Fact vs Fiction: 50/50 Weight distribution is "ideal"

[MR2 Fan]

I think this has been mentioned in passing here before, but wanted to get everyone's opinion on this.

In my opinion, since most cars have been front engined...the idea of having 50/50 weight distribution seems to be the best ideal they can hope for, however due to this I think a lot of "experts" dismiss the idea of having cars, usually mid or rear-engined having a slight rear weight bias as being better as they can use that weight shift to get around a turn faster.

Also, I believe the original Lotus Elan was designed to have more weight in the rear even though it was technically front engined.

I also think that it's better to have most of the weight close to the center of the car anyway...having a car with a massive amount of weight outside of the wheel base in any configuration is probably a bad thing.

Of course this is an 'all other things being equal' scenario and I don't know how having AWD vs RWD affects these things.

Thoughts?

[Freude am Fahren]

For what though, a race car or a road car?

I doubt there are many modern race cars that don't have more than 50% on the rear, outside of maybe touring cars. I think something like a F1 car would be more than 60% rearwards.

For a road car, especially one not geared towards performance, it's more marketing than anything. Especially with modern stability systems, I think it's probably pretty moot. Great bullet point for an E30 M3. Kinda meaningless on a modern 7 series.

Having that mass low and centralized is key though.

[Godson]

Low center of gravity and mass centralization is better than 50/50

/Thread.

[Rare White Ape]

And it shouldn't be too compact, some of it needs to be spread over the axles to increase grip. And its centre should be ahead of the centre of aerodynamic force to increase stability.

[thesameguy]

For a race car, sure, but it's probably not a great idea to give average drivers cars with a low polar moment of inertia.

[neanderthal]

Low center of gravity and mass centralization is better than 50/50

/Thread.

This.

Plus good visibility and predictable responses in a reasonably priced, reliable, package is pretty much all Joe Consumer needs.

[balki]

isn't 45/55 (maybe 40/60) ideal for a rwd because of weight transfer during braking and accelerating plus (usually) wider tires in the back?

[samoht]

There is a specific benefit of 50/50, which is that front and rear tyres take equal share of the cornering load, and thus they will be tracking the same deflection angle in a turn, so you don't have to wind on more/less lock as the cornering load increases, the steering angle/path relationship stays constant.

There are other benefits of a rear-biased distribution, it's better for braking, and traction in a rwd car. I question 'agility' to be honest, I think cars with a rear bias almost need wider tyres at the back, I don't think that many people would like steady-state oversteer (ie not provoked by power, lift-off etc).

I don't think there are any ways that a front-biased weight balance is beneficial to performance, unless in a FF car.

[Crazed_Insanity]

Naturally a dragster, F1 car, sports car, passenger car will have slightly different ideals.

Different drivers may prefer different ideals too.

Key is achieving the right balance for maximum performance in any given car, track and driver.

Still, I think 50/50 is a good starting point when you test a new car on a new track with a new driver. I don't really think there's a good reason to purposely design a car to be butt heavy? If so, all sports cars would copy 911!

[Alan P]

Naturally a dragster, F1 car, sports car, passenger car will have slightly different ideals.

Different drivers may prefer different ideals too.

Key is achieving the right balance for maximum performance in any given car, track and driver.

Still, I think 50/50 is a good starting point when you test a new car on a new track with a new driver. I don't really think there's a good reason to purposely design a car to be butt heavy? If so, all sports cars would copy 911!

It only took Porsche 50 years and a boatload of computing power to tame the 911 Turbo's awkward handling and deathly thin limit.

[Godson]

It only took Porsche 50 years and a boatload of computing power to tame the 911 Turbo's awkward handling and deathly thin limit.

996 is rather tame...

[MR2 Fan]

Still, I think 50/50 is a good starting point when you test a new car on a new track with a new driver. I don't really think there's a good reason to purposely design a car to be butt heavy? If so, all sports cars would copy 911!

The difference between rear engine and mid-engine comes into play on that one.

[Rare White Ape]

I don't really think there's a good reason to purposely design a car to be butt heavy?

Porsche thinks that fitting a family of 4 into a high-end sports car makes it worth it. As a result, they've made a contribution to motoring that has become iconic, and arguably got the WV group through some tough times.

Yes, the profitability of a sports car company may have helped Volkswagen stay afloat while they tried to sell volume econo-boxes. Pretty amazing. But nowadays that's not as much of a focus, because they make four-door sedans and giant shopping trolleys like the Macan to feed the family market.

[balki]

Porsche can make a 40/60 (38/62) car handle well, has any made the opposite happen? 60/40 or at least 55/45?

[thesameguy]

I'd imagine that's most FR cars!

[retsmah]

Porsche can make a 40/60 (38/62) car handle well, has any made the opposite happen? 60/40 or at least 55/45?

Back when I was the engineer for the World Challenge series we had Volvo S60s running competitively in GT, they were around 60/40. Also all wheel drive, with equally sized front and rear tires. Raced against Vipers and Corvettes around 50/50, and Porsches that were at 42/58, all with wider rears than fronts. If you want to really balance cars you need to run full course lap simulations. It turns out you can also get pretty close to the right answer by just calculating (front axle weight/front tire width) and (rear axle weight/rear tire width) and keeping those ratios the same for all the cars, at least if you are just comparing a field of all rear drive or all front drive cars.

On the street car front, I think the Nissan GT-R is right around 55/45.

In short, I would say yes, 50/50 weight distribution being described as 'ideal' is just a marketing thing, it sounds like a nice number and it's probably pretty good for a front engine, rear drive production sports car for street use.

In reality there is no ideal weight distribution, it's one variable of many that contribute to a car's overall performance. Even if you are in a situation where you are pretty much only changing weight distribution, like you have a car, you are road racing it, and you are required to add some ballast (by, say, the series engineer!) and have to decide where to put it, the ideal spot will depend even on what track you are racing on. In the World Challenge series we went to one course with several unusually tight corners and the Porsches ended up being faster there because the track favored a rear weight bias.

[Rare White Ape]

In that case it might be more realistic to say that the ideal grip bias is 50/50. But then again it probably isn't, but it would be more important than just weight dist.

Grip bias would then be the sum of:

Weight
Tyre size
Engine location
Aero and downforce
Suspension geometry
Suspension stiffness
Chassis flex

...across both ends of the car.

Etcetera, etcetera.

[Kchrpm]

Back when I was the engineer for the World Challenge series
I feel quite dumb for not knowing this.

[Crazed_Insanity]

I didn't know that either. Retsmah sure has had a super interesting career! :) :up:

[retsmah]

I feel quite dumb for not knowing this.

This was quite a while ago, like 2007 to 2010!

[Kchrpm]

It almost kind of sort of sounds familiar, like I might have known and then forgot. Still, I feel insufficiently knowledgeable.

[retsmah]

I think Bryan kinda upstaged me when he started driving in the series too ;)

[Dicknose]

From an agility point of view it's important to realize that a turning car doesn't rotate about its centre, its biased to the rear. Although some 4 wheel steering systems do try to move that point forward (but they don't turn the rears as much as the fronts)
So in terms of moment of inertia for rotating the car, a rear bias is preferred.
I got asked about this in a job interview! For a software job! By a guy who later helped found Tesla.

[Crazed_Insanity]

I suppose that's the main reason why f1 indycars and pretty much all modern super cars moved their engines behind the driver now...

Slight rear weight bias is helpful during hard acceleration with the 2 rear wheels, good for turning(as noted by DN), and distribute the weight to all 4 wheels better under braking...

That's probably as ideal as it gets...