Aspiring suspension buff

[Tkosinski2]

Hello, this is my first time on a forum like this. I have a few questions an a little history. I have a background in automotive repair which is what lead me to want to be an engineer. I find suspensions so fascinating and I love watching them in action. I'm starting my physics education and calculus to transfer into and engineering program hopefully soon. With that being said I was wondering if anyone could point me in a direction of good suspension books that will help me get more excited about physics and relate more of it to automotive so that I understand te numbers better.

I have a 2wd pick up truck that I kind of want to make into my own little engineering project by designing an off road long travel or mid travel front suspension and also to design a cantilever rear shock set up. Can you help point me in the right direction? Thank you!

Also are there any clubs I should be joining during my studies?

 

[GregLocock]

there is a list of books in the faq for this forum. i think most suspension engineers have several books but most have rcvd by milliken.

long travel suspensions tend to be dominated by practical effects rather than theoretical niceties.



Cheers

Greg Locock


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[WhatsE]

That's right, Race Car Vehicle Dynamic is super coll!

 

[Tkosinski2]

Practical effects as in trial and error? I would really like to design my own off road suspension for my truck.

 

[rmk36]

RCVD is great, but can be hard to swallow if you're new to this. I would recommend simpler books to start such as Tune to Win by Carroll Smith and How to Make your Car Handle by Fred Puhn.

Vehicle suspensions are definitely a fun field. While you're in school, you should get involved with Formula SAE if you want to learn a lot about complicated suspensions. Baja SAE also does off road suspension, but I'm biased toward FSAE.

What school are you attending?

 

[Tkosinski2]

I'm currently at el camino community college taking my physics and calcs hoping to transfer to cal state long beach in a year.

 

[BrianPetersen]

With regards to ultra long travel suspensions "practical effects" relate to matters such as roll center migration, camber curves, etc. Camber curves for independent suspensions that have normal road-car or pavement-race-car travel dimensions (100 ~ 150 mm total up and down travel) won't work when the suspension moves up and down two feet. If you use an axle, the slight arc that a panhard rod swings in and pulls the axle slightly one side or the other which doesn't really matter with normal road-car travel range (100 ~ 150mm) starts really mattering when the foot of displacement from its nominal height pulls the axle a few inches to the side. The arcs that other types of suspension links move in with normal suspension movement start really mattering when the vertical travel is considerably increased.

I've seen some lifted 4x4 trucks in which the front panhard rod and steering rod are inclined at a rather severe angle with the vehicle at nominal ride height, which will make the axle kick sideways enormously when going over a bump and will cause a jacking effect when cornering one way and a pulling-down effect when cornering the other way. Every suspension geometry book that talks about beam axles will tell you to keep a panhard rod as horizontal as you can within the range of normal suspension movement. It's rather apparent that the 4x4 truck enthusiasts don't seem to care much about road manners.

This is what's meant by "practical considerations". The ideals of camber movement and roll center largely go out the window to accommodate the way it has to be for it to fit in the vehicle.

 

[Tkosinski2]

I don't mean to pry but how does that work with a standard hotchkis set up in rear? No panhard rod to sway one way or the other just extreme travel leafs and a drive shaft arc no?

 

[patprimmer]

A Hotchkis rear end with long travel will have some fairly serious geometry problems due to bump steer and sideways deflection and twisting of the springs as the springs pull together as the axle inclines significantly. Simplicity and variable load carrying ability is their strength. Long travel on one side only is one of their more severe weaknesses.

Regards
Pat
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[BrianPetersen]

The serious rock-crawlers etc that I've seen aren't using leaf-springs any more, because of poor articulation. Most of them are using coil-sprung solid axles with some type of linkage locating the axle, generally using very long links in order to minimize the effects of swinging in an arc rather than a straight-line motion.

If you were to hypothetically make a leaf spring soft enough to allow this much up and down motion then it would have to be soft laterally and in torsion to allow the axle to move around, thus giving about as much guidance to the axle as a piece of cooked spaghetti.

Some desert race trucks are using independent suspension, but they are custom-designed, generally with lower control arms as long as possible (the chassis-side pivot point is essentially at the centerline of the vehicle). Some use Ford Twin-I-Beam, which has the pivot all the way on the other side, and even then has excessive camber change with vertical suspension movement away from nominal ride height.

 

[patprimmer]

I have to say I like extra long trailing arms for off road suspension. Why where cut down Beetles so successful for so long.

Regards
Pat
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[rmk36]

T,

CSU Long Beach has a team for both Formula and Baja. I have competed against their Formula team.

These projects will help gain you practical experience and great job opportunities that would be impossible to achieve without SAE on your resume.

I'm biased toward Formula as I feel there is more engineering involved, but to each his own.

http://www.csulbsae.org/index.html

Ryan

 

[Tkosinski2]

Thanks Ryan. Was CSULBs team any good?

I have seen the move from leafs to coilovers and linked suspensions in crawling and even in prerunning with really long beams pivoting from under the cab to get the most travel but I also know that one of the most popular modifications in prerunning is to just get leafs made by a company called Deaver. People are getting anywhere from 16-18" of suspension travel in the rear of there trucks. Using a cantilever shock set up(which is what I want to figure out how to calculate length and size of the cam and push rods) there getting away with having the whole bed clear for use as a truck.

 

[GregLocock]

One practical effect on rear suspensions is that the driveshaft angles can get rather ugly. On front suspensions one discovers the limitations of tie rod ends.

So you tend to end up with a suspension which is dominated more by the practical considerations of not breaking things, typically by overarticulation, than theoretical niceties like bump steer curves.

That's not to say they aren't worth analysing, just that those of us who need to think about 1-2mm errors in hardpoints tend to think in a different way.





Cheers

Greg Locock


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[Tkosinski2]

So your saying the designing a long travel suspension is kind of a basic way or designing suspensions? A sort of "as long as it works" way of makin it?

How do you design something like a cantilever shock set up? How would you go about knowing the length of the sides of the cam(fulcrum?)? Or rod lengths for it? Also I can imagine that a shock ratio of 1:1 would be awesome but what is A standard when working with rear leaf springs for trucks?

 

[patprimmer]

You need to design it so the shocks won't bottom out before the axle and won;t top out while there is still load on them from the springs unloading.

The maths involve is about grade 3.

The physics is about grade 7 or 8 or wherever your schools do levers and mechanical advantage

Regards
Pat
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[Tkosinski2]

Where would I find the physics on levers and mechanical advantage?

 

[patprimmer]

google and/or high school.

Regards
Pat
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[Tkosinski2]

Hmm.... Maybe I'm thinking More of a pushrod/lever based shock assembly for the long travel of the springs

 

[moon161]

My dad worked w/ Cornell's FSAE team on ignition & engine management, said they lived it and had to be kicked out of the shop at class time. I've seen a few FSAE cars, a lot going on in them.

Lot less power in a mini-baja, think they're given a 10 hP lawn mower engine. FSAE start IIRC w/ a 660 cc motorcycle engine.

Fred Puhn, How to make your car handle is good general reading, graphical problem solving. Most examples were autocrossers, street racers or track cars. Probably <$10 used on abesbooks or amazon. A good gateway drug.

I haven't done more than glance and Miliken & Miliken (father & son). I've seen it used in a 400/500 course at University at buffalo. I sat in on the first class, prof. spent half of it discussing tire/grip relationships, i had the impression he could go on for a couple more.