[westphone]

Almost all the performance cars come out advertise this 50:50 or near 50:50 distribution, but this is measure as stationary standing weight correct?

However, doesn't it matter more to think about the "proper" weight distribution for cars driven close to or at the limit? In BMW terms, shouldn't the correct weight distribution consider the kinematics of the vehicle?

I wonder how 50:50 is achieved when the engine and gear box are all up front...

[SteveC]

Originally Posted by westphone

Almost all the performance cars come out advertise this 50:50 or near 50:50 distribution, but this is measure as stationary standing weight correct?

However, doesn't it matter more to think about the "proper" weight distribution for cars driven close to or at the limit? In BMW terms, shouldn't the correct weight distribution consider the kinematics of the vehicle?

I wonder how 50:50 is achieved when the engine and gear box are all up front...

I imagine that for best acceleration you want maximum weight on the rear wheels, for best braking you need more weight on the front wheels, steering you'll need adequate weight on the front with bias to the outside turning wheel.

50:50 weight distribution gives the 'optimum compromise' for all those situations, given that each action causes a weight shift in the desired direction. Any other distribution would favour one over another. 50:50 will give a balanced performance between steering, turning and traction

50:50 distribution is achieved by moving the engine and gearbox as far back between the wheels as possible and by placing the battery in the boot

[ovekvam]

Most supercars, both for road use and single seater race cars, have a rear biased weight distribution with the engine behind the driver. With RWD, you want more than half the weight on the driven wheels, and 50/50 weight distribution when braking. This will give you optimum performance.

When it comes to handling, a slightly front biased distribution is usually better. I think the Toyota GT86 has something like 53/47 for this purpose. It makes the car more stable, and easy to drive on the limit. Neither traction nor braking performance will match the rear biased cars, but you will usually be able to go faster in the corners.

To achieve 50/50 distribution with the engine in front of the driver, the engine should be behind the front axle. It is in BMWs, but not in Audis. Technically, most BMWs are actually mid engine cars.

[johnnydad]

There's a lot to like about a well set-up car with 50:50 weight distribution. Likewise punting a mid-engined Lotus with rear bias, or a 911 with even more rear bias is just as much fun. Even a nose-heavy FWD can be silly good fun if done properly. It's about getting the best out of what you are given.

[Bob UK]

Originally Posted by westphone

Almost all the performance cars come out advertise this 50:50 or near 50:50 distribution, but this is measure as stationary standing weight correct?

However, doesn't it matter more to think about the "proper" weight distribution for cars driven close to or at the limit? In BMW terms, shouldn't the correct weight distribution consider the kinematics of the vehicle?

I wonder how 50:50 is achieved when the engine and gear box are all up front...

The weight distribution of a vehicle or any object, does not change whether it is standing still or in motion so is the "Proper" weight distribution regardless of circumstances.

Suspension and drivetrain tuning affect the dynamics and work with the balance to provide the desired driving experience.

[ttimbo]

There are multiple factors at play, not just weight distribution. The position of the vehicle's centre of gravity, in particular, has a vast impact on handling.

[ovekvam]

Originally Posted by Bob UK

The weight distribution of a vehicle or any object, does not change whether it is standing still or in motion so is the "Proper" weight distribution regardless of circumstances.

Actually the weight distribution changes a lot while driving. The mass distribution stays constant (except for the fuel tank getting lighter as you go). During braking, a lot of weight will move from the rear axle to the front axle, but the mass stays where it was.

[Bob UK]

Originally Posted by ovekvam

Actually the weight distribution changes a lot while driving. The mass distribution stays constant (except for the fuel tank getting lighter as you go). During braking, a lot of weight will move from the rear axle to the front axle, but the mass stays where it was.

Agreed but on review of the OP the answer would have to be that you can't use weight distribution in the same context for a vehicle in motion compared to static distribution stats.

There are simply too many factors that are adjustable or modifiable by the owner to make any manufacturer figures meaningless.

I'd suggest a 50:50 weight distribution gives you the most level playing field from which to develop a package of dynamic characteristics that suits your needs.

[ovekvam]

I think evenly worn tyres is a good indication of a well balanced car that is properly set up for what it is used for.

If you are a drag racer, and your car is rear wheel drive, you would want a 0/100 weight distribution during the launch. The trick to achieve this, is to have a high center of gravity, so a lot of weight shifts back when you accelerate. If you want to win stop light races with your F20, don't lower it.

[ttimbo]

Originally Posted by ovekvam

Actually the weight distribution changes a lot while driving. The mass distribution stays constant (except for the fuel tank getting lighter as you go). During braking, a lot of weight will move from the rear axle to the front axle, but the mass stays where it was.

Yes, I recall learning about terms such "polar moments of inertia" "angular momentum", "angular torque" and "angular acceleration" waaaaaaaay back in Physics101, when I used to carry around a sliderule. The sliderule is now passé, but those terms for physical forces and actions continue to apply.

[SteveC]

Originally Posted by Bob UK

Agreed but on review of the OP the answer would have to be that you can't use weight distribution in the same context for a vehicle in motion compared to static distribution stats.

There are simply too many factors that are adjustable or modifiable by the owner to make any manufacturer figures meaningless.

I'd suggest a 50:50 weight distribution gives you the most level playing field from which to develop a package of dynamic characteristics that suits your needs.

Static weight distribution of a vehicle is a good indication of how a vehicle will perform dynamically. There are however a number of other factors, far more difficult to calculate and measure that also contribute to handling. Centre of gravity, as mentioned earlier is of course important, as is the way the weight is distributed in terms of rotational moment of inertia.

In essence any weight between the axles will contribute to downforce on both axles, whereas in front of or behind the axles will create downforce on 1 axle and lift on the other due to the lever and fulcrum effect. The further weight is from the CG, the higher its rotational moment of inertia.

[Bob UK]

Originally Posted by ovekvam

I think evenly worn tyres is a good indication of a well balanced car that is properly set up for what it is used for.

If you are a drag racer, and your car is rear wheel drive, you would want a 0/100 weight distribution during the launch. The trick to achieve this, is to have a high center of gravity, so a lot of weight shifts back when you accelerate. If you want to win stop light races with your F20, don't lower it.

We just won't tell the Clio / Nova Halfords performance modified crowd, makes it easier to embarass them in our boggo F20's when the need arises.

[logiclee]

Originally Posted by westphone

I wonder how 50:50 is achieved when the engine and gear box are all up front...

Most of the engine is behind the front axle (Especially on the 4 cylinder models) and the gearbox is mostly in the car which is why we end up with a massive transmission tunnel and small footwell.

Then the diff, drive shafts and battery are at the back.

In most FWD transverse engined cars the engine, gearbox, diff, driveshafts and battery are all in the engine bay in front of the bulkhead and nearly all the weight is on the front axle.

Audi are a little wierd as they do longitudinal FWD cars. Can't see the point really as you get the longitudinal layout drawbacks (Big transmission tunnel and poorer packaging) but then none of the RWD benefits.

Cheers
Lee

[jabugui]

I searched a bit before posting about dynamics, and found this post.

I think the subject and the already started discussion is interesting enough not to be forgotten and maybe we could add a bit of information here (maybe with a proper title change, like F20 dynamics discussion or whatever).

My main interest is to (again) retrieve some expert information about the car, which otherwise I couldn't find anywhere else, nor I could collect because I don't have access to any proper test facility, and also I'm not so experienced driver to reach the limits of my car.

Maybe ovekvam can tell something as he drives on ice track in winter.

Where is aproximately located the center of gravity? Only someone used to drift the car heavily on ice can really tell about the rotation of the car, the center of gravity and the moment of inertia as the car starts spinning.

How does it affect the variations in body weight, and distribution.

I imagine mainly two easy variables:

- To keep the petrol reserve low (55L are aprox. 40kg), so you can have a 20-30 (2.2%) weight reduction on the rear axle, but the center of gravity of the car would then rise (as this mass is located low).

- To fold down the rear seats. They may well weight around 15kg and you lower the weight and also put that weight further front between the axles.

May this small modifications have an impact on handling?

Cheers

[ovekvam]

The center of gravity is probably somewhere between the front seats. I don't know how high it is. The Toyota GT86 has it 46 cm over the ground, which is rather low. Porsche cayman has it 48 cm above ground, and Nissan GT-R at 49.5 cm. I would guess just over 50 cm in the F20.

If you put the car on some scales, the weight of the people in the front seats is distributed evenly on the front and rear axle.

I have not tried to run low on fuel on ice with the F20, but I have done it with older BMWs. I also removed the spare wheel to make more difference. In grippy conditions, this makes the car faster, even though it understeers more, and has lousy traction. In very slippery conditions, it is better to add weight in the trunk. Then you will be faster off the line. It does make the car more difficult to handle on the limit, and can spin out more easily.

The height of the CogG is not easy to notice from the driver seat, but a tall car with short wheel base will transfer more weight between the axles when you drive. The Z3 is like this. When braking, it feels like the rear wheels are off the ground, and under full power it feels like it is close to doing a wheelie.

Back in the days I was autocrossing a lot, I usually folded my passenger seat all the way down in the back seat, to get more weight down and back. I didn't feel a difference, but when fighting about hundreds of a second, everything counts, at least mentally!

The F20 has a suspension that compensates for pretty much everything, making it hard to upset the balance. Even a passenger in the back seat (100 kg on the rear wheels) is difficult to notice handling wise. It does affect lap times, but the car feels rather similar on the limit.

[westphone]

Thanks

[dishy]

Originally Posted by SteveC

steering you'll need adequate weight on the front with bias to the outside turning wheel.

Inside turning wheel.

Actually when cornering you're not supposed to be braking. So weight would be 50/50 at the start of the cornering. Obviously this will shift as you begin to turn. When you accelerate the weight will shift to the rear anyway.

5050 weight distribution, well the battery is in the boot right?
Also if you take notice of where the front wheels are in relation to the body of the car and the engine in the bonnet you will notice that the majority of the engine sits on and behind the front wheels, the gearbox is entirely behind the front wheels.
I don't think it's quite a Front mid-engine classification though. FYI, Ferrari F12berlinetta is an FMR.

You will probably find bolt-in weights in the back of the car somewhere too. I can't remember if it was Mercedes or BMW that we found bolt-in weights before.

[ovekvam]

Originally Posted by dishy

Actually when cornering you're not supposed to be braking. So weight would be 50/50 at the start of the cornering. Obviously this will shift as you begin to turn. When you accelerate the weight will shift to the rear anyway.

In a typical corner, you will start turning in while braking, and exit the corner accelerating.

[dishy]

Originally Posted by ovekvam

In a typical corner, you will start turning in while braking, and exit the corner accelerating.

I agree with the last bit but I've been told you shouldn't corner while braking because the force being used to slow the car down is then taken away from being used to steer the car, and can make the car unbalanced and dangerous. The idea is you want the car to be as stable as possible in the corner.

Links:
http://www.wikihow.com/Drive-Tactica...hnical-Driving)
see the bit at method 2

http://www.drivingfast.net/techniques/track-corner.htm
This link gives quite a lot of detail.

[ovekvam]

In the old days, before modern ABS systems, that was generally the rule, to finish all braking before turning. Still all the best drivers have always been trail braking, and now it is safe to do so for rookies as well. The F20 is very stable during braking, and you can gain a lot of time on other cars by braking deeply into corners when going from a fast section to a slow section.

Even in an emergency situation on the road, you should keep your brake pedal planted while trying to steer around the obstacle.

[ttimbo]

Thanks for saying this. Too often, people labor under the "rules " of driving that existed before electronic driving aids but no longer apply. That includes me, before I did some advanced driver training where the benefits of the electronic aids were exploited. The "lane change under emergency braking" exercise is something everyone should try.

[ovekvam]

Originally Posted by ttimbo

Thanks for saying this. Too often, people labor under the "rules " of driving that existed before electronic driving aids but no longer apply. That includes me, before I did some advanced driver training where the benefits of the electronic aids were exploited. The "lane change under emergency braking" exercise is something everyone should try.

Indeed. I used to be a skidpan instructor, and it is quite interesting to see people try this exercise with and without help of stability systems. It is also a bit scary to see that a 10 km/h speed difference can be the difference between "easy" and "impossible".

It is also interesting to see people with track experience do this, as they are better at picking a very tight and smooth line around the obstacle. That allows them to clear it at higher speed.