Tire sidewall height vs rolling resistance?

[lasitter]

I was wondering if there was a relationship. Taller vs shorter, does one or the other tend to roll farther / more easily?

[BabyDiesel]

Subbed. I am curious about this as well, partly due to I have heard both sides of the question give a lower RRC.

I do know that tire construction is the most critical aspect. 165/65r14 Bridgestone Potenza Re92s have ~40% less RR than my cheap Chinese 185/70r14 BlackLion Cilerro BH15s.

[lasitter]

I was also wondering about tire & wheel weight and rolling resistance, vs fuel economy.

I know that a heaver tire and wheel package always takes more energy to get turning and to stop.

What I don't know is about the effect of tire weight on CRR. Can tires that weigh less have a lower CRR even if they are not engineered to be LRR tires, as opposed to outright heavier LRR tires.

In this comparison I'm looking for the amount of energy to keep a tire turning as opposed to getting it turning.

[Frank Lee]

I think if you can have the thinnest tire at a pressure that results in the least sidewall, bead, and tread flex, that will result in lowest R.R. because less rubber is flexing and unflexing with each revolution.

[Focus-Ak]

I was looking into tire width vs. profile recently, and found it is a complicated topic and not intuitive. Here is an interesting interactive URL about it (a wheel and tire size comparator): Custom rims, wheel tire packages for your ride - RIMSnTIRES.com

Profile is a percentage of rim width.

My interest (theoretical - not looking at buying new rims or tires any time soon) was bigger outer tire diameter to better fill the fender arch, combined with narrow tires so the rubber is inside instead of outside the sides of the car. Narrower tires would make adding rear skirts easier (no need to bulge outwards). The other complication is offset and spacers, to assure mechanical clearances. Playing with the above link shows it is hard to have cake and eat it.

Not trying to hijack this thread -- seems related to me.

[BabyDiesel]

Check around here: Barry's Tire Tech

The writer of the site, CapriRacer, frequents the site. I will message him and see if he can give any insight that is not on his website.

[CapriRacer]

Thanks for the vote of confidence, Baby Diesel,

First, here's my webpage on the subject of tire size and RR:

Barry's Tire Tech

Short version: Compared to other things - like the composition of the tread rubber - SIZE is a pretty small contributor in RR. single digit percentages vs double digit.

I developed an equation based on some data - and based on that, sidewall height is counter proportional to RRC. That is, taller tires have less RRC.

I generally refer to all of this as "Bigger Is Better". So if you want to minimize RRC, choose the biggest tire that will fit under the fenders - BUT - careful selection is much more important. Spend most of your time there.

[user removed]

Most LRR tires have less tread depth. My Mirage's Ensaves were 8/32nd new. The Contis on the wife's Sorento have 7/32nds on one end and 5/32nds on the other. 45k miles on the Sorento, about 7k on the Mirage.

Tread wear ratings reflect the difference, with most of the lowest RR tires simply having less thickness in the tread area thus less energy lost in flexing of the tire.

regards
mech

[lasitter]

Originally Posted by CapriRacer

I developed an equation based on some data - and based on that, sidewall height is counter proportional to RRC. That is, taller tires have less RRC.

I generally refer to all of this as "Bigger Is Better". So if you want to minimize RRC, choose the biggest tire that will fit under the fenders - BUT - careful selection is much more important. Spend most of your time there.

My truck currently has Kumho Solus KR21 235/75R15 tires, 108T XL 2183 lbs weight rating, 6.5" tread width and weighing 28-29 pounds. These are not LRR tires.

The General Tire Grabber HTS is the only (non-winter) LRR tire available in that wheel size, so I am considering buying that tire, and also tires for 16-18" wheel sizes, where there are many more options.

One question I'm trying to answer is this: Given that I'm already getting very good highway fuel economy (up to 32mpg @ 55mph under ideal conditions), what is the biggest bump in fuel economy that I might get as a result of tire selection?

Then: How much would I have to give up in terms of driving and performance characteristics, in order to achieve those benefits?

General Tire Grabber HTS LRR 235/75 R15 109T XL 2271 lbs./51psi 12.0/32" 32lbs 7.2"
Michelin Latitude Tour HP LRR 255/65 R16 109H SL 2271 lbs./51psi 10.5/32" 33lbs 8.5" (owners hated it)
General Tire Grabber UHP --- 255/65 R16 109H SL 2271 lbs./51psi 12.0/32" 34lbs 7.7"
Pirelli Scorpion Verde+ AS LRR P235/70 R16 106T SL 2094 lbs./44psi 11.0/32" 30lbs 8.0"
Pirelli Scorpion Verde AS LRR P235/70 R16 106H SL 2094 lbs./44psi 11.0/32" 31lbs 7.2" (2011 Production)
General Tire Grabber HTS LRR 235/70 R16 106T SL 2094 lbs./44psi 12.0/32" 33lbs 6.5"
General Tire Grabber HTS LRR 235/70 R16 106T SL 2094 lbs./44psi 12.0/32" 33lbs 7.0"
General Tire Grabber UHP --- 255/55ZR18 109W XL 2271 lbs./51psi 11.0/32" 32lbs 8.5"
Pirelli Scorpion Verde AS LRR 255/55 R18 109V XL 2271 lbs./50psi 11.0/12" 36lbs 9.0"
Continental CrossContact LX20 LRR 255/55 R18 109H XL 2271 lbs./51psi 12.0/32" 35lbs 8.6"

I'm very suspicious about tire manufacturer claims regarding LRR. No one is releasing CRR data for their products. That said, I'm generally aware of the claims made for LRR tires.

The tires above cover lots of different options and strengths. I'm going to have dedicated winter tires so that one tire does not have to accomplish everything.

Just looking at the tires above, and considering the weight, PSI inflation, rubber patch on the road, and approximate sidewall height, and forgetting price, which ones would likely show the greatest improvement in MPG?

The greatest difference in weight above is the Verde+ at the 16" wheel size with 30 lbs. and 8" of rubber on the road, and the 18" wheel with Verde with 36lbs and 9.0" of rubber on the road. That's a pickup of 2-8 pounds per corner for me. What does that cost me just in weight, or in terms of the six pound difference between the Pirelli's?

Compared to my current 6.5", it looks like I can have a lot more tire on the road if I want it, and that might represent a big improvement in stopping and handling. That's partially why you'll see the UHP summer tires in the list, in case MPG improvement isn't enough to matter.

It also looks like I can shave 2-3 pounds off the wheels. Still working on that.

[CapriRacer]

Originally Posted by lasitter

My truck currently has Kumho Solus KR21 235/75R15 tires, 108T XL 2183 lbs weight rating, 6.5" tread width and weighing 28-29 pounds. These are not LRR tires..........

I'm truncating the post to save space, but I do want to indicate what I am replying to.

First, "LRR" is a relative term, not an absolute one. It means the tire in question has lower RR than a tire with similar treadwear and traction characteristics. It does NOT mean it has low RR.

Second, does your vehicle NEED a 235/75R15 XL? I ask that because tire shops are not likely to apply a tire with a lower load index. Put a different way, what is your vehicle - year, make, model?

Third, I hope you realize that wheels are going to be expensive and you are not likely to recoup the cost. So are you willing to spend the money in spite of knowing you won't recover the cost in fuel economy?

And lastly, the actual amount of improvement in fuel economy you will receive is very much dependent on your actual driving conditions. For example, someone doing stop and go driving is not going to experience much of an improvement in FE compared to someone who has a long commute on an Interstate highway.