Rolling Resistance

[404NotFound]

If someone has the time, could they help me figure out the rolling resistance difference of two tires based on tire weight alone? I have looked up the formula for rolling resistance online, but I haven't found that specific formula. I don't want someone to do the work for me, just to know how to figure it out based on tire weight. Basically I have the AT20 Dunlops that are 36lbs, and I am looking at the Cooper ATW which has a blend of rubber and silicon and supposedly weighs 44lbs. Personally I don't think the company actually weighed it and they just used the weight of the AT3 but whatever. I was going to switch to a LT245/70/17 from the 265/65/17 dunflops. The overall circumference is .05" different and the width is something like .75 or less different. I was curious how much of an effect on gas mileage the extra 32lbs would make due to rolling resistance. I have a 2005 SE V6. If anyone could help me equate that I would appreciate it, if the difference in gas would be so small that it isn't worth calculating (<1) then we can just leave it alone.

Thanks all.

 

[radlynx]

the heavier the tire, the more gas the engine will consume. so, get the tire with the less weight.

 

[Range]

Don't forget tread pattern. An equal weight highway tire and a MT will still have different resistance although I know this isn't a great comparison. I think in your situation the difference is so small, minute actually, that you wont be affected. 32 lbs is basically a bunch of groceries or a bag full of guns, ammo and porn.

 

[404NotFound]

the heavier the tire, the more gas the engine will consume. so, get the tire with the less weight.

That is what I am trying to do but unfortunately the closest tire size wise that they carry is the LT245, they don't make a P in the 17" rim size. In testing I will say some people said they had an increase in MPG due to the tires composition making it lighter. Like I said I am not sure how genuinely accurate the particular website is on weights, sadly.

 

[404NotFound]

Don't forget tread pattern. An equal weight highway tire and a MT will still have different resistance although I know this isn't a great comparison. I think in your situation the difference is so small, minute actually, that you wont be affected. 32 lbs is basically a bunch of groceries or a bag full of guns, ammo and porn.

I think you're probably right. It's not like I'm going from 50lbs to 90lbs per wheel. Plus all my porn is digital so that saves weight for more guns and groceries.

 

[KidVermicious]

I'm thinking weight is not as big a factor in rolling resistance as PSI and tread pattern/road surface. Where weight plays a bigger part is in inertial resistance, starts and stops.

 

[404NotFound]

I'm thinking weight is not as big a factor in rolling resistance as PSI and tread pattern/road surface. Where weight plays a bigger part is in inertial resistance, starts and stops.

I've read that a lot on here about how important the proper PSI is. I knew PSI was important but how does one determine what is the best PSI to run? I have read about a "chalk test" on the forum but I don't know what that is.

 

[KidVermicious]

I've read that a lot on here about how important the proper PSI is. I knew PSI was important but how does one determine what is the best PSI to run? I have read about a "chalk test" on the forum but I don't know what that is.

So to do a chalk test, you color your tire treads with chalk and roll down the street a couple blocks. Get out and look at your tires. If the chalk came off even, that's a good sign. If there's more left on the middle of the tire, you're running a lowish PSI. If there's more left on the inside and outside, your PSI is high. If there's more wearing off just the inside or outside of a tire, your alignment is off.

Or that's the theory. I've never done one. When I'm running factory tires I inflate to whatever the sticker on the door tells me to, and when I'm running E rated offroad tires I run 40-45 PSI and watch my treadwear closely.

 

[progress4m]

Let me start by saying that I never had LT tires on any of my 4runner and never had a need for one (even considering towing and off-roading I do);

And despite the fact I have looked into this before unfortunately I could never find exact info for tires weight and\or rolling resistance formula (s) or data;

Based on my personal experience and info I have found on this site (as well as other) I have to say that weight of the tire will impact your gas mileage and handling (not necessary I would call it rolling resistance). Weight of the tire is very important because it is unsprung and rotational weight… it cannot be looked or compared to the same weight as “32 Lbs of groceries” in your vehicle…. Unless you are planning to spin that weight with the same speed as tire spins going 75 mph on the highway and move up and down with the same speed as wheel moves up and down on EVERY bump and road imperfection…

Rolling resistance itself is more of the factor of the tire compound, structural characteristics, its width, tread pattern, tire pressure and road surface; (again I have no formula to quantify those factors);
Based on above, is the one of the reasons I never had used LT tires;
P rated tires in AT form served me well on and off road;

To OP: have you looked at 255/75R17? That size is not offering many tire choices, but they do have P rated Cooper and other AT tires… I have come across reports on this site with very positive comments about this tire size; People have said that after switching to that size they had great feeling of steering respond, road manner and also some even got better mpg despite the fact of increase tire size and going from hwy to AT tire; also IMHO, I would not go as narrow as 245/70…

I will be seriously looking on getting 255/75R17 as my next set (currently have 265/70R17)

My $0.02;

 

[404NotFound]

Let me start by saying that I never had LT tires on any of my 4runner and never had a need for one (even considering towing and off-roading I do);

And despite the fact I have looked into this before unfortunately I could never find exact info for tires weight and\or rolling resistance formula (s) or data;

Based on my personal experience and info I have found on this site (as well as other) I have to say that weight of the tire will impact your gas mileage and handling (not necessary I would call it rolling resistance). Weight of the tire is very important because it is unsprung and rotational weight… it cannot be looked or compared to the same weight as “32 Lbs of groceries” in your vehicle…. Unless you are planning to spin that weight with the same speed as tire spins going 75 mph on the highway and move up and down with the same speed as wheel moves up and down on EVERY bump and road imperfection…

Rolling resistance itself is more of the factor of the tire compound, structural characteristics, its width, tread pattern, tire pressure and road surface; (again I have no formula to quantify those factors);
Based on above, is the one of the reasons I never had used LT tires;
P rated tires in AT form served me well on and off road;

To OP: have you looked at 255/75R17? That size is not offering many tire choices, but they do have P rated Cooper and other AT tires… I have come across reports on this site with very positive comments about this tire size; People have said that after switching to that size they had great feeling of steering respond, road manner and also some even got better mpg despite the fact of increase tire size and going from hwy to AT tire; also IMHO, I would not go as narrow as 245/70…

I will be seriously looking on getting 255/75R17 as my next set (currently have 265/70R17)

My $0.02;

Well my goal was to get as close to the stock size as I could, although you have raised a good point with the 255. In the particular tire I want Cooper has a 255/70/17 which should be slightly narrower but not too tall, since I am completely stock in my suspension.

I'll be honest I, like you, have no real use for the LT tire. The only reason it was in play was because that was all cooper had in that size, on that particular tire model. But now since you have brought the 255 to mind, I will seriously consider that because they offer it in a P rating that is only 2lbs heavier per tire. 12lbs is better than 32.

 

[404NotFound]

Okay let me further my inquiry and ask this:

If one tire (current 265/65 AT20) is 30.6" in diameter and the potential tire (255/70 ATW) is 31.18", that is a difference of 0.58", or 1.8%. That means for every mile I go it would be 1.8% off per mile correct? So for every mile registered on the odometer the actual would be .982/1?