In issue 4/2008 of the magazine "Us carowners" (name translated from Swedish), there was a tire test, with figures on rolling resistance.

Dimension tested was 195/65-15, the same that is used on Civic Hybrid.

Result (unit is "CR"):

Michelin Energy Saver 0.855
Barum Bravuris 2 1.063
Nokian Hakka V 1.101
Vredestein Sporttrac 3 1.143
GT Radial Champiro GTX-65 1.212
Continental Premium Contact 2 1.222
Dunlop SP Fastresponse 1.241
Goodyear Hydragrip 1.296

According to Michelin, rolling resistance accounts for around 20% of the total resistance for a car, so reducing the rolling resistance by 30% should reduce fuel consumption by 0.2 L/100 km. Personally, I think that's on the low side. The rule of thumb used to be that at 90 km/h, air drag is about the same as the rolling resistance (including all moving parts, like bearings, shafts, gearbox). But still, I think tires account for more than 20% of the total resistance at 90 km/h, and of course even more at all speeds below that.

In any case, 0.2 L/100 km is about 4% for a hybrid.

The tires are European specification and can probably not be directly compared to US versions.

 

Excellent!

Were all tires tested at the same inflation pressure or their maximum?

I need this data to test a tire performance model. In particular, I need the following data:

1. inflation pressure during test
2. tread width
3. revolutions per distance traveled (km is fine)

Thanks,
Bob Wilson

 

So, the lower the better right? (as far as FE goes) I have dunlops on my HCHII, but I'm not sure which dunlops they are. I just know that they are LRR.

 

CAUTION:
The Michelin Energy Saver, the very low RR in this survey is not the Michelin Energy series sold in the Americas at the current time. It is only released in Europe, and is scheduled for the US sometime in the near future, probably under another name. The rumor flying around in the retail tire outlets is that it will have a "Primacy" label -- probably the "Primacy Energy". To date, it is only available for a few cars, and Saab is one of them.

 

Bob,
if no one else told you before, you are really demanding. But in a good way.
1. The inflation pressure was the recommended for the car, but they don't say explicitly what it was. They used a VW Jetta for most tests, Audi A4 for some. I guess recommended pressure is around or little above 2.0 bar for them. But, the rolling resistance test is usually done in a machine, where the tire (one tire only) is pushed against a roller. They could have used any pressure for that test, but I would be surprised if it deviates much from 2 bar. The test was done in Texas, temperature was around 25 C. And unless my memory fails me, there is a standard procedure describing the rolling resistance test (including which pressure to use). In this issue they don't say exactly which procedure they used. All tires had load index of 91 (615 kg).
2. Tread width. They don't seem to have measured it separately. You could make some guessing from the dimension (195) but it won't be exact.
3. Revolutions per distance. Again, they don't say. You can make some guessing from the dimension (195/65-R15).

 

Thanks!

My curiosity got the best of me so I've ordered a pair of Sumitomo 175/70R14 to test against the Sumitomo 175/65R14s already on my car. I have enough instrumentation that I should be able to detect any difference. There are also some other Prius control laws I also want to test.

The parts should arrive this week and I'll try to get everything installed over the weekend. Then comes testing and publishing the results.

Sad to say but after ordering all of the parts, I reverse engineered some rolling resistance data from a "Rubber Manufacturer's" presentation; Smithers Scientific Services "Task 4 Rolling Resistance Testing: California Energy Commission's Fuel Efficient Tire Program" presentation; Firestone FR380 specifications; and Sumitomo T4 specifications. The direct measurement suggests I may see a 6% loss instead of the expected 8% gain in performance. These are small values so my testing methods may need some alternate thinking.

Bob Wilson

 

Rumored to be the tire on the 2009 Ford Escape Hybrid.

 

I'm confused. Presumably the rolling resistance coefficient numbers quoted by rgx are percentages, and need to be divided by 100 to get the rolling resistance coefficient. I'll make this assumption. Now, according to the attached report, the measured rolling resistance for the Michelin MXV4+ tires is 0.009, whereas the new "lower" rolling resistance Michelin "Energy Saver" tires is 0.00855. This sounds like the same to me! Are different measurement standards the explanation? What's going on?

Stan

 

I don't know Stan, but the tire I posted the caution on above was this one, designated by Michelin as the "Energy Saver" in Europe:

http://www.michelin.com/corporate/fr...112603&lang=EN

Note the test date on the page note. It could not be the MXV4+ or any of the "old" Energy series.

Its origin was the Michelin prototype designated "Proxima" from here:
http://www.michelin.com/corporate/fr...57_100&lang=EN

To quote from the prototype URL above:
The quote is restated and is slightly different form on the first URL, presumably the "as built" as compared to the "plan":
RFB