Ultra 4 and King Of the Hammers (same rulebook) have a very unique rule as it pertains to Tire Run Flat systems.
2.18.6 States that Tire Liner type products with a OD of up to 27" are allowed. Since Tire Spines are not a Secondary Inflation Apparatus, and are a Tire Liner type product, they are allowed but cant exceed 27" OD tall.
Fortunately, a 27" OD Tire Spine FULLY fits a 29" tall tire and in some cases, a 30" tall tire. Tire Spine has designed an Ultra 4 & King of the Hammers Legal 27" Spine and has been in testing at Ultra 4 races with podium proven results.
More Information Soon!