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Well, I looked at "Mycroft's" presentation and see that it belongs to a Dr Pat Hollis at Florida State University, I note. Maybe that's who Mycroft is. Golly, that would be clever if he was.

Slide 26 shows:

V Load = 900 lbs - coefficient of friction = 1.1
V Load = 1350 lbs - coefficient of friction = 1.05
V Load = 1800 lbs - coefficient of friction = 0.95

i.e. more load = less friction.

If the car has, say, 1350 lbs on each wheel then axle weight is 2 * 1350 lbs = 2700 lbs. The cornering force it can generate from the tyres is 1.05 * 1350 * 2 = 2835 lbs.

If there is a circumstance where one tyre has 900 lbs weight on it and the other has 1800, the cornering force it can generate is 1.1 * 900 + 0.95 * 1800 = 2700 lbs. 900 + 1800 is still 2700 lbs so the weight of the car hasn't changed at all, it's just more on one wheel than the other, which I think is what happens when a car goes round a corner.

So let me see:

Without weight transfer = 2835 lbs
With weight transfer = 2700 lbs

So if there were no weight transfer each axle could corner at 1.05 g. Which I think means the whole car can corner at 1.05 g? If there was weight transfer at both ends then the whole car could only corner at 1 g?

So is weight transfer bad for cornering? Is that why racing cars are always low?

If there was weight transfer at, say, the rear of the car then the rear axle could only corner at 1g and it would run out of friction first. I don't know if it's important which end of the car runs out of friction first, I usually drive very slowly. It feels like it might be important, though.

Of course I'm not an expert like Mycroft is. There might be something I'm missing. I would be really grateful if he could explain it to me and fill in the gaps, this all seems so complicated.



BBB
 

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Hey Mycroft, im impressed with ur knowledge, and everybody elses, but u must have alot of free time to think about this compleecating stuf, hell i guess it must mean alot to you, ?!?!?!?!?!

Harry
 

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As this goes a bit over my head... can I ask a down to earth question related to a specific car ?

A Merc SL55 AMG weighs in at about 1970 kg :)eek:) but can still do the Nordschleife in 8:12 and corner at 1.15g in one particular bend at Hockenheim. (an Evo 7 did about 8:25, max G 1.1)

Sure, the Merc has good power but a car that weighs the same as a small truck shouldn't be able to get such an incredible time should it (or higher G's)? Is that just pure suspension genius ?

As a side question: isn't it true that a heavier car allows you to fit wider tyres ? Which should aid with lateral grip ?

Sorry if I misunderstood.

Theo
 

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Hi Theo

First of all the SL55 AMG is an absolute beast of a car. Wonderful engineering and design. Awesome power, and the might of billions of dollars worth of development experience and technology. So it's going to be a corker :D.. but...

There could be any number of reasons why the car would be quicker than another. If we assume they are both being driven to the absolute limit of their capabilities, these range from ..

Components :
- Tyres
- Suspension Components
- Engine
- Wheels
- Etc (sorry for the etc, but there are bound to be more I'm not thinking of)

Set-up
- Aerodynamics
- C/G height
- Suspension Geometry
- Damper, Spring, Bar set-ups
- Gearing
- Tyre Pressures


Then environmental issues
- Track Surface Condition (including temporatures)
- Ambient Temperature
- Humidity
- Air Pressure

But sticking with the actual set-up issues. If you take two cars and one is heavier than the other and you know nothing else about the set-up, there is no way to determine which will be quickest. A heavier car isn't automatically slower than a lighter car. But weight is a negative to performance, so if you set-up a heavy car to the limit of it's performance, you would be able to make it go faster by reducing the weight and setting it up again.

Not sure if that answers the question?

Cheers

Simon
 

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I'm not even sure what my question was :D

But... ok, I understand that it's silly to compare 2 cars out of the blue. The reason I took the SL55 AMG was because when you read it "on paper" it weighs 2 tonnes, has an autobox ... doesn't sound like a fast car at all. Power to weight: 4.13 kg per BHP. Cw: 0.31

An Evo is a nimble car, less power sure, but about 4.90 kg per BHP.

The big difference seems to be tyres: 225/45/17 for the Evo, 255/40/18 front and 285/35/18 rear for the Merc.


Say you could indeed save 300 kg on the SL (there's quite a bit to throw out :D ), would you still be able to use the same tyres, or would you be forced to step it down a bit (not enough vertical load to get optimal contact patches etc...)

More in general: the Germans seem to be able to make heavy cars pretty fast (M5, RS4 etc)

These stats come from Sport Auto, and yes, we can be pretty sure they were driven right on the limit (always same pilot who holds quite a few lap records in production cars - Horst Von Saurma)

A car you may know first hand: an Esprit Sport 350 did a 8:13 lap, 1.2 G lateral force, Cx of 0.35. With a power to weight which is way better than the Merc: 3.7 kg per BHP. And you surely will admit Lotus does know a thing or 2 about handling :p

I can give you outside temp/track temps, humidity as well for all these tests, but it would get a bit boring I think. Not trying to prove anything, just wondering how on earth they can make a 2 tonne Merc slightly faster on the Ring (say just as fast OK ?) than an Esprit.

So to wind back to a simple question: lose 300 kg on the Merc, can you still fit the same tyres ?

Theo

PS: these stats are online here. German I'm afraid, but you can read the numbers :) About 60 cars in the database.
 

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But to slightly rebutt myself... the Hockenheim times are very different : 1.15,3 for the Esprit, 1.18,4 for the Merc. Ho hum. Massive difference, Hockenheim being more of a handling circuit.

I'll shut up now :D
 

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I'll shut up now
Not at all!!! This is a mega subject, and it's exactly this kind of thing that sparks off healthy discussion.

On the tyres issue.. If you lower the pressures in line with the load, the area on the contact patch can remain the same. It's little known (although thanks to the internet way more widely known now) fact that the area of the contact patch is (almost 100% accruately) derived from the load on the tyre and the tyre pressure.

In other words.. if you had a 285 wide tyre and a 205 wide tyre, inflated them both to 30psi and stuck the merc on top of them, both would have approximately the same contact patch area.

Can you fit a wider tyre to a heavier car? Well, you would certainly want to, as a wider tyre creates a wider contact patch (although shorter) which theoretically gives you more lateral grip. You could also then lower the pressures to give you a larger contact patch area which allows the tyre to produce grip more effectively (not more grip - strangely enough - but it won't heat up as much and will spread the load more evenly).

But if you fit the same tyres to a lighter car, the pressures would have to be incredibly low in order to retain the contact patch area, or it would be too short to produce good longitudinal grip.

So in essence (which means, we've moved on to the thing that mycroft was harping on about constantly) you can theoretically say that a heavier car can utitlise a wider tyre better.

All the best

Simon
 

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Sorry... I forgot about the merc / lotus thing.

The reason for my vague post is that it's really difficult to tell what the reasons are without testing them properly.

But, possibly the reason the merc was quicker was due to the long stretches of downhill sections at the ring outweighing the long stretches of uphill... Seems too simple to be an explanation, but you never know.

In addition, possibly high speed sections are longer, which means power to drag ratio becomes important (haven't checked the numbers, but maybe the SL has better power to drag? - otherwise, it could be the other way round?).

Maybe the Lotus produces less lift, in which case high speed corners would favour it?

Sorry there's not a easy straight forward answer to this, anyone who suggested there was would be guessing.

All the best

Simon

PS. Great questions
 

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Discussion Starter #110 (Edited)
So many posts!

Pat Hollis is not me, but obviously must have been down this road before. :D

Theo, yep the Mercedes does do rather well doesn't it, proving my point rather well from the first thread, make a big car do the same as a little'un and it will be expensive but quite formidable.

BBB,

You posted this...

V Load = 900 lbs - coefficient of friction = 1.1
V Load = 1350 lbs - coefficient of friction = 1.05
V Load = 1800 lbs - coefficient of friction = 0.95

And many here see that confirmation of Simons assertion that 'double the weight and you get less than double the grip'

Is that right Simon?

Bowl of popcorn at the ready.
 

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Mycroft said:
V Load = 900 lbs - coefficient of friction = 1.1
V Load = 1350 lbs - coefficient of friction = 1.05
V Load = 1800 lbs - coefficient of friction = 0.95

And many here see that confirmation of Simons assertion that 'double the weight and you get less than double the grip'
Damn, that was a long read (the thread).

Now, I am really confused here, loads, weights, mass, grip, friction, lateral acceleration all seem to be mixed up. :confused:

When looking at the above quote, and assuming the numbers are correct, it looks to me like when you double the load, ie. look at 900 lbs vs 1800 lbs, the friction coefficient for 1800 lbs is indeed less than double that of 900 lbs since 0.95 < 2.2. Now: is "coefficient of friction" and "grip" the same thing? I think Simon said it isnt because of chemical reaction of the tyre with the tarmac or something like that.

Anyway, good to see that you guys are actually talking about the subject rather than just flaming each other. :)

Oh, and one more thing: are you guys saying the same thing with different words like you were talking about rebound on scoobynet or are you really saying different things?
 

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Discussion Starter #112
Originally posted by black_bird_blue
So is weight transfer bad for cornering? Is that why racing cars are always low?

If there was weight transfer at, say, the rear of the car then the rear axle could only corner at 1g and it would run out of friction first. I don't know if it's important which end of the car runs out of friction first, I usually drive very slowly. It feels like it might be important, though.

Of course I'm not an expert like Mycroft is. There might be something I'm missing. I would be really grateful if he could explain it to me and fill in the gaps, this all seems so complicated.
Well, my post above this one does say the same thing, so you are indeed right... well done :D

I have attached it to save you the hassle of looking:-

''Where Simon has gone wrong is that he has taken the fact that weight transfer across the axle line will on all suspensions systems [except the Active type I have mentioned before] deplete the 'grip' those graphs also work for that phenomenon also and if you go to the link I have posted you get further confirmation of both these facts.''
 

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Discussion Starter #113 (Edited)
Hi Claudius... damn it man in your first post you start to spoil my game. :D

Claudius, staggeringly these fools actually do think that co-efficient of friction = grip. :D:D:D

Cancel the popcorn... bast..d!

Don't mention the 'rebound thing' from scooby-net, they'll get all upset again. This 'Act 2' of that fiasco...

Mycroft 1 Scoobs 0 [Scoobs retired early to the showers with bruised egos] :D
 

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And many here see that confirmation of Simons assertion that 'double the weight and you get less than double the grip'
*sigh* Mycroft, that is only part of the story. Give me your best shot.
 

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Iain, my ego isn't bruised ???

This shouldn't be about ego's IMHO.

This stuff is way too fascinating to turn it into a shooting match.

I honestly don't know who is "right or wrong", hence why I posted the "heavy German syndrome" :D

Simon, I understand you can "fiddle" the contact patch through playing with the pressures. A guy I know inflates his rear tyres to 40 psi, and then has a ball on track, going slightly sideways :D F1 cars have almost no weight but have very low pressures.

But wouldn't lowering the pressures (on the big tyres) mean you would lose some stiffness / make the tyre too compliant ? Or would you indeed fix that with a different tyre design ?

Again, not trying to prove a point or taking sides, I hate everybody :D ;)

As for the Ring thing... I understand there are so many variables. But you do start at 600 m. above sealevel, go down to 297 m., and then logically you have to get back up to 600 m to finish :D

But there is indeed a section where power/drag play an important part, mainly from just after BBQ corner (where Lauda had his moment) up to one corner before the Carrussell.

Maybe it's time to take an SL 55 AMG to Hethel ? :smokin:
 

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Mycroft said:
Hi Claudius... damn it man in your first post you start to spoil my game. :D
I'm sorry, Iain, but this time you made it much less obvious! :D


Mycroft said:
Don't mention the 'rebound thing' from scooby-net, they'll get all upset again.
Let me get the link... ;) :D


Mycroft said:
'Act 2' of that fiasco...
Hold on, I go get some popcorn! LOL :D


Mycroft said:
Mycroft 1 Scoobs 0 [Scoobs retired early to the showers with bruised egos] :D
Hmmm... in fact, they stop responding when they cant take the heat anymore (which does not take too long btw!) :p :D
 

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Discussion Starter #117
Originally posted by Wide-O
Iain, my ego isn't bruised ???
Theo, [evilbevel] no i don't thinnk you were much effected by the last debacle these guys suffered but, i assume that is because you are a little older and wiser than the average SN'er.

You are OK in my books.
 

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Discussion Starter #118
''*sigh* Mycroft, that is only part of the story. Give me your best shot.''

Simon, you are firmly in the drivers seat, strapped in very firmly indeed.
 
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