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How it got 34 mpg average over 125 miles


TDK

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Well,

I was entering a long straight stretch of I-80 where the divide between is almost 1/4 mile. The BWD "Big White Dog" AKA '99 DeVville, was in the mid 80's when a pace car / sponsor passed me. Never missing oppertunity, I matched velocity in the mid 90's - but quite a ways back to not upset the sponser.

After a bit I noticed the road was getting noisy and decided to check the tires. Sure enough I had a flat on the passenger-front on the a Michelem XW4 with just a few thousand miles on it. That is one problem with the smooth ride and good suspension, it is hard to note a flat at speed until the damage is done. Unfortunately, the sidewall was almost smokin and very soft (it was well done). I installed the doughnut and had to wait until the air compressor, (that I always have onboard along with a few tools) brought it from near flat to 60#.

Back on the road, I took it easier since I had about 125-miles to go on the doughnut. The car settled in at 65 on cruise on the relatively level road. I reset the average mileage after a few minutes and to my surprise, it maintained 34-mpg average over the entire 125-miles. Amazingly, the little, rock-hard doughnut rode great on the the highway, (a testament to Caddy suspension).

So, does anyone think the smaller diameter doughnut caused a speedo error or is 34-mpg at 65-mph reasonable?

Oh by the way, the tire shop could not get another WX4 and installed a Michelem Harmony instead. The tread pattern appears to be a bit more square shouldered and aggresive. However, while the WX4 treadwear is 400, the Harmony is 740! I was surprised at the differance. The Traction is still A and the Temperature B (I might need an A here...).

Add power to leave problems behind. Most braking is just - poor planning.
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Yep, I think thats possible.

Jason gets 28mpg on his STS, using a full time donut spare. :D

1989 FWD Fleetwood, Silver

1995 STS Crimson Pearl on Black leather

1997 STS Diamond White

1999 STS Crimson Pearl

2001 STS Silver

2003 STS, Crimson Pearl

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Yep, I think thats possible.

Jason gets 28mpg on his STS, using a full time donut spare. :D

You're evil! :lol:

-Dusty-

- 02 Seville STS, white diamond

- 93 Sixty Special, Tan with vinyl top

- 79 Coupe DeVille, Tan with Tan top

- 06 GMC Sierra Z71, Black

- 92 Silverado C1500, black and grey

- 83 Chevy K10 Silverado, Black and Grey

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It is apparent that Jason is never going to live this down. :D

Nope! :)

-Dusty-

- 02 Seville STS, white diamond

- 93 Sixty Special, Tan with vinyl top

- 79 Coupe DeVille, Tan with Tan top

- 06 GMC Sierra Z71, Black

- 92 Silverado C1500, black and grey

- 83 Chevy K10 Silverado, Black and Grey

b80385550.jpg

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The tires on the front (or any tires on a differential) absolutely must be matched for diameter or the differential spider gear will have an early death. Rotate your tires and put the mismatched pair on the rear.

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No, I don't ever do think I will live this down!

And actually, 28 mpg is more likely in the SLS. The STS averaged about 24-25 mpg on our recent road trip to Florida and back (avg. highway speed between 70 and 90).

TDK, the Michelin Harmony is Michelin's current premium passenger all season tire. The Harmony actually has three sister tires, the Agility, the Destiny, and the X Radial. All four are really the same tire, with some differences in the tread pattern. The XW4 is a very old tire design (still sold in small numbers I think) that was replaced by the Symmetry almost a decade ago. The Symmetry is still pretty easy to find, but I haven't seen an XW4 in a store for a LONG time.

Anyway, treadwear above 600 is very common among passenger all season tires today. The fact that the XW4s are only 400 really shows their age. Most performance all season tires today have at least that. The Harmony's treadlife is warranted for 80,000 miles. I doubt you'll get that much, but you should get close. We have the Agility on our Grand Caravan and X Radial on the '97 SLS. I figure to see an honest 70,000 out of the tires on the van. The ones on the SLS show almost no wear, and I've only driven them about 7000 miles, so it's hard to determine their treadlife, but it should be similar.

Jason(2001 STS, White Diamond)

"When you turn your car on...does it return the favor?"

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The tires on the front (or any tires on a differential) absolutely must be matched for diameter or the differential spider gear will have an early death. Rotate your tires and put the mismatched pair on the rear.

Good point!

Scott

1996 El Dorado

2006 STS

2000 Corvette

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caddy includes speed rated donuts to 90mph. You should always replace tires in sets unless you can find the exact replacement, never a good idea to mix tread patterns and tires, especially for winter driving..that could be interesting. (not an issue this late in the season I hope).

The Green's Machines

1998 Deville - high mileage, keeps on going, custom cat-back exhaust

2003 Seville - stock low mileage goodness!

2004 Grand Prix GTP CompG - Smaller supercharger pulley, Ported Exhaust Manifolds, Dyno tune, etc

1998 Firebird Formula - 408 LQ9 Stroker motor swap and all sorts of go fast stuff

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Similar experience years ago in my 95 etc. Right front went flat at 70+ and it was only the slight change in noise that indicated that anything was amiss.

unfortunately, i was not carrying a compressor and unbeknown to me the donut must have been low, so even at 50 mph it only lasted about 10 miles...

moral of the story, check that donut from time to time ... or carry a compressor <_<

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Advance Auto Parts has a cigarette lighter powered compressor that's shaped like a little tire for 10 bucks, isn't the quickest but does a good job in a pinch.

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http://www.partsamerica.com/ProductDetail....egoryCode=3483A

The Green's Machines

1998 Deville - high mileage, keeps on going, custom cat-back exhaust

2003 Seville - stock low mileage goodness!

2004 Grand Prix GTP CompG - Smaller supercharger pulley, Ported Exhaust Manifolds, Dyno tune, etc

1998 Firebird Formula - 408 LQ9 Stroker motor swap and all sorts of go fast stuff

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