First look + First ride: Metron 81 & Metron Disc top-end wheels from Vision
The new range-topper for 2013... yup, 2013
Vision will be extending their wheel range next year with a new 81mm-deep carbon option that they say is the lightest in its category, and a new rear disc.
A sub-brand of component giant FSA, Vision have spent a lot of development time on their 2012 wheels (we’ll come back to those later) and they’re pushing things further forward in 2013. I’m at the press camp in Majorca right now where they’ve shown these 2013 wheels for the first time.
The new Metron 81 comes in at the top of the range, taking over from the 2012 Metron 90. The 81 refers to the depth of the full-carbon tubular rim, in millimetres (which might sound obvious but the 90 is actually 88mm deep).
It’s unidirectional carbon except around the spoke bed where Vision use a 3K weave to cope with the concentrated loads, and on the braking surface where they use 3K to provide better support for the load and heat generated by the brake pads.
The rim shape is interesting. Many of the big players in the aero-wheel market have widened their rims recently, largely to manage the airflow better once the tyre is in place. The idea is that there’s little point having a super-skinny aero rim with a fatter tyre on top. For the best aerodynamics, have a wider rim and a smooth interface between the rim and the tyre.
A wider profile also offers increased support to the tyre. It keeps more of the tread in contact with the road because it deflects less under side loads, stopping the tyre from rolling to the side.
Vision have gone down the wider rim route too. The Metron 81 is 23.734mm across at the brake track – call it 23.7 for cash. This compares to the 20.4mm that Vision had on their Trimax Ultimate.
The maximum foil width (the section between the brake tracks and the spoke bed) is 24.5mm – so the rim bulges outwards very slightly below the brake track. The rim profile shape stays wide a long way down towards the spoke bed. It’s not quite as much of a U-shape as Zipp’s Firecrest design, for example, but it’s certainly towards that end of the spectrum rather than a sharp V-shape. Making sense? Basically, Vision have gone for a wider, rounder rim profile.
How have they got to this shape? They spent six months on research and ran over 100 profiles and 900 simulations through their CFD (computational fluid dynamics) software to come up with the design. Then they validated their findings at the San Diego wind tunnel and created what they reckon is their fastest wheel ever.
The Metron 81 spins on Vision’s new front and rear PRA hubs. Vision are keen to emphasize that they design and build their own hubs rather than getting something off the peg and dapping their logo on it.
They say that the new front hub shell is 10% faster than the previous generation thanks to improved aerodynamics and a weight of just 98g – 20g lighter than before.
The non-driveside flange of the rear hub has been shifted outwards by 10mm to increase the angle of the spokes and the lateral rigidity. Vision say it’s up to 26% stiffer than before. They’ve also removed the steel from the freehub so it’s now 100% alloy that’s hardened to add strength. That takes the weight down by 20g.
The other key feature of the hubs – the feature that gives the PRA hubs their name – is the Preload Reduction Assembly. Do what? The preload adjuster is a threaded collar – aerodynamically designed, of course – that allows you to adjust the preload easily once the wheel is fitted to your bike.
Essentially, this collar separates the load on the bearings from the quick release and hub assembly. You sling the wheels on your bike, do up the quick release, and then you can adjust the preload – you need a 2mm Allen key – so that you don’t overload the bearings. The idea is that it gives the wheel better rotation and a longer lifespan - which makes sense you want to have the amount of preload in the bearings dialled in just so, too little and you'll get play in the hub and too much will cause the bearings to wear out quickly. You can put too much preload on the bearings in a standard hub by doing your QR up really tight - what this system allows you to do is get that QR nice and tight and ajust the preload on the bearings once it's all in place. These PRA hubs are used across most of Vision’s 2012 wheels – all except the cheapest ones.
Oh, one other thing about the hubs, then we need to get on… the front one runs on a pair of sealed ceramic cartridge bearings while the rear one gets another four.
What else do you need to know about the Metron 81? The front one comes with 18 radially laced spokes while the rear gets 21 – 14 laced two-cross on the driveside and seven radially laced on the non-driveside.
In terms of weight, Vision say the 475g rim weight is 145g lighter than the current 88mm-deep Metron 90 rim. A pair of complete wheels hits the scales at 1,495g, and they claim that’s lighter than anyone else’s of the same depth. That sounds right although we didn’t get the chance to verify the weight. Still, when has anyone in the bike world exaggerated the lightness of their components? Ahem!
Anyway, the main feature of these wheels is their aerodynamics. How do they perform on that front? Well, Vision claim the aero performance is similar to that of Zipp 808 Firecrests. I know! That’s what they’re saying. According to Vision’s own figures (not independently verified), the Metron 81 is on a par with – and even a little better than – the Zipps at some yaw (apparent wind) angles.
Vision aren’t actually publishing those figures but they claim that at 0° (a direct headwind) the 81s are about equal to the Zipps; the 81s have a slightly lower drag at 5 and 10°; the Zipps are slightly better at 15 and 20° – and they’re roughly equal beyond that. Obviously, it would be great to have those figures ratified by somebody other than the manufacturer.
If you want some more figures – hell, let’s go the whole hog – Vision say that, compared to their Trimax Ultimate, the Metron 81 requires 12W less power for the same speed at 10° yaw.
Bored of all the stats yet? Yeah, that’s probably enough to be going on with. Let’s move on…
So, guess who’s had a go on a pair of these. Yup, you got it in one. And the sun was shining in Majorca today too. Tough gig!
There are a few things I’d say about the way the Metron 81s perform…
They accelerate fast. Yes, weight is of secondary importance to aerodynamics when it comes to deep-section wheels but, all other things being equal, you want light wheels if that’s an option. These pick up speed super-fast for wheels this deep. Sub-1,500g is a decent weight for any wheels never mind ones that are 81mm deep.
Stiffness is good. Slinging the bike hard into the corners, these wheels stay straight. Get up on the pedals and chuck the bike around and it’s the same story. No worries on that score.
In terms of aerodynamics, it’s really hard to judge on a brief test ride – that’s why wind tunnels were invented – but these feel like they’re slicing along efficiently with the minimum of effort. Get up to a decent clip on a descent and they feel great.
The other key thing is that they feel really steady in crosswinds. It’s really blowy out here at the moment (I know, your heart bleeds, right?), but I was virtually unaffected by winds from the side. Seriously! Go out in gusty conditions with some 80mm-deep rims and you’d better be ready for a fight. You spend your whole time struggling to keep the front end under control so you concentrate less on getting the power in.
Here, I kept asking people which direction the wind was coming from because these seem to handle a lot like wheels that are half the depth. Maybe that’s down to the wider shape providing greater stability, I’m not sure; it’s certainly very impressive.
Just one more thing: they make a fantastic humming noise too. The downside is that it forewarns other people that you’re on their shoulder, but it’s cool to have your own little signature tune to announce you’re in the area.
We don't have any details on prices yet - the Metron 81s are from the 2013 range, after all. They'll be available for Shimano/SRAM and Campag and will making their debut on the bikes of the pros from next month, though, so keep your eyes peeled for them.
The Metron Disc is brand spanking new for 2013 too. Or, rather, next year’s version is very different from the current model.
To let you into a secret – don’t tell anyone but there’s a spoked wheel under there. Those side panels are carbon fairings bonded over the top.
Hang on a minute! Surely the UCI will have something to say about that if they get wind of it, fairings being ruled ‘not cricket’ or something by the boys in the lab coats. Apparently not. How come? The thing is, those carbon fairings are ruled structural – an integral part of the wheel – because they produce extra stiffness. You can’t run the wheel without those fairings in place, allegedly, so they’re all fine and dandy.
Those fairings are side-specific. The one on the driveside sits flat while on the non-driveside it’s convex – clearly, it has to be in order to fit over the angled spokes.
The tubular rim (there are no clincher versions of any of Vision's all-carbon rims) comes from the existing Metron 90 which means it’s an 88mm-deep – full carbon, natch – with a reinforced braking surface.
The hub is Vision’s new wider design and, like the Metron 81, it runs on ceramic cartridge bearings. You’ll be able to get Shimano/SRAM and Campag freehub versions.
Truing up the wheel is easy enough – you can do it yourself – but break a spoke and the wheel will have to go back to a Vision service centre because removing that carbon fairing isn’t for the likes of you and I.
At 1,100g, the 2013 Metron Disc is 180g lighter than this year’s version. Vision say that the drag is reduced over the previous generation too, although they don’t give a figure on that, and it’s stiffer thanks to that wider hub.
More to follow on the rest of the range...