Sadly it seems the tires designed for the first generation Honda Civic Hybrid are no longer available (Bridgestone B381).

Low rolling resistance alternatives that you are happy with?

Anyone tried changing to 185/65R15 and getting replacement tires that came on the Prius?

 

Very few choices.

http://www.tirerack.com/tires/TireSe...r=17&zip-code=

Probably simpler to put on 4 Defenders than put on 4 new wheels AND tires.

Unknown how the different wheel diameter will affect rotational inertia. Size is within about 1%, so no real issues there.

 

Getting a set of Defenders is what I decided to do. At least Michelin made some attempt at low rolling resistence with the Defenders.

You are correct that there just too many variables (rotational inertia, unsprung weight, etc.) to properly make an educated decision.

For now the Michelin Defenders are at least comfirmed by a friend who switch to the Michelins on their Prius and suffered no notable effects.

 

I put Michelin Harmonys on the 2005 a few years ago. They last MUCH longer than the Dunlops and still get good gas mileage. Not sure but I think 100K on the tires and still rolling.

 

With the Michelin Defenders (supposedly a low rolling resistance tire). I have seen an 8 MPG decrease with the new tires.


The new Civic Hybrid and Prius are coming with P195/60R15 or P195/65R15 tires. There seem to be numerous low rolling resistance tires that size.


What are you other MPG nerds doing to retain 50+ MPG? Has anyone taken the plunge and gone with a larger (more modern) rim size?

 

8mpg is a lot, but I notice a very typical 3-5mpg drop that seems to go away slowly after the first 1000-2000mi. I would reserve judgement until spring where temps are more mild and you have some miles on them.

 

That is at least hopeful. I have seen this happen twice before when I have to change tire sizes (a 165/70R13 and a 175/75R13), but the fuel economy loss is permanent.

 

So now I'm a little concerned. I drive an 05 HCH-I, and my local shop just recommended I replace my front pair of tires with Hankook Optimo H-724's [185/70 R14] due to some uneven tire wear that damaged that pair of tires.


They said those tires would fit fine and replaced them (just the front pair) for me recently. I've noticed an increased MPG since then (maybe ~4MPG), although I still have a pair of the old Cooper Trendsetter SE tires [205/75 R14] on the rear. There were 4 of these Coopers on the car when I bought it used (the only tires I've had on the car since I got it).


First off: the Hankook's are not showing up on that site or a few others I'm looking at, as being compatible. Are they really not compatible? If not, how the heck did my local shop get them on the vehicle and I've been driving on them for about a week without apparent issue? Am I risking damage in some way? I thought as long as they were R14's they'd fit and the tire widths and heights were more or less able to be interchanged...


Secondly: your mention of different diameters affecting rotational inertia is also concerning. Since two of my tires are at a height of 70 and the others at 75, am I putting some kind of shear force / added pressure onto parts of the vehicle now that the front and back tire pairs are at different heights (via the decreased diameter of the Hankook tires)? I asked if I should replace all 4 tires together, and the shop said it wasn't necessary to replace the other pair, as they were in OK condition. Is this something I should be worried about?


Last: is my increased MPG noticed just a side affect of the car driving strangely now that it's using two different height tires in front and rear, or is the increase real? Is there any danger of that affecting the IMA charging? The two tire pairs - front and back - are at different heights and should therefore have different rotational speeds (diameters are different), right? Could that impact IMA charging vs. them all turning at the same rate of rotation? Cause for concern / possible risk of damaging anything due to the tire pair difference?


I always read to expect an MPG *decrease* with new tires, at least until broken in. Seeing my MPG go up is kind of throwing me for a loop. Could it just be the thinner Hankooks mean less friction = better MPG, even though only half the tires were changed out?

 

You are seeing a couple of things happen here.

First, all things being equal, "skinnier" tires will have less rolling resistance that "fatter" tires and therefore get better fuel mileage. Second, the difference in rolling radius has effectively changed your comparative criteria that you are now using to determine your fuel mileage.

Those two things will alter your "fuel mileage".

 

To add to Doc's comments, you can't just compare the second numbers. The second number is the % of width, not an absolute height. 75% of 205 is more than 70% of 185.

Distance is measured in tire revolutions. The car expects a certain size tire for this to be accurate. The 185/70 travel 3.5% less distance per revolution than the 205/75. There will be a 3.5% difference in distance traveled between the two tires. The smaller tires will turn more telling the car that more miles have been traveled than actual. This will create a 3.5% increase in mileage alone.

The only source of danger comes from the ABS system. There is now a default 3.5% difference in the speeds of the tires, so the ABS system MAY be less effective in an extreme condition (panic stop), but there is likely very little risk, and you can test it by smashing the brakes as hard as you can on a deserted road to check for lock-up and controllability.

EDIT: I HAD AN ERROR IN MY SPREADSHEET. THE DIFFERENCE DUE TO TIRE DIA IS 7.3%, WHICH IS PRETTY MASSIVE.

Steve