Yep!

Very much so. Change the ride height and it all appears to become a bit of a mess to straighten out again. It's another benefit of stiffer springs when lowering, not only do they keep you off the bump stops but there is less sweep for the same loadings so you could still maintain good dynamic geometry in your operating range.

Certainly can, however I have no optimisation routine for this so it's very much trial and error. I have some 8000 hours seat time on this program so it's intuitive to me, but it is pretty difficult for a n00b to work with. I struggled even with prior experience of Solidworks.

I had a quick play around earlier and I reckon it would be in excess of a 2" drop, possibly closer to 3". Anyhow, I'm done for the day, off to the Alps tonight and hitting the slopes tomorrow afternoon!

 

Yes it does it appear that way, I think what we are seeing is a combination front end lift and jacking effects from KPI and castor.

RE: Droop. You are right that droop limiting will lower the front of the car, but I think this is mostly of benefit for aero equipped cars? I'm not sure it is something I would want to do on my own car unless it was the last resort for a significant problem that I had run out of solutions for, it violates the KISS principal.

 

Ah yes. KISS is pretty important when working on setup. I do know that droop tuning is very powerful in RC circles. It's become one the first steps in getting your setup right for given conditions. But without those adjustments built into our 1:1 scale chassis, you would have one hell of a time trying to mess with it.

Enjoy the slopes! Let us know when you get back.

 

Hey guys haven't read thru it all but thanks for posting the math and science bits. Appreciate the input!

 

im sorry guys, i didn't mean camber. I was just thinking of ride height or the angle of each of the arms.

 

Testing for Bump is super easy. you just need to make very good very flat plate.
i used an 3/8" thick 6061 plate that mounted to the hub. dial gauges were placed at both ends of the plate to measure the bumpsteer. with the spring disassebled, the suspension movement was recorded for damper stroke, wheel travel, and bumpsteer.
The plate was flat to .005" +/- .001
gauges are good to +/-.001
chasis was layed chasis table to .0005" and was machined that season.

BUMPSTEER/MOTION RATIO TESTING

the motion ratio was linear. the bumpsteer graph did have a little dip but in our 2" the dial gauges which were located 6" from center, saw .02" of movement on one, the front d. gauge moved .01"

 

IF you are lucky enough to have access to a copy of books like RCVD. READ PG 724 and 725

 

Ride and roll steer are a function of the suspension geometry and the steering system geometry.
As discussed in Chapter 17, every suspension has an instant axis of motion. If
. the tie rod is not aimed at the instant axis then steer will occur with ride because the
steering and suspension are moving about different centers. If the tie rod is not the correct
length for its location then it will not continue to point at the instant axis when the
suspension is traveled in ride. Thus, choice of tie rod location and length are both important.
If the tie rod height and angle are adjustable it is usually possible to tune most of the ride
steer out ofa suspension. Figures 19.7, 19.8, and 19.9 show various cases and the general
direction of the solution.
Curved ride steer plots, as shown in Figure 19.9, are to be avoided because they result in
a net change in toe with ride. Another problem with curved ride steer plots is that the
steer effect changes from understeer to oversteer depending on the wheel ride position.
If the ride steer plot is curved as shown in this figure, another possible solution (with
SLA suspension) is to raise both ends of the tie rod, to move it closer to the shorter, upper
A-frame. Once this is done, the tie rod angle will also have to be adjusted.
A linear, but sloped, ride steer plot, as shown in Figure 19.8, may be used to add roll understeer
to a suspension; this may help driver feel and may also compensate (somewhat)
for undesirable compliance effects, as discussed in the next paragraph.
RCVD PG.722

The steering rack attachment and the suspension link attachments will determine how
much compliance steer there is in each case. Another place where compliance can occur
is in the cross link on cars with recirculating ball steering boxes--often these links are
not straight for packaging reasons: A bent link in compression or tension will change
length much more easily than a straight link
RCVD pg 723

 

Not entirely true. Bump steer is caused by the variation in the arc of travel of the control arm and tie rod. If both arms follow the same path, theoretically there will be no bump steer since both attachment points are working in unison.

If the paths very from each other they can be corrected at either the tie rod or control arm, so that the arcs follow the most similar path possible. This is fairly easily achieved with "roll center adjusters" or "anti bumpsteer kits" but it is very specific to each application. control arm and tie rod length, mounting points, and angle at static ride height all contribute to exactly what amount of "adjustment" needs to be made.

Another, more simple aspect of changing the lower control arm angle is also very crucial. The lower control arm absorbs a huge amount of lateral load while cornering. The suspesnion is designed to work with the lower arm parallel to the plane of the chassis (when viewed from the front). This way all of that lateral load can be transfered directly to the chassis. Now when you lower a car the arms may begin to point upward at static ride height, or when the car begins to pitch. Depending on the upward angle of the arm under load, a certain percentage of that load will now be transferred upward into the suspension, making for increases transfer of force to that outside wheel cause loss of traction.

As far as these being mislabled as "roll center adjusters", this is incorrect.
Chaging the angle of the lower arms directly affects roll center height, as you can see in this image:



So in essence, these act both to reduce bumpsteer, and alter roll center. Whether or not it will benefit your specific setup and by what percent is up to the user to figure out. I can say however that on a low car, simply correcting an upward pointing lower control arm angle will help improve the cars geometry for the better.

 

good info keep it coming

 

As per the title, I would be super interested in an Adjustable Ball joint. It would be kind of difficult on a FWD due to CV clearances but there would be room for up to 1/4 inch of adjustment room, maybe a bit more. Changes could be made with different thickness spacers, all placed between the knuckle and retaining clip on the ball joint for full control arm "drop" and one or more could be moved to the top side of the knuckle between it and the base of the ball joint to lessen the effect on the control arm. Adjustability would be key for a truly marketable mass produced item.

 

Your right and wrong. The more adjustable, the more expensive AND complicated. Thereby you narrow your market. Probably only pro-level racers would be into this if they felt they even needed it.

With the current crop of extended ball-joints, all they need to do is TELL us the ideal ride height for their product. But that will never happen because it would narrow their own share of the market. Plus there isn't really a simple way to compare ride heights between different setups (tire diameter plays a big roll here).

 

Youre right and wrong

I dont think that an adjustability feature would increase cost that much. They would be almost identical to the J's racing parts, just longer with an assortment of collars instead of just one.



.

.

Concerning what you said about a fixed RCA coming with a recommended ride height will not only be complicated by the rest of the vehicle's setup, but now a user is limited to one ride height and can no longer use this aspect for car setup while keeping the nature of the RCA useful.

 

Keep in mind if the companies selling "extended ball joints" and "RCAs" would have to do the engineering to figure out recommended ride height. I doubt all are doing their own engineering - especially those that market their products as "extended ball joints."

I think some of you see what I'm saying.

 

Right, which is why I think a longer ball joint that has adjustability would be premier in the fact that there is no R+D on behalf of the manufacturer per specific use and geometry. That is left for the purchaser to do for themselves depending on their needs.

 

But that wouldn't work. There is no clearance between the back top of the balljoint and the driveshaft. You would need to come up with something completely different.

This is ALREADY the case. Your just not being given the info.

 

I realize this, and therefore i see a need for an adjustable option, or manufacturers to sell different length parts with catchy JDM names like Type 1,2,3 for example.

On my EP3 for example I have 1/4" possibly a tad more room to raise the top of the ball joint. Im sure every chassis is different but I can only speak on my needs specific to my application.

I know as of now there are generally 2 length options, at least for the EP/DC5. Its seems as though all of the japanese companies offer approx 1/2" extension, while Hardrace US's parts extend 3/4". For one manufacturer to offer different size options, or an adjustable option would be great.

 

OK I had a look at this, seems if we have the tie rod pointing at the IC at a nominal 7.85" ride height, then for a 3/4" ball joint to point to align the 3 arms again we would need to be lowered around 5.8" after ride height is raised to compensate for the RCA's lowering effect. I'm pretty sure you can't even run that low on our cars, so these parts are beginning to look more and more like snake oil...

Here's how the bump steer plots look, alignment as close to center and camber corrected to around 1.05° each time. This is total steer angle between the front wheels:



Now I know the rack position on this model isn't accurate, but this seems to suggest that the RCAs make bump steer worse?

 

DOH!

Oh well, so much for that. I had a feeling because I traced some of your images into autocad, and found that it takes very little lengthening of the ball joint to get the lines to intersect once again.

So there it is folks. RCAs *** up your bump-steer unless your car is lowered 6 inches. Bwahahaha

 

It does rather beg the question, what are people feeling as an improvement when they fit these? I guess the more aggressive camber curve and improved steering response could outweigh the bump steer effects?

 

Everyone always says "the steering is so much lighter!"

I always attributed this to the loss of traction caused by the raised roll center. It's common knowledge in race-car tuning that raising roll center reduces traction at that end. I just can't figure out why you would want to do this to the front of a FWD. Especially if your killing bump-steer.

Honda typically uses fat sway-bars to induce oversteer in FWD chassis. The mini cooper, on the other hand, uses a ridiculously high rear roll center to accomplish the same thing.

 

Keeping the RC above ground may be a valid reason as inducing pro-roll into the suspension with a below ground RC is bound to cause problems, but other than that, I can't see many benefits either. One reason for having a higher rear RC is that the load transfer through it is quicker, which speeds up the response and allows the rear axle to react closer to the speed of the front. Raising the front RC would only speed front reaction speed and undo this characteristic, the sort of kinematic analysis required to match RCs with spring rates, dampers and everything is the realms of the manufacturers and top flight motorsport only TBH, I doubt any sport compact tuning outfits are doing that level of reseach...

Interesting. It offers better independance, but the high RC brings its own problems of lateral scub and track width changes in bump though. I think I prefer the big bar approach personally...

 

Very interesting information here regarding the effects on double wishbone suspesnion. Here is some great info kindly supplied by a user over on CRSX regarding strut cars. Very in depth, and easy to understand for us noobs. He also throws in alot of variables so it's easy to get an idea of what happens at each extreme and why.

Here is his thread with his Excel spread sheet as well as results for the modeling he did.

http://forums.clubrsx.com/showthread.php?t=717355

 

That made for superb reading, thanks for the link! Seems I need to do a much more accurate measurement of my car, I had assumed control arm pivot axes parallel to the XY and ZY planes which was a little niave. There could be hope for these snake oil salesmen yet...

 

That is a good point. Our double wishbone setups could have "anti-dive" or "sweep" geometry built in. The pivots for the UCAs do "seem" to be parallel to both xy and zy planes though. It would probably be very easy to simply measure bolt separation across the engine bay to be sure. Same goes for the LCA mounts across the bottom of the car.

BTW: I'm having a hard time applying all that MacPherson strut info to our double-wishbone setups. What did I miss something to do with the RCAs?