Tire to Rims sizing help

[Michael Yount]

Checking out your car Legendary, with all your suspension work you seem to put a premium on handling - that tire on your stock wheel is definitely not the way to go. Also, as Maverick said - they are so tall, they'll turn your 3.73's into effectively a 3.41 gear. I think it's a losing proposition from every angle - wheel fitment, traction, handling, and effective gear ratio.

 

[Legendary]

Thanks guys. I'll pass them up. I totally forgot about the gear ratio.

 

[Qwk88LX]

My brother has been in the wheel and tire business for over 30 years. The rule of thumb they use in his shop is to not have the section width of the tire (the 225, 255 number) in inches (225 is in millimeters -- 225/25.4=8.85") exceed the rim width by more than 2 inches. So a 225 tire needs to be on a rim that is at least 6.85" wide. That's why the stock 225 tire comes on a 7" rim. Doing the math - a 255 tire has a section width of 10.03". 10" - 2" = 8". You'd want the 255 tire on a rim that was at least 8" wide to properly support the tire.

Hope that helps.

What would be the reason not to go over 2"? As I'm 3.61" over on mine (295's on 15x8 Welds)..I do plan on switching to 10 inch Welds soon.

 

[Qwk88LX]

Also, as Maverick said - they are so tall, they'll turn your 3.73's into effectively a 3.41 gear. I think it's a losing proposition from every angle - wheel fitment, traction, handling, and effective gear ratio.

So in theory if I went with 295/65's and put some 4.10's on the gearing wouldnt be that low right? closer to 3.90's..hmmm I just might have to try it out

 

[Michael Yount]

qwk88 - read the whole thread - we've already covered the reasons why having a wide enough wheel is necessary. Don't know what size you have on the car now, nor what diameter your 295/65 is. If you're switching from 225/60/15's to 295/65/15's, that's a tire height change from about 25.6" to a little over 30". That would reduce your effective gear ratio from 3.73 to 3.17; reduce the 4.10 to about a 3.50. I'd think with that tall a tire, you'd have clearance issues, not to mention, most folks would probably think it wouldn't look very good. You'd need a 9.5" - 10" wide wheel to keep all the tread on the ground effectively.

Edit: made a slight error in my gear calculations, my bad.

 

[5.0guy]

If you're switching from 225/60/15's to 295/65/15's, that's a tire height change from about 25.6" to a little over 30".

the width affects the tire height, too? the change from a 60 to a 65 doesn't equal 4.4+"..I'm not trying to gettin in ur ****, I'm just wondering about that.

 

[Michael Yount]

The wheel width doesn't affect the height, but the section width does. Ok - here we go.

To calculate the height of a tire you take the section width (225, 245, etc.) and multiply it by the aspect ratio percentage (60, 65, etc.) and convert it from millimeters (the 225 is in millimeters) to inches (25.4 mm/in). So far then - (295X.65)/25.4=7.54". That calculation tells you how high the sidewall is. To calculate the tire height, you simply multiply that number times 2 (there's a sidewall at the bottom and the top) and add the wheel diameter. So then - (7.54"X2) + 15" = 30.1". A 295/65/15 tire is approx. 30.1" tall. Same math for a 225/60/15 tire results in a tire height of 25.6" tall. You are correct - difference is about 4.5". You see, it's not just the aspect ratio change that impacts tire height - the width change (225 to 295) impacts the height as well. So a 255/60/15 tire is 27" tall; a 225/60/15 tire is only 25.6" tall - same aspect ratio and wheel diameter for both tires.

The impact on rear end ratio is inversely proportional to the change in tire diameter - the taller the tire, the smaller the gear ratio number. So, 30.1/25.6= 1.17 or a 17% reduction in gear ratio. So, 3.73/1.17= 3.17 (sorry, my bad on my math before); 4.10/1.17 = 3.50.

 

[5.0guy]

alright, thanks for clearin that up for me