Tire Selection Wins the Class at the DirtFish RallyCross Nationals
In autocross, I tell novice drivers the biggest gain in speed is likely tire selection (that is, after they master the “look ahead” concept), but RallyCross tire selection may be even more important.
Before I get into tire talk, I want to give a big shout out to our Kansas City region members who participated in the Dirtfish RallyCross National Championships last month at HMP in Topeka, Kansas. The event had 112 drivers participating from 21 states (including Alaska!) in 2 dusty, long, and sweepy courses…of that, KCR had a strong 17 drivers.
When I say participate, I mean PARTICIPATED – hauling in 5 trophies (1 first place, 1 second place, 2 third place and 1 fourth place). Two more drivers—Ryan Redenbaugh and Joshua Mefford were just barely out of the trophies. Ryan was just 4/10ths out of the final trophy spot!
Congratulations to:
- Howie Johnson—Prepared Rear—3rd place
- Mike Coons—Prepared All—2nd place
- Niles Davis—Modified Front—3rd place
- Todd Wicker—Modified All—4th place
You can argue that in RX, only Prepared and Modified classes get to have “tire selection.” After all, they can run any “kind” of tire, any size—from RE-71R’s (which I’ve seen and he had the FTD) to huge lugged mud knobbies. But the stock class has more options than they realize even between the “go to” snow tires. Of course, all tires are course dependent…soft ‘n curvy, slalom intense, sweepy, or tight with turns. And to make it harder to decide, throw in the over-the-day-changing variable of if it’s grass, loose dirt, packed dirt, and/or clay-ish, pure clay, wet/soft, mud, or pure mud, etc. In fact, it’s so hard to choose, often I’ll bring 3-4 full sets of different tires and am not surprised to have to change tires during the day due to changing course conditions.
Although the stock class is limited to a “street tire,” most drivers choose a snow tire or sometimes an all-season tire. Actually, all-seasons are great for packed dirt/clayish or hard clay, given that they are available in many more sizes, usually they are of lower profile, better rubber-to-ground ratio, and provide better stability almost anywhere— slaloms, sharper turns, straights—and maybe less chance of a de-bead than their soft side-wall, snow tire counterparts. However, their tread depth is usually limited to up to 10/32 and they have rounded shoulders for increased traction on dry pavement (more about this later, keep reading).
What snow tires give up on hard pack they gain in almost all other surfaces. However, almost all snow tires have 5 plies in the tread (2 steel, one polyester, one nylon) and a single polyester ply in the side wall. A tall profile and a single ply sidewall makes them feel sloppy in slaloms and offsets and can induce de-bead risks. This is an area where you have a choice:
BLIZZAK’s commonly have two polyester sidewall belts and 11/32 tread depth. They have a high silica compound for softness that makes them grip snow/ice better, but on packed dirt in the summer they can chunk. They offer a run-flat snow tire, which would solve the sidewall issue.
The HANKOOK WINTER iPIKE has a high hardness bead stiffener technology added to increase side wall stiffness and a tread pattern that “mimics that of the paw print of a Siberian Husky” to enhance traction. Good shoulder edge.
Also, look to the GOODYEAR ULTRA GRIP, with more aggressive tread pattern and one of the deepest with a tread depth at 13/32.
The ALTIMAX ARTIC with 12/32 tread depth, is available in quite a few sizes, and a pretty sharp shoulder makes it a good choice, though like most, it’s a single-ply sidewall. These are just some examples and its best to do your own research.
Shoulder…there’s that word again. Out of any snow tire, one aspect that is very important is the shoulder design. A tire’s shoulder is the area where the tread meets the side wall. A “sharp” shoulder edge is common in rally tires. You won’t find sharp shoulders on any AX tire…probably not many in all-season tires and even harder in snow tires. The idea of a sharp shoulder (where the rubber is at its thickest and encounters the highest lateral stress) is it will “cut-in” and bite the dirt in corners and offsets—reducing sliding, and increasing stability which results in trimming off time and, of course, yields a faster run. Imagine if you do that 10 or 12 runs.
Case in point and why tire choice matters:
The last 3 out of 4 years it has rained at the RALLYCROSS Nationals. I’ll be frank…they were mud-fests! If you were in Prepared or Modified and didn’t have dedicated lugged mud tires you had NO chance. The stock folks drove around as fast as if they were still in paddock. This year it was dry. Sounds easy, right? Not so fast…at the beginning of the event almost everyone agreed that aggressive tires would be the one, but as the day(s) and the course(s) wore on, people started changing to less aggressive tires.
I’m in Prepared All (wheel drive) and we ran dead last of the three run groups. When it was time for us to run the course on day 2, it was dry and basically well worn.
However, oddly not bare or hard packed as you would expect and is as usual after 108 cars. The entire course was covered with at least a half inch of loose dirt, with perhaps, 8 to 12 inch piles of “fluff” on the outside of every corner. I had mounted on my car INDYSPORT SG rally tires—a relatively knobby, dedicated rally tire that excels in loose conditions. The SG’s are 205mm wide—kind of wide, but not too wide—and I thought they should dig through loose dirt and bite. If I get into the fluff…well they will dig me out for sure. BUT, you guessed it, they have round(ed) shoulders.
No time to fret, time to go. My first of four runs felt fine. The tires gripped, felt stable, and I stayed out of the fluff, everything was o.k. ‘till I saw all my competitors pretty much matched my time. Between runs, I switched to INDYSPORT F81 gravel tires. They’re lower profile and very wide for a RX tire at 225mm and I feared the risk of “skating” on the half inch loose dirt…not to mention wallowing in the fluff. BUT, they have sharp shoulders. My next three runs were each 3 seconds faster than the first and I could feel the tires biting in the corners and offsets. They got me a win, which supports my point that tire choice (for a
nyone) clearly matters…and sharp shoulders.
See you out there!
Mark Hill,
4-time SCCA Champion, 500+ class AX wins
How much faster would you take the next AX/RX element, if you knew you could not fail?