11 replies to this topic

[mick_in_oz]

Hi All, anyone want to offer up information in relation to installing and setting up a Triangulated 4-Link in a Street Rod?

 

Cars a 38 Chevy Business Coupe, front suspension is a new IFS from Curleys, and rear is a Triangulated 4-Link, I want it to be nice to drive but also stop and turn, the rear of the chassis is having some additional kick up for differential clearance, and part of this I get to choose how much Anti Squat the rear will have.

I've looked at a bunch of websites but nearly everything is in relation to drag racing or full on race cars.

 

Maybe I'm over thinking it but knowing what Anti Squat can do, I am wanting to see about putting everything at what hopefully is better than just put it where it fits.

So, do I aim for 100%, or 75% or 50% ............

I can do a few extra holes if need be to be able to accommodate some tunability once everything is done, but I feel if I measure and plan it properly now I shouldn't need them.

 

Standard line is to put the lowers parallel with the ground, but the 4-Link kit positions them up at the front (its a generic kit and I can re-manufacture things if needed), and the uppers, some say close to parallel, but then I know a significant amount down at the front some people also like.

 

Then  there's the potential for odd things happening under heavy braking if the Anti Squat is to high a %%%

 

Thoughts???

[dattoman]

What aren't you using a Jag IRS ?

[mick_in_oz]

Live axle 9", easy, no need to recondition an old rear end, endless selection of ratios and hemispheres.... 

 

Plus I already have a bunch of 9" stuff laying about.

 

Boring hey!

[EunUCh]

I am no suspension expert but i did have an article that was an interisting read about 4 link supension ,this is just  from memory but I think the article said  when you set up the arms you extend imaginary lines from the lowers and uppers until they intersect , where they intersect is called the "instant center" , the IC theoretically should intersect with the COG of the car and also with the center line of the car which according to the article is generally the camshaft (in a push rod engine ).

Will try and find the write up for more info and to test memory  , it was only a "basic" write up but interesting none the less.

 

[76lxhatch]

^ If it were me I'd be looking at it more from that perspective too, roll centres and instant centre. Thinking about it purely in terms of anti-squat is probably why you're only getting info related to drag racing. Circuit racing info is probably still very applicable albeit a bit more finicky than you need to be. Don't forget to match it with the front end, no point in the ideal rear geometry if it just creates a massive front to rear imbalance.

[mick_in_oz]

Using on-line calculators, to calculate Anti Squat, they (or at least the one I'm using) take into account CG and wheel base and show where the instant center is. A long or short instant center doesn't seem to effect anti squat, it's more the relation to the CG that determines how much anti squat you get. The shorter instant center will make the vehicle respond more quickly to changes in weight transfer, or at least that's what I take from all of my reading.

As for it matching the front end, yes, first person I asked was Curly's, and got an unexpected response more or less saying, "put em parallel, followed by, the guy that designed the front doesn't work here any longer, but you sound like you know more than we do" that was a bit of a surprise and a little disappointing...

 

The IFS is supposed to have geometry to provide things like anti-dive and anti-roll, so with all this nice geometry built into the front, I thought for a little research and not being ignorant to the way it all works, there may have been a benefit in aiming towards a certain Anti Squat figure.

 

I've not looked LOTs at circuit racing stuff, but certainly some, and not really gotten what I expected. I've also looked specifically at street rod stuff, but nothing definitive has popped up.

 

I'll keep looking, and maybe someone will post something on here.

[ozyozyozy]

Google 3 links and 4 links for pro touring.
Guy by the name ron sutton has posted some great info around this stuff on the pro touring forums.

[76lxhatch]

As for it matching the front end, yes, first person I asked was Curly's, and got an unexpected response more or less saying, "put em parallel, followed by, the guy that designed the front doesn't work here any longer, but you sound like you know more than we do" that was a bit of a surprise and a little disappointing...

Yikes, but at least they were somewhat honest about it I guess.

 

The IFS is supposed to have geometry to provide things like anti-dive and anti-roll, so with all this nice geometry built into the front, I thought for a little research and not being ignorant to the way it all works, there may have been a benefit in aiming towards a certain Anti Squat figure.

As above personally I don't think targeting certain anti-squat figures should be the main aim if you're not drag racing. Sounds like you don't have much info on the front end either, I'd calculate the its roll centre (with an idea of how it changes throughout travel), that will help give you a ball park as to where the back should be to complement it. Also consider how the spring rates and bars will play into it at minimum.

I don't think you will get any definitive advice unless you can find someone who has done the work with front and rear suspension that has the exact same geometry and the same setup all round. You have to run your own numbers and draw from your own experience (or that of a third party you really trust) as to what will not only make it handle well but give it the driving characteristics you're looking for. Sounds like a lot of work (and it kind of is) but you can only copy someone else's homework if its for the right subject. The only shortcut is to pay someone else big bucks to do your homework for you, and hopefully they know their stuff!
 
 

Guy by the name ron sutton has posted some great info around this stuff on the pro touring forums.

He turned out to be a bit of a snake oil salesman, he did post a lot of theory but apparently not a lot of real-world experience... still worth reading some of it but take it with a grain of salt. Lots of other info on those forums to work through too.

I also find that some of the Grassroots Motorsports (and similar) forums tend to have some good simplified/practical discussions, for example:
https://grassrootsmo...ps/43604/page1/
Again you have to collect all the info (and weed out the Internet trolls from those who know what they're talking about) and apply it to your vehicle and requirements.


While we're at it take my opinions with a grain of salt too, I have enough knowledge on the subject to be dangerous but I'm not formally trained and I don't build suspension systems or race cars either :-(

[ozyozyozy]

Thanks for heads up 76lxhatch

We have looked into alot of this aswell with targa cars unfortunately there really is bugger all people out there that really know how to set all this up and as mentioned whats on one car doesnt always work for another.
Just looking at some of the so called kits available i can see alot are average at best.
Unless you know a true suspension engineer all the info out there is based on universal guidelines.
I suggest if possible build some adjustments into the setups, for street driving its not quite so critical, most street cars are designed with packaging in mind for greater internal cab space.

Common thing for people to do is use multi holes at a pivot point for height adjustment, down side to this usually a bolt hole change in height can be quite dramatic change.

An issue with triangulated rears, they suffer from bump steer, torana’s are a prime example of this, they are quite bad for it.

[madtoranajzedded]

I liked this short artical when i first wanted to know
about how it works.but seems i was only fresh on
subject and never bothered to keep learning,after 5ys
the brains gone blank hahaha..

Can someone fix this link for mick..

http://www.how-to-bu...ing-4-link.html

[mick_in_oz]

Back from the weekend away, collecting seats for the 38!

 

Thanks for the suggestions and info above, plenty of additional reading.

 

The link that MAZ put up I'd already read through.

 

Really, it seems everything is regurgitated from a common source, but the simple fact is its a relationship of the trailing arms to a line specific to the vehicle in question...

 

I had gotten to the point of wondering if simply adding some holes to have the option to "try" a few different settings may have been the go. Also leaning towards  a longer intersection point, IC, why, because it feels like that is a preferred position, coming from lots of places or reading, suggesting the lower arm should be parallel to the ground at ride height, but that could also be monkey see monkey do...

 

I also was thinking, unless it had some unexpected traits, then most people would tune around how it was, or learn to love its personality.

Thanks for the info so far, and now some more reading...

Edited by mick_in_oz, 23 February 2020 - 09:14 PM.

[EunUCh]

 squat1.JPG   250.05K   2 downloadsThe picture shows what happens when the arms are moved up or down and the effect on IC and squat/anti- squat , obviously in the real world the IC will be "moving" due to road conditions/accelerating/braking , it is an oversimplified illustration but hopefully gives a bit more to add to what you have already looked at.