Torsional Rigidity?

George

CURRENTLY BANNED
Hi

I found some numbers of torsional rigidity of certain cars.

Lamborghini Aventador 35,000 newton meters per degree of twist

Bugatti Veyron 60,000 newton meters

Pagani Zonda F 27,000 newton meters

Ford GT 27,100 newton meters


Given the huge difference between the Veyron and the rest of them, does weight of the car have a role in howmuch Torsional Rigidity you actually need or could the lighter Aventador run 60,000 aswell?

Can toomuch hurt the car and thus there is a sweet spot dependent on the weight of the car or how does that work?
 
No expert here, but I cannot see how too much rigidity could be a bad thing? From a handling/performance point of view that is. Any compliance should be handled by the suspension, not the chassis.

However I guess road cars need to be soft in certain areas to absorb inpacts etc? So I guess there are compromises built in.
 
You cant be too stiff (Funny jokes aside); suspensions need a stiff chassis to work. Otherwise, your making the chassis become a part of the suspension which is a bad thing because its not really tunable and is effects will always be somewhat of an unknown.

There is no magic number for torsional rigidity, higher is always better, but you will see diminishing returns past a certain point. There is, however, a ballpark number for a given type of car. For instance, a high downforce car that sees a lot of cornering load will require more rigidity than a typical saloon car to prevent adverse handling effects.

Street cars also benefit from high torsional rigidity. Low rigidity in a street car can manifest itself as squeeking and rattling as chassis flexing works body panels and interior pieces loose over time.
 

George

CURRENTLY BANNED
You cant be too stiff (Funny jokes aside); suspensions need a stiff chassis to work. Otherwise, your making the chassis become a part of the suspension which is a bad thing because its not really tunable and is effects will always be somewhat of an unknown.

There is no magic number for torsional rigidity, higher is always better, but you will see diminishing returns past a certain point. There is, however, a ballpark number for a given type of car. For instance, a high downforce car that sees a lot of cornering load will require more rigidity than a typical saloon car to prevent adverse handling effects.

Street cars also benefit from high torsional rigidity. Low rigidity in a street car can manifest itself as squeeking and rattling as chassis flexing works body panels and interior pieces loose over time.

In other words they end up sounding like my 68 Dodge Charger lol.

This may perhaps be silly, but, the Veyron runs 60,000 NM while the aventaor is 35,000 and yet the aventador is 'quicker'. I assume the weight of the veyron makes it harder to control and thus the lighter car doesnt 'need' per say such high Newton meters per twist?

I read this somewhere...

A little flex in a vehicle’s structure doesn’t hurt, but overall you don’t want too much torsion in your vehicle’s body. Low rigidity in a vehicle results in vibrations and degrades handling performance. Good handling performance relies, in part, on suspension designs that optimize wheel/road contact under all conditions. Introduce too much torsion to a vehicle’s body and the wheels are no longer where they are supposed to be relative to each other. In these cases, even well-engineered suspensions don’t stand a chance.


THis is why I wondered if he car is 'lighter' then it doesnt need as much as a heavy car like the Veyron. Howcome the veyron is talked about as comfortable when its SO stiff yet the Aventador is talked about as really stiff and uncomfortable and yet its 25 000 NM less than the veyron?
 
John is absolutely correct, in my opinion. You want all movement in the suspension, none in the chassis/monocoque. But there is a practical point of diminishing returns as he has spelled out.
 
Everything in a car is a compromise. For instance, you cant have 100,000nm/° of rigidity then expect a light car.. it takes material to make a stiff chassis. As a designer, you would want to design for a number that's going to make the suspension work and no more than that. Any more would be over engineering and add weight. This goes for all parts of the car...
 
Don't forget that the Veyron is putting close to a 1000 BHP and 1000 lbs ft of torque through its chassis. Hence the need for such high torsional rigidity. This rigidity also comes at a price, mass, the Veyron is close to 2 metric tons.
 

Ian Anderson

Lifetime Supporter
Would the Veyron being 4 wheel drive require a higher number?

Not sure on any of the others being 4 wheel drive Pretty sure Pagani and ford are not the Lambo - who knows - on my salary it is made of unobtanium

Ian
 

George

CURRENTLY BANNED
Thanks for the feedback.

So just to clarrify... basicaly the suspension in a general term will dertermine how a car feels not the rigidity. Also, the more rigid the chasis the 'better' the Suspension can control the car as there isnt twisting happening throughout the whole car so more is better in this sense as nothing but suspension moves. Also there is a point where there is no real point going more rigid because it will add more weight, which then means more suspension needed to control all that and thus more $$$ for that and it just goes up and up.

Do I get it in a general way at least?
 

Mike

Lifetime Supporter
Are you factoring this into your GT40 design? Have you considered an Aventador? Too heavy for you?
 
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