Rear end ratios

[Ralph]

I have a 71 challenger 383 RT with 4 speed. The previous owner put in 3:23 gears and I believe its supposed to have 3:55.

I was thinking on installing 3:73 or 3:90 gears with the down the road potential of installing a 5 speed.

So the questions is for those in the know !

Does tire height affect the effective gear ratio and since I have 17 inch taller tires on it now does that mean a 3:73 ratios acts more like a 3:55 ?

Any information would be helpful.

Thanks to all, Ralph

 

[Adam]

17 in taller? Wow...jk

If the overall height of the tire is larger it will have some effect. Search for a gear ratio calculator on the web, it will help with your decision. Some of the places that sell 5 spd conversions will have the calculator; you need to know the overdrive ratio, e.g .78 or .82, big difference.

 

[Ralph]

So thanks for the information, the tires are 17 inch tall - not taller.
I will look into
Ralph

 

[Steve340]

The diameter of the rear tires will affect the final ratio you need. The rim size does not matter in the calculation.

 

[Adam]

Sorry, J/k = just kidding.

I have a TKO 600, 5 spd in my 71 challenger, with 3.55s. It is a great combo because the first gear is so low it is equal to 4.11s (according to tremec) but 75 mph is only 1900 rpm. It lights up the tires at will. I would not go taller than 3.55s, but 3.73 or 3.90 would also be great. Depends on what kind of driving you want to do..

 

[rbbruno3]

Like Adam I have the TKO . I run 4:10’s in mine but with 31” tall tires . Awesome driving on the interstate and off the line too

 

[Ralph]

Hey, thanks to all.

I did the TKO 600 tremec in my 73RR.

This time looking for a passion 5 speed or 4 speed hemi OD from them when possible.

Like the fitment.

Ralph

 

[moparleo]

Here is a list of several types of calculators for tire sizes, gear ratios etc... Good info for everybody to put in their saved folders.
Wallace Racing - Automotive Calculators

 

[Dodgeboy]

Tire height makes a huge difference, a taller tire "reduces" rear end ratio, smaller tire "increases" it. I originally went with 3.23 gear's (from 2.76) with my factory tires to 4.30 gears and 29.5inch tall tires. (I love it). The taller tire grips 200% more then my shorter tires and 3.23's. I used a tire/gear ratio/rpm chart to figure out my setup. My current setup (4.30/tall tire) see's the same rpm/speed as my old 3.23 short tire setup with the bonus of having traction

 

[Dodgeboy]

I just came across this....

Tire Math: Calculating the Effects of Tire Diameter on Final Drive Ratio

 

[Ralph]

Wow, that's great just what I was looking for

Thanks Much