Interesting articles concerning tire size and it's effect on fuel economy

[mikeyjd]

http://www.barrystiretech.com/rrandfe2.html

http://ecomodder.com/forum/showthread.php/tire-width-vs-drag-cd-7475.html

[Movin]

That is interesting enough to keep me occupied a few days, thanks for sharing!

[sketchman]

Huh. A wider tire is better for fuel economy?

I haven't ever experienced that, and I still don't get it.

[sketchman]

I think I've started to get it.

Pressure in the tire is equal on all surfaces per square inch. So, given the same inflation pressure and a wider tire, there would be more pressure available per inch of circumference to push back against the tire trying to flatten out. The less width there is in the tread area the more the tire has to flatten out and increase its contact patch to provide the needed amount of area for the available air pressure to hold the rim/car up. Simply, the wider the tire(when everything else remains the same), the rounder it stays, and so the less it has to deform as it rotates.

Here is another interesting article.

http://www.performancesimulations.com/fact-or-fiction-tires-1.htm

After reading that article I also think there is an optimal(not necessarily the highest possible) pressure unique to different tires and sizes that creates the most resistance possible to flattening out and further contributing to lowering the RR.

I think I'll start some experimenting with this.

[Safety Guy]

Variables!

Just so many #$%^&* variables!!!!

Good reading nonetheless. So much for ASSuming skinnier tires will roll better, etc.

Karl

[TominMO]

Variables!

Just so many #$%^&* variables!!!!

Good reading nonetheless. So much for ASSuming skinnier tires will roll better, etc.

Karl

I would still bet that for long-distance hwy driving, skinny tires pumped up to max sidewall pressure or beyond are the way to go. For everyday driving involving cornering, then maybe not so much.

[sketchman]

I aired my 165/60/14s up to 40psi when they were first installed. First few tanks showed a drop of 5mpg average. Regardless of what caused that, my last tank just showed me 45. 2 up from the previous post 14" change over. I checked the tires and they'd gone down to 31psi all around. To add to this, I'd also done 2 very easy aero mods. So, most probable scenario, the underinflated tires caused a drop and the tiny bit of aero more than made up for it, OR perhaps I can get away with lower pressure in these wider tires than the 12s I had before.

I've just aired them back up this time to 45 up front and 42ish in back. Have to wait and see what's what. If it gets me back to 48mpg or better, I'll be floored that the tiny bit of aero did it.

[jason_]

And yet my tandem dualled 32ft kingpin pulls harder then my kingpin 35ft single triaxle...

Skinny 16s, same sizes, same pressure, tubeless, and the tandem dual is lighter.... Regardless both are heavy, but the lighter one makes the 383-stroker work her ass off in overdrive.

I've been told the same from big trailer dealers. I moved to 10k# axles for weight reasons, and it's noticeable. More tires turn harder.

Food for thought. Love those variables.


Sent from my rooted HTC Supersonic using Tapatalk 2 Pro

[sketchman]

^That would change things quite a bit I would think. That's also double the sidewalls and double the rims isn't it? Not just double the width.

The thing the tire engineer was arguing was that just a change in tire width(when everything else stays the same) would create less resistance. I noticed a while ago that big fat front tires were getting popular on coal trucks around here. Wish I knew someone in the business who could tell me why.

EDIT: Look what I found.

http://www.alliedoil.com/2011/03/the-benefits-of-wide-base-tires/

http://www.greencarcongress.com/2006/06/single_widebase.html

http://www.bigtrucktv.com/video/single-wide-tires-reducing-resistance-driving-success

Seems like good info to back up what Mr. Tire said.

[sketchman]

Some more interesting thoughts.
If you take 2 of the things he said and use them together:

So if I want to estmate what using a wider tire would do:

• 10 mm wider results in a reduction of about 2%. My experience is that you can only go about 20mm wider before you start to interfere with the fenders, frame, and suspension components - and that means that you should be able to get up to a 4% improvement.

AND

Inflation pressure has a lesser effect: 10% for the first 8 psi - and diminishing after that. Be aware that increasing the inflation pressure also decreases the size of the footprint.

You should be able to theoretically go from a 145/12 to a 185/13, inflate them to 40psi, and see a reduction in rolling resistance of 18% given the common OEM tire pressure of 32psi, AND given you use the same brand and model(probably not gonna happen these days).
Now before we get all excited, check this out from tirerack.

During stop-and-go city driving, it's estimated that overcoming inertia is responsible for about 35% of the vehicle's resistance. Driveline friction is about 45%; air drag is about 5% and tire rolling resistance is about 15%.

Overcoming inertia no longer plays an appreciable role in the vehicle's resistance during steady speed highway driving. For those conditions it is estimated that driveline friction is about 15%; air drag is about 60% and tire rolling resistance represent about 25%.

So decreasing RR by a whopping 18%, "should" influence your fuel economy VERY little. Tirerack says an increase of 20% would only hit you for about 3% city and 5% highway. In the long run 185s should still be better than 145s or 155s on the highway, but you're changing a part that only really influences 15% and 25% city/hwy. I think what I take away from it all is to worry less about tire width and more about overall diameter and weight, and really most of the attention should go to aero.

[mikeyjd]

Some more interesting thoughts.
If you take 2 of the things he said and use them together:

AND
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You should be able to theoretically go from a 145/12 to a 185/13, inflate them to 40psi, and see a reduction in rolling resistance of 18% given the common OEM tire pressure of 32psi, AND given you use the same brand and model(probably not gonna happen these days).
Now before we get all excited, check this out from tirerack.


So decreasing RR by a whopping 18%, "should" influence your fuel economy VERY little. Tirerack says an increase of 20% would only hit you for about 3% city and 5% highway. In the long run 185s should still be better than 145s or 155s on the highway, but you're changing a part that only really influences 15% and 25% city/hwy. I think what I take away from it all is to worry less about tire width and more about overall diameter and weight, and really most of the attention should go to aero.

Agreed