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PostPosted: April 28, 2014, 6:45 pm 
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Joined: February 8, 2014, 10:47 pm
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Location: Cornelius OR
I am building an autocrosser.

I have suspension F&R I need to model to find optimum pick up points, roll centers, and rack location (bump steer), rear roll steer, etc.

Since I am building a frame I can raise the mounting points instead of cutting springs and I don't want to just replicate what was stock as it likely can be improved on.

Is there anyone in the Portland OR area (westside?) that has suspension software and a soft spot for a guy who is trying to do it right?

I am not opposed to trading and not unskilled.

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PostPosted: April 28, 2014, 7:54 pm 
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Joined: February 19, 2014, 4:27 pm
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Location: Vancouver WA
I am in the Portland area, but suspension design scares me so I'm building from plans. Let me know if you need anything else though. :cheers:


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PostPosted: April 30, 2014, 11:36 am 
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Location: Raleigh, NC
the trick with suspension is knowing what your goals are for the car. vsusp is great at telling you what the suspension will do (at least how the control arms will act) but what you have to do is set your goals and expectations for roll centers, ride height, camber curves, etc... before you'll ever know if the suspension you design will work for your application. I've gone through the same thing trying to design an race-able road car and my hardest decisions were deciding what each end of the car actually needed to do

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PostPosted: April 30, 2014, 4:29 pm 
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Joined: July 4, 2006, 5:40 pm
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Location: Novato, CA
anavrin is exactly right. The suspension calculators won't find the answers. Time and again we see people post their latest suspension numbers from some design they've worked out, and then ask if the numbers seem 'reasonable'.

If you haven't built some custom suspensions and seen for yourself how they work on the road and track, then you should start doing that. And if you're not sure what 'numbers' to use, start with a proven design. The best designs seldom started from a clean sheet of paper, they evolved from someone else's design.


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PostPosted: May 1, 2014, 8:26 am 
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Joined: August 12, 2012, 6:38 pm
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Location: worcester county, Massachsetts
nick47 wrote:
anavrin is exactly right. The suspension calculators won't find the answers. Time and again we see people post their latest suspension numbers from some design they've worked out, and then ask if the numbers seem 'reasonable'.

If you haven't built some custom suspensions and seen for yourself how they work on the road and track, then you should start doing that. And if you're not sure what 'numbers' to use, start with a proven design. The best designs seldom started from a clean sheet of paper, they evolved from someone else's design.



what he said. find a proven design and copy it. unless you have extensive experience building suspensions, you won't know what any of those numbers mean in terms of actual dynamics.

you can even use TLAR methodology, and have decent results...that's what I did on hte B-3 ;-)

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PostPosted: May 1, 2014, 6:13 pm 
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Location: Cornelius OR
Don't I need to know where I am at before firing up the welder?

And the steering geometry surely can be modeled to discover correct rack placement?

And how will harrowing the Supra rear section affect the geometry?

My plan is an autocross beater on street tires and 250 to 350 HP and under 2200#

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PostPosted: May 5, 2014, 12:05 pm 
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Location: Raleigh, NC
Bent Wrench wrote:
Don't I need to know where I am at before firing up the welder?


absolutely

Bent Wrench wrote:
And the steering geometry surely can be modeled to discover correct rack placement?


yes. there are some basic rules to get decent placement without an actual model but this is the best scenario.

Bent Wrench wrote:
And how will harrowing the Supra rear section affect the geometry?


that's the real question. check out vsusp, it's a free online program that will give you results if you know what to feed in

Bent Wrench wrote:
My plan is an autocross beater on street tires and 250 to 350 HP and under 2200#


if you're building from scratch you should be able to make it much lighter than that

What you've posted here that you want better handling that what you have (I don't know what you have though, presumably a supra if that's what you're modeling after) and that you want to use suspension components off of the car (I think?) but may move around pickup points to avoid cutting springs. That's all really kind of a mess.

If you're building a new chassis you're better off figuring out what you want the suspension to do then modeling and building a suspension that will do what you want instead of trying to use some components from an existing setup that may or may not meet your end goal, or may create too many compromises.

Do you have numbers you're looking for? body roll limits, camber loss per degree of roll, camber gain per degree of bump, roll center heights, roll axis inclination? Anything?

There are absolutely ways to figure out what your current suspension is doing if you know the geometry measurements. Then if you have parts you want to keep you can use those same parameters and change around chassis points and whatnot but you always have to keep in mind what you intend for the suspension to actually do.

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PostPosted: May 5, 2014, 1:07 pm 
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Location: Novato, CA
The reason there are suspension calculators is because you can't change one thing without affecting a dozen others. If you narrow the rear suspension, you'll lower the roll center, which you can compensate for by changing the upper A-arm angle, which will affect camber gain, which you can compensate for with other changes, and so on and on until you've changed everything. And then you'll change the CG or F/R balance and everything will change again.

There are books written on suspension design and none of them cover everything. There are a million different suspension designs out there because no design is right for everyone. You are so much better off finding a car that does what you want it to, and then learn why it does what you want it to, and then do that. You will have a lot fun building a car, and you will get a great deal of satisfaction out of it if it does what you want it to. Good luck, and I really think you have the right attitude to do this.


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PostPosted: May 8, 2014, 2:44 pm 
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Joined: March 13, 2014, 10:05 pm
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If you're serious about understanding and developing a suspension, try and find a copy of Race Car Vehicle Dynamics by Doug Milliken. I'm an FSAE chassis/suspension guy and it's my bible.


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PostPosted: May 17, 2014, 4:19 pm 
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Joined: October 3, 2009, 1:33 pm
Posts: 33
Location: FL
My personal favorite references: Carrol Smith, 1) Prepare to Win, 2) tune to Win, 3) Engineer to Win; Allan Stanifort, Competition Car Suspension; Herb adams, Chassis Engineering. Read them and you will be able to talk sensibly about what you want and how to get it. You will also be ready to use VSUSP. MY MOTTOS: Didn't have time to do it right, found the time to do it twice. If you tinker with it long enough it is broken. Poor design can not be saved by fantastic workmanship and the best design can be ruined by poor workmanship. The biggist hit to schedule is It'll be better if... Building your own car is a personal expression, only you can judge it, so build it to please yourself. G;-)

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PostPosted: May 17, 2014, 10:02 pm 
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Joined: February 8, 2014, 10:47 pm
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Location: Cornelius OR
I have Race Car Engineering, Rowley It covers a lot of this but maybe some other input will be beneficial.

Thanks for the Vsusp tip I will plug in what I have and see where I'm at.

Thinking about not narrowing the rear but widening the front to match, using some wheels with more + offset will help with scrub.

I think the car will be classed as an EM so I should take advantage of what that class allows.

Playing with Vsusp now....

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PostPosted: May 17, 2014, 11:32 pm 
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Joined: February 8, 2014, 10:47 pm
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Location: Cornelius OR
This is what I have now, missing hub offsets.

ovlov <<< Vsusp linky

I can ditch the crossmember and change the arm length to widen it out to match the rear I'm guessing I'll need to extend the lower ball joint and lower the upper inner mount.

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PostPosted: May 17, 2014, 11:54 pm 
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Bent Wrench wrote:
Don't I need to know where I am at before firing up the welder?


Here is a picture of what one of the World's leading race and rally car builders, Lancia, did with their suspension of the fastest 2 wheel drive rally car ever built, the 037 ...


Attachment:
lancia 3.jpg


Attachment:
lancia 4.jpg


The upper control arm inner mounts front and rear are 4 hole adjustable while the lower control arms have 2 options. Lancia were late developing the car and didn't have a lot of time for testing so homologated the car with the ability to change the pickups.

My point is there is no set rules for suspension design, not even for Lancia.

Notice the typical Italian welding, never look underneath a Lamborghini, you will be shocked! :lol:


You do not have the required permissions to view the files attached to this post.


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PostPosted: May 18, 2014, 12:50 pm 
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Joined: September 11, 2012, 5:20 am
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Location: Lithuania
Lancia was used on quite different surfaces than just tarmac and because of this there is lots of possibilities to change roll center and camber gain. In any case it is good to have few options more than just one.


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PostPosted: May 25, 2014, 2:36 pm 
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Joined: February 8, 2014, 10:47 pm
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Location: Cornelius OR
Mail man still has reference materials. (I'm starting to turn blue)

Still looking for someone to share time on their modeling software.

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