Tyres

[alkel1948]

Hi Everyone ! I'm in London England with a Jan 2006 T Spirit which has done 25000 miles. In December 2007 the Toyota dealer replaced the original Bridgestones (the front two of which were worn out) with four new Michelin Pilot Primacy's. These are the only Michelins that meet the specification for the Prius and I stupidly decided to go for Michelins on the basis that I thought they are supposed to last longer than other brands. Since the Michelins were fitted, my fuel consumption has dropped from 53 mpg to 42 mpg. The dealer doesn't want to know and neither do Toyota GB. Is there anyone out there who has had a similar problem or can shed some light on this? Thanks.

[bwilson4web]

Hi,

Originally Posted by alkel1948

Hi Everyone ! I'm in London England with a Jan 2006 T Spirit which has done 25000 miles. In December 2007 the Toyota dealer replaced the original Bridgestones (the front two of which were worn out) with four new Michelin Pilot Primacy's. These are the only Michelins that meet the specification for the Prius and I stupidly decided to go for Michelins on the basis that I thought they are supposed to last longer than other brands. Since the Michelins were fitted, my fuel consumption has dropped from 53 mpg to 42 mpg. The dealer doesn't want to know and neither do Toyota GB. Is there anyone out there who has had a similar problem or can shed some light on this? Thanks.

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

[Bill Merchant]

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

[ken1784]

Originally Posted by alkel1948

Is there anyone out there who has had a similar problem or can shed some light on this?

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

[bwilson4web]

Hi,

A couple of questons:

Originally Posted by ken1784

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

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

Originally Posted by ken1784

. . . 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.

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

[sleeka]

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.

[alkel1948]

OK...Here in the UK all Prius's come from the factory on 16" wheels not 15". Every Prius comes to the UK fitted with Bridgestone Turanzas 195/55 R16 87V. My local Toyota dealer has fiited Michelin Pilot Primacy's 195/55 R16 87V. I have inflated them to handbook spec of 35lb front/ 33lb rear which is as spec'd for 1/2 occupants up to 100mph. My consumption is about 42mpg or 15 kilometres per litre.

Michelin do a tyre here in the UK called Energy which I think is low rolling resistance but not in the correct spec (size and speed rating) for a UK Prius.

[ken1784]

Originally Posted by bwilson4web

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

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.

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?

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.

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.

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

[ken1784]

Originally Posted by alkel1948

Since the Michelins were fitted, my fuel consumption has dropped from 53 mpg to 42 mpg.

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

[bwilson4web]

Thank you Ken,

Originally Posted by ken1784

Both tires are same diameter, approx 620mm.

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

Originally Posted by ken1784

. . . 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?

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.

Originally Posted by ken1784

. . . We compare mileage using the same tire pressure between 15 inch and 16 inch.

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.

Originally Posted by ken1784

. . . The touring wheels are 16 inch (inner diameter rjw) and the normal wheels are 15 inch, so touring wheels are larger (interior rjw) diameter. Again, the (outer rjw) tire diameters are the same, approx 620mm.

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.

Originally Posted by ken1784

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

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