The CSIs in the Tire Shop #technogeek

The CSIs in the Tire Shop #technogeek

Our guest writer Bob Rutherford is back this week, along with a new hashtag (#technogeek), to talk technical about the CSIs in the Tire Shop.

At the last TMC meeting there was a lively discussion about the shock absorber and the role it plays in vehicle safety. As with most things trucking related, correct answers can be hard to come by. This is one example. The answer is totally dependent on what type of suspension system the shock has been incorporated into. 

From the textbook* on the subject, here are the various categories of suspensions: 

  Leaf spring 

  Equalizer beam:  leaf spring and solid rubber spring 

  Rubber block and torsion bar 

  Air spring:  pneumatic – only or the combination of pneumatic/leaf spring 

*Above from page 814 fifth edition Heavy Duty Truck Systems by Sean Bennett 

This white paper is concerned with only the air spring only system at this time (in bold above). The reason for this is explained in detail on page 826 about the air spring only system: 

“The primary disadvantage of the air spring is a ZERO ability to dampen suspension oscillations. For this reason, they use auxiliary dampening mechanisms such as shock absorbers.” 

Further research needs to be conducted to draw conclusions about the role of the shock in the other suspension systems listed above. One thing that is known for sure, a monoleaf spring design is very dependent on a working shock absorber as opposed to the multi-leaf spring packs have a self-damping capacity. It looks like the monoleaf design is gaining in popularity for the advertised weight savings of up to eighty-five pounds in some applications.

The more leaf springs in a spring pack the more self-damping against suspension oscillation the system will have. This reduces the need for a working shock absorber in this type of system.  

My conclusion is that on the air spring (AKA air ride) system the lowly shock has been crowned the King of Safety and needs to be recognized as such by all concerned with safety. A properly functioning shock can make the difference between a tire having the proper footprint or merely only having the equivalent of a toe print on the pavement. 

From a braking standpoint, how good is the braking system if the tires are rebounding off the pavement because the shock is worn-out? The shock is the key to keeping the tires on the road. 

Based on comments received on my prior published works I know many in the trucking industry think a shock, even on an air ride system, is not a key safety component. I am sure this is because in their mind’s eye they see an 80,000 GVW just bouncing down the interstate without a care in the world. I don’t look at that scenario; I see the last thirty seconds of an accident where a distracted driver cuts off the big rig and the driver is jamming on the brakes and turning the steering wheel with all the might the driver can muster. At that exact moment, the shocks had better be keeping the biggest and baddest tire footprint on the highway. 

So why would a truck driver drive on bad shocks? As stated, when I quoted the list of suspension systems, if the truck driver and mechanics were used to a vehicle with a leaf spring suspension, maybe worn shocks were never an issue; and that could be a very big “were never an issue.” 

In my research I have found that many tire dealers are not in the shock business and actually benefit in more tire sales when a customer brings back a cupping tire that is not covered under warranty because of a bad shock, other suspension problem, or an out-of-balance wheel end assembly. 

I have found those tire shops that see the future are using the ABC’S system (explained below) for wheel end management and so are fighting an uphill battle. 

Many drivers see a conversation in a tire shop with a CSI tone as the tire shop attempting to pull off a dreaded up sell of an unnecessary shock absorber just to pad the bill. 

Explaining the ABC’S and the CSI conversational tone with the truck owner 

It should be no mystery to anyone who has watched TV during this decade that CSI is short for Crime Scene Investigators. The ABC’S will be explained next. 

Michelin Tire Company has been distributing tire wear analysis charts to tire shops for years. The charts are titled “The Usual Suspects.”  I assume (and hope to verify someday) that someone in the Michelin marketing department saw the relationship between a tire that is dead on arrival (DOA) that like the TV show, there are always certain suspects that the death of the tire can be pinned on. 

The premise of the movie is that every time there was a crime they would round up the usual suspects, perform a crime scene investigation and figure out who done it. 

It is to the advantage of tire manufacturers to showcase the usual suspects as a troubleshooting tool for several reasons. First, they don’t have to warrant the tire and second, they might solve the mystery and have a happy customer in the future. 

I named the usual suspects the ABC’S gang. It is up to someone in the tire shop to look at the tire corpse and figure out who done it. The simple version of the gang members: 

  • Air pressure is not correct. 
    • Alignment issues 
    • Balance issues 
    • Bearing issues 
  • Centering/mounting issues 
    • Shocks & suspension issues 

It is my belief that every tire shop should have a whiteboard near the usual suspects’ chart and use it to explain what happened to the tire. 

I think every tire shop should have a whiteboard to help communicate with the driver about the wheel end system. The whiteboard could start out like the illustration, then be erased, to explain the Usual Suspects chart as it relates to the tire that arrived dead on arrival (DOA). 

As far as explaining that a shock needs to be replaced for safety reasons, the following steps need to be considered. 

First – Know how to identify an air ride suspension that needs good shocks. 

Second – Every new tire that was replaced because it was worn-out should have a new shock, again, depending on the suspension system.

Third – Further research into the cupping issue needs to be done. I think this can be a big tipoff that the shock was not replaced or there is some other unsafe condition, such as an out-of-balance wheel end that is not allowing the tire to have the proper footprint as it rotates down the highway. 

Fourth – I believe once the word is out, most tire shops will be interested in implementing the ABC’S and CSI system for their customers; the problem will solve itself.

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