Understanding the Slow Tire Allowances
- droseberg
- Jul 22
- 2 min read
A distinctive feature of the classing system is the Slow Tire Extra Modifications Allowance rule. Introduced last year and expanded this season, it aims to better balance the classing based on the types of cars participating in the events.
Simply put, if your car has modifications or tire width that disqualifies it from the Sport or Tuner class, you can use a less competitive tire to re-enter the class, provided your car meets the class Weight to HP rule.
In fact, most drivers don't even need to purchase new tires, as they are likely already using a tire classified as a Slow Tire!
What defines a slow tire?
Any tire with a 220TW rating or higher, or those on the specified list. Commonly used tires like the Hankook RS4 and Continental Sport 2 are considered Slow tires! Generally, all tires that are known to be slower than the "Super 200 tires" most commonly used for Autocross events are considered a Slow Tire.
Currently, there is no width limit if you're using a slow tire. This was a major factor in drivers being placed in a class where they weren't competitive, as nearly all were using a "slow tire".
Have a BRZ or low-hp BMW with headers or added aero? Equip a set of RS4's or any tire on the slow list, and you can return to the Sport Class without major modifications to your car!
Running 255 RS4's on your BRZ or RX8 with some engine bolt-ons? No problem, you're still eligible for the Sport class!
Added a turbo to your car that originally had a 13:1 hp to weight ratio? No worries, you can still compete in the Tuner class.
Why is this considered fair?
The tires on the slow list are known to produce times that are approximately 1 second or more off the pace of the best "Super 200" tires on a 60 second course. Being restricted from using the superior tires offsets the performance gains from the additional allowed modifications.
To date, no car using the slow tire rule has won 1st place at an event or shown a significant advantage over similar cars that adhere to the class rules. It's extremely hard to make up the performance difference that using a top tier tire provides!
What additional modifications are allowed?
Sport Class
No tire width restriction
External engine bolt-on upgrades excluding adding forced induction.
Full interior removal & aero upgrades allowed
"Drop in" turbo upgrades are allowed if the vehicle has a 18:1 Weight to HP ratio or worse, otherwise turbos & superchargers must remain O.E
Tuner Class
No tire width restriction
Intercooler & downpipe can be upgraded on 12.99 :1 or better cars with no restrictions
Any 2000 & older vehicle can use a "Drop In" upgraded replacement turbo
Forced Induction can be added to any naturally aspirated vehicle with a 13:1 ratio or worse if using an O.E available engine for that model.
-Dan
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