Prius v (Wagon) OEM tire RPM and speedometer accuracy

I found a little bit of info on those tires. Interestingly they use orange peel oil just like dB Super E-Spec tires!

Toyota Taps Yokohama BluEarth Tires For New Prius v Crossover

Cool Fuel Efficiency Tire Tips from Yokohama
[ame=http://www.youtube.com/user/YokohamaMotorsports#p/u/15/bJHVabIDtoE]YokohamaMotorsports's Channel - YouTube[/ame]

 

I hate to burst your bubble. Revs per mile is not an exact measurement. There are too many variables that are hard to control. Examples tread wear, air pressure in tire, vehicle load, and rotational speed.

I also highly doubt all tire manufacturers across USA, EU, and JP use the same methods for calculating or measuring revs per mile.

Here is a fun experiment for you. Drive through a small puddle of water at <5 MPH. The tires will leave marks on the dry pavement from the part of the tire that got wet. Measure the distance from the start of the first water mark to the start of the second water mark in inches. There are 63360 inches in a mile. Divide 63360 by your measurement to get revs per mile. Now drive through another small puddle of water at >45 MPH. Measure again, you will find the distance is longer due to the tire growing with increased rotational speed.

Now run the same experiment with the tire air pressure changed by 5 psi, another one of the many variables that cause us to have a 2.5% tolerance on the speedometer. This is why radar guns and GPS measurements are much more accurate.

 

Mike, while what you are saying is true revs/mile is still an important measurement to consider when buying your tires. If your tire has less revs per mile than your previous tire then you may erroneously assume you are getting worse mpg when in fact you may not be. Then we must consider speedometer readings with different size tires. A few revs per mile may go unnoticed but change it enough and the speedometer reading will change as well. I've observed this on my car when swapping tires. I also notice that the speedometer gradually becomes less accurate the faster you go. Like you mentioned above.

 

My first question: this thread dates 2012. Is this subject so dead there's been no newer info????

Two Prius V 2015 sidebyside: ours is a V 5, bros is V 3. Ours has 215/50-17 W tires; his has 60-16 tires. Our calipers showed his tire dia. about 5/8" GREATER than the V 5. Likewise his height was about 1/2" higher than the V 5.

Searching for a smoother quieter ride. I'm Contemplating putting 60 ratio tires on the V 5 17" wheels to raise it (comfort in and out) and provide more flex/cush to the ride in general. I recognize that might throw the speedometer off. Any hard data out there from those who've been here, done that??

 

First, I find that ride comfort can vary widely with tire brand. I always use Michelin and find the ride and road noise better than most OEM tires of the same size.

Changing to a different sidewall and tire width:
There will be a change on your speedometer directly related to the circumference of the tires. The existing accuracy is pretty good and highly repeatable based on radar signs I routinely go by. Usually my Prius v3 is about 1-2 miles high depending on speed. Perhaps 1 mph at 30 and 2 mph at 60 (~3.3%). Some suggest it is intentional to keep you closer to the limit. There are enough radar speed signs that show me the number is repeatable.

With a larger circumference tire, a speedometer will display a lower speed and the odometer will show less distance traveled. Doing a little "back of the napkin" math seems to show that replacing a Michelin 215/50/17 at 815 rpm (revs per mile) with a Michelin 215/60/16 at 800 rpm (and 16" wheels) will result in a larger circumference tire that covers more ground with each revolution. This would decrease the speedometer by ~1.84% over what it reads now. It could actually help calibrate a high reading speedometer. Regardless, 1.84% only represents a change of 1.1 mph at 60 mph which is not significant. Especially considering older electro-mechanical speedometers were often off by +/- 5%.

A second option would be a 215/60/17 at 766 rpms, assuming it would fit the wheel well. Now we are talking a speedometer decrease of ~6% which might be noticeable.

For reference, the examples were all Michelins with data from Tirerack.
Diameters: 215/50/17 OEM = 25.5"; 215/60/16 = 26.1" ; and 215/60/17 = 27.2"
Add from Air_Boss below: 225/50R/17 = 25.9" at 803 rpm

 

We went with 225/50R17 which at 3% larger circumference just about perfectly square-up the indicated with the GPS road speed indication.