Boanerges said:
That is interesting. I would have thought by increasing the pressures to near the setting for four passengers and luggage the ride would be harder and less forgiving.
The Sporting has lower profile tyres than the regular models. I will see what effect this has on my Dynamic model. My main issue with the tyres is lack of grip. By increasing pressures it may reduce the size of the contact patch making my problems worse.
The boyz over on the other car forums I lurk on spent years arguing over contact patch areas, or they did till one of the tyre designers came on the forum, the gist of it was that the contact patch area is only dependent on the downforce on the tyre and that the 'grip' is the product - mathmatically speaking - of the downforce and the co-efficient of friction provided by the road/tyre interface. So wider tyres don't give more 'grip' but they do provide lateral stability. The contact area stays the same for the same downforce (and the same tyre construction) , but changes shape with wider tyres. More rubber on the road only gives stability when cornering, not more grip. For more grip you need tyres with a softer compound, or a road with a grippier surface, or more downforce on the tyres, all other factors being equal.
Increasing the tyre pressures by 10% or so won't therefore affect the grip, or adversely affect the contact patch size. It may help decrease tyre wall flex and therefore reduce noise, and also help the tyre run cooler. Low profile tyres provide better steering/cornering stability as there is less sidewall flex, but have been mentioned as noisy items by a few car writers, including 'Honest John' of the Telegraph. Incidentally the chunky Pirelli Winter tyres on my 4x4 are quite noisy on the motorway, with most of the noise in the cabin coming from the tyres..
The tread pattern on a tyre only serves to allow water to escape from the tyre to minimise aqua-planing, and doesn't otherwise provide more grip on tarmac, although on loose surfaces the tread pattern on say, winter tyres or snow & mud tyres provides traction, as opposed to grip. On tarmac they function like road tyres. Grip = Downforce/CoF.
Don't shoot me down for this info, I'm only the messenger, but it bears up with what we were told when a couple of cops from the Police Accident Investigation Unit came round to our club to talk about road safety, braking distances and suchlike.. Grip= downforce over coefficient of friction. Not contact patch size. The cops had a formula for working out braking distances during accidents by measuring skid marks on the road, consulting a table from the tyre manufactures, then measuring the coefficient of friction at the road surface by firing a piece of chalk at it. Then they went back to Plod HQ and spent a morning working out the CoF, and the skid mark distance, from that, the speed at which the vehicle was travelling when it braked..
So for more grip it sounds like a bag of cement in the back of the Panda, or a Formula 1 type wing might help here..
There was a neat illustration of the Downforce/CoF thing on 'Top Gear' the other week, where Stiggy was testing the Konisegg (sp?) 200 mph car, and it veered off into the bushes. Top Gear told Konisegg (sp?) that the rear of the car needed more grip, so the manufactures added a rear wing for more downforce. Not new tyres!
I rest my case. Flames and brickbats welcomed.
