Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post

slowmover · 06-13-2010, 11:55 PM

My thinking is in line with what I have read CapriRacer post.

My experience, beyond personal, has been with big trucks where the dollars are huge (fleet) and one of the most often sighted supplier reps on the lot is the guy from the tire company. In example: a new front "steer" tire is holding a max rated 9,000-lbs. Each. Costing over $400. Each. Doesn't break in until past 35,000 miles, BUT, the truck will go through three/fours sets per year. Multiply that by dozens or even thousands of trucks.

Now, just down the road was a competitor who ran the same equipment and the same loads. But the tire pressures required were different. Same tire suppliers. Same rep, even. I did not run into anyone who could explain that satisfactorily. Big bucks, full-time accredited rep, a major line item on a fleet budget, etc, . . . .

Here is some info I pulled for some notes awhile back:

(Article) OVERDRIVE Magazine 12/2008

"Matching Tire Pressure to Load" (John Baxter)

The tire’s contact patch should be as large as possible while keeping a healthy amount of pressure and maintaining even contact between all the areas of the patch and the road. That means adjustment to reach “the optimal pressure for the load,” rather than inflating the tire to the same cold pressure all the time, says Doug Jones, customer engineering support manager at Michelin North America.

http://www.overdriveonline.com/match...ssure-to-load/

---------------------------------------------------------------------------------------------------

(Article) BULK TRANSPORTER NEWS 9/2008

"Five tips to control your tire costs and improve vehicle performance, safety

With tires ranked as the second highest operating cost after fuel, a solid tire maintenance program can help reap solid dividends. Knowing the proper inflation level for your truck tires is crucial. TMC Recommended Practice (RP) 235 states the following determines the correct air pressure for a given load:

• Tire size and load rating
• Weight carried on each axle
• Number of tires on each axle
• Maximum speed the vehicle travels during its operation

http://bulktransporter.com/fleet/tru..._control_0908/

----------------------------------------------------------------------------------------------------

(Website) Barry's Tire Tech

. . I hope you noticed how flat the wear index is for the radial tire. I interpret this to mean that conducting a "chalk test" is not a good way to determine what the best pressure is for wear.

http://www.barrystiretech.com/sae800087synopsis.html

(One of the screwups in the Ford Explorer/Firestone fiasco was that the tire pressure spec'd by Ford left no reserve. 20% is recommended.)

----------------------------------------------------------------------------------------------------

(.pdf) FIRESTONE MEDIUM & LIGHT TRUCK DATA BOOK

(see pages 52 for truck fuel economy discussion; and page 64 (+/-) for load /pressure tables.) (Go to the man'f'r of your tires, download and copy).

http://www.trucktires.com/firestone/...ckDataBook.pdf

My personal experience is pretty simple: I don't want to upset the balance of ride and long life where the factory (since the era of radial tires pretty much) has established a guideline for empty and loaded conditions. Experimentation is limited, IMO, as long life and best braking/handling are paramount.

As with another post above I'm not so sure some of you guys understand that overinflation exacts a toll on the car that is, truly, unacceptable. Have you priced a front end rebuild? Is it understood that the entire structure is deleteriously affected, and that this takes place in every system? Your air-conditioning is leaking, and we have to remove the dashboard now?

Best handling, best braking, best tire life are probably within a very short range of what is recommended. I wouldn't go below the vehicle manufacturer recommendations (although the table allows it on mine, and, yes, I have tried it to no benefit), and going above it doesn't work so well either when load & pressure aren't a good match.

I've read/heard that 75% of sidewall maximum is a good place to start. Same with keeping rim width and tire tread width a match. It has worked for me on cars . . and until recently I have not ever been without a car at least twenty years old. And been the one to rebuild them. 200K on several of them as daily drivers. Where everything worked. I hate electrical reliability problems. Go ask a hardcore 4-wheeler about his trail rig. Or, why cop cars get retired with not so many miles. Vehicles taking hard hits to suspension, etc, wear out faster.

Even the best tires are cheap compared to suspension, steering, body bushings, unibody cracks, HVAC systems, electrical shorts and the rest that abused vehicles undergo.

So, the question is, how much money from marginally higher fuel mileage be needed for premature repairs? Permanently lessened reliability? I can't see a match, here. The cheapest car, the most economical car, is the one that lasts the longest for the least amount of money.

I shot a question or two to Barry of the Tire Tech site a few years ago and he was good to reply. I don't remember the entirety of it, but tire pressure and temperature relationships can be examined to dial in a combination past the Load Tables after a certain time/distance in steady-state driving. But, not much. You'll also need to put the car on a certified scale to find out weight per axle. And, if you're slick, use same to find weight per wheel. Published shipping weight is meaningless.

I regularly use an infrared laser thermometer on truck and trailer tires (as well as hubs and brakes) and I just look for consistency. Same with using a tread depth gauge. I rotate based on wear, mainly. I have handful of scale tickets showing the truck (and trailer) under a variety of loaded/unloaded conditions. The notes include various tire pressures.

On the current pickup it looks as though I'll be buying the second set of replacement tires at about a quarter-million miles. Stock size & brand. Factory pressures.

Where would increasing the pressure and upsetting an engineered "balance" benefit me?

.

06-13-2010, 11:55 PM	#47 (permalink)
slowmover Banned Join Date: Oct 2009 Location: Fort Worth, Texas Posts: 2,442 2004 CTD - '04 DODGE RAM 2500 SLT Team Cummins 90 day: 19.36 mpg (US) Thanks: 1,422 Thanked 737 Times in 557 Posts	My thinking is in line with what I have read CapriRacer post. My experience, beyond personal, has been with big trucks where the dollars are huge (fleet) and one of the most often sighted supplier reps on the lot is the guy from the tire company. In example: a new front "steer" tire is holding a max rated 9,000-lbs. Each. Costing over $400. Each. Doesn't break in until past 35,000 miles, BUT, the truck will go through three/fours sets per year. Multiply that by dozens or even thousands of trucks. Now, just down the road was a competitor who ran the same equipment and the same loads. But the tire pressures required were different. Same tire suppliers. Same rep, even. I did not run into anyone who could explain that satisfactorily. Big bucks, full-time accredited rep, a major line item on a fleet budget, etc, . . . . Here is some info I pulled for some notes awhile back: (Article) OVERDRIVE Magazine 12/2008 "Matching Tire Pressure to Load" (John Baxter) The tire’s contact patch should be as large as possible while keeping a healthy amount of pressure and maintaining even contact between all the areas of the patch and the road. That means adjustment to reach “the optimal pressure for the load,” rather than inflating the tire to the same cold pressure all the time, says Doug Jones, customer engineering support manager at Michelin North America. http://www.overdriveonline.com/match...ssure-to-load/ --------------------------------------------------------------------------------------------------- (Article) BULK TRANSPORTER NEWS 9/2008 "Five tips to control your tire costs and improve vehicle performance, safety With tires ranked as the second highest operating cost after fuel, a solid tire maintenance program can help reap solid dividends. Knowing the proper inflation level for your truck tires is crucial. TMC Recommended Practice (RP) 235 states the following determines the correct air pressure for a given load: • Tire size and load rating • Weight carried on each axle • Number of tires on each axle • Maximum speed the vehicle travels during its operation http://bulktransporter.com/fleet/tru..._control_0908/ ---------------------------------------------------------------------------------------------------- (Website) Barry's Tire Tech . . I hope you noticed how flat the wear index is for the radial tire. I interpret this to mean that conducting a "chalk test" is not a good way to determine what the best pressure is for wear. http://www.barrystiretech.com/sae800087synopsis.html (One of the screwups in the Ford Explorer/Firestone fiasco was that the tire pressure spec'd by Ford left no reserve. 20% is recommended.) ---------------------------------------------------------------------------------------------------- (.pdf) FIRESTONE MEDIUM & LIGHT TRUCK DATA BOOK (see pages 52 for truck fuel economy discussion; and page 64 (+/-) for load /pressure tables.) (Go to the man'f'r of your tires, download and copy). http://www.trucktires.com/firestone/...ckDataBook.pdf My personal experience is pretty simple: I don't want to upset the balance of ride and long life where the factory (since the era of radial tires pretty much) has established a guideline for empty and loaded conditions. Experimentation is limited, IMO, as long life and best braking/handling are paramount. As with another post above I'm not so sure some of you guys understand that overinflation exacts a toll on the car that is, truly, unacceptable. Have you priced a front end rebuild? Is it understood that the entire structure is deleteriously affected, and that this takes place in every system? Your air-conditioning is leaking, and we have to remove the dashboard now? Best handling, best braking, best tire life are probably within a very short range of what is recommended. I wouldn't go below the vehicle manufacturer recommendations (although the table allows it on mine, and, yes, I have tried it to no benefit), and going above it doesn't work so well either when load & pressure aren't a good match. I've read/heard that 75% of sidewall maximum is a good place to start. Same with keeping rim width and tire tread width a match. It has worked for me on cars . . and until recently I have not ever been without a car at least twenty years old. And been the one to rebuild them. 200K on several of them as daily drivers. Where everything worked. I hate electrical reliability problems. Go ask a hardcore 4-wheeler about his trail rig. Or, why cop cars get retired with not so many miles. Vehicles taking hard hits to suspension, etc, wear out faster. Even the best tires are cheap compared to suspension, steering, body bushings, unibody cracks, HVAC systems, electrical shorts and the rest that abused vehicles undergo. So, the question is, how much money from marginally higher fuel mileage be needed for premature repairs? Permanently lessened reliability? I can't see a match, here. The cheapest car, the most economical car, is the one that lasts the longest for the least amount of money. I shot a question or two to Barry of the Tire Tech site a few years ago and he was good to reply. I don't remember the entirety of it, but tire pressure and temperature relationships can be examined to dial in a combination past the Load Tables after a certain time/distance in steady-state driving. But, not much. You'll also need to put the car on a certified scale to find out weight per axle. And, if you're slick, use same to find weight per wheel. Published shipping weight is meaningless. I regularly use an infrared laser thermometer on truck and trailer tires (as well as hubs and brakes) and I just look for consistency. Same with using a tread depth gauge. I rotate based on wear, mainly. I have handful of scale tickets showing the truck (and trailer) under a variety of loaded/unloaded conditions. The notes include various tire pressures. On the current pickup it looks as though I'll be buying the second set of replacement tires at about a quarter-million miles. Stock size & brand. Factory pressures. Where would increasing the pressure and upsetting an engineered "balance" benefit me? . Last edited by slowmover; 06-14-2010 at 12:40 AM..