WTB Asym i35 Rims, 27.5”
Inner Rim Width: 34.5 mm (measured)
Stated Weight: 570g
Blister’s Measured Weight: 591g
Mounted to: White Industries XMR hubs / Devinci Spartan
Reviewer: 5’9” 155 lbs.
Test Duration: about a month
Test Locations: Northwest Montana, British Columbia
While they’re getting a lot more attention these days, wide rims aren’t a new phenomenon—DH rims have been pretty wide for quite some time. On bigger bikes, there’s a lot to like: wider rims are generally stiffer, and they offer a more squared-off tire profile that can improve cornering traction.
But until relatively recently, extra wide rims haven’t found their way onto trail bikes. Part of that is because of their weight, but another part is that the market didn’t seem ready to embrace them. Then a bunch of wide carbon options started popping up on the market, which mostly pacified the weight weenies. But upgrading to wide carbon rims remains a fairly expensive proposition. Even the cheapest generic options are still twice the price of their aluminum brethren.
Enter the WTB Asym rims, some of the widest aluminum rims on the market. And at $84.99, they’re priced pretty reasonably.
Options and Stats
The WTB Asym comes in two flavors, the i29 and the i35 (tested). As the name implies, the i35 measures about 35mm bead to bead (34.5mm to be exact). Externally, it measures 40mm.
Both widths come in 27.5” and 29” versions. I rode the 27.5” option, and mine weighed in at 591g without rim tape—that’s about 21g more than WTB advertises for these rims. To be sure, 591g is not a light rim. In fact, it’s about in line with some downhill rims like the DT Swiss FR570 (although that rim is about 7mm narrower).
The Asym is made out of WTB’s WT69 alloy, which is a proprietary aluminum. For some rambling pontification on rim materials, take a look at my review of the WTB Frequency i25 rim, which is made out of the same material. The short story: it seems to be a reasonably robust material that’s not as soft as some 6000 series alloys.
The aftermarket Asym is only available in a 32 hole pattern (some OEM spec wheels have 28 holes), and those holes get WTB’s “4D” treatment, which is to say that the holes are drilled at the same angle that the spokes will enter the rim. This means that the nipple will sit nice and flush against the rim instead of being cocked at an angle, and that ultimately means there’s less stress on both the rim and the nipple, which is a good thing.
The Asym also has WTB’s “TCS,” or Tubeless Compatible System. TCS is a UST-compliant rim profile that’s approved for use with sealant. This means that tires (especially TCS / UST-compliant tires) lock into the rim really tightly and reduce the possibilities of burping air.
Like most of WTB’s mountain rims, the joint on the Asym is sleeved; there’s a chunk of metal at the seam that keeps everything in place. This is generally cheaper to manufacture than a welded joint, and it avoids any issues with a brittle area around the weld. It also doesn’t have the downsides of a pinned joint, which requires the entire rim to be extruded to accept the pins in the area of the joint.
A Digression on Asymmetry
Astute readers will already have guessed that these rims are asymmetric, which means the spoke holes are offset to one side of the rim—in this case, they’re 4.5mm off center, which is a lot. If you’re already familiar with the concept of asymmetric rims, you can probably skip ahead.
On a normal symmetric rim (where the spoke holes are equidistant from both sides of the rim), the spokes come in at different angles. This is because the flanges on hubs are not equidistant from the centerline of the hubs. On rear hubs, the drive side flange is set inward to make room for the cassette, and on front hubs, the non-drive side flange is set inward to make room for the disc brake.
This means that the spokes on one side approach the rim at a steeper, more “vertical” angle. The practical effect of this is a weaker, less stiff wheel. The issue gets complicated at its extremes, but for the purposes of this review, it’ll suffice to say that broader hub flanges make for a wheel that’s laterally stiffer. It also means that the spokes on either side of the wheel hit the rim at closer to the same angle, which means they can come closer to having the same tension on both sides. Again, this makes for a stronger wheel.
Of course, we can’t make wider hub flanges without redesigning frames (see: Boost spacing), but there’s a couple ways to cheat the system. One is to make the hub flanges taller, and another is to make asymmetric rims.
Essentially, the asymmetric rim means the bead (and thus the tire) is centered in the frame, but the spokes hit the rim off to one side. By setting the spokes off center, the approach angle of the spokes on both sides is closer to being the same, and the wheel comes out stiffer and stronger.
NEXT: The Build, The Ride, Etc.