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Old 09-05-2010, 05:27 AM   #121 (permalink)
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Originally Posted by CapriRacer View Post
You would think that but the data suggests that there are other things that may have more impact. I've tried to catalog them here:

Barry's Tire Tech
Thanks, interesting reading. To me though, that "tast 4 results" graph showing 235 section tires with six pounds more rolling resistance force than the 175 section tires is quite a difference. The effect of tire width on resistance is fairly easy to demonstrate.

Dump the clutch in a car on narrow tires and then try the same car with fatter tires and it's fairly clear which one has the more resistance (/friction). Fatter tires would make for more rolling resistance and aero drag I would think, by all normal rules of physics. Obviously compound matters too, but like-for-like the narrower tires would have less rolling resistance.

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Old 09-05-2010, 07:51 AM   #122 (permalink)
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Quote:
Originally Posted by AJI View Post
Thanks, interesting reading. To me though, that "last 4 results" graph showing 235 section tires with six pounds more rolling resistance force than the 175 section tires is quite a difference. The effect of tire width on resistance is fairly easy to demonstrate.

Dump the clutch in a car on narrow tires and then try the same car with fatter tires and it's fairly clear which one has the more resistance (/friction). Fatter tires would make for more rolling resistance and aero drag I would think, by all normal rules of physics. Obviously compound matters too, but like-for-like the narrower tires would have less rolling resistance.
There are 2 things you have confused:

1) Rolling Resistance has nothing to do with grip (friction). You can not measure RR by doing a burnout. RR is caused by internal (to the tire) friction and the net result is heat.

2) Rolling Resistance Force (RRF) is an important property, but when you apply a tire to a car, the load on the tire doesn't depend on its size - unlike the way the tire is tested. So you need to use Rolling Resistance Coefficient(RRC). If you look at the graph marked "Rolling Resistance Coefficient" (It's the one under the one you were referring to), you'll see that the lowest RRC values occur with fairly large tires and the narrow ones (which also happen to be small) are fairly high. That's why I did the analysis: to find out what was occurring and what was the most sigificant - and while it seems intuitively wrong, wider tires seem to be of benefit.

The problem is that "width" can never be isolated by itself. Every time you go "narrower" you also lower the diameter and the load carrying capacity - and these have negative impact on RRC. If you trade width for aspect ratio - which results in the same load carrying capacity and the same diameter, then that may be true.

But what usually happens is that folks have the space to go wider AND go taller - and both of those are beneficial.

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Old 09-05-2010, 10:13 AM   #123 (permalink)
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First I want to thank you for posting the link:
Quote:
Originally Posted by CapriRacer View Post
You would think that but the data suggests that there are other things that may have more impact. I've tried to catalog them here:
Barry's Tire Tech
I was aware of and have a copy of the Smithers report as well as a few SAE papers and graphs.

I've been testing Sumitomo T4s on my NHW11 and have these lessons learned:
  • GPS distance and speed - due to tire wear and geometry effects, we can not use the vehicle MPG because it is based upon wheel rotations WITHOUT compensation for the tire diameter change.
  • tread width is NOT found in xxx/yyRzz - the "xxx" is a width of the inflated tire portion but the tread width is different. Go to Tire Rack and you'll find there is a column called "tread width" and there is considerable variability that tends to follow but is only loosely associated with the "xxx" metric.
Our 2003, NHW11 Prius has had these tires:
  • 175/65R14 - Mastercraft (sears) brand suffered abnormal wear patterns that were corrected by fixing the rear toe and camber. The front right camber was off and fixed with the next set.
  • 175/65R14 - Sumitomo T4s, 51 psi, were undersized according to the specs. This means the indicated speed was higher than true leading to lower true speeds. The indicated MPG was also high. But due to the tripmeter errors, the pump calculated MPG was probably high.
  • 175/70R14 - Sumitomo T4s, running at 51 psi, slight improvement in stability and no change in the corrected, calculated MPG. The adjusted MPG showed no change from the previously 'optimistic' MPG . . . a true improvement of ~3%.
  • 195/70R14 - Sumitomo T4s, 51 psi, largest that fit on the NHW11. No change from 175/70R14s although some evidence of more steering input.
Sumitomo T4 is listed as low rolling resistance by Consumer Report.
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Old 12-01-2010, 12:16 PM   #124 (permalink)
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anyone have test data on khumo ecowing kh30?

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Old 12-01-2010, 12:19 PM   #125 (permalink)
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As an update, I just ordered a second pair (I will now have them in all 4 corners)of P195/65R-15 Bridgestone Insignia SE200-02 firrst set is holding up well and provides acceptable everything.
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Old 09-24-2011, 11:04 PM   #126 (permalink)
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I have 13" tires!!!!!!!!!!!
NOW WHAT!
AND I ONLY FOUND 2 TIRES ON TIRERACK that make my oen size!
The other option is the current tire I have on my corolla which is a 175/70/13.
I am thinking going back to the oem 155/80/13 tire size will same me some drag/resistance.
OR
I can go up to a 185/60/14 and keep most of the spedo difference in check at .09% difference but the tires will get heavier and 1.1" wider which might reduce my efficiency/MPG and raise rolling resistance, un-sprung weight and other factors??
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Old 09-25-2011, 01:43 AM   #127 (permalink)
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Quote:
Originally Posted by HighMPG View Post
I have 13" tires!!!!!!!!!!!
. . .
I can go up to a 185/60/14 and keep most of the spedo difference in check at .09% difference but the tires will get heavier and 1.1" wider which might reduce my efficiency/MPG and raise rolling resistance, un-sprung weight and other factors??
What I found is the rear wheel well is the ultimate, size determinant. As an experiment, buy one wheel and tire and then mount it in the rear and later, swap it in the front. You won't be driving far as much as taking measurements and then looking for a 'speed bump.' You want to make sure there is no interference on a bump or problems at steering limits.

GOOD LUCK!
Bob Wilson
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Old 09-25-2011, 01:58 AM   #128 (permalink)
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Quote:
Originally Posted by bwilson4web View Post
What I found is the rear wheel well is the ultimate, size determinant. As an experiment, buy one wheel and tire and then mount it in the rear and later, swap it in the front. You won't be driving far as much as taking measurements and then looking for a 'speed bump.' You want to make sure there is no interference on a bump or problems at steering limits.

GOOD LUCK!
Bob Wilson
Thanks Bob,

I am going back to the OEM size 155/80/13 tire since it seems to have the least RR due to contact patch size comparison. I will save about 1" on tread width which should reduce my RR a bit and seem to have a stiffer compound for the Kumho Solus K21. You can find some of the factors in me deciding on a tire in my Sig **Choosing a Tire**
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Old 09-25-2011, 06:53 AM   #129 (permalink)
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Quote:
Originally Posted by HighMPG View Post
I have 13" tires!!!!!!!!!!!
NOW WHAT!
AND I ONLY FOUND 2 TIRES ON TIRERACK that make my oen size!
The other option is the current tire I have on my corolla which is a 175/70/13.
I am thinking going back to the oem 155/80/13 tire size will same me some drag/resistance.
OR
I can go up to a 185/60/14 and keep most of the spedo difference in check at .09% difference but the tires will get heavier and 1.1" wider which might reduce my efficiency/MPG and raise rolling resistance, un-sprung weight and other factors??
Forget the "narrow is better" approach. Not only has that limited your choices, but it is fundamentally flawed.

Put the largest tire that will fit without rubbing. Discount Tire might be able to help you. On their web site, they list alternative tire sizes after you input your vehicle. Find the size with the largest load index. THEN look at your choices.
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Old 09-25-2011, 08:02 AM   #130 (permalink)
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Quote:
Originally Posted by CapriRacer View Post
Forget the "narrow is better" approach. Not only has that limited your choices, but it is fundamentally flawed.

Put the largest tire that will fit without rubbing. Discount Tire might be able to help you. On their web site, they list alternative tire sizes after you input your vehicle. Find the size with the largest load index. THEN look at your choices.
Thanks I may just get another set of Radial X if I can find them on my size since consumer reports puts them in their top spot for good RR.

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