Upright and Control Arm Dimensions???

atomicjoe23

Well-Known Member
What's the ~normal spread between the upper and lower control arm mounts on a deserrt truck/buggy's upright (steering knuckle)?

Next. . .what's the ~normal spread between the front and rear chassis side mounts on the front control arms of a desert truck/buggy?

Thanks!
 

stoprez2006

Well-Known Member
That would be a hard question to answer because the dimensions depend on all the factors contributing to the geometry of the car. the lengths of the lca and uca, the kpi, all of it comes into play.
 

atomicjoe23

Well-Known Member
I'm just looking for a range of what is normally seen on a 2-seat desert buggy or a TT really. . .I'm not looking for a hard and fast rule. . .just if you have one tell me what yours measures if you don't mind. . .

Thanks!
 

Triaged

Well-Known Member
What's the ~normal spread between the upper and lower control arm mounts on a deserrt truck/buggy's upright (steering knuckle)?.....10-18 inches. (taller than the tire radius starts to get stupid)

what's the ~normal spread between the front and rear chassis side mounts on the front control arms of a desert truck/buggy?............12-36 inches. (Having it longer front to back than side to side starts to get stupid)
 

stoprez2006

Well-Known Member
th spread center to center on my uprights for my project is 9.5" and the LCA mounting spread is 15" front to back. I can't remember what the UCA spread is off the top of my head but I will post it up when i get home tonight.
 

atomicjoe23

Well-Known Member
What's the ~normal spread between the upper and lower control arm mounts on a deserrt truck/buggy's upright (steering knuckle)?.....10-18 inches. (taller than the tire radius starts to get stupid)

That makes sense. . .

what's the ~normal spread between the front and rear chassis side mounts on the front control arms of a desert truck/buggy?............12-36 inches. (Having it longer front to back than side to side starts to get stupid)
I guess that makes sense also. . .

Thanks!!!



th spread center to center on my uprights for my project is 9.5" and the LCA mounting spread is 15" front to back. I can't remember what the UCA spread is off the top of my head but I will post it up when i get home tonight.
Cool. . .thanks to you as well. . .
 

atomicjoe23

Well-Known Member
Let me add this to increase my knowledge. . .

1) What advantages do you gain as you increase the vertical spread between the upright mounting points of the control arms? and what are you comprimising at the same time. . .if anything???

2) Same question, but with regards to the horzontal spread between the fore and aft mounting points of each control arm?

3) I have seen some desert vehicles where the control arms are mounted nearly directly above each other (inline as you are looking down at them in the form of somewhat equilateral triangles) and I have seen other where the arms are designed as 90* triangels with the 90* angle inline with each other but flipped or mirroed. . .so the UCA is pointing forwards and the LCA is pointing backwards. What is the reason for this and what, if any, advantage is there to each design???

Thanks again!
 

Triaged

Well-Known Member
1) As the knuckle/upright gets taller it gets heavier and the loads on the upper control arm get lower (so you can build it lighter). The knuckle is 100% unsprung mass while the UCA is about 50% unsprung mass. A taller knuckle means the UCA will mount on the chassis higher. That helps spread the load over a larger area and can help get the mounts out of the way of the steering. Do some math and figure out what the ideal height is...then just build what fits...

2) See 1

3) If your LCA's are shaped like an equilateral triangle they will fit on both sides of the car making manufacturing and spares easier. Uppers can sometimes just be flipped over to be used on the other side.
 

atomicjoe23

Well-Known Member
Triaged. . .thanks for the clarifications!!!

Time to get started. . .now if one were wanting to make their own uprights. . .where would one go about getting a spindle???

I see that ProAM has a bolt on version. . .and I'm sure that some of the stock spindles are press on, but I don't know much about the stock truck components. . .I'm new to the truck scene and have always worked on muscle cars and sportbikes previously. . .

Thanks!
 

stoprez2006

Well-Known Member
For hubs on my car I am planning to run Dana 44 hubs from the 2nd gen Dodges. It is a unitized hub so you can't replace bearings or anything but they are fairly cheap and have a 5x5.5 lug pattern.
 

Bigger Valves

Active Member
blah blah blah......
3).....and I have seen other where the arms are designed as 90* triangels with the 90* angle inline with each other but flipped or mirroed. . .so the UCA is pointing forwards and the LCA is pointing backwards. What is the reason for this and what, if any, advantage is there to each design???

Thanks again!
The #1 reason this should be done is loading. Loading is a huge issue with suspension design and as a designer you need to be able to approximately calculate all loads and then properly apply that information to your design. This will answer many of your questions. Although for most efficient loading with a rear wheel drive application the front upper control arms will point aft and the lower front control arm will point fore, not the opposite as you've said you've seen.
 

atomicjoe23

Well-Known Member
The #1 reason this should be done is loading. Loading is a huge issue with suspension design and as a designer you need to be able to approximately calculate all loads and then properly apply that information to your design. This will answer many of your questions. Although for most efficient loading with a rear wheel drive application the front upper control arms will point aft and the lower front control arm will point fore, not the opposite as you've said you've seen.

So for the UCA the slanted member should point backwards (from the upright toward the chassis) when looking from above and just the opposite for the LCA???

Just want to make sure I correctly understand. . .

Thanks!
 

darinz

Active Member
The #1 reason this should be done is loading. Loading is a huge issue with suspension design and as a designer you need to be able to approximately calculate all loads and then properly apply that information to your design. This will answer many of your questions. Although for most efficient loading with a rear wheel drive application the front upper control arms will point aft and the lower front control arm will point fore, not the opposite as you've said you've seen.

Why?
Not in anyway questioning, just want to understand.
 

FABRICATOR

Well-Known Member
Are you guys talking about this sort of thing? If so, the lower arm sweeps back (from the upright) so its front leg can be kept out of the frontal "skid/impact" zone (which starts at the bottom of the chassis just a few inches ahead of the axle line, and goes up to the bumper). The uppers sweep forward (from the upright) to reach around the shocks. It has nothing to do with strength (quite the opposite...). Trucks especially, need full clearance up front so nothing can catch on the ground and flip the whole enchilada end over end.

(There has to be a photo that shows an LCA better)

(Mike's Photo!!!)
 

darinz

Active Member
That makes sense as from a strength or geometry point of view I couldn't see how it would have any effect other than negative.

FYI I'm in the process of stripping a D21 Pathfinder that is getting a custom IFS, VH45 etc etc
 

Bajated

Well-Known Member
The other reason for the upper arm being so far forwards is packaging, it provides clearance for the engine and allows the pivots to be close together for more wheel travel.
 

atomicjoe23

Well-Known Member
That makes sense as from a strength or geometry point of view I couldn't see how it would have any effect other than negative.
What do you mean??? which part makes sense and which part would result in a negative effect??? Please clarify. . .

The other reason for the upper arm being so far forwards is packaging, it provides clearance for the engine and allows the pivots to be close together for more wheel travel.
What do the pivot points of the UCA being closer together have to do with getting more travel??? not disagreeing. . .trying to learn more. . .Thanks!
 

Bajated

Well-Known Member
A longer UCA allows more droop before the ball joint binds, so moving the pivot points in is a good thing, but if there's an engine in the way, you've got to move them forward, hence the "J-Arm".
 

atomicjoe23

Well-Known Member
OK. . .which pivot points are you talking about and how are you moving them closer together. . .I think that I thought you were talking about one thing and you were actually talking about another. . .

. . .I thought you were talking about moving the the front and rear pivot points of the UCA closer to each other. . .I now think you are either talking about moving the pivot points of the right and left UCA's closer together or moving the pivot points of the UCA closer to the pivot points of the LCA? Which one are you talking about???
 
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