A Shocking Controversy

Why do we need vehicle shock absorbers?  From the monroe.com website:

In their simplest form, shock absorbers are hydraulic (oil) pump like devices that help to control the impact and rebound movement of your vehicle’s springs and suspension. Along with smoothening out bumps and vibrations, the key role of the shock absorber is to ensure that the vehicle’s tyres remain in contact with the road surface at all times, which ensures the safest control and braking response from your car.

What do shock absorbers do?

Essentially, shock absorbers do two things. Apart from controlling the movement of springs and suspension, shock absorbers also keep your tyres in contact with the ground at all times. At rest or in motion, the bottom surface of your tyres is the only part of your vehicle in contact with the road. Any time that a tyre’s contact with the ground is broken or reduced, your ability to drive, steer and brake is severely compromised.

Since I’m talking about travel trailers/fifth wheels, the only action that applies would be keeping the tires on the road while underway, with an emphasis during braking.  It’s interesting to note not all trailers have shock-absorbers.  I can’t ever recall seeing a leaf spring configuration with shocks.  However, all of the Airstream trailers come factory equipped with shock-absorbers on their Dexter Torflex axles.  Incidentally, there is no requirement for shocks mentioned in the Dexter Axle “Applications Manual”.

Enter: controversy.

Here’s my experience.  It’s a little bit involved, so bear with me.

Our 2008 30′ Slide-out Classic Limited came equipped with GoodYear Marathon ST tires on 15″ aluminum rims.  After dealing with multiple tread separation failures (two of them catastrophic; you can read about all that here), I swapped them out in April 2012 for Michelin LTX tires, on 16″ aluminum rims (there were no tires on 15″ rims that meet load requirements- I find it interesting that 15″ ST tires somehow do meet load rating… hmm).  Note, I never experienced any strange wear or ‘notching’ on the ST tires; but then, each ST tire never lasted more than 5-6,000 miles, so there was hardly any wear on them, at all.  Also something else to note, I never rotate trailer tires.  There’s no reason for it with a properly balanced rig, and additionally it would only mask potential running gear or loading problems.

After about two years and roughly 16,000 miles on the larger LTX tires, I started to notice very distinctive ‘feathering’ on the tread.  It resembled the type of wear when a vehicle has bad alignment.  Fast forward about 10,000 miles, and the treads were not just heavily feathered but had chunks out of them, or what I call ‘notching’.

Serious feathering and ‘chunks’ missing

The Michelin LTX’s had almost 30,000 miles and 63 months when the curbside front tire blew out on a Tennessee freeway.  It wasn’t a ‘tread separation’ like the ST tires- that is, it wasn’t a strip of tread coming off the tire, but more like a ‘blow-out’ at a specific point.

Getting it replaced, I had two tire guys from different shops, tell me it looked exactly like what bad shocks will do to a tire at highway speed.  Apparently, bad shocks will allow the tire to ‘bounce’ along causing ‘chunks’ to be torn off on the roadway, especially under braking.

I suppose the first thing I should do is check the axle alignment.  That might explain the strange wear, but not the ‘chunking’.  Or maybe I should just replace the other three and watch what they do.  Five years is pushing RV tire service life anyhow.

Your Mileage May Vary…

See you down the road.


Wheel Upgrade

Just over four years, and approximately 30,000 miles, we’ve gone through FIVE Goodyear Marathon ST tires.  Two catastrophic failures, that included massive trailer damage, one tread separation, and two large sidewall bulges.

one year old

For all you backseat drivers: this is under extraordinary scrutiny and care, as recommended by Goodyear. 

Catastrophic failure outside Jacksonville, FL


◊ TPMS to monitor proper PSI at all times.  

◊ Regular visits to CAT scale to insure proper loading.

◊ Never exceed the 65mph speed rating of an ST tire.

◊ Tucked each tire in at night with a blanky and bedtime story.

This was attached at one end, causing significant ($12,000+) trailer damage

I should note: one of the GYM’s was replaced in March 2009 with a MAXXIS 8008 ‘E’.  Had no problems with that one, after three years and 16,000 miles…  I should also note, Goodyear stepped up and paid the deductible on each separate claim, and also reimbursed me for the cost of the tires.

Tread separation

Regardless, I wanted the peace of mind knowing the trailer was outfitted with more substantial rubber- not these “ST” classified donuts… and the only way to do that was upgrade the rims from 15” to 16”, because tires with an adequate load rating are not available in 15″ size.  With a 10,000lb GVWR, I need a tire with a minimum 2,500lb load rating. 

Tredit T02, Michelin 225/75R16 LTX MS

Enter Michelin LTX load range ‘E’.  Low rolling resistance, all season traction, 2,680lbs max load (compared to 2,540lbs max on the Goodyear Marathon ST’s).  According to specifications, it’s 1.1″ larger in diameter than the OEM 225/75R15 ST’s, but there appears to be plenty of clearance.

OEM on the left, 16" upgrade on the right

As confident as I am with this new rubber, I’ve still got the TPMS installed…

We've got a lot riding on our tires...