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 Post subject: suspension design
PostPosted: August 8, 2022, 4:18 pm 
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Joined: May 7, 2009, 6:24 pm
Posts: 29
I know nothing about suspension. So, if I am trying to use suspension software to design my suspension, how do I know what parameters or settings I need to shoot for in the design? Are there basic setups to start with or do I need an engineering degree to build a Locost suspension?


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 Post subject: Re: suspension design
PostPosted: August 8, 2022, 5:54 pm 
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Mid-Engined Maniac

Joined: April 23, 2006, 8:26 pm
Posts: 6261
Location: SoCal
No, you don't need an engineering degree, but do need a logical mind.

Search on threads, do a lot of reading, find what books to buy, and do more reading. The question is like asking "how do I build a house" and expecting a few dozen-word answers to make it all clear - not going to happen. The phrase "teach a man to fish" vs "give a man a fish" comes to mind, because any brief explanation here will just cause more confusion and doesn't educate. Strongly suggest buying some of the design books mentioned both here and elsewhere and plan on a couple years before even starting on the design.

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Midlana book: Build this mid-engine Locost!, http://www.midlana.com/
Kimini book: Designing mid-engine cars using FWD drivetrains, http://www.kimini.com/book_info/


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 Post subject: Re: suspension design
PostPosted: August 8, 2022, 8:16 pm 
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Joined: January 2, 2009, 1:45 pm
Posts: 1333
Location: Halifax, Nova Scotia
Kurt is perhaps a bit harsh, but his advice is sound. Jumping right into design software is not going to do more than block understanding and probably generate frustration. As he suggests, do some reading (books like Staniforth's 'Competition car Suspension' for example) to develop and understanding of principles and perhaps even play with cardboard flat plane models (Staniforth's 'string computer') to get an appreciation of the compromises/conflicts in suspension design.

Some guidance will help, but it's simple stuff like 'what are normal roll values' (something like 2 degrees maybe?) for design purposes, and what are typical camber, caster and roll centre values. Trolling the site is your friend, as far as determining typical values, and ranges of them. But these key values don't generate suspension designs per se, they merely provide targets for your design effort.

I did mine with the string computer, with much compromise and iteration. You can expect your own efforts with suspension software to be more 'accurate' than my cardboard models and push pins but your accuracy won't give you a better (or even equivalent) result if you don't have a good idea of what you are aiming for.

At the other extreme, if you a building a cruiser you can do some pretty pragmatic stuff as Perry has done in several builds.

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Isuzu Pickup/SR20DE, +401 COLD frame
Build Log: viewtopic.php?f=35&t=11601


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 Post subject: Re: suspension design
PostPosted: August 8, 2022, 8:16 pm 
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Joined: January 2, 2009, 1:45 pm
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Location: Halifax, Nova Scotia
[double post]

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Warren
Isuzu Pickup/SR20DE, +401 COLD frame
Build Log: viewtopic.php?f=35&t=11601


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 Post subject: Re: suspension design
PostPosted: August 8, 2022, 10:05 pm 
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Joined: October 24, 2008, 2:13 pm
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Location: Carlsbad, California, USA
While what Kurt and Warren said above is accurate, you can gather up information on what satisfactory, or good target values might be. For example, castor angles in the range of 3-5 degrees likely will work, or be good initial targets. If you ask, "What the heck is castor angles", then you definitely need to do more reading first.

Also, if you know what donor you're to use, then you'll know what suspension types you'll have at front and rear. That will help simplify your research and reading.

I actually compiled a list of target values before I started my design. I did a lot of reading before I compiled the list, however.


Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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 Post subject: Re: suspension design
PostPosted: August 9, 2022, 7:55 pm 
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Joined: August 28, 2010, 7:53 am
Posts: 317
I can add that creating a design that is easy to fabricate accurately is just as important as the design. Straight lines and right angles don't make a sexy looking chassis but they are much easier to fabricate accurately.
Also, use square tube whenever possible as it is much easier to clamp, jig, position etc. I very carefully drill a 1/16 hole in the center of all my crossmembers and use that as a reference. Using strings to align parts is great - they are cheap, portable, always straight and never go out of calibration! (I prefer fishing line.).


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 Post subject: Re: suspension design
PostPosted: August 9, 2022, 8:48 pm 
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Joined: July 7, 2011, 12:17 am
Posts: 378
Location: Oregon City, OR
Along the lines of what Lonnie said, I copied an existing rear suspension geometry (Miata) and am very pleased with it.

If you build your suspension with adjustability you can cover a lot of variations if you’re willing to do some testing.

It’s been my experience and observation that genuinely light cars are more forgiving of less than ideal geometry than their heavier counterparts. As KB alluded it takes a great deal of knowledge to wring the most out of a car, but a light car can still perform reasonably well on any reasonable geometry.

Pay attention to what experienced builders here have done and you’ll do fine.

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 Post subject: Re: suspension design
PostPosted: August 10, 2022, 7:55 am 
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The parameters depend on the parts you are using, what the intended use will be, and personal preference.

Generally:
Scrub under 1/2 inch from tire offset and size for the spindle balljoint locations.
1 deg neg camber at ride height
minimal bump steer
Roll center low and no migration through 3deg roll.
60-90 virtual swing arm length
As much camber gain in bump per degree of roll and still meet the criteria above.

Basic setups can be found on the vsusp topic but it relies on the builders accuracy in measuring the critical dimensions and enter them into vsusp.

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Miata UBJ: ES-2074R ('70s mazda pickup)
http://www.vsusp.com
ford IFS cheap viewtopic.php?f=5&t=13225&p=134742
Frame L x cockpit W x eng bay HT (w/o hood/bonnet/cowl)
Lotus Super Seven: 115 (no spare) x39x7.25
Tiger Avon: 114x40x13.3-12.6
Champion (Book): 114x42x11
Gibbs Haynes: 122x42x14
Voo Doo: 113x44x14
McSorley “442”122x46x14
Collins “241” 127x46x12


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 Post subject: Re: suspension design
PostPosted: August 10, 2022, 9:50 am 
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Mid-Engined Maniac

Joined: April 23, 2006, 8:26 pm
Posts: 6261
Location: SoCal
All good direction, but you'll likely hear: "What is scrub, camber, bump steer, roll center, and virtual swing arms?" That's why I advised self-education first, because learning the basic terminology is fundamental to understanding everything else.

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Midlana book: Build this mid-engine Locost!, http://www.midlana.com/
Kimini book: Designing mid-engine cars using FWD drivetrains, http://www.kimini.com/book_info/


Last edited by KB58 on August 10, 2022, 10:08 am, edited 1 time in total.

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 Post subject: Re: suspension design
PostPosted: August 10, 2022, 9:57 am 
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Joined: December 4, 2011, 6:19 pm
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All good advice but you can also do it the simple way. Watch Jim McSorley's videos starting with https://www.youtube.com/watch?v=6crOSs6LCTQ

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Winnipeg, MB, Canada


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 Post subject: Re: suspension design
PostPosted: August 10, 2022, 11:39 am 
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Joined: December 22, 2006, 2:05 pm
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Arbalest has been on here 13 years. There could be a clandestine build involved or maybe he just wants to tinker with a suspension program. We may never know........

_________________
Miata UBJ: ES-2074R ('70s mazda pickup)
http://www.vsusp.com
ford IFS cheap viewtopic.php?f=5&t=13225&p=134742
Frame L x cockpit W x eng bay HT (w/o hood/bonnet/cowl)
Lotus Super Seven: 115 (no spare) x39x7.25
Tiger Avon: 114x40x13.3-12.6
Champion (Book): 114x42x11
Gibbs Haynes: 122x42x14
Voo Doo: 113x44x14
McSorley “442”122x46x14
Collins “241” 127x46x12


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 Profile  
Reply with quote  
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