Is there a reason why the tire's Aspect Ratio (275/25ZR20) is suppose to be larger in the front than the back? Is there a performance advantage?

Would switching to 35 series in front and back hurt?

 

it is larger in the front to keep the wheel Diameter the same .

 

your back tires are wider in the rear so if you had the same ratio on the rear that's on the front the rear tires would be taller.

 

^+1 for what they said.

 

FYI, that is NOT the right aspect ratio for G37 rear tires. It should be 275/35/20 if you are trying to maintain factory circumference. A 25 aspect ratio is too short (3.7% shorter diameter than stock).


Any particular reason you want to run the same aspect ratio front and rear on a staggered setup?

 

Aspect ratio is a % of the tire's width. The height depends on the with and vise versa. The numbers wont always be lower in the front.

Calculating Tire Dimensions

 

I know...I was sleepy and copied and pasted a tire size from who knows where....anyway It just one of those things I've always thought about. And remember when looking at 3 series that there was a wheel setup with the same ratio front and back but was staggered.

explain?

 

275/35/20

275 is tire width in MM
20 is the rimsize
35 In this case is the the height of the sidewall in percentages.
In other words the sidewall are 35 percent of the tire width, wich translates into 35 percent of 275 ( in MM ). Changing the percentage will result in a smaller wheel-diameter if the width stays the same but the percentage of the sidewalls are less than the 35 as given above.

35 % taken from 275 = 96,25MM ( 3.789 inches ) plus rim size ( 20 inch )
will add up to a total wheel diameter of 23.789 inch.

25 % taken from 275 = 68,75MM ( 2.706 inches ) plus rim size ( 20 icnh )
will add up to total wheel diameter of 22.706 inch, wich is significantly smaller than the 35 tires.

Since the G has smaller tires ( in width that is ) in the front, the percentage automaticly changes to a higher percentage to keep the same wheel diameter.

So taking a 245 tire for instance, with a 20 inch wheel should be 23.789 minus the 20 inch wheel is 3.789 inch, convert that into MM, wich is 96.25.
Now devide 245 by 100= 1%. Take 96.25 and devide with the 1% ( 2.45 ) and you'll get 39.28. However their are no tires with 39% sidewalls. They are all made even numbers like 25 / 30 / 35 / 40 and so on. (Therefore it's very unlikely to get the exact even diameter when changing to wider tires or bigger rims.)
So 39.28 automaticly changes into a 40 percent sidewall.

So since we know what percentage sidewall to get, we can calculate the the overall difference in diameter compared to the rear wheels (275/35/20)

40% of 245 = 98.00MM wich is 3.858 inches, plus 20 results in a 23.858 diamater of the whole wheel.


So hopefully this explains why the rear tires have a lower value written on the tires.

the calculations above do not only show how the whole tire specs work, but they also show you that you should always have a close look at getting new wheels. Since bigger or smaller wheels WILL affect your speedo. Differences like 1 % aren't that big of a deal, but you should remember that your speedo will be off.


By the way here is a site that helps you figure out wich size to choose.

http://www.1010tires.com/tiresizecalculator.asp

 

^^^WOW

THANKS I FULLY UNDERSTAND NOW!!!

a 245/35-20 tire would have the same overall diameter of a 285/30-20 tire....

while a wheel with same aspect ratio MIGHT not have the same OD and possibly making the tires uneven in height...

I wish there was some reputation button but thank you alot...

 

^^

No problem