The theory 1000 euros extra for carbon - good investment or money wasted? To get to the bottom of this question, we had two 29er wheels built by Shocker Distributions. The matching rim pairing came from WTB in the form of the KOM i29 (aluminium, 486 g, 29 mm inner width) and the Ci31 (carbon, 485 g, 31 mm inner width). Same weight, similar dimensions. Nevertheless, the rims represent two completely different price categories. What can the wheel with the carbon rim do that its aluminium counterpart cannot?
The measurements in the BIKE test lab show: With an identical construction (32-hole, triple-crossed) and the same spoke tension, the carbon wheelset is 15 to 20 per cent stiffer. Lateral loads are dissipated more evenly and even a short load peak, such as occurs during a rough landing, is absorbed with less deformation. In theory, this means a more precise ride feel and higher load capacity. In terms of acceleration, however, the two rivals are on the same level.
In practice For trail use, both wheelsets are fitted with the same tyres and ridden on a hardtail with identical air pressures. The experiences of the testers are consistent: both wheels are reasonably stiff and easy to accelerate. They ride almost identically. None of the testers noticed any real differences. Only at very high pressures (over 2 bar) is a slightly better inherent damping of the carbon wheels noticeable. However, this is completely overshadowed by the damping and suspension of the tyres at a practically relevant 1.5 to 1.8 bar. Result of the practical test: undecided.
That leaves us with the carbon rim's presumed showpiece discipline - its robustness. On the Syntace rim test rig, an aluminium and a carbon rim are each maltreated with a drop weight until total failure. As expected, the aluminium rim shows dents early on, which become more and more pronounced as the drop height increases. Surprisingly, the point at which the deformation becomes a safety risk, i.e. the tyre no longer fits securely and needs to be replaced, is only slightly below the load at which the carbon rim also fails. Due to the material, the carbon rim only showed superficial flaws for a long time, but then developed safety-critical cracks in one fell swoop. This means that although the carbon rim has higher reserves, it immediately acknowledges a critical overload with a total loss. Replacement costs for a rim: 699.90 euros for carbon and 109.90 euros for aluminium. Any more questions?
Conclusion: In the tested pairing with identical rim weight, the carbon rim is slightly wider, 20 per cent stiffer and shows damage later. However, the load level in the event of total failure is the same, which could be due to the design of the carbon rim flange with hooks. Hookless carbon rims are generally more robust. No differences were noticeable on the trail.
To test the durability of the rims, we used the Syntace impact test rig. This allows us to simulate practical loads such as punctures. In the test setup, a drop weight (15.3 kg) falls onto the fixed rim. This is mounted at a slight angle, which is why the load from the round hard plastic block only acts on one side of the rim flange. The drop height is gradually increased until total failure occurs. The almost identical load level at total failure (photo) corresponds to the comparative values of the Syntace specialists. Syntace developer Nathaniel Goiny: "The WTB carbon rim wastes additional potential due to its classic design of the rim flanges with hooks. The carbon rim could be even more stable if the wall thickness remained the same, i.e. with a hookless design."
WHAT THE TESTERS SAY
Christian Artmann, BIKE test author:
I was expecting bigger differences, especially in the impact test. Because both rims ride almost identically in practice, the aluminium wheel remains the winner of the duel for me.
Stefan Frey, BIKE test editor:
The comparison completely deprives the carbon rim of its raison d'être. Why should I spend 1000 euros more for a set of wheels with almost identical performance? For me, the winner is clearly the aluminium rim.
Peter Nilges, BIKE Test Manager: With wide tyres and air pressures of around 1.5 bar, the rim material takes a back seat. No differences were noticeable when riding, especially as the weight difference in this comparison was also very small.
TECHNICAL DATA
Shocker Custom Carbon
Price 1779 Euro/set (rim: 699.90 Euro)
Weight 1815 grammes
Stiffness 60 (VR) / 57 (HR) N/mm
Components WTB Ci31 rims (29"), Sapim spokes & aluminium nipples, Aivee MT6 Boost hubs
Shocker Custom Alu
Price 779 Euro/set (rim: 109.90 Euro)
Weight 1841 grammes
Stiffness 50 (VR) / 50 (HR) N/mm
Components WTB KOM i29 rims (29"), Sapim spokes & aluminium nipples, Aivee MT6 Boost hubs
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