New 15” Wheels. What gear ratio?

[gungfudan]

It has been a while since my last post hello everyone. My friend gave me some wheels and tires off of a 99 Mustang. The tires were an OK condition but one of them ended up developing a bubble probably because they’ve been sitting so long so I got new tires. I got 225/75R 15. I’m looking at changing the gear ratio in the rear end what gear ratio should I go with? I was thinking 3.73. I have a 94 Mazda B 3000. My current gear ratio is 3.43 I believe.

 

[19Walt93]

Thank you for calling them wheels instead of rims, the rim is only part of a wheel.
You can look up the diameter and revolutions per mile for the old tires and compare with the 15's. For example: if the old revs per mile was 800 and the 15's show 700, 800/700=1.1428 I expect your current gear is 3.45 if you have a 7.5 so 3.45x1.1428= 3.94. My revolution numbers are random to use as an example, a tire catalog would have more accurate numbers.

 

[SenorNoob]

These are probably way more complicated than you need...

Gearing Analyzer with Shift Tracer

Enter gear ratios, tire and diff ratio to analyze RPM vs velocity at shift points with tracer

www.blocklayer.com

Tire Size Comparison

Calculate tire diameter from code and compare tire size speedometer differences

www.blocklayer.com

,but super handy. There are other calculators on that site. Good fun to do some digging and find other useful things. I think it was originally built for construction. (Roof pitch, 2x6 vs 2x8 floors and walls, etc.)

 

[gungfudan]

Thank you. Looks like 4.10 ring and pinion.

 

[alwaysFlOoReD]

There are calculators on TRS as well. I've used them lots.

 

[Curious Hound]

Once you get the overall diameter of the tire (not the wheel. That 15" number is useless) I find this page incredibly useful.

Gear Ratio & RPM Guide For Larger Tires - The Ranger Station

This Gear Ratio & RPM Guide will enable you to see how many RPM's your engine will turn based on gear ratio and tire size.

www.therangerstation.com

 

[scotts90ranger]

I think you would be happiest with 4.10's, that's what my '97 with a 2.3L has and I like it with 225 70 15, since they're a similar power band I figure a 3L would like them too... it would be easiest to find a whole rear axle...

 

[sgtsandman]

Going from 3.45:1 to 4.10:1 on the 1998 Ranger I had made a world of difference and the fuel mileage didn't change. It had 225/70R14 tires but it should still make quite a bit of difference with 225/70R15 tires. It think there is only an inch of difference in diameter between the two, if I remember correctly.

 

[alwaysFlOoReD]

Going from 3.45:1 to 4.10:1 on the 1998 Ranger I had made a world of difference and the fuel mileage didn't change. It had 225/70R14 tires but it should still make quite a bit of difference with 225/70R15 tires. It think there is only an inch of difference in diameter between the two, if I remember correctly.

Hmmm... 15 minus 14...

 

[sgtsandman]

Hmmm... 15 minus 14...

Ha Ha! The rim size doesn't always correlate to the same difference in tire diameter, but in this case, it does.