Front SLA, need help finalising design.

[BenE64]

Hi, I am in the final stages (hopefully) of designing my front SLA conversion for my truck. I have PT suspension analyser from a previous failed attempt at building a nice track car, so I have been using it to help with this new project. The truck is going to be built in pro touring "style" as it really has all the performance qualities of a large brick. It has a long wheel base and a high CG but I'm working with what I have got.

I am using a chevy C20 front sub frame which needs cutting to fit where I want it on the chassis. As a part of engineering to be able to register it on the road I am not allowed to have fabricated arms/ spindles etc so I am using all the standard componentry, this doesn't stop me from re-arranging them a bit to make it handle a little better.

After some fairly elaborate set up I got the subframe to sit in its factory position and measured it up to get the data points. I then made a jig to position the spindle in its correct location for my truck and re measured all the arms steering rack etc to the draw it in CAD. Once in CAD I can move it around while keeping the arm dimensions, spindle dimensions all the same but I can get the co ordinates to plug into the suspension program, make a small change, do it all again. Many weeks later and hours of forum and book reading I have narrowed my design to this

https://www.pro-touring.com/attachment.php?attachmentid=112252&stc=1


I have a few worries due to my lack of knowledge and real world experience! I am stuck with the spindle as it is, which leaves me with the following parameters to work around

SAI 8*
Scrub radius is 9.5cm

I have set Static Caster at 7.5* and camber at -.5*

With the arrangement of the links I have now I have .86* of caster gain and -.41 camber gain. 53% of anti dive. and a RCH of nearly 2in.

Can anybody give some pointers to where I may have gone wrong? It is a build once no real adjustability deal when finished so Id like to get it close to good as possible.

I have concerns on the following,

7.5* of caster and the high scrub radius, will this be a heavy steering pig or not really all that noticeable? the front tyres are only 225 wide will this reduce the effort anyway?

Is 53% anti dive to high? should I be in the high 30-low 40 range?

Being that it is a high centre of gravity land whale, would I benefit raising the FRCH a bit more, and with the current arrangement I have a fair bit of lateral RC movement in roll? at 3* it is nearly under the opposite tyre if that makes sense. will this cause excess jacking?

I have tried to arrange the arms differently but cant get the sort of figures Ron has talked about with out this lateral RC movement, is this a compromise I need to live with?

Sorry for the long winded post, If this isn't the right place for this style of truck let me know.

Thanks Ben

[iadr]

I'm interested, as I am re-suspension'ing the front of a 1993 Suzuki Vitara, and went through similar quandries.
Here are some conclusions:
1/ I think getting the outside tire to stay vertical in roll has to be abandoned fairly early in the compromised making process. Or at least you go back to some static neg camber.
2/ Even given #1 your VSL (virtual swing arm length) is likely to be shorter than anything OE...remotely modern and OE, anyway.
3/ Concerns over jacking. Hmm. Best/only way** is to lower the inside LCA mounts. And yes that changes a bunch of other things.


I am not sure your question "Where have I gone wrong" is just self deprecating or you think a 2" RCH is that bad? Sounds fine to me. As to teh preceding specs in that sentence.

** to the best of my present understanding.

[iadr]

Also your photo is too small by far. I cannot scroll to a resolution where the numbers are clear.

[BenE64]

G'day, thanks for the reply, No I wasn't intending to come across self depreciating :pat: Was meant as " what have I overlooked?"

Not sure why the picture resized so crap? As it stands I have had to make further adjustments from that design, I had issues with the ball joint angles once I mocked it up.

At this stage I have fairly good camber on the outside wheel but I am not quite there with the inside wheel, ie it is still in neg camber under dive/roll/steer conditions. although only by .5*. I can easily get there by adding more static caster but then I'm back to my questions on how much static caster vs scrub radius?

Front view VSL is nearly 120in so not to bad from what I can tell. I upped the RCH to about 3.5 - 4in and reduced the amount of lateral migration considerably to about 10in at full roll. I did this because of my CG height is going to be really high, I'm thinking it will be at least 30in. 2in is good for a car maybe not for a large vehicle like mine?

112630

I need to continually tell myself to tone it back as its not going to be a full blown race car, its a truck, but very easy to go off on a tangent!

If you have perf trends and want to share your design I can go over it and see what I can see? not that I know what I'm doing but 2 heads are better than 1...... maybe.