grip is dependant on, primarily, the coefficient of friction(u) of the 2 materials in this case rubber and tarmac - strange as it sounds it is only dependant on the weight of the object ( mass X gravity) and CoF (u)and has nothing to do with the surface area a 125 tyre will have the same grip as a 195 tyre if the vehicle weight is the same and the compound of the tyre is the same

larger footprints are to do with heat dissipation wear etc and allow the tyre to be made from softer materials( higher u = grippy)

i always fit the thinnest tyres i can to normal cars and vans makes life easier fat tyres are just heavy steering, tracking aquaplaning PiA

ps racers use toyos because:
1 they have to
2 they are cheap so everyone can have some
3 they fit and can be bought easily, not because they are better

ask what was on the Belgain racer, they had some "track day" semi slick toyos that the Belgains took a huff over.

So I should run 135s really (standard for a super?) the front of the car will be heavier by a fair amount, due to the sud engine though.

2, cheap, that would be my reasoning too.

They were Toyo R888 165 50 r15s I remember the arguments

135s on a Alfa engined 2cv will stick more than 135s on a normal 2cv because its being pulled down on the road more

the extra weight may make it under steer more ( much more all that weight hanging in front of the axle) and the extra power may get you in to all sorts of bother, it wont be that the thinner tyres are less grippy its that there are more lateral forces at work due to greater mass and higher velocity
( youll end up stuffing it in a ditch, to keep it simple )

Yeah, I know, I was just trying to delay the stuffing into a ditch part, oh well, I'll get some cheap black circles and make it quick then haha.

Because I haven't got much to do, mainly for amusement, and certainly not because it's a good idea, I'm providing you with a picture of a 195/50 15 fitted to a 4 1/2" Peugeot wheel. It was a bastard to get on there and I'm sure would be absolutely useless were you to try it on a car.



My car's got 145s on, and as a gut feeling I'd say don't go any bigger than 155, or 165. As Sean has said the friction between two surfaces, ie the tyre and the road, is down to the coefficient of friction between the two surfaces and the force pressing them together(the weight of the car). And also that the weight of the car is an equally contributing factor to the centrifugal force trying to put you in a ditch. That leaves you with the coefficient between the tyre and road being the most important factor.
If you're not concerned with how long they'll last, then look at track day tyres, also try someone like 'Longstone' who supply classic race tyres, although I'm not sure how the compounds would compare with road tyres.

One last consideration, there's a lot more to tyre chemistry than softer=grippier. Race tyres are designed to work best under race conditions, and I've heard directly from tyre technicians that they're no use at all on the road because you can't get them hot enough to work properly.

Try finding a tyre company rep who knows what they're taking about, next time your at a motorsport event. Find out the front and rear weight of the car, and the power and see what they'd recommend.

Joolz,
bet it's going to be even more a b#gger to get that tyre off the rim...
Ken

( Won't GS size tyres, 145 width, be close enough for Louis' car? )

155 tyres
5 inch rims
Quaif diff for extreme cornering!!!!!
good shocks
uprated springs,

and a good driver that will do the trick!!

Nothing will beat a good driver.......

I'm baffled.

Louis, I admire your, (admiration?) is that the right word..? Interest, and that, but with all due respect, at your age, you should be watching gentileman's literature on the Internet

Sorry I don't mean to be rude, keep going

Anyway on topic, I think majorly wide wheels would look not right on an a series....

Peugeot 404 rims are half inch wider IIRC, should be fine for 165