Vittoria Diamante Pro Radiale clincher cycle tyre review
Vittoria Diamante Pro Radiale tyre review
A very different riding experience
Posted 10 August 2012
Words by Richard Hallett
The clue’s in the name; Vittoria’s Diamante Pro Radiale clincher tyre is different and the reason it’s different is because it has a ‘radial’ carcass. The carcass – that part of a pneumatic tyre, composed of close-packed fibre cords laid in plies held together by rubber, that gives the tyre its shape and resists the pressure exerted by the air inside – of a conventional cycle tyre is of cross-ply layout.
Cross-ply means that the plies – almost invariably uni-directional and usually two in number with an additional breaker ply under the thread to improve puncture resistance – are overlaid at 90degrees to each other and, therefore, at 45degrees to the wheel’s direction of rotation.
Vittoria’s radial plies are, instead, laid at 85degrees to the direction of rotation and, therefore, at 10degrees to each other, meaning they run almost directly across the tyre from bead to bead rather than, as with the cross-ply layout, diagonally from one bead to the other. Since they run almost parallel, the net result is that the two radial plies can move together as the tyre carcass flexes and, suffering from less interference with each other, allow the carcass to deform more readily.
This is no fantasy; the technology is proven to work in motor vehicles, where radial carcass technology typically offers a tyre with better ride comfort and lower running temperatures than the cross-ply equivalent (if there is one).
The lower running temperatures come from the reduced friction between plies that run near parallel; this lowers energy lost as heat to hysteresis in the carcass. Reduced energy loss and improved ride comfort are both attractive properties in a cycle tyre, and here is one that is claimed to offer them both.
When it comes to rolling resistance, the tyre performs on smooth roads well but not notably so, rolling about as fast as the high-end clincher competition. It is fast, but does not represent a quantum leap in rolling resistance. But, given that the thread count is equivalent to Vittoria’s Nylon Plus 220TPI (threads per inch) carcass, its speed is impressive.
But not as impressive as the tyre’s ride quality, which is exceptional. It is best enjoyed on rough, broken tarmac, over which the suppleness of the carcass allows the tyre to float in the manner of a roughly equivalent (say 24mm) cross-ply tyre inflated to about 0.7 bar or 10psi less. There is some comparative reduction in rolling resistance over such surfaces as the tyre comforms more readily to the surface. For sure, over the poorly-maintained lanes of the Surrey Hills, the Radiale rolls very nicely.
Inevitably, however, there is a caveat – and a big one at that. Let’s start with the observation that it is illegal to drive a motorcycle with a radial front tyre and cross-ply rear. Same with a car, for that matter. A radial tyre’s carcass has less inherent lateral stiffness and requires stiffening belts under the tread to provide the required steering response and precision. Without them, a motorcycle with radial front tyre and cross ply rear would understeer – run wide – dangerously.
Now, the first time I rode a pair of Radiale clinchers, I arrived at my destination in a state of nervous exhaustion. My first act on getting home was to take them off and it was only after some reflection that I gave them the longer trial they deserved.
Why? Because the radial carcass offers a fraction of the lateral stiffness of a cross-ply. This can be demonstrated by applying pressure to the sidewall of the inflated tyre; where a cross-ply barely moves and the pressure appears to act on a section of tyre extending either side of the point it is applied, the radial carcass simply gives way at the point of pressure to an almost amusing degree, leaving the section of tyre just 30mm either side unaffected. Said a mate who tired it; “It feels like a rubber snake.”
So what happens is that the tread, which grips the road surface, is less directly connected to the rim by a radial carcass. Because the tread can move sideways to a greater degree relative to the rim, the tyre conveys less immediately the lateral force generated by the tread when steering. This force is transmitted via the spokes, hub, fork legs and so on to the handlebars and, essentially, tells the rider how much grip is available.
The Radiale front tyre conveys the sensation of riding on a surface with significantly less grip than is, in fact, on offer; it’s like riding with a greatly under-inflated cross-ply. Try riding on a regular clincher inflated to 60psi (0.5bar) and you’ll get the idea.
If the effect is unsettling when riding in a straight line, it is downright unnerving when it comes to corner entry, where that sense of uncertainty makes it hard to judge line and apex even in the dry. Until you get used to the feel of the tyres, that is. This takes some doing.
Once well-acquainted with their unique feel, the Radiales are, in fact, perfectly useable. The tread, which uses Vittoria’s Isogrip compound, is perfectly grippy, so once laid into a corner the tyres stick as expected, provided you don’t try to change line part way through. One way to improve cornering still further is to over-lean by pushing the bike inside the rider’s centre line; this reduces the height of the inside sidewall and dials in some useful oversteer.
Is the tyre worth the effort? On balance, yes, provided it is to be used for a suitable purpose. I’d be reluctant to fit them for a bunch race, since handling precision is important to safety when riding in close company with others. The tyre looks a good choice for training and touring if ride comfort be a major consideration, which it is on the super-stiff steel frame and fork I ride most of the time. Of course, you can always run a cross-ply clincher at a lower pressure than the Radiales, but than that invites pinch-flats.
In any case, the view of the tyres expressed by one of the German journos at the recent Trek Madone KVF launch is surely too extreme; “I went down the road and fell off on the first bend, ruining a pair of shorts. So I sent them straight back to Vittoria.”
Persevere and you may well come to like the tyres as much as I do. They sure do roll nicely.
Vittoria Diamante Pro Radiale clincher tyre £38.50; 700x22c, 700x24c (tested, 210g); black only