Mr Clive
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| posted on 25/1/07 at 11:05 PM |
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Bump Load Calculations
When designing suspension componants, how do you work out design loads?
If you were to design for a bump load of say 8g for example (which includes the factor of safety already), would you design componants to be able to
take 8 times the weight on that wheel or 8 times the total car weight
for example, a 500kg car split evenly between all 4 wheels. Would the 8g bump load be 8x500kg or 8x125kg?
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chriscook
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| posted on 25/1/07 at 11:23 PM |
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3g is a fairly standard static vertical loadcase. That's 3x the load on that wheel. A while ago I posted a link to a powerpoint/pdf online that
had a selection of static loadcases - you'll have to use search as i'm not planning on being awake for much longer.
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cymtriks
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| posted on 26/1/07 at 08:01 PM |
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5g vertical
4g axial
2g lateral
I picked those up from a thread on "engineering tips" which has an automotive section.
On the thread mentioned:
Turczinator said-
Typically you start with a 10 to 100 occurence loading of 3g vertical and 2g Fore/Aft through the center of the wheel to simulate a pothole event.
Also working with 1g lateral loads for cornering and max braking loads in forward and reverse driving directions, which can be upwards of 10,000
occurences for these events. You may even want to do an analysis for curb push offs and dry scrub turns. These events will give a pretty good
estimate of the durability of your parts.
GregLocock said-
those values are fine for a circuit car (although 1 g lateral may need to be adjusted), they are a bit light for a road car, where I'd be
inclined to use 4-5g vertically, 3-4g fore-aft, and 2g laterally. The range covers low profile tires with stiff suspensions (the high end) through to
more sensible designs.
3-2-1 , or as I have suggested, 5-4-2, is a pretty good approach, designs based on that rarely need significant re-designs. Make sure your billet
aluminium has a guaranteed elongation at failure of at least 7% right through the billet.
turczinator said-
My 3g vertical and 2g fore/aft that I referred to was not soley based upon the unsprung mass, but the corner weight of the vehicle. Though I do agree
4/5g vert and 2/3g fore/aft would be more reasonable for pothole events, but I must disagree that the lateral load is do to the reation of the moment
created by the accelerating vertical mass striking the jounce bumper. It is due to the bump steer event as the tire impacts and exits the pothole and
the moment at the tire patch about Mx.
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Syd Bridge
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| posted on 27/1/07 at 10:29 AM |
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All of this depends on whether you are designing to the elastic limit, a percentage of it, or expect plastic deformation when these limits are reached
or exceded.
BIG differences.
Cheers,
Syd. 
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Mr Clive
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| posted on 27/1/07 at 01:39 PM |
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Many thanks for the responces.
I think I will be designing for the elastic limit so when the design load is exceeded, plastic deformation or componant failure will occur. I will
include the factor of safety in the design load.
I am designing a road car and I would rather go slightly over the top on strength and take a weight penalty than build something which could break and
crash when subjected to the british road network
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dnmalc
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| posted on 28/1/07 at 12:04 AM |
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Remeber that these are not static loads so when considering the design loads you will need to account for these as shock loads which is typically
considered to at least double them.
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