Ok - with regard to dirt on the road - well definitely that throws out the usual equations. They only apply in dry contact with clean (or predominantly clean) surfaces.

This dirt road stuff (or dusty road even) is actually very important. not so much for a performance car launching hard, but in general. Early ABS systems are close to life threatening on dirt roads. The problem there is that to improve traction on loose surfaces, you actually want blocky or chunky tyres that cause a 'buildup' of gravel in front of the tyres (for braking) or behind them for acceleration.

On wet surfaces - I'll have to beg to differ. wider is _not_ always better. The problem is that the wider the tyre, the greater the volume of water it has to shift out of the way, and the further it has to shift it, so the tyre can grip. So once you go beyond a certain width (and it's a lot narrower than what would be 'useful' on a dry tyre overall) the tyre will actually be MORE likely to aquaplane.

Have you ever watched formula one when it rains to the point the cars aquaplane? They are basically just 'floating' in whatever direction inertia leads them, and worse still, as they slow down, there's less and less aero downforce, and then they are totally adrift (no bull) I can't remember which year it was, I think it _might_ have been the year Raikkonnen won the championship, or possibly the year after, and there was a huge downpour during one race, wiping out a good portion of the front end of the field as they all floated helplessly into one another, or the barriers/sand traps etc.

But back to real cars which are heavy enough to push the water out of the tread at reasonable speeds. What you need is two things - very generously sized gaps between each tread block, and the 'horizontal' gaps angled forward so they help push the water out, and lastly, the edges of each tread block need to be as 'sharp' at 90 degree angles as possible, so it can cut and push the water. curves/rounded edges will encourage it to aqua plane. Additionally, you want the tyre pressures higher for wet roads than for dry (even though most will think it is the other way around, trust me, it is well proven that higher pressures make the tread blocks more rigid and help them to push the water out.

On dry ground, you tend to want larger blocks of tread, less grooves, to make the tread more stable and consistent, to enable downforce from the car/suspension to actually maximise mechanical 'grip' at the tyre tread to road surface contact point. Whilst you want 'wider' 'longer' blocks of tread, you actually want LESS tread depth, as that leads to less deformation (the bad sort, not the good, gripping perfectly to the undulations sort). To this end, in racing classes that specify a treaded tyre, especially a specific brand of tyre, the racers all get the tread buffed down to minimal levels. They grip a _lot_ better like that in the dry (and are much worse in the wet) - and that's understandably the reason you'll find that any class of racing that demands a control tyre also regulates minimum tread depth (usually they specify it either has to have at least xmm of tread depth either at the start of the race meeting, or after the last race.


what I'm trying to get at with regard to tread compound being better than width (within sane limits) is that it really is the main thing. Yes, larger wider tyres often have a tread compound that is softer - a good thing for performance to be sure. BUT THE BIG DEAL is that even AMONST THE WIDER TYRES there's still a HUGE variation from tyre brand/specific model to one another. Basically I'm suggesting that finding 'the right' tyre is going to be the go, not specifically the precise size of the tyre.


L18_b110 - without more info it'd be hard to explain why the wider tyre (if they were truly the same compound exactly) were light years ahead of one just a little bit narrower, but I could make some guesses (and that's all they'd be without seeing it in person, and knowing more about the setup). It could be something as simple as shock setting being more suited to one size than the other (as they would transfer weight/alter contact patch differently for different sized tyres) You could even look at difference in track width from the wider tyres, and whether weight transfer during cornering or accleration (or whatever) differed with wider tyres. I'd also wonder as to the relative difference coming from the fact they were newer (even if the same compound when manufactured). Tyres don't stay the same with the passage of time, and even if they are very well stored, each race use will affect them.

I understand what you are saying about ipra control tyres being softer in smaller compounds (I didn't actually know that) but if anything, that makes it worse, because the bigger cars can't (afaict) stop their tyres going off anyway due to overheating (which does mean that width and overall thermal mass is important, but is getting off tangent a little). I just don't think that width is the be all end all on the street. The sort of tyres that people would 'love' on the street, wouldn't last more than a lap or two on the track, it's horses for courses. you could make the same argument about brake pads. a1rm pads have an almost cult following for a good all round high temperature range pad for the street or limited sprints (or maybe hillclimbs, for an all rounder, not a purpose built competition machine)

I'd go further about tread compound being vital - and put forward a few categories where there are soft and hard treads, and at least one set of each must be run during the race. The cars aren't always faster on the softer treads, long term. They overheat and go off, on some tracks (and I realise hard and soft are relative terms and the actual two compounds vary from race to race/track to track) whereas on others the soft compounds are 'ideal' and produce best and most consistent lap times, and they just can't get enough heat into the harder compounds.

You also have to look at the unsprung weight. That can (admittedly) be an advantage in some places, not always, but it's possible. It also depends on how much of an excess of power there is. I remember a website did a very tongue in cheek 'before and after' writeup where they kept modifying things on a car, a stock low-performance import of some description, and ran it down the 1/4mile. One of the first things they did was to remove the big diameter bling wheels and tyres and re-fit the stockers, and despite the stockers being less grippy, the motor just wasn't that powerful (it was running 18 seconds or so iirc) and they improved the time by a few tenths just with the stock wheels/tyres.

Back on the original topic though - when I mentioned suspension setup being vital, it is possible to get a good combination that is reasonable off the line and also through corners. And it _is_ possible (if the suspension geometry/particulars happen to cross over a certain point) to actually be too low for cornering to be optimal.

Last but not least - you could also look at (relatively simple) stuff like having different boost/timing curves that are switchable based on what gear you are in. In some drag racing, they have different timing curves for each gear, not so much as traction control (which is the way I'm suggesting it for helping traction) but rather the fact that the engine is cooler off the line, so more timing is safe/desirable, but toward the end of the 1/4mile with heat soak, chamber and piston surface temps are higher and less timing is both more optimal for power, but also necessary to avoid engine damage.