[Caveman]

So over the years, I have slowly bought into the GTR engineer's claim that the additional weight of the GTR is deliberate and what makes it perform as well as it does. I slowly learned to accept that conventional wisdom being that 'light is best' was flawed, and that the extra weight was what made the GTR perform so well in the bends, providing more grip when needed.

BUT, then I stumbled across the spec for the Nismo GT3 racecar, and all that logic is blown out of the water... The racecar weighs 1300kg!?? If the so called secret weapon of the GTR was down to weight to some degree, why lose weight on the racecar - didn't Nissan say that's what makes it faster?

http://www.jrm-group.com/files/NissanGT-R-NISMOGT3.pdf

Even the GTR Nismo tries hard to lose weight and is about 100kg lighter than the road car with heavy use of carbon. Again, this feels like a contradiction. Either the additional weight is of benefit to the car or it isn't.

I'm confused, and back to thinking that the car would be substantially better to drive if it lost 2-300 kgs.

Thoughts?

 

[Adamantium]

I think the weight makes it easier and more predictable to drive in the hands of the average man.

More predictable and consistent means more confidence inspiring and therefore faster on track in the hands of someone who is not a race driver.

if you remove the inability of the driver to take the car by the scruff of the neck and force it around a track then the lighter car will be quicker. That would explain why the race versions and the nismo versions aim to cut out weight, they rely on better than average drivers to make more use of their performance.

 

[Brad1979]

What I got from the video of the making of the gtr is that to make a sports car convention is low weight high power but this doesn't have to be the case you can still have a great handling sports car if the weight is that of the GTR but you need to manage that weight and nissan proved that you can make a heavy sports car that handles well.

But I do think that it's not the weight of the GTR that's makes it less nimble it's the size it takes up a lot of road.

 

[harryturbo]

weight

power and weight ....its what all race teams strive for ,more power and less weight ...you loose weight ...on any car it gives more power ..then you need aero dynamics to keep it down also with less weight you need less braking force to stop ....so basically the weight thing is bullsh....thats why they get a weight penalty to slow them down . its like putting a 8 stone bloke and a 16 stone bloke in a go cart .....:thumbsup:

 

[Caveman]

Thing that gets me is that half the point of a sports car is its agility and light weight, unencumbered by the normal duties of an everyday road car.

The GTR manages its weight effectively, but you can really feel the weight transfer on fast bends and under braking especially. Can't imagine any owner or prospective buyer would frown at the loss of a few hundred kilos, at the expense of driving ease. Surely mastering a complex car is half the thrill?

Still don't geddit.

 

[Chronos]

I think the weight makes it easier and more predictable to drive in the hands of the average man.

More predictable and consistent means more confidence inspiring and therefore faster on track in the hands of someone who is not a race driver.

if you remove the inability of the driver to take the car by the scruff of the neck and force it around a track then the lighter car will be quicker. That would explain why the race versions and the nismo versions aim to cut out weight, they rely on better than average drivers to make more use of their performance.

Being an average non race driver, I find the weight and control of the r35 as is fun to handle, and less likely to kill me on the U.K. Roads.

 

[Little Nismo]

If you actually recall the explanation; what big M said was that in order to get maximum traction on the selected 20inch wheels you need about 1600kg, for all weather snow and other technical reasons etc you need about 1800kgs.

If you have an f1 car that weight can be created from aerodynamic downforce but for a road car which must travel at 75kph as well as 200kph downforce isn't a sensible solution.

So I have previously considered how this plays out with the nismo. On the face of it it probably does. The nismo is track focused, so it trades some of the all weather snow, and low speed capability for nurburgring slaying potential. It's a couple hundred kg lighter but makes more downforce in about the same amount. This is is keeping with the original principle.

The GT3 version is just an amplification of this. It is a racecar so can rely heavily on downforce as it will be operating only at speed, never in snow or on cold tires on a poor B road. So it runs a big rear wing front spliter and diffusers which generate over half a ton of downforce, oh and guess how much less it weighs Oooh 500kg.

Now I'm not saying the original premise is correct I'm simply pointing out that at a basic level this is all consistent.

I would imagine that in launch, snow and the low speed wet conditions the gt3 will be a much greater handful or outright suicide by comparison to the road vehicles. But obviously that is a compromise which is a no brainer on a racecar. Oh I would imagine running slicks further changes things; the massive grip they generate for any given weight is well above road tyresc and may allow further low downforce situations to be overlooked.

 

[borat52]

Don't confuse downforce with weight.

Essentially its basic physics - the heavier a car the more momentum momentum = mass x velocity which means you have to apply more force to accelerate the car and more force to decelerate the car.

Friction = mu (co efficient if friction which is a constant for a given surface pair) x R where R is essentially mass.

What does all of this mean? If you want to turn a heavy car then it has lots of momentum which means you need proportionally more friction (equates to more tyre and brake wear) and if you want to accelerate a heavy car then you need proportionally more power.

An F1 car uses downforce to create more R (reaction) while maintaining low weight so it gets the best of both worlds - more friction and less momentum.


The GTR is heavy and it copes, at the expense or brakes and tyres. If it were 500kg lighter with all other things equal it would be a lot quicker.

 

[Little Nismo]

Don't confuse downforce with weight.

Essentially its basic physics - the heavier a car the more momentum momentum = mass x velocity which means you have to apply more force to accelerate the car and more force to decelerate the car.

Friction = mu (co efficient if friction which is a constant for a given surface pair) x R where R is essentially mass.

What does all of this mean? If you want to turn a heavy car then it has lots of momentum which means you need proportionally more friction (equates to more tyre and brake wear) and if you want to accelerate a heavy car then you need proportionally more power.

An F1 car uses downforce to create more R (reaction) while maintaining low weight so it gets the best of both worlds - more friction and less momentum.


The GTR is heavy and it copes, at the expense or brakes and tyres. If it were 500kg lighter with all other things equal it would be a lot quicker.

And don't you confuse weight and mass. Downforce effectively increases the weight of the vehicle. For any given downforce the less the mass of the car the better. But if you have a total of 1800kg from mass alone or 1300kgs mass and 500kg from downforce doesn't that, mean that 1800kgs still has to turn the corner or be accelerated? It still requires the same traction.

If you have ever driven a powerful Ute you would wish for some more weight in the rear; zero traction. It seems to me there is a cross over point where you have too much power for the mass of the vehicle given the traction it can produce from the wheels selection... Clearly a weightless car will not perform well.

The point then is that datsun are saying that the optimum is 400kg per corner for at GtT car of the dimensions and wheel selection of the gtr.

Otherwise why does the gtr perform so well? What's their secret it's heavier and less powerful than a number of other vehicles but yet quicker? Is it all lower gearing and 4wd? I doubt it.

 

[Little Nismo]

Noting of course a light vehicle has an acceleration advantage until it is creating all that downforce.

 

[borat52]

And don't you confuse weight and mass. Downforce effectively increases the weight of the vehicle. For any given downforce the less the mass of the car the better. But if you have a total of 1800kg from mass alone or 1300kgs mass and 500kg from downforce doesn't that, mean that 1800kgs still has to turn the corner or be accelerated? It still requires the same traction.

Yes I was sloppy with weight and mass but the above is wrong.
Downforce affects neither momentum nor kinetic energy and as such a 1300 kg car with 500kg of downforce will require 13/18ths of the braking and/or turning force of a 1800kg car.

That's the appeal of downforce, going back to our friction equation it increases R (reaction) with zero increase in mass so we can counter any given momentum or kinetic energy with more friction.

Also a weightless car in theory has zero mass so would require an infinitely small force to go infinitely quickly (ke = 1/2mv(squared) so it's not something that makes sense in the real world.

Your ute is a function of bad design, it has significant mass to accelerate but only a small mass over the drive wheels and hence the Reaction force and friction over the drive wheels is small. Iff all of its mass was over the drive wheels it would be as quick to accelerate as any vehicle with the same mass and same tyres.

The GTR is quick simply because of the efficiency in which its able to manipulate its power through the 4wd system maximising the friction on each tyre at all times coupled with a chassis and suspension set up which helps to ensure the tyres are generating lots of friction all the time.

Its weight is really a consequence of its design, not an objective in itself.

I stand by it that losing 500kg would make it significantly quicker. Yes it would spin the wheels easier but remember less mass means we need less energy to accelerate/brake so less power from the engine would give the same acceleration.

 

[Little Nismo]

That's the appeal of downforce, going back to our friction equation it increases R (reaction) with zero increase in mass so we can counter any given momentum or kinetic energy with more friction.

Also a weightless car in theory has zero mass so would require an infinitely small force to go infinitely quickly (ke = 1/2mv(squared) so it's not something that makes sense in the real world.

Your ute is a function of bad design, it has significant mass to accelerate but only a small mass over the drive wheels and hence the Reaction force and friction over the drive wheels is small. Iff all of its mass was over the drive wheels it would be as quick to accelerate as any vehicle with the same mass and same tyres.

The GTR is quick simply because of the efficiency in which its able to manipulate its power through the 4wd system maximising the friction on each tyre at all times coupled with a chassis and suspension set up which helps to ensure the tyres are generating lots of friction all the time.

Its weight is really a consequence of its design, not an objective in itself.

I stand by it that losing 500kg would make it significantly quicker. Yes it would spin the wheels easier but remember less mass means we need less energy to accelerate/brake so less power from the engine would give the same acceleration.

Ok not a weightless but a very light car. The point was really asking is there a cross over point at which your vehicle is too light for the power and the selected wheel size?

Ie if the gtr weighed 1200kgs is that too light? What about 1000kgs? 900, 800.

Of course I don't deny that light can be good the lotus formula of 800-900kgs and 250hp makes for great track cars.

I'd be interested in whether you believe the weight has no advantage in snow ice wet at low speeds and on launch?

If I hear you right you are saying making a 4wd road gt car means that you will have to have 1800kgs or I'm guessing make it expensive (carbon fibre) and the rest of the specs are all to overcome that weight? You are saying there is no trade off for less weight in low downforce situations?

Yup that's certainly a possibility but why would they make up porkies about it? It seems a little pointless. Why not just say that the weight is a function of the car dimensions engine and 4wd drive and the power wheel size suspension etc are selected around this.

Which I guess is the point of this thread.

Is it that now engines with massive power and torque can be made so manufacturers look to make the most of this. But to have a 1200kgs car with 600hp is gomna be a handful in amateur hands in adverse conditions?

 

[mindlessoath]

mizuno is not right.

lighter is better. they engineered the car around the weight and it sufferers from alot of things. .. for instance brakes, tires and cooling system.

sure it goes fast but a lighter gtr will go faster, and its components will work longer... eg brakes wont over heat as easily and last longer, cooling system wont over heat so easily, and tires wont wear out as fast.

but nissan found a nitch, a car thats fast in one or two laps give or take depending on track... thats it. thats all it needs for sales.

mizuno is also not the boss man anymore.

 

[WingedBeast1968]

Little Nismo is right in his original, if long winded, statement.
It's a road car. A multi performance road car. The GT3 is required to spend as much time as possible at or above 100mph. Lack of mass causes instability as the speed increases. Down force gives you grip, but not much in stabilising the car at high speed. That's why racing drivers operate at a different level to all of we wanna be racers. Mass is required for stability. Mizuno San was tasked with creating a stable and fast platform, not just fast. That's easy.

I'm all gobby tonight, and I'm not allowed to drink. Antibiotic soberness sucks.

 

[borat52]

Ok not a weightless but a very light car. The point was really asking is there a cross over point at which your vehicle is too light for the power and the selected wheel size?

Ie if the gtr weighed 1200kgs is that too light? What about 1000kgs? 900, 800.

Of course I don't deny that light can be good the lotus formula of 800-900kgs and 250hp makes for great track cars.

I'd be interested in whether you believe the weight has no advantage in snow ice wet at low speeds and on launch?

If I hear you right you are saying making a 4wd road gt car means that you will have to have 1800kgs or I'm guessing make it expensive (carbon fibre) and the rest of the specs are all to overcome that weight? You are saying there is no trade off for less weight in low downforce situations?

Yup that's certainly a possibility but why would they make up porkies about it? It seems a little pointless. Why not just say that the weight is a function of the car dimensions engine and 4wd drive and the power wheel size suspension etc are selected around this.

Which I guess is the point of this thread.

Is it that now engines with massive power and torque can be made so manufacturers look to make the most of this. But to have a 1200kgs car with 600hp is gomna be a handful in amateur hands in adverse conditions?

My position on this from a physics point of view is that reducing the weight would not affect the launch performance with a very big caveat.

The Co-efficient of friction is only valid until you break traction, at that point it is significantly reduced and is also highly variable. The problem with reducing weight to 1000kg and keeping power at say 600bhp is that its easier to break traction, although we could equally argue that dialing the power down to 10/18ths would keep the traction profile the same as the heavy 600bhp car. Same story with snow.

You make a good point with tyre sizing, we've got to remember here that when you corner or brake the weight shifts significantly towards front or rear, left or right and as such if you know the car is going to be 1800kg and 4wd you need to spec each tyre to be able to deal with a majority of the weight bearing down upon it. Making a lighter car would definately affect the tyre choice.

 

[borat52]

Little Nismo is right in his original, if long winded, statement.
It's a road car. A multi performance road car. The GT3 is required to spend as much time as possible at or above 100mph. Lack of mass causes instability as the speed increases. Down force gives you grip, but not much in stabilising the car at high speed. That's why racing drivers operate at a different level to all of we wanna be racers. Mass is required for stability. Mizuno San was tasked with creating a stable and fast platform, not just fast. That's easy.

I'm all gobby tonight, and I'm not allowed to drink. Antibiotic soberness sucks.

I agree that mass gives you stability in a straight line at speed but it definately contributesto instability in the corners, you need to change the momentum in corner to a different direction and mass and momentum are propertional.

A car with properly set up downforce will be far more stable in corners as your increasing the friction required to change the momentum but decreasing the mass relative to a heavy non downforce car. (and therefore decreasing absolute momentum)

 

[borat52]

Sorry for the spelling, written asI'm boarding my 18th flight in 2 weeks.

 

[WingedBeast1968]

I don't think I'll be going around corners fast enough to generate any usable downforce on the road

So it isn't bull or marketing. It's a fact of how it will be operated most of the time.
A compromise.

And we did go to the Moon. Six times.

 

[Little Nismo]

mizuno is not right.

lighter is better. they engineered the car around the weight and it sufferers from alot of things. .. for instance brakes, tires and cooling system.

sure it goes fast but a lighter gtr will go faster, and its components will work longer... eg brakes wont over heat as easily and last longer, cooling system wont over heat so easily, and tires wont wear out as fast.

but nissan found a nitch, a car thats fast in one or two laps give or take depending on track... thats it. thats all it needs for sales.

mizuno is also not the boss man anymore.

Ah. Mizuno wasn't fired for incompetence he is on a health enforced sabbatical.

Though whatnyou say about durability has some merit. A Porsche will lap all day out of the box. A gtr needs some work. But its not a track car out of the box and its a lot cheaper. On the open road this matters a lot less...

 

[Little Nismo]

I agree that mass gives you stability in a straight line at speed but it definately contributesto instability in the corners, you need to change the momentum in corner to a different direction and mass and momentum are propertional.

A car with properly set up downforce will be far more stable in corners as your increasing the friction required to change the momentum but decreasing the mass relative to a heavy non downforce car. (and therefore decreasing absolute momentum)

This thread is getting interesting now... I'm learning something.