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Author Topic: Wheel & Tire Upsizing Explanation & Chart  (Read 18317 times)
Coelacanth
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« on: September 25, 2012, 02:58:54 PM »

Many people are confused by the idea of upsizing their wheels & tires, so I did some number-crunching and came up with a chart that hopefully might be a useful reference to those of us who want to put more modern rubber & wheels on our cars, while trying to preserve a more-or-less "muscle-car look", and not negatively affect alignment & suspension geometry. To do this, you have to upsize to a wheel & tire combination that's almost the exact same total height as the tires we used back in the day. The total height is a simple formula of tire width multiplied by the aspect ratio, double this, then add the height of your wheel, converted to millimeters. Understandably, this metric business is confusing to you Americans. LOL (Just kidding!)

I'll start by explaining the formula, it's not rocket science, just simple math.

195/75R14: (195 mm x 0.75) x 2, + 355.6 mm. Total Height is therefore = 648.1 mm.

 -195 x 0.75 is the height of ONE tire sidewall; you need to multiply this by 2 to factor in both sidewalls; i.e. the sidewall ABOVE the wheel & also BELOW the wheel.

 -355.6 mm is the height of a 14" wheel, converted to millimeters. Use www.onlineconversion.com to calculate the height of 15", 16" or larger wheels.

 -Add the thickness of both sidewalls to the rim diameter and you have your total tire height, which can be used to mathematically compare total heights of bigger wheels, and ultimately find options that are nearly the same height (give or take 5 or so millimeters, preferably).

Of course, some of the results may be tire sizes that don't even exist, or are quite uncommon or rare. The more common sizes are easier to find and will have more brand & tread options, and will probably be cheaper.

I did several calculations and Google searches and came up with the following chart, for wheels up to 17" tall. I tried to focus on "thicker" sidewall aspect ratios, 50 to 60 series, as ratios lower than that start to look ridiculous on muscle-cars. I also limited my searching to 17", as (again) I think 18" and bigger wheels look ridiculous. So hopefully the following chart will be useful if you're wondering what your wheel & tire options are, if you're wanting to upsize your wheels & tires and take advantage of the corresponding benefits in handling, braking & cornering. These sizes shouldn't affect acceleration much as the widths of the rear tires & tire footprints are basically the same. These sizes should not require speedometer calibration, either, assuming you're using 255's or 275's already.


Tire Size | Total Rim & Tire Height | Allowable Rim Width | Notes

Front

195/75R14 | 648.1 mm | 5.0" - 7.0"
205/70R14 | 642.6 mm | 5.5" - 7.5"

205/60R16 | 652.4 mm | 5.5" - 7.5" | Commonly available size
215/55R16 | 642.9 mm | 6.0" - 7.5" | Commonly available size

215/50R17 | 646.8 mm | 6.0" - 7.5" | Commonly available size


Rear

255/60R15 | 687.0 mm | 7.0" - 9.0"
275/60R15 | 711.0 mm | 7.5" - 9.5"

275/50R16 | 681.4 mm | 8" - 10" ?? | Rare size
275/55R16 | 708.9 mm | 8" - 10" ?? | Rare size

275/50R17 | 706.8 mm | 7.5" - 9.5" | Rare size
255/55R17 | 712.3 mm | 7.0" - 9.0" | Uncommon size
245/55R17 | 701.3 mm | 7.0" - 8.5" | Fairly common size
« Last Edit: September 25, 2012, 03:32:59 PM by Coelacanth » Logged
joerg
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« Reply #1 on: September 25, 2012, 05:56:04 PM »

Im using 295/50/15 on 8,5s for rears and 235/60/15 on 7,5s for the fronts
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Coelacanth
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« Reply #2 on: September 25, 2012, 06:27:54 PM »

Im using 295/50/15 on 8,5s for rears and 235/60/15 on 7,5s for the fronts

Your rears would be 676 mm total height, only about 1 cm undersized (compared to a 255/60R15). Did you have to recalibrate your speedo? Your fronts on the other hand are about 2 cm oversized--that's quite a bit, without other modifications anyway. Any issues with rubbing on the fronts, and if so, what was done to resolve it? I'd imagine without any mods to the suspension, there could be rubbing under full suspension travel while turning fully, though stiffer suspension components might prevent that...
« Last Edit: September 25, 2012, 06:32:20 PM by Coelacanth » Logged
moparsr2fast
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« Reply #3 on: September 25, 2012, 07:33:18 PM »

235 60 15 on an 8" rim on the front of mine. No clearance issues Marc. 
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« Reply #4 on: September 26, 2012, 05:24:02 AM »

My current rear rim is 8" and I have 245 60R 14 on them, they look good, I hope they are safe, because they are staying that way for a while,,, thanks for the work on the chart,,,Brian
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Brian
Coelacanth
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« Reply #5 on: September 26, 2012, 09:57:37 AM »

Brian, your rears should be just fine. A lot of different sizes could be used on the rear, from dinky little 195/75R14's all the way up to 255's, 275's, or even larger, depending on wheel width & backspacing. The only consideration would be speedometer calibration. Any total tire height significantly different from the stock tire height will throw off the speedo. Bigger and the speedo will read lower than you're actually going, and vice versa.

I'm more intrigued about the decision to use fronts that are 20 mm higher than stock, though. Why 235/60R15's? Evidently with even fairly wide rims, there are no clearance issues, but putting on tires that much taller than stock would have an effect on alignment & suspension, effectively making the car's front end ride nose-up slightly. Alignment could be easily adjusted to compensate, but the suspension geometry would also be affected. Comparable-to-stock tire sizes in 15" would be 205/65R15, 215/60R15 or even 235/55R15. Although 235/55's sound close to 235/60's, the actual height difference is 23.5 mm, which is quite a big difference. (I don't even know if 235/55R15 even exists as a tire size, mind you--this is just a mathematical calculation.)

I'm not saying it can't be done, but I wouldn't do it on my own car. My plan is to go with 215/55R16's on my Charger eventually, for two reasons: It will keep ride height, alignment, suspension geometry the same as original, and if I ever get rich and want to upgrade the brakes to an aftermarket Wilwood setup, I've read that you need 16" or larger wheels.
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A6USMC
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« Reply #6 on: September 26, 2012, 06:13:50 PM »

I think you are talking about Bobs front tires??? mine will be 235 60R 14's  for now until I get 15 inch rims, next year
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Brian
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« Reply #7 on: September 26, 2012, 06:24:28 PM »

   I kinda like the way my baby looks. If anything, maybe reduce the back tires from 275 60s to 255 60s for a more even appearance

 
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Because, there is no way to have owned a Charger without having some cool stories to go with it.

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70 FC7 Charger 500
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« Reply #8 on: September 26, 2012, 06:28:18 PM »

 
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2003 Jeep Grand Cherokee Limited 4.7
Brian
Coelacanth
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« Reply #9 on: September 26, 2012, 06:30:39 PM »

I think you are talking about Bobs front tires??? mine will be 235 60R 14's  for now until I get 15 inch rims, next year

Yes, Bob & joerg's fronts. 235/60R14's are actually shorter than a 195/75R14 by nearly half-an-inch. To give a comparison:

235/60R14 = 637.6 mm
205/70R14 = 642.6 mm
195/75R14 = 648.1 mm
235/60R15 = 663.0 mm

I wouldn't worry about yours because they're not that much shorter.
« Last Edit: September 26, 2012, 06:32:33 PM by Coelacanth » Logged
70Charger500
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« Reply #10 on: October 04, 2012, 04:27:38 PM »

I have been having fun with the tire size calculator on this web site.

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

You can input your stock size (or any size for that matter) and compare up to four tire sizes to it all at once!
 
Tolley
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Coelacanth
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« Reply #11 on: October 04, 2012, 05:37:15 PM »

I've used that site for reference, but didn't notice their calculator. I like the extra info such as how the size difference would affect RPM needed to rotate a tire and how a size difference would affect the speedometer. Cool. :)

I still think 235/60R15's are too big for the fronts, regardless whether they physically fit or not, and this calculator indeed provides a warning for upsizing from a 205/70R14 to that size. I didn't know it could potentially cause brake failure, though...
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Plasma Nut
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« Reply #12 on: October 04, 2012, 05:47:10 PM »

i really wanted to put 15" 50's on the rear with a 12 wide tread pattern. i have 245/60/14 all around now. i like a wide stance all around. i will buy 15 x10 with a 5.5 backspace on the rear and 15x7or 8s on the front. but will be sticking with my 14" keystones for now
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70Charger500
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« Reply #13 on: October 04, 2012, 05:51:54 PM »

Rich, to each his own, but the 8" rears will give you tons of size options, and help keep you out of "trouble" (rubbing etc). I know in some configurations 10" wide wheels can work on the rear, but... A little extra room never hurt.

 

Tolley
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1970 Charger 500
1972 Dart Swinger
1963 W100
1997 Ram 2500 SLT Cummins
2008 Dodge Caliber
See my Charger restoration on this forum at:
http://www.1970chargerregistry.com/mboard/index.php?topic=26.0
And on the web at:
http://www.1970dodgecharger500.com/2004present/
Coelacanth
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« Reply #14 on: October 04, 2012, 06:54:11 PM »

I also prefer the look & performance benefits of going with the widest tires that will fit in a wheel-well and look good, but overall tire height should be the most important consideration, for any vehicle one is upsizing or downsizing wheels on...because it impacts much more than looks & stance. Rich, your 245/60R14's are fine on your fronts provided they don't rub. They're just a smidge taller than stock, but are about a half-inch shorter than 235/60R15's.

If you like wide 15" tires on the rear, you might look into 295/50R15; it's over an inch shorter than a 275/60R15, but still quite a bit bigger than stock size, which would keep that muscle-car "higher & wider in the back" look that most of us love. The thin 50-series rubber might look a bit weird to some purists, but you'd have better cornering & braking.
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