Subscribe Archives Calendar ContactLogging & Sawmilling JournalMadison's Lumber DirectoryAdvertise Media KitHomeForestnet


TimberWest November/December 2013

January/February 2016

Photo taken at the 2015 Oregon Logging

Download the OLC Showguide

Running Big, Running Strong
Jerry DeBriae, owner and founder of Jerry DeBriae Logging Inc. of Cathlamet, Washington, has over five decades of experience tackling just about every challenge a logging contractor will face.

A Road Well Travelled
R D Reeves Construction finds the solutions to stay diversified and local.

Woody Biomass
Stripping fact from fiction

All Hands on Deck
Miller Timber Services and Wildland Firefighting Crews

Tire Evaluation Test

China Amping up Imports
China aims to increase the volume of timber imports from the U.S. despite stagnant economy.

Foresters Face Paradigm Shift 
for Logging Steep Slopes

Technology from New Zealand is set to create a whole new — and safer — way of logging

Gradual Growth for North American Sawmill
Vancouver Urban Timberworks started out modestly and grew into their new Wood-Mizer WM1000


In the News

Association News

Machinery Row

New Products

Guest Column








 CLICK to download a pdf of this article

Tire EvaluationTire Evaluations Test to Get the Best

By Reuben DeBolt, 
Commercial Technical Services 
Manager for Cooper Tire

When it comes to tires, the only way to determine what’s best for you is to test them yourself. That means developing an ongoing tire evaluation program—an extra step that can end up saving you significant dollars.

At Cooper Tire & Rubber Company, when we test new tires for our Roadmaster brand commercial lines, we benchmark against tier 1 and tier 2 brands. Our tests are macro in scale, and we run the same test with multiple fleets. We then compare the data to see how our tires stack up to the competition.

Most fleets do not have the capability or bandwidth to conduct exhaustive testing, yet you can still do a valid evaluation within a fleet and get results that give you confidence in what to expect from selected tire brands.

Steer Tire Evaluation

To conduct an apples-to-apples comparison, you need to keep all unnecessary variables out of the equation, which may not be easy in an operation with some off-highway elements. You should run like-brand and like-model tractors or trucks, and they should be the same age with the same specs. In addition, drivers comparable in skill level should run the trucks. Drivers can impact tire performance in subtle ways. Routes and loads should be identical or as similar as possible.

Once proper “like” equipment is identified, you’ll want to outfit four of the trucks with your new evaluation steer tire and outfit another four with the steer tire you’re currently running. You’ll be doing a head-to-head analysis. There are two reasons to run at least four vehicles:

1. To get a good average wear rate considering any variation in vehicles, routes, or driver.

2. If you lose a tire due to a road hazard, you will still have three vehicles left running.

Tire EvaluationDrive Tire Evaluation

Drive tires are somewhat easier to evaluate. Instead of pitting vehicles against each other, you can use one vehicle to test two brands of tires. The only caveat is that their diameters need to be within 1⁄4 inch of each other. To put that into perspective, you can run one drive tire with 30/32nds of tread depth and have the competing drive tire within plus or minus 4/32nds of that figure. Any larger variances will cause tire scrubbing and inaccurate results.

With this evaluation, you can run two trucks with eight wheel positions. The key is doing an X-pattern (or cross-axle) on the two rear axles. However, don’t run the tires identically on the two trucks as different positions tend to have different wear rates. For example, tires on the trailing axle typically wear faster than the forward axle, and there can be side-to-side differences. Be sure to reverse the X pattern from one evaluation truck to the next truck.

Trailer Tire Evaluation

To evaluate trailer tires, follow the same procedure as for drive tires. In order to effectively track trailer mileages, install hubometers on the trailers being used for the evaluation. Even in a fleet where trailers typically stay with a given tractor, there is a chance that tractor and trailer could get separated from each other, and you would lose track of trailer mileages.

Maintenance Practices

After the tires are mounted, start the evaluation off properly by having each vehicle undergo a total vehicle alignment on the front and rear axles. Once that’s done, you should not have to do a re-alignment during the evaluation period unless you detect irregular wear or have a suspension issue with a vehicle.

It’s important to have the drivers conduct proper pre-and post-trip inspections. That means tire inflation needs to be checked properly — not with a tire thumper. Tires need to be gauged to ensure tire inflation pressure is at the predefined level for the specific position. To make it easy on your drivers, install flow-through valve caps, so they don’t have to spend time taking off valve caps.

What’s more, drivers must keep their eyes (and fingers) on the tires to inspect for wear; a weekly fingertip diagnostic (simply running a hand over the tread) can detect signs of irregular wear. Should toe or feather wear be found, for example, it could mean an alignment problem, suspension problem, or bent tie rod.

If drivers detect early signs of irregular wear, your fleet can fix the underlying problem and continue with the evaluation. Be sure to keep a record of any wear issues and vehicle adjustments.

Tire EvaluationEvaluation Periods

Evaluation units should be checked at intervals that correspond to about 20 percent of typical tire life. The main item to analyze is tread wear, and for this you need a quality tread depth gauge that measures to 1/32nd or 1mm. Electronic gauges with digital readouts are easiest to read. When checking the tire, you should have three points for gauging across the tread face—the outside, middle, and inside of the tread.

Again, a fingertip diagnostic should be conducted as well and any signs of irregular wear reported. Irregular wear could indicate a problem with the vehicle, as mentioned earlier. If the irregular wear is found to be severe, in the drive or trailer position, rotate the tires in cross-axle design (for example, LRI & O to RFI & O). However, don’t rotate side to side.

Since deeper tread squirms, wear rates will be faster at the start of the evaluation when the tread is near full depth, then level out toward the end.

Projecting Tread Wear

After two or three checks, you should have solid wear data on your tires. With this wear data in hand, you can now make projections on how many more miles the tires will last before they’re pulled for retreading. This will give you an apples-to-apples mileage comparison and provide the basis for your first cost-per-mile figure on virgin rubber, once you factor in the purchase price.

Now that you have data on how much tread is worn on your tires, how do you make your calculations?

First, calculate tread wear rate in miles per 1/32nd of tread — miles traveled divided by tread consumed. Tread wear rate = (current mileage – installation mileage)/(original tread depth – current tread depth). Following is an example:

A truck’s current mileage is 124,000 miles and tires were installed at 100,000 miles. The original tread depth was 30/32nds and the current depth is 24/32nds, which means 6/32nds were worn off. The wear rate is 24,000 miles divided by six, thus 4,000 miles per 1/32nd of tread.

Next, calculate projected miles to removal. You’ll need the original tread depth of the tire and the pull tread depth. For drive positions, a typical pull depth might be 4/32nds and in our example, the evaluation drive had 30/32nds of tread. Projected total miles to removal = wear rate x (original tread depth – pull point tread depth). In our example: 4,000 x (30 - 4) = 4,000 x 26 = 104,000 miles.

Provided that your operation is not so severe that you lose many tires to damage, the projections give a good measure of relative performance and a good basis for calculating cost per mile.

Casings and Retreads

With projected mileage in hand, the next step is to understand and get a feel for the tire’s next life — retreading.

If time weren’t a factor, you could run a full-blown evaluation getting true mileage figures on your evaluation tires, plus the number of times the tire could be retreaded. This is cradle-to-grave documentation, which is good to maintain as part of normal operations. But that could mean years to accumulate quantifiable data.

Instead, we recommend two things:

First: Look at the warranty on your evaluation tire and compare it against the tire you’re currently running. The manufacturer should offer a casing warranty in the event that the tire is not retreadable for certain reasons (but not for damage caused by severe operations). The warranties typically range from four to seven years from the date of manufacture, and casing credits range from about $40 to $130 on the first retread. Most manufacturers also offer a reduced casing credit for the second retread. This warranty comparison should give you a feel for how well the manufacturers back their products.

Second: Talk with your tire dealer or retreader and ask about retreadability of the evaluation tires compared to your current tires. The retreader may give you actual rejection rates for the two brands (also known as RAR or “returned as received”), but be sure the information relates to operations similar to yours. Also, ask them what they will pay for a virgin casing of each brand.

Your tire dealer may also be able to refer you to other fleets that are running the tires you are considering. You could ask them what they’re experiencing in retreadability.

Determining Cost-Per-Mile

You have your data, now you can crunch some numbers. The original tire cost-per-mile is a simple calculation. Take the purchase price of your evaluation tire and divide by your projected mileage. As an example, you may be paying $400 for your evaluation drive tire and your projected mileage is 104,000 miles. Divide your cost by the mileage and you come up with $0.003846 per mile ($3.85 per 1,000 miles).

If your current tire costs $600 and is projected to deliver 10 percent more mileage or 114,000 miles, you’d be at $0.005263per mile ($5.26 per 1,000 miles). Even if your evaluation tire didn’t outperform the incumbent tire in mileage, it had a better cost-per-mile, and that’s the metric that’s most important.

If you expect to sell the casing and not retread it for your own use, then there is another step in the calculation to account for the casing re-sale. (This example assumes that 100% of casings are retreadable.) Take your purchase price and subtract the retread casing re-sale value to determine the net cost of the tire, then divide the result by your mileage. For example, if you paid $400 for the tire and expect to sell the casing for $90, your net cost would be $310. If you received 104,000 miles on that drive tire, your cost-per-mile of tread would be $0.002981 ($2.98 per 1,000 miles).

After the Evaluation

If your evaluation tire outperformed the incumbent, as in our example above, do you make a wholesale change in up-fitting your equipment? Our recommendation is to move forward to confirm your findings, but not all the way forward.

If you have followed through properly, you have completed a very important evaluation, which now gives you confidence in the new tire and how it should outperform the incumbent. It won’t take long to see the proof on a grander scale. Begin to purchase 50 percent of the “new” tires for six months—both in replacement and through your truck OE if available—at one year, move forward on full-scale standardization.