If you look on the sidewall of most medium commercial truck tires you will find the word “regroovable.” Those new to the trucking business have probably never heard the term before, while those of us who've been around for 20 years or so have at least one story about how regrooving a tire went wrong. For those of you still in the dark, regrooving is the practice of carving out the rubber in the grooves of a tire to create additional tread depth so the tire with 2/32nds of tread magically gets 4/32nds or more.
DOT still has regulations for regrooving on the books. According to 49 CFR 569.3 (c): “Regroovable tire means a tire, either original or retread, designed and constructed with sufficient tread material to permit renewal of the tread pattern in a manner which conforms to this part.” Part 569.7 says: “After regrooving, cord material below the grooves shall have a protective covering of tread material at least 3/32nd-in. thick.”
When this process was first implemented, bias ply tires on multi-piece rims dominated the market. A lot has changed since then. Retreading truck tires was not a common practice for fleets, so it was logical to carve out a few more 32nds of tread once the tire was worn. Tread patterns were relatively simple, so if you could color within the lines you could probably operate a regrooving iron.
Although it's still fairly common in bus fleets, regrooving has basically vanished from the landscape of today's standard fleet operations for obvious reasons. Most importantly, once a tire is regrooved, its chances of being retreaded are significantly reduced. I won't even go into the challenges of preserving the 3/32-inch without the proper equipment. So fleets that want to save money by retreading their own casings rarely regroove their tires.
As it stands right now, “regroovable” really only means that the casing is probably retreadable. In other words, it's designed and constructed in a manner that has enough tread material between the bottom of the groove and the top belt to make it a prime candidate for retreading. Manufacturers are required by DOT to mark it “regroovable,” even though they don't encourage or endorse the practice for most of their tires.
You may be wondering why I decided to dedicate this valuable space to a subject few people have heard of or even care about. The reason is that regrooving may make a comeback in an environment where tire manufacturing costs continue to rise and fleets are forced to squeeze every last 32nd out of every tire. Since fleets and tire manufacturers have different age requirements, the five-year-old worn out retread that would normally head to the scrap pile may actually find new life after a visit to the regroover.
In addition, the ultra-low-profile wide-base tire that may not be a good candidate for retreading might see a few extra miles after a little regrooving.
And finally, if the giant chaos butterfly flaps its wings and does something crazy to the rubber farms in Southeast Asia, fleets will do almost anything to keep a tire in service a little longer.
If you don't believe me, think about this: A shortage of new tires had led the earthmover industry to dig giant tires out of playgrounds so they can be repaired and returned to service.