Rene Herse approves ZIPP 303 XPLR rims
Zipp latest gravel wheels, introduced last year, went into uncharted territory: The 303 XPLR rims measure a whopping 40 mm wide. Their inner width is 32 mm. According to the ETRTO standards that govern rim/tire compatibility, rims that wide are suitable for 58 to 71 mm-wide tires. And yet Zipp suggests running tires as narrow as 40 mm.
That brings up the issue of tire compatibility. Manufacturers design their tires to be compatible with ETRTO-compliant rims. If a rim does not meet the standards, all bets are off. This doesn’t mean the combination doesn’t work—it just means that it needs to be tested individually. So far, Zipp has approved only their own tires, plus one other brand.
Now the 303 XPLR rims are starting to show up as OEM equipment on complete bikes. A number of customers have asked: Is it OK with these wheels to upgrade to Rene Herse tires?
To answer that question, we got our hands on a set of 303 XPLR SW wheels and started testing. Unpacking these wheels, it becomes apparent how wide and deep the new rims really are. They are huge!
To keep the weight of the rims down to an acceptable level, Zipp made the walls ultra-thin: Simply pushing down with a thumb causes visible flexing of the rim. That makes me wonder what happens if a big rock bounces off the tire and hits the rim.
Zipp shared their own protocol for testing tires. It takes a cautious approach: Inflate the tires to 33 psi, hold for 60 minutes, then increase the pressure by 10 psi, hold for another 60 minutes. Continue until 150% of the maximum pressure is reached. Zipp tests the tires dry, probably to reduce the mess if a tire blows off the rim.
For us at Rene Herse, rider safety is the most important concern. First we tested the tires according to Zipp’s protocol. Then we tested the tires with sealant, because liquid sealant can act as a lubricant and cause a tire to blow off the rim, where a ‘dry’ tire might stay on. We also know from experience that tires can blow off after repeated inflations, so just going to max. pressure once is not enough. Instead, we inflated each tire at least 5 times to 150% of the maximum pressure—to 75 psi or 5.2 bar. (Don’t do this at home—the rim may not survive that type of abuse.) We tested four different tires on the front and rear wheel, to account for variability between rims and tires of the same model.
We started our test with the ‘worst-case scenario’: a well-worn tire, in this case a 44 mm Manastash Ridge Extralight that looked like it had been ridden to hell and back. Why a worn tire? Because beads can stretch a little, and the casing also loses stiffness over time. Both can make a tire easier to blow off the rim.
Mounting the tire, we noticed that Zipp kept the well in the center to ETRTO spec—the extra width is on the ‘shelves’ where the bead sits. That’s an interesting design choice, as it means that the tire needs to traverse the wide shelf when you put it on the rim. That makes tire installation a little harder, but not excessively so. Lubricated with a little soapy water from a spray bottle, the tire popped into place at around 35 psi, just as it should. As with other Zipp rims, diameter and sidewall height (G height) are spot-on.
The remainder of the test was uneventful. The rims are rated to 50 psi for tires narrower than 50 mm. Even at 75 psi, the tire stayed on the rim for more than an hour. At this pressure and on the ultra-wide rims, the normally 44 mm-wide Manastash ballooned to a width of 48 mm.
The next tire we tested was a brand-new 44 mm Manastash Ridge with Standard casing, from a different production run. The result was the same—no problem with multiple inflations to 75 psi.
Then came a 42 mm-wide Hurricane Ridge Extralight—the narrowest, most flexible Rene Herse tire you can run on these rims. It passed with flying colors.
Zipp suggests you can run tires as narrow as 40 mm wide on the new rims. To push the limit, we decided to test a 38 mm Barlow Pass. It also passed the test. Perhaps that’s no surprise—before ETRTO established standards for wide road tires, we recommended running rims at least 20% narrower (internal width) than the tires. (The 32 mm 303 XPLR rim is 19% narrower than this tire.)
The result of our testing is clear: If you have a set of 303 XPLR rims and would like to run Rene Herse tires, there is no reason why you wouldn’t. A few additional points:
- All casings (Standard, Extralight, Endurance, Endurance Plus) are safe to use with 303 XPLR rims.
- Don’t run tires narrower than 40 mm (nominal) on 303 XPLR rims.
- Don’t exceed the maximum pressure of the rims. We went higher for testing, but that doesn’t mean it’s safe to do so in the real world.
- Our testing applies to all Rene Herse tires. It does not apply to tires from other brands, which have other dimensions and bead materials.
To summarize it in one sentence: Rene Herse Cycles approves the Zipp 303 XPLR rims for use with Rene Herse tires (40 mm wide and up).
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