Any tips for grooving dirt tires?

[dirtmodwrench]

I'm planning to build a few 60's and 70's sprint cars that ran on dirt tracks (Opperman, Snellbaker, Nace).  I've been looking for suitable rear tires and haven't found any yet.  I've ordered the correct knock-off wheels from Larry at Big Donkey, but the tires he sent me are resin versions of the Revell sprint kit tires and are too wide for that period of time.  Today I took a rear tire (slick, no tread) from a Tobias modified kit and sliced and diced to narrow it down and am actually happy with the result.  It's about 1 5/16 tall and 7/16 wide, so it looks right to me for a right rear sprint tire.  I then took a shot at adding grooves to it.  I measured and marked three grooves around the circumference, then started the grooving process with a fresh #11 X-Acto blade (used both the front and backside of the blade). Once I had a groove started, I switched to a razor saw blade. Once those were done, I added some diagonal grooves. They weren't cutting deep enough, so I tried a fiberglass cut-off wheel in a Dremel. That tended to melt the tire plastic as it cut the groove.  The end result looked messy and uneven. 

Anybody got any tricks that they have used to cut realistic looking grooves?  I'm open to any suggestions you want to toss my way!

[Brian Conn]

....Any drag slicks (60's - 70's) would have been siped by hand so the pattern would not have been symmetrically correct anyway.  If your going the purpose built dirt tire route I have had decent  luck with holding the tire in place...I use a bench vice...and making the cuts with a regular length hack saw blade.  It doesn't take much to make the cuts.  I then sand the surface down to smooth the surface.
     
     Aftermarket , if you can find exactly what your looking for, is by far the easiest way. 

[dirtmodwrench]

Brian - Thanks for the hacksaw blade idea, I'll give that a try.  Back in the day, I hand-grooved a boat load of M&H Racemasters that we ran on the rear of our dirt mod.  The car owner was very particular about everything, so I can attest to the fact that the grooves had to be cut very precisely and were symmetrical!  I recall using a template we rigged up from a piece of scrap plywood so I could replicate the pattern over and over....perhaps that is the source on my anal-retentive desire to make these models look realistic

David - The DT-12 will be my likely default choice for a RR if I can't get a pattern cut in the Tobias kit tires.  Perhaps the DT-6 will be the LR.  I have some of the DT-2's earmarked for modified builds that I'll find and see how they look too.

[Brian Conn]

...................  I recall using a template we rigged up from a piece of scrap plywood so I could replicate the pattern over and over..........

   
Heck, all I can remember,...its been a minute ..., is using a Yellow grease pen on Goodyear or was it Firestone drag slicks to mark where to cut with the grooving iron....wasn't the prettiest , but it seemed to work.

   Those tires that David spoke of look absolutely great...I used them on my '59 Galaxie build     http://www.shorttrackmodels.com/index.php?topic=993.0

[sentsat71]

I remember someone posting on IIRC Fred's site, but when I went back to look for it, before the FRW site faced away....
The party used wooed pieces, a sturdy piece that cold be clamped in a vise, a round dowel that fit the hole in the tires and an angle cut somewhere above the dowel that was wide enough for the hand saw blade that was used to cut the diagonal cross cuts in the tire.....Seem to remember a mark of some kind that would allow one to evenly space the cuts. not sure how the straight cuts along the circumference of the tire....

[Brian Conn]

....The round wooden dowel was 5/8" dia. clamped in a vise

I remember someone posting on IIRC Fred's site, but when I went back to look for it, before the FRW site faced away....
The party used wooed pieces, a sturdy piece that cold be clamped in a vise, a round dowel that fit the hole in the tires and an angle cut somewhere above the dowel that was wide enough for the hand saw blade that was used to cut the diagonal cross cuts in the tire.....Seem to remember a mark of some kind that would allow one to evenly space the cuts. not sure how the straight cuts along the circumference of the tire....

...The wooden dowel was 5/8" clamped in a vise....the marks where made with a very thin colored pen as measured with a measuring tape.

[dirtmodwrench]

I messed around a bit tonight with another tire and tried making light scribe lines with a dental pick and masking tape template, then trying to deepen them with a hacksaw blade.  Still looked pretty awful.  I'll take David's advise and scope out resin options and try cutting those.  I've ordered tires from Big Donkey previously, but not Ron Coons so I'll check out his site.  Are there other resin casters making asphalt or dirt tires?


Brian - Thanks for the link to your Galaxie build

[Bob P.]

Big Donkey resin should have tires for that era already grooved, just give Larry a phone call and he will be glad to help you pick the proper tires.

Bob

[sentsat71]

I have a DT-2 & DT-6 from Big Donkey.....and the DT-2 looks like it would be the RR tire you would be looking for....

[Olderndirt]

When I was about 12, or 13, I bothered the local dirt track star with a million questions. His cure for my nonstop questions, was to put me to work on something noisy enough that I couldn’t chatter over it. He built a “wobble washer” for an old Skil saw and put me to work grooving his tires. He had specific patterns for every tire on the car. To this day I wonder if some of those tires needed grooving, or he just needed a break from all the questions. He’s long gone now, so I guess I’ll never get that question answered.

  Olderndirt

[Lefturns75]

I have been around a lot of Redneck Racers in my time but never saw that.  Sounds like a good start for an amputation.  Did he give you some Grenades to take apart or a plugged in electric fan to wash in the sink?  Sounds like a real Pal. 

[Olderndirt]

I never said it was a gear drive skillsaw, those came after all you young puppies came along. And as for the danger of a kid that young running it, as a farm boy I started driving tractor when I was seven, and it was a track layer, not a wheel tractor. My parents work us on the farm as soon as we were old enough to start causing trouble.

  Olderndirt

[Olderndirt]

Stop and think about using a skilsaw to cut tire grooves. It’s depth adjustable, pretty easy to keep going in a straight line, and leaves nice sharp corners on the new tread, unlike the hot irons that are hard to control, and leave rounded edges. There’s a reason this guy was a top competitor, even though he was always strapped for cash. He raced with his head instead of his wallet.

  Olderndirt

[Marty W]

I got it. Why not just use a big ole chain saw? That will put some nice, fat grooves in that sucker!

[Alan Barton]

Just spotted this.  I have a jig much as described, a block of wood with a piece of tube through it and a saw cut at the desired angle to guide my junior hacksaw, much like a mitre box.

One idea I read a long time ago was to run a bolt through the tyre and with a nut and washer on either side of the tyre.  Do the two nuts up against each other to clamp the tyre and get it the tread to balloon somewhat.  Then when you cut with your saw, you get a nice deep groove in the face of the tyre without cutting way down the side wall.  Sounded good to me!

Cheers
Alan