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Old 18th June 2003, 11:37 AM   #1 (permalink)
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Mass of car, cornering and braking

I'm asking this because I have become confused.

Does a heavy car benefit cornering and braking, or not ?

I (think I) understand that by adding downforce to a car by a wing or other, you are making the car seem heavier at speed, at which point it benefits from this by pushing the wheels/tyres onto the ground more and thus more grip, but therefore would a heavy car benefit from this at all speeds?
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Old 18th June 2003, 12:33 PM   #2 (permalink)
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My (laymans) view of it is this:

when you want the cr to turn, your fighting momentum. The car actually wants to go straight on so your fighting against this force. The heavier the car, the greater the force, therefore the harder to turn in.

Once in the turn, the car is also being acted upon by centrepetal forces which make the car want to move in a straight line to the outside of the bend, again, the greater the mass, the stronger the force.

Grip is one way to counteract this force, however, grip is a function of friction, for a given contact patch, greater weight will create more friction, but whether the greater friction is enough to counteract the higher centrepetal forces will decide whether your weight is a positive or negative factor.

Of course this is stuff I've semi-remembered from GCSE Combined Science so is very simplistic and probably innacurate
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Old 18th June 2003, 04:37 PM   #3 (permalink)
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2 cars... 1 weighs 1 tonne the other 2 tonnes they both have equal power-to weight ratios and torque curve/gearing coincide exactly for each... they are perfectly matched... even down to the 'G' force each can generate in any given curve...

In a race the 2 tonne car will eat the 1 tonner... quite easily....

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Old 18th June 2003, 04:44 PM   #4 (permalink)
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Not sure I beleive you

My belief is "there are no stupid questions, only stupid people". In that spirit:

Why would the heavier car "eat" the lighter one? Surely the lighter one will be able to change direction more easily than the heavier one, despite the fact that both can pull the same max g's once in the corner?
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Old 18th June 2003, 04:55 PM   #5 (permalink)
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Quote:
Originally posted by NotoriousREV
Re: Not sure I beleive you
Fair enough... there is a huge thread on here that explains exactly how this works... to me it is blindingly obvious.
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Old 18th June 2003, 05:10 PM   #6 (permalink)
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wheres the link? if you arent winding us up id be very interested to know how it works
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Old 19th June 2003, 07:34 AM   #7 (permalink)
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Ahh good, Mycroft has found this thread

I'm gonna do a fuller search for the other thread now Mycroft, see if I can find it... Was chatting with someone on the way to work about this. Mentioned the identical power/weight. Didn't mention the G in cornering though so he was saying the heavier car's main advantage will be in cornering. Although the heavier car will have the disadvantage in braking - similar force must be applied for longer to slow a larger mass down - it will be able to enter the corner faster and have more friction to stop any sliding mid corner.

Now, off to find that thread ..

EDIT: Well I've had a look.. There was the 'Soarer Drifting' thread, the 17" Wheel thread, and the 'How to make my car corner better' thread, but I couldn't find anything solid on the effects of mass on cornering. Mycroft, any pointers to the thread where this has been discussed?
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Old 22nd June 2003, 04:45 PM   #8 (permalink)
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Quote:
Originally posted by Mycroft
2 cars... 1 weighs 1 tonne the other 2 tonnes they both have equal power-to weight ratios and torque curve/gearing coincide exactly for each... they are perfectly matched... even down to the 'G' force each can generate in any given curve...

In a race the 2 tonne car will eat the 1 tonner... quite easily....

Well, the 1 tonne car will corner quicker if they both have the same tyres on, due to the non-constant nature of the overall coeffiction of friction of heated tyres on a tarmac surface. As the tyres are loaded up, the coeffiction of friction will drop slightly, so doubling the normal force will not result in double the grip. It's for this reason we want to minimise lateral weight transfer on racing cars when searching for maximum levels of grip.

Mycroft will no doubt have some smart explaination as to why this long established and still correct statement is somehow wrong. Pinch of salt to the ready.

However, the larger car will more that like have a huge advantage in the power/drag ratio area. But if the lighter car managed to half its CDA as well as it's mass, it would kill the heavy car.

Paul
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Old 22nd June 2003, 05:14 PM   #9 (permalink)
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The answer is on here... and not even posted by me. [although I did confirm the posters conclusion to be correct]

Kepp going Pavlo... I want to be entertained... and you seem to make me laugh almost as much on here as on the Scooby site. :thumbsup
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Old 22nd June 2003, 05:25 PM   #10 (permalink)
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Well it's good to see people don't change, and Mycroft, you are still full of the usual crap when it comes to your lack of vehicle dynamics understanding.

Paul
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Old 22nd June 2003, 06:49 PM   #11 (permalink)
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If you say so then i'm sure you must be right.
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Old 22nd June 2003, 07:23 PM   #12 (permalink)
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Thankyou, I am glad we've cleared that up.

Paul
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Old 23rd June 2003, 07:48 AM   #13 (permalink)
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Go on Mycroft, give us a hint as to the thread or poster where the information is .. ?
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Old 23rd June 2003, 08:10 AM   #14 (permalink)
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It might be on the old Elise thread....?
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Old 23rd June 2003, 02:03 PM   #15 (permalink)
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The lighter car would kick ass. A lighter car can corner much quicker than a heavier one due to the lower forces on it. A Lotus Elise can corner inside a ferrari 360, and at a greater speed for this reason, it just gets whipped on the straights.

http://racingarticles.com/article_racing-3.html


The point about the heavier car having the advantage at high speeds due to its greater power to drag ratio is true though.
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Old 24th June 2003, 01:36 AM   #16 (permalink)
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Although that article states that a lighter car corners quicker than a heavy one, the maths given does not support that.

In a massive over simplification;
the 1st formula states that a car which is twice as heavy as another needs twice as much lateral force to 'break' the friction.
the 2nd formula says that a car which is twice as heavy as another generates twice as much lateral force as the lighter one.

In order to break the friction the force from the second formula needs to exceed the force in the first equation.
So, if you assume tyres etc and cf of friction does not vary then both cars corner at the same speed for the same radius of corner.

This is how I read it anyway - someone tell me if I'm wrong.

Anyway, I agree with Mycroft (uh-oh) that the heavier car would beat the lighter car on the track if the other conditions were comparable.
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Old 24th June 2003, 01:01 PM   #17 (permalink)
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Quote:
if you assume tyres etc and cf of friction does not vary
And therein lies the problem. The coefficent of friction does vary. It drops with increasing surface pressure. I know this is not normal, but a specific case with tyre rubber on the road.

If you ensured a contact patch of double the area, the surface pressure would be the same, and your statement would hold. however, it was stated by Mycroft the same tyres would be used, I take that to mean same size too.

There is also the added problem of higher polar moment of innertia, and that brings with it increased loads to change the direction of the car.

With soft rubber, there is also a ceiling on available grip, as the tyre material may not have the strength to sustain high loads caused be higher normal force (surface pressure) and lateral loads. This also comes back to needing a larger contact patch.

In the wet however, the situation can be reversed, as the extra pressure works to displace water between the tyre and road surface. Tyres will also run cooler, meaning less change of the rubber breaking up with high loads.

Paul
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Old 24th June 2003, 02:39 PM   #18 (permalink)
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Quote:
Originally posted by Pavlo

it was stated by Mycroft the same tyres would be used, I take that to mean same size too.
Could you highlight that bit for me?

I can't recall typing that nor can I find it...

Quote:
Originally posted by Mycroft

2 cars... 1 weighs 1 tonne the other 2 tonnes they both have equal power-to weight ratios and torque curve/gearing coincide exactly for each... they are perfectly matched... even down to the 'G' force each can generate in any given curve...
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Old 24th June 2003, 08:05 PM   #19 (permalink)
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My apologies Mycroft, I seem to have misrepresented you.

But I take it that in this instance, "perfectly matched" doesn't include power/drag ratio?

I think you have to take the hypothetical race track into consideration also. TIght and twisty will favour the lighter car, with it's better grip/polar moment ratio, and not much chance for the heavier car to excercise it's higher power/drag ratio.

It's not all bad for the heavier car though, as they tend to carry more speed into the corners with most drivers, as they tend to over slow with the lighter car.

I think this thread looks like "I want a skyline but am worried it will be to heavy to handle properly". In which case, it's worth saying a well set up heavy car will be much better then a poorly handling light car.

Paul
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Old 24th June 2003, 08:41 PM   #20 (permalink)
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Remember this?...
Quote:
By Mycroft
#Location: Mycroft's shadow# the 'last' person to be my shadow found the role very uncomfortable...
If you want to continue to be my shadow, then please follow me very closely, I had to 'sack' the last man who claimed to be my shadow [MartinF, occasional poster here.] for constantly mis-quoting me or putting words in my mouth...

The parameters are plain and simple... and are unchanged... just as the fact that the heavier will win every time.
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