Rose-joint alignment

[ChrisL]

A question to some of our more knowledgeable race car engineers.

I had the opportunity to look closely at the front suspension of a V8 Supercar (local touring car) and noticed something very interesting. All rose-joints were mounted horizontally (with mounting-bolts vertical rather than horizontal). The V8 Supercars here in Australia are the leading category of motorsport and teams have multi-million dollar budgets so you can bet that nothing in this area is done by chance. So I began to wonder and it became obvious to me that htere are some real advantages. All large forces applied to the rose-joints are either in the plane of travel or along the plane of the wishbone. So with a conventionally mounted rose-joint, under braking the spherical bearing will be trying to pop out of its housing. However, with the horizontally mounted rose-joints, the spherical bearing will always be pushing into the socket of the housing in all circumstances. Consequently, the forces within the rose-joint will be applied over a larger surface rather than a thin shoulder… much more reliability and less prone to wear. A still further advantage is to the rose-joint mounting brackets on the chassis. The forces will be applied along the plane of the bracket rather than being perpendicular to the plane, so reducing the bracket’s urge to bend. Anyway, thats how I see it.

This is a long way to ask the question but given these apparent design advantages, why is it that so many cars are designed with rose-joints placed vertically? And is it enough of an advantage to consider a modification to horizontal mounts?

[Steve Kulper]

Chris,
I recently rebuilt a crashed saker and they have a similar set up, the problem I found was getting the rose joint in the the bracket. It looks easier on the super car than it was on the saker, you had to get it wound out just right for it to slide in. This would lead me to believe that to adjust the set up on the saker was a pain, i'd say it was easier on the V8's though.

Steve

[Malcolm]

If a rose joint is what you call vertical it will have the advantage of a vertically transmitted load going into the casing of the rose joint. If horizontal as per your picture only the rose retaining clip or whatever will resist the load and may fail under duress. I would not be keen to see some of my suspension joints with horizontal rose joints for this reason. IMHO of course!!!!

[Chris P.]

Horizontal, vertical, diagonal... since it is a spherical bearing, why does the position affect the forces and wear in the rod end (rose joint)?

One advantage to the horizontal mounting shown is quick suspension geometry adjustment (roll center, anti-dive, etc...) Another is the simple fact that if the nut should come loose and fall off (small chance), the bolt has a better chance of staying put until someone has a chance to look the car over (which happens every day in a race environment).

[Hemipanter]

This is a picture of my own rear upper A-arm. The inner heimjoints is having the bolt vertically. It is also so that the treaded balljoint shaft is inline with the A-arm leg, making for a straight load A-arm leg-treaded shaft-spherical bearing. Even the outer, uppright bearing, is having its centre inline with both A-arm legs. That way we have eliminated all bending loads on both A-arm legs and heimjoint shaft.
However, in my case where the rear A-arm leg is possitioned 90 dgr to centerline of the car, the inner ball-joint could be mounted vertical or horizontal.
We must also take icoilover mounting in to concideration in the case of a lower A-arm.
Goran Malmberg

[aji]

This is a long way to ask the question but given these apparent design advantages, why is it that so many cars are designed with rose-joints placed vertically? And is it enough of an advantage to consider a modification to horizontal mounts?

Let define the planes of reference
X is the lenght of the car
Y if the height of the car
Z is the width of the car

The configuration as pictured provides contraint of motion along the X plane with reference to the control arm

If you installed the joint rotated 90deg you would not contrain motion along the X plane with reference to the control arm.

I guess it depends on what you want to do.

best

[Russ Noble]

The prime reason for mounting them horizontally as Chris P has said is for suspension tuning. If you look at your photo the joints are held between wide based brackets with long bolts, not ideal from a theoretical viewpoint but makes for easy and relatively quick handling adjustments merely by shimming the joints up or down within the brackets. Being able to adjust these also means you can change your ride height without compromising your suspension settings.

With a softer sprung road driven car you would most likely need more movement in the heim joint than a horizontal setup would offer particularly on the top link. Obviously binding of the heim joint could cause it to snap. With vertical mounting this is not likely to happen.

Cheers

[Chris P.]

Actually, upon a second consideration, there is an advantage to horizontal mounting which Chris Liokos has mentioned already. To give a specific example, braking. There are longitudinal loads (in the x direction as set forth by capaci) which will be held better by horizontal mounting. Since on the upper arms in that photo there are no sway bars, springs, or shocks, the suspension arm forces are purely in plane with the suspension arm (depending upon the slight angle of the outer ball joint if there is any, and the design of the ball joint). However, large enough inner rod ends in a vertical position will hold these forces that tend to "pop" the ball out of the socket just fine. These maximum loads are always provided by rod end manufacturers. Look at the outer rod ends on the lower front arms of just about any race car. They are in the "horizontal" position for steering movement and carry vertical loads from springs / dampers / shocks. Also, the bottom arm takes higher compression / tension loads then the top arm due to simple geometry reasons.

One reason for using a vertical position is simply to have enough room for travel. If you have a very short suspension arm and appreciable wheel travel, you might require a vertical orientation unless you use a more expensive high misalignment rod end, if it will even fit.

[aji]

Yes

On my tow vehicle with stiff springs and poly bushings for the control arms and large tires. This is a must stiffer ride. Noted when the caster angle is large the front mount point stud breaks under tension loading. This happens under very light loading the upper control arm has applied to it as compared to the lower arm at road speed. The break happens at low speed when backing up with a wheel locked to the right. I had to reset the caster to near zero and I'm fine now!

The hime joint rod end is far stronger then the stud setup. I also do not see the lower arm in the picture. I assume is has a much larger mechanical joint to withstand the far greater loads.

as used the hime joint allows for rotation in the xplane about a Z axis which is constrained by the two mount points.

If you mounted the hime joint vertical in this configuration it would allow for rotation in the xplane about a Z axis unconstrained at both mount points which would allow caster and camber to move all over the place! This would be a fun ride indeed at over 150mph

This is exactly how my alfa spyder is setup only with very soft rubber mounts on the control arms and a caster strut the contrains the Xplane rotation somewhat by rubber mounts at points on the frame and a ball joint on the control arm,, makes for very good handling on corners

There is no caster strut in the picture, They do not want it changing dynamically. So the hime joints make it very solid! I bet the car also has "Power Steering"!

best

[Hemipanter]

Originally Posted by Russ Noble

The prime reason for mounting them horizontally as Chris P has said is for suspension tuning.
Cheers

You mean that they adjust instant centre of the suspension geometry?

Goran Malmberg

[aji]

as Kalun D wrote:
a 2,000 lbs car has no need for power brakes or steering. It just adds weight, complexity and crowding, this is supposed to be a race car. Adjust pedal feel with hydraulic cylinder sizes and a bias bar. Adjust steering feel with KAI and caster.


so No KAI and Caster dynamics of given the "super car"

I wonder on the size of the brake cylinder for complexity and crowding

come on Kalun D, we need your technical input here race engineer!

LMAO!

[Russ Noble]

Originally Posted by Hemipanter

You mean that they adjust instant centre of the suspension geometry?

Goran Malmberg

Yes they can raise and lower rollcentres front and rear to effect handling changes. They can do this very quickly at the rear (live axle, watts linkage) during a pitstop to fine tune for grip problems at either end of the car.

[Howard Jones]

Here's my 2c's. The main and by far the most damaging loading on the rose joint either way you deside to mount it is going to be as the suspensions "bumps" In this case isn't either method equally effective? Rose joints are not intended to be loaded beyond their maxium defection angle and certainly nothing like 90 degrees to the threaded shaft.

[Eric]

Having designed competition and road suspensions, I fully agree with just about everything written here already.

The main factor for using a horizontal mount joint (vertically pinned), is for adjustability. The upper and lower arm can be moved independently with different bushes to allow for: roll center change, instant center change, anti-dive/anti-squat changes, and changing the relative angles between the arms for different camber curves.

Secondary is to put the joint in its strongest position to deal with braking forces. ( peak decel is usually the highest G load) Most suspensions are designed with enough reserve strength in the joint such that lateral loads are not a true issue, and competition cars generally have very short travel and little body roll to deal with.

For a road car, I would not put the joints in the horizontal position only because of the greater travel and steering angles can put too high a load with included larger angles on the joint.

cheers
Eric

[Malcolm]

A race car would have their rose joints changed regularly so having them horizontal is less of a concern. If you had a road car do you want to be changing the joints that often? Not me. This is why I use nylon blocks. But then as with a lot of things, joints in the UK are far more expensive than the equivalent I have seen in the US. A decent three peice suspension joint here can be upwards of £30 each. (1/2 inch by 1/2 inch).

[Hemipanter]

Originally Posted by Russ Noble

Yes they can raise and lower rollcentres front and rear to effect handling changes. They can do this very quickly at the rear (live axle, watts linkage) during a pitstop to fine tune for grip problems at either end of the car.

So, this is a live rear axle car? Do they have a more specific explanation about the effect of altering the Rc height? Do it maybe have something to do with rules. To me altering watts Rc height is not the same as altering
Rc height using instant centre.

Goran Malmberg

[Russ Noble]

Originally Posted by Hemipanter

So, this is a live rear axle car? Do they have a more specific explanation about the effect of altering the Rc height? Do it maybe have something to do with rules. To me altering watts Rc height is not the same as altering
Rc height using instant centre.

Goran Malmberg

Yes, live axle.

I don't know about the specifics but was under the impression that with all suspensions generally, however you do it, raising the rear rollcentre increases the roll stiffness at the rear causing more oversteer/less understeer and vice versa. With the watts linkage they have it setup so they can very easily and quickly change the height of the watts linkage pivot point which is the roll centre height. I don't know whether this has anything to do with the rules, I think it is probably just an effective tool that is pretty universally used by all the Oz Supercar teams

[ChrisL]

Originally Posted by Hemipanter

So, this is a live rear axle car? Do they have a more specific explanation about the effect of altering the Rc height? Do it maybe have something to do with rules. To me altering watts Rc height is not the same as altering
Rc height using instant centre.

Goran Malmberg

The rules define which rear diff is to be used (even the ratio) and that it must be a live axle. The rules also define the rear suspension mounting points with some tolerance for adjustability and design. I'm very much guessing here, but I assume that these definitions also dictate that a watts linkage system will be used??? In any case, the TV broadcast always refers to adjusting the "roll centre" whenever the team adjusts watts linkage pivot point in the pits.