Really big drop in MPG after two new front tires...from 400 miles a tank to 250.

i don't think it's the tires, might be a coincidence. search mpg threads. could be a bad 12 volt battery, maybe brakes are rubbing? jack up the car and make sure the wheels they worked on spin freely. i put 2 new tires on my daughters 04 and she still got 55mpg, no drop at all. not sure ir 80 mph would make it more severe?

 

Any other work get done? Did you have an alignment check?
I would assume the back are the same orginal. Put them on the front and try it again.
10mpg is a drop. Could also be the gas. Invest in a $1 fuel additive. Have the mass air flow sensor cleaned (use the correct cleaner).
If I ever replace 2 tires the old ones go on the front. More wear on the front.
not likely the tires. I just changed mine out and no difference in mpg.

 

I just got an 04 a couple of weeks ago and got 48mpg driving it home about 150 miles. I put new tires on front and a new aftermarket airfilter and the mpg dropped to about 44. I increased the air pressure up to 40/38. One other variable, I'm at 6,000 ft vs 3,500 where I bought it and drove home from on that first trip. What's going on? I assume altitude wouldn't have a 10% affect on mpg.

 

Replacing the tires with new LRR tires gives you a minor hit in fuel economy. Replacing them with generic crap, and you become extremely inefficient.

I would say it is definately the tires. Could be made worse by bad alignment and low tire pressure, but the bulk would be in the tires.

 

1. What brand/type are the new tires.

2. Try measuring the MPG a bit more accurately over a few runs.

The MPG drop you've stated does seem a bit large to be caused just by the tires. But the tires could still cause a significant drop.

 

dokeefenm - new tires will drop the mileage - untill they break-in (4 mpg is about right). Was the second tank city stop and go miles or a lot of hills? As far as mileage goes, hills are your enemy - they suck-up the gas like nothing else.
Two tanks do not sufficiently test your car and a 4 mpg swing is not a significant change.

 

It's probably the tires. Try inflating them up to the maximum pressure stated on their sidewalls and see what difference it makes.

As a safety matter, two new tires should always be installed at the rear, not the front.

 

My old nonhybrids would regularly do roughly 5% better after climbing that much altitude, not counting the extra fuel required to climb the hill first. The benefit is both from reduced drag in the thinner air, and reduced engine pumping loss. Prius should still get the benefit of the former, but its Atkinson cycle engine should mostly discount the later.

But there are so many other variables that it will be difficult to isolate them without controlled experiments. Get used to significant day-to-day and tank-to-tank variations.

 

I reported this about April time when I changed my front tyres (uk spelling) to non eco tyres. My mpg's fell considerably. The garage tried telling me to let them bed in and see if that helped. After 1500 miles it didn't.

To cut a long story short, Bridgestone Ecopia tyres (their low rolling resistance brand) were fitted and straight away my mpg's went back to what they were previously! And these tyres are still on the car and still have good life left in them.

Link to my old thread from April ;
http://priuschat.com/forums/gen-iii-2010-prius-fuel-economy/78650-these-bridgestones-same.html

 

I've never heard that 2 new tires should be on the back for safety...why's that? It's front wheel drive and more weight up front from the engine.

 

The idea is you want understeer instead of oversteer in an emergency handling situation since most people tend to over correct the wheel. So lesser tread up front. Probably not a big deal, but it makes sense at the edge of the traction envelope.

 

You want more grip on the tyres that you have more control over!

Ask any racing or rally driver.

 

there is an article on tirerack.com explaining it.

 

Understeer is Nature's way of telling you to slow down. Oversteer is Nature's way of telling you're gonna die :_> So put the better tires at the rear.

 

I use to manage a tire store years ago, and 99% of the people that would buy just two tires had them mounted on the front. I tried to tell them to put 'em on the back, but they never did.

The reason why?...if you have a blow out at 80 mph, you want to have that blow out on your steering axle tires. That way you can maintain control. If you have a blow out on the rear at 80 mph, chances are you will loose control of your vehicle.

Every tire manufacturer will recommend to put the new tires on the rear.


Also: (copy/paste from tirerack.com)
"When tires are replaced in pairs in situations like these, the new tires should always be installed on the rear axle and the partially worn tires moved to the front. The reason is because new tires on the rear axle help the driver more easily maintain control on wet roads since deeper treaded tires are better at resisting hydroplaning"

 

In panic braking on slippery roads, the tires with the best grip automatically try to become the rear tires. Even if this could happen cleanly -- it can't -- few drivers are capable of handling the transition well.

 

huh?

I have 5 prii. 2 have replaced with the orginal tire manuf as what was on the car. No diff in mpg. As GrumpyCabbie said the type of tire can make a difference. I did upgrade one set/car and saw an increase 5mpg right away.

As far as a blow out at 80mph. Ummm front/back 80mph that would leave you flying all over the place. You would loose control either case unless you are a waaay experienced race car driver. 2 accidents I've seen blowout on the front dug the wheel into the pavement flipped the car. In this case if the old tires had a bulge in them and you were driving them not replacing right away, I would look at replacing the other 2. I;m also someone that doesn't drive 100mi further on the blinking gas light.

 

On the subject or tyres the old cliche applies - they're your only contact with the road!

I personally take good care of mine and check them very regularly and fit branded tyres. It's just not worth trying to save a few quid/bucks getting cheap ones as you don't want to end up sitting in your car upside down in a field wishing you'd not cut costs.

Tyres last for a long time and are an important safety feature of the car - don't skimp on them.

 

wow.