62.JPG” border=”0″ ” align=”right” alt=”uhptires that excel in wet handling may give unprofessional drivers the false feeling that they are about to lose grip when cornering in the dry. this is due to a lack of soft lateral firmness, rather than shortcomings in dry handling. “/>
That doesn’t make them bad tires. Far from it, as this sensation is common. Most tire companies term this sensation a lack of “lateral firmness.”
Lateral firmness has nothing to do with a tire’s ultimate, race-track-style grip. Instead, during spirited cornering a lack of lateral firmness gives the average driver a sensation of instability, especially from the rear tires. Many will assess the car is about to spin out even though they and their tires are nowhere close to the limit.
A standard, non-performance tire has soft lateral firmness in comparison to any ultra-high performance tire. This was done on purpose because its designers aspired to produce a soft-riding, comfort-oriented tire. UHP tires, though, don’t necessarily design in soft lateral firmness; if it exists it is usually the product of a trade-off. Remember your basic tire performance rule of thumb: enhancing one attribute of a tire almost always degrades one (or several) other attributes.
The reason a particular tire can be great in the wet but unsettling in the dry is that there are several theories on resisting hydroplaning. I know that a “theory” is not a straight answer, but even tire designers and engineers disagree on the cause.
One theory says beating hydroplaning is best done by putting wide, circumferential grooves close to the center of the tire tread. That’s where water pressure is highest, after all, and this theory works wonderfully for straight-line driving. A wide circumferential groove does cut through the water and aids handling and driver feel.
On the other hand, it appears the designers of those UHP tires that do well in the wet – like the Eagle F1 GS D3 and Proxes T1R – think it’s more important to give water an escape route when the vehicle is cornering. In aggressive cornering, long, curving ribs place the tires’ grooves close to the direction of travel. The grooves sweep water away from the tire footprint and allow more rubber to reach the road surface, which seems perfect for both cornering and straight-line travel.
So why the difference in hydroplaning theories, often within the same tire company? Here’s my partially substantiated supposition: Tire companies that employ parallel, circumferential ribs determine hydroplaning resistance with the familiar underground camera objective test. In this test, the tire is mounted on a trailer and is pulled straight across a clear plate while a photo is taken from underneath. We’ve all seen these photos countless times.
Engineers of all stripes love such objective, repeatable tests. On the other hand, I bet that those who design tires with long, diagonal ribs rely more on subjective testing, which is based on professional drivers’ opinions.
(From my experience, there is a lot to be said for the “science” of feel. Yes, a glass plate photo provides clear evidence that the tread design is doing its intended job, but an experienced test driver can tell you if the tread design and tread compound and casing and sidewall are all working in proper concert to provide the kind of real-world performance and road feel that regular drivers expect.)
The long, curving-rib designs are not too dissimilar to how we used to hand-groove dirt track sprint-car tires: we aspired to have the longitudinal grooves parallel – and the lateral grooves perpendicular – to the racecar’s direction of travel. On a sticky clay track, the car would be very sideways, so the grooves were cut at about a 30-degree angle from the centerline of the chassis.
On a dry, slick dirt track, the car would be driven almost as straight as if it were on pavement, so the longitudinal grooves were parallel – or nearly so – with the centerline of the chassis. (Engineers and other pickers of nits: I understand a dirt-track sprint car is very different from a road-going car being hustled around a wet freeway transition ramp. I was trying to provide an image for those who don’t work complex math problems in their head for entertainment.)
While the long, curving longitudinal grooves are great at giving water an escape route while cornering, they’re fairly flaccid compared to the straight longitudinal ribs on, say, the Michelin Pilot Sport PS2 and Bridgestone Pole Position S03. The point is this: long, unsupported ribs hurt lateral firmness.
At the point a civilian driver might feel instability on dry roads, both the Goodyear and Toyo are still far below their ultimate dry grip. If the driver pushes past this point, these tires – and similar designs – have plenty of dry grip left. Going past the feeling of instability, after all, takes a bit of faith.
It’s my experience in racetrack testing that the ultimate dry grip of these tires is competitive with – or superior to – that of virtually any max-performance tire.
But unless you’re on a racetrack, there’s no usable difference in grip among UHP three-season tires. In fact, if you can tell the difference in ultimate dry grip of UHP tires while driving on a public road, I suggest you pull over to the shoulder, turn off your car, engage your emergency flashers and put your hands on the steering wheel. The police officer will be along momentarily.
If a customer complains about lack of dry grip with the Eagle, Proxes or a similarly designed tire, suggest he or she go to an autocross (scca.org) and push the car hard to its true limits. If he/she enjoys autocrossing, that customer will start buying a lot of tires and you will have a new loyal customer.
Recently, I diagnosed an autocrosser’s “handling problem.” He was running on a quite competent brand and model of tire and was failing to drive the car aggressively enough. The driver thought he was at the limit when he was sensing a lack of lateral firmness, but that was not the case.
By using less brake, allowing the car to roll faster through the center of the corner and then getting on the gas sooner, the problem was solved.
