Tyres

I can help but I need to know:

1) Original tires: brand and size (?)
2) Current tires: Michelins and size (?)
3) Latest tire/wheel alignment report (need for all four wheels)

You might check the "Tire Modeling" thread started in Fuel Economy to see what needs to be done.

Bob Wilson

 

Welcome to PriusChat, alkel1948. First, and most obvious, what pressure are you running in your tyres?

 

Japanese Turing version comes with the Michelin Pilot Primacy 195/55R16 as standard and normal version comes with the Goodyear GT3 185/65R15.

The Japanese 10-15 test mode data is 30km/L for Turing and 33km/L for normal version. We see 10% less mileage on Turing in real field too.

Ken@Japan

 

A couple of questons:

• Goodyear GT3 185/65R15 - revolutions per mile (or km?)
• Michelin Pilot 195/55R16 - treadwidth?

Testing my tire model spreadsheet, I set the tire pressures to the same value and used 6.2" (15.7 cm) for the Michelin treadwidth. I had to guess Michelin tread width of 6.2" using the relative rim and side wall width. The model shows a 10% performance penalty with the Michelin. However, if I set the Michelin pressure to 51 psi (351.6 KPA), the performance loss drops to 2%. Have any of the Japanese touring owners tried maximum side wall pressure?

Do I understand that the touring wheels are a larger diameter? The reason I ask is there may be more tire options on a 16" wheel to gain a larger diameter and mileage reduction.

Thanks,
Bob Wilson

 

The Australian Prius runs a Michelin Energy XV1 195/60/15 tyre as standard.
We usually get in excess of 40,000 km wear and average 4.6 - 4.8 l/100 km (around 58-60 mpg) economy from our cars.
The Michelins have proved to be an excellent tyre all round, and we run 42/40 psi pressures in them.

It sounds as if your dealer has fitted an incorrect size tyre to your car (probably smaller in diameter) which is rotating more times per km/mile, and therefore changing the effective gearing (and speedo reading) on the car, in turn making the consumption readout worse.

Contact your nearest Michelin Tyre distributor there, tell them the original tyre specifications from your owner's manual, and ask what size they would recommend as a direct replacement. If their recommendation is different to what you have now fitted on the car, then you need to take it up again with your Toyota dealer. If they still refuse to admit they made a mistake, then phone the National Toyota Distributor (which should be listed in your Service book), and tell them your problem. That should get some action.

 

Both tires are same diameter, approx 620mm.
I'm not sure about the tread width, but the size parameter says 185mm for the 15 inch and 195mm for the 16 inch.

Where does the 6.2" (15.7 cm) for the Michelin treadwidth come from?
What treadwidth did you set for the 185/65R15?
We compare mileage using the same tire pressure between 15 inch and 16 inch.

The touring wheels are 16 inch and the normal wheels are 15 inch, so touring wheels are larger diameter.
Again, the tire diameters are the same, approx 620mm.

I believe the most cause of their mileage difference is the tire rubber compound characteristics.

Ken@Japan

 

Additinal comments for my opinion is...

Michelin Pilot Primacy is 10% worse than Bridgestone Turanzas.
(rubber compound and tread pattern)
Brand new tire is 10% worse than wornout one.
The total would be more than 20% worse.

Ken@Japan

 

Thank you Ken,

I had to ask since some times the tires can have slight differences.

I used The Tire Rack - Your performance experts for tires and wheels to get the tread width but could not find anything for the Michelin even on their web site. The other dimensions are the width of the sidewall, more of a fit in the wheel well dimension. So what I did for the Michelin is use the rim width, sidewall width and relative weight to make an educated guess, 6.2" (158 mm.) It could be less but given the advertisements, I suspect they are a wider tire.

It would very useful if someone with these tires could drive over a damp paper towel, piece of cloth and piece of paper. The water should squeeze up and by measuring with width, we'll know how much tread comes in contact with the road. I can then plug this value into the model and we'll know.

Hummmm, what pressure? I see the 10% difference using 44 psi, the rated maximum pressure for the standard tire. It might be interesting if someone could run the maximum side wall pressure for these two tires and bring back the results.

Exactly. I was trying to suggest that it should be possible to find larger external diameter tires for a 16" rim size. The model suggests that the maximum mileage will come from: (1) larger external diameter, (2) smallest tread width, and (3) highest pressure.

Unfortunately we don't have any hysteresis numbers for the different tires . . . at least not yet. It may be possible to derive a useful number from some other tire parameter but I haven't seen anyone report a methodology. The literature suggests rubber compounds with more silicon will have lower rolling resistance due to lower hysteresis losses. It is a factor I can not quantify, yet. Have you seen anything?

Bob Wilson

 

You're collect about slight differences, but it is only 0.1% difference.
185/65R15=2*(185*0.65)+15*25.4=621.5mm
195/55R16=2*(195*0.55)+16*25.4=620.9mm
Their manufacturing differences are also less than only 0.2%, therefore I believe the slight difference does not matter.

The Tire Rack says 6.2" for 195mm and 5.9" for 185mm.
Of course, 195mm tire is wider than 185mm.

I reported the 15inch Prius is 10% better mileage than 16inch Prius on both 10-15 mode test and real life.
The absolute tire pressure does not matter here.

OP needs to know the reason why Bridgestone Turanzas 195/55R16 is more than 20% worse than Michelin Pilot Primacy 195/55R16.
I think it is not a good suggestion to replace his brand new Michelin with another one.

I haven't seen neither.
I believe we'll see never because it is manufacturers know-how/secret to offer their own characteristics including tread patterns.

Japanese Prius drivers are looking for the best mileage 185/65R15 tires and tested a lot of 185/65R15 tires, but we've not found any better tires than the stock Goodyear GT3 brand yet.

Ken@Japan

 

My apologies, I had failed to include the details from an earlier posting and made a mistake in the data. I was using a spreadsheet from another model and failed to realize some of my data was inaccurate. So let's start with the data we have available:

Tire Specs for Goodyear Integrity
Tire Specs for Michelin Pilot Primacy

Everything but tread width is reported and that is one of three important parameters: (1) maximum inflation, (2) tread width, and (3) revolutions per mile. But let's make sure we're using the same terms:

1010tires.com Tire & Wheel Tech

The section width, is the distance between the side walls and is not the treadwidth:

Now one of the most important tire characteristics is inflation pressure and using maximum cold inflation pressure, which tire manufacturers report and is the load rating test pressure:

By inflating to the maximum side wall pressure, we minimize the amount of tread that has to bend to conform to the road. It is this bending of the thick rubber of the tread that leads to significant hysteresis energy losses. Higher tire pressure also reduces the front-to-rear distance of the contact tread and thus the amount of bending needed.

Sad to say but both Goodyear and Michelin are not releasing their tread width. This makes shopping for mileage performance difficult or you have to make your own measurement or make educated guesses. Fortunately, better tire companies do report their tread width so looking at 185/65R15, Tire Rack reports these tread widths with identical side wall, 185 mm, and aspect ratio, 65:

5.5" - Firestone
6.0" (152.4 mm) - Bridgestone
6.5" (165.1 mm) - Dunlap
7.4" - Kumho
​

For now, I am using 6.0" for the Goodyear and 6.5" for the Michelin. It is very likely that the Michelin tires are even wider because so many people associate a wide tire with performance not realizing this is not mileage performance. This is an area where we need owners to measure the tread width by driving over a piece of paper and measuring the actual tread width from the impression.

Tire hysteresis is a function of both construction, radial tires are more efficient than cross-belted, and rubber. But both are sensitive, proprietary data not widely available. Still, we do have access to some mileage performance information, the tire geometry.

The state of California Energy Board has an effort to rate the rolling resistance of different tires by measuring the values. Although they have published charts that hint at having done the measurements, they have not published a table with tires and brands. But they have published a paper on rolling resistance and tire rolling resistance performance, "Tires, Technology and Energy Consumption" by K.G. Duleep. Using this paper, I built a spreadsheet using these formulas:

=1/SQRT(pressure) - relative inflation effect (higher is better)
=1/tread_width - relative tire tread effect (smaller is better)
=1/revs_per_mile - relative diameter (larger radius is better)
​

Unfortunately this paper does not give us a weighting of these measurable effects so I have rated all three equally. After purchasing the tires, the owner only has tire pressure as an independent variable. Using this model and these values, I get the following tire mileage ratings:

real_% - pressure / tread_width / rev_per_mile - tire
100.00% - 44 psi / 6.0" / 855 - Goodyear Integrity
100.27% - 51 psi / 6.5" / 852 - Michelin Pilot

107.95% - 44 psi / 6.5" / 852 - Michelin Pilot at same psi
116.67% - 44 psi / 7.0" / 852 - Michelin same psi and wider
​

I find it interesting that the reported loss of mileage for Michelin tires seems to be mirrored by this model. However, I have not done enough testing, yet.

Sad to say, sharing this spreadsheet with the PriusChat community is not easy because we can't upload an "xls" attachment. However, I've tried to zip up the spreadsheet and hopefully folks can download the spreadsheet model and try their own values.

Bob Wilson

ps. I have a better data for the 14", NHW11 tires and plan to test what I think will be the best tire later this year. If it works as the model predicts, I should see a 7% improvement in mileage.

 

Hi Bob,
I think you refer following model study.
http://www.iea.org/textbase/work/2005/EnerEffTyre/duleep.pdf
On page 14, it says RR increment is "5% per 20mm" of tread width.
On page 8, it says RR affects approx 30% of total energy use.
A 20mm tread width difference affects 5% X 30% = 1.5% energy difference.

I still believe the most cause of their mileage difference is combination of the rubber compound characteristics and tread patterns than their tread width.

Ken@Japan

 

Hi Ken,

Good point although making a model will take a little work. Using the suggested, linear relationship and starting with a tire 20 mm wide, we get a table like this:

width - relative drag
20mm (0.8") - 5%
40mm (1.8") - 10%
60mm (2.4") - 15%
. . .
120mm (4.7") - 30%
140mm (5.5") - 35%
160mm (6.3") - 40%
180mm (7.1") - 45%
200mm (7.9") - 50%
. . .
400mm (15.7") - 100% (reference tire)
​

This cuts the rate of tread width, drag in half but the math is a little tricky. We have three orthogonal metrics and their cumlative effect is the product of each. I've attached a revised spreadsheet, V1.1, in the zip file that should be close to the exact formula.

Thank you because this improves the accuracy of the model.

I believe that chart is for the standard USA cars, not hybrids and the Prius. Our Prius minimizes both "Aerodynamic Drag" and "Inertia Force" energy losses and this makes "Rolling Resistance" energy losses greater than "30%." Our "Aerodynamic Drag" has a lower coefficient of drag and often smaller profile than the typical USA vehicle. Also, the Prius regenerative braking reduces the "Inertia Force" losses and careful driving and route planning allows us to cut this down further. Unlike the typical car, Prius rolling resistance appears to be a larger portion of our energy loss and this is based upon:

= 190 + .42*(V*V)
​

I just wish there were some way to quantify either the rubber or tread pattern from the published specifications. I would also add the lay-up pattern of the internal belts.

Yokohama is unusually open in their tire construction and I suspect some of their internal structures are more efficient than others:
http://www.yokohamatire.com/TireFeatures.asp?TireID=80

Bob Wilson

 

Hi Bob,

If RR is fixed only with the tire dimensions, your math works.
However, we see a lot of variances between the tire brands.
We never see same mileage on the same 185/65R15 tire size of different brands.

Every tire manufacturers are trying to sell their own characteristics, such as shown on page-23 of the model study.
- Mass
- Rolling Resistance
- Handling
- Wet Traction (20 m ph)
- Wet Traction (60 m ph)
- Dry Traction
- Tread Depth
- Ride
- Noise
- Wear

The RR is only one of them.
Again, I believe we'll never see the quantified number of the rubber or tread pattern characteristics because they are manufacturer's know-how/secret to offer their own sales point.

Ken@Japan

 

Has there been any effort to collect and document the values returned by the different brands?

Bob Wilson

 

Recently we had a posting in GreenHybrid.com about a rolling resistance report in a Swedish magazine. The "Michelin Energy Saver" was rated with the lowest rolling resistance, 0.855, and this [ame="http://www.youtube.com/watch?v=se-W2R615oU"]video[/ame] shows a demonstration at an auto show. Unfortunately, this tire is only available for Peueot diesel.

I just checked the Consumer Reports and for rolling resistance of USA tires, they list with an equal "best" symbol:

• Michelin X Radial
• Michelin Agility Touring
• Michelin Harmony
• Toyo 800 Ultra
• Sumitomo HTR T4

Sad to say, they do not report any values, just one of five different bubbles. But within a family of tires, geometry rules.

Bob Wilson

 

I have never seen any fair comparison data from third parties.
However, each makers do advertisement for their new tires.

Yokohama: ECOS vs Earth-1: 21% RR reduction
‰¡•lÆ’Sƒ€/THE YOKOHAMA RUBBER CO.,LTDÂFÆ’jƒ…Â[Æ’XÆ’Å Æ’Å Â[Æ’X

Bridgestone: B'style vs Ecopia : 30% RR reduction
Å â€Å½Â®â€°Ã¯Å½ÃÆ’uÆ’Å Æ’aÆ’XÆ’gƒ“ | ECOPIA EP100 “‹ÂÚ‹ZÂp

Dunlop: EC201 vs Enasave 97 : 35% RR reduction
Æ’^Æ’Cƒ„‚ÃDUNLOP(Æ’_ƒ“ƒÂÆ’bÆ’v)|ENASAVE97(Æ’GÆ’iÆ’ZÂ[Æ’u97)

Ken@Japan