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-   -   New tires = big hit to MPG thoughts? (https://www.greenhybrid.com/forums/f22/new-tires-big-hit-mpg-thoughts-15159/)

jhfarr73 09-04-2007 05:56 AM

New tires = big hit to MPG thoughts?
 
Ok so we have nearing 45k on our 07 TCH. A couple of weeks ago my wife hti something along the road and totaled her right front tire (big hole in the sidewall). Because of the milage and the need to get at least 2 tires (to avoid damage to differential) we decided to get 4 new tires. So off the stock Michelins and got new Good Year Triple treads because they are rated better in most catagories. Well the wet and dry traction are great...the ride seems quieter...and we have taken a 3-4 mpg hit in our fuel economy...formerly running 37-39 mpg and now 34-36 mpg....still good but not great.

The other day we were passing a radar stand (those deals the police put along the road to tell you your speed and get you to slow down) and while the speedo said ~26-27 MPH the sign said 23 MPH...before (old tires) these things would be closer...so I am guessing the new tires are different enough in dia that it is throwing things off...but with the speed info doesn't that mean my miles should now be over reporting? Or do I have my math off some place?

bwilson4web 09-04-2007 06:15 AM

Re: New tires = big hit to MPG thoughts?
 

Originally Posted by jhfarr73 (Post 141581)
. . .
The other day we were passing a radar stand (those deals the police put along the road to tell you your speed and get you to slow down) and while the speedo said ~26-27 miles per hour the sign said 23 MPH...before (old tires) these things would be closer...so I am guessing the new tires are different enough in dia that it is throwing things off...but with the speed info doesn't that mean my miles should now be over reporting? Or do I have my math off some place?

When I replaced my tires, I took a 90 mile trip along a road that has state installed mile markers. I used the 1/10 th mile reading as I passed each mile marker and the 10 mile marks to measure the actual versus indicated distance. I also double checked my tire specifications on how many revolutions per mile.

In your case, it is good that your indicated speed appears to be lower than the actual. However, you really need to know how accurate your trip meter miles are to accurately calculate mileage and any speed correction factors.

GOOD LUCK!
Bob Wilson

jdenenberg 09-04-2007 06:57 AM

Re: New tires = big hit to MPG thoughts?
 

Originally Posted by jhfarr73 (Post 141581)
Ok so we have nearing 45k on our 07 TCH. A couple of weeks ago my wife hit something along the road and totaled her right front tire (big hole in the sidewall). Because of the milage and the need to get at least 2 tires (to avoid damage to differential) we decided to get 4 new tires. So off the stock Michelins and got new Good Year Triple treads because they are rated better in most catagories. Well the wet and dry traction are great...the ride seems quieter...and we have taken a 3-4 mpg hit in our fuel economy...formerly running 37-39 mpg and now 34-36 mpg....still good but not great.

The other day we were passing a radar stand (those deals the police put along the road to tell you your speed and get you to slow down) and while the speedo said ~26-27 miles per hour the sign said 23 miles per hour...before (old tires) these things would be closer...so I am guessing the new tires are different enough in dia that it is throwing things off...but with the speed info doesn't that mean my miles should now be over reporting? Or do I have my math off some place?

Your Michelins (MXV4+, I believe, which are currently on my Prius) were Low Rolling Resistance (LRR) tires and the TTs are not which is why the drop in MPG. Another LRR tire to consider next time is the Nokian WR (especially if you sometimes drive in snow/ice).

Bob Wilson is correct about checking the specifications on your old and new tires. You need to match or exceed the load rating (for safety) and you should also come close in revolutions per mile (to maintain speedo-odo-MPG consistency). I also will never buy a tire that is not H rated or above. H rated tires are generally much better construction than S or T rated tires.

JeffD

bwilson4web 09-04-2007 07:15 AM

Re: New tires = big hit to MPG thoughts?
 
I forgot to mention, did you get a printed alignment sheet? The reason is the front wheel toe can be manually set, camber is harder and caster very difficult. But toe and camber do impact rolling resistance.

The real problem is the rear wheels are fixed. There is a Toyota alignment process for the rear axle but it involves a complex tool and often, they recommend replacing the rear axle, a terribly expensive affair. However, if you have the alignment printout, there are shim-kits that can bring the rear alignment to pretty much optimum.

You mentioned having a road impact causing at least one or more tires to fail. Such stresses can easily throw the alignment off. But do get the printed alignment sheet even if it means going back to get it done and printed out. Better to fix an alignment problem now rather than after losing tire rubber and wasting gas.

Bob Wilson

msantos 09-04-2007 08:05 AM

Re: New tires = big hit to MPG thoughts?
 
Please someone correct me if I am wrong, but I suspect the Camry Hy has a fully independent suspension at all four corners with no "rear axle" to deal with. This should make rear alignment concerns less dramatic, no?

Cheers;

MSantos

bwilson4web 09-04-2007 08:23 AM

Re: New tires = big hit to MPG thoughts?
 

Originally Posted by msantos (Post 141609)
Please someone correct me if I am wrong, but I suspect the Camry Hy has a fully independent suspension at all four corners with no "rear axle" to deal with. This should make rear alignment concerns less dramatic, no?

GOOD POINT!

I was thinking Prius and I don't know enough about the Camry suspension other than a general rule that after a tire damaging road incident, check the alignment and get the printout. I learned that our local shops were quite happy to be 'mum' about their inability to deal with rear wheel Prius alignment. The alignment printout solved that problem.

Bob Wilson

jhfarr73 09-04-2007 09:21 AM

Re: New tires = big hit to MPG thoughts?
 
We did get an alignment done when we got the new tires for the exact reason you mention (the impact). Everything was in spec.

WaltPA 09-04-2007 11:45 AM

Re: New tires = big hit to MPG thoughts?
 

Originally Posted by jhfarr73 (Post 141581)
So off the stock Michelins and got new Good Year Triple treads because they are rated better in most catagories.

Sorry, but you got me curious.

What size was the old tires and what size are the new tires?

bwilson4web 09-04-2007 11:49 AM

Re: New tires = big hit to MPG thoughts?
 

Originally Posted by jhfarr73 (Post 141623)
We did get an alignment done when we got the new tires for the exact reason you mention (the impact). Everything was in spec.

My experience with the Prius is "in spec" may not be optimum but if you're happy, no problem. Getting toe closer to zero has a measurable impact and camber can be reduced too but with less effect.

Bob Wilson

jhfarr73 09-04-2007 02:48 PM

Re: New tires = big hit to MPG thoughts?
 

Originally Posted by WaltPA (Post 141647)
Sorry, but you got me curious.

What size was the old tires and what size are the new tires?

215/60R16 both stock and new tires are the same size.


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