J-arm vs. A-arm

DUMP!

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Really kind of a nebulous statement. A better roll influence would negate the need for a sway bar of any sort. Nye Frank vehicles are not know for handling "like crap," and they "appear to have" have a zero or below ground roll center.

True enough that the infinite roll center (parallel control arms), increases weight transfer. It also makes for a very sluggish handling vehicle. Example is that no road car has parallel control arms. We're talking best handling be it on ice, dirt, mud or asphalt. Traction is traction. period.

And a proper camber curve would help to "present" the corner of the tread to get a sharp edge and possible more traction. The same dynamics are in play for road racing cars. But for a different medium. Same reason NASCAR racers have both wheels leaning on an oval. They help compensate for vehicle dynamics to maintain contact patch.
Great topic!
GD

While Nye Frank is absolutely one that should be respected. I can only ever remember one desert car that he designed that was ever a consistent winner and at that the guy that drove it could win in a garbage truck. :D :D :D

I made a simple sketch to illustrate. The better way is to reduce the length of the upper arm and lower the inboard pivot, approximately as shown. Then body roll pulls the upper spindle pivot inward, producing negative camber. And yes, all other race vehicles do it this way. It works with long travel dirt suspension too, because the short upper arm produces neg camber at bump and droop, which reduces horizontal tire scrub. Long parallel arms are more tradition than proper engineering.

Scott, I'm not debating the validity of any of your statements except the one "I don't care how much travel a vehicle has, if the wheels lean out in corners (as most dez cars/trucks do) the suspension geometry is poor." That's a BS statement to make. By that statement your saying that Engineers like Trevor Harris and Nye Frank, builders like Mike Smith, Robby Gordon, Russ Wiernemont, Geiser Brothers and race teams like PPI have been doing it wrong for years. Because I can say with very little doubt that I could probably find pictures on the net some were that shows the out side tire of a vehicle any one of them has designed in a positive relationship to the ground when cornering hard. :D :D :D


Great points and they solidly represent two schools of thought with regard to the traction medium available. Dirt or sand.

1) You're on dirt so there's no traction, so don't worry about a camber curve.

2) You're on dirt so there's no traction, so make the most of every bit of proper tire control you can.

I like the second one. You've got the back end flailing with too much throttle. Wouldn't you agree that the front suspension better be the best you can design to help point the vehicle in the general direction?
I hope that's what seperates the $500K from the $200K vehicles. Details...

On the type of arm? Which ever you prefer and can package efficiently.
GD

Ya, your right. I got news for you. If the back end is flailing you don't have enough traction to create any body roll unless you are on pavement so why would you even be worried about camber curve at that point. :D :D :D



The only time this is critical is when at medium/high speed. That is the only time you are going to be able to turn into a corner and produce enough body roll and use up a significant enough portion of the suspension travel to even be able to take advantage of the camber curve.

So my question is, if all the above people mentioned have got it wrong then what is the proper amount of camber to have from ride height to full bump??

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gawdodirt

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Wow! That's alot to consume in one day!

The outside tire with positive camber thing.

I think that it's because of chassis lean/roll that it goes positive. Not because of any curve. Or is that what you're stating too?

The statement that there is a,

"proper amount of camber to have from ride height to full bump??"

Shouldn't it be a curve with varying amounts of camber and in both directions (+/-), dependent on position in travel?

Just trying to learn some things. Appreciate the time you take to answer these things!

Thanks!

GD
 

DUMP!

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Wow! That's alot to consume in one day!

The outside tire with positive camber thing.

I think that it's because of chassis lean/roll that it goes positive. Not because of any curve. Or is that what you're stating too?

Exactly, If you have 6-8 deg of chassis roll (for the sake of a number) does that mean your suppossed to have 6-8 (or more) deg of camber gain in your design so that tire never goes positive? If so where do you draw the line. That's what makes that statement about poor design if the tire goes positive questionable.


The statement that there is a,

"proper amount of camber to have from ride height to full bump??"

Shouldn't it be a curve with varying amounts of camber and in both directions (+/-), dependent on position in travel?

Yes it should and will, there is no way to make the design not gain camber unless you are using equal length wishbones. So what should the camber be at ride height and what should it be at full bump, I'm dieing to find out if I got it right??

Just trying to learn some things. Appreciate the time you take to answer these things!

Thanks!

GD

Really kind of a nebulous statement. A better roll influence would negate the need for a sway bar of any sort. Nye Frank vehicles are not know for handling "like crap," and they "appear to have" have a zero or below ground roll center.

Sorry, that quoted statement doesn't sound like you are trying to learn. Sorry I misunderstood you:rolleyes:

Thank You,
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partybarge_pilot

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So what should the camber be at ride height and what should it be at full bump, I'm dieing to find out if I got it right??

Just enough to get rid of wheel scrub? :p

I think it would depend on how much travel the vehicle is going to have and how much body roll you plan on having. There is no universal answer, every vehicle/driver will be different.





Garbage truck............
 

scottm

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I dunno Derek, do you think positive camber and cornering on the sidewall is a good thing? I dont think it is, and I don't want my truck to corner on the sidewall. I started designing my truck 2 1/2 years ago by talking to people about susp design. The most knowledgeable person I found was Steven Arlia, the builder of Nick Vanderwey's class 8, probably the winningest truck in baja over the last 10 years. Think about it - they finish every race, they have very few flats, and they make very few driver mistakes resulting in truck damage. Of course thats the result of many factors, including, in my opinion, proper suspension design that has long travel and road-race style camber control. Steven is an experienced road race driver himself, and he worked for Chris Harrison, a well known road race fabricator here in the Phx area. Nicks design has more camber change than most, but otherwise is not majic, and there is no reason why anyone else cant build trucks that way. My truck will have about -8° camber at full bump. I am certainly not saying cars and trucks by x-y-z builders are no good, because that is obviously not true. But positive camber in corners is simply not a good thing. I'm sorry to everyone who paid 300K for a tt, but if your truck goes 2° or more positive in corners, you will have squirrely handling from cornering on the sidewall, and you will likely get flats and wheel damage from exposing the sidewall to rocks. But dont worry, you will fly through whoops and you can win any race you enter. If you blow a corner and break the truck, dont worry your helicopter will be along in a few minutes to pick you up. I am building from scratch with no money, and I am fortunate to have great resources and contacts available. I NEED to design for reliability and low operating cost with my budget!
 

CRAIG_HALL

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On one of my recent projects the chassis at the front would roll approx. 20° Now thats if you could completely compress one corner in a turn and have the other completely drooped (which is easy for the droop side). I highly doubt you could easily compress a corner in a turn. The frontend was designed with around 8° camber at full bump so IF it could corner that way the tire would be around 10° positive.

I'd bet most class-1's & TT are around 8-12° at bump.
 

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DUMP!

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If you blow a corner and break the truck, dont worry your helicopter will be along in a few minutes to pick you up.

I'm wondering what a helicopter has got to do with this. Regardless of what you think. Even though I think your statement is BS I do respect your thoughts and opinion. But statements like the one above make me loose a little of that respect.

I've said all I care to,,,,,,,,,,,next.

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scottm

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Sorry I made 2 mistakes. Dump dont go to bed angry at me, our relationship will never last:) First, the heli comment was rude, probably a little envy showing of the guys who dont have to figure this crap out the hard way. Also I remembered wrong, saying 8° neg at bump. My model measures 22° neg at bump with 5" ground clearance (with no tire compression from impact). That is more than necessary for cornering camber, and reflects the limitations of getting travel with factory frame rails. I expect to move the upper arm mount position around to find the best balance between ride height and ground clearance here soon.

Thats cool Craig, now for kicks try lowering your inboard pivot an inch or two and watch how it improves cornering camber and horizontal tire scrub.

OK I'm done too. Until I work up some street cred from race results, I'm no better than a drunk in a bar talking ****...
 

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FABRICATOR

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Moving the inner pivot point of the UCA up or down is not any kind of new magic, and basically does two important things for long travel suspension.

The first is that it moves the camber curve up or down. Lowering the pivot point produces less camber change toward full droop and more toward full bump. Raising the pivot point produces more camber change toward full droop and less toward full bump.

The second is that it changes the amount of body roll transferred to the wheel. In simplified terms...when the arms run parallel, body roll and wheel tilt are the same. When the arms run closer at the chassis end, the wheel will tilt less than the body. When the arms run closer at the wheel end, the wheel will tilt more than the body.

During the design stage, parallelism of the control arms should be based largely on spindle design, total wheel travel, and ride height.
 

gawdodirt

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I think that is one of the questions. How much body roll and how much camber built into the suspension.

Hey!

Let me add Anti dive while we're designing the perfect suspension.

GD
 

OneUpFabrication

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since were talkin about suspension heres a full scale mock up i did for the suspension for my baja. it cycled clean it will be strapped at 20" or maybe 18" i have some pix one is at ride height, full droop, and full bump ( keep in mind the full bump pic bumped a lil more than it should be i just wanted to see how far it would go)

also these arms are mounted center point ( upper and lower inner pivots are parallel to each other)
droopbug.jpg

fulldroop.jpg

fullbump.jpg

rideheight-1.jpg
 

philofab

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gawdodirt:

There is no perfect suspension, any suspension made will have compromises. Drivers also like different feedback and feel... so what works for one person may not work for another.




OneUpFabrication

That suspension on your bug would work better off road and on if you shortened the upper a-arm a little bit (about 75% of lower is my favorite starting point) and lower the upper-inner pivot an inch (again, starting point) or so.
 

OneUpFabrication

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philofab: right on dude thanks for the advice. right now the arms are upper 26" long and the lower is 28" i was thinking of making the upper arm 2 more inches shorter and than taking the upper inner pivot and moving it out towards the tire more by 2" so when cornering it wont have to much camber...

never thought of lowering the upper pivot some. what wil that help with camber at bump? i always though that the inner and outter pivots should be the same distance apart to get proper wheel travel..

thanks again for the advice im going to make another mock up with a shorter upper and inner pivots closer and see what happens
 

OneUpFabrication

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hey philofab I would like to thank you again for the info you gave me I tweeked the mock up a little bit, I first tried making the upper arm shorter my 75% like you said that brought my upper arm to 21-22" I also moved the inner pivot out 5" and down by one inch... doing that gave me way more camber at full droop then I wanted. so I tried making the upper arm 2" shorter than what I originaly had (26) so it is now 24" long and the upper inner pivot was moved 2" out and 1" down this gave me more down travel and kept the camber straight also it gave full bump a little bit more camber so the results are....

ride height--- 15" of ground clearence, lower inner and outer pivots are even with each other

full bump--- getting 9" of up travel from ride height leaving me with 5" of ground clearence at full bump

full droop--- getting 15" of down travel from ride height all together getting 24'metal to metal depending on steering I should be getting around 20-18" of travel on a 1969 baja I have some pix ill post of before and after te adjustments on the mock up..

thanks again guys now to just make it work out of metal haha
 

Tech Tim

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Mourning the death of this thread.

Well then ask some questions and get this thread back rolling!


Moving the inner pivot point of the UCA up or down is not any kind of new magic, and basically does two important things for long travel suspension.

The first is that it moves the camber curve up or down. Lowering the pivot point produces less camber change toward full droop and more toward full bump. Raising the pivot point produces more camber change toward full droop and less toward full bump.

The second is that it changes the amount of body roll transferred to the wheel. In simplified terms...when the arms run parallel, body roll and wheel tilt are the same. When the arms run closer at the chassis end, the wheel will tilt less than the body. When the arms run closer at the wheel end, the wheel will tilt more than the body.

I know it's an old thread, but thanks Fabricator for posting that description up when you did, it was timely information for me and helped me along in learning more about IFS suspension.
 
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