In 2023, ISO and ETRTO harmonized their standards and recommendations for hookless wheels, stating that a tire cannot deviate more than 2mm from its marked size.
Many existing 700x28mm tires are designed around a 19mm internal rim width. When you place most 700x28mm tires on a 25mm internal rim (like a 303 Firecrest or a 353 NSW), the tire will measure greater than 30mm, exceeding the +/- 2mm ISO standard. For this reason, most 28mm tires fall outside the current ISO hookless recommendation.
Zipp's goal with hookless wheels is to move the industry forward while following the standards the industry has agreed upon. To this end, we have changed our tire and rim recommendation to match the new standard. However, we understand that there are riders with bikes which are limited to a 28mm tire, or riders that just prefer the feel of a 28mm tire. To allow these riders to continue to use 28mm tires, we have partnered with select tire manufactures to validate 28mm tires for use on 303 Firecrest and 353 NSW wheels. We do this in a 3-step process:
- Zipp validates tire retention with our internal standards. This includes stepped pressure increments to 1.5x the max system rating for 1 hour at each step.
- The tire manufacturer validates tire retention and performance using their own testing.
- If the wheel + tire system passes all the tests from both Zipp and the tire manufacturer, the tire is listed on the Zipp Tire Compatibility Chart and marked by a black check.
Finally, the Goodyear Fitment Series VectorR SW 30 and NSW 30 are designed to measure 30mm on our 303 Firecrest and 353 NSW wheels. This means the Z30 SW and Z30 NSW tires will offer more frame clearance than a standard label 28mm tire on the same wheels.