www.will they fit.com and Tire Size Calculator | Check Tire Size Conversion | Discount Tire both allow you to calculate how different tires will affect the speedometer, with WillTheyFit also offering a visualization of how diferent tires and wheels along with diffferent offsets mioght possibly affect fitment.
@funinthesun is correct in that Polaris only provides the parameters for Base/SL/LE/SLR wheel/tire sizes. When selecting new tire or wheel candidates, the safest thing to do is use one of the tools just listed to ensure the speedometer won't be too affected. Also, trying to keep the same ratio between the diameters of the front vs rear tire/wheel candidates as closely as possible to the stock ratio to keep the safety systems happy.
REAR TIRE
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In an attempt to get more sidewall for hopefully a better ride I want to go with a 45 instead of the factory 35. Here are the specs, think I may be in trouble here.....
Sidewall Height: 3.51'' 4.52'' 1.01'' Section Width: 10.04'' 10.04'' 0'' Tire Height: 27.02'' 29.04'' 2.02'' Tire Circum: 84.89'' 91.23'' 6.34'' Rev. / Mile: 746.38 694.51 -51.87
If your speedometer reads 65 mph, you are going about 69.9 mphSo o may have to go with a 40....
Sidewall Height: 3.51'' 4.02'' 0.51'' Section Width: 10.04'' 10.04'' 0'' Tire Height: 27.02'' 28.04'' 1.02'' Tire Circum: 84.89'' 88.09'' 3.2'' Rev. / Mile: 746.38 719.26 -27.12
If your speedometer reads 65 mph, you are going about 67.5 mphWhat say the pros?
Thanks
LC
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At least one person has posted (can't remember who or which forum) about using a 295/45R18 tire on the stock rear Base wheel and says he hasn't experienced any problems with the safety systems although at an indicated 65 mph he's doing closer to 73. IIRC, he did have his Base model ECU reflashed to the SL tire/wheel specs. HIs 295/45 tire is about 12.5% larger than his stock tire. (TBH, I still don't understand why his nanny systems haven't triggered any warnings.)
In your case, the 45 aspect tire is about 7.4% larger than the stock 35 tire. Normally, I'd feel that is pushing compatibility with the nanny systems, but based on his experiences, you may be OK as long as you remember you're going 7.5% faster than indicated.
The 40 aspect tire is much closer to the stock size and only about 3.8% larger, so it should be less likely to cause problems and hopefully won't get you pulled over if you're doing an indicated 65 and should therefore be a safer choice as far as nanny system compatibility is concerned.
Unfortunately, things like this are not cheap to try since you can't return a tire because you don't like it for some reason. Good Luck. -
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I ran a couple 275-40-20's on my previous 16.5 stock wheel with no Nanny probs. To my eye, taller tire looked better, and it certainly gave a better ride.
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I know for a fact that having a difference of -49 will not turn on the nanny lights or mess with the abs or traction control. I friend of mine is running that setup. The stock tires have a -30 differential and I thought for sure -49 would have been a problem but so far...nothing and hes has had them a while. I do not know at what point the system will give up and say hey way to out of whack. You may get away with -51 or you may not....Justs my .02.
SSREAPER
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I put the 255 45 20 tire on the back, took a 150 mile ride and had absolutely no problems with the nanny controls so you can call it a successful up size. Wife and I both agree the ride is so much better, softer over the bumps and seam laps, and the normal old guy driving is not effected. Did find the speedometer is off but in a weird way. At an indicated 60 mph the GPS says 57, and it seems to hold true from about 30 up to 80, about 3 mph high on the speedometer than gps.
LC
BFGoodrich G-Force Comp 2 A/S Tires | Passenger Performance All-Season Tires | Discount Tire
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I put the 255 45 20 tire on the back, took a 150 mile ride and had absolutely no problems with the nanny controls so you can call it a successful up size. Wife and I both agree the ride is so much better, softer over the bumps and seam laps, and the normal old guy driving is not effected. Did find the speedometer is off but in a weird way. At an indicated 60 mph the GPS says 57, and it seems to hold true from about 30 up to 80, about 3 mph high on the speedometer than gps.
LC
BFGoodrich G-Force Comp 2 A/S Tires | Passenger Performance All-Season Tires | Discount Tire
A 255/45R20 tire should have about a 1" taller sidewall than the stock 255/35R20 aspect tire and should be turning at almost 70 mph at an indicated 65.
According to the Discount Tire tire size calculator (Tire Size Calculator | Check Tire Size Conversion | Discount Tire) the larger tire should be turning at 69.9 mph at an indicated 65, (This is where things get weird) yet WillTheyFit.com reports the larger tire should be turning 60.5 mph at an indicated 65 (6.92% slower). Something between these 2 sites doesn't make sense! -
And what is really weird is mine is off the other way.
Actual speed is 3 mph SLOWER than indicated by gps speeds. That is at 70 mph indicated on the speedo the gps reports actual speed to be 67.
Go figure.........
LC
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At least one person has posted (can't remember who or which forum) about using a 295/45R18 tire on the stock rear Base wheel and says he hasn't experienced any problems with the safety systems although at an indicated 65 mph he's doing closer to 73. IIRC, he did have his Base model ECU reflashed to the SL tire/wheel specs. HIs 295/45 tire is about 12.5% larger than his stock tire. (TBH, I still don't understand why his nanny systems haven't triggered any warnings.)
In your case, the 45 aspect tire is about 7.4% larger than the stock 35 tire. Normally, I'd feel that is pushing compatibility with the nanny systems, but based on his experiences, you may be OK as long as you remember you're going 7.5% faster than indicated.
The 40 aspect tire is much closer to the stock size and only about 3.8% larger, so it should be less likely to cause problems and hopefully won't get you pulled over if you're doing an indicated 65 and should therefore be a safer choice as far as nanny system compatibility is concerned.
Unfortunately, things like this are not cheap to try since you can't return a tire because you don't like it for some reason. Good Luck.You can at Discount Tire!
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Do we know the largest size tire people are running on the rear 20" sl rim with no issues and close to original tire diameter? What brand is recommended?
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Use Online Wheel and Tyre Fitment Calculator. Offset, Tyre Stretch and Speedo Error | Will They Fit to input your tire and wheel info for your stock tire and then enter the tire/wheel info you're curious about. You'll see a visual representation of the differences.
