Light truck LRR tire question ...

[oldtamiyaphile]

Originally Posted by oil pan 4

The mileage stayed the same on my suburban, it may have even trended up a tiny bit. I expected fuel economy to go down by full numbered MPGs. But lucky for me everyone was wrong.

My experience is annecdotal, but when I when from 235/75R15's street pattern tyres on my Jeep at 1000km from new to 31x10.5 A/T's I don't think there was a milage hit. My Wrangler is still the most economical TJ I can find on Fuelly, by about 2mpg.

You can bet the new tyres added weight, CRR and added aerodynamic drag, but the lower cruising RPM (with a six speed mind you), seem to be enough to offset that. I'm soon going to 33's and expect a milage hit, but I guess we'll see.

[CapriRacer]

Originally Posted by lasitter

The report is old and the data is older. Until I see CRR data from different sizes of tires by the same tire maker / same class, I will remain unimpressed.

The CRR for every tire of every size should be readily available to us as consumers.

https://en.wikipedia.org/wiki/Low_ro...esistance_tire

"... 2003 California Energy Commission (CEC) preliminary study" ... some of this data may be 11 years old. I think it's a disgrace that we don't have better data, and the primary reason is that people who make and sell tires don't want us to have it.

1) The fact that the data is old doesn't mean it is invalid.

2) That data is the only data that is available - and it is likely that there will not be new data any time soon.

3) And the data IS of the same tire line - as best as I can tell.

So: "Bigger is Better"

But to answer the original question: Yes, a wider tread generally means more RR.

- BUT -

All other things have to be equal.

When you change tire diameter, you've changed more than just diameter. You also changed load carrying capacity - and load carrying capacity has a major affect on RR.

And as I point out on the web page: There are HUGE!!! differences between tires. Tire size is NOT a big factor in RR.

And while you may be thinking that measuring tread width gives you some insight into fuel economy, the material properties of the rubber itself have a much larger effect. In other words, measuring tread widths is enough information.

[CapriRacer]

I'm making a separate post to talk about why RR values aren't published by the tire manufacturers.

1) There are quite a few tests for RR and they give different results. In order to compare tires, the tests need to be the same.

2) The test facility needs to be the same - or at least correlated to some standard. There have been correlation studies for RR and indeed, each facility gives a slightly different result.

3) Then there is the problem of how to express RR. There is a major disagreement. The Feds want to use force (RRF) because those values emphasize smaller tires and therefore smaller vehicles.

But the tire manufacturers want to use the coefficient (RRC) because tire buyers already have their vehicles (and their tire size) and they need to know what the differences are for the particular size tire they would purchase.

This dispute was put in front of the GSA - and the GSA ruled that the Feds needed to go back and reconsider their position. That is what that Feb 2012 meeting was all about.

But even after that is resolved, there's the problem of tire size.

Both RRF and RRC vary by tire size. (That was the point of the CEC study that Smithers did). Unless a way is devised to resolve the tire size issue (like a formula or something), EVERY tire in EVERY size in EVERY tire line for EVERY tire manufacturer would need to be tested. It's been estimated that if EVERY testing facility in the world were to go 24/7/365, this would take 3 years - and in the meantime, no other testing could be done. No development of better tires or better rubber compounds. Not to mention testing of new products.

That, of course, is unacceptable.

So that's where it stands. There is a HUGE!!! obstacle.

I have my own opinions about how to overcome it, but having talked to the engineers at NHTSA, I don't think they will go there.

[oil pan 4]

Originally Posted by lasitter

Very interesting. Then what is your theory as to why bicycle tires are as thin as possible / highest possible pressure? Other things being equal, why not have all tires as thick as mountain bike tires?

Is your theory all about thin tires being more aerodynamic?

Tire Fuel Efficiency Consumer Information Program

I don't think we'll have straightforward answers to these questions until disclosure is forced by the final implementation of these rules ...

I don't believe a slightly thinner tire will be worth anything on a car that is normally operated below 200mph.
Bike tires can be tiny because they hold a tiny amout of weight and they put a tiny amout of power to the road. They have to deal with a tiny amout of heat. On a bike the tire is all exposed and makes up much more frontal area of the vehicle. The round things installed on bikes and cars we call tires are both called the same thing but they are about as different as the 2 vehicles them selves.
Look at a car from the front, how much does tire frontal area compair to the rest of the vehicle, you can hardly see the tires. So there is hardly any effect.

On one of our cars we put yoko avid ascends that were about 1 inch taller than the OEM recomended size. The price difference between the OEM recomended size and the larger tire was about $50 less, the cost of a full tank of gas.
So before I even put them on the car these tires had already saved me about as much money as you can hope to save by switching to LRR tires, over the life of the tire.
The car also rides better with the larger tire. With more inches of rubber on each tire they should last longer too.

I see no reason to down grade to a smaller tire. My mechanical engineer friend has ran all the numbers and also sees no reason to go to a smaller tire.

[California98Civic]

Originally Posted by lasitter

Very interesting. Then what is your theory as to why bicycle tires are as thin as possible / highest possible pressure? Other things being equal, why not have all tires as thick as mountain bike tires?

Is your theory all about thin tires being more aerodynamic?

Tire Fuel Efficiency Consumer Information Program

I don't think we'll have straightforward answers to these questions until disclosure is forced by the final implementation of these rules ...

Thanks for that link. On your question. There is a thread here with some great testing "taller tire test." Take a look. Narrower is better for aero and contact area, but it offers less traction, which might be significant for your needs. Taller is better for gearing, but it distributes weight differently, most especially further from the hub, increasing rotation mass effects. A taller tire if it is heavier will also have a negative effect on FE if you do a lot of stop/start driving (again, rotational mass). But in cruising of a freeway that weight will matter less.

The take away: taller, lighter, narrower, and LRR is better, though you will never get exactly that combination (most likely) so judge your choices against your driving conditions. There is no absolute rule, as we often find...

[freebeard]

I'd really like to get back to what I originally asked, about the difference between 7.2" and 6.2" ... any guesses as to what downsizing might mean?

I will need to extrapolate from a vehicle that weighs about 1 ton. That said, and assuming your F-150 is 2WD, this may apply.

My stock tire size would be 165R-15. Following the lead of street rodders (big-n-littles) and Cal-Look VWs I downsized to 145s in front for years. With RWD the engine RPMs don't change (althought the speedo run off the left front wheel is a different matter). Caster is affected. Narrowing the tread relative to the rim width does a number of things. Mileage up is the one you're looking for. The narrower tread presents a smaller 'attack surface' for road irregularities. The tire/wheel edge is more aerodynamic. Road feel improves, and what's called 'turn in' improves. That's how long it takes for the tread to respond to input at the steering wheel.

OTOH you may also find that in downhill runs, you may have more brakes than traction. Plus weight transfer from the rear. I've gone to a Federal Formosa 165-50R 15. They sell sizes in 10mm increments in size and .05 increments in aspect ratio. Carrying capacity varies with aspect ratio.

I don't know if they have a tire that fits your need. But that's the kind of choice you should have available. Here's the tire I want:


Bridgestone Ecopias on 4x19" rims. I heard Rolls Royce used a 30" tire on 4x19. Coke Tire may have them.

[Varn]

I put on Toyo all terrain tires last time on my Econoline. Mainly because it is important to be able run on our gravel/mud road. This summer the van is pulling down 19-2o mpg. It is rated at 17 and importantly the mileage is better than it has ever been since we have owned it. The tires run quiet and have good traction. I run them at 50psi. They have been on it for a year and a half. I will buy them again.

[Hersbird]

A bigger tire is going to be heavier and all rotating mass which is 10 times the penality of static mass. So if you put bigger tires on your stock rims and add say 10 pounds per tire it is equal to carrying around 400 pounds in the trunk. Once up to speed on the highway it may not be a penality but around town stop and go it will hurt. Same thing going to larger wheels even if keeping the overall tire width and diameter the same as the bigger rim/lower profile tire usually weighs more then the smaller rim/higher profile combo. 20's look cool and my handle better but they hurt acceleration.

Although if I had a one ton duelly diesel for a 5th wheel camper I would consider going to a 255/60-22.5 on Alcoa wheels for the 120psi semi low rolling resistance and heavy load carrying ability. They are only an inch taller and slightly narrower then a common 275/75-17 found stock on many 2000s Chevy's.

[California98Civic]

Testing is better than guessing and testing that is close to your conditions can at least make for better guessing: http://ecomodder.com/forum/showthrea...tml#post246084

[ECONORAM]

Originally Posted by lasitter

Of course most of the posts here are not about old F-150 trucks, but that's what I have, and one of the mods I've been studying for a long time is the switch to LRR tires.

I have this sense that the size of the rubber patch on the road matters in terms of fuel economy, and so I was wondering what the difference might be (same LRR brand, etc.) between a tread width of 7.2" vs 6.2"?

General makes the "Grabber HTS" which is about the only option for LRR on my 1996 Ford F-150 in the 235/75R15 size.

I think it should be required, but there is still no coefficient of rolling resistance available on a tire by tire basis.

I did a look on TireRack, and you should be able to get some Firestone Destination LE2s in that size. I bought a set, but neglected to track a fuel economy difference from my OEM tires. I did notice reduced steering effort once these tires were installed.

Originally Posted by Vern

I put on Toyo all terrain tires last time on my Econoline. Mainly because it is important to be able run on our gravel/mud road. This summer the van is pulling down 19-2o mpg. It is rated at 17 and importantly the mileage is better than it has ever been since we have owned it. The tires run quiet and have good traction. I run them at 50psi. They have been on it for a year and a half. I will buy them again.

I tried running 10 psi higher on my LE2s, and noticed my speedo was a bit off. Can't remember the exact amount, but it was noticeable (running 275/60R20s). Now I run about 3 psi above...ride is smoother too.

Originally Posted by Hersbird

A bigger tire is going to be heavier and all rotating mass which is 10 times the penality of static mass. So if you put bigger tires on your stock rims and add say 10 pounds per tire it is equal to carrying around 400 pounds in the trunk. Once up to speed on the highway it may not be a penality but around town stop and go it will hurt. Same thing going to larger wheels even if keeping the overall tire width and diameter the same as the bigger rim/lower profile tire usually weighs more then the smaller rim/higher profile combo. 20's look cool and my handle better but they hurt acceleration.

Although if I had a one ton duelly diesel for a 5th wheel camper I would consider going to a 255/60-22.5 on Alcoa wheels for the 120psi semi low rolling resistance and heavy load carrying ability. They are only an inch taller and slightly narrower then a common 275/75-17 found stock on many 2000s Chevy's.

I was studying tire weights when I was shopping for the LE2s I put on my truck. This is part of what makes me consider getting smaller wheels and tires.