Prius 15's are better than aftermarket 17's! (Wrong wheels/tires can wreck your MPG)

[RedDevil]

Originally Posted by Frank Lee

IMHO Capri Racer's advice to go wide makes sense if you are loading the tires to near max capacity. I would expect a tire engineer- who is always concerned with liability issues- to have that position.

However I think if your vehicle is always at the lightly loaded end of the spectrum, fe gains can be had from going narrower, to tires with fewer plies and thinner sidewalls and treads. I have yet to personally test that theory.

The one does not have to rule out the other. Give me a tire thats both narrow and has thin layers anytime, if it is a quality tire and strong (enough).

Was wondering, are there commercially available tires where the layers have indeed been thinned and lightened, like having the steel belts replaced by carbon, kevlar of even glass fiber?

[user removed]

In my not so humble opinion, I would rather have a 40k mile tire than an 80k mile tire that dry rots before it is worn out. I think most of the real LRR tires are made this way.
Even then a hypermiler will get significantly more mileage out of the same LRR tire due to the lower stresses in their driving technique.
I remember when OEM tires would wear out before 10k miles. My aunts 1965 Cadillac wore out it's original tires in 6k miles and she was in no way an agressive driver. She asked me what tires to get for replacements, in 1967. I told her Michelin X. She replaced them 13 years later after the car reached 70k miles total, when the Michelins were dry rotted, not worn out. That is the basis for my opinion.
My father in law had his Michelins replaced due to dry rot, when they had 90% of the tread remaining, without any warranty assistance. No rationale can convince me to buy tires that dry rot that quickly.

regards
Mech

[Smokeduv]

Maybe someone made the comment already, but in the original post it doesn't mention if the wheels use the same tire width, as I think it would have a major impact on mpg instead of the many other parameters. The wheel weight can be compared only if all the parameters stay the same and just changing the wheel diameter, if not, then you are testing many parameters at the same time, which would ruin all the calculations.

[RedDevil]

Originally Posted by Smokeduv

Maybe someone made the comment already, but in the original post it doesn't mention if the wheels use the same tire width (...)

Wyatt did mention it in his second post:

Originally Posted by wyatt

(...) the rims were 8" wide, vs the 7" wide Prius rims.

If the rims were an inch wider, so were the tires. That does have an impact of economy, but not enough to be solely responsible for the difference in FE. IMHO.

[Smokeduv]

Originally Posted by RedDevil

Wyatt did mention it in his second post:

If the rims were an inch wider, so were the tires. That does have an impact of economy, but not enough to be solely responsible for the difference in FE. IMHO.

Oh, didn't noticed. I was looking for a 205/50/17 or something on that format. Sorry

Just a thought, I'm no expert, but if the rims are an inch wider, they will be heavier plus the added weight of a wider tire, they will have an impact on frontal area and a bigger contact patch, considering there are 4 wheels. Maybe all those parameters are negligible, but in my car, changing from 205 to 225, which is less than an inch, is very noticeable, even if I just change the front tires.

[TexasCotton]

Originally Posted by F8L

fuel economy

Anyway, I just thought I'd share my opinion because I don't know anyone who has tried more wheel/tire swaps on the Prius than I have and I still can't solve this issue without throwing ridiculous amounts of money at the problem. So for now, if you want max FE, stick with the OE 15" wheel and a set of Energy Saver A/S tires! The Ecopia EP422 is pretty good too. Maybe well get lucky like Europeans and get the new Ecopia EP001s.

Thank you

I am stickin with the 15 inch rim OEM ......... for my Gen 2 Prius, However I am considering a purchase of 175/65R15, 175/70R15 possible to give FE/mpg postive bump up. Michelin Energy X are okay 185/65R15 but kinda pricy in my personal IMHO retrospective perspective.

[CapriRacer]

Originally Posted by Frank Lee

IMHO Capri Racer's advice to go wide makes sense if you are loading the tires to near max capacity. I would expect a tire engineer- who is always concerned with liability issues- to have that position.

However I think if your vehicle is always at the lightly loaded end of the spectrum, fe gains can be had from going narrower, to tires with fewer plies and thinner sidewalls and treads. I have yet to personally test that theory.

Originally Posted by RedDevil

The one does not have to rule out the other. Give me a tire thats both narrow and has thin layers anytime, if it is a quality tire and strong (enough).

Was wondering, are there commercially available tires where the layers have indeed been thinned and lightened, like having the steel belts replaced by carbon, kevlar of even glass fiber?

I think the "wider is better" works regardless. Look at it this way,

If RR is energy loss - and the energy is lost in form of heat by the internal friction of the tire and the friction with the road surface plays a minimal role - then most of the heat is generated within the tread rubber, because it is both the largest mass and because it is deflected the most. Sidewalls have a much smaller mass and depending on where on the sidewall you look, they are defected as much as the tread.

That means the ply materials, such as polyester and steel don't have a very big impact on RR so replacing them doesn't result in much difference. But changing the tread rubber does.

Also, the amount of deflection is controlled by both the inflation pressure and the load. So going to higher inflation pressures gives you better RR - and going to a lighter load gives you better RR.

In fact, RRC (Rolling Resistance Coefficient), where RRC times the load on the tire = RRF (Rolling Resistance Force), is fairly linear and not dependent on how close to the rated load you are. You could be above it or below it and the RRC is still fairly linear - and for a given inflation pressure, the same value.

While as a tire engineer, I am happy that is so - keeping people safe should be my first priority - that doesn't change the laws of physics. It's just the way it works.

[TexasCotton]

Originally Posted by CapriRacer

I think the "wider is better" works regardless. Look at it this way,
.

While as a tire engineer, I am happy that is so - keeping people safe should be my first priority - that doesn't change the laws of physics. It's just the way it works.

Nothing personal however, if we wait on tire, engineers, designers, mfg,marketers, distributors, and you only the current status quo will be embraced. That mindset means new invovtive technology like airless tires will barely see the light of day and never go mainstream........................

I am not following your thinking at ALL Capri...............

I am likely going with others suggestion I like the mindset of a smaller foot print,or contact area.
I have 15 inch rims and have 185/65 currently
tirerack 15 sizes
http://www.tirerack.com/tires/sizes/...sp?diameter=15
wiki
http://www.tirerack.com/tires/sizes/...sp?diameter=15

[TexasCotton]

wiki
Tire code - Wikipedia, the free encyclopedia

better .............................

[TurboDieselInjection]

I think I would brush up on my physics before dispelling Capri racers info , there is plenty of science involved in tire technology and I think that there is more to rolling resistance than just width or lack there of.

At the other end of the spectrum , when I was a young lad getting into auto performance , someone with more expierience than me suggested to me that you would get MORE traction by running a skinnier rear tire than the fatties I was looking for , his theory was that given the weight of the car , and less sq inches of foot print you would achieve *greater* pounds per square inch , sounds logical , if you only look at a single variable , but after doing more research I found that there is more to traction than just psi , there is different rubber compounds , coefeicents of friction , temperature and the ability for the rubber to interlock with the pores and imperfections of the asphalt or concrete ,hence why wider softer tires create more grip . I am no engineer but I am open to the Idea that wider does not nessacarily translate into more RR , if you optimize other factors .