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Old 10-04-2011, 07:07 AM   #1
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A Bias to Radial Question

Up until two weeks ago, I used bias ply LT tires because that was what AS installed on our rig in 1976. Some of the reports I read on airfourms.com discouraged using radials because they claimed that there was a problem with height. Since we have had to install two complete sets of bias tires in the past three years (because of unusual cupping and wear patterns and one tred separation) I decided to try a set of radials. I was most concerned about the tire height but the 225 75 R15s we have put onto our AS are exactly the same height under load as the 7.00 15s. I think I have also resolved the worry about the radial tire shredding the wheelwell by installing a TPMS system.

The only difference I have noticed is the "wobble" we feel when walking around inside the AS when it is parked. It feels like the AS is sitting on Jello. It is not extreme, its just different. I am presuming it is because of the difference in side wall construction and the unacostomed feel of the radial sidewalls flexing but that is only because I cannot come up with any other explanation. Any guesses as to why the AS seems to wobble with the new radial tires?
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Old 10-04-2011, 10:18 PM   #2
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Don't blame the tire

Cupping and unusual wear patterns in tires would indicate that you have balance ,suspension , or alignment problems ;especially when you are going through tires this fast. Might be a combination of these things. Problems in these areas will wear out any type of tire.
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Old 10-04-2011, 10:41 PM   #3
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All four tires are suffering from cupping at the same time?

That's also making me thing there are suspension issues going on, they simply shouldn't be suffering from those kinds of problems if they are on good rims and balanced properly. Cupping only happens when you have a lot of wheel bounce going on. Not really a bias vs radial issue going on here.

What load rating were you using, and what pressure were they at?

-Hans
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Old 10-05-2011, 12:31 AM   #4
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Quote:
Originally Posted by Eagle & Bear View Post
I cannot come up with any other explanation. Any guesses as to why the AS seems to wobble with the new radial tires?
Hi, air pressure! What is the maximum pressure marked on the tire's sidewall and what have you put in it?
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Old 10-05-2011, 10:27 AM   #5
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Thanks for getting back to me. The axles are Henchen (sp?). The axles were installed with new bearings and shocks 2 1/2 years ago. The hub/wheel/tire assemblies were all balanced together. Although all of the tires showed an unusual wear pattern*, two tires had to be replaced after 2000 miles. After sending in photos of the tire wear pattern* the manufacturer decided that the axles needed to be algned. The axle manufacturer paid for the alignment but did not cover the cost of the two tires. After the axles were aligned, I ran the next set of 7.00 15LTs (with the two new tires) for about 5000 more miles. The tread wear pattern only got worse so I bought another set of tires from Big O. After about 3000 miles this set began to show the same tire wear pattern. Big O replaced that set with 4 new Carlisles. The Carlisles lasted about 12,000 miles but they too exhibited the same unusual tread wear pattern.

This model has two axles. Each axle is rated at 4000#. The combined weight on the axles is 7000#. I have rotatated the tires at 3000 to 4000 mile intervals and kept the tires inflated to 60psi. I monitor the tire pressure with a Dill TPMS. Wheel bearings are packed each year. All of the bearings are adjusted to spec.

*The tread wear pattern: On the last set of Carlisles, there were 5 tread bands on the tires. The two outside bands (1&5) look ok even after 12,000 miles. They do not look new but do show some road wear. If only looking at bands 1&5 I would not replace the tires. The single band in the center (number 3 band) also looks fairly good. Looking at bands 1,3 & 5 it appears that the tire pressure was within an acceptable range. The problem is that bands 2 & 4 showed extreme cupping. One of the tires had developed a small area of tread separation but the rest seemed intact. I did not see any signs of side wall distortion. The other sets of tires showed the same wear pattern but they had to be replaced much earlier than the Carlisles.
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Old 10-05-2011, 10:50 AM   #6
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Strange! I'd measure for yourself the distance from the tongue jack or a center point on the A frame to each front of the axle cutout on the frame and see if these points are the same. This will tell you if the axles were mounted out of square. Even if the wheels are trued side to side, they may be "crabbing" and out of parallel to the frame of the trailer. The reason for the increase wear and cupping on the bias ply vs the radials is probably due to the radials "absorbing" the crabbing better with the softer sidewall construction. The bias ply's are stiffer, creating more friction and cupping action over a shorter time period.

If you get the same wear pattern with these tires, then something is seriously amiss. There's been some cases of the factory putting the cutouts out of alignment when building them... Uwe at area63 and Andy at Inland have both noticed this trend in some of the tandem '70's trailers. That's why it's important to check the cutout's and their squareness at time of axle replacement.

Jello... yes, radial tires are much softer in the sidewalls. You don't mention the load range, but I'm assuming at least D based on the inflation pressure? (You probably would need E, but I digress). I run 65 psi in my tires, and still we still have more deflection than one would notice on the bias ply. Those tires are like rocks compared to radials (and heavier too!). The trailer will like the softer ride (as long as it's not inducing sway, which it shouldn't in a properly hitched trailer).

Marc
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Old 10-05-2011, 11:54 AM   #7
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PS All of the tires have been load range "D". When it stopps raining I will measure from the jack to the axle mounting holes.
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Old 10-05-2011, 02:19 PM   #8
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Any chance maybe you can get somebody to fly chase for you, and watch the wheels and trailer at highway speed?

I know this is going to sound odd, but running hubcaps or something else that may be throwing the balance off but not show on the balancer?

What pressures are in the tires? Should be around 55-50psi for that load rating and trailer weight.

-Hans
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Old 10-05-2011, 05:32 PM   #9
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Hans, The guy who installed the tires put them at 65psi but I lowered them to 60psi because of the weight. The wheels are the original Alcoas and they are in good shape. We have been traveling along the east coast and are now at Cape Cod. Will have to wait until we get to AZ before I can have someone watch the tires while we are rolling.
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Old 10-05-2011, 06:32 PM   #10
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The wobble is from the radials sidewalls, that flex side to side much more than bias.
Bias do absorb vertical bumps better, as softer ride, but only to the limit of a pavement joint.
Your not going to riding back there anyway, so your not going to feel it.
On a car or motorcycle, you can tell.
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