View Thread: Weight is an advantage?


Pennzoil GT-R
Everything ive ever been told or taught points to weight being a disadvantage in cornering. However over at gtr.co.uk there is a member who is usually very knowledgeable about most things physics related, and he seems to believe that in two identical cars, one weighing 1 tonne, and the other weighing 2 tonnes. The two tonne car will corner quicker. So what gives?

mustangdriver
Sounds like crap to me :D They don't try to add weight to race cars to help them corner....

Sia Bani
Well, let's think this out...

I can understand what your knowledgeable bud is saying. He's talking about momentum, inertia, etc...

First let me say that it's obvious everyone wants a lighter car. Weight is an advantage on a corner, but overall it's an obvious disadvantage etc.

That's the main issue...it's like saying a cargo plane will fly faster if it was much smaller, and weighed less. That's obvious, but it won't serve it's overall purpose.

Sia Bani
moved to garage.

Carlos Carrera
it depends...... on the curve,
what ur friend might told u, is that more weight = more gravity force against the wheels (suspension, tires) so more grip, but theres another physical fenomena, called inertia.. if the curve is not wide, the weight of the car could break the tire grip and understeer.

lexus1581
Well how about this. With more weight more downforce is created at higher speeds. This then leads to better grip, and handling compared to a lighter car. The heavier car as long as its just as agile as a lighter car should be able to perform just as well or better than the lighter car according to physics.

Just my insight.

Sia Bani
Carlos, the force of gravity won't change on the car; it's not depnedent on the weight of the car.

And about inertia...my theory is that it would be the exact opposite of what you said. The car will tend not to lean as much because of the heavier weight, and therefore can turn easier.

911GT2
Wait for a long, drawn out reply.

911GT2
And carlos is right. Weight=mg. Mass times gravitational force constant. More mass=more gravitational pull, or force.

Sia Bani
Originally posted by 911GT2
And carlos is right. Weight=mg. Mass times gravitational force constant. More mass=more gravitational pull, or force.

weight does equal mg...but the "FORCE" of gravity is constant. :banghead: Weight depends on gravity, not the other way around.

911GT2
Originally posted by Sia Bani
weight does equal mg...but the "FORCE" of gravity is constant. :banghead: Weight depends on gravity, not the other way around.

Force of gravity is weight.

Stop thinking about weight, think of mass.

Sia Bani
Force of gravity is not weight.

Mass times gravity (just like you previously said :banghead: ) is weight.

Blake, I really don't feel like getting into this with you....and you're already coming off like you think you know everything.

I just finished a semester of physics, and did well.

Feel free to shoot around the bush while I eat dinner. :cheers:

911GT2
Look at the units Sia. G is measured in N/kg. Otherwise known as dependent on mass.

lexus1581
This might help in proving the heavier car is actually less likely to handle, corner, etc. better which proves a lot of us wrong including myself.
http://racingarticles.com/article_racing-3.html

911GT2
OK, first Iíll start off by saying this guy is somewhat right. Why you say?

Centripetal force, thatís why.

To start off, letís look at friction though. Given the exact same car except for the weight, one would initially think that since Frictional force (weíll call it F) equals the normal force (think of that as the gravitational force) multiplied by the coefficient of friction (a constant). So since F isnít dependent on speed, F is a constant, with the heavier car always having twice the frictional force, right?

Now we take centripetal force into account. Check this to get a jist of what it is before continuing:

http://hyperphysics.phy-astr.gsu.edu/hbase/cf.html

Now, we can call the frictional force keeping the car going at a particular radius, or call frictional force equal to centripetal force.

Centripetal force=mv^2/r

Letís look at the two situations:

Lighter car: Letís call the frictional force acting upon it F. So F=mv^2/r

Heavier car: Frictional force must equal 2F. So 2F=2mv^2/r. The 2ís cancel.

The cornering speeds are identical.

NOTE: THIS WORKS ONLY IN AN IDEAL PHYSICS ENVIRONMENT. CAPRICE OWNERS SHOULD NOT ATTEMPT A ROAD COURSE AGAINST AN ELISE!!! The physics gets quite muddled when you look at varying coefficients of friction and chassis design. Also gets fucked up when you start applying power to the wheels, this example is in a neutral gear situation.

I certainly wouldnít say it handles better. But it does have equal roadholding ability (read: roadholding is not handling).

911GT2
Lexus, you made my response totally useless. I hate you.

lexus1581
Originally posted by 911GT2
Lexus, you made my response totally useless. I hate you.

:cheers: :tongue:
Sorry i didnt mean to waste your time but i thought that would help greatly (which it did). Now I side with you that the lighter car will actually be better off than the heavier car.

911GT2
Well that was already proven. Watch a Caprice and an Elise on a road course and you'll see the results.

The guy at gtr.co.uk is probably bullshitting this to say his fatass R34 corners better than an R33 or 32

Carlos Carrera
ok i didt mean FORCE of gravity.
i just meant MORE WEIGHT = MORE FORCE DOWN to the suspension so more grip..
lets go back to the topic

Carlos Carrera
fuck my internet its too slow,, that post belongs 5 post before...

FYRHWK1
Doubling the weight doesn't double the traction remember, it's a case of diminishing gains, I remember seeing a graph that started out with 1 lb = whatever unit of traction they were using, I forget which, but then slowly it started taking more and more weight for increased traction. Also remember, each half of the vehicle, even each corner, has it's own specific weight which leads to different amounts of inertia and would require more or less friction.

Basically more weight can be more traction, but you need to disperse it properly in order to handle well, thats why you won't see a 3000 lb+ car with smmall tires handling well, and a smaller one usulaly wont have them since it wont help them corner better and would just add a ton of unsprung weight. Then you have to look at weight transfer to the outside wheels, the leverage of the weight above the wheel hubs efect on the suspension, all of it, but the basics are more wheel friction is better, now how you get that is up to you. . .

911GT2
Well in a totally smooth operation the only friction you want is the acceleration, laterally and otherwise. Rolling in itself is an ideally frictionless property.

Pennzoil GT-R
for what i originally thought was total bullshit by this guy its turned into quite an interesting dbate.

911GT2
It is definitely total bullshit. Take a look at the racetrack.

But there's physics backing to it for some parts of it.

A-Tech
it may help a bit but you forget, lighter cars stop quicker and accelerate faster. So if they are slightly ahead in the turns anyways they blow em away on the straight, later braking points, and faster acceleration

silverTA2002
This is actually a debate????

I thought it was pretty widely known that decreasing weight helps acceleration, braking, AND handling.

Sorry, but a Miata has a distinct handling advantage over a Lincoln towncar.

It's all about inertia. Trying to turn a heavier car is harder than a lighter one.


Downforce is good for handling, weight is bad.

FYRHWK1
Originally posted by silverTA2002
This is actually a debate????

I thought it was pretty widely known that decreasing weight helps acceleration, braking, AND handling.

Sorry, but a Miata has a distinct handling advantage over a Lincoln towncar.

It's all about inertia. Trying to turn a heavier car is harder than a lighter one.


Downforce is good for handling, weight is bad.

well remember, inertia is calculated by mass * velocity^2, so if you could double the traction by doubling the mass, the 2's would cancel each other out as 911 said, only thing is it doesn't work out that way so the inertia overcomes it.

911GT2
Exactly. The chassis can't respond nearly as fast to so much weight.

But how do you think something totally independent like a suspensionless go kart would perform given the same situation??

Run-GSX
If weight is such a bad thing , why have downforce in racecars? It effectively just makes the car heavier , a LOT heavier. The Saleen S7 generates about 7000 lbs of downforce at speed. How is this different and in what way , from the car just weighing that much to begin with , aside from the effect on acceleration.....:scratch:

Pennzoil GT-R
because downforce only pushes the car down under cornering

weight pushes it sideways aswell as downwards.

FYRHWK1
yeah, downforce is essentially free traction, during turns it doesn't carry inertia so you don't have that problem.

911, damn good question, as long as you keep the right pressures on the tire contact patch you should gain traction since the weight isn't soaked up by the suspension. One thing ot note, jsut adding weight won't work, but corner weighting your car can add a ton of traction and stabiliity, there's a 3rd gen guy running an iron bock and over 150# of corner weights most of it at the rear adding traction so it doesn't get loose on the brakes or any other time.

911GT2
Originally posted by Run-GSX
If weight is such a bad thing , why have downforce in racecars? It effectively just makes the car heavier , a LOT heavier. The Saleen S7 generates about 7000 lbs of downforce at speed. How is this different and in what way , from the car just weighing that much to begin with , aside from the effect on acceleration.....:scratch:

7000?? Those numbers aren't accurate. It can travel upside down at 140 mph, so it must generate ~2700 lbs at that speed. I forget the weight of the car though...

But 7000 is racecar level, like F1/Bentley LMP level. Not feasible or possible in a street car.

911GT2
Originally posted by FYRHWK1
yeah, downforce is essentially free traction, during turns it doesn't carry inertia so you don't have that problem.

911, damn good question, as long as you keep the right pressures on the tire contact patch you should gain traction since the weight isn't soaked up by the suspension. One thing ot note, jsut adding weight won't work, but corner weighting your car can add a ton of traction and stabiliity, there's a 3rd gen guy running an iron bock and over 150# of corner weights most of it at the rear adding traction so it doesn't get loose on the brakes or any other time.

Wouldn't that cause a ridiculous amount of understeer and totally ruin your polar moment of inertia?

Run-GSX
Originally posted by 911GT2
7000?? Those numbers aren't accurate. It can travel upside down at 140 mph, so it must generate ~2700 lbs at that speed. I forget the weight of the car though...

But 7000 is racecar level, like F1/Bentley LMP level. Not feasible or possible in a street car.

Read that # somewhere.......:scratch: Maybe I was dyslexic that day.........:shitfaced

911GT2
Originally posted by Run-GSX
Read that # somewhere.......:scratch: Maybe I was dyslexic that day.........:shitfaced

Here's some general aero figures, no S7 though:

http://www.mulsannescorner.com/data.htm

According to that, the Bentley LMP only makes around 6000 lbs downforce at 150 mph so the S7 making more at lower speeds sounds very odd to me.

A-Tech
because that downforce is only created at a certain speed, not when its just sitting there not moving

Carlos Carrera
Originally posted by Run-GSX
If weight is such a bad thing , why have downforce in racecars? It effectively just makes the car heavier , a LOT heavier. The Saleen S7 generates about 7000 lbs of downforce at speed. How is this different and in what way , from the car just weighing that much to begin with , aside from the effect on acceleration.....:scratch:

downforce doesnt produce inertia. weight does.


S7: 2870lb of downforce at 167mph

Run-GSX
Originally posted by Carlos Carrera
downforce doesnt produce inertia. weight does.


S7: 2870lb of downforce at 167mph

I can accept that. Apparently I heard 2700 and switched some #'s :scratch: :scratch:

FYRHWK1
Originally posted by 911GT2
Wouldn't that cause a ridiculous amount of understeer and totally ruin your polar moment of inertia?

Not at all, with so much weight on the front tires it's always the rears that give away due to lack of traction, plus with the corner weights being placed properly the weight is low in the chassis and right by the coil mount. He did add some rear tire to make up for the extra inertia that he'll have to counteract, but between the 2 he dropped a significant amount of time off. Plus when it comes to these cars, the rearend is so light it wasn't to swing itself around the front being it's got the most mass, even with the weights the fronts still got more then the rear does.

911GT2
Originally posted by FYRHWK1
Not at all, with so much weight on the front tires it's always the rears that give away due to lack of traction, plus with the corner weights being placed properly the weight is low in the chassis and right by the coil mount. He did add some rear tire to make up for the extra inertia that he'll have to counteract, but between the 2 he dropped a significant amount of time off. Plus when it comes to these cars, the rearend is so light it wasn't to swing itself around the front being it's got the most mass, even with the weights the fronts still got more then the rear does.

Hrm...so it would actually improve your polar moment by rotating around the fronts rather than the center eh?

Very cool.

FYRHWK1
Pretty much what would happen is that the fronts had so much traction, if he threw it into a turn har d and got alot of sideload on the tires going, the rear would basically start sliding but the fronts would keep traction, adding weight to the rears it trying to shift the center of rotationg back further actually, the most will always be up front but lessening the difference allows the car to make the most of the front tires large amount of traction.