Is drop of MPG Normal w New Tires?

check your inflation!

the idiots who put my new tires on did not inflate them properly!

WHAT TIRES DID YOU BUY?

 

<div class='quotetop'>QUOTE(PriusOwner2006 @ Oct 21 2006, 06:26 AM) [snapback]336045[/snapback]</div>

You bought good tires that are LRR (I have the Michelin MXV4+ LRR tires).

As tires wear, the tread gets thinner. At end of life the tire radius is reduced by about 1/4 inches. This increases the revs/mile by about 2% (at 185/65R15 tire size - 24.5 inch diameter reducing to 24 inch diameter with wear). So when you replace your tires there will be an apparent 2% decrease in MPG which is not real, it's due to a change in the calibration of your speedometer (and odometer).

My new tires actually increased my MPG slightly (compared to the OEM Googyear Integrity tires, without taking the new tire penalty or the 0.7% lower revs/mile of the MXV4+ tires into account), especially at low temperatures.

JeffD

 

<div class='quotetop'>QUOTE(jdenenberg @ Oct 24 2006, 11:27 AM) [snapback]337338[/snapback]</div>

So true and well explained.

On top of this, worn tires generally have lower rolling resistance than ones with full tread depth. This is the reason that human powered and solar vehicle contestants often shave tires to reduce the tread depth. Rolling resistance is primarily due to the deformation of the rubber. This deformation in the rubber in the tread is reduced when there is less tread to deform.

Both of these explanations apply to those replacing worn tires with new ones, but probably not to someone replacing tires on a two month old Prius. I also suspect PriusOwner2006's increase in fuel consumption is largely the same change that all of us in colder climates observe when the temperatures drop.

 

<div class='quotetop'>QUOTE(PriusOwner2006 @ Oct 18 2006, 08:51 PM) [snapback]334835[/snapback]</div>

I recently replaced the tires that came on my 2005 with new larger tires and wheels. Two things were immediately obvious 1. the ride improved miracously 2. there was about a 10% drop in MPG. Discount Tires underinflated the tires to 35 front 33 rear. I raised the psi to 42 f 40 r and saw no change other than a bumpier ride. After 600 miles the new tires were less sticky but they are definately not low rolling resistance tires. As tires age the roll easier. I am now getting less than 4% lower MPG and the car still handles much better than with the original smaller tires and wheels. The Max psi on the tire wall is 50. If I wantd to join the high milers I could inflate the tires to 48 f and 46 r and still be safe but. It is a big but -- the road would get a lot bumpier, the tire foot print smaller so handling would worsen. Everyone will tell you that there is a trade off between comfort and performance. You have to decide which you prefer looks - chrome wheels big tires; high mileage; soft ride; etc., etc. A lot of the fun in having a Prius is making all those decisions. No matter how you choose to go -- after 5000 miles you will find it very hard to not get better than 40 MPG. If you want to get 60 MPG consistently you have some learning and modifying to do. Priuschat and Hybridcars.com have most of the information you need or links to it.