Tire ratio table
03-10-2011, 02:03 PM
#1
Registered User
Thread Starter
Tire ratio table
Attached is an Excel sheet that will calculate the rear/front tire rolling width ratio.
I've tried to include all the known good sizes that people have run. You can add your own in the last few empty lines in excel.
WARNING : this is using the nominal calculated tire size; you should know that many tires in reality differ greatly from their nominal size; always check before making a decision based on nominal size.
In plain text it looks like this :
I've tried to include all the known good sizes that people have run. You can add your own in the last few empty lines in excel.
WARNING : this is using the nominal calculated tire size; you should know that many tires in reality differ greatly from their nominal size; always check before making a decision based on nominal size.
In plain text it looks like this :
Code:
rim width height width heihgt front rear R/F ratio notes 19 235 35 305 30 25.47637795 26.20472441 1.02858909 OEM C4S & C2S 19 235 35 295 30 25.47637795 25.96850394 1.019316953 OEM C4 & C2S 18 235 40 295 35 25.4015748 26.12992126 1.02867328 OEM T4 18 235 40 265 40 25.4015748 26.34645669 1.037197768 OEM C2 winter size 0 0 18 245 40 305 35 25.71653543 26.40551181 1.026791182 mdrums RA1 only R-comps 18 245 35 315 30 24.7519685 25.44094488 1.027835216 good ratio smaller expensive 19 245 35 325 30 25.7519685 26.67716535 1.035927228 OEM GT3RS 18 255 35 285 35 25.02755906 25.85433071 1.03303445 less stagger many choices cheap 18 255 35 325 30 25.02755906 25.67716535 1.025955639 wide 18 255 35 335 30 25.02755906 25.91338583 1.035394054 wider 18 240 40 270 40 25.55905512 26.50393701 1.036968577 slicks 18 265 35 345 30 25.30314961 26.1496063 1.033452622 max wide
Last edited by cbzzoom; 03-11-2011 at 01:24 PM.
03-11-2011, 09:37 AM
#4
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03-11-2011, 11:28 AM
#5
Rennlist Member
Yeah, there are plenty of other single wheel calculators on the web.
What's special about cbzzoom's spreadsheet is the front/back rolling width ratio calculator, which is useful for predicting whether a new setup will increase understeer or oversteer compared to the factory sizes.
For the staggered size setups that our cars use, it's also crucial to check the circumference difference between front and rear wheels. That's vital if you're changing sizes if you want to avoid confusing the ABS/PSM operation in the car. If that ratio strays too far from the factory ratio you can have problems. That's what my calculator does and I've never seen that elsewhere.
I guess since most cars don't run staggered sizes it's not common to encounter online resources that incorporate those issues.
What's special about cbzzoom's spreadsheet is the front/back rolling width ratio calculator, which is useful for predicting whether a new setup will increase understeer or oversteer compared to the factory sizes.
For the staggered size setups that our cars use, it's also crucial to check the circumference difference between front and rear wheels. That's vital if you're changing sizes if you want to avoid confusing the ABS/PSM operation in the car. If that ratio strays too far from the factory ratio you can have problems. That's what my calculator does and I've never seen that elsewhere.
I guess since most cars don't run staggered sizes it's not common to encounter online resources that incorporate those issues.
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03-11-2011, 02:37 PM
#9
Registered User
Thread Starter
Well heck, I just did an exhaustive search to find all sizes that get the front & rear diameter within 3% of stock and the ratio within 1.5% of stock. This is the result :
Code:
F : 235/40-18 , R : 265/40-18 , FD : 25.402 RD : 26.346 ratio : 1.037 , error percents : 0.2 0.6 0.8 F : 235/40-18 , R : 285/35-18 , FD : 25.402 RD : 25.854 ratio : 1.018 , error percents : 0.2 1.3 1.2 F : 235/40-18 , R : 295/35-18 , FD : 25.402 RD : 26.130 ratio : 1.029 , error percents : 0.2 0.3 0.1 F : 235/40-18 , R : 305/35-18 , FD : 25.402 RD : 26.406 ratio : 1.040 , error percents : 0.2 0.8 1.0 F : 235/40-18 , R : 335/30-18 , FD : 25.402 RD : 25.913 ratio : 1.020 , error percents : 0.2 1.1 0.9 F : 235/40-18 , R : 345/30-18 , FD : 25.402 RD : 26.150 ratio : 1.029 , error percents : 0.2 0.2 0.0 F : 245/35-18 , R : 275/35-18 , FD : 24.752 RD : 25.579 ratio : 1.033 , error percents : 2.7 2.4 0.4 F : 245/35-18 , R : 315/30-18 , FD : 24.752 RD : 25.441 ratio : 1.028 , error percents : 2.7 2.9 0.2 F : 245/35-18 , R : 325/30-18 , FD : 24.752 RD : 25.677 ratio : 1.037 , error percents : 2.7 2.0 0.8 F : 245/40-18 , R : 265/40-18 , FD : 25.717 RD : 26.346 ratio : 1.024 , error percents : 1.0 0.6 0.5 F : 245/40-18 , R : 275/40-18 , FD : 25.717 RD : 26.661 ratio : 1.037 , error percents : 1.0 1.8 0.7 F : 245/40-18 , R : 295/35-18 , FD : 25.717 RD : 26.130 ratio : 1.016 , error percents : 1.0 0.3 1.3 F : 245/40-18 , R : 305/35-18 , FD : 25.717 RD : 26.406 ratio : 1.027 , error percents : 1.0 0.8 0.3 F : 245/40-18 , R : 315/35-18 , FD : 25.717 RD : 26.681 ratio : 1.038 , error percents : 1.0 1.8 0.8 F : 245/40-18 , R : 345/30-18 , FD : 25.717 RD : 26.150 ratio : 1.017 , error percents : 1.0 0.2 1.3 F : 255/35-18 , R : 275/35-18 , FD : 25.028 RD : 25.579 ratio : 1.022 , error percents : 1.7 2.4 0.7 F : 255/35-18 , R : 285/35-18 , FD : 25.028 RD : 25.854 ratio : 1.033 , error percents : 1.7 1.3 0.4 F : 255/35-18 , R : 315/30-18 , FD : 25.028 RD : 25.441 ratio : 1.017 , error percents : 1.7 2.9 1.3 F : 255/35-18 , R : 325/30-18 , FD : 25.028 RD : 25.677 ratio : 1.026 , error percents : 1.7 2.0 0.4 F : 255/35-18 , R : 335/30-18 , FD : 25.028 RD : 25.913 ratio : 1.035 , error percents : 1.7 1.1 0.6 F : 255/40-18 , R : 275/40-18 , FD : 26.031 RD : 26.661 ratio : 1.024 , error percents : 2.3 1.8 0.5 F : 255/40-18 , R : 285/40-18 , FD : 26.031 RD : 26.976 ratio : 1.036 , error percents : 2.3 3.0 0.7 F : 255/40-18 , R : 315/35-18 , FD : 26.031 RD : 26.681 ratio : 1.025 , error percents : 2.3 1.8 0.5 F : 255/40-18 , R : 325/35-18 , FD : 26.031 RD : 26.957 ratio : 1.036 , error percents : 2.3 2.9 0.6 F : 265/35-18 , R : 285/35-18 , FD : 25.303 RD : 25.854 ratio : 1.022 , error percents : 0.6 1.3 0.8 F : 265/35-18 , R : 295/35-18 , FD : 25.303 RD : 26.130 ratio : 1.033 , error percents : 0.6 0.3 0.3 F : 265/35-18 , R : 335/30-18 , FD : 25.303 RD : 25.913 ratio : 1.024 , error percents : 0.6 1.1 0.5 F : 265/35-18 , R : 345/30-18 , FD : 25.303 RD : 26.150 ratio : 1.033 , error percents : 0.6 0.2 0.4 F : 235/35-19 , R : 265/35-19 , FD : 25.476 RD : 26.303 ratio : 1.032 , error percents : 0.1 0.4 0.3 F : 235/35-19 , R : 295/30-19 , FD : 25.476 RD : 25.969 ratio : 1.019 , error percents : 0.1 0.9 1.0 F : 235/35-19 , R : 305/30-19 , FD : 25.476 RD : 26.205 ratio : 1.029 , error percents : 0.1 0.0 0.1 F : 235/35-19 , R : 315/30-19 , FD : 25.476 RD : 26.441 ratio : 1.038 , error percents : 0.1 0.9 0.8 F : 245/30-19 , R : 275/30-19 , FD : 24.787 RD : 25.496 ratio : 1.029 , error percents : 2.6 2.7 0.1 F : 245/30-19 , R : 285/30-19 , FD : 24.787 RD : 25.732 ratio : 1.038 , error percents : 2.6 1.8 0.9 F : 245/35-19 , R : 265/35-19 , FD : 25.752 RD : 26.303 ratio : 1.021 , error percents : 1.2 0.4 0.8 F : 245/35-19 , R : 275/35-19 , FD : 25.752 RD : 26.579 ratio : 1.032 , error percents : 1.2 1.4 0.3 F : 245/35-19 , R : 305/30-19 , FD : 25.752 RD : 26.205 ratio : 1.018 , error percents : 1.2 0.0 1.2 F : 245/35-19 , R : 315/30-19 , FD : 25.752 RD : 26.441 ratio : 1.027 , error percents : 1.2 0.9 0.3 F : 245/35-19 , R : 325/30-19 , FD : 25.752 RD : 26.677 ratio : 1.036 , error percents : 1.2 1.8 0.6 F : 255/30-19 , R : 275/30-19 , FD : 25.024 RD : 25.496 ratio : 1.019 , error percents : 1.7 2.7 1.1 F : 255/30-19 , R : 285/30-19 , FD : 25.024 RD : 25.732 ratio : 1.028 , error percents : 1.7 1.8 0.1 F : 255/30-19 , R : 295/30-19 , FD : 25.024 RD : 25.969 ratio : 1.038 , error percents : 1.7 0.9 0.8 F : 255/35-19 , R : 275/35-19 , FD : 26.028 RD : 26.579 ratio : 1.021 , error percents : 2.3 1.4 0.8 F : 255/35-19 , R : 285/35-19 , FD : 26.028 RD : 26.854 ratio : 1.032 , error percents : 2.3 2.5 0.2 F : 255/35-19 , R : 315/30-19 , FD : 26.028 RD : 26.441 ratio : 1.016 , error percents : 2.3 0.9 1.4 F : 255/35-19 , R : 325/30-19 , FD : 26.028 RD : 26.677 ratio : 1.025 , error percents : 2.3 1.8 0.5 F : 255/35-19 , R : 335/30-19 , FD : 26.028 RD : 26.913 ratio : 1.034 , error percents : 2.3 2.7 0.5 F : 265/30-19 , R : 285/30-19 , FD : 25.260 RD : 25.732 ratio : 1.019 , error percents : 0.7 1.8 1.1 F : 265/30-19 , R : 295/30-19 , FD : 25.260 RD : 25.969 ratio : 1.028 , error percents : 0.7 0.9 0.1 F : 265/30-19 , R : 305/30-19 , FD : 25.260 RD : 26.205 ratio : 1.037 , error percents : 0.7 0.0 0.8
03-13-2011, 05:37 AM
#11
yes, very critical. if 4wd and staggered be extremely careful.
have also a cayenne with the 20 techno, i.e.: 20x9 front and 20x10 rear. i use staggered (275 and 315) against oem all 275 but circumference must be the same.
Interesting to note that on lambos diablo vt (4wd) front are smaller, but ..the diff has different ratio ..to compensate !
have also a cayenne with the 20 techno, i.e.: 20x9 front and 20x10 rear. i use staggered (275 and 315) against oem all 275 but circumference must be the same.
Interesting to note that on lambos diablo vt (4wd) front are smaller, but ..the diff has different ratio ..to compensate !
