[TJandGENESIS]

As in, I put seventeen inch rims on the car. With the tires, they are about the same diameter as the stock wheels/tires.


So does this mean, that I might have to set some sort of, shoot, setting or something, to make sure the mileage calculates about the same? Or am I just worried about nothing?

 

[DanMan32]

If the overall tire diameter deviates from factory specs, then your speedometer, odometer, and MFD will be off, since the system assumes a certain circumference. All these systems measure distance based on wheel revolution so if the circumference changes, so does the distance traveled per wheel revolution.

With one exception: NAV. Because NAV also has GPS feedback, it can fine tune the travel distance per wheel revolution to caclulate ded reconing navigation. Unfortunately the Prius was not designed to have the NAV return the adjustment back to the rest of the car. There are no other adjustments that can be made for the rest of the car.

 

[TJandGENESIS]

If the overall tire diameter deviates from factory specs, then your speedometer, odometer, and MFD will be off, since the system assumes a certain circumference. All these systems measure distance based on wheel revolution so if the circumference changes, so does the distance traveled per wheel revolution.

With one exception: NAV. Because NAV also has GPS feedback, it can fine tune the travel distance per wheel revolution to caclulate ded reconing navigation. Unfortunately the Prius was not designed to have the NAV return the adjustment back to the rest of the car. There are no other adjustments that can be made for the rest of the car.

Thanks Dan. I sort of thought that would be the case.

 

[DanMan32]

Also, your displayed MPG may drop some, since the car will be seeing less miles than you actually travel on the same gallon of gas.

 

[sub3marathonman]

It looks like the new tires are ever so slightly larger than the originals.

That would increase your true speed given the same reading on the speedometer. However, ususally there is an overestimation of speed by the speedometer, so that if you're indicating 50 mph you might only be doing 48 mph.

It is possible to determine the difference between the new and the old tires a couple of ways. The easiest way is to measure each tire's circumference, and the ratio will tell you how much faster or slower the car is going with new tires relative to the original.

Or you could get an accurate measurement of true speed over about 10 miles on the freeway with accurate mile markers and compare that to your odometer. This method works better the longer you can do the test.

For my Honda Rebel motorcycle the difference was about 5% under the indicated speed. This also means that when you go over 100,000 on the odometer you've actually only gone 95,000 miles. Some people in Europe have said that it is a law for the speedometer to indicate a certain percentage higher than actual speed.

 

[Phoenix]

Larger wheels & tires

Use a GPS to check actual speed. The 2002 Prius speedometer was right on with the OEM tires. With HydroEdges in the next larger size, the GPS indicated that the speedometer was reading 1 mph below actual vehicle speed (the car was actually going 1 mph faster than the indicated speed on the speedometer), but that slight error was gone after about 10,000 miles.

 

[sub3marathonman]

Re: Larger wheels & tires

Use a GPS to check actual speed.

Hey, that's cheating! :? All this new technology and I'm still trying to figure out the old technology.

Also, it seems that the new Hydroedge tires Phoenix put on were initially that ever so slight bit bigger than the OEM tires, but after 10,000 miles they had worn down to the same size as the OEM tire's original circumference.

 

[mrbigh]

Re: Is there a way to reset the car when you put new rims on

Hi, what type of tires and size have you used, I'm also in the task of new 17" shoes for my Pri. :wink:

 

[TJandGENESIS]

Re: Is there a way to reset the car when you put new rims on

Hi, what type of tires and size have you used, I'm also in the task of new 17" shoes for my Pri. :wink:

http://www.priusonline.com/viewtopic.php?t=8352&highlight=

This thread should help you out. Let me know if it does not.

 

[ken1784]

With one exception: NAV. Because NAV also has GPS feedback, it can fine tune the travel distance per wheel revolution to caclulate ded reconing navigation.

Japanese Prius Navi system has the tire size manual adjustment menu.
Doesn't the US model have such?

[email protected]

 

[DanMan32]

Didn't I say that in the quote you quoted? It is the non-nav functions that don't have tire adjustments, nor do they take any from the NAV. Unless that changed in 2006.