Potentially dumb newbie question

IIRC your original wheels are 6 inches wide. A range of tire widths will fit this, both wider and narrower than the original 185 mm width tires.

Whatever tires you choose they should be within one or 2% of the orginals in terms of circumference. Also often expressed as revolutions per mile. A tire with wider tread would need to have a lower profile to present the same circumference.

A search of tire discussions here will reveal what tire sizes have been successful on Prius in the past.

 

Newbie, maybe...potentially dumb, no.

 

<div class='quotetop'>QUOTE(appgap @ Apr 12 2007, 06:55 AM) [snapback]421984[/snapback]</div>

To echo tochatihu's post, there are a number of options for replacement tires for your Prius. The OEM tire (Goodyear Integrity in 185/65-15) has the following critical specifications: Overall Diameter 24.4 and Rotations/Mile (typically measured at 60 mph) 855. The most critical specification is the Rotations/Mile, since that measures circumference and thus is determinant of speedometer and odometer accuracy. The next dimension to keep in mind in your search for tires is the Rim Width Range. Rim Width Range is the range of specified wheel widths the tire can be mounted on. Since the standard Prius wheel is 6 inches wide, the Rim Width Range for the tire you are considering will need to accomodate 6 inches. For example, a tire with a Rim Width Range of 5-6.5 inches would fit on the standard Prius wheel quite nicely; a tire with a Rim Width Range of 6.0-7.0 inches would be compressing the tire on the wheel. I personally would not fit a tire with that specification on the 15x6 inch wheel of the standard Prius.

With the above as a guide, you can go with larger (16 inch for example) wheels and tires as long as the Rotations/Mile are close to the 855 standard. How close is open to debate, but +/- 1% (as low as 846 or as high as 864) is probably as far as you can go without having an effect on speedometer and/or odometer accuracy (although I have not actually tested the limit on speedo/odo accuracy). With my Touring Edition, I chose to swap out the 16 inch wheels and tires for 15x6.5 inch wheels with 205/60-15 Michelin Pilot Exalto A/S tires. The 6.5 inch wheel width was right in the middle of the Rim Width Range for the Exaltos (5.5 - 7.5 inch) and the Rotations/Mile of the Exaltos was 5 off the standard (850 vs. 855 standard). I have checked the speedometer accuracy with the replacement wheels and tires over a measured mile (the highways in California are marked with perpendicular white bars at one mile separations to assist in aerial speed traps (but guess what - there is no budget for airplanes...)) and the speedometer and odometer are dead on - 60 seconds at 60 mph indicated and the odometer adds 1 mile to the count.

Hope this helps.

 

Here's a link to a very informative The Wheel & Tyre Bible which explains up-and down-sizing, and includes a calculator for approximate comparison of different sizes. The next size up from the OEM 185/65R15 is 195/60R15 – wider tire, shorter sidewall, calculated -1.05% difference, so 70 mph reads as 69.27 mph, but speedos usually read high.