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

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

 

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

 

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,

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.

 

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?

 

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

 

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.

 

This was my impression too. I know there are differences, but I thought they were minor. Some other PCers have switched to the same tires. Perhaps one of them will post on this thread.

Tom

 

Assuming that OP bought "Primacy" MXV4, and not "Energy" MXV4 (which have been out of production since early 2007), I have switched to the same tires. Now have 2 or 3 months and 5000 miles on the Primacy tires and see no hit on milage. Don't think I even saw a hit during break-in, or if there was, it was very small.
The only change I've seen is less noise on the highway, and better handling in turns.

From my conversation with Michelin customer service, the Primacy is NOT a direct replacement to the Energy, even though they both use the "MXV4" in their names. The Primacy has a higher rolling resistance than the Energy, but it is still one of the lowest resistance tires they sell. It not the lowest LRR tire in their product line, but I chose it because of the balance between rolling resistance and all-weather performance (safety). You can check out my post from a few months ago to get more details from my conversation with Michelin.

 

we replaced with primacy mxv4 several weeks ago, for the first 1000 miles or so i lost 3-4 mpg, now i'm just down overall because it's cold in the morning. the tires are a fair bit sticker than the energy mxv4 we replaced, which were stickier than the oem junk. i bet that part of it is that you're just not used to having a good grip on the pavement.