Power to weight ???
Discussion
All things being equal, if two cars have same power to weight will they both be as quick round a circuit?
Obviously I understand there are many factors affecting it, but for the sake of argument - same car, first weighs 1000 kg with 100 bhp, then 1500kg with 150 bhp.
Or if it's easier, the real reason I asked, will my 306gti be as quick as a 205 gti if I get a similar power to weight ratio - mainly on hills where inertia and weight have a big impact
Obviously I understand there are many factors affecting it, but for the sake of argument - same car, first weighs 1000 kg with 100 bhp, then 1500kg with 150 bhp.
Or if it's easier, the real reason I asked, will my 306gti be as quick as a 205 gti if I get a similar power to weight ratio - mainly on hills where inertia and weight have a big impact
Generally (I am lead to believe but will probably be corrected shortly!) the heavier the car the slower it will be around the corners as the tyres have more work to do to change the vehicles direction so the lighter car with the same power to weight ratio will theoretically be faster round a circuit. Think American muscle car vs Lotus Exige etc.
There are of course many many more factors that just weight and power that affects a vehicles performance!
There are of course many many more factors that just weight and power that affects a vehicles performance!
too much to take into consideration.
Tyres have better propeties when lightly loaded, so despite less 'grip' in the lighter car, it would be able to corner quicker than the heavier car if they have identical suspension, identical tyres, identical CoG height, identical geometry etc.
but a high speed circuit would favour the heavy, more powerful car.
But then you have to take aero into account, depending on the circuit.
There is no way to have an all things even situation because of the number of factors.
Tyres have better propeties when lightly loaded, so despite less 'grip' in the lighter car, it would be able to corner quicker than the heavier car if they have identical suspension, identical tyres, identical CoG height, identical geometry etc.
but a high speed circuit would favour the heavy, more powerful car.
But then you have to take aero into account, depending on the circuit.
There is no way to have an all things even situation because of the number of factors.
RegMolehusband said:
Given similar brake specifications and tyres, the heavier car would have to brake earlier. This factor would have the greatest impact on lap times.
but depends on your idea of all being equal.50% more weight deserves 50% more grip and 50% more braking force.
Too many variables.
torqueofthedevil said:
All things being equal, if two cars have same power to weight will they both be as quick round a circuit?
Obviously I understand there are many factors affecting it, but for the sake of argument - same car, first weighs 1000 kg with 100 bhp, then 1500kg with 150 bhp.
Or if it's easier, the real reason I asked, will my 306gti be as quick as a 205 gti if I get a similar power to weight ratio - mainly on hills where inertia and weight have a big impact
Impossible to answer without more info.Obviously I understand there are many factors affecting it, but for the sake of argument - same car, first weighs 1000 kg with 100 bhp, then 1500kg with 150 bhp.
Or if it's easier, the real reason I asked, will my 306gti be as quick as a 205 gti if I get a similar power to weight ratio - mainly on hills where inertia and weight have a big impact
A circuit with 2 long straights and 2 hairpins will favour the more powerful but heavier car.
A twisty circuit with short straights will favour the lighter car.
But if it helps, ask yourself why F1 cars have a minimum weight limit, and why touring cars get weight penalties for winning too many races.
There must be an optimal weight, and it's not at either end of the graph.
Imagine a 100Kg, 10hp vehicle (this is easy - it's a kart).
Now imagine a 1000Kg, 100hp vehicle (this is also easy - it's a hatchback from not too long ago).
Which is faster in a straight line? (Hatchback)
Which corners faster? (kart)
What sort of track are we racing them round?
The weight of the driver has a large effect at the "smaller/lower" end...
C
Imagine a 100Kg, 10hp vehicle (this is easy - it's a kart).
Now imagine a 1000Kg, 100hp vehicle (this is also easy - it's a hatchback from not too long ago).
Which is faster in a straight line? (Hatchback)
Which corners faster? (kart)
What sort of track are we racing them round?
The weight of the driver has a large effect at the "smaller/lower" end...
C
John D. said:
Ozzie Osmond said:
Weight
Weight distribution
Height
Wheelbase
Tyres
Brakes
BingoWeight distribution
Height
Wheelbase
Tyres
Brakes
But as I said previously, do you refer to these as being equal or equal per unit mass (i.e 50% more brake force available to the 50% heavier car)
This thread does highlight that people still thing that power and weight are the only 2 criteria involved in making a car quick....
Ross Brawn is an advocate of stating the importance of tyres, to the extent that many engineers won't bother designing a car until they know what tyres will be on it.
then you get your ruler and calculator out and propose track width.
and then so on and blah blah and that and the other etc etc
the last thing you do is check how much power the engine guys can give you (and the aerodynamicists govern this on alot of cars based on how much cooling you're allowed) and what the rule book says your car has to weigh.
so power to weight is an after thought.
I would agree that lightness leads to fast cornering, but I also seem to remember the Nissan GT-R bloke in the video on here a while back making quite a convincing argument otherwise. If I remember right it was something along the lines of an F1 car's mass and downforce combine to make ~1700kgs, while the Nissan GT-R actually weighs ~1700kgs, meaning that it's fast because F1 cars are fast. I suspect downforce and mass aren't quite the same thing, but there must be something in it because the GT-R's so damn fast!
David87 said:
I would agree that lightness leads to fast cornering, but I also seem to remember the Nissan GT-R bloke in the video on here a while back making quite a convincing argument otherwise. If I remember right it was something along the lines of an F1 car's mass and downforce combine to make ~1700kgs, while the Nissan GT-R actually weighs ~1700kgs, meaning that it's fast because F1 cars are fast. I suspect downforce and mass aren't quite the same thing, but there must be something in it because the GT-R's so damn fast!
downforce and mass are very different.cornering grip is based on load going through the tyres
the force that grip has to counteract is based on mass.
so if you have a 700kg car and add downforce equivelant to 1000kg you have the same amount of grip as if you had 1700kgs.
BUT the cornering force of a 700kg car is much lower than that of a 1700kg car, so the 700kg car can go MUCH faster with the same grip.
grip=friction constant * vertical load (mass*gravity + aero load)
cornering force=(mass*speed squared)/radius of corner
so aero load will increase the amount of grip without increasing cornering force required.
that's why aero makes you quicker through corners.
Cost Captain said:
Ross Brawn is an advocate of stating the importance of tyres, to the extent that many engineers won't bother designing a car until they know what tyres will be on it.
For sure 
But that is in reference to F1 where it is a given all the cars will be basically the same weight and power. Not really the same as two road cars or two cars from vastly different race categories that happen to have the same power to weight.
John D. said:
Cost Captain said:
Ross Brawn is an advocate of stating the importance of tyres, to the extent that many engineers won't bother designing a car until they know what tyres will be on it.
For sure But that is in reference to F1 where it is a given all the cars will be basically the same weight and power. Not really the same as two road cars or two cars from vastly different race categories that happen to have the same power to weight.
put an F1 car on bald ditchfinders and you'll be surprised how slow it is.
Cost Captain said:
John D. said:
Cost Captain said:
Ross Brawn is an advocate of stating the importance of tyres, to the extent that many engineers won't bother designing a car until they know what tyres will be on it.
For sure But that is in reference to F1 where it is a given all the cars will be basically the same weight and power. Not really the same as two road cars or two cars from vastly different race categories that happen to have the same power to weight.
put an F1 car on bald ditchfinders and you'll be surprised how slow it is.
All things are equal in this scenario though, right? So both cars are on ditchfinders
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