weight distribution

[patrick10]

i saw in the fwd thread that 45:55 weight distribution is the best. why is this? i thought 50:50 was the best because it blends the perfect amount of front tire grip to eliminate understeer without losing a lot of grip from the rear tires.

[freerider]

I'm to lazy to write it myself, so I just picked it from the net. But you'll get it (if you think about it, you'd probable think of it on your own)

I've said it on the other thread. You should see static as theoretical and dynamic as in practice.

Static versus dynamic is the weight distribution when the car is parked (static) and not in any motion, versus when the car is braking, accellerating, and turning (dynamic). There is a huge difference between the 2 figures.

For example, with a car like the RS 6 (58/42 front to rear) the figures quoted are static (standing still). Those figures can change drasticly when the car is in motion. When accellerating, more weight will be transfered to the rear (perhaps closer to 50/50) but when braking then more weight is then tranfered to the front (like 70/30). That last figure is obviously not good and contributes to the cars "push" (excuse the Nascar term for understeer). Nord's example of 40/60 would give much more balance under braking and put far more weight over the rear wheels under heavy accelleration (great for wheel rear drive cars). Hope that helps.

And it's not that 45:55 is THE BEST solution. It was just an example. The best distribution will be different with each car.

Greetz Johan

[Leppy]

Also depends on what the car is setup for.

[Raven18940]

I think 45:55 is better than 50:50 is because the front wheels have to steer as well as grip, but the rear wheels just have to grip.

[MXM]

^ And how steering isn't gripping?
It's not that simple at all. Look at 911 for example, it has over 60% of weight at the back, and it works. With so much grip at the back, rear end stays firmly in place, and with gentle throttle/brake control you load front wheels before turn and load rear wheels on exit. Of course when you loose rear end that weight becomes pretty difficult to handle (but they sorted it out somehow). And on higher speeds downforce starts helping to keep the car on the road.
50:50 is good neutral distribution. A compromise for front-engined RWD car, which makes it pretty easy to handle and not that hard to recover slides. Put more at the back to make it more demanding but potentially faster, and move to front if you're afraid of understeer
A mid-engined car with 50:50 distribution on other hand, is much more easier to spin, because of lower angular moment of inertia (wieght is more concentrated in the middle). And FWD of course needs it all at the front for obvious reasons.

But there's SOOO much more to tweak in suspension to compensate weight distribution, that perfect setup is really unique for every car.

[Z Draci]

I know that the Infiniti (Nissan) sedans have something like 53:47 weight distribution so that its perfectly at 50:50 when accelerating.

Porsche is at around 40:60. THIS IS WHY THEY UNDERSTEER AT TURN IN!
If you've ever driven a Porsche and drive it like any other car, you'd find that it'll understeer like mad. Why? It's because there's no weight up front! If you have extra grip available to any tyre, you shift the car's weight so that it digs into it.
I found that by trail braking into corners with a Porsche, you can actually dig the fronts in while having the tail slide out from behind. If you're not careful the rear is heavy enough to spin you out before you realize it. (Many mid-engined cars with something like 45:55 have a less exaggerated version of the same problem.)

In a FWD car with 90:10 ( sorry, it seems like it but it's more like 65:35), the car will still understeer. This is because the reverse situation of the Porsche occures. Now, there's so much weight at the front that the front tyres are overwhelmed by it. Therefore, it's so much easier to slide the front out before the rears lose traction.

50:50 is the compromise for the most well balanced car. What the engineers decides to do after that is up to them. A 50:50 car can be an understeerer or a tail happy drifter. At this point, other things come into consideration.

Also, 99.99% of road cars DO NOT GERERATE DOWNFORCE! Those wings and spoilers are only there to MINIMIZE lift. The overall value of lift is still positive. It's a myth!
Most road cars have such huge passenger compartments and high road clearance that lift is inevitable. They can only work to minimize it.

[Nitemare]

I know that the Infiniti (Nissan) sedans have something like 53:47 weight distribution so that its perfectly at 50:50 when accelerating.

Porsche is at around 40:60. THIS IS WHY THEY UNDERSTEER AT TURN IN!
If you've ever driven a Porsche and drive it like any other car, you'd find that it'll understeer like mad. Why? It's because there's no weight up front! If you have extra grip available to any tyre, you shift the car's weight so that it digs into it.
I found that by trail braking into corners with a Porsche, you can actually dig the fronts in while having the tail slide out from behind. If you're not careful the rear is heavy enough to spin you out before you realize it. (Many mid-engined cars with something like 45:55 have a less exaggerated version of the same problem.)

well there's much more to handling than just the weight distribution.... by modifiing suspension, you can change the rate, at which the weight transfers, as well as overall grip levels..
even a car with bad weight distribution can by made to handle quite well.. i believe that porsches set-up for racing have minimal understeer...

for example, some things that will make a car less understeery at turn-in

tires: wider front tires, narrower rear tires
dampers: ...less compression damping on front, more rebound damping on rear
springs: softer on front, harder on rear
anti-roll bars: stiffer on rear, softer on front
suspension: more caster on front
..and so on...

[Cubits]

Porsche can engineer around their weight distribution, and there are a few manufacturers who can engineer around a fwd.

Renault can make fwd's which don't understeer, but peugeot are the masters. Put a 205 at a corner too fast and the car will break traction at the tail first! The 405 (big family sedan) will lose both ends at the same time! These cars have far from perfect weight distribution.

It's amazing what you can achieve with some smart engineers.

[Z Draci]

Yes, I understand that but we're only discussing weight distribution here!

[Cruzz563]

Yes, but you were talking about handling of the car with different types of weight distribution. So he intern put his in his views.

[Leppy]

Originally Posted by Cubits

Porsche can engineer around their weight distribution, and there are a few manufacturers who can engineer around a fwd.

Renault can make fwd's which don't understeer, but peugeot are the masters. Put a 205 at a corner too fast and the car will break traction at the tail first! The 405 (big family sedan) will lose both ends at the same time! These cars have far from perfect weight distribution.

It's amazing what you can achieve with some smart engineers.

Better be looking over my way 8) 8) But alas tomorrow I go back to working out airconditioning loads on buildings instead of working out how to setup up my lancer with a perfect weight distribution for peak hour traffic along the pacific freeway.

[Cubits]

Originally Posted by Z Draci

Yes, I understand that but we're only discussing weight distribution here!

My point is that weight distribution has very little to do with oversteer/understeer. Much more important is the suspension setup.

You can't make a sweeping statement like "front heavy means understeer" because the real reason most front heavy cars understeer is because they are set up to have safe handling.

[Raven18940]

Originally Posted by Cubits

My point is that weight distribution has very little to do with oversteer/understeer.

No, it actually it has a lot to do with weight distribution. Front heavy cars understeer and rear heavy cars oversteer. You can combat these tendencies with a good suspension setup, but weight distribution at least determines the starting point before you fiddle with the suspension.

[Leppy]

Originally Posted by Raven18940

No, it actually it has a lot to do with weight distribution. SHIT Front heavy cars understeer and SHIT rear heavy cars oversteer. You can combat these tendencies with a good suspension setup, but weight distribution at least determines the starting point before you fiddle with the suspension.

You forgot something in your post.

[Cubits]

Hahah, good one.

[general]

but then the best handling cars from japan have 50:50 or almost the same weight distribution