MPGs have dropped by 7 (50 to 43) since switching to Michelin MXV4

[Danny]

A little less than 2 weeks ago I made the switch from the OEM Integrity's to the Michelin Primacy MXV4. At the same time I did an oil change with my standard Mobile1 oil and filter. I'm now 1,000 miles on the tires and have seen an overall 7 MPG hit since installing them (from 50 to 43).

The other curious thing is that every time I check the tire pressure it's different. I originally had them pumped up to 42/40, but now when I check sometimes the front left will be 37.5, the rear will be 40, and the front left will be 40. Yesterday I was at my in-laws house, borrowed my father-in-law's compressor to pump my tires and of course he had to watch. While I was going to pump them up I couldn't quite explain to him why I wanted my tires pumped up to 42/40 (it's quite difficult to explain to non-MPG minded folks), and so he suggested that I try 40/38 and that the pressure might go up due to the elevation change on the way home (+3,000 ft). Well, this morning I went out and checked them and it's 38 in the rear, 37.5 on the front left, and 40.5 in the front right.

I am also noticing that the car feels like it's being drug down by something, like it's always going into a headwind. I have also noticed that the hybrid battery stays full a great deal more than it ever used to (especially while on the interstate). The temperature has gone down over the last couple of weeks (sometimes by 10 or 20 degrees), but my mileage during the winter has never been below 48.

Getting 43 when I used to get 50 is making me tear my hair out!

I realize that there is going to be a break-in period with new tires, but I didn't think I'd see a change of 7 MPG after 1,000 miles and driving the same routes.

Ideas?

[qbee42]

Interesting. We didn't see any drop in mileage when we switched to MXV4+ Energy tires. Did you use the stock size, or go to a wider one?

Any chance the brakes are dragging?

Tom

[Danny]

I went with the standard size - 185/65/15.

[FireEngineer]

These are not part of the "Energy" series as Tom was referring to with his tires. These are more a performance all-season and will produce less MPG's.

Wayne

[Bob64]

Check that front left tire for leaks... Pump it up to 44 and use a squirt bottle with soap and cover the tire with the soapy solution... with luck, you'll find your air leak. You need to pump it up, because sometimes the rubber can seal punctures at a lower psi, but a high-enough psi will cause the rubber to "lose" against the air pressure.

[Danny]

Originally Posted by FireEngineer

These are not part of the "Energy" series as Tom was referring to with his tires. These are more a performance all-season and will produce less MPG's.

Wayne

Weird. Everything I read about them on here made it seem like, while they aren't direct replacements for the Energy series MXV4+ tires (no longer produced), that they still offer at least the same FE as the Integrity's.

[Shawn Clark]

Danny,

I'm still a novice with the Prius, but this first cold weather is giving me some greater appreciation for the temperature related mileage hit. If the defog/defrost is running at all it really hammers my mileage. And the cooler weather itself forces the ICE to run more to keep the engine warm. Even when the conditions were milder I could see a slight decrease in mileage compared to late Summer weather.

So I think you have three effects all pushing down mileage: 1. The difference in the tires themselves. 2. The cooler weather. 3. The fact that the tires are new and mileage will improve with break-in. (Perhaps there is a fourth related to pressure.)

The second part (weather) you can probably account for by comparing to some similar periods last year. Obviously, it is likely to get cooler for several months before it gets warmer on average over a full tank. And in another few thousand miles you can rule out break-in effects.

[subarutoo]

I switched to BFG G-Force Sport 205-60-15 on stock rims about 3,000 miles ago. After several tanks in the low 40's (from a usual 49-50 mpg), its finally climbing back up to 47, last tank. All of my driving is pretty consistant, 90 miles a day, 99% freeway, about 70-75 mph when I can. I think the break-in time may vary. I didn't get these tires for max mpgs, but for better handling. I can live with a 2-3 mpg hit for that. I also found some erratic pressure readings for a few weeks, too, but it too has stabilized 40/38. It hasn't been real cool here is SoCal, but a few degrees drop will affect tire pressures. Hopefully after a few more break-in miles your mpgs will get "well" again.

BTW, I too notice a kinda "draggy" feel when accelerating or cruising at low speeds. I think its psychological, but the BFGs do weigh 5 lbs. more than the Goodyear OEMs, according to Tire Rack. How do your new ones compare with the OEMs weight wise?

[roadrunner]

Originally Posted by Shawn Clark

Danny,


So I think you have three effects all pushing down mileage: 1. The difference in the tires themselves. 2. The cooler weather. 3. The fact that the tires are new and mileage will improve with break-in. (Perhaps there is a fourth related to pressure.)

Winter gas maybe? In PA it is October 15th that we go 100% winter gas, and I see a 3 mpg hit each year.

[brick]

The green bars thing interests me. My car (as any other Prius) typically hangs out with 6 bars (blue) unless I do a lot of braking or P&G. The only notable exception is on the rare occasion that I cruise at ~70mph or more for an extended period of time, which usually gets me to the first green bar until I slow down. It suggests to me that your car is seeing higher than normal load for whatever reason. It would surprise me if the tires were enough to do that.

I'm local to you and the weather has not impacted me that much. A month ago I was getting 58-59mpg cruising up and down I-77, currently I'm getting 55-56mpg now that it's cooler in the morning and I use a little cabin heat some days. If the gas changed over I haven't noticed anything.

The first thing I suggest is that you inspect all four tires closely. Look for feathering, cupping, or other funky wear that would come with bad alignment. Do you notice any vibration at speed or under braking? How about after you drive at highway speeds for 15-20 minutes or more, is any one wheel warmer than the others? If you put the car in neutral and brake, does it pull to one side? (Be careful testing that one!) Failing that, you might consider jacking up the car and turning the wheels by hand.