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TDI Fuel Economy Discussions about increasing the fuel economy of your TDI engine. Non TDI related postings will be moved or removed.

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Old April 26th, 2005, 12:43   #1
mrGutWrench
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Fuel Economy: 63 MPG/56/47 (2nd tank) '02 Sedab
Default MPG Tires -- 205/65R15 versus stock (195/65R15)

__. I have nearly 85K on my '02 Jetta sedan and the original Michelins are nearly worn out (yeah, us grey-haired, broken down, old, thrown away, retired guys who drive slow are real hard on tires) and I'd love to go with tires that will give good mileage. I know in my mind that I'll never recoup the cost of new Michelins versus cheaper tires in fuel savings but my heart tells me to stick with them. Anybody got any experience with 205 tires versus the original 195's?

Here's what Michelin says:
"You may want to consider moving up to the 205/65R15 94H Energy MXV4 Plus. This is an approved alternate tire by Volkswagen for use on the Passat. You will find the 205/ 65R16 is a little wider and and taller than your original 195/65R15. Since it has been approved by Volkswagen, it will work without rubbing, and it this tire will fit on the your stock rims."

__. Anybody got any experience with these tires? I don't have price quotes for the two; that will make some difference, too.

Thanks, MrG
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Old April 26th, 2005, 12:51   #2
gdr703
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Default MPG Tires -- 205/65R15 versus stock (195/65R15)

I got two new Michelins for my Golf recently. (at 63,000 iles). I got the MXV4 S8, (part number 71716) in the standard size and am very happy with them.

ps I did not rotate the tires, I didnt see the need. The fronts were just about down to the wear bars, and the rears half worn.
So now I have the MXV4 plus (half worn) on the front and the S8's on the rear.

I think these tires grip just fine, why would you want a wider tire?

cheers.
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Old April 26th, 2005, 14:29   #3
IndigoBlueWagon
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Default MPG Tires -- 205/65R15 versus stock (195/65R15)

I went round and round on this (pun intended) when I replaced my tires. I was going to go up one size becuase they are 3% larger diameter which is exactly my speedo error. Then it would be spot on. However, posts here say the odo is spot on now and I didn't want it to be pessimistic.

I stuck with the stock size. However, before you take the plunge into Michelins again look at Kumhos. They make a couple of great all season tires, are really inexpensive, and are great quality tires. I have them on two cars now and love them. Great ride, too, for us old guys.

If you have to stick with the Michelins, at least consider sticking with the stock size, buying three, and rotating the spare into the mix. It's a good reason to not change sizes and it will save you some $$ (but you'll still spend more than on the Kumhos).
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Old April 26th, 2005, 18:06   #4
Lug_Nut
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Default Re: MPG Tires -- 205/65R15 versus stock (195/65R15)

Wider tires usually lower fuel economy.
Taller tires usually lower fuel economy, but the longer "miles" may mask this effect.
The 205/65/15 (or is it 16?) is a size approved by VW for the Passat. You don't have a Passat.
If you want better lateral grip, a wider tire will usually help, but expect to give up some straight line tracking consistency as well as less hydroplane resistance for a given tread depth and pattern.
If you need a low cost ground clearance increase, a taller tire will help, but the 1/4 inch added (195x.65 on 15s vs. 205x.65 on 15s) is negligible for those sizes. A 16 inch wheel with 205-65 will add 3/4 inch ride height over the 195-65-15.
If you want improved fuel economy, then a narrower tire, operated at higher pressure, will do the most. Consider a 175-70-15 on the original wheels. Higher pressure will lower rolling resistance and the taller sidewall will retain most of the ride qualities.
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Old April 27th, 2005, 10:13   #5
KorMelisTDIJetta
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Default Re: MPG Tires -- 205/65R15 versus stock (195/65R15)

I am considering going with the 205/65/15 hydroedge tires. They are not quite as big as regular 205/65 tires according to tirerack. I have heard of a couple people on here doing this and were pleased with the results with virtually no mpg loss. Kory
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Old April 27th, 2005, 13:16   #6
mrGutWrench
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Default Re: MPG Tires -- 205/65R15 versus stock (195/65R15)

Quote:
I am considering going with the 205/65/15 hydroedge tires. They are not quite as big as regular 205/65 tires according to tirerack. I have heard of a couple people on here doing this and were pleased with the results with virtually no mpg loss. Kory
__. Hmmm, not what I have in mind. I don't want "virtually no mpg loss" -- I want a MPG gain. If there's no gain (of worse, "virtually no mpg loss") between 205 and 195 tires, I'll just stick with the 195's.

__. Thanks for the info.
'
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Old April 27th, 2005, 13:24   #7
watercop
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Default Re: MPG Tires -- 205/65R15 versus stock (195/65R15

too bad no one makes a low rolling resistance 185 75 r15 tire - that might be just the ticket.

I just replaced my remaining two OEM (110k on them - can't complain) Michelin Energy MXV4+ with the very same model. The only difference is the new ones indicate a max tire pressure of 51 psig. Th old ones showed 44 psig - exact same model tire, right down to the load range and speed rating - 91H
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Old April 28th, 2005, 10:09   #8
riihlc
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Default Re: MPG Tires -- 205/65R15 versus stock (195/65R15

I put bridgestone insignia se 205 70 15 on my 03 golf and have put 35,000 miles on them.
Will never go back,handling and ride is greatly improved.
Odometer is now dead on.
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Old April 28th, 2005, 23:19   #9
GotDiesel?
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Default Re: MPG Tires -- 205/65R15 versus stock (195/65R15

Wow. That's weird. My odometer was dead on with the OEM tires.

I now have 205/60s and the odometer is now a touch optomistic (like 1%) due to the slightly smaller diameter.

Next time around I may try 205/65s. I have yet to hear of anybody having clearance issues with them.
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Old April 29th, 2005, 10:21   #10
riihlc
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Default Re: MPG Tires -- 205/65R15 versus stock (195/65R15

sorry. my speedo is dead on, odometer is now off.

No clearance issues,more ground cleaance,great in snow.
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Old May 3rd, 2005, 23:31   #11
Ernie Rogers
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Default MPG Tires -- 205/65R15 versus stock (195/65R15)

Mr. G,

You may find my numbers a little strange because I have a Beetle. The stock tires were 205/55R-16, Michelin MXV4 Plus. They were replaced with 205/60R-16, Michelin MXV4 S8. The change to the S8 formula was decided after talking to an engineer at Michelin U.S.--his opinion was that the S8 should give better efficiency. I traded out all four tires while they still had good tread, so I should not have so much trouble with wear giving a serious mileage effect at replacement. Using my calculator, the diameters of the two tire sizes are:

205/55R-16 24.88 inches diameter
205/60R-16 25.69 inches (replacement tires)

These are calculated, actual diameters could be different. I have 20,000 miles on the new tires now. Before the change, I would do all my long trips and most mileage tests at 65 mph on the gage. After the change in tire size, I used 62.5 mph, which gives about the same true speed. The speedometer is now close to reading true. The odometer requires a correction of:

True miles = odometer x 1.047 +/- 0.002

Now, the results: I have enjoyed a very noticeable increase in fuel economy. My guess is an extra 4 mpg, or about a 7% improvement. This compares to a 5% improvement from the drag reducer on my Beetle.

My guess is that the improvement in mileage gets a nearly equal contribution from increased diameter and the improved tire rubber formula. Tire diameter improves fuel economy in two ways. First, there is actually less rolling resistance. For some types of engineering wheels, the rolling resistance is RR = k W/R for a fixed modulus, or pressure for a pneumatic tire. My understanding is that this formula is NOT accepted by automotive engineers, but is universally used by engineers of steel wheels. (Trains for example.) Larger diameter also improves fuel economy by lowering the engine RPM (increasing torque) for a given speed. This is very important-- you can check this by looking at the engine maps that are posted on this site, or you can find them in the original SAE papers, about 1994.

As I said, I think the rubber formula is equally important, but I have no measurements to prove it. Finally, I do run my tires at high pressure, 40 psi currently--this is well known to increase tire life, improve mileage, and increase load capability for example in truck tires.

About tire width-- most engineers currently believe that tire width is not a factor in rolling resistance. I do think that narrow tires will do better. From listening to others on this web site, I believe that low-profile tires give lower mileage than more "normal"-profile tires.

Ernie Rogers

Now that summer fuel is here, I look forward to getting some very good mileage numbers-- I got 61+ on my last tank.
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Old May 4th, 2005, 05:13   #12
mrGutWrench
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Default MPG Tires -- 205/65R15 versus stock (195/65R15)

Quote:
Mr. G,
You may find my numbers a little strange because I have a Beetle. (snip)
__. Not strange at all. Actually, this is very good info. Thanks!
'
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