[Crazyquik]

I dont understand this concept too much. A lot of people tell me a car will have an ideal 50/50 front to rear weight distribution, and this makes them superiour. Can someone explain this to me? Bob Riley said that a 43/57 was ideal in a rwd car, so right now I believe that would be closer to ideal than 50/50.
J.

 

[gtivr4]

Re: Is a 50/50 weight split really ideal? (Crazyquik)

Wouldn't it depend on what you are doing? I would assume that a 911 is optimized for acceleration, with the most traction on the rear wheels, as there is more weight there. Of course its not optimal for handling, as it has proven over and over again (although clearly very good results can come from it).
I would also assume it would be best to have as much weight in the middle and as low as possible (as in a 914-6), so that the car rotates around its mass, instead of behind it. But thats an assumption

 

[997Timbo]

Re: Is a 50/50 weight split really ideal? (gtivr4)

the new 350Z is supposed to have 52/48 F/R.. something to do with weight shifting in corners providing 50/50 through the turn. my understanding is that a car with more weight in the back will have a tendency to oversteer (which is why dotcommers crash porsches more than any other car), while cars with more weight in the front would have less tendency to understeer... which wheels are driving affects that too... i think 50/50 is supposed to give it "neutral" handling. Also, it matters where the weight is. I'm not sure about which handles *better* as such, but a car with 50/50 but all the weight in the very front and very rear is going to be handle "worse" (i think) than a car with 50/50 but all the weight in the middle... same concept as if you try to sit in your office chair an spin around. You slow down when you extend your arms and speed up when you contract them.

 

[Crazyquik]

Re: Is a 50/50 weight split really ideal? (nsadhal)

Yeah you're starting to touch on the polar moment of inertia there. The Porsche 911 was going to be one of my prime exapmles against the 50/50 split. When it came out it was kinda underpowered, huge front to rear weight difference, and kinda low tech considering Germany had had fuel injection decades before then. Still it forged ahead, won races, and became a timeless design and has a legacy as one of the greatest cars of all time. That along with Bob Riley's statements make me think a weight bias with more in the rear would be better.

 

[BananaCo]

Re: Is a 50/50 weight split really ideal? (Crazyquik)

50/50 means that during a corner (not accelerating or decelerating) the front wheel and the rear wheels both get the equal amounts of load, hence maximizing the car's grip.....
am i right?

 

[matt007]

Re: Is a 50/50 weight split really ideal? (BananaCo)

Mmmmmm, 50/50
Instead of steering the car, you steer with the car, and you can feel the weight shift immediately.
It's easier to control drifting, its safer than rear-bias when turning, and generally makes it more fun to drive.
Most cars that are almost perfect 50/50 have a midengine design.

 

[Crazyquik]

Re: Is a 50/50 weight split really ideal? (matt007)

NSX - 41/59
F355 - 41/59
F40 - 43/57
Boxster - 47/53
C5 - 51.4/48.6
E36 M3 50/50
Honda S2000 50/50
RX7 50/50
Just cause its mid motored doesn't nearly mean its 50/50. A front engine car has just as much chance of a 50/50 split. Since in a race car you accelerate a good deal in the turns, and accelerating off the turns is a key aspect, a rear weight bias might be beneficial to allow a better "foward bite" coming off each corner.

 

[germanrox]

Re: Is a 50/50 weight split really ideal? (Crazyquik)

944/944T 50/50. These cars can outhandle almost any 911 stock for stock, and it gets worse when on the track. 911's are inherrently tail happy, and with a little flip of the wrist and a stab at the throttle you'll be backwards before you know it. 944's just squat and go, I know, I owed one!

 

[matt007]

Re: Is a 50/50 weight split really ideal? (Crazyquik)

quote:[HR][/HR]Most cars that are almost perfect 50/50 have a midengine design.[HR][/HR]​

quote:[HR][/HR]Just cause its mid motored doesn't nearly mean its 50/50. A front engine car has just as much chance of a 50/50 split.[HR][/HR]​

Do you know what midengine means?

 

[dmc]

Re: Is a 50/50 weight split really ideal? (germanrox)

Just as important as front-to-rear weight distribution is a car's rotational moment of interia about its yaw axis.
If the engine is located too far forward, e.g., in front of the front axle, the car will essentially be very resistant to rotations about the yaw axis and thus will feel less "tossable". Mid-engined cars attempt to lower the moment of interia by putting the heavy stuff near the axis of rotation. Cars like the McLaren F1 even go to the extreme of moving the driver over to the center of the car, a design decision more likely motivated by reducing a the car's moment of interia than anything else.

 

[Crazyquik]

Re: Is a 50/50 weight split really ideal? (matt007)

quote:[HR][/HR]Most cars that are almost perfect 50/50 have a midengine design. - matt[HR][/HR]​

quote:[HR][/HR]Just cause its mid motored doesn't nearly mean its 50/50. A front engine car has just as much chance of a 50/50 split. - me after showing some midengine cars with 41/59 weight splits[HR][/HR]​

quote:[HR][/HR]Do you know what midengine means? - matt[HR][/HR]​

What are you getting at? You said that most midengine cars have a perfect weight split. I showed 2 cars with the engine infront of the driver but behind the front axle centerline that have a near 50/50 split, 2 front engine cars that have a 50/50 split, and 4 cars with the engine behind the driver but infront of the rear axle that dont nearly have 50/50 splits. 50/50 can easily be attained in a non mid engine car, especially with the use of a rear transaxle.
J.

 

[Kierf - ¿§?]

Re: Is a 50/50 weight split really ideal? (Crazyquik)

quote:[HR][/HR]What are you getting at? You said that most midengine cars have a perfect weight split. I showed 2 cars with the engine infront of the driver but behind the front axle centerline that have a near 50/50 split, 2 front engine cars that have a 50/50 split, and 4 cars with the engine behind the driver but infront of the rear axle that dont nearly have 50/50 splits. 50/50 can easily be attained in a non mid engine car, especially with the use of a rear transaxle.[HR][/HR]​

Well...I see where this arguement is going. Done this one before. Anyways...an engine in front of the driver and behind the front axle is still a mid-engine design. The RX-7 and S2000 are both mid engine cars that have 50/50 weight distribution. Albeit a front-mid engine design, it is still mid-engine nonetheless. I can't think of a front engine car that has 50/50 weight distribution...

 

[lizerd]

Re: Is a 50/50 weight split really ideal? (Kierf - ¿§?)

i thought bmws mostly had pretty close to 50/50 front engine rear drive?

 

[Obin Robinson]

Re: Is a 50/50 weight split really ideal? (germanrox)

quote:[HR][/HR]944/944T 50/50. These cars can outhandle almost any 911 stock for stock, and it gets worse when on the track. 911's are inherrently tail happy, and with a little flip of the wrist and a stab at the throttle you'll be backwards before you know it. 944's just squat and go, I know, I owed one![HR][/HR]​

i can back that up, i own two

yes, a 50/50 is great, but you want a tiny bit more weight over the wheels, because this will add for your traction.
how does a 924 compare to a 911 turbo at a race track? note wher he loses me, and not where i catch him:
http://209.4.91.164/Watkins_Glen_Events/lap_in_924/
obin

 

[Crazyquik]

Re: Is a 50/50 weight split really ideal? (Kierf - ¿§?)

Thats why I listed the S2000 and the RX7 in a different grouping. FWIW I also listed 2 true front engine cars that have a 50/50 split. Also the 924/944 is a front engine car that has a 50/50.

 

[Rice_Box[Sentra]]

Re: Is a 50/50 weight split really ideal? (Obin Robinson)

good example Obin. 50/50 weight distribution is a good platform to start with, but without good suspension tuning the cars would handle like crap.

 

[matt007]

Re: Is a 50/50 weight split really ideal? (Rice_Box[Sentra])

quote:[HR][/HR]What are you getting at? You said that most midengine cars have a perfect weight split.[HR][/HR]​

No I didn't! Geez.
I said that most cars that have almost perfect 50/50 have a midengine design--not that most midengine design cars have almost perfect 50/50.
If its between the axles, its a midengine design.

 

[matt007]

You just read it a little dyslexically

 

[Sharpix]

Re: Is a 50/50 weight split really ideal? (matt007)

It's not weight distribution the only thing that matters!
There's something more than 50/50 weight distribution, is how the weight is distributed vertically, an example: The car is 50/50 balanced but the weight at the front side, the mass center is 50 cm higher than the rear one, relative to the road. Im pretty sure this is something that has to be taken in consideration, too, but im not sure how.

Someone explain this, pleaseeeeeeeee!

 

[Roberto]

Re: Is a 50/50 weight split really ideal? (Sharpix)

quote:[HR][/HR]It's not weight distribution the only thing that matters!
There's something more than 50/50 weight distribution, is how the weight is distributed vertically, an example: The car is 50/50 balanced but the weight at the front side, the mass center is 50 cm higher than the rear one, relative to the road. Im pretty sure this is something that has to be taken in consideration, too, but im not sure how.

Someone explain this, pleaseeeeeeeee!

[HR][/HR]​

There aren't two separate masses (front and rear) that you're dealing with. The car is one mass with one center of gravity. The car's mass acts like it's all at the center of gravity. If the center of gravity is halfway between the front and rear wheels, there's 50/50 weight distribution.
The center of gravity (center of mass) actually has a height too, as you've pointed out. Suspensions have a roll center. It's a theoretical point around which the car rolls (leans). With some suspension designs, the roll center moves around depending on whether the suspension is deflected (from brake dive, squat from acceleration, or as the car tilts in a corner). If you draw a line through the roll center of the front suspenson and the roll center for the rear suspension, that's the axis around which the car body rolls. The height of the center of mass to this roll axis indicates how sensitive the car is to roll and it gives an idea of how it transfers load as the car corners.
So, yes the height of the center of mass has an affect on handling, but, it's also tied into suspension design. The higher the center of mass, the more the outer tires have to work in a corner. For the same center of mass, suspension design can affect how evenly the load transfer is distributed between the outer tires. If one tire is working much harder than the other, it's going to limit the cornering capability.