I have a 1070 Roadrunner with a 383, 4 speed, 3.55 gears, 14in tires.


I want to do more highway driving ( tours ) but I turn 3000 RPM at 60 miles an hour which I feel is high for a length of time.


I was looking at 2 things to lower the RPM, but I only want to do one of them.


1. Installing 15 in tires on stock rally wheels.
2. Installing 3.23 gears.


My question...Which one would lower the RPM more.


Thanks John

 

I'll put it this way. If your RPM is really that high going that slow, you have WAY too small tires on the car now. My old V code car came with F70X14 stock, and those soon came off the rear (via the original owner) and G60X15 went on the rear. This was a 4 speed, 3.54 rear It used to run really close to 3000 at SEVENTY

According to this an F70 X 14 is 26.2" dia

and a G60 X 15 is the same size

According to this calculator,

http://www.apexgarage.com/tech/gear_ratios.shtml

a 26.4" tire with 3.54 going 3000 RPM is 67 mph, so my memory is pretty close

The old girl about 73 or 74. Those are NOT what is on the rear, here, I had switched to radials and put taller rear tires under it. It always had F70 X14 or equivalent on the front


https://moparforums.com/forums/f62/m...-back-day-596/




The car when nearly new with my friend and original owner, George. He has just trophied at Lions in pure stock

 

Go with tires. The 15" will give you larger diameter options but still limited depending on wheel width.

These cars can accommodate big diameter tires. Fool around with this calculator and speed calculator provided and you should be able to find just what you need.

http://www.rimsntires.com/specspro.jsp

Here's an easy one http://www.advanced-ev.com/Calculators/TireSize/

 

28" tire! Don't forget to change the speedo gear..