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PostPosted: December 16, 2015, 3:40 am 
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I've done some reading here and there but, when it all comes down it it, I'm a visual/hands on learner... I can read all day long but, until I touch/apply my self to a project, it doesn't really make much sense. Vsusp is great for the visualization for me...

I've been playing with middy frames, trying to create the front end using miata front spindles and based on 225/45R17 tires as an "average" normal tire these days.

Here is my Vsusp for what I'm working with right now.. What do you think? (the rear has not been worked on)

http://vsusp.com/#0.8%26project_name%3A ... enter.y%7D


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PostPosted: December 16, 2015, 7:37 am 
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viewtopic.php?f=5&t=13928&hilit=vsusp&start=75

You can widen the frame rails to shorten the control arms in order to keep the lca and uca near level.

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PostPosted: December 16, 2015, 9:56 am 
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Location: Cornholio OR "Where the magic happens"
Long travel or short travel?

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PostPosted: December 16, 2015, 10:44 am 
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Just playing around with your dims:

default values

I think your wheel offset, tire od, or wms position may be off since you have that much scrub. Not sure.

Raise a wheel an inch at a time in bump to see the gain.

Not saying you should run this exact setup. Just giving some ideas.

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PostPosted: December 16, 2015, 1:23 pm 
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The only thing I was really confused about from the start was the whole "parallel" lower control arm thing.

If you use the pivot point of the Miata ball joint and the pivot point of the LCA (wherever you put it on the frame) the actual control arm will actually look like it's sitting at a downward angle... So do you design it so that the control arm is visually mounted parallel to the ground or so that the actual line between the two pivots is parallel?


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PostPosted: December 16, 2015, 3:09 pm 
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It's up to you. The suspension only cares about the relationship of the pivots, the shape of the arms is arbitrary and is "interesting" sometimes because of things the designer does to clear other things.

The angle of the lower arm will affect the roll center and the Miata spindle has a high location of its lower pivot. So having that downward tilt towards the chassis helps lower the roll center.

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PostPosted: December 16, 2015, 5:22 pm 
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Miatav8,MstrASE,A&P,F wrote:

I think your wheel offset, tire od, or wms position may be off since you have that much scrub. Not sure.



Maybe a lot of scrub because I used a 1in backspace instead of the 55mm like a stock 17in would be? Enter in 2.16in for the offset and it changes from +.78 to -.38

horizenjob wrote:
It's up to you. The suspension only cares about the relationship of the pivots, the shape of the arms is arbitrary and is "interesting" sometimes because of things the designer does to clear other things.

The angle of the lower arm will affect the roll center and the Miata spindle has a high location of its lower pivot. So having that downward tilt towards the chassis helps lower the roll center.



What are we looking for in camber gain in roll? In bump? I was reading that you're really looking for a bit of positive in droop (up to a degree) but, how much body roll do they typically see? Obviously available droop/bump is based on the shocks used and the space I have.

What about roll center though? What effect does it's movement have in the turn? Whats the difference between the roll axis, say in a left hand turn, moving to the left while the car leans right vs in the same left hand turn moving to the left of center as the car rolls left? What about the relationship between front and rear there?


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PostPosted: December 17, 2015, 8:13 am 
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I was misreading the results so I deleted the pic.

Ideally, when the car is cornering and rolls, the outside wheel stays at near zero camber.
That is easily accomplished ( default values ), but the swing arm length at ride height is very short; about half the track.
This causes problems with one wheel bumps having excessive camber gain, straight ahead braking with a reduced contact patch due to dive and camber gain, high roll center, and jacking forces.

Aim for 0.6-0.7 camber gain per degree of roll, a roll center that does not move vertically and stays below 4 inches, and a swingarm length over 60" at ride height. The swingarm length changes with bump and should never get below 30 inches due to the reasons mentioned above.

Use control arms where the uca is around .625 x the lca length and the arms are as long as possible.

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PostPosted: December 21, 2015, 3:12 pm 
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Miatav8,MstrASE,A&P,F wrote:
I was misreading the results so I deleted the pic.

Ideally, when the car is cornering and rolls, the outside wheel stays at near zero camber.
That is easily accomplished ( default values ), but the swing arm length at ride height is very short; about half the track.
This causes problems with one wheel bumps having excessive camber gain, straight ahead braking with a reduced contact patch due to dive and camber gain, high roll center, and jacking forces.

Aim for 0.6-0.7 camber gain per degree of roll, a roll center that does not move vertically and stays below 4 inches, and a swingarm length over 60" at ride height. The swingarm length changes with bump and should never get below 30 inches due to the reasons mentioned above.

Use control arms where the uca is around .625 x the lca length and the arms are as long as possible.


Thanks for guidelines. I'm curious what about my original link is no good? And please don't hold back, like I said, I'm a visual learner so, unfortunatly I have to see what I'm doing wrong hahaha.

With the original link the actual design of the control arm is parallel with the ground when built but, the pivot is at a bit of an angle.
Attachment:
Capture.PNG
Capture.PNG [ 71.83 KiB | Viewed 4451 times ]


And with the first link it's got:
1 deg of left roll (right turn) = -.67 camber inside wheel .64 outside
2 deg or left roll (right turn) = -1.35 camber inside wheel +1.18 outside.
The roll center stays at 2.05in through 2 degrees and only moves to 2.13in after 4 degrees of roll.

If I run 1 degree of front camber at 2 degrees left roll the outside wheel is near 0 degrees camber and the inside is -2.35. Is that too much? It thought I recalled reading in a book 3degress inside is about as far as you want to go in roll but, I could definitely be recalling the details incorrectly.

Swingarm length at ride height is ~80in and after 2 in of bump reduces to 57.8in and extends to 129.7in in 2in droop.

The only major difference is the UCA to LCA ratio of about .722 vs .625.


There is literally almost unlimited design constraints for the front mounting points though, anything can be changed at this point, it's not really a middy with the intentions of "looking like a 7" at this point. It's just a middy chassis because of the powerplant I want to use, I'll worry about looks after I get function down haha.


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PostPosted: December 21, 2015, 7:27 pm 
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I’d pay attention to the outside or “laden” tire, keeping it vertical.

I’m not saying anything is wrong with your design, just providing food for thought imho.

On the outside with one degree roll, you’ve lost .64 of a degree so the actual gain is .36 of a degree.

I raised the lca inner pivot to level the lca (pivot center to lbj ball center so your arms will actually droop), then moved the pivot inboard to zero the camber. This improved the gain in roll (.5 deg loss from .64 degree loss at one deg roll and .893 deg versus 1.18 deg at 2 deg roll) and reduced the swingarm to 58.9 inches but raised the roll center too high by most racing standards at 4.37 inches.

I then tried shortening the uca to be close to 62.5% of the lca and chose 10 inches to see the affect, moving the frame out as required to zero the camber. Swingarm was shortened to 51 and the rc was raised to 4.96 inches, but now we only lose .421 deg for one deg and .803 deg for two degrees and even at 5 deg roll, the swingarm is still over 35 inches.

I then raised the ucap to lengthen the swing arm to 60 inches, pushed the ucap out to rezero the camber, resulting in an rc of 4.252 inches that is flat through 10 degrees, .487 deg loss at one deg roll and .9 at two deg, and the swing arm stays over 39 inches through 5 degrees roll.

Here is my tweaking if you care to see it (default values). A higher roll center offsets the need for a swaybar so a thinner bar may be used on none at all. If the swingarms are long enough, all those other nasty habits can also be avoided up to a point you may never cross, particularly as a street car. However, I’m sure you can improve on these numbers with further manipulation.

You might also start with putting the lcaps far enough apart to work with the rack width (inner pivot to inner pivot) you want to use. I don’t know how high up the spindles your outer tierod pivots will be to know how far up the line between the ucap and lcap the pivot will need to fall on a line between the instant center and the tierod pivot.

On the chart, you can select more than one parameter to display by holding cntrl. Select the cambers before the roll center in Y otherwise the chart does strange things.

I will also add that this is just my opinion. Even the experts do not agree.

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PostPosted: December 22, 2015, 6:46 pm 
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Here is another improvement with level lca, 4.094 rc, 62 inch sa, only 1.9 deg loss in 5 deg roll, 39.829 inch sa at 5 deg roll:

default values

Here is another improvement with dropped lcap, 52 inch sa, 2.047 rc relatively flat to 5 deg roll, only 1.538 deg loss in 5 deg roll, 34.883 inch sa at 5 deg roll:
default values

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PostPosted: December 23, 2015, 2:14 am 
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Here's a variant using some elements from the various links we've had so far.

http://vsusp.com/#0.8%26project_name%3A ... _camber%7D


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PostPosted: December 25, 2015, 3:46 am 
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I changed quite a bit of things for this go around. I used a different design for the ball joint attachment to the control arm, Midlana style actually. It allows the control arm to be more inline with the balljoint pivot and allows a visually parallel control arm to be almost parallel as far as actual pivot points go. I also changed the tire size, and therefore changed the ride height as well and decided to add 1 degree of static camber.

Here's where I am.

http://vsusp.com/#0.8%26project_name%3A ... _camber%7D


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PostPosted: December 25, 2015, 7:40 am 
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It sounds like your changes to the arms are only visual. The visual references are there to show the virtual arm, not how yours will appear. If the changes do not alter the location of any pivots, it is only visual and makes no difference.

Anybody can add static camber to an existing car. You can add static camber to mask a problem with the suspension design but tire wear is a tradeoff.

The wheel size and offset chosen to support a 205-50-15 may not clear the brake caliper if the spindle donor was not available from the mfg with a 15 inch rim.

I would not compare your results to those of other builders based on their geometry. The spindles dictate the geometry in several ways up to a point. Note the greater the distance between the lbj and ubj, the less the camber gain will be for any given geometry.

This is what you are running after tweaking an adjustable uca to zero the camber:
Middy
RC 1.77, SA 104, 1 DEG roll .656 loss, 3 DEG roll 1.906 loss

Your first design:
RC 2.07, 1 DEG roll .67 loss, so slightly higher roll center and slightly less gain, but more ground clearance.

I’ve tweaked your new design for zero static camber:
Middy
RC 1.65, 1 DEG roll .595 loss, 3 DEG roll 1.562 loss

Lower RC, greater camber gain. RC not completely flat but stable.

I think my 52 inch SA with the bigger tires and higher gc was pretty good, depending on how far you will allow the suspension to roll. Note the curves:



Also, when you copy the link to post, use the link in small type at the bottom of the page instead of the address at the top of the screen. It makes for a much shorter link.


Attachments:
autoxinvr62.JPG
autoxinvr62.JPG [ 19.51 KiB | Viewed 4325 times ]

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PostPosted: December 27, 2015, 2:26 am 
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Miatav8,MstrASE,A&P,F wrote:
It sounds like your changes to the arms are only visual. The visual references are there to show the virtual arm, not how yours will appear. If the changes do not alter the location of any pivots, it is only visual and makes no difference.

Anybody can add static camber to an existing car. You can add static camber to mask a problem with the suspension design but tire wear is a tradeoff.

The wheel size and offset chosen to support a 205-50-15 may not clear the brake caliper if the spindle donor was not available from the mfg with a 15 inch rim.



Miata spindle is what I'm using so we should be good to go with a 15.

The change to the arm is somewhat visual but, it allows the LCA inboard pivot to be closer to the actual pivot of the balljoint. You can see the difference between the two if you compare where the LCA tubes would be welded to the balljoint bracket. The first version is parallel with the balljoint cross bolt where as the second version is above the balljoint crossbolt. Doesn't neccesarily change the pivots but, it helps in the "parallel control arm" thing for ease of building...
Attachment:
Capture1.PNG
Capture1.PNG [ 89.45 KiB | Viewed 4299 times ]


For what it's worth, I've planed around a QA1 shock mounted at 12.5in @ ~39 Degrees. It allows for just over 3in of bump and 2in of droop, which I highly doubt it would ever need fully. Planned use is mostly autocross and random drives to work and around town.

I've been playing with it a little more today. I changed the track width a little bit and I modified your link to mimic the same track width as well.

Mine @ 58in
Middy 58in

Yours @ 58in
MV8 58

Yours with the lower LCA pivot definitely keeps the roll center more stable over all but, I think for "ease of building in a garage" (haha) I'm going to stick with this final link. It's pretty close to yours with the lower LCA pivot and seems fairly inline with the gains mentioned in the books.


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