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Our Formula Fords use 13" wheels. Do Australian use 14"?

In rain / dirt / snow I'd rather have narrow tires in a light car. You have to realize that you could go a safe speed with any decent tire.

Handling dynamics are part of the issue. I used to have a subaru impreza wagon, thing went 100 mph in the rain and you never knew it was wet until you'd watch cars behind you going slower in the same lane spinning out.

i have 195x50x15's on my datto now, those might be slightly too wide, I think I'd like the front tires to be a little narrower. Biggest problem I see so far is that the center of rotation for the front wheels is a bit outside of the center of steering, so it wanders a little under severe breaking.

Wide tires are best on dry pavement where you have alot of cornering loads to make up for the wider contact area, so hopefully they're low profile or you'll hear alot of tire scrub.

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This is not a theory in kart racing people have a lot of trouble with the engine boging down in low rpms and it can be hard for them to find the right tune up.

As for drag racing we should stay away from this because it is a different ball game and we will just get people confused.

yeap dattodude is right the heat build up or lack of heat in a tyre is going to have a great effect. like a Formula ford could never heat up a Formula 1 tyre to its optimum.

If you own a car with some decent H/P and it does great burnouts with its wide tyres; what happens when you bolt on your skinnies ?
Yeah SUPER burnouts!
You guys can draw your own conclusions.

This has been covered in detail on www.performanceforums.com.au for those interested. My personal preference is for a good quality narrower tyre over a wider and lesser quality tyre. Aquaplaning is scary!
I have a set of Falken 175/60R14 semi slicks which have far more grip than my Michelin rubber which is 195/60R14. I'll leave the science to the experts. I just know what feels right on my car.
Matty

converted, I think that book you read is focussed heavily on open wheelers. The aero argument is all but irelevant for tin tops, especially those with 70's aerodynamics.

first thing to point out is that there are two types of grip and people get confused jumbling it all up into one thing. There is straight line traction, and then there is lateral cornering grip. And there are different physics at work in each. to explain that simply, putting more weight over a tyre that's trying to get straight line traction will increase its grip on the road, but adding weight to a tyre that's trying to produce lateral grip will reduce your cornering speed. A given tyre can generate only a certain amount of lateral force. The force acting against it is a combination of the mass and speed of the vehicle on it. increase the mass on it, and you reduce the speed that brings you to its maximum force. the small increase in lateral grip you get from pushing it harder against the road isn't enough to make up for that effect.

Weight transfer is king in straight line traction and the enemy to cornering grip.

when you go from a stock 155r12 (or whatever it is) say to a 205/60*13, the contact patch of the tyre changes shape, from a fairly long, narrow oval to a very short, wide oval shape - you've probably almost taken the first contact patch and turned it 90 degrees. The total size/area of the contact patch doesn't change significantly. The change in contact patch changes the way it interacts with the road and the amount of cornering force it can generate. Put simply, the tyre will generate its best grip in a direction iin line with its wide part of the contact patch.

The heavier the car, or the faster you want to go around corners, the wider the tyres should be. The only limitations to this rule in the real world are the restrictions of the available space in the gaurd, or the rules in the racing category - eg restricting rim width, rules govering flares etc. Open wheelers have the areo tradeoff to contend with, but the main limitation in most cases is the rules again.

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B210sleeper, your'e a legend. In the real world, where we encounter rain, dusty roads, mud, hot pavement or concrete, the issue is not quite so clear as it might be for a single purpose race vehicle. Generally speaking, a sizeable improvement will be gained with a relatively modest change in tyre size. 235's on the front & 275's on the rear might look hot, but they would be more grief than they're worth under a small light car.

I ran 185x13x60's on the front of my 1000 sedan & they never ever let me down. They never touched any part of the body either.
The rears, however had a diferent spec to fullfill. I needed a bit more gearing, so the outside diameter was increased to the largest that would successfully fit & work under the rear guards. The rear also has a greater lateral [sideways] load when cornering, so i went for a wider section there too. I tried 195's & eventually settled on 205x60x13's for the rear. This also gave it a nice little rubber rake & the Big 'n' Little look apealed to me as well.
Now these are not the sort of sizes that inpress the racers, or the wannabees, but the air volume in the 60 series tyres allowed a quite acceptable ride quality & these tyres never let me down in the twisties with the power that was available to me with my GX & 5 speed. The beauty of these sizes is that they are readily available in a few diferent brands at VERY reasonable prices.
I absolutely loved that car, so much so that the memory of it is what is driving my KB10 project. I was on a good thing & i'm going to stick with tyre sizes that i know worked well for me, rain, hail or shine.

What is it that old farts say,... everything in moderation? Well, combine that with "Horses for courses" That means, use as much tyre as you need, which may be a lot less that what you would like.

Yeah the book does deal with open wheelers but the author actually has a 1600 which the books focuses alot on too...it is a hard book to digest, there are many, many factors which a may get a small flash of comprehension of before I die in my old age.....

I use 205x60x13 on my 1200 in the summer, and switch to my 185x70x13 in the winter months. this works really well for me.