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Discussion Starter #1 (Edited)
Well you DID ask!

We first look at what causes tyres to get traction and what makes them to 'break away' and slide. This will make you realise that your inputs with the accelerator, brake pedal, and steering wheel are all limited by the Nature of the Physics involved. This bit of background knowledge will also allow you to slide the tyre slightly and by transferring the weight of the car to it bring the car under control. Driving is not just pressing hard on the pedals, knowledge of the physical limits combined with a good feel for the weight of each corner of the car will help you predict the consequences of your actions, developing a good feel for these limits will keep you out of trouble. Tazio Nuvolari, probably the greatest racing driver of all time, said he knew the weight on each corner of his car to within a kilo. If he had not this 'ability' then driving that damned Auto Union would have killed him.

Lets look at real time static friction, (you will like this) take a wheel off your car, go and weigh it and take 5lbs of air out of it, my rear wheel (265/40×17 on a 9½"wide rim) weighs 19.9kgs.
Now make a 'cradle' for it, I made my cradle out of a couple of coathangers and 4 pieces of wood, I know this is a little 'Blue Peter' but bear with me, it'll be worth it, honestly, it will. The cradle allows the tyre to stand upright but unable to roll, onto this assembly you put a strain gauge marked in Kilos, now with the help of a friend (who is by this time convinced you are well on the way to losing your mind and is only helping so as to ensure when you do finally lose the plot and take hostages he has a bargaining chip) you attempt drag this along the ground at right angles to the natural 'roll' you pull from fairly low down and you pull smoothly, your neighbours contribution is to ensure the tyre stays very upright and doesn't 'skip', you then read the gauge, on my car my reading with F1 GSD2 the reading was 36.4kgs, this was on dry tarmac, on concrete it was 35.7kgs on some high friction anti skid surface it 43.4kgs

These figures give the following potential g-force under braking and acceleration of 1.82, 1.79 and 2.18 G and that is the limit of your adhesion.

"HANG ON, HANG ON it can't be as simple as that, what about heat and weight and all the other 'things' " I hear you say well you are right there are lots of other 'things' and weight and heat but the strangest thing is that they all cancel each other out, I have a truly wonderfully complex Computer program for this and the results mirror the results of our little driveway trick almost exactly. you can even do it with tyre and no wheel, but remember that, the less the weight the greater the margin of percentage error.

You can pull from the front and there is sometimes a difference my tyre numbers were 37.1, 36.0 and 48.4kgs (you work out the Gs')

So this little experiment has given you the limit of you adhesion, this is all you have, you will never have more and unless you can make the suspension perfect you will always have less.

Do this and you will know your limits, that tyre on tarmac if I had enough power and perfect suspension could give me a take off the square root of that 1.87G, about 1.37G I have done a 1.0G start, but i believe that a 1.2G start is possible, in reality this is about as good as I'm ever gonna get.

Whilst we are on the subject of starts, read this and ponder... a good start at 0.5G will get you about 8 feet in the first second (2.45metres) a 0.7g start will take you 16 feet (4.9metres) down the line, a 1G start takes you 32feet (9.8metres) and as I said all in that first second.

This is the first part of many, now if you want ask some questions we can expand into grip specifics then this time next week we move on to the next part.

Bet you really can't wait eh!
 

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very interesting and informative thank you mycroft,

as you mentioned

but remember that, the less the weight the greater the margin of percentage error.

forgive me for being dumb, but arent we missing a very big weight, that being the weight of the car itself ?
Surely with the increased weight factored into this experiment, the the adhesion of the tyres would increase greatly?

Cheers,
AK
The Orginial Scouser
 

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Nice one Iain.

I guess weight is tied up with contact area of the tyre so as the weight increases, the contact area of the tyre increases but overall there is the same weight distributed per mm2...?

Tyre pressure is critical to grip and handling. Too high and the contact area decreases leading to more kg/mm2, too low would lead to less kg/mm2 but sidewalls would not be stiff enough...?

Can't get my head around the heat issue though, more heat should make the tyre stickier initially before they start 'going off'...?
 

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Discussion Starter #4 (Edited)
I know this is hard to get your head around but this test developed by Dunlop in the 1950s' is still far more accurate than we like to admit.

The weight of the car is immaterial as is the number of tyres! You get the same result just slightly more accurate.

I have seen footage of guys doing this at Indianapolis so as to get readings for different parts of the curcuit.

Now to heat, this is gonna be difficult to swallow but heat does not improve the maximum traction available. It does allow you to use what you have as the speed increases and the tyre has to gain and then release its grip.

Think, with cold hands, can you grab and release anything as quickly as you can on a warm day, is your apparent strength and grip lessened with the cold, are you actually weaker?, No, your ability to use the strength you have is impaired by the cold, now take the corollary on and with the tyre we are trying pull the tyre across the surface, the molecules have time to search out the imperfections of the tarmac and interact with the surface molecules it finds there, heat only means this searching happens at a faster rate, in this test we don't need heat because we have extended the time frame allowing the tyre time to do what we ask to happen normally in a split second.
 

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Discussion Starter #5 (Edited)
PeterE said:

I guess weight is tied up with contact area of the tyre so as the weight increases, the contact area of the tyre increases but overall there is the same weight distributed per mm2...?
No.

PeterE said:

Tyre pressure is critical to grip and handling. Too high and the contact area decreases leading to more kg/mm2, too low would lead to less kg/mm2 but sidewalls would not be stiff enough...?
See post above.

PeterE said:

Can't get my head around the heat issue though, more heat should make the tyre stickier initially before they start 'going off'...?
Irrelevent, don't confuse dynamic usage with static parameters
 

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Peter,
You werent the only one batting those ideas around in your mind... looks like we failed as a class ;)

Paul
 

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Discussion Starter #8
Don't "beat yourself up" too badly lads, I catch even the most experienced engineers with these things.
 

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Mycroft,
Im not disapointed, i have a mind like a sponge and i am on a quest voraciously absorbing information,

Paul
 

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Mycroft,

Fantasticly interesting and informative, and with a practical exercise too! (Did it in the workshop at tea break).

Good shout mentioning Tazio Nuvolari too, hardly anyone has even heard of him, but for sure his driving ability and car control was bordering on super-human. Hopefully people might do a bit of research into him... Makes for good reading.

Looking forward to the next part - its great having all this stuff to make you think while driving...

Cheers,

Dan
 

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Haven't heard of Nuvolari!!! The legendary flying Mantuan.

I wonder if people will say the same of Schumacher in 60 years?
 

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Tazio Nuvolari

Lightspeed, Search around on the web and you'll find loads. Makes good reading.

Great on two wheels also. He was the machines he drove/rode.
 

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Ears pricked up, notepad at ready, google open in second window ready to look up anything I dont understand... Fire away Mycroft! :D
 

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Discussion Starter #19 (Edited)
Then let's begin, ;-)

Unsprung Weight and Braking.

There are 2 elements to unsprung weight, there is the suspension itself (including the lower half of the shock absorber and the A/R bar) the brake calipers and the 'Halfshafts' these constitute the first element.
The second element are the wheels, the brake discs and the Universal joint.

It is important to separate these elements as they have very different effects on the car and have very different forces acting upon them, the first element has simple 'stroke' forces acting on them, they basically travel just up and down, any weight saving in these components is hard won and any benefit gained is minor, for road cars, frankly any gains will be at the cost of long term reliability so unless you are really going for broke (in all 3 connotations) just keeping these components clean is likely to be the most rewarding thing to do.

Somewhere on the web is one sad bastard who has weighed the amount of dirt that he found on the suspension of various cars, such dedication scares me, but he did discover that the average IRS/IFS carries 2.5lb of rust and dirt overall, that is on a road car that had travelled 24k.

Now to remove 2.5lb from the components on the car suspension would cost anywhere from £500 to £5000.
Simple cleaning prior to a trackday 'may' see the same benefit, as to whether anyone would notice such change with standard suspension... I don't really think so but then again I clean all my 'components' monthly anyway, the 'personal' ones more regularly than that!:smokin:

The real gains are made on those bits that rotate, it is these items that have the most marked effect on the car.

To put this into perspective let's look at the Disc and Caliper on one corner travelling at 150ft/sec (102mph) at this speed if you remove 10grams from the weight of the disc it has the same effect as removing 100grams from the caliper and at higher speeds the effect gets greater, so a lghter disc is the goal NOT lighter Calipers, in fact it is better to have heavy calipers made from good old heavyweight materials as they are superior in all parameters that matter.

We should all be screaming out for 'high tech' discs not sexy, 6/8/10 pot 'flash' calipers. Cem (I think) has the ATE 'Atom' type discs and although he maybe blissfully unaware of it, ownership of these lightweight high tech units means he has probably the best braking system on the site, irrespective of whatever calipers anyone else has, unless they run these discs, he wins, hands down.

Now let's see if I can challenge conventional thinking, we all know that our Braking systems convert motion into heat via the medium of friction and the amount heat generated is entirely a corollary of the weight and speed of the thing being stopped.

So, imagine we have 2 cars, one of them has a combined rotational weight of 100lbs and the other 200lbs, the systems are IDENTICAL in performance, the only difference is in their weight, now due to the 'race regs' these 2 cars each has to weigh 2000lbs, so both cars have to stop 2000lbs at 'say' 150mph
discarding all handling etc 'things' you know that logically these 2 cars should stop in exactly the same distance and in theory the heavier system should be better at continual stops...but you know that because I have framed this 'paragraoh' in this manner that this is not the case, the car with the lighter (rotating) braking/wheels set-up will ALWAYS perform better.

It is the 'lecturer' part of me that asks 'Can anyone tell me WHY this is so.

And as my supper is waiting for me at the Ho-wah Chinese Take-wawy, I will leave you with this, until I return in about an hour or so, Beaujolais is 'interesting' with Sweet and Sour Seafood.

Back soon.
 

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we all know that our Braking systems convert motion into heat

Not sure I follow this one Mycroft."IDENTICAL in performance"
If Cem has a few extra squiggly lines on his disc's he has a better setup?
Assuming Cast Iron is the norm material for disc's,to reduce the weight you will have reduce the brake surface area.
If this is so, then I guess it doesn't take a rocket scientist to work out in your test example braking from 150mph the car with
tiny disc's might stop quicker..once.....what happens when it turns up at the next corner and its super light weight
discs are red hot and it cant stop?

Or have you been having a quiet Ho-wah waiting to reel in someone like me for the slaughter:)
 
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