is it true that if you change the size of your wheels it can mess up your spedometer and give you an inaccurate reading? just curious, if so how do you fix it?

 

it's not the size of the wheels that matters, it's the size of the tires


you avoid the problem by getting tires that have the same overall diameter as your stock tires

 

ok cuz my friend had stock tires and switched to low profile so is there something he should get adjusted?

 

Most of the time people will plus size their tires, meaning they will go with larger wheels and they will run tires that are as sized to keep the overal diameter the same as stock. The simpliest way to see what the numbers look like or to have your questions answered in better detail than I could muster I'd head over to TireRack. The site has the tire sizes for every vehicle OE as well as what plus size tires would be and it has explaination links all over.

 

before i bought my wheels and tires, i search around alot. i found a site that u entered ur OE tire size, and u add in ur new tire size, and it gave u the diffrence in ur speedometer reading...mine..

185-65R14 to 195-55R15
it said if i was doing 60MPH on my speedometer, i was actually doing 59.9 MPH.

it does affect ur speedometer but by staying in the same OE tire diameter, u will minimize ur speedometer error.

 

If you install lower-profile tires on the same wheels, your speedometer will show speeds that are higher than they actually are. As was mentioned, keep the overall diameter of your tires the same as the OEM tires, regardless of wheel size. Here's how you can calculate wheel diameter: (remember that 1 inch = 25.4 mm)

Width x Aspect Ratio = Section Height
Section Height x 2 = Combined Section Height
Combined Section Height + Wheel Diameter = Tire Diameter
Example: 185/60R14 85H or 185/60HR14
185mm x .60=111mm
111mm x 2=222mm
222mm + 355.6mm(14")= 577.6mm or 22.74"
The first number is the width of the tire in millimeters, measured from sidewall to sidewall. To convert to inches, divide by 25.4 In the example above, the width is 185mm or 7.28".
The second number is the aspect ratio. This is a ratio of sidewall height to width. In the example above, the tire is 7.28" wide, multiply that by the aspect ratio to find the height of one sidewall. In this case, 185x0.60=111mm or 7.28"x0.60=4.36".
The last number is the diameter of the wheel in inches.
To figure the outside diameter of a tire, take the sidewall height and multiply by 2,(remember that the diameter is made up of 2 sidewalls, the one above the wheel, and the one below the wheel) and add the diameter of the wheel to get your answer.

 

okay but say i DO change the size of the TIRE. how do i fix it in the computer so that it isnt ****ed up.

 

I don't know of any way to do this and there's probably good reason why you can't - changing the speed calculation would allow someone to slow down the accumulated mileage (odometer). On the other hand, installing low-pro tires may increase the rate at which you accumulate miles on the odo.

 

Check this speedo calculator... http://www.paspeedo.com/calculator.htm

 

well then whats someone to do if they change the size...