Photos by author unless noted

One of the biggest expenses in racing is tires. In rally, we have to deal with not only worn tires but also the occasional puncture or three. Teams chasing the overall win in heavy AWD cars may want fresh tires every service as tires lose their turn-in over the course of a few stages. This presents an opportunity for us lower in the field as we buy used rally tires for a fraction of what they cost new. With a tire groover, grip can be restored to worn gravel tires and they’ll live to race more stages.

Full disclosure: Team Illuminata Motorsports let me use this tire groover in exchange for some #content and an honest review.

Initial Condition

My tires are Pirelli K4 medium compound gravel tires. I purchased six of them from another team after Lake Superior Performance Rally 2015. So far, I had used four of them for three races at ~120 racing miles each. This is one of the rear tires I used at my last race. I was getting immediate oversteer and wheelspin on every corner exit. At the next service, I put newer tires on the front axle and moved the front tires to the rear.

Rear tire used at STPR, LSPR, and SOFR
Less abused K4 with grooves still in the tread blocks

These tires are severely worn. There is no groove left in the center tread blocks and barely any on the outer blocks, which is why the car had a very hard time putting power down.

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The edges are also completely rounded, which reduces lateral grip and turn-in ability. Nobody likes understeer.

With a tire groover, rubber can be removed from the sides of the tire to create an edge and grooves can be added to the center tread blocks to give longitudinal grip again.

Using It

Contents of the basic kit

The kit comes with the knife, two heads, two sets of blades, and some basic instructions. I decided to use the Square #4 blade (7/32") first to do the edges of the tires.

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The #4 head just pops in to the body of the knife and is held with a set screw. I put the blade between the plates on the head and clamped it down to the length a little shorter than the height of the outer tread blocks.

After that, I just plugged it in. There are no controls on the knife at all, just plug and play. After about 10-15 minutes I could feel the heat radiating from the tip and got started. Gloves are highly recommended.

Once I figured out the ideal angle to keep the tip heating the rubber (and could use two hands instead of one to film) I started making good progress. Once I got familiar with it, I could do both sides of a tire in 20 minutes. I would recommend doing the edges on all tires at once since the knife takes a while to cool off and switch blades.

Another bonus: easy to dig objects out of the tire. Didn’t go flat!

To do the interior blocks, I switched to the #2 round blade which is 3/32". I used a shallower depth than what I used for the edges, since I did not want to cause a leak or reduce the integrity of the tread blocks too much.

This was very tedious due to the number and angles of the blocks on the K4. By the the time I was doing my last set, I was doing each tire in approximately 1 hour.

Doing this to six tires took two full evenings. It’s definitely laborious but still cheaper than buying brand new tires.

Below you can see a raw and a finished tire. I suspect that the initial depth of the block grooves was to keep strength in them, and that as rubber is removed the grooves can be cut deeper without significant loss of strength.

Field Testing

I took my freshly grooved tires up to Summer Sno*Drift in Atlanta, Michigan this past weekend. This involved approximately 45 stage miles and 100 transit miles.

The stages were very rocky in sections. Several competitors got flat tires and one lost his whole exhaust. I was standing on the gas often and powersliding around corners while hearing rocks bash the skid plate. I ran the same set of tires I’ve been using for most of three full rallies. I had some issues putting power down due to the loose dirt, but braking and turning grip was vastly improved from their worn state.

Verdict

Front tire after Summer Sno*Drift

The tires performed much better than they had been at my previous race. The braking performance was higher than it had been before cutting, so much so that I was initially braking too early expecting the car to slide a bit. Even just driving at the speed limit down a dirt road, I could feel much better steering response.

Rear tires used at Summer Sno*Drift

The rear tire also held up very well, though as expected there is more wear on the driven axle. I was able to accelerate out of corners much better than before. The car was also very predictable on trail braking and power oversteer.

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I would recommend a tire groover to any budget rally driver. I used the same blades for all six tires, and they did not feel noticeably dull. The only issue I experienced was when trying to switch between the heads. It took some effort to extract them once they were in. Other than that, I’m very happy with my experience using this tire groover.