Why have those BIG BIG wheels??????

[Paul-Tll]

This is fine if the entire surface of the road is flat, clean ,no man hole covers and no camber:3Confused
P.

[od404]

This makes no sence if F= M x A and you increae A surely you have more force.
 
ie
 
M is 10
A is 10
so F = 10 x 10 so F = 100
and if we increase A to 20 F= 200

The A stands for acceleration in that particular equation. The equation that links Force and Area is F = U x A where U is the coefficient of friction between the two surfaces in question.
 

why do people get so tecnicall about antsy things. . .

Speaking for myself only, I like to be able to understand why things happen rather than just accept it at face value.  Obviously I don\'t stand a chance at understanding everything (though I do sometimes try :Giggle ), but certainly where my car is concerned it helps me to make what I believe to be more informed decisions on it.
 
Threads like this are good though as they can benefit those that want to learn a bit more of the techy stuff.

[ashc]

however as i found out to my detriment 18 months ago, a bit of water under a wide wheel breaks the traction quicker than if it were a narrow wheel.

[dthebuk]

The A stands for acceleration in that particular equation. The equation that links Force and Area is F = U x A where U is the coefficient of friction between the two surfaces in question.
 .

its not A is R, the reaction force, like i said before thats a simple model to make life simpler, tho it is incorrect.

i think the other guy was thinking of P=F/a where P is pressure and the force is the weight making P=mg/a

overall the level of mechanics is scary so i can\'t explain it to you, as i dont know!!!

[Timmy]

however as i found out to my detriment 18 months ago, a bit of water under a wide wheel breaks the traction quicker than if it were a narrow wheel.

That\'s to do with aqua planning. Ie large surface area on water so technicaly at a certain speed the car actualy floats.

[marco]

a wide wheel is more likely to aqua plane than a thin wheel, taken to it extreme that is why you can ride silly thin tyres on bicycles with no tread on them and still have grip through puddles (just avoid the white lines!!!).
it has been a long time since i did A level mechanics (and all my uni notes are at home!) but i thought that frictional force= (mu) * the net force acting perpendicular to the direction of frictional force. i.e push down hard on something on a table and it is harder to push it along that table. this frictional force is the static frictional force (the maximum amount of friction that is capable of being generated is greater when the two bodies are static relative to each other, rather than when they are moving- think about pushing a book on a table again once you have got the thing moving, it requires less effort than to actually get it going) and this is the type we want on the tyres, otherwise we have wheel spin.

Unfortunately, this pretty simple equation doesn\'t hold too well in the real world (what A level equations do!) as it comes down to the fact that the relationship between the normal, and maximal frictional, force is not constant- i.e. mu varies. it is this variation which account for the fact that wider tyres can give more grip. note also that mu is a function of the system as a whole, temperature, tyre composition, road composition etc etc all factor into the value of mu; as such it can only really be determined experimentally for a system, although there will be guideline values knocking around! so changing the width of the tyre is changing the system and so a new value of mu is required!

Right i have babbled on about this from my own rusty memory, and from what a could gather from wikipedia in a couple of mins, no doubt i have stated something incorrectly, if i have then feel free to shoot my argument down in flames!

Marco

[chrisJDM]

well im not sure about anyone else but thats gone straight over my head, well i didnt do too well in science at school :p

If you take out all of the science behind it then its not hard to work out that wider wheels have more grip as there is more tyre on the road, i was thinknig about this a while back, do i have smaller lighter wheels or bigger wider wheels with more grip.

it depends what i see as more important weight or handling, more wieght is going to slow the car down where wider wheels give the car more grip and traction.  I know this from experience, i use to be able to wheel spin the standard alloys with ease and now with my wider wheels they do feel heavier but its harder to wheelspin and the can get alot more grip and has definetly improved handling

[od404]

its not A is R, the reaction force, like i said before thats a simple model to make life simpler, tho it is incorrect.

i think the other guy was thinking of P=F/a where P is pressure and the force is the weight making P=mg/a

overall the level of mechanics is scary so i can\'t explain it to you, as i dont know!!!

Quite right!

Clearly 9pm is too late for me to be thinking :rollin

[normski]

I think the idea is connected to the friction brake point which basically maintains no matter how wide the rubber surface rubber it will loose grip at a given point, of course some things can be improved like the compound to make it softer which helps, but take 2 of the same cars, same compound rubber, but one has 10 inch wide rubber the other has 5 inch wide rubber, take them both to 100 mph and stuff your foot on the brake till it locks up, the point at which both cars loose grip and begin to skid will be about the same, ie loose of traction!

It\'s a physics law, friction loose point is friction loose point, and is independent of area covered.   :flamed

[Timmy]

so what you are saying is bigger brakes won\'t help either on that principle. Despite it been proven. I think you more of looking at there is a maximum amount of friction you can get and the point at which it comes into effect is probably alot more than 10inches.

[dthebuk]

^^ yea but bigger brakes look better and dissipate more heat

[marco]

by friction loose point to you mean the point of limiting friction, i.e. the maximal force that can be overcome by static friction before movement between the surfaces occurs? if so then this is given by by the equation i gave above, and as i said before, is therefore dependent on mu. the value of mu is calculated empirically, and is dependent on the system, of which the surface area of the contact is a variable. while you are correct that the increased surface area will mean a reduced force per unit area, the value of mu does not vary linearly with this (it is just assumed to in very basic calculations to make them easier) and as such increasing the size of the contact patch, i.e. the tyre, should increase the maximal available grip.

again i could be wrong, so if anyone wants to shoot me down feel free!

[RemarkLima]

so what you are saying is bigger brakes won\'t help either on that principle. Despite it been proven. I think you more of looking at there is a maximum amount of friction you can get and the point at which it comes into effect is probably alot more than 10inches.

Bigger brakes DO NOT make you stop any quicker! They just last a lot longer

Track work it\'ll make a huge difference and a "normal" road car I can make the brakes fade in about 5 minutes of driving in anger.

Plus you can (read sometimes depending on setup) get better modulation as the yanks call it. Better brake feel.

But if you can make the wheels lock, you can\'t stop any quicker than a tyre will grip. Q.E.D.

[Timmy]

this is where it will get more complicated. Because a larger surface area on the disc makes it eaisier to put the correct amount of brake pressure down due to having more progression because it is not optimal to lock the brakes. Than the limiting factor becomes tyre grip. Otherwise the only upgrade required is pads.
At the end of the day in real life big brake and wide tyres work.

[RemarkLima]

At the end of the day in real life big brake and wide tyres work.

TBH I\'ve tracked loads of different cars and raced a few too and only ever upgraded the pads. I\'ve never done the big brake thing. Always just used the stock discs or whatever was cheaper in grooved (never used cross-drilled after one set that cracked to peices after on decent trackday!).

Track days are much harder on the brakes than sprint / short races, and unless you\'re doing serious endurance events with slicks or semi slicks, I\'d really not bother with big brakes and spend the grand or so it costs on driver training. Just get the most from the available grip.

I do agree wider tyres help, but don\'t agree that bigger brakes mean better stopping.

Your limiting factor is tyres, it\'s why it\'s soooooo important to get decent rubber before everything else, they\'re the single most important factor of a car, everything else comes from the tyres.

Just MHO