Twitchy steering at freeway speeds.

Glad you enjoyed it Evan. Here is the number for the Michelin. I have included The Nokian and Bridgestone because their RR is even better than the Michelin. The Nokian NRT2 is actually very favorably reviewed and would probably be an excellent choice.

The Bridgestone has the very lowest RR, on the other hand, it is even wimpier than the Goodyear Integrity so I don't think anyone would like it.

Enjoy,
Bob

[font=Courier New:71065c13ca]
Bridgestone B381 0.0062
Nokian NRT2 0.0085
Michelin EnergyMXV4 Plus 0.0090
[/font:71065c13ca]

 

Thanks Evan, I'll add it to my list. Where did you find it?

Thanks,
Bob

 

Evan,

Those numbers are terrifying! I hope that this is one place where the model is not holding up because I can't stand the thought of being stuck with the Integritys, yuck!

Since the MXV4 is one of the better (lower rolling resistance) tires around, I am hoping that the modeller just needs an update, if not then I am switching hopes to some fantastic discovery in the reduction of rolling resistance which will be announced tomorrow morning

Thanks,
Bob

 

Evan,

Now you really have me scratching my head. I trust that the model is good since you like it. What is bugging me is why we haven't heard compalaints of massive fuel economy drops (more than 3 or 4 MPG) when owners are chamging to non-LRR tires, when the model shows such a huge drop between two LRR tires. nAm I making sense?

Where can I gat a copy of the modeller, I'd love to tinker with it.

Thanks,
Bob

 

One thought is that the RR is calculated at 32 PSI or something, so if the pressure is upped to 42 PSI by zealous Prilots not only would the actual RR go down, but the difference (percentage wise) between the two would shrink.

 

And I'm not sure where Wayne got those numbers. There are a couple of tests to determine rolling resistance and there will be lots of variance unless you're comparing the all tires of the same size tested with the same test. I may be wrong but I think Wayne might have derived his number from road coast down tests. And you'll notice he has a number in there for the road surface effect on rolling resistance of about .001. I don't know if that is additive or not and have not been able to contact Wayne anymore after he left (driven from) Yahoo. I'm just pointing out that the .006 works in Wayne's program, but any other number you plug in should be derived using the same size tire and test.

I've been looking into the Michelin Harmony tire (called Destiny at Discount Tire). The real world comments on Tire Rack only say good things about it's effect on gas mileage. The Hydroedge on the other hand has about the same number of negative comments about the gas mileage.

We have the Energy on our Acura RSX and it really tracks well. I just don't know about the gas mileage. Sure wish the manufacturers would start to publish those RR numbers. I hear they may do that here in CA next year on some tires.

 

I think that what you are saying is absolutely critical when comparing different rolling resistance values. I just downloaded the program (Thanks Evan) and had the same questions about rolling resistance. We need to know how the RR figure in the program was derived to be able to make sense of it . It is a coast down value, or SAE J2452 or J1269? They will all give different values. The values I posted earlier were all based on an independent lab performing SAE J1269.

As for the Michelin Energy series, they directly told me that it was specifically designed as their "green" tire. I do think that rolling resistance keeps getting better so it may have been matched or exceeded by a newer tire. I went on to ask them to supply me rolling resistance values for their tires but that is when they told me that it was proprietary (yeah right) I personally do not find online tire review satisfactory for the level of detail we are dealing with here. I have found just too many conflicting reports on every tire I look to make sense on anything, hence my desire for scientific testing.

California has been making some noise about disclosing RR to either the general public or to the State for state vehicle tire purchases, but nothing big is on my radar.

Bob

PS Here is the intro to California State Senate bill 1170, the full text is available online.

As required in Senate Bill 1170 (Sher, Chapter 912, Statutes of 2001), the California Energy Commission (Energy Commission) is pleased to submit the California State Fuel-Efficient Tire Report.

The report is submitted in two volumes:

Volume I: Summary of Findings and Recommendations
Volume II: Consultant Report

Volume I summarizes the major findings and recommendations of the Energy Commission regarding the potential for a state, fuel-efficient tire program.

The Energy Commission’s consultant, Ecos Consulting, developed and wrote Volume II. The report is due to the Governor and Legislature no later than January 31, 2003. Vehicle tires, particularly replacement tires, show a wide variation in fuel efficiency based on their composition and design. Because these variations can have a significant impact on vehicle fuel economy, investigating ways to improve the fuel efficiency of tires and making information available to the public is a desirable goal.

SB 1170 requires that the Energy Commission make specific recommendations to:
• Establish a test procedure for measuring tire fuel-efficiency.
• Develop a data base of fuel-efficiency of existing tires in order to establish an accurate baseline of tire efficiency.
• Develop a rating system for tires that provides consumers with information on the fuel-efficiency of individual tire models.
• Implement a consumer-friendly system to disseminate tire fuel-efficiency information as broadly as possible. The Commission shall consider labeling, Web site listing, printed fuel economy guide booklets, and mandatory requirements for tire retailers to provide fuel-efficiency information.
• Study the safety implications, if any, of different policies to promote fuel-efficient replacement tires in the consumer market.
• Mandate a fuel-efficiency standard for all after market tires sold in California.
• Offer a rebate to purchasers of replacement tires that are more fuel-efficient than the average replacement tire.

To respond to this legislative request, the Energy Commission contracted with TIAX, LLC and Ecos Consulting to help define the necessary parameters for a fuel-efficient tire program. The Energy Commission held two workshops in the fall of 2002 to solicit comments from interested parties. The following stakeholders provided input to the report:

• Tire manufacturers,
• Energy Foundation,
• Natural Resources Defense Council,
• Union of Concerned Scientists,

 

Dear Gen2, Thanks for that mighty post! I will set my pressures to your spec and see how the car tracks. Also Frank Hudon's explaination of the strain gauge is thought provoking.

The steering road feel, or response, from the road to the steering wheel, when the steering wheel is centered and driving at freeway speeds is non-existant. It almost feels as though the rack is too tight.

I would appreiciate if any of you could try what I did about reaching behind the tire and touching the rack-frame interface while someone else rocks the steering wheel. I would like to know if anyone else has play there. Thanks, Tom.

 

So if Amped, the 2nd poster on this list is around.....how are you doing with the gas mileage on those RE-950 Potenzas? I did notice that you went slightly wider with a slightly lower overall profile. I'm sure that the wider tire probably hurt the mileage slightly but probably helped the handling too. I guess I'm just going to wait a bit and see how this rolling resistance issue sorts itself out with replacement tires. The Energy from Michelin does look like the best choice but I'd love to see rolling resistance numbers in our 185 15" size.

For whatever reason, I'm one of those who believe that the std recomended pressure of 35/33 feels a little less squirrely on my car. As near as I've been able to telll, there's only about a 3% reduction in gas mileage from the 42/40 settings. I did a series of experiments one weekend to approximate this. But these values are not really significant from a statistics stand point. However they do pretty much match some of the numbers that I think Goodyear published for an 8 psig underinflation on a variety of vehicles so I think they may at least be in the ballpark.

 

Rolling resistance for the Michelin:
Michelin EnergyMXV4 Plus 0.0090
Nokian NRT2 0.0085

I threw in the Nokian because they are also available in our standrad size 185/65R15. The Michelin is good (I've used them for years on my other cars) but I find one point you made extra interesting.

That is that you find only a 3% reduction in fuel economy by dropping to 35/33 from 44/42. This is interesting because some of the tire manufacturers are telling my their LRR tires give about a 3% improvement in fuel economy. So we have 3% we don't worry about and 3% we do worry about.

My research continues because no tire manufacturer has given me any rolling resistance numbers at all, therefore I haven't been able to estimate how much I might lose by choosing something different, bummer.

 

That Michelin number isn't for the 185 size though is it. I seem to remember it was for the 2.05 or something like that. The 185 then would like be much lower thne if that's true...maybe even around .006-.007. Wishful thinking I know, as an engineer like you, I crave useful data.

Yes I also thought that by changing to Mobil 1 I would see some positive effect. But it seems like all 3 tanks since switching have been "off". I've had more trouble trying to keep the mpg above 50 and I'm in the 48 range like when I first got the car. These 2nd order effects sometimes get lost in the noise or overwhelmed by the major effects like length of commute, traffic, etc. Still a very low rolling resistance tire can't be a bad thing and I don't want to make the mistake of putting a much higher rolling resistance tire on my car than I have now.

 

The only published number I could find for the Michelin is for a 205/55R16. It would be wonderful if there would be such a gigantic drop to the .006 range (one can only hope). I did note that this is about 1 inch taller so the difference in RR may come out to be a wash.

I'll post if I can get some better numbers.

Bob

 

For awhile I was looking at the Potenza RE 950. I had very good luck a few years back with a similar Bridgestone (750 I think) on my RX-7. That car was just like this. I tried everything before resorting to the tires. I just used the same size tire. It had Yokohamas on it that the selling dealer had installed and they were new. They were my last thought in this type of a problem but taught me (reminded me) not to overlook anything. It was amazing the difference. I never found out if it was a defective tire or just that Yokohams style, but met several other sports car owners with simillar experiences.

Coming to a stop the car would also follow any road crown change so it almost felt like an alignment pull. I have noticed that a couple of time with my Prius. The steering sort feels heavy in the direction of the road crown while coming to a complete stop....just not an outright pull.

 

Its quite amazing what the right set of tires can do. I had a similar experience to yours on my Lotus. It was the squirreliest car I had ever driven. Going through all the usual, several alignments, new sway bar bushings, control arms, trunnions, etc. I finally got rid of the Riken tires that the previous owner just loved. I put on a set of Yokohama AVSi n the same size and the car was transformed. It now felt like a race car with fantastic grip and stability.

It just goes to show that various tires can behave differently depending on the chassis configuration. Its so early in the Prius' lifespan that it may be a while before we figure out which collection of tires works best. I guess its up to us to figure that out.

Bob

 

I had to take my car the dealer for the recall today. I decided to try Escondido Toyota. I found myself next to another Salsa Red owner. And guess what, he says his car wiggles too. He says it's almost unpredictable but that he had some close calls in his 15,000 miles of ownership. We explained this to a service writer who said this is the first he's heard of this problem.

Now what are the odds that there would be a red 2004 parked next to me in the service bay, there for the recall, that had exactly the same freeway issues I do? Yet the dealers and Toyota seem to act surprised when you mention this to them. Even a few of the major magazines picked up on the the less than stellar straight line handling. What's it going to take, a major accident caused by this to get Toyota to at least recommend a fix...even a specific different tire that won't hurt gas mileage. They have the resources to test something like this for us. This other owner had not thought of trying to get the dealer to look into his problem. He just thought that's the way it is. I told him to complain so that Toyota at least was aware.