Spaceframe Comparison

[Darnel A.]

3 times Wheel Frequency is usually a good design point. Anything above this point is over engineering.

Darnel

 

[Doug Clark]

I would have thought the chassis only needed to be stiff enough to resist input force from the greatest load introduced to the spring mount? Anything more would be a waste of engineering.

Hi Bruce,

Here in lies the issue resist can mean anything between not break (and move all over the place) and not move which implies infinitely stiff. The reality of what I would have thought you would want is somewhere between the two.

BTW Dampers induce a lot of force also as speed sensitive devices, looking at some random damper curves on the web you might see another 200kg of load going into the system in compression due to this.

3 times Wheel Frequency is usually a good design point. Anything above this point is over engineering.

Darnel

Hi Darnel,

Thats an interesting statement is there a method behind it or is this derived from observation?

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On stress analysis, even the OEM's don't have 100% accurate stess and fatigue analysis. This is why they test the heck out of prototypes and still get surprises. This does not make the tool any less useful to them and they still spend huge on the exercise in the first place.

Another point... What does 1 degree of twist look like? It doesn't sound like much but on my car its 14mm of movemnt at the wheel, on a car where you might have only say 65mm of movement in compression before you hit the bumpstops that 14mm is a significant amount of uncontrolled movement if it were allowed to happen. So if 14mm is too much whats an acceptable amount? And what are the real cornering and other loads you put into the car to generate the load in the fisrts place? These are some questions that you can drive yourself nuts trying to workout if you choose to think hard on the problem. You also might not be bothered about it all thats also fine, each to their own.

 

[Darnel A.]

Whoops, sorry Doug, I meant 10 times Roll Rate. (I gotta stop writing these things when I am half asleep!)

 

[Wayne M.]

Doug
A good approximation of 1 deg is to lift one end of a length of pipe 5' long 1" (actually 4.77' or 57.3"). This works pretty close up to about 10 or 12 degrees. Like I said, pretty close but not exact. Do the trig calc to see the variation. Sounds like 1" side to side across the chassis is about 1 deg.

Wayne

 

[Doug Clark]

Hi Wayne,

Of course you are right I was just looking at the inputs into a stress run I'd done.
One wheel up by 14mm the other down by 14mm so roughly an 1" at onw wheel.
Which makes the point even more than previously