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Old Mar 17, 2016 | 04:49 PM
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Default Outer tire diameter question

I have another thread asking about going wider in rear and got some great responses! I've decided, for now, to go with 305/30/19. My question is since I'm going smaller sidewall ratio, I'm assuming that the overall diameter will be smaller? Right? If so I'm wondering how that would look.since fronts are 18. Suggestions? Or pics?
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Old Mar 17, 2016 | 05:23 PM
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Originally Posted by Prodago
I have another thread asking about going wider in rear and got some great responses! I've decided, for now, to go with 305/30/19. My question is since I'm going smaller sidewall ratio, I'm assuming that the overall diameter will be smaller? Right? If so I'm wondering how that would look.since fronts are 18. Suggestions? Or pics?
Go to the Tirerack website. They have outside diameter and even better revolution/mile.
Aspect ratio and diamter give a good indication but tires are different. Look up the tire your thinking about using.
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Old Mar 17, 2016 | 05:32 PM
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Originally Posted by Prodago
I have another thread asking about going wider in rear and got some great responses! I've decided, for now, to go with 305/30/19. My question is since I'm going smaller sidewall ratio, I'm assuming that the overall diameter will be smaller? Right? If so I'm wondering how that would look.since fronts are 18. Suggestions? Or pics?
Your vehicle probably came stock with 285-35-19 = 26.8 o/d
Vs. the ones you are running now, 305-30-19 = 26.2 o/d
Which is a difference of .6 in basically a half inch difference.
I hope this helps...
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Old Mar 17, 2016 | 06:59 PM
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Originally Posted by JerryU
Go to the Tirerack website. They have outside diameter and even better revolution/mile.
Aspect ratio and diamter give a good indication but tires are different. Look up the tire your thinking about using.
Excellent suggestion! Thank you sir
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Old Mar 17, 2016 | 07:01 PM
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Originally Posted by Edward@StrasseWheels
Your vehicle probably came stock with 285-35-19 = 26.8 o/d
Vs. the ones you are running now, 305-30-19 = 26.2 o/d
Which is a difference of .6 in basically a half inch difference.
I hope this helps...
Actually I'm not running on them yet. I'm trying to figure out whether I go to 30 or 35. Because I don't want it to look bad from the side view from the front with sidewall compared to the rear with sidewall. However I don't think a half inch is going to make that big of a difference that you could notice. As always thanks guys
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Old Mar 17, 2016 | 07:38 PM
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Originally Posted by Prodago
Actually I'm not running on them yet. I'm trying to figure out whether I go to 30 or 35. Because I don't want it to look bad from the side view from the front with sidewall compared to the rear with sidewall. However I don't think a half inch is going to make that big of a difference that you could notice. As always thanks guys
If you do it please post a few pictures. I would like to do the same when the time comes.
I did it with my C6 and the fatter tire looked good. My C7 only has 2000 miles on it so i have awhile.
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Old Mar 17, 2016 | 11:35 PM
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Old Mar 18, 2016 | 12:12 AM
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Originally Posted by Zymurgy
do you have the web page URL for the above?
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Old Mar 18, 2016 | 01:34 AM
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In C5 and C6 the computer would get quite upset if the rear tire diameter was smaller than the fronts, they need to be larger in the back. Even sizes were OK from what I remember, but smaller was definitely not an option. C7 is probably the same way, just so you're aware.
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Old Mar 18, 2016 | 02:07 AM
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Originally Posted by Prodago
I have another thread asking about going wider in rear and got some great responses! I've decided, for now, to go with 305/30/19. My question is since I'm going smaller sidewall ratio, I'm assuming that the overall diameter will be smaller? Right? If so I'm wondering how that would look.since fronts are 18. Suggestions? Or pics?
305/30/19 = 305 times .30 times 2 divided by 25.4 plus 19 equal 26.2 inches tall. 285/35/19= 285 times .35 times 2 divided by 25.4 plus 19 equal 26.8 So the wider rubber is .6 inches shorter than stock. EZ to calculate tire height. Just multiply width times aspect ratio, times 2 because there are 2 sidewalls, convert this figure to inches by dividing by 25.4, then add rim size. 245/40/18=245X.40X2 divided by25.4+18=25.7 inches

Last edited by shakeydog; Mar 18, 2016 at 02:54 AM.
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Old Mar 18, 2016 | 03:30 PM
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Originally Posted by markcz
In C5 and C6 the computer would get quite upset if the rear tire diameter was smaller than the fronts, they need to be larger in the back. Even sizes were OK from what I remember, but smaller was definitely not an option. C7 is probably the same way, just so you're aware.
Yeah, I thought about that last night. Definitely do not want to change any of the size I guess because I don't want to throw the speedo off or any other computer-related gas mileage. Excetera issues. Good point to raise up
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Old Mar 18, 2016 | 03:45 PM
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Originally Posted by Prodago
Yeah, I thought about that last night. Definitely do not want to change any of the size I guess because I don't want to throw the speedo off or any other computer-related gas mileage. Excetera issues. Good point to raise up
The difference Zymugy showed is relatively small if you look at different brands, all season tires etc of the same size spec you can see that much difference! Also consider warn rears with new fronts, etc!

Last edited by JerryU; Mar 18, 2016 at 03:46 PM.
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Old Mar 18, 2016 | 03:54 PM
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Originally Posted by JerryU
The difference Zymugy showed is relatively small if you look at different brands, all season tires etc of the same size spec you can see that much difference! Also consider warn rears with new fronts, etc!
Dang, you guys just get smarter and smarter. Because I indeed have bald tires and brand new front tires!
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Old Mar 18, 2016 | 09:38 PM
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Originally Posted by JerryU
The difference Zymugy showed is relatively small if you look at different brands, all season tires etc of the same size spec you can see that much difference! Also consider warn rears with new fronts, etc!
ABSOLUTELY TRUE! If you look at TireRack's Specs on Pilot Super Sports in 295-30-20 for instance, there are 3 different one's available and all have different measurements. If you're buying a different brand, the numbers can be all over the place.

That's why I always check TireRack before I buy, even if I don't buy from them.
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Old Mar 18, 2016 | 10:26 PM
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Originally Posted by brettlid
do you have the web page URL for the above?
http://www.sizemytires.com/calculators/compare
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Old Mar 23, 2016 | 11:58 AM
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I’m looking at the Nitto nt 555g2 305/35/19. I know the calculation, but is there a way to find out the exact sidewall height for this tire, since sizes vary from tire to tire? Also I want to know the exact sidewall height of the stock super sports that came on car? If one of you could just take a tape to your rear wheel to find this out even.
Thanks
John
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Old Mar 25, 2016 | 01:35 AM
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The calculation will be correct.
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