17" safer more stable than 15" wheels?

They might be safer if you're an extreme hypermiler and like to the practice the dangerous technique of taking sharp curves at high speeds to avoid losing energy to braking. However, if we trust the European version of EPA mpg ratings, the 17" wheel Prius takes a 1.8 mpg hit compared to the 15" wheel counterpart.

 

Toyota clains the 17"s take a 2mpg hit on fuel economy, however, this does not seem to be substantiated by most of the V owners on this forum.

There is also a considerable sporty steering gain from the additional European tuning and the tighter steering ratio (2.7 turns Lock to Lock for the V's and 3.8 for the II's, III's and IV's).

David (aka Blind Guy)

 

Very tough to say with great precision. I have not driven my Prius V without 17" wheels, so I can't say that it is more stable or gets worse gas mileage than it would with 15" wheels, but I can describe how it compares to my 2007 with 15" wheels.

At highway speeds with significant winds and bad weather, I feel the 2010 with 17" wheels is much more stable. I feel that I have better contact with the roadway and I feel the car is not going to be buffeted by variable winds.

Also, cornering and higher-speed handling is more more comfortable in the 2010 with larger wheels. Some of this could simply be due to the stiffer frame.

Fuel efficiency? I can't really compare here, because you'd need to look at two 2010s being driven the same way (one with 15s and one with 17s). I do have better mileage in the 2010, though -- even with the larger wheels. (See my signature below.)

 

What changes for improved handling and stability?

I'd think if the tire width is increased, wouldn't the contact patch be larger and therefore friction be increased, too? Similarly, if the composition results it improved grip, friction would increase because of that, also.

Also, if a larger tire increases ground clearance or unsprung weight, those factors should be detrimental to fuel economy, too.

All else equal, it seems like any significant improvement in handling and stability due to the tires would also correspond to a decrease in fuel economy. Maybe there are other factors that compensate somehow?

 

I think you've named everything I could think of.

Also, please remember that my comparison for purposes of stability and handling issues is not between my 2010 Prius V and another 2010 Prius (w/ 15" wheels), but between my 2010 Prius V and my earlier 2007 Prius (non touring). The 2010 15" wheels carry 195 tires, where my 2007 wore 185s.

 

Sorry, I had no issues with your comments;-) It was just a general comment on the topic that happened to be after your post.

 

I have a Gen II with 15 inch wheels and a Gen III with 17 inch wheels, so I can offer a comparison.

Friday on my way home, a typical moron tried to pass someone across the yellow lines, on a turn, and in the rain. They nearly hit me head on at 50 mph. Having driven the Gen II for 4 years, I know I would have slid and maybe lost control getting away from the moron. But the Gen III handled beautifully, and I tracked onto the shoulder and back onto the road with no loss of control and a feeling that it could probably do even more.

The moron fishtailed, then did some 360's and finally went off-roading. Luckily they didn't hit any other vehicles.

I'm very happy I paid the extra for the wheels. I have no interest in
"sports handling", just having more control to avoid Maryland drivers.

I say they are absolutely safer and more stable.

 

Did the Gen II have stability control? There could also be a difference in the general handling characteristics and even between the 15" tires from the two models.

 

I would hope that you are not losing traction so frequently that friction has a measurable impact in your fuel consumption! As long as you aren't skidding, it's rolling resistance, not friction, that we are concerned about, which may or may not correlate.

 

Oh, and another factor that could affect mileage would be the wheel weight, and weight distribution. Thanks to rotational velocity, weight in the wheels has a substantially higher impact than weight in the vehicle body.

 

Whatever you wish to call the force that impedes motion, the question is what aspects of the tire size and composition improve handling and stability. When those aspects are improved, is there a tradeoff with fuel economy? I would think so, but perhaps this isn't the case and we should all be putting 20" low profile ultralight alloys on the Prius if it is a no-lose situation?

 

Both my cars have traction control. I also noticed they fixed the bug in the traction control that caused the Prius to lose power when there was a microscopic amount of slippage, for example, starting off from a stop sign.

The Gen III just goes. My Gen II will often flash the yellow and slow WAY down.