2010 Prius Connection notes from San Francisco

From other posts I have read on this site, the 17 inch wheels (with lower sidewall profiles) will costs us 3 mpg, on the high end Prius. Here we read that the same tires will save .5 mpg.

The Michelin folks I spoke with at the Chicago Auto indicated the new tires do reduce drag, and are environmental, but could not tell me the mpg improvements that this tire allowed.

Could someone from the Toyota team (or anyone who knows for certain) respond to this, and let us know one way or the other.

I, like others here are very keen on the higher end Prius, but less so if there is a mileage penalty for that model. Which is it?

 

From the Detroit meeting the Head Engineer indicated the new tires on the 17" rims would cause approx 2 - 3 mpg mileage loss.

Some are debating buying the solar panel version and adding the wheels, while others are wanting the platinum package without the wheels.

I'm sure some folks will be able to work out trades here on PC between the wheels/tires.

3 mpg seems like no big deal on the surface.. but if you get 50mpg, its about 6% loss.
Or if even if you "would have" gotten 55 mpg and lose 3mpg, thats still about a 5.5% loss.

What I hate is that 3mpg equates to a "75% loss" of the overall savings of 4mpg that the 2010 brings verses the older models.
When thinking about it in that light, its quite a penalty to have the sporty wheels.

Some pretty impressive technology was brought to the table with the 2010 to achieve better mpg in spite of what is now a heavier vehicle due to better suspension, slightly bigger interior, sunroof etc.. I hate to eat up 75% of that just for the sake of looks alone.... too bad they can't figure out a way to have bigger wheels without eating up the mpg.

I've never completely understood why its such a problem.
if the outside diameter of the 15" wheels with tires is the same as the 17" wheels with tires, aren't we only talking weight differences between the two?

Put that same weight difference in the back seat of a car with the 15" set and I wouldn't think you would have a 3 mpg penalty by far!

A good percentage of kinetic energy lost getting the tires moving is gained again with the regen when slowing down anyway.... with that in mind, the mpg loss for the 17" set is even greater if regen wasn't working in our favor!

No wonder big cowboy trucks get crappy mileage!

 

Japanese staff manual says 40mm (more than 1.5inch) adjustment.

Ken@Japan

 

What I am having a hard time understanding, is the reason that larger wheels, with approximately the same final dimensions cause such a tremendous difference in average fuel economy. I would understand if the car sat a couple of inches higher off the ground, allowing for more airflow underneath, thus increasing drag. But from what I have read, the difference in height is minimal here.

Does anyone have the reason that this minor difference eats up so more more fuel?

 

when going for different sized wheels, it's recommended that the new tires have as close a diameter as possible to the stock ones... which translates to lower sidewall height for larger rims but maintains the overall same diameter and hence minimal differences in stance height

 

Well the only factors that make sense to me is the extra width makes a wider cut through the air, and also gives more traction on the road surface thus raising road resistance.
The air turbulence from larger wheels, I would think would be negligible based on speculation alone.
I can see how extra weight would be harder to get moving but as I stated, that in turn also generates more regen when stopping. Although regen has losses, its still an equalizing factor.

Since the outside diameter is the same, it shouldn't be a gearing issue... so I don't quite get it.

I just can't seem to grasp how it would have a 3mpg impact... "maybe" 1/2mpg.. but not 3?

 

A lot of factors come into play with wheel sizes.

Weight: While many plus size wheels weigh more than the originals this doesn't have to be the cause. Every wheel and tire combination is different. We won't know if the 17" wheel and tire combination is heavier then the 15" until the vehicles are on the road and someone can weigh them.

Width: The 17" wheel is also a wider wheel. This increases the size of the contact patch between the ground and the tire. This increases grip but also the rolling resistance.

Tire Compound: Tires come in many different compounds from very soft to very hard. Generally soft compounds will have more grip, more rolling resistance, and wear out quicker. Harder compounds have the opposite effect. Every tire is a balance between grip, ride, and life.

Tread Pattern: Again tires come with many different tread patterns for different purposes. Every pattern has a slightly different rolling resistance. For example the large tread blocks on snow tires give good grip on snow and ice but less grip on dry pavement. They also have more vibration, road noise, and lower fuel economy.

 

I know that these are all part of the interplay which will, in turn affect the ultimate mpg on the vehicle. That said, I have yet to hear (read) anywhere what the specific cause for this difference is.

More specifically, I am questioning whether it is a 1/2 or 3 MPG difference between the two tires. Some sites and posts have said 3, others only a .5 difference.

Ideally, I would really like to hear from someone from Toyota, as I am sure that a lot of us would like to know the final (official) answer to this. For me for certain, and likely for others, it is a hard choice to determine between the most fuel efficient hybrid on the market, and one that is less than that.

 

Thats the point.. we did hear!
We talked face to face with the Chief Engineer of Toyota at the Detroit Reveal "don't ask me to spell his name" and the 3mpg figure came straight from him.
Thats why you keep hearing that figure tossed around so much.

Who knows.. maybe he is wrong, or there was a communication breakdown.. but I doubt it.. he was a pretty smart cookie!

 

I can vouch for this. I was there asking questions. We had some trouble with the language barrier, but the chief was very clear about the 3 mpg figure. He said it several times.

Tom

 

Excellent. Sorry to be a pest. I appreciate the information. I was only asking again because I read .5 on anther post here today.

 

My explanation is a simple one, suggesting that the decrease is artefactual -- take it with a grain of salt:

The mpg calc uses rpm based on the standard 185 sized tyre.

 

There is a photo floating around here somewhere on PriusChat that shows the chief engineer's notebook. This photo shows raw and calculated EPA results for 2nd gen, 3rd gen w/ 15", and 3rd gen with 17".

 

I think the information eglmainz is getting from is the PDF from EU Prius. It listed l/100km for both 15" and 17". The difference was not much. I guess you can translate it to 0.5 MPG.

From the interview with the chief, I have the video and picture of his notebook that shows the difference of 3 MPG.

EU test cycle is very gentle like our pre-2008 EPA test cycle. Post-2008 EPA test is more aggressive and it could be why the 17" took 3 MPG hit.

 

Well it could me half inch if you start from 27mm extended.

When will people get that the sidewalls don't touch the road, it's the wider tread that increases drag on the road with the 17 inch wheel option?

 

Actually, I was getting that .5 information from the very first post in this thread. (http://priuschat.com/forums/2010-to...onnection-notes-san-francisco.html#post810767)

So maybe it is only "200Volts" who is not clear. It is possible that what he meant is that all other things being equal, these 17 inch tires, as opposed to other similar sized 17 inch tired, improve your efficiency by .5 mpg. This would mean that with an other 17 inch tire, maybe the Prius would have to overcome a 3.5 mpg difference? Or maybe he is just wrong. I am not sure, but this is why I was asking the question to begin with.

 

No prob eglmainz, and welcome to the forum... sorry if I sounded abrupt.. didn't mean to.
.5 would certainly make more sense to me... but based on pre-2010 models, folks that added larger wheels usually admit to at least a 2 mpg hit...

Some folks hate the stock look and are willing to pay the price to "style and profile"... especially if your young and trying to attract the cute butterflies, it may be worth it!

I'm less enamored with them as I was at first... I"ve started noticing other cars with and without. There are some technical disadvantages to low profile tires.. although those aren't too bad as they seem less aggressive. Plus although I still like them for looks, I think sometimes I just want something "different".... if everybody had low profile tires, the stock may be more appealing!

I do like the feel of a tire thats slightly wider for stability and turning.
I've gone to tires on my existing car that are about as wide as the 17" tires and I haven't noticed a real mpg hit that I can measure without getting down and dirty about it.
I still get between 48 and 55 mph based on how I drive and what the outside temp is.

And I don't drive like grandma, except when I'm half asleep going to work and half dead going home after my 12 hour shift!

 

eglmainz you raise a good point. While there is a lot of info floating around about the 2010 Prius, some of it can be confusing and sometimes even misleading so do exercise some caution when relying on details and let us know if/when we need to clarify. In fact I am working on putting together some answers we have owed you all so stay tuned for that info.

In the meantime, I'd like to just clarify some info posted earlier in this thread that I find confusing to readers reviewing the SF event:
"No prices were given, option packages were not all defined.
Option #2 and maybe#3 will NOT have a MFD (and hence no backup camera)....Option #6 (static display) had the solar powered roof."

About a month ago, Doug posted model and packaging details on this site. Please refer to this link (http://priuschat.com/forums/2010-toyota-prius/58321-2010-prius-models-option-packages.html) for the most accurate info on how Prius will be offered at launch. We do not refer to the 2010 Prius with Option #2, #3 and #6 so I think the above post can be confusing. Here's some clarity: the Multi-Information Display will come standard on Prius II-V but the backup camera is part of the Navigation optional package available on Prius III-V. The Solar Roof is available on the Prius III or Prius IV (and includes the Navigation package). The two static displays at this weekend's event were a Sandy Beach Prius III (no packages added) and a Blue Ribbon Metallic Prius IV with Solar Roof (and therefore Navi).

Please let me know if this clarifies some of your questions about the cars on display in SF.

Best,
Erica