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Old 08-05-2004, 05:06 AM   #1
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Default Chassis Flex?

I've been having a debate with a couple of fellow racers about the benefits or otherwise of chassis flex.
I thought it might be interesting to hear other opinions on the subject.
Is it conceivable that there might be situations that having control over chassis flex would result in faster lap times, or should you simply try to make the chassis as rigid as possible?
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Old 08-05-2004, 09:53 AM   #2
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I have turned faster lap times, and the car seems more planted with a flexible light weight chassis on my MTX3 in low traction conditions than with the stiff thick chassis. High traction, I will always use the stiff one, less traction roll.
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Old 08-05-2004, 11:11 AM   #3
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Use a flexible chasis for bumpy tracks
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Old 08-05-2004, 01:17 PM   #4
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size of the track and numbers of tight turn/corner
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Old 08-06-2004, 10:36 AM   #5
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I'm one taking the contrary position to rjl.

As I understand it, the object of the exercise in chassis design is for absolute rigidity, any flex being an uncontrolled variable and therefore to be avoided.
With a theoretically rigid chassis, any track conditions are then accommodated with suspension settings - i.e. we don't need uncontrolled variables influencing these settings.

So, who changes chassis' between tracks?
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Old 08-06-2004, 11:03 AM   #6
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Quote:
Originally posted by Taylor-Racing
I'm one taking the contrary position to rjl.

As I understand it, the object of the exercise in chassis design is for absolute rigidity, any flex being an uncontrolled variable and therefore to be avoided.
With a theoretically rigid chassis, any track conditions are then accommodated with suspension settings - i.e. we don't need uncontrolled variables influencing these settings.

So, who changes chassis' between tracks?
A flexible chassis allows for the front suspension to rotate along the axis of the car for high bumps and not affect the rear suspension. If it was rigid a high front bum will upset the rear grip.
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Old 08-06-2004, 11:41 AM   #7
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ziggy,
I'm unclear as to wheather you are describing a torsional load being fed into the front suspension, the front end of the chassis, or both.

In any of those events, there will be a torsional load fed into the rear suspension.
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Old 08-08-2004, 05:46 AM   #8
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it seems like the "right" thing to aim for a super stiff chassis and letting just the shocks doing the work, but in RC it seems a bit of chassis flex in some situations is advisable. hara for example uses the 2mm chassis on ashphalt sometimes i think, and i've heard some dudes at moorebank NSW saying that on low bite days the stock chassis is better.
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Old 08-10-2004, 01:48 AM   #9
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Seems strange that having manufacturers chase the stiffest yet lightest chassis material is going to waste if having some flex is best.

From my readings, a super stiff chassis would allow the ability to more accurately control shock absorber and spring settings. I would imagine that the only time you would want some uncontrolled flex in the chassis is when you can't come to a satisfactory suspension setup to cater for all parts of the track. For example, if 90% of the track was wicked smooth but 10% had some fearsome bumps, then a stiff setting is going to suit the 90% and not the 10% and vice versa.

If you could have some 'controlled' flex (torsional but not longitudinal) you may be able to come to a status quo with your settings to absorb the bigger hits.

Low grip days at a particular track resonding better to a less stiff chassis really only equates to a shock/spring setting that is right for the conditions that hasn't been set in the more correct manner. On the other hand the stock chassis might be heavier in certain sections creating a different centre of gravity and hence roll centre that could just be outside the scope of the settings the chassis has.

Cheers,

Mike.
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Old 08-10-2004, 03:11 AM   #10
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Yup i agree with what Z00M is saying.
If the car is set up perfectly then in theory the stiff chassis will always be better. However I suppose that the flex can be seen as a tuning option too.
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Old 08-10-2004, 08:16 AM   #11
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Yes, any chassis flex is uncontrolled and therefore must be considered in addition to any suspension settings made. Any flex in that platform must diminish the relevance and effectivness of those settings as it is uncontrolled and largely uncontrolable.
Why? Because there is no damper on the chassis.

When talking of the desireabilty of some chassis flex, the ramifications may be extremely difficult to control.

For instance:
Can the flex can be limited to a single plane?
Can we permit single plane flexing and at the same time maintain torsional rigity - or vice versa?
Can we control squat and dive at either end of this chassis (the wave effect) together with their interactions?
Since the chassis is acting as a spring, how do we damp it?

For any given track, there is only a finite amount of grip available. We can't suddenly find some extra grip because the chassis moved as opposed to the spring. In fact we can move the tyre to the track with a spring much faster than by moving the whole chassis.
The vast differences between sprung and unsprung weight is surley the primary reason we use suspension systems.

And given that chassis flex is uncontrolled, I can't see how we might attach a benefit to it.

I say the remedy is in springs and damping - something you can control.
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Old 08-10-2004, 06:25 PM   #12
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Go stiff. Although a flexy chasis might work good in some situations, it is more by luck since it isn't controllable. There is other ways to get the car to do what you want in a controlled manner. On a smooth track, you'll be worse off since you want all your movements to be the result of input, not uncontrolled twisting.
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Old 08-11-2004, 03:09 AM   #13
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Hmmmm, going to have a talk to a go-karter. Then someone who drives 1/12th.
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Old 08-13-2004, 07:48 PM   #14
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Quote:
Originally posted by rjl
Hmmmm, going to have a talk to a go-karter. Then someone who drives 1/12th.
Just glue a couple of credit cards together end to end. That should do the trick!
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Old 08-13-2004, 10:57 PM   #15
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Theoretically, you are correct but the world is not theoretical. We have to take into account that these are not real cars no matter how similar they are. Therefore, certain tuning aids won't work as well on RC cars as they do on real life counterparts. An example of this are the rear wings we run on our bodies. You will never find a wing in that proportion on a real touring car and that is because air molecules are not scaled down like our cars. Neither are gravity, surface tension of the road..etc.

Also, I doubt the contact patch of the tires is more than 10 sq. mm. The little suspensions can only do so much to produce mechanical grip and retain a quick direction change. So with all that being said you throw a little something that might seem counterproductive and it all turns out for the better.

Real life examples of "flex" are top fuel dragsters and believe it or not Formula 1 cars. They don't use springs but control the deflection characteristics of the carbon fiber arms.
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