Imagine you just durometered a D30A and an A40 back to back. Cold, same temperature, same spot on the tire. They punch within five points of each other. You think you're looking at a simple soft-to-hard progression. You are not. Those two tires will drive nothing alike, and if you bolt the wrong one on without changing your chassis window, you are in for a long night. This is Hunter's Column Lab. I'm HUNTER, with Hast on the call. Tonight we are going full Black Book on Hoosier dirt kart rubber — the structural break between the D-series floppy family and the stiff A40 and FK, the treaded outlaw sizes including that new D10AS that dropped in early 2025, prep by family so you stop killing tires with the wrong chemistry, and the Friday night band-aid rules for when someone hands you a one-off Hoosier twelve minutes before your heat. Also in the quick-hits, Michael Kofoid just banked his sixth World of Outlaws win of 2026 at Huset's Speedway and the series rolls into River Cities tonight. This is Hunter's Column Lab. We read the column so you don't have to skim the data boxes.
HUNTER Column thirty-seven is live at racer dot wiki and it is the column I have wanted to write for a while. Hoosier kart tires get lumped together as one brand with one soft-to-hard ladder, and that framing is wrong in a way that costs racers grip and chassis feel every single weekend. The headline take: there is a structural break between D30A and A40 that splits the Hoosier kart line into two completely different tire families, and most online references — including the ones that pretend to be comprehensive — completely miss it. We also have the treaded outlaw line in this one, the D10AS soft treaded rear from early 2025, and a full Friday-night one-off protocol. That is the main column.
HAST Right, and the timing on this is good because SoCal Dirt Karters just ran Round Three of their championship series at Perris Raceway Flat Track on May ninth, which is a flat-track momentum circuit where tire family selection is genuinely a race-deciding variable. Parker Drottz has been the junior driver to watch early in that nine-race series, and the Outlaw class there is showing some interesting matchups between open-displacement karts and the smaller two-fifty packages. Tire science is not abstract at a track like Perris — you feel the family choice in the first lap of the feature.
HUNTER Hoosier Racing Tire makes kart rubber in two completely separate families that share a logo and nothing else. One family has a floppy, spongy sidewall that behaves like a Burris. The other has a stiff, thick-shouldered carcass that behaves like a Vega or Maxxis. Pick the wrong family for your track and you will fight the carcass all night long — compound won't save you. Open a Hoosier kart tire catalog and you see a ladder of compound codes — D10A, D20A, D30A, A40, FK, 50. Looks like a simple soft-to-hard progression. It is not. There is a structural break between D30A and A40 that changes everything about how the tire rolls, flexes, grows under heat, and responds to prep. Miss that break and you are tuning blind.
HAST The D-series — D10A, D20A, D30A — is Family A. Soft, floppy sidewall. Low spring rate. The carcass deflects under load like a Burris SS-series tire. It absorbs surface irregularity. It rolls onto the shoulder progressively. It grows circumference under heat more than you expect. Each step up that ladder adds compound hardness and a modest bump in sidewall stiffness, but the fundamental carcass architecture stays spongy. These tires accept prep internally and externally through paths that mirror the Burris approach. Then you hit the break. A40, FK, and 50 are Family B — high spring rate, thick shoulder, stiff. The carcass resists deflection and holds its shape under side-load like a Vega Yellow or Maxxis Pink. It does not absorb bumps — it transmits them. It grows less circumference per degree of temperature rise.
HUNTER The practical consequence of that break is blunt. A D30A and an A40 can punch within five points of each other on a cold durometer after prep, and they will drive nothing alike. The D30A will roll and soak up surface with a mushy contact patch. The A40 will skate on top of it and demand a completely different chassis window. Same duro. Different tire. Different car. That is the entire column in three sentences. Now here is the treaded line — and this is not a footnote. On a fifth-mile or larger track, the treaded tire gives you a specific roll-out target that slicks in the same compound family cannot match, plus carcass durability over a twenty-lap feature on an abrasive surface where a slick D-series might cord. The D10AS twelve-point-oh by nine-point-oh-by-six treaded rear released in early twenty-twenty-five gave outlaw and cage kart racers something they did not have before: a soft floppy-sidewall compound in a treaded carcass. Before that, if you wanted treaded, you were in A40T or A50T territory — stiff family only.
HAST The D10AS also changes your stagger math because it is taller than the eleven-by-nine slick D10A by nearly a full inch of roll-out. Which brings us to the prep-by-family section, and this is where more Hoosier tires get killed than anywhere else. A racer reads a prep recipe online, applies it to whatever Hoosier is on the kart, and wonders why one compound thrived and another turned to grease. D-series prep — internal and external paths work. The soft sidewall and porous carcass absorb prep chemicals at a rate comparable to Burris SS-series tires. Crosshatch scuff with thirty-six grit to remove glaze, Trac Tac SAA Grape or a wet-track formulation, wrapped and soaked forty-eight to seventy-two hours pre-race. Pressure target on a wet or tacky surface: six psi right side, five psi left side. A40 and FK prep is the opposite direction — you are prepping down from fifty-five to sixty-two cold, like a Vega Yellow or Maxxis Pink. The dense carcass absorbs less volume of chemical per unit time. Seventy-two hours minimum for meaningful penetration on an FK. Do not use the same internal prep recipe you use on D-series. A Burris-style pour-and-roll inside an A40 will not penetrate — you get a sloshing puddle of wasted chemical and the tire blisters in the contact patch because the liquid trapped inside overheats against the tread rather than absorbing into the structure. And batch variation is real — always durometer all four tires on the same day, at the same ambient temperature, at the same spot on each tire. If one tire in a set punches three or more points different from the other three, flag it. That tire will prep differently and grow differently under heat.
HUNTER The Friday night band-aid protocol is the section I am most proud of in Column thirty-seven, because this is the real world. It is Friday night. Someone handed you a D30A right rear because your Maxxis corded in hot laps. You have twelve minutes. The rules are clear: never mix Family A and Family B left-to-right on the same axle without expecting a handling earthquake. A D20A left rear and an FK right rear have a sidewall spring rate difference of roughly forty to fifty percent. That is not a pressure adjustment — that is a chassis tuning problem. The kart will jack weight to the stiff side and you will chase it all night.
HAST Okay but I am going to push on that, because I have seen programs run mismatched families left-to-right and get away with it for a heat race. The argument I hear in the pits is that you just over-correct your crossweight to compensate for the stiff side and call it a night. Are you really saying that is never survivable, or are you saying it is not a tuning strategy worth defending? Because those are two different claims.
HUNTER Survivable for a heat race and competitive for a feature are not the same thing. The column is very specific: if you must do this, you are surviving, not competing. The crossweight band-aid will get you to the checkered flag without spinning out, but the stiff-side carcass is still transmitting every bump differently than the floppy left rear is absorbing it, and your kart is sending you two different messages from the rear axle simultaneously. You cannot tune out a forty-percent spring rate mismatch with crossweight adjustment — you can mask it enough to survive. The correct protocol is to match cold roll-out within a quarter to a half inch within the same family, run the Hoosier pressure window on that corner and the Maxxis pressure window on the other corner — not an average — and recheck hot pressures independently after three laps. They will diverge.
HAST That is fair and that is the honest answer. Survive the heat, score your points, and sort the tire problem before the feature. That is the actual takeaway.
HUNTER Other dirt racing results from the past week worth noting. Michael Kofoid in the Roth Motorsports number eighty-three got his sixth World of Outlaws win of 2026 this past Monday night at Huset's Speedway in Brandon, South Dakota — the Stars and Stripes Salute presented by Folkens Brothers Trucking. He started seventh, took the lead on lap thirteen, and pulled away by nearly four seconds. Sheldon Haudenschild was runner-up, Aaron Reutzel third, David Gravel fourth, and Donny Schatz fifth. That is six wins on the year for Kofoid, most on tour in 2026.
HAST And the World of Outlaws is at River Cities Speedway in Grand Forks tonight for the Don Mack Classic, so if you are not already watching on DIRTVision, get there now. Kofoid swept both Series events at River Cities last year and comes in as the clear favorite. From a setup standpoint that high-banked bullring in Grand Forks is a very different animal from Huset's — shorter straightaways, more side-bite demand — so the shock and valving conversation from this week's column is directly relevant to how those cars are dialed in tonight.
HUNTER Quick hits on adjacent dirt kart news. The 2026 AKRA four-cycle dirt tech manual is out — version one is live at akraracing dot com and it sets the engine rules for Clone and Ducar class structures for the full season. If you are running an AKRA dirt program, that is your rulebook. Hoosier also has its interactive 2026 spec tire catalog live at hoosiertire dot com — worth a cross-reference against the family data in Column thirty-seven because the catalog compounds list can look deceptively linear until you know where the structural break lives.
HAST And English Creek Speedway in Iowa just ran championship night number three of their 2026 season this week — Iowa outlaw kart racing, fast program, real racing. No results pinned yet but they are running on a regular weekly schedule. Worth following if you want to see real-world D-series versus stiff-family decisions getting made every Friday on a tight Midwest track. That is Column thirty-seven. Know which family you bolted on before you touch the prep bottle or the crossweight sheet. Next week we are going back into the crossweight conversation for floppy-carcass tires specifically — why copying an FK setup number onto a D-series kart is the single most common mistake in outlaw karting right now. Hunter out. Read the full column at racer.wiki.