Switched to conventional tires...MPG question

Deal with that, right away. For starters, check your oil level, and coolant levels. And I'd go with this advice:



Regarding the tires: what specific make/model did you have on there? And same question for the new tires.

 

I have a 2005 and a 2012. I got the tires replaced at Discount Tires and chose cheapo tires instead of the OEM tires. I saw a drop of 3-5 mpg on each vehicle. However, they dropped from a healthy low 50's mpg to land on mid to upper 40's.

 

That sounds spot on. Both 2005's in my family had about a 5 mile per gallon loss when running cheap normal tires. low rolling resistance tires really do make a difference on the Prius.

 

@Mendel Leisk, I think Jim's referring to the yellow motor light on the MFD. If that's the case, of course the ICE runs 100% of the time at 70 mph. You can only go up to about 34 mpg on pure battery with a Gen 2 Prius, IIRC. And even then you can barely touch the "gas" pedal.

@Jim Caldwell, if I read you right, everything looks normal for your conditions. You'll lose several mpg with regular tires. And the previous 44mpg or so at 70-75 mph is really pretty respectable. Slow down to 60 and you'll get well over 50 mpg. At least with low rolling resistance tires. Not sure what to expect with your new shoes.

 

Without even taking into consideration the difference from LRR tires to conventional, you should expect a drop in mpg with any new tire. This article from Tire Rack explains it well.

Fuel Efficient Low Rolling Resistant Tires

Note their conclusion.

"While many of these individual differences may seem insignificant, it is easy to understand that when they are added together, the new tires may appear to reduce vehicle fuel economy. It also means that a Toyota Prius appearing to get 50.0 mpg just before replacing its worn-out tires with new tires of the same brand, type and size, might be reduced to registering just 47.25 mpg afterwards, even if all of the driving conditions were identical."

 

I think you need to rethink a bit: there is nothing particularly "special" about the stock tires. They are just regular, readily available tires, that (as often as not) happen to be a little better for rolling resistance. You need to research which do better. For sure post: what you had on there, what you have now.

 

My observations about ICE usage:

Above 42 mph, the ICE will be used more.

Between 55-65 mph, the car will only use battery power if it is fully charged or at 7 green bars. After that it will only use ICE exclusively.

The only exception to this is if you are going down hill. Regenerative braking will kick on and charge the battery up. If its a long enough hill, ICE may or may not kick off. I've never seen or felt it do so tho.

IMHO, you are expecting too much from the Prius speeding along at 70-75 mph. Its most efficient at low speeds.

 

But not snail slow. It will still get very respectable MPG at 60 MPH.

 

avoid discount tyre in the future. i got michelin energy savers a/s for $700. installed from tyre rack. and you can get oem's for cheap money.

 

Avoiding Discount Tire depends a lot on what kind of service you expect and are willing to pay for as well as the availability of exceptional service on the road if you travel a lot. I, too deal only with America's Tire/Discount Tire. They're located coast to coast along the major highways we travel and easy to find. Whether it was a separated belt in Texas on California-purchased tires, taking over the rotating and balancing in California of Indiana-purchased tires or a road hazard replacement in North Carolina on a California-purchased tire they've always been fantastic and pleasant and prompt, no questions asked and always with a smile. The discounts, stand-up attitude and service when we had the TPMS issue last year and had to replace one on the road (the other three replaced at a big discount when we returned home) add to my faith in them. Throw in the free rotations on my wife's car even though we didn't get those tires from them and it adds more value to their higher prices as well. If I was always local I might consider someone else but not with the amount of time we spend driving around the country every year.

There's a lot more to value than price.

 

that all sounds fine, but if they are charing $900. for oem prius tyres, i would avoid them. i don't spend all my time on the road though. certainly there's some value to that.

 

LRR tires.

IIRC, there is no official standard for LRR. I could cobble together some charcoal, chewing gum and leaves and call it a LRR tire if I wanted.

There are some "standard" tires that get better mpg than designated LRR tires. And, LRR often seem to come with a premium price tag.

 

there is testing though, and a standard is coming soon. i don't think it's totally bogus.

 

Sure there is testing. Lot of the LRR do well, some do poorly and most are in the middle.

Same with conventional -- whatever that is -- some do well at MPG, some do poorly and most are in the middle.

 

There's also some "under the table" hijinks? Our stock Michelin Pilot HX MXM4 215/45R17 (87V SL) have the GreenX label, Michelin's indicator of LRR. If you look them up on TireRack, the ones they're selling are not labelled GreenX.