how does tire size affect rear end gear ratio?

[APGTS]

Trying to figure out what the jump from the stock size 335/35/17 (26inch diameter) to 345/30/19 (27.1inch diameter) turns the rear end gear ratio into?? Also does anyone know what 3:55s would really be with the taller tire?

 

[dave6666]

Tire size does not affect rear end gear ratio. The only way to change your gear ratio is to change your gears.

To your concern though, changing to a different tire diameter will change the effective gear ratio of the drive line in comparison to a smaller or larger diameter tire. There are plenty of on-line calculators for that.

For instance, when I put 20" PS2's (28" vs 26" stock) on the rear of my GTS, the effective ratio moved from 3.07 to 2.82.

When I installed 3.73's, the larger tire resulted in an effective drive line ratio of 3.45.

But in any of those cases, I had 3.07 or 3.73 as a ratio. The change in tire diameter is only an effect on the drive line, not a true change to it.

 

[ViperNM]

Tire size does not affect rear end gear ratio. The only way to change your gear ratio is to change your gears.

To your concern though, changing to a different tire diameter will change the effective gear ratio of the drive line in comparison to a smaller or larger diameter tire. There are plenty of on-line calculators for that.

For instance, when I put 20" PS2's (28" vs 26" stock) on the rear of my GTS, the effective ratio moved from 3.07 to 2.82.

When I installed 3.73's, the larger tire resulted in an effective drive line ratio of 3.45.

But in any of those cases, I had 3.07 or 3.73 as a ratio. The change in tire diameter is only an effect on the drive line, not a true change to it.

Good explanation Dave. Now I know.

Do you happen to know if the 6-spoke Gen IV wheels (18/19) fit on an 01 GTS and what does that do to the accuracy of the speed? I already have 3.55s with a speedo calibration box.

 

[dave6666]

The wheel size means nothing. Well, as long as the tire diameter remains the same. If going to the SRT 19" wheel results in a larger tire OD, then your speedo will read low.

They make a 20" tire that's close to factory OEM outside diameter for the Gen 2. But I didn't want the micro tall sidewall, hence I jumped from 26" to 28" OD. The Pirelli is damn near stock height, making the effective gear ratio almost the same as with factory components. But short sidewall tires are not driver friendly.

Remember... Your drive line is the clutch, transmission, drive shaft, differential, half shafts and hubs. All the wheels and tires do is transmit the output of the drive line to the driving surface. They do affect the output... the result... the load on the drive line... But they are not gears.

 

[Detlef]

You must be registered for see images attach

I put the 6 spokes on my 2001 and they fit great. I have 3.73s and the speedo is 5mph slower than actual speed with the 19" wheels instead of the stock 18", at least as measured with my GPS unit in the car.

 

[ViperNM]

You must be registered for see images attach

I put the 6 spokes on my 2001 and they fit great. I have 3.73s and the speedo is 5mph slower than actual speed with the 19" wheels instead of the stock 18", at least as measured with my GPS unit in the car.

Great color! Do you know if the center caps that come with the 18" ACR wheels will fit these Gen IV 6-spoke centers?

 

[Detlef]

I don't know for sure as I reused my GenII center caps with the GenIV wheels. But I'd imagine they would fit.