calculations. : / LoL

 

[BSB67]

It is simple linear math.

If you’re at 50 mph at 2500 rpm w/ a 26” tire and want to know the rpm with a 27” tire, multiply 2500 by 26 and divide by 27.

If you’re at 50 mph at 2500 rpm and want to know your rpm at 80 mph, multiply 2500 by 80 and divide by 50.

 

[71 Runner]

Simple yes, but getting the number I was after includes the simple math with tranny gear ratios of 2.66, 1.78, 1.30, 1.00, 0.80, 0.63 included in the mix. I’m not building my car for the 1/4 mile.