Other than looking good, there is totaly NO benefit to those 13inch wide wheels regards grip! You may just as well have 2CV wheels on your RX7!
Why? well all to do with the law of friction.
THE laws of static friction are usually described as: (1) F = R, which governs the relation between limiting frictional force F and normal reaction R; and (2) the coefficient of friction is independent of the apparent area of contact.
Ummmmm!
Thats silly. So what you are saying you could get better times drag racing on 2cv wide wheels than drag radials even if the rubber and compound was exactly the same ??
Why do formula 1 cars not just run on bicycle tyres ??
Shaun
Heh heh, that old chestnut!
Yes, the contact patch is the same area on wider tyres (given the same construction, sidewall stiffness, temperature and pressure), F(orce) = M(ass) x A(rea).
However, on a wider tyre there\'s more lateral grip as you have more rubber going sideways.
And the major benefit? Better heat dissapation, sounds bizzare but the wider the rubber the more rest it has between contact with the tarmac, even if it\'s only a small amount it allows the tyre to remain cooler and maintain grip without overheating.
Apparantly ;)
The following link might shed some light on the mechanics behind tyre grip. Needless to say it\'s a complex subject (kinda makes me glad I design engines and not tyres :P ).
http://reviews.hspn.com/articles/128/1/The-Physics-of-Racing-Part-10-Grip-Angle/Page1.html
thats a good link and shows just how complicated anything is when you try and do anything but a rough estimate.
I remember reading somewhere that they amount of grip given by a proper top fuel style wrinkle wall slick actaully defies some of the formula\'s used to try and estimate grip due to the fact that the tyre deforms and absorbs energy + the fact that it is practically stuck to the track as well!
wider = more rubber on ground... period.
wider wheels ... or tyres? oh there\'s another debate :) narrow tyres on wide rims and wide tyres on narrow rims ... a can of worms on many forums :)
Bit confusing this thread
I think as I understand it the diameter of the wheels has an effect on grip as well.
Eg having 18 or 19 inch wheels on the drag strip degrades the amount of traction you have off the line, you better off with 16 inch diameter wheels as you have more of a sidewall of the tyre which will allow flex and less prone to wheel spin.
Thats why a lot of drag tyres have huge sidwalls mounted on 16 or 15 inch diameter wheels to allow flex and deformation of the tyre to gain traction
Quote from: RedRummywider = more rubber on ground... period.
How so? Pressure = Force / Area
So if you get wider tyres, there\'s a wider area for the same weight (add in gravity to you mass), so that same area must be thinner (front to back) ;)
But of course this is all static... Add some movement into the equation and it get\'s weird.
My thinking is a wider tyre would be more likely to find the \'grip\' point over a larger area.
So if yout tyre was a foot wide and only 1inch of the ground had grip and say the other 11 inchs was pollished metal, Ice or grease you would have at least 1 inch of good contact, where as a Bike wheel may never find that one inch of available grip.
P.
why do people get so tecnicall about antsy things. . .
once i was listening to a raceing driver at knockhill being interviewd. he was asked why dose he still weav about the track on warm up when its "proven" it dosent heat tyres up any more due to bla bla bla.
answer: if i dont, i crash at 1st corner.
easy answer.
if you think skinny tyres are good go for it. ill just keep my wide ones thanks,
Quote from: normskiOther than looking good, there is totaly NO benefit to those 13inch wide wheels regards grip! You may just as well have 2CV wheels on your RX7!
Why? well all to do with the law of friction.
THE laws of static friction are usually described as: (1) F = R, which governs the relation between limiting frictional force F and normal reaction R; and (2) the coefficient of friction is independent of the apparent area of contact.
Ummmmm!
its a simple model like assuming theres no air resistance on a falling body
makes its easier to understand a level mechanics apparently :Hammer
i like the look of wide tyres hence having 19x12 rear wheels :D
i went from standard alloys to 18x8.5j front and 18x9.5j rear, the new ones weigh alot more and i think they have maybe taken a slight bit of acceleration but not alot, i had similar tyres on both sets, on the new ones the handling is alot better and much more grip.
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
This is fine if the entire surface of the road is flat, clean ,no man hole covers and no camber:3Confused
P.
Quote from: TimmyThis 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.
Quotewhy 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.
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.
Quote from: od404The 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!!!
Quote from: ashchowever 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.
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
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
Quote from: dthebukits 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
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
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.
^^ yea but bigger brakes look better and dissipate more heat :D
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!
Quote from: Timmyso 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.
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.
Quote from: TimmyAt 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 ;)
You can\'t go down that road regards brakes! you bring into play things like maerials tech ie carbo fiber heat Dispersion and alike. we are on about road rubber here. Fact, same car, same contions, same road, same compound, but 1 has wider wheels and rubber than the other, stopping distance ie friction brake point will be the same, It\'s the Law!! can\'t get around physics man! :burnout
you can\'t simplify physics to the point you have either ... we will never fully understand the "laws" and there will always be exceptions.
Decent pad material and a good set of calipers is all that really matters imho. The last time i chcked RX7\'s come with 4 pots as standard which is more than enough to stop the car.
If you scrimp on pads then there is no wonder you\'re getting brake fade. Either that or your on the brakes alot longer than you should be. Short/Hard braking for track will pro-long brake fade. I only attend open pit events so you can go out for 10 minutes and then come back in to let things cool down before going out again.
a quick mental experiment. you have a length of 2x4 wood flying on the floor and you have to push it along the ground. in order to account for the way in which the rubber lightly beds in to the tarmac (rubber is squishy, and tarmac has a number of small holes in it, so its going to happen) by your account then pushing the wood sideways will required the same force as if you were pushing it length ways. I am sure you will agree that from experience from shifting heavy stuff you move it in the direction of the smallest side. so the value of mu has changed even though NOTHING has changed in the two bodies, just the direction of movement. now consider you get a piece of plywood that is the same weight as the 2x4. and try pushing that flat on the carpet. again by your statement then because the weight is the same the force required will be the same. again i hope you can see that this is intuitively wrong.
from your first post, your original equation is wrong, f does not = r, it is in fact f=mu*r if f=r then it would mean that all materials have the same frictional coefficient- all materials would require the same force to move them. it is \'mu\' that is the key to this, and as i have said before they calculate this empirically for a system.
\'ok so this thing weighs 10kg, so thats 100newtons. on this surface, at this temperature, etc, etc, etc, it takes 50 newtons to move it, therefor \'mu\' is 2\' for an example. in A level problems they give you mu to allow you do do a nice sum that can be marked. but by changing the size of the tyres, of the pressure in them, or the temperature of the day, or the surface they are on, or the make up of the tyre, or any other of hundreds of variable, you change \'mu\' therefore you cannot compare a tyre of 3inch width with one of 10inch, as there aren\'t like for like. all \'mu\' does is give a conversion factor between the weight (or normal force) to the maximal frictional force. and even then it is a rough estimate as i doubt the weight/frictional relationship is linear in real systems.
marco
(again the usual, \'if you know better, shoot me down\' applies:o
Your bits of wood, of course there will be a Difference, as it will take more energy to move the whole weight of it than pushing it sideways, as you will not have the weight of length to overcome. So that doesn’t work! Weight is different from friction which is what you would feel when pushing length ways opposed to sideways.
Anyway, it depends how pedantic you wish to be regards width of rubber, of course you may find very, very slight differences if measured precisely, but the point still remains, if one takes two things of exact equals ie car weight, conditions, everything except width of rubber you will find almost no difference in the point of friction loose, that is a fact! Put it to the test if you don’t believe it, but things have to be as near as possible to each other except width of rubber, and don’t forget the compound, which also has to be the same.
i don\'t think you have understood me. there is a plank of wood on the carpet. you push it one way (so it travels with its longest edge leading, lets call the sideways) and 90 degrees to that (so its shortest edge leads, lets call that forwards) going forward will take less effort than going sideways, even though the weight remains constant (same wood) and contact area remains same (same wood). try the same with a piece of plywood of the same weight (constant weight, but different contact area) again would expect the effort required to vary from intuition. do you agree with this?
another way of thinking, it is well known that over inflating tyres leads to a reduction in grip available, no? and why do you think this is the case? it is because the increasing the pressure tends the tyre to become more bulbous, and as such has less contact with the ground. a small change in pressure can give a noticeable change in grip, not measurable, i mean noticeable as in you can tell by driving. if your statement is correct, then how come such a small change in pressure in the tyres (which will produce a change in the contact area of only a square cm at best) can affect grip, whilst increasing the width of the tyre by inches cannot? or are you implying that changing tyre pressure affects grip on another way? if so can you please tell me how it does so?
The way i see it, on a road car there is an Optimum contact area to weight, if you exceed this you will start to suffer from Aquaplaning.
It works the same in the dry but obviously the rubber tyres will heat up and give a better Grip (another reason you shouldn\'t go to wide, as the tyres won\'t warm up properly unless your Flat out i.e. racing)
Don\'t get Racing on a track and Road use mixed up, you don\'t see F1 cars driving down the road.
An example http://www.youtube.com/watch?v=I0O7gFycPho