Tire Height and Speedometer Error

[Jack B]

Many vipers do not have the original rear tires or wheels, therefore, the speedometer is not correct. The range of oem tires can create approx a 6% range of error.

Here is a great link fo tire size:

http://www.wheelcityusa.com/tires/chart.htm

 

[aloushi]

so if your tire is slightly bigger/higher than oem does it mean that your car is actually registering slightly less mileage than actually driven and vice-versa???

 

[DrumrBoy]

Yes, but I think the post had more to do with mph error than odo error..... big tires will earn you a little at resale but may cost you a lot at a speed trap. Its a good calculation to make just so you're aware of how high/low your speedo reads at, say, 60. When you pass the gendarmes you can make the adjustment....nothing says "stop me" more than going too slow (except for possibly exceeding the limit by 20 or more....)

 

[7TH_SIGN]

Stock OEM wheels and spec tires. I WAS under the impression that I was buying a stock Viper I have the same issue. My speedometer reads approximately 10mph slower at 60mph than the actual speed. The lower the vehicles actual speed of travel the smaller the gap in incorrect reading.

 

[dave6666]

Good to see no one has asked yet what tire sizes do to your gear ratio. Which the answer is they don't. The only way to change your gear ratio is to change gears.

That is all

 

[Big Al]

The speedo on a GPS is very accurate and that is how I checked the accuracy of my speedo.

 

[aloushi]

This only applies to rear wheels right???

 

[LifeIsGood]

I also use a GPS speedo application on my DROID phone. I use a mount for the phone that is just under and to the right of my rear view mirror...easy to see while driving.

 

[7TH_SIGN]

The speedo on a GPS is very accurate and that is how I checked the accuracy of my speedo.

That's how I verified mine was off. I still believe I have the stock gears in the car. Just can’t pin point what is causing the speedo to be off if the wheels are stock and the gears are as well.

 

[GTS Dean]

Nearly all tire manufacturers provide a data column listing the number of revolutions per mile. This is the best way to determine the degree of match to OEM specs.

 

[Jack B]

The following table is based upon a viper with 18" tires traveling at a true 60 mph. That is the first row. I also included the tire at the minimum (2/32") thread depth. The ta ble shows the max diff at 60 mph to be approx 4 mph.

I was not quite sure on the newer cars, did I miss any tire sizes? Obviously all the cars have the same gear set and are in the same trans gear. It is apparent if your speedo is off by more than 4 mph (at 60 mph) you probabily have other than 3.07's. A higher numerical rear gear is going to have your speedo registering higher than actual.

Tire Size	Max Dia	Min Dia		Car Speed = 60 MPH
				Speedometer at Max Dia	Speedometer at Min Dia
18 X 30 X 335	25.91	25.41		60.0	61.2
17 X 35 X 335	26.23	25.73		59.3	60.4
19 X 30 X 345	27.15	26.65		57.3	58.3

 

[Jack B]

The following table is based upon a viper with 18" tires traveling at a true 60 mph. That is the first row. I also included the tire at the minimum (2/32") thread depth. The ta ble shows the max diff at 60 mph to be approx 4 mph.

I was not quite sure on the newer cars, did I miss any tire sizes? Obviously all the cars have the same gear set and are in the same trans gear. It is apparent if your speedo is off by more than 4 mph (at 60 mph) you probabily have other than 3.07's. A higher numerical rear gear is going to have your speedo registering higher than actual.

Tire Size	Max Dia	Min Dia		Car Speed = 60 MPH
				Speedometer at Max Dia	Speedometer at Min Dia
18 X 30 X 335	25.91	25.41		60.0	61.2
17 X 35 X 335	26.23	25.73		59.3	60.4
19 X 30 X 345	27.15	26.65		57.3	58.3

I found a couple more tire sizes:

18 X 35 X 335 @ 27.23
18 X 35 X 345 @ 27.51

I will update the chart with these sizes.

I found a couple more tire sizes:

18 X 35 X 335 @ 27.23
18 X 35 X 345 @ 27.51

I will update the chart with these sizes.