Low Rolling Resistance Tires...Which is Best?

watercop

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205 / 70s seem an easy way to reduce engine rpms at a given speed but I have two doubts about potential mpg increases:

1) Tire is wider and heavier, increasing rolling resistance and unsprung weight.

2) Tire is taller, increases vehicle height and therefore aero drag.

Do keep us advised on results...
 

ruking

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My guess is a loss of 2/3 mpg on the switch! But yes I would agree keep us all advised. The only other minor complication is the speedo will probably remain uncorrected. I also did a 6200 mile trip with a portable GPS. I did every so often compare the speedometer reading with the GPS mph reading and they were consistently different. The problem will become like looking at three watches: 1. the old reading with the smaller tires that you now will only "recall" 2. the current reading with the new and wider and bigger diameters of unknown correction 3. the GPS.a. old b. new

So for practical purposes, I am guessing one will just make do with a SWAG.
 

LNXGUY

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I would not at all be surprised if a 1.5cm taller FULL TREAD new tire would rub. I'd say chances are real good it would.
1.5cm's above stock?
I was running 225/50/17's at a 35mm offset and was 2inches lower then stock, with no rubbing issue's at all...
 

moondawg

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Fitment

They may rub at full lock. Even at full lock, I am able to get my hand between the tire and fenderliner all along the edge of the tire. This crude measurement shows at least 1" of clearance all the way around. That would allow a slim error margin for a radius increase of 1.5cm. We'll see. I have a jeep, so I'm used to troubleshooting tire fit issues!

Height/width

The difference in width is small, but height a little larger. The frontal area of the car won't change by an appreciable amount, but it will lift the car, allowing more air underneath. I don't know how much that affects drag. Where's Ernie?

"Actual" Distance.

I will be marking tires and measuring the distance of 10 revolutions on both old and new tires. I will also measure speedo and odo before and after with a GPS. That should give me a reasonable basis for comparison.

moondawg
 

ruking

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Cool, it will be good to see the differences, especially in some of the longer distance performance parameters.

UPDATE: I am still running the 195-65-15 oem GY LSH's. I am at app 68,000 miles. A min of 100k still seems within reach. Wear is dead even across the tread (minor variations of course) TP has been 38-36 psi fronts and 36-34 psi rears measured between weekly and monthly. I do a 5 tire cross rotation per 10,000 mile intervals. Fuel mileage is between 44/62. A bread and butter commute 50 R/T still yields 48-51. As a comparison the same route yields 36-41 in a Honda Civic VP. Another data point 6200 mile R/T pre Katrina trip had a range of 45-52 mpg with overall (12/13 fills) of 48 mpg.

So given the update data, a 2/3 mpg difference over 100,000 miles say 48/46/45 yields 2083,2174,2222 gals = 91-139 gals (x ones current price, in my case 2.85 corner store) or $259./396. So depending on how much you spend on a set, a 2/3 mpg difference can be a new set of tires!!! ie savings or much earlier expenditure: ie you only get 50,000 miles from a set. Upshot: low rolling resistance tires can indeed affect your long distance "ROLL ON".
 

Ernie Rogers

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Hi, Moondawg,

Everyone agrees that lowering ordinary cars lowers drag. The appendix of the Bosch Handbook I think gives a rule of thumb, guess from memory: One inch lower reduces drag by five percent. Maybe somebody can look it up.

Remember, guys, that I am running oversize tires--about one inch increased diameter. My conclusion was that mileage improved a lot, but I've forgotten the numbers (posted around here somewhere).

It's crucial to comparing mpgs that the new tires be measured at the same true speed as with the old tires, and that true distance be used. I felt that using highway mile markers gave reliable results.

Ernie Rogers

Height/width

The difference in width is small, but height a little larger. The frontal area of the car won't change by an appreciable amount, but it will lift the car, allowing more air underneath. I don't know how much that affects drag. Where's Ernie?

"Actual" Distance.

I will be marking tires and measuring the distance of 10 revolutions on both old and new tires. I will also measure speedo and odo before and after with a GPS. That should give me a reasonable basis for comparison.

moondawg
 

ruking

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Using the tire calculator, with a 195 65 15 size, a one in increase in diameter can be 215 65 15. This would be 4.1% difference and 60 mph on the speedo would be 63.5 actual. The rest of the calculations, i.e., circumference can be compared/contrasted side by side.

http://www.miata.net/garage/tirecalcold.html

In addition, most tire manufacturers have the EXACT data either on hard copy or web site.
 

moondawg

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It's crucial to comparing mpgs that the new tires be measured at the same true speed as with the old tires, and that true distance be used. I felt that using highway mile markers gave reliable results.
Ernie,
For the monthly competition, I plan on using a conversion factor that converts new tires to old tires, and not new tires to "real"

That way, my results from month to month will be apples to apples. If I were to switch to "real" miles it would give me an unfair "boost" in posted results.(my current odometer is around 2% low, IIRC.

Thanks for your input!

moondawg
 

Ernie Rogers

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Hey, Moondawg,

If you really want to be fair about it, you could drag an anchor behind your car to compensate for the higher efficiency you are getting.


Anyway, you will adjust your speedometer reading to match your previous speed, right? I did that when I changed tires-- I had done most testing before at 65 mph on the speedometer, now I do my highway driving at 62.5 mph on the speedometer. This happens to also be the true speed, just the luck of the tire change.

Ernie Rogers

It's crucial to comparing mpgs that the new tires be measured at the same true speed as with the old tires, and that true distance be used. I felt that using highway mile markers gave reliable results.
Ernie,
For the monthly competition, I plan on using a conversion factor that converts new tires to old tires, and not new tires to "real"

That way, my results from month to month will be apples to apples. If I were to switch to "real" miles it would give me an unfair "boost" in posted results.(my current odometer is around 2% low, IIRC.

Thanks for your input!

moondawg
 

moondawg

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The tires are ON. They do NOT rub.

The ride is much better than the energies... but I expect that has alot to do with the bigger size.

The treads are freeking huge... this is a directional tire, so make sure you get them on the right way. They also make a funny sound when you drive on sealed asphalt. Ever wear cheap flip-flops with wet feet? It sounds like that when I drive.


I haven't roll measured them yet, but here are the speedo results from the GPS:

Old tires: 55 mph indicated is really 52.8 mph. Odo is 1.15% pessimistic (reads fewer miles than actually travelled)

New tires: 55mph indicated is really 55.5 mph. I haven't had a long enough trip to measure odo vs gps yet.

My measuring helper is working nights until Friday... so no roll measurments until then.

I'll keep you posted.

moondawg
 

IndigoBlueWagon

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Two questions: Noise, how is it?
And I'm very interested to see what happens with your odometer. I've read that the speedos on our cars are about 5% fast but the odometers are spot on.
 

moondawg

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Noise on the road is not noticeable. So, they may be louder than my previous tires, but are still below detection behind the engine and wind noise.

I did finally get a tiny bit of rubbage on my passenger rear tire when I go pretty hot through a tight left-hand turn. Since this is not my normal driving style, I'm not too concerned. I think it was rubbing on the inside fender liner at the rear of the tire.

As far as the odometer, I expect it to be affected by 5% (same as the speedo) I'm measuring it on the way home today.

moondawg
 

watercop

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Based upon your stated ratio of new actual speed verses old actual speed at the same indicated speed, as well as your stated old odo error, I calculate that your odo will now be 6.9% 'pessimistic', indicating 6.9% fewer miles than actually traveled.

1.015 * (55.5 / 52.8) = 1.069

It will be interesting to see if that pans out.

There is provision for an 'either / or' choice in speedo / odo calculations, adaptable via Vag-Com. Awhile back, annoyed by the 5% speedo error, I changed to the 'other' choice, ?presumably? provided for smaller tires. My speedo became more or less dead on, but my odo went from being about 1.75% pessimistic to about 5.25% pessimistic. I have confirmed these values through repeated GPS readings as well as occasional long Interstate highway runs where I log the odo indication as I pass every 10th milepost.
 

moondawg

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Based upon your stated ratio of new actual speed verses old actual speed at the same indicated speed, as well as your stated old odo error, I calculate that your odo will now be 6.9% 'pessimistic', indicating 6.9% fewer miles than actually traveled.

1.015 * (55.5 / 52.8) = 1.069

It will be interesting to see if that pans out.

There is provision for an 'either / or' choice in speedo / odo calculations, adaptable via Vag-Com. Awhile back, annoyed by the 5% speedo error, I changed to the 'other' choice, ?presumably? provided for smaller tires. My speedo became more or less dead on, but my odo went from being about 1.75% pessimistic to about 5.25% pessimistic. I have confirmed these values through repeated GPS readings as well as occasional long Interstate highway runs where I log the odo indication as I pass every 10th milepost.
Results for the odometer with the new tires are:

GPS miles: 47.1

Odo miles: 44.3

(47.1 - 44.3)/47.1 = 5.9%

Watercop was close. I'll wait to see where the roll measurement falls to determine the odo correction factor.

moondawg
 

watercop

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hmm...I'm suprised at being a full 1 percent off. Any GPS signal degrading circumstances in your sample, such as tunnels, parking garages, tall buildings in an urban area or heavily tree-lined narrow roads? All of the above have at some point killed my GPS signal, slightly harming GPS accuracy for a given trip or tank.
 

LeeM

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I don't know if anyone answered your question about what a friction tire is. Nokian divides their winter tires into two categories, studded and friction.
 

moondawg

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hmm...I'm suprised at being a full 1 percent off. Any GPS signal degrading circumstances in your sample, such as tunnels, parking garages, tall buildings in an urban area or heavily tree-lined narrow roads? All of the above have at some point killed my GPS signal, slightly harming GPS accuracy for a given trip or tank.
I found part of it. Unless you posted a typo, you should have used 1.0115 in your calculation. (instead of 1.05)

That would give a calculated error of 1.067 Small difference.

Given the accuracy of everything involved, I'm not too concerned about a small discrepancy.

I don't pass through any tunnels or overpasses on my way home. The only GPS signal blockers would be roadside trees or clouds, or lack of reliable satellites in the constellation.

Tire measurements tomorrow night, hopefully.

moondawg
 

moondawg

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I don't know if anyone answered your question about what a friction tire is. Nokian divides their winter tires into two categories, studded and friction.
And, the WR's available in the US are labeled as all-season tires instead of winter. I assume that is because most 'muricans don't want to be bothered by changing tires appropriate for conditions (and I admit I am in that camp) OR, a "friction" winter tire is really the same thing as an All-Season tire, and a "studded" tire is the same thing as a dedicated winter tire. (what with the studs, and all.)


I was surprised at how soft the tire compound feels, especially for the treadwear rating (420 A) Although this number is pretty subjective, you can get a general idea of how a tire will wear. The rating is higher than the Energies, but the tire is noticably softer to the touch.

Time will tell how well they wear.

As to MPG: For the past couple of days, my MFA readings have been consistent with what I had with the older tires. This would imply an improvement. So, I am cautiously optomistic that I didn't harm my mileage. Again, only time will tell.


moondawg
 

alex_tdi

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All these talk has me tremendously confused.

Using taller tires seems interesting. I'm thinking of going from 195/65/16 to 205/65/15. According to the tire calculator link, the diameter will increase by 0.5 inches. I'm hoping it wont be too tall to rub the wheel wells.

If I go ahead with this, how would this affecy my odometer reading? All I care is mpg, so speedo error isn't all too important for me.

I like the Continentals because they are only $64 on Tirerack.com, much less than the Nokians and the Michellin Energies.

What do you experts think?

Alex
 

watercop

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Odo reading will change (be multiplied by) a factor equivalent to new tire revoulutions per mile divided by old tire revolutions per mile. Tire revs per mile are posted at Tirerack for most of what they sell.

I have a question for all y'all tire experts: Does the advantage conferred by low rolling resistance tread compound (silica) decrease as tire pressure is raised? In real world terms, folks that like to run 30 or so psig for reasons of ride and handling may well gain a lot more than those of us who max out tire pressure.

My pickup uses load range E tires with a max pressure of 80 psig. A big boat trailer I owned for awhile had tires rated at 100 psig, and I have read that commercial truck tires are rated as high as 120. I haven't come across much info about low rolling resistance tires for trucks, and I gotta figure the commercial fleets would adopt any proven technology to eke out another 0.1 mpg or whatever.

In other other words, if I run tires at 51 psig am I wasting money buying low rolling resistance tires? Are they "pearls before swine"
 

alex_tdi

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Is there a way to make the changes using VAG-COM? Believe it or not, my old '97 Saturn had an ECU that allows you to make minor changes to the wheel diameters. How about these new high tech VWs?

Alex
 

RIP TDI

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Yes, but it requires a factory chart that correlates different tire/gear combinations with impulse distance codes.

Alternately, an aftermarket pulse frequency adaptor can be installed inline with the VSS signal. This is the way to change odo/speedo readings on A3/B4s since impulse distance codes cannot be changed via VAG-COM on these models.
 

moondawg

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Well, I was finally able to measure my new tires.

My old tires measured 63'8" for 10 revolutions

My new tires measure 66'9.5" for 10 revolutions.

That gives me an error 4.8%. I also think this is the most accurate way for me to measure the differences in tire size.

I will try to double check during my trip to Ft Wayne for T-day. A longer trip with GPS should give a more accurate measure than my previous ~40 mile trip.

More about the tires: The wet traction is head and shoulders above the Energies. Maybe within the next month or two I'll get to try some snow traction... but I'm not holding my breath.

Using the 4.8% conversion factor, my last tank was 684.9 miles, and 15.208 gallons, for 45.03 mpg. Exactly the same as my previous tank with the Energies.

So, I didn't lose any mpg, and I gained some seriously grippy tires. Color me happy.

moondawg
 

ruking

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Way cool! I am glad it worked out for you.

I just ordered a set of Toyo TPT's, oem sized. Since I do have a lot of wear left in the GY's, I will get the Toyo's mounted on their own set of rims (identical to the ones that came oem with the car) break them in for 200-300 miles and start the SOTP tire mpg comparison. If folks are interested, I can keep this board up on the progess, if not, thank you all for the information covered in this thread.
 
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moondawg

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Update on the WRs in the snow.

Well, Mother Nature provided some opportunity to try these out in the snow. Keep in mind, that I have nothing to compare these to, except the Michellin Energies that I ran for the previous 110,000 miles.

These things are awesome.

I've never had a set of tires that gripped so well on snow/ice. Traction is very predictable. I can still force the car to slide, or the wheels to spin on takeoff, but it takes a much more concerted effort than it used to.

The treads seem to clean themselves very well, and I wasn't throwing alot of snow up off the ground like I seemed to with the Energies.

When turning, even when the tires slide I make a fair bit of progress in the direction the wheels are pointing. Once the Energies started sliding, there was not much you could do but shut up and hold on and hope you weren't sliding towards something big or deep.

I really hope that these last at least as long as the energies did,although even if they don't I feel the improved traction more than makes up for a shorter life.

Conclusion: If you live in an area that sees weather on either end of the spectrum, you can't go wrong with the Nokian WR. I'll try to update again in another 50k miles!

moondawg
 

Ernie Rogers

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You be the judge

Okay, the question is--

Does it pay to buy efficient tires if you intend to run them at high pressure?

I ran some cases through my fuel economy program. Standard tires probably have Crr = 0.015 at their normal pressure. Good energy tires are probably at Crr = 0.009 at normal pressure.

According to one hypothication, the rolling resistence varies inversely with tire pressure. Let's assume this is true. For comparison, let's say normal pressure is 30 psi and high pressure is 50 psi. Changing from normal to high pressure changes rolling resistance like this--

Standard tire: 0.015 x 30/50 = 0.009
Energy tire: 0.009 x 30/50 = 0.0054

Here is the effect on mileage at 70 mph, for a Jetta, my calculation:

Crr = 0.015: 15.1 hp for aero + 8.6 hp for tires = 23.7 hp, 43.4 mpg
Crr = 0.009: 15.1 hp for aero + 5.1 hp for tires = 20.2 hp, 48.2 mpg
Crr = 0.0054: 15.1 hp for aero + 3.1 hp for tires = 18.2 hp, 51.6 mpg

Remember that for lower highway speeds and around town, the power for aerodynamic drag will be much lower, but the horsepower needed for rolling resistance will still be the same, making the effects even larger.

Okay, you be the judge, if you put 50 psi in the tires, are the energy tires better (Crr = 0.0054 at 50 psi) than regular tires (Crr = 0.009 at 50 psi)?

Ernie Rogers

watercop said:
Odo reading will change (be multiplied by) a factor equivalent to new tire revoulutions per mile divided by old tire revolutions per mile. Tire revs per mile are posted at Tirerack for most of what they sell.

I have a question for all y'all tire experts: Does the advantage conferred by low rolling resistance tread compound (silica) decrease as tire pressure is raised? In real world terms, folks that like to run 30 or so psig for reasons of ride and handling may well gain a lot more than those of us who max out tire pressure.

My pickup uses load range E tires with a max pressure of 80 psig. A big boat trailer I owned for awhile had tires rated at 100 psig, and I have read that commercial truck tires are rated as high as 120. I haven't come across much info about low rolling resistance tires for trucks, and I gotta figure the commercial fleets would adopt any proven technology to eke out another 0.1 mpg or whatever.

In other other words, if I run tires at 51 psig am I wasting money buying low rolling resistance tires? Are they "pearls before swine"
 

ruking

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While the syllogism seems correct, your question has a interesting structural anomoly. Upshot: what are /would be the results for high pressure in so called standard tires? i.e., high pressure in standard vs energy tires. My intuitive guess it the variable would affect/effect the test in proportionately the same way.

Another way to approach the structural defect is high pressure in standard tires vs normal pressure in energy tires.

The possible nexus would be cheaper normal tires at hp would yield similar results (as normal pressure in energy tires) as to not be cost effective to spring for the more expensive energy tires if you will run them at normal pressure.

What am I missing here?
 
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donfromnaples

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If you increase from 195 to 205, then you will increase friction. This will not help gas mileage. Instead move to a 70 series tire instead of 65 stock size. This will yield a small gain in mpg.
 

moondawg

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donfromnaples said:
If you increase from 195 to 205, then you will increase friction. This will not help gas mileage. Instead move to a 70 series tire instead of 65 stock size. This will yield a small gain in mpg.
This may be true if you change sizes while staying with the same brand/model of tire. If you switch to a tire that has a lower rolling resistance, you may not increase friction overall.

If you go to a slightly wider, moderatly taller tire, the increase in engine efficiency at a given speed may be enough to counteract any increase in friction.

I only had one tank of similar weather/fuel conditions to make a comparison when I switched tires. I did not lose any fuel economy by making the switch, but I'm not sure I gained any either. Also, I have not checked my tire pressure since I got the tires installed, I've just been using what the garage put in there. I may have some gain by running higher psi.

But as I stated earlier, the increase in traction worth a loss in mpg for me. If I find that the larger tire size doesn't help at all, I'll probably go back to stock in 80k when these tires wear out.... but it will definitely be stock sized WRs.

moondawg
 
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