What: Michelin Pilot Road 4: 120/70 ZR17 front,180/55 ZR17 rear.
How much: $259/$419 RRP.
How long: Two weeks, one track day
How good: ★★★★★ [five stars]
When Michelin launched the Pilot Road 3 it caused a revolution. Previously, motorcycle tyre designs had converged on patterns that featured a large rubber area with a few deep grooves. You chose a sporty tyre that could handle a lot of heat and gripped well when warm, or you chose a touring tyre that warmed up more quickly and lasted longer.
Then along came the Road 3, with some very fancy compound chemistry and an unmissable visible difference: sipes. Some will tell you that the Road 3 pioneered the use of sipes on a motorcycle tyre, which is utter tosh. The Dunlop TT100 of the late 1960s was famed for its use of sipes and feted for its wet-weather performance. Further back, sipes featured on just about every motorcycle tyre available. How they work is theoretically simple. They act a bit like a sink plunger, sucking water up off the road surface as the tread distorts, producing a slight vacuum in the narrow space between the sipe’s walls.
Dunlop TT100 information on Wikipedia.
Front and rear of the ground-breaking Michelin Road 3s.
The problem is, that also means the tread is moving around a fair bit. That can make the steering and grip feel vague, and with a lot of ‘tread shuffle’ temperatures can shoot up to overheat the tyre. So it’s easy to see why, as motorcycle performance and power escalated dramatically from the late 1980s, tyre designers favoured the stability offered by lots of rubber and just a few grooves.
So how did Michelin manage to reintroduce sipes that would stand up to the forces produced by a modern motorcycle? In short, smart design. If you look carefully at the overall block shape (excluding the sipes) of an old Road 2 and the Road 3 (see the images below), they’re almost identical. At the front, Michelin removed the top of the groove that linked the left of the tyre to the right and added elliptical sipes across the tyre. On the rear, the added sipe grooves follow the contours of the main grooves. They managed to achieve this, while maintaining stability, with smart compound chemistry. The blocks are stiff so, even though they’re weakened by all the sipes and grooves, they don't move around much. They also stick.
The Pilot Road 3 immediately won plaudits for its combination of wet-road grip, confidence-inspiring feel and decent longevity. As a pure road tyre it was close to unbeatable and it sold by the truck load. But it did have its downsides. On track, for example, it felt a little vague–not unexpected on a tyre optimised for road riding, especially in the wet. Also, under certain circumstances the leading edge of the sipes on the front tyre would start to flare or ‘cup’.
webBikeWorld's Pilot Road 3 review
To address these issues Michelin developed the Pilot Road 4. Or, rather, the Pilot Road 4, the Road 4 GT and the Road 4 Trail. (We’ll come to the differences shortly.)
Pilot Road 4 information on Michelin's website
Immediately noticeable is the different tread pattern on the front tyre. Gone are the continual, long, unbroken sipes across the tyre’s width and the long grooves taken from the Road 2 pattern. Instead, the sipes alternate between unbroken and being broken on each side by a wider channel. The deeper grooves are shorter and isolated, so they no longer stretch from the middle to the tyre edge, and the left and right are offset from one another.
One other difference from the Road 3 became apparent before fitting. I’d been getting a tyre education from our good friend Dave Moss, and he demonstrated the marked difference in carcass stiffness between tyres. His point was how this would affect the tyre pressures. It turns out the carcass of the Road 4 rear is much stiffer than the Road 3.
Dave Moss on Facebook
With this is mind, I was a little worried that the precious grip and feel might be compromised in the new tyre, especially at the front. How pleased I was, then, wandering the aisles of Cycletreads, to find that the front of the Road 4 was about the same stiffness as the 3. The GT, though, was stiffer front and rear.
The new Road 4 range features some fiendishly clever compound chemistry. A unique new blend of functional polymers and silica creates an electrostatic charge in use that repels water, helping the tyre cut right down onto the tarmac surface. As you’d expect, different compounds are used on the edges and the middle. The Road 4 and GT have a hard rear centre with medium edges, but the Road 4 Trail has a medium centre and soft edges–the same combination you'll find on the front of all three tyres. The GT’s carcass construction is different, too. It has both radial and bias belting, making the structure much stiffer in every direction. It’s specifically engineered to handle the stresses of big touring bikes, and is the factory fitment for BMW’s R 1200 ST.
The tyres were going onto my Monster 821, replacing the OEM Pirelli Diablo Rosso IIs. After 6,500km, the rear was shot. The Pirellis are typical of a modern, sporty tyre. In the dry they’re superb, with good feel and masses of grip. But when the bike was a few months old, with the tyres still in top condition, I got a good scare on a slightly damp and twisty road when the front stepped out. It ruined my confidence for the rest of that ride and I absolutely knew the Pilot Road 3s on my previous Speed Triple wouldn't have budged at all.
My review of the Ducati Monster 821 and 1200
After the good sorts at Cycletreads had swapped the boots over, I tentatively rode the few kms home then adjusted the tyres to ‘ball park’ pressures. The next day was to be spent riding down to Pukekohe then on track.
Ducati’s 821 Monster runs an unusual 180/60 rear which is not available in many tyre ranges, including the Pilot Road 4. The profile is used by World Supersport teams, the theory being that a slightly narrower rim width and ‘thicker’ tyre ratio results in the tyre being squeezed in at the bead. This produces a tyre shape that puts slightly less rubber on the road when upright, with a more V-shaped transition towards the edges. The benefits are said to be faster steering and a bigger contact patch at full lean.
Substituting a conventional 180/55 rear, I was alert for any steering issues but there were none. Differences exist in tyre profiles and actual ratios between makes, and measuring the heights of different tyres that purport to be the same size can be interesting, as Dave Moss taught me.
The dry ride down helped scrub in the tyres but the extreme edges were still virgin for the first sighting laps. The tyres soon felt ready for action and the pace picked up as the sessions wore on.
Right from the get-go, feel on the brakes and turn-in were excellent, as was trail-braking into the chicane. The front end felt planted, inspiring heaps of confidence, and even a missed gear going into the complex before Castrol didn't result in an off-track excursion: hard braking and a fast turn got the bike back on line.
Leaving the traction control on its sportiest setting, there were absolutely no dramas. Applying a lot of throttle at high lean angles resulted in a little squirming at the rear and the TC light flashing away on the dash.
Wear was even and light, with a nice orange-peel effect at the edges and zero evidence of cupping on the tread. At pressures of 33psi front and 35 rear (warm) they seemed to be working perfectly.
The only criticism, and it’s almost unfair given the road-orientation of the tyres, was a vagueness at full lean. The tyres don't ‘talk’ to you very well in these circumstances, so switching the traction control off was never a temptation. Bear in mind, this is knee-down, foot-peg-scraping angles of lean with the TC light burning orange. At lower levels of attack, the tyres are totally communicative.
While the day was mercifully dry, the weather turned wet as everyone headed for home. Steady drizzle was enough to produce a greasy film on the road, and the traffic built up to add to the joy.
It was a perfect test of the Road 4s, and they shone. The confidence and feeling of grip was like a dry road. It was absolutely remarkable.
Just like the Pilot Road 3s, then? Well, certainly every bit as good. If you’re a fan of the Pilot Road 3s and about to face changing them, you won't be disappointed by the Road 4. There’s also plenty of evidence that the new tyre has even better braking performance in the wet and that it last up to 20% longer.
I’ve certainly never encountered a better road tyre. And the easy answer if you do a lot of track days is a spare set of rims with some Supercorsas. Just keep the Road 4s handy if the skies start to cloud over.
Pirelli Diablo Supercorsa tyre