tires and fuel economy?

Hi madprof, welcome to PriusChat. Tires can have a great affect on fuel economy. Use the Search button at the top pf every page and the search term tire to find probably hundreds of threads on tires, brands, pressure, and fuel economy.

You didn't say what brand and model of tire you bought, or the pressure you operate them at. This information could help get you a better answer. In general, all tires have an amount of rolling resistance. The Goodyear Assurance Integrity tires that Toyota fits on non-Touring models are low-rolling resistance, or LRR, tires. Goodyear makes other LRR tires, as do other tire manufacturers. An LRR tire will give you better fuel efficiency, all else being equal.

But you can do things to improve FE even without LRR tires. Your new tires are aligned and balanced which is the first step for anyone. Next is the pressure you run your tires at. Since the Prius is heavier in the front with the Hybrid Synergy Drive, Toyota recommends that the front tires be 2 psi higher than the rear tires. Some members of PC have raised the pressure they run to 42 psi front/ 40 psi rear. This is above Toyota's recommended pressure, but well within the safe operating limits of the tires. This pressure makes the tires harder which can improve FE.

Still, even with your reduced MPG, you're getting better milage than almost nay other car on the road.

 

Since you said the Goodyear dealer aligned the car, did they also have a Toyota scan tool to reset the steering zero point calibration and the VSC sensor. If not take it to Toyota and have it done.

Wayne

 

Hi Madprof,

You should expect lower mileage on new tires for two reasons. The edges of the grooves are sharp, and will result in more drag. And the sidewalls are not run in, and thus not as limber as well used tires. Everytime a tire rotates, the sidewall flexes, and if that flex is stiffer, the tire takes more force to roll.

Higher air pressure reduces the degree of flex. 42/40 seems to be the concensus here or PC. I also recommend you give that try.

The other possible cause is the basic tire design.

If your not seeing back over 45 mpg within 2000 miles, then tire design is probably the difference.

 

Actually, I believe you've got that halfway backwards- stiffer, *less* flexible sidewalls reduce the rolling resistance because the tire stays rounder vs a soft sidewall which deforms easier- it's the constant deformation as the tire moves in softer tires that costs energy and mileage.. You do have it right in that higher air pressure reduces the flex, and in general, the higher the pressure, the better the mileage.. Hypermilers have often gone way up over the sidewall limit, approaching 60 PSI in some cases in their quest to reduce the tires' rolling resistance and get the best mileage possible.. Another way to get similar benefits is to get an XL-rated tire if it's available in your size, which has stiffer sidewalls to support a heavier vehicle load with less tire pressure.. We have a trolley at work for moving equipment around and the lab manager though it would be a great idea to put on pneumatic tires on the thing- not! When you put on half-a-ton of test equipment, those tires flatten out and the thing is nearly impossible to push, especially when we have to go out into the carpeted hallway.. We compensated by pumping the tires way up and that worked well until we blew the tubes.. After that, I went and bought a set of hard casters to replace the pneumatics and that made all the difference- the thing now rolled like there was no weight on it at all because the tires did not deform- it was still harder to move over the carpet because the carpet is still squishing down, but nowhere near as bad as when both carpet *and* tire were soft.. Of course the dumbass manager complained about the replacement, but shut up when he actually used it and found that it moved much easier..

In any case, if you haven't gone to a different size/model of tire and your pressures are OK, another reason for the lower mileage could be that the Goodyear dealer's "alignment" actually made things worse.. The car is quite sensitive to alignment issues, so if the tire dealer screwed up slightly, you may not be able to feel anything in the car, but the mileage will suffer..

I don't know if I subscribe to this "tire break-in" period or not.. It sounds logical, but in my experience, with every new set I've put on, the mileage when brand new is always better than when the tires are nearly worn out, ie, what I get when new is what I get, it *never* gets better as the tire wears.. I think it's perhaps more likely a *driver* break-in period where some people, who are extremely sensitive to the feel of the car on the tires, perhaps if only subconsciously, take some time to adjust to the way that the new tires feel (particulary if they are a different brand/model) before they can acheive good mileage again..

 

With tire technology you will always have many different perspectives and opinions, and sometimes various studies to support a perspective.

The bottom line is that in general, a harder rubber compound, smoother and less agressive tread design, and somewhat higher inflation pressures will provide minimally better gas mileage when dealing with the general all purpose middle of the road passenger car tires.

When comparing radically different designs, such a comparring a hard rubber long life tire with a very agressive off road tire the differences are often far more pronounced and comparing the extremes is one of the best ways of quantifying the various tire principles that affect mileage.

Bear in mind that as rolling resistance goes down, so does traction, and that can affect braking distances as well as road handling qualities, especially in less tham optimum weather conditions. The goal is usually a reasonable balance of harder rubber compounds, increased pressure, proper camber and alignment, and a proper wheel size/tire size ratio to provide a good balance of ride quality vs handling characteristics.

Tires are the last suspension component and have a direct relation to road noise, "tracking" in grooves and road crowns, and softness/firmness of ride quality. Taller sidewalls generally provide a softer ride but sacrifice cornering stability in the process while shorter sidewalls generally improve handling qualities but often result in a harsher ride. Tread design greatly impacts road noise and traction in poor weather. Tire width affects tracking qualities of the steering subsystem. Softer rubber compounds have more traction and generally wear out sooner. Harder rubber compounds generally have a longer life and less traction.

Tire pressure greatly changes the wear properties of tires and ride quality and improper pressures can also have a significant impact on the overall safety of the vehicle.

Everybody has an opinion. A particular tire on one car may work very differently on a different car.

You should, in my opinion, crefully read through what other Prius owners have done and examine the details of how they quantified the results very carefully. Never trust a gas station tire gauge. Buy one for your own use and always use that one gauge when calibrating tire pressure. Each gauge is different.

 

<div class='quotetop'>QUOTE(FireEngineer @ Apr, 09:44 AM) [snapback]426648[/snapback]</div>

Interesting. Why does the zero point calibration and the VSC need to be reset when realigning the wheels?

Rick
#4 2006

 

quick question

when people reccomend 42 psi on the front and 40 psi in the back
does this also cover the larger tires in the touring version? arent
the tires bigger?

i had my first 5k service done and they redid all my tires to 30psi on all 4. so i redid it to 35 in the front and 32 in the back

 

Hi C4,

I was referring (poorly) to the tire sidewal material, not the tire as a whole. If the sidewall material is stiffer (usually, but not neccassarily more hysterical), and yet forced to flex due to lower air pressure, there is more heat dissipated, and the tire takes more force to roll.

Rigormortis, I have not seen any concensus on the 16 inch tires yet. One person on PC said 42/40 was just to stiff and skiddy and went down to the recommended pressures on the door panel. I think setting the pressure to even the ware across the width of the patch is probably the right level. As that should give good traction, and safe wet weather handling, besides long tire life.

 

My experience is that tires shouldn't affect mileage that much. When I went to a heavier wheel/tire combo, with significantly wider and stickier tires, I did not loose any mileage. I was able to get an average of 52 mpg even after the switch.

Even now, after reverting to my standard heavy foot driving style I'm getting 47 mpg average for the past year.

 

Everything depends...

on your driving- the terrain, the weather, the traffic , your tires... typically I don't think the tire folks nor the dealers really understand the prius the way that priuschat members do!!!

you did not say what you had to replace and what you bought- maybe you need to up the inflation a bit.

I know I am taking a hit for the Hydroedges, but the ride is so much better. I drive a lot for work, in all kinds of weather...and I'm now back to 50 mpg with the warmer weather....

 

A small part of the answer lies in the larger diameter of the new tires.

The difference between a new tire, versus a fully worn out tire is about 2%. Meaning that the car's odometer and speedometer will read 2% less miles with the new tires as compared to the old tires. That would also mean that your MPG calculation would be 2% worse than before... So, if you were getting 50 MPG before, the new calculated MPG would be about 49. (Note: you are actually getting the same mpg performance - its just the calculation that has changed).

Another related factor is the tire size of the new tire brand versus the old tire brand. As discussed in other posts, various brands have slight differences in the number of revolutions per mile. If you picked a tire that was slightly larger than what was replaced (and, as a result has a smaller revs per mile specification), you will have a similar issue as discussed above.

 

I'm having the same problem...I had to replace my tires in December..(Goodyear integrity)
but I haven't had the car aligned as it hasn't needed it...I'm running in 70-80 degree weather with
no significant change in driving patterns..46-47 mpg...I used to get 52 in the warm weather....I have
a 2005 Prius with 52k....I'm noticing the ICE not shifting right(per se) like its running pretty rough... someone
at the dealership told me it might be an oxygen sensor problem...but I don't know...
I've changed the tire pressure ect....
Help!!

 

<div class='quotetop'>QUOTE(rigormortis @ Apr 21 2007, 12:02 PM) [snapback]427298[/snapback]</div>

I run higher pressure than the service tech pumps but 42lbs? On a hot CA summer day, at high speeds, your tires can easily expand 5 or 6lbs and that's going to put you over the manufacturers safty level, right? Or did I miss something.

 

The manufacturers specifications are for cold tires. There is a factor of safetly built into it for expansion under driving conditions. You should check tire pressure occassionaly as outside temps/seasons change and adjust as necessary.

 

I, too, have realized a huge decrease in my MPG since I replaced my tires. Partly it's because I installed 195/60/15 vs the stock 185/65/15. In 85 degree weather I used to get 54 - 58 MPG. Now I can't get 50! I've had them on for 6000 miles but the "break in" theory has proved itself to me.

I love the tires! THey look good and drive great. However, I'd rather have the MPG back.

 

<div class='quotetop'>QUOTE(tbstout2 @ May 1 2007, 02:26 PM) [snapback]433494[/snapback]</div>

What brand and model of tire did you install?

All this talk without referring to specific tires is meaningless.

 

<div class='quotetop'>QUOTE(Bill Merchant @ May 2 2007, 01:53 AM) [snapback]433792[/snapback]</div>

I agree with ya. I wonder what the diameter of the aforementioned 195/60-15 is compared to the OEM tires.

CR

 

The tires I bought are: Yokohama AVID TRZ, P195/60R15 87T. If yooz guys have any info on why those would be extra bad for MPG I'd be grateful!

 

Well, stupid is as stupid does! I've shot myself in the foot by buying the different size tires. I found a good site that will calculate tire stuff:

http://www.csgnetwork.com/tireinfo4calc.html

The attached screen shot shows the diff. between the OEM and the new.