My car has 4.10 gears in the rear. However, I need to be able to drive 65-70mph on almost a daily basis and I don't want to keep the engine reved high while cruising.

Now, here is where it gets difficult (for me anyway). The car currently has the original 13" wheels on it, but I am going to put on 16" wheels with 225/50 tires. What gear ratio should I put in so I can cruise at 65-70mph at 3000rpm?

The current tires are 185/70-R13
The side wall height is 5.1 inches (185 x 70%). 13 + 5.1 = 18.1

The tires on on the 16's are 225/50-R16
The side wall height is 4.43 inches (225 x 50%). 16 + 4.43 = 20.43

I am going 2.33 inches over stock diameter, so that needs to be figured in when determining the gear ratio.

I don't know how to calculate the gear ratio and I was hoping someone here would know how.

http://www.ring-pinion.com/c-rpm_1.htmlte,

OR this one

http://www.ring-pinion.com/c-rpm_1.html
It looks to me that 3.25 would be has high as you would want to go.
And 3.00 would even be better.

Glen I've been looking for some gears for my 65 Mustang with a 8".Let me know if you have a 8" and you want to sale the 4.10.

Thanks Ron

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65 Coupe with a 351w, RPM intake,carter625,shorty 1-5/8 headers,2.5 exhaust,Flowmasters,Black Magic electric fan,stock C4,peg leg 8" 2:80,Big Boss 429 hood scoop,Cragers SS,Black Suede finish.