Since 2012 ... The Highest Performance & Most Durable Carbon Fiber Rims for MountainRoad, Gravel, & E-Assist Bikes

MOUNTAIN RIM SPEC'S

XC, AM, or DH - Which type?

The 35i AM Derby Rims are about the same weight as 22mm inside wide major brand's "light weight" XC aluminum rims.

The external design and all dimensions of the rims are the same for either XC layup, AM layup, or DH layup, for each wheel size. Additional carbon-fiber layering inside the hollow "double-wall" rims is thicker and stronger than XC in the AM and further reinforced DH options. The AM is about 20 to 25 grams heavier in carbon-fiber layering than the XC layup, and the DH is about 35 to 45 grams heavier in carbon-fiber than the AM layup.

XC (Cross-Country) rims are for small light weight tires under 600 grams 2.25 tire size and smaller, with short knobs or semi slicks for mainly smooth hard pack and gravely conditions, and where wheel rolling climbing weight and acceleration is more important than descending control. Although DH bike riders call their 6-inch travel Enduro-DH bikes their "XC" bikes, use of aggressive tires more than 600 grams is not "XC".

AM (All-Mountain) rims are for technical trail medium size knob tires under 800 grams, except if plus size for technically difficult trails and where climbing wheel weight and rear tire rolling ease is as important as descending control, through rocks or roots with rare in trail small drops less than 2 foot vertical. Free-ride larger drops and stunts and Enduro-DH high speeds are not AM technical trail conditions, for such extreme riding DH (Downhill) rims are required for shuttle and DH park and for the rear wheel for Enduro-DH racing descending speeds.​

DH (Downhill, Enduro-DH) rims are for maximum durability under the hardest riding conditions for any weight rider of extremely rocky trails. "DH"is required for DH bikes, and required for at least the rear wheel of Enduro-DH racing and high descending speed uses, also required for tandem mountain bikes, and mountain E-bikes, and riders over about 250 lbs.

Rider weight is almost not a factor for durability. Sharp rock hits and suspension bottoming loads focus more than 1000 lbs of acute input causing flex to a rim. Aluminum rims could bend or dent from sharp or heavy hits, but carbon-fiber will flex. And excessive flex and repeated excessive flex damage carbon rims. Usually excessive flex causes internal damage at first, called "micro-fracture", where the actual carbon fibers split microscopically. Additional excessive and normally intended flex will open the internal fracture further, until the internal layers separate enough to become unable to support intended loads, and many months later after the initial excessive hit flex the rim wall collapses showing as a surface crack.

Derby Rims are not for weight weenies. These very wide trail rims are for high performance bike handling, improving the performance of nearly any trail tire. The AM rims are about 0.75 lb, about 300 grams lighter per set than an equivalent width aluminum rim. This is a huge weight improvement in rolling weight. With wide Derby Rims there are additional effective ways to reduce weight. Some examples: Wide rims with smaller tires have more traction and cornering grip than a high volume tire with bigger knobs on narrow 25 mm internal width rims. And Sapim CX-Ray spokes drop about 100 grams compared to common double-butted spokes.

27.5" x 35i
AM, DH layup options
- ideal for 2.3 to 2.6, & up to 2.8 tires
Weight +/-10: 485g [All-Mountain] or 545g [Downhill] 
Outer width: 40mm, Inner width: 34.5mm, Depth: 31mm
ERD: 542mm (DH add 1mm) 

27.5" x 45i - for 27-Plus tires and frames
AM, Enduro-DH layup options 
- ideal for 2.8 to 3.0 & up to 3.8 tires
Weight +/-10: 530g [All-Mountain], 560 [Enduro-DH]
Outer width: 50mm, Inner width: 44.5mm, Depth: 34mm
ERD: 538mm, Note: Spoke off-set from rim center: 5mm


26" x 35i
AM, DH layup options
- ideal rim width for 2.3 to 2.8, & up to 3.0 tires
Weight +/-10: 470g [All-Mountain] or 510g [Downhill]
Outer width: 40mm, Inner width: 34.5mm, Depth: 31mm
ERD: 518mm (DH add 1mm)

XC Derby rims maximum tire size: 2.25 inch
AM Derby rims are for technical-trail riding, no large drops.

Enduro racers and other high speed trail riders, should use a Derby DH rear rim

All Rims


  • Material: UD carbon-fiber
  • Spoke holes - Mountain: 32, 28.
  • Spoke hole size: 4.5mm (for external nipples)
  • Spoke hole alignment, for all rims (except 27.5: x 45i and 29" x 40i): Rim centered, All rims have spoke holes angled towards hub flanges. Key/First spoke: Stand up the rim vertical as if ready to roll forward, with valve hole at the ground. Looking down at the valve hole, the 1st spoke hole forward of the valve hole angles to the right-side hub flange, next spoke hole forward angles to the left side hub flange, etc.
  • Presta valve hole, required length: 40mm minimum (48mm Orange Seal valves are recommended)
  • Recommended max spoke tension: 125KgF
  • Recommended rider weight limit: 175 lbs / 90kg  for XC rims, 225 lbs 100Kg  for AM, 300 lbs 135Kg for DH rims
  • Max tire pressure (mountain): 35 psi (for road use of mountain rims), 22 psi for 2.6 and larger tires. Max for DH race/park/shuttle: 30 psi, ProCore max pressure: 70 psi, 4.5-bar
  • Tire pressure to seat beads of most new tires, with soapy water or bead seating lubricant: 35 to 40 psi for mountain rims
  • Tubeless rim tape maximum width: 18mm or ¾ inch for 30i and 35i rims; 25mm or 1 inch for 40i and 45i rims; Only tape within the center channel, do not taping over the bead seats, for best results.
  • Recommended rim tape : Orange Seal rim tape 18mm or 25mm wide (two rounds), Stan's 12mm wide for BX & CX used for XC race (two rounds).

29" x 30i
XC, AM, DH layup options
- ideal for 2.0 to 2.3, & up to 2.6 tires
Weight +/-10: 450g [XC]  or 485g [ All-Mountain] or 525g [Downhill] 
Outer width: 35mm, Inner width: 29.5mm, Depth: 31mm
ERD: 582mm (DH add 1mm)

29" x 35i
AM, DH layup options
- ideal for 2.3 to 2.6, & up to 2.8 tires
Weight +/-10: 495g [ All-Mountain] or 535g [Downhill] 
Outer width: 40mm, Inner width: 34.5mm, Depth: 31mm
ERD: 582mm (DH add 1mm)

29" x 40i - for 29-Plus tires and frames
AM, Enduro-DH layup options
- ideal for 2.6 to 3.0 & up to 3.5 tires
Weight +/-10: 520g [All-Mountain], 565 [Enduro-DH]
Outer width: 45mm, Inner width: 39.5mm, Depth: 31mm
ERD: 582mm, Note: Spoke off-set from rim center: 5mm