Dear Tire Doctor,

Our fleet is running Bridgestone M844F wide base radials in the steer position on our 10-wheel grain tanker. Regular steer tires need to be removed at 2/32 or 4/32. Is this the same for wide base radials? The 844F tires float big time on water and snow/slush, so when the tread is down to 4/32, we believe there is not sufficient depth to evacuate water from the footprint.

Right now, the inner edge of the driver's side steer is at 2/32, with 84,818 miles on virgin casings; the passenger's side is 4/32. When they are driven in rainstorms, there is drastic steering loss due to floatation. Why?

Regards, Keith

Dear Keith,

Federal law requires that steer tires be removed when remaining tread depth reaches 4/32˝. This applies to “regular” steer tires as well as “wide base.”

However, regardless of the law, fleets need to make decisions on removal based on individual needs and experience. There are many fleets that will remove even “regular” steer tires with as many as 6/32˝ to 8/32˝ remaining tread depth, based on the needs and experience of their operation.

You are correct that a wide base tire may not evacuate water as efficiently as a “regular” steer tire. This can be due to several reasons: Water is dispersed from a tire’s path in a couple of ways. Much of the water is actually “pushed” out of the tire’s path as the tire makes contact with the road surface.

1.         The wider the tire, the more water it has to push out of the way. Water that is not “pushed” is channeled through the tire’s tread grooves.

2.         Most “over the road” steer tires have four “straight” grooves that allow water to travel a short distance through them, and with low turbulence.

3.         On the other hand, a wide base M844F on/off-highway tire has three grooves instead of four.  Since these types of tires need traction for use on all-wheel drive applications, the grooves are zigzagged with a fairly aggressive pattern. This zigzag pattern is a great help in pulling a vehicle through mud or snow, but less so with water. When evacuating water, the zigzag pattern requires the water travel farther to escape the footprint, which creates turbulence and slows the water’s flow.

4.         And of course, as tires wear out, tread grooves become shallower, and cannot channel as much water volume as a deep groove. On/off-highway tires, such as the M844F, need to be very resistant to cuts, tears and stone drills and require a different rubber compound than “regular” tires. But, one of the trade offs for cut/chip resistance can be wet pavement traction.

You may want to remove steer tires prior to reaching the legal limit to overcome the problems you mention.

Your letter didn’t mention the type or load capacity of your steer axle. If your steer axle is not a driven axle, and has a 20,000 or less gross axle weight capacity, you may want to consider other alternatives to the on/off-highway wide base design, such as a 315/80R22.5 load range L.

We hope this has been helpful to you.

Best regards, Tire Doctor

Dear Tire Doctor,

How can I protect my tires from ultra-violet rays? I remember tires in the 1950s used to crack when exposed to the sun's rays – but today they seem to not be affected by sunlight. Please explain.

Sincerely, John

Dear Tire Doctor,

With air pressure and tire temp sensors installed in aluminum wheels, what kind of temperatures should be observed while driving in 90- to 100-degree temperatures?

What air temperature reading would be too high? I am using the Smart Tire system.

Thank you, Tom

1. Probes inserted into the tire
2. Contained air temperature (which your system uses)
3. Tread (surface) temperature