Astral Back Bone Aluminum 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 32mm 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 Aluminum 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 32mm 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 32mm 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 32mm 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 | 561.5 (27.5in) |
| Inner width | 32 mm |
| Depth | 20 mm |
| Drillings | 28h, 32h |
| Weight | 535g (650b/27.5in) |
| Material | Aluminum |
| Tire type | Clincher Tubeless Compatible |
| Brake | Disc |
| Nipples | External |
| Finishes | black |
Which version this is
What this listing covers: the Backbone in 27.5in with 28h, 32h drilling, about 535g, 32mm inside, 20mm deep, disc. If you need it in another size or for the other brake type, it is listed separately.
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 Aluminum 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.
Build it into a wheel
This rim is live in our Custom Wheel Program for tandem and e-bike, mountain bike, MTB single-speed and fat bike builds. Start a build with the Astral Back Bone Aluminum Rim and the configurator opens with this exact rim pinned at the top of the Astral / Rolf list — you choose the rest of the parts and it validates every combination as you go.
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.
Astral's testing and certifications
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
Everything in this section is published by Astral. ProWheelBuilder is the wheel builder, not the tester, and the rim reaches us as the maker ships it.
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 aluminum Back Bone, 535g in 27.5in, with a published ERD of 561.5mm. It is tagged for tandem use as well as mountain and fat riding, which the carbon version is not - on a tandem the loads are roughly doubled and an aluminum rim's habit of deforming rather than failing outright is worth more than the weight saving.
The carbon Back Bone saves about 115g a rim and has a different ERD, so the two are not interchangeable in a build - spoke lengths differ. If you want the light one, it is a separate listing.
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. Our one-year wheel warranty applies to any wheel we build around this part, alongside whatever the manufacturer offers. Inside that year, broken spokes are replaced no matter how they broke, and the wheel labor is ours - truing, re-tensioning or a full rebuild. A rim or hub failure that the maker covers, we claim for you and see through; one the maker declines, we answer with an eligible replacement at 25% off current retail. Shipping both ways is yours, and components you supply yourself fall outside this cover.
Full terms are on our Policies & Warranty page.
Back Bone Aluminum Rim questions
What tire width suits this rim?
32mm inside is an enduro width, meant for 2.3 to 2.6in tires. It gives a big casing a square, supported profile so you can drop pressure for grip without the tire folding, which is the whole point of a rim this wide.
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 32mm 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 Aluminum Rim?
No. The rim is made by Astral; we are the wheel builder in Georgia who laces it into a finished wheel to your spec and stands behind the build.
Is it tubeless-ready?
Yes. Astral lists the Back Bone Aluminum 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.
