Astral Back Bone Carbon Rim
The Astral Backbone rim is the one we reach for when a customer says the word "bomber" and means it. It is a 27.5in trail rim with a 28mm internal width, which is wide enough to hold a 2.4in tire square and stable at low pressure and still happy under a 3.0in plus tire if that is what your frame runs. Astral is the rim brand of Rolf Prima in Eugene, Oregon, and the Backbone carries the same habit those wheels have of being slightly over-built in the places that matter.
We have laced a lot of these. The alloy version is the value pick: heavy enough to shrug off rock strikes, light enough that a 27.5 trail wheel on a good hub still comes in under what most complete bikes ship with. The carbon Backbone is the same profile in a stiffer, lighter layup for riders who want the width without the grams.
Either way, the Astral Back Bone Carbon Rim arrives here as a bare rim and leaves as a finished wheel. You pick the hub, spokes and nipples in the configurator, we cut spokes to the measured ERD of this exact rim, and it ships laced, tensioned and trued by hand.
Design and construction
The Backbone profile is a shallow, wide box with a 28mm inner bed and a hookless-style bead shelf Astral calls Tubeless Easy. In practice that means a tire seats with a floor pump on the first try more often than not, which is not something we can say about every wide alloy rim that comes through the shop. The Backbone's bead wall is thick where it needs to be, so a hard bottom-out dents the sidewall rather than cracking the bed.
Spoke holes are angled toward the hub flanges, so the nipples sit straight and the spokes do not bend at the rim. That sounds like a small thing until you are tensioning a wheel and notice the nipples turn smoothly all the way up instead of binding at the last quarter turn. It is one of the reasons Backbone wheels hold tension so well after the first few rides.
The carbon version is molded with a 28mm inner width against the alloy rim's 32mm and keeps the same spoke geometry, so the two build almost identically; the difference you feel is lateral stiffness and about a hundred grams per wheel.
How it rides
On the trail a 28mm rim changes how a 2.4 or 2.5in tire behaves. The casing stands up straighter, so you run a few psi less without the tire folding in corners, and the contact patch gets wider and flatter. That is the whole point of the Backbone: grip and support first, weight second. Riders coming off a 25mm rim usually comment on the cornering before anything else.
The Astral Backbone is not a cross-country race rim and does not pretend to be. If you are chasing the lightest 27.5 wheel possible, look at the Backbone Carbon X in a 30mm width. If you ride trail, all-mountain or a hardtail with big tires, the Backbone is the right amount of rim.
Specifications
| Wheel size | 27.5in |
|---|---|
| ERD | 544.5 (27.5in) |
| Inner width | 28 mm |
| Depth | 30 mm |
| Drillings | 24h, 28h, 32h |
| Weight | 420g (650b/27.5in) |
| Material | Carbon Fiber |
| Tire type | Clincher Tubeless Compatible |
| Brake | Disc |
| Spoke bed | Offset 3 mm |
| Nipples | External |
| Finishes | black |
This version
This version is the Backbone in 27.5in, drilled 24h, 28h, 32h, about 420g, 28mm inside, 30mm deep, disc. Where the same rim is sold in another size or brake type, that is a separate listing with its own page.
This is the disc-brake Backbone: plain sidewalls, no brake track to wear, a touch lighter. It fits any disc-brake bike and it is the version most of our customers now build; the rim-brake version is a separate listing.
Sizes, fit and compatibility
The Astral Back Bone Carbon Rim is made in 27.5in (ISO 584) only, in the drillings listed on this page. Tires from 2.3 to 3.0in work; Astral rates it for wide trail tires and plus sizes. Disc brake only, tubeless-ready with tape and a valve, which we fit when you choose the tubeless option in the build.
The Backbone pairs naturally with a Boost trail hub: Industry Nine 1/1 or Hydra, DT Swiss 350, Hope Pro 5 or an Onyx Vesper are the combinations we build most. Straight-gauge or double-butted spokes both work; for a heavier rider or an e-bike we lean toward Sapim Strong or DT Champion on the drive side.
Put it in a custom wheel
Build a custom wheel around the Astral Back Bone Carbon Rim — the link drops you into our Custom Wheel Program with this rim pinned, ready for you to choose the rest. It is set up for gravel and road disc, mountain bike, MTB single-speed and fat bike builds.
Spoke head is decided by the hub, not the rim: this rim builds equally well with J-bend or straight-pull spokes, and the configurator only offers the spokes that match the hub you pick.
How Astral tests its rims
Astral Cycling is the rim brand of Rolf Prima; both operate from one facility in Eugene, Oregon, where Rolf Prima states alloy rim production has been in-house since 2014. Astral joins alloy rims with a press-fit sleeve about 2.5 inches long weighing 4-5 g that doubles the wall thickness at the joint, avoiding the heat-affected zone of welding. All wheels are hand-built in Eugene. Rolf Prima states it does not farm out testing and has logged "over 10,000 hours of lab testing to above industry standards."
Astral and Rolf state they use ISO 4210 "as a base starting point but it is not tough enough." Their drum fatigue tester runs at 47 mph against the ISO 15 mph, putting over 3 times the energy into the wheel, with a life requirement 66% higher than ISO. Impact tests use a calibrated steel anvil to the UCI 40 J standard and then a higher in-house level, at spokes, between spokes and at the valve hole, including pre-heated rims. Rolf's carbon brake protocol runs ISO 4210 dry and wet tests, 300 W for 15 minutes twice, 400 W for 16 minutes twice, 450 W and 500 W for 16 minutes, and 500 W for 3 minutes followed by the UCI impact test with no failure allowed. No rider weight limit is stated.
Astral's videos
From Astral
Certifications
- Made in USA (alloy rims and wheels) — Astral and Rolf Prima state alloy rims are rolled and all wheels hand-built in their Eugene, Oregon facility; rim production in-house since 2014 (source)
- ISO 4210 base + in-house standard — Fatigue drum at 47 mph vs ISO 15 mph, life requirement 66% above ISO; UCI 40 J impact plus higher in-house level; ISO 4210 dry/wet brake tests (source)
- UCI note — Rolf Prima FAQ: Aspin and Elan family are 'Standard' wheels not requiring UCI approval; no approved-model list verified (source)
- Rolf Prima Certainty — In-house engineering and testing lab, eleven patents, over 10,000 hours of lab testing, 5-year warranty, lifetime crash replacement (source)
Sources on Astral's site:
- Testing – Astral Cycling
- FAQ's – Astral Cycling
- Astral Rim Warranty – Astral Cycling
- Technology – Astral Cycling
- Rim Joining: The Process and the Mystery – Astral Cycling
Astral publishes those results; ProWheelBuilder builds the rim into a wheel and does not test it in a lab.
Building it at ProWheelBuilder
We are not the manufacturer. Astral designs and makes the Backbone; ProWheelBuilder is an independent wheel builder in Georgia that buys the rim and turns it into a wheel to your spec. That distinction matters because a Backbone rim only rides as well as the build behind it. We measure the ERD of the rim in hand rather than trusting a catalog figure, cut spokes to the tenth of a millimeter, bring the wheel up in stages, stress-relieve it and true it to well under half a millimeter before it goes in the box.
The configurator only shows hubs, spokes and lacing patterns that can actually be built with the drilling you choose, and anything not made in a combination is struck through rather than hidden. Prices update live as you pick.
Aluminum or carbon Back Bone?
This is the carbon Back Bone, 420g in 27.5in, with a published ERD of 544.5mm - about 115g a rim lighter than the aluminum version and with a noticeably different ERD, so the two take different spoke lengths and are not interchangeable mid-build.
It is tagged for gravel, mountain and fat use. It is NOT offered for tandems, which the aluminum version is; on a tandem we would build you the aluminum one and tell you why. For a single bike where weight matters, this is the one.
Warranty
Manufacturer's warranty. Rolf Prima gives a one-year limited warranty on its wheels under normal use. Astral is Rolf Prima's rim brand; ask us and we will confirm the current terms for the exact rim before you buy.
ProWheelBuilder. If we lace this into a wheel for you, that wheel also carries ProWheelBuilder's own one-year warranty, which covers broken spokes regardless of cause and all wheel-related labor, including truing and rebuilding, for a year from purchase. Where a rim or hub is covered by its maker, we make the manufacturer's claim for you and coordinate it; where it is not, we offer an eligible replacement rim or hub at 25% off current retail. Shipping to and from us is the customer's. This cover does not extend to wheels built from components you supply yourself.
Full terms are on our Policies & Warranty page.
Back Bone Carbon Rim questions
What tire width suits this rim?
At 28mm inside this is a trail width, sized around 2.1 to 2.4in tires. That is wide enough to stop a modern trail casing rolling under you in a corner without pushing the tread so flat that it wears down the middle.
Is the Astral Backbone hookless?
Astral describes the bead as Tubeless Easy: a shelf profile designed for tubeless tires that seats with a floor pump. Run tubeless-ready tires on it and stay within Astral's pressure guidance for wide rims.
What tire width suits a 28mm inner rim?
Anything from about 2.3in up to 3.0in. The sweet spot for most trail bikes is 2.4 to 2.6in, where the wide bed gives the tire a stable, square profile at lower pressures.
Alloy or carbon Backbone?
Alloy if you want the width at the best price and do not mind the extra weight; carbon if you want the same width in a stiffer, lighter wheel and ride hard enough to notice. Both build into excellent wheels.
Which hub should I pair it with?
Any Boost trail hub. Tell the configurator your bike type and weight and it will recommend hubs and a spoke count that suit the Backbone's drillings.
Is ProWheelBuilder the manufacturer of the Astral Back Bone Carbon Rim?
We are not. Astral manufactures the rim; ProWheelBuilder's part is the wheel: measuring, lacing, tensioning and truing it here in Georgia.
Is it tubeless-ready?
Yes. Astral lists the Back Bone Carbon Rim as clincher tubeless compatible; we tape and fit a valve when you choose the tubeless option.
Not sure? Text or leave a voicemail on 470-253-0929 or email info@prowheelbuilder.com — you will be talking to the people who build the wheels.
