Technical please delete. Drama

So I was over at a friends shop and they were putting a triangulated 4 link in the back of a model a streetrod style frame. Probably the worst design in my opinion. With the amount of information available doesn't anyone actually research how this stuff works? Or do you guys weld in whatever in a Willy nilly sort of way where it fits?

 

Some know how stuff works, some think they know how stuff works, and some dont care either way.

Then it becomes a concern when it breaks, and someone gets hurt.

 

What exactly was the problem with the triangulated 4 link?

 

That type of system can made several different ways and still work.

What did it look like?

 

I still see a lot of torque tube closed drive setups with guys running split radius rods to the frame, or some sort of ladder bars to the frame, and then don't understand why parts keep breaking. I think a lot of guys just don't know any better or someone said it would work. Bad ideas get recycled and repeated.

 

• We need pictures to reply with accurate comments.
• Did you call your friend out on it?
• What's your take on the setup vs. his?

 

Rear steer, roll steer, pinion angle change, limited lateral location, unknown instant center, unknown roll center.

 

Looks to be one of the cheap short upper street rod kits. We had a discussion off possibilities, the customer doesn't really understand and I wasn't calling him out on what he bought. That would be rude.

 

I’d worry about safety first, and then being rude second.

 

The worst statement is "I've never had an issue." Sure, but they neglect to mention that they've driven their car 500 miles in 25 years and never taken it over 40 mph.

 

I bought one with '70 GM upper arms and '39 lower arms that were 3 times as long and suspension was bound up.
I cut out uppers and will add a panhard bar

 

All that depends on the specifics.

Note that this can be set up with bottom bars parallel and top bars angled, top bars parallel and bottom bars angled, angled bars converging to the axle, angled bars converging to the frame, any or all bars ahead of the axle, any or all bars behind the axle. In each case you have a different range of options for locating the instant centre and roll centre. In each case it requires some thinking through.

 

Monkey see, monkey do in some cases. It must be good, I saw it on the internet! just whip out your credit card.
Some are building for a certain "look", and don't care how it works.

 

@Ned Ludd I'm well aware of how it is supposed to work, the drawing you posted is nice concept but doesn't actually fit almost any hot rod. The kits come with hard poly bushings, they just bind in that configuration. Never mind the gross pinion angle change that set up can provide.
My point was "why do people not do the math?" There are tons on calculating programs, good diagrams and you can test your whole suspension system before you weld it solid.

 

An off topic example. My son's drift truck when it was under construction. Parallel 4 link with Panhard. Negligible roll steer. 100 percent antisquat. Handles like a slot car and will do donuts in a parking spot, because that's how it was designed. Note that if we move the front upper link mount down one notch and change the angle of the coilovers it's set up to provide enough drag launch to be fun but probably not perfect. It's been on the road now for months and works very well. I've driven it and it's super tight.

 

In a lot of cases it doesn't matter much for what the owner expects out of the car. The average unaware guy having a shop do his work just wants it to look cool and be able to drive between their local cruise night and home at a moderate rate of speed, but they don't want to spend the money on a proper chassis shop. There are a lot more rods than we think out there that ride, handle, or steer less than optimally, but the owners will claim that they're great. Often an owner down the road who is actually going to drive or use it will get it improved for better driving manners.

My dad had a customer who bought a finished appearing 30's street rod and it had nearly no brakes. The pedal was essentially an on-off switch from nothing to full lockup with nothing in the rear. We got it sorted, but this was a car that had been finished for years and didn't have a lot of road miles. Easy to see why.

From my experience, triangulated 4-links are recommended by parts suppliers since they "don't need a panhard" and are (relatively) "easy to install". That doesn't mean with the easiest install it's set up right, it's just an "easy" way to get coilover rear suspension.

 

There is no reason to not do the math on set up and design geometry but I think the biggest concern on this type of thing is has it been put together and welded in safely. With a street driven car design flaws and imperfect geometry are very rarely noticed and pinion angle change is usually small and not an issue. If the car is getting drag raced or auto cross raced it's a different story. I just don't want to see someones crappy workmanship coming apart on the highway.

 

Crappy workmanship you say? This was on a 46 Chevy pickup for sale on Facebook back in 2018 in NJ. The guy swore it was perfectly designed and worked great. There were also two parallel links that went forward from the rear end to the chassis that you can't really see in this photo. Never seen turning your frame rails into torsion bars before.

 

Wow that's amazing!

 

So, your issue is not with the triangulated 4 link as a suspension system, more with poor installation due to lack of skill and understanding. A properly set up triangulated 4 link will work very well. A bad set up of any system will work poorly, and can be unsafe. Lots of people manage to get lots of things wrong.......

I will get shot down for this, but this is where a vehicle registration system that includes an inspection process can be a plus. We have it down here in Australia, and it helps to keeps the sub-standard quality and dangerous shit off the roads......

Fire away.......

 

We have an inspection process for modified/amateur built vehicles here in Sweden too, and I agree that it makes a huge difference in how safe the vehicles become. Sure, jumping through a few hoops and following specific rules about how you are allowed to build may be annoying, but at the same time it's good to have someone who knows what they are doing check the basics and not let you run something that will not work well. The organisation handling this process even sells a book showing you what they think is suitable, so information isn't hard to come by, if you have questions they're happy to answer.

Being a hotrod & custom forum I'd say a LOT of what we see here is built mostly for looks, with little regard for the function. Some has no impact on how the car handles, others has a lot of impact but the builder knows this and accepts it, or doesn't know and doesn't understand what the problem is - and that's why doing the research first is so important. What worked good enough with 50hp 90 years ago may not work as well with 500 hp today.

 

I was under the impression there wasn’t a pinion angle change with a tri-4 bar setup.

 

But , it still beats the hell out of someone telling you what & how you HAVE to do ! TO THE O. P. , Did you mention that , according to you, everything the were doing was wrong ? Did you consider the possibility that they might know something you don't ?

 

There always is dynamic pinion angle change even on 4 links if the upper arms are shorter than the lowers.
There are design benefits to this. When the rear squats the instant centre shortens and tries to use torque reaction to prevent squat [and the pinion angle tries to straighten up with torque]

This



Have a good one Mike and Steve, this is my last post until January 8th .
I'm off to South America in a few hours

And Merry Xmas and Happy New Year to all of the HAMB

 

Have fun and be safe Kerry.
Happy Xmas to you both.

 

Mine just needs to hold the rear axle.

 

You both have a great time!

 

A parallel system with equal length links will have a constant angle. Unequal lengths renders that impossible.
@2OLD2FAST . Actually the builder and I had lunch today. We discussed the issues. He has already corrected most of them based on my suggestion. He knows me well. I'm more interested in being helpful and keeping his customers cars safe and working than hurting someone's pride.
Sometimes what I lack in people skills I make up for in geometry and experience.

 

A short while back, I looked at buying a...nice looking...car, on the outside.
I asked about a few under car pictures if he could, He sent me a bunch of pictures.

The first thing that I noticed, the Panhard rod, while the car was sitting on the ground was at about a 45 degree angle ! When asked about it, he told me the car drove fine.

I guess not everyone's 7th grade geometry teacher had proper credentials.

Mike

 

@krylon32
Damn has an N in it. If your math is like your spelling and attitude you should run and hide... lol