Brad91Rs

My car had 225/60/16's on it, I put 245/50/16's on it. Will this throw off my speedometer reading? If so how much, and how can I fix it?
Thanks,
Brad

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91 metallic blue RS Flowmaster exhaust, Eibach Sportline Springs, Open element, 323 posi rear w/ 4 wheel discs. 350 comming soon.

AlkyIROC

You'll be going from a 26.6" tall tire to a 25.6" tall tire.

Your speedometer will be going faster than you actually are going.

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87 IROC-Z SuperPro ET Bracket Race Car
461 naturally aspirated Big Block

Best ET on a time slip: 11.242 altitude corrected to 10.89
Best MPH on a time slip: 121.52 altitude corrected to 125.89
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Best 60 foot: 1.546

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87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley

Mark A Shields

This will affect your odometer as well.

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'86 IROC
T-TOPS, TINTED WINDOWS, BRAKE LIGHT BLACKOUTS
GM GOODWRENCH 350
EDELBROCK TES HEADERS
3" Hooker CatBack w/Aero Chamber muffler
EDELBROCK 600CFM CARB.
KN AIRFILTER
ACCEL HEI DISTRIBUTOR
160* Stat
3:73 Posi
Rebuilt 700R4
B&M Megashifter, 5" Autometer Tach w/shift lite

Ozzy88GTA

Go to this site for a Tire Calculator
http://www.intercotire.com/calculators.htm
First check the diameter of the tire by using the calculator on the link: "Metric Tire"
Then use those diameter numbers on calculator in the "True MPH" page. You have to plug in the spedometer reading before you calculate to get the actual MPH.
Take a look at it.

Brad91Rs

Thanks for the help. Ozzy88gta that link was just what i needed. According to the calculator my speedometer is off 2-3 mph depending on the speed. Is there anyway to correct this?

RB83L69

Well, you went from the wrong size of tire, for which the car's speedo system was not designed, to the stock size. So what's to fix? By doing that, you should be fixing what was previously broken.

Regardless, the smart thing to do is to drive down a section of freeway or something like that with mile markers; and compare your odometer to the measured mileage. Use a good long stretch of road like 10 miles at least. It's easier to measure error in the distance than the speed.

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"So many Mustangs, so little time..."
ICON Motorsports

Brad91Rs

I'll give the milage idea a try. However didn't the RS's w/ 16 inch wheels come stock w/ 235/55/16 tires? The 225/60's were put on by the previous owner, but either way (60 or 50 series) the tires would be 1/2 inch different from the stock height of 55. I guess the 2-3 MPH doesn't really matter, i can learn to live w/ it, and i don't plan on selling this car. I'll still try the milage test though.
thanks,
brad