Light truck LRR tire question ...

[lasitter]

Originally Posted by CapriRacer

Actually, No! Larger tires generally give BETTER fuel economy for 2 reasons:

https://en.wikipedia.org/wiki/Talk:R...ct_of_diameter

Larger tires almost always have wider tread widths, 29" vs 31", but there is some dispute as per the Wiki discussion page. A lot apparently depends on the characteristics of the wheel and the surface, as well as tire composition.

The discussion assumes all the tires are the same width, and that only the diameter changes. 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?

[oil pan 4]

Down sizing your tires means you have to run your engine faster to go the same speed as before and you get more tire revolutions per mile. The belief that smaller tires are better started about 10 years ago when the prius and other small tire cars were hitting the roads and getting very good mileage. Yes the smaller tires worked for those vehicles because they were geared to take advantage of a small wheel. People wrongly assumed the smaller tire could be applied to any vehicle.

Hey frank, A P265 tire could easily be a 32 inch tire. That might be too much, when going from a vehicle setup for 235/75. I replaced my P235/75r15 tires after I figured out the hard way they couldn't carry any where near the weight the suburban was rated for.

[lasitter]

Originally Posted by oil pan 4

People wrongly assumed the smaller tire could be applied to any vehicle.

I wish someone would speak to my issue which is one of width vs tire diameter.

The case that I'm looking at involves shrinking the tread width (and approximately the contact patch) by about 14 percent.

I understand that this has completely separate implications (usually bad) for traction, handling, stopping distances, etc., but I am focusing on the fuel economy benefits alone here.

[oil pan 4]

Originally Posted by lasitter

I wish someone would speak to my issue which is one of width vs tire diameter.

The case that I'm looking at involves shrinking the tread width (and approximately the contact patch) by about 14 percent.

I understand that this has completely separate implications (usually bad) for traction, handling, stopping distances, etc., but I am focusing on the fuel economy benefits alone here.

Contact patch is obviously what holds up the vehicle. Barry has said in the past something to the effect of a smaller contact patch typically causes higher rolling resistance when the same load is applied to the tire with the same air pressure and that the smaller tire will deform more, building more heat.

I say building more heat on a smaller tire surface = bad.

And what does the smaller tire do you your carry capacity?

[lasitter]

Originally Posted by oil pan 4

Barry has said in the past something to the effect of a smaller contact patch typically causes higher rolling resistance when the same load is applied to the tire with the same air pressure and that the smaller tire will deform more, building more heat.

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 ...

[lasitter]

I spoke with an engineer from Continental / General today and he was able to enlighten me further on this subject.

As I suspected, industry is fighting the labeling requirements tooth and nail and implementation dates have been pushed back.

Second, there is no one size fits all answer because of the way cars and trucks have evolved to the use of completely computer controlled drivetrains. Computerized systems are built and tuned to expect specific tire sizes and inflations so that the traction control, emergency brake assist, ABS, etc., etc., all work as planned.

My truck was built 19 years ago, and doesn't have much more than rear anti-lock brakes, so it is a different animal altogether.

He did offer the opinion, however, that other things being equal, a narrower tread width and smaller contact patch would likely have a lower rolling resistance than a larger tire. Lighter weight tires also tend to produce better fuel economy.

But as the current state of regulation has not forced the company to publish this information for consumers, specific CRR values for specific tires are considered to be trade secrets and cannot be revealed.

[freeside]

One factor is that larger diameter tires can increase vehicle height, thus potentially affecting aerodynamics by being higher off the road. This is one of the easiest ways to get more ground clearance on an off-road vehicle.
Typically smaller contact patch is better for off-road traction, and larger contact patch is better for on-road traction.

How that relates to rolling resistance is beyond me.

[lasitter]

freeside: I've posted some links that explain why I believed this or that about rolling resistance. It is not a cut and dried subject. I just wish that others would post links that support the information they are putting forward, so that we might all have the benefit of it, and adjust our thinking accordingly.

[redneck]

Originally Posted by lasitter

I wish someone would speak to my issue which is one of width vs tire diameter.

The case that I'm looking at involves shrinking the tread width (and approximately the contact patch) by about 14 percent.

I understand that this has completely separate implications (usually bad) for traction, handling, stopping distances, etc., but I am focusing on the fuel economy benefits alone here.

Look here...

Barry's Tire Tech

He goes through all the data and calculations.

>

[lasitter]

Originally Posted by redneck

Barry's Tire Tech>

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.