Watched something very interesting last night that threw up a theory I'd never heard before. An exact 50:50 weight distribution is a bad thing (despite what BMW ads. say).

WHat you actually want is a 52:48 split front to rear. This way you have some additional weight over the front to aid turn-in yet under accleleration the 2% shifts back far enough to give a 50:50 distribution.

An interesting theory that I thought I'd share.

Is that split with or without the driver? I suspect a BMW being driven is no longer a 50:50 weight split

Chris

The car they were talking about has the driver sat perfectly between the wheels.

Interesting. I believe the MR2 is a perfect 50:50, or not so perfect so it seems :rubchin:

Still a hoot however, especially when the back end flicks out....

Interesting. I believe the MR2 is a perfect 50:50' date=' or not so perfect so it seems :rubchin:

Still a hoot however, especially when the back end flicks out....[/quote']

I expect all your hair products will be making it uneven walkie.

One thing that did make me think though is that petrol in the tank is probably a big enough factor to influence this theory quite heavily.

Pretty much irrelevant anyway, unless you quote corner weights with driver and half-fuel such that you get 25% mass on each wheel, and even then irrelevant unless you also have equal size tyres all round.

What difference does having equal sized tyres make as that is incuded in the distribution calcs. ?

:confused:

What difference does having equal sized tyres make as that is incuded in the distribution calcs. ?

:confused:

A fair question - I was basing that on knowing that people much smarter, and better educated in vehicle engineering, than I am, say that for best stability with equal corner weights and 0g longitudinal acceleration, you need equal grip all round, which logically requires the same size wheels and tyres all round.

Larger rears will tend to give understeer because you've got less front than rear end grip and the same loading on each tyre. The reason for fitting them on powerful RWD cars is because dynamic weight distribution moves aft when you accelerate, and you're more likely to accelerate than brake whilst turning.

Hi

I cant see two percent making much difference TBH. Also, 2% weight transfer seems a bit conservative under power.

I think that essentially, near enough 50/50 split gives you a much more throttle steerable car as you can use the engine to move the weight distribution to whichever end you want it. Get something very nose heavy and it will be nose heavy regardless of throttle state.

Not too sure the MR2 is 50/50. Feels tail biased to me and looking at the springs front and rear would bear this out. The key advantage of the mid engined layout is the reduction in rotational inertia as the engine sits on the centre of rotation of the car. This makes turn in much more direct quick.

Chris

I've got a bit of experience in this area, I currently own an Alfa 75 3.0 V6 which is almost 50:50 weight distribution, but have owned 2.0 T-Spark 75's which are 50:50, they handle exceptionaly well, infact i'd go as far as saying they are probably one of the best handling RWD cars you could lay your hands on and still to this day, some 15 years after they stopped making them, they consistently lap the Nurburgring quicker than most normal road cars (not counting big money supercars!).

You get a fantastic bite and turn in, followed by very slight understeer which can be controlled and countered by using the throttle making very small adjustments to bring the back out slightly into a perfect drift, it great fun and very easy.

The 3.0 V6 however does not have the same adjustability, the extra weight up front does not aid turn in at all, and just provokes understeer that is not so easily countered, the back then snaps out very quickly, which is why despite being considerably more powerfull and sounding awesome, most track guys use the 2.0

The fabia vRS has 77:23 weight distribution (presuming a base spec model weighs 1250kg)

Ive heard that the 2.0l has a perfect 50:50

But considering the weights.. its utter bulls**t.. how much does 40l of fuel weigh?

which in 90% of cars sits just infront of the rear axel.. and if were talkin a car that weighs about a tonne a driver alone could add 10%+ the total weight of the car.

I guess any weight distribution advantages would be minimal compared to a decent chassis and a low centre of gravity.

The fabia vRS has 77:23 weight distribution (presuming a base spec model weighs 1250kg)

Ive heard that the 2.0l has a perfect 50:50

But considering the weights.. its utter bulls**t.. how much does 40l of fuel weigh?

which in 90% of cars sits just infront of the rear axel.. and if were talkin a car that weighs about a tonne a driver alone could add 10%+ the total weight of the car.

I guess any weight distribution advantages would be minimal compared to a decent chassis and a low centre of gravity.

Hi Neo

I think it is a cumulative thing. Big heavy engines up front mean turn in will suffer, even if the weight ditribution is 50/50. The optimum weight distribution helps balance as well, by making it easier to adjust the vertical forces acting on the front and rear tyres with the throttle, as in the case of the Alfas with the 2lt T spark and ther gearbox on the rear axle. Definately an all time great drivers car.

Move a much mass as possible as close to the axis of rotation as possible and turn in improves hugely as the tyres have to overcome less inertia of the masses, which increases as the masses get further from the rotational axis. The difference is not subtle at all when you do this.

Plonking a 100Kg driver in the middle of the car will make a difference to turn in intertia (unless you drive a Caterham or similar where the driver sits almost directly on the rotational axis), but as the driver will be near enough between the front and rear wheels, the difference in distribution will be relatively minor.

Chris

Hi Neo

I think it is a cumulative thing. Big heavy engines up front mean turn in will suffer' date=' even if the weight ditribution is 50/50. The optimum weight distribution helps balance as well, by making it easier to adjust the vertical forces acting on the front and rear tyres with the throttle, as in the case of the Alfas with the 2lt T spark and ther gearbox on the rear axle. Definately an all time great drivers car.

Move a much mass as possible as close to the axis of rotation as possible and turn in improves hugely as the tyres have to overcome less inertia of the masses, which increases as the masses get further from the rotational axis. The difference is not subtle at all when you do this.

Plonking a 100Kg driver in the middle of the car will make a difference to turn in intertia (unless you drive a Caterham or similar where the driver sits almost directly on the rotational axis), but as the driver will be near enough between the front and rear wheels, the difference in distribution will be relatively minor.

Chris[/quote']

Yeah, but the Alfas should have poor transitional reactions anyway, due to having heavy lumps at both ends.

Yeah, but the Alfas should have poor transitional reactions anyway, due to having heavy lumps at both ends.

I had the pleasure of driving one of the 2L cars once and it did feel pretty tidy and well balanced. Turn in was not demonically fast, but certainly better than average. The gearbox being closer to the rotational axis may help here. Remeber the car does not rotate about a point mid way between the front and rear wheels, but a point a little forward of the rear axle.

Having a big heavy lump up front does have some good points. Mainly in stability terms, the car tends to act like a dart and keeps going in or returning to a straight line making it easier to regain control in extreme situations.

Chris

If anyone wants to experiment with forces and weight distribution download a game called "live for speed" its a full simulation where you can tune and tweak every aspect of the suspension and drivetrain... theres also an option to show the forces acting on each wheel whilst driving...

Its quite fun just messing about and learing the basics of how the various suspension components affect the car overall.

Edit: example in this pic.... im doing a donut so you can see where the forces are and how much weight is over each wheel