Tire size v.s. engine power

[willem]

Hi there,

I am about to buy a set of wheels for my 1972 Coronet Wagon. The tires are a bit large though:

7J 235/60-15 for the front
8J 275/60-15 for the back

I was wondering, the car itself is pretty heavy and with its 225 cui slant six a bit underpowered.

Could tires like this make the car undriveable?

 

[R413]

What is your rear end gear ratio? Those are tall tires and they will kill the torque. Could make it a slug that won’t be able to pass or pull a hill very well.

Remember stating out in 10th gear on your 10 speed bike? no power to get it moving.

***With the manual trans it is most likely 3.2 gears which will help.***

Enter 2 sizes to compare. Use your current size to see the differences.

 

[willem]

Yeah that's what is was afraid of

I dont know what the gear ratio is, but its the stock 3 speed manual at the column

 

[willem]

What is your rear end gear ratio? Those are tall tires and they will kill the torque. Could make it a slug that won’t be able to pass or pull a hill very well.

Remember stating out in 10th gear on your 10 speed bike? no power to get it moving.

Does Tire Width affect the torque as well?

 

[451Mopar]

Hi there,

I am about to buy a set of wheels for my 1972 Coronet Wagon. The tires are a bit large though:

7J 235/60-15 for the front
8J 275/60-15 for the back

I was wondering, the car itself is pretty heavy and with its 225 cui slant six a bit underpowered.

Could tires like this make the car undriveable?

The tire thread width (235 or 275) is just width in mm, so 235mm = 9.25", 275mm = 10.82"
Sidewall height (aspect ratio) of 60% is 9.25*.6 = 5.55, 10.82*.6 =6.492
Need to double sidewall height for top and bottom of tire, 11.1 and 12.984
Add rim diameter of 15 = 26.1" tire height (diameter) for 235/60-15, and 27.984" for the 275/60-15 tires.
The percent difference in tire size (27.984-26.1)/26.1 = 0.072184, or about 7.2%
The wider (and taller) tires will reduce gearing about 7.2% compared to the narrower (shorter) tires.

 

[PurpleBeeper]

Does Tire Width affect the torque as well?

no.

 

[451Mopar]

Adding to the earlier post, the 7.2% difference between the shorter and taller tires would be like going from a 3.23:1 rear gear to a 3.00:1 rear gear

 

[willem]

thanks for the calculation! allthough i have to admit, i'm not that experienced to know what it's going to do to the car.

i suppose Coronet becomes turd?