Red9Design Double A Arm Front Suspension

[fastbacker]

Anyone have any experience or opinions on this unit?

http://www.red9design.co.uk/wishbones.htm

[turbobaja]

Looks a little iffy to me. Welds don't look all that solid here and there. Questionable design too, in my opinion. Upper shock mounts look kinda weak and so does the steering knuckle/tie-rod mount toothpick thingy. The A-arms look solid, though.

The front and rear coil-over conversion they're pushing looks scary too. Supporting all the vehicles weight from the shock mounts, front and rear, not a good idea.

Just my .02

Karl

[fastbacker]

What about this one? Definitely looks way more adjustable.

http://www.eyeball-engineering.net/a-arm.html

[turbobaja]

It does look more adjustable, but would require a lot of disassembly to make any adjustments. Also it looks like the weight of the vehicle is all on the lower control arms and ball joints, which don't look to be all that well designed ('pulling' from the bottom rather than pushing from the top on the lower ball joint, and threaded into the lower control arm instead of pressed in like the upper).

Niether one of these kits look like they have any provisions for a front sway-bar in their design. These are obviously for street use, not off-road, they should have been designed with sway-bars in mind, in my opinion.

I'm kind of a picky guy, so my opinions will reflect the problems I see with this stuff. There are probably things I can't see from these pics, like overall geometry, bump-steer, etc, that may have been well designed. I'm mostly looking for strength in important places and how well it's been designed 'overall'. I don't have any experience with aftermarket bolt-on A-arm kits, so you'd be better off hearing from people who have used the kits you're looking at in 'real life'.

If you're patient and search around, I think there are some kits that have been used with some success on this site. Both on and off-road.

Good luck

Karl

[kdf]

I've got only opinions of these, hope they help.

Red9design: Nice solid looking design with proper joints and looks pretty well designed. The steering arm on the upright looks a bit scary, a long arm mounted with two smallish bolts, but it is probably calculated to last (I guess I've designed a even more scary looking steering arm for my race car). The steering geometry is a bit off, it has anti-ackermann steering (Meaning toe in when you steer). This won't probably be a problem, but could cause a plowing condition when steering with extreme angle at parking lots. It's usually said that a car has 100% ackermann when both front wheels follow the radius of the turn. This is usually a bit difficult to achieve at low steering angles, so passenger cars usually have something like 80% or less. Parallel steer is when both front wheels steer the same amount, it's considered to be 0% ackermann. This setup has negative percentage.
It might be that camber is adjustable by eccentric upper a-arm mounts, but you can't tell from the picture. Caster might also be adjustable somewhere with eccentric parts, shims in the a-arm mounts or something else.

Eyeball engineering: Scary looking setup, especially the lower a-arm. The outer ball joint is a tierod end looking solution that has a narrow thread end. You can guess where it will break. Also the coilover is mounted at the middle of the lower a-arm, which isn't the best place to mount it. The front mounting point for the lower a-arm looks a bit weak. It looks upside-down that they have put a proper joint at the top a-arm.

The geometry on both of them is pretty ordinary. Double a-arm with shorter upper a-arm. You can't go much wrong with that design. The tie rods follow the trend of the suspension links, so it seems that they have made effort to design bump steer out of the geometry.

[volkdent]

I've got only opinions of these, hope they help.

Red9design: Nice solid looking design with proper joints and looks pretty well designed. The steering arm on the upright looks a bit scary, a long arm mounted with two smallish bolts, but it is probably calculated to last (I guess I've designed a even more scary looking steering arm for my race car). The steering geometry is a bit off, it has anti-ackermann steering (Meaning toe in when you steer). This won't probably be a problem, but could cause a plowing condition when steering with extreme angle at parking lots. It's usually said that a car has 100% ackermann when both front wheels follow the radius of the turn. This is usually a bit difficult to achieve at low steering angles, so passenger cars usually have something like 80% or less. Parallel steer is when both front wheels steer the same amount, it's considered to be 0% ackermann. This setup has negative percentage.
It might be that camber is adjustable by eccentric upper a-arm mounts, but you can't tell from the picture. Caster might also be adjustable somewhere with eccentric parts, shims in the a-arm mounts or something else.

Eyeball engineering: Scary looking setup, especially the lower a-arm. The outer ball joint is a tierod end looking solution that has a narrow thread end. You can guess where it will break. Also the coilover is mounted at the middle of the lower a-arm, which isn't the best place to mount it. The front mounting point for the lower a-arm looks a bit weak. It looks upside-down that they have put a proper joint at the top a-arm.

The geometry on both of them is pretty ordinary. Double a-arm with shorter upper a-arm. You can't go much wrong with that design. The tie rods follow the trend of the suspension links, so it seems that they have made effort to design bump steer out of the geometry.

Just wondering what you might have to suggest on mine?

http://www.germanlook.com/Forums/showth ... 76&page=15

Jason

[raygreenwood]

The balljoint installation from the guys at eyeball design is only really iffy on the top balljoint. Why they did not make it like the one on the bottom in the picture is beyond me. Both balljoints should have the flanges on the outer section of the arm so they cannot pull out.
But the eyeball stuff....looks a bit more spindly to me than the other design....especially in the tubular areas where the ball joints are pressed in...and their weld points to the control arms. I think they should have a lot more meat. Ray

[Ozzie]

Just wondering what you might have to suggest on mine?

Jason

Looks great. The only thing I would change is to move the caster adjustment to the upper A inboard clevises like the Heidt unit. Weight is an issue, but thicker crosssections for your brackets & gussets might be a good thing.
How does it handle?

[kdf]

Just wondering what you might have to suggest on mine?

Sorry for the slow reply.

I've spent much time looking at different suspensions, seeing many of them break and I've designed a couple. I don't know your background or how much you've design work you've done before making the suspension, but hopefully I can help.

Your design looks good. In engineering terms I'd call it sturdy, but in racing terms heavy weight. It could have been done a bit lighter, but you designed it so you probably know that lightweight adds complexity and breaks more easily.

It looks like it has "fuses" in all three cases (vertical, longitudinal and lateral) direction, and it looks like in most cases the wishbones will bend leaving other suspension components intact and keeping the car on four wheels. The tie rod end on the upper suspension arm is wrong, but many (including me) have designed such upper arms and haven't had problems. I broke one by driving my car at the race track, but the suspension arm tubes bent and mounting points broke instead (just like designed and the frame didn't get damaged).

Anyone designing a suspension of a car, should read Pat's article on the Formula Student Germany site about rod ends in bending: http://www.formulastudent.de/academy/pa ... n-bending/

Can't get to bigger conclusions on suspension or steering geometry, but it doesn't look wrong from the odd angle pics you have. How's your bump steer?

I can give a couple pointers that I've learned.
Using square tubing is easy, but the problem is that loads don't distribute equally in the welded joints. In race cars sizes are usually close to 1" 16swg square tubing, so yours look quite over engineered in comparison. Welds are always a source for problems, and so is square tubing. I don't think you will have problems with this.

The shock towers and the steering rack mount looks a bit suspect, but they both might be OK. I would check them with a dial indicator with a magnetic stand (every car workshop should have one). The steering is easy to check. You mount the magnetic stand to the chassis of the car and put the dial indicator in contact with the steering rack. You then have a friend sitting on the front (as weight and checking the dial) of the car while you sit in the car and steer. There are three possible outcomes. 1 the dial doesn't move and you feel silly you measured the flex 2. It flexes a bit and you feel confused if you should fix it. 3. The steering rack flexes in your eyes and you feel stupid that you designed it that way.
To check the shock towers you should put the dial indicator in contact with the shock tower in the same direction as the shock. Then lift the front off ground, zero the dial indicator and when the car is back on wheels you start jumping on the front axle. The outcome for this measurement should be the same as for the steering rack. And while you are at it you could also measure how much the lower a-arm flexes when there is load the front.

Ozzie. Jason uses Ghia spindles, so caster is adjusted just like in any balljoint front, by rotating the upper asymmetric piece on the spindle.

I checked the pictures from your site, the thread on germanlook.com was a bit too lenghty (20 pages of posts, cmon! ): http://www.geocities.com/volkdent/A-arm_Suspension.html
Is the car already on the street?

[volkdent]

Hi KDF,

Thanks for your input. I didn't design the suspension myself, it was way over my head and still is, although I think I'd feel comfortable fabricating it now. Bob at Rorty Design did the design work, and Walt at Walt's Custom Services did the fabrication.

Bob wasn't entirely thrilled with the design, but he had to make some compromises being that he did it all over the internet, he lives in Australia, I live in California. He knows about the round tubing, he used square to make referencing the whole thing easier for a novice just in case I decided to fabricate it myself. The parts where my selection, so he didn't have an option there. My goal was to use easily sourcable parts so anyone could build this thing.

It is built to be "sturdy". The main use for this thing is on the road, so we designed it to handle big impacts but still stay together. It could be made considerably lighter, but unless it is used by someone for all out racing, the sturdiness is a benefit for longevity.

The shock tower in the CAD design you viewed would have worked out just fine, but it was too low, so a new shock tower was designed. It ended up losing the lower vertical component, which created a severe stress area at the bottom edge and finally ended up tearing the weld. There are pictures of the failure amongs the 20 pages!!!! This project had been going on for years, thus the number of posts.

So I gusseted the broken area and it's been just fine. I recently realized that when the alignment was done the shop never bothered to center the rack, so I've just finished doing that and not surprisingly I now have a decent turning radius to the left...

There is very little if any bump steer, I really don't really have any complaints about the ride or handling up front, it's my rear end that needs work. My complaints have to do with how much sheet metal had to be opened up to allow for the system to be attached. Two areas of the inner fender well had to be opened up to allow for the clearance of the tie rods, the "wings" on either side of the front frame had to be removed, and an area next to the original opening for the steering column had to be opened up.

In a future design, I'd like to not have ANY modification to the body at all. I've got my eye on Mazda MX-5 spindles which would allow for a front steer setup similar to what Red9 ended up with, without the hokey arm they added. It may be possible to not cut the frame at all by placing the rack right against the frame horn, or 2 holes may need to be opened through the front frame to allow for a pass through of the rack. Who knows, I just like the challenge!!!

Jason

[kdf]

I checked the thread at germanlook.com (or the pictures in it) and the video you have on youtube. Your ride is really sweet, I remember reading about it when you started to build it.

I would still concentrate on the front. Measuring bump steer, ackermann and checking the stiffness of components will improve the design. If you haven't measured them, you don't know what they are.
You should calculate the spring, anti roll bar and damper values for your suspension. A pretty basic spreadsheet is enough, the inputs you need to measure are the mass of your car (sprung/unsprung for each corner) and the suspension geometry. If you need any assistance with this, I would gladly help.

Oh yeah. One big deficiency in all the double wishbone suspensions for bugs is that they don't have an anti roll bar. Especially your car with mid engine layout and low front end geometric roll resistance should benefit from having one.

[fastbacker]

All good stuff here but to get back to the original question, I got some info on the red9design front end. The below comments are from the company via several e-mails:


"Its built with full ackerman and the usual toe gain at 20deg. So its works like as a normal car."

"Optimum ride is 3” lower than stock."

"Camber adjusted with the nut as the stock Beetle, Caster is done by moving the wishbones for and aft using the spacer washers, Toe is set with the track rod on the rack."

"The ride is 3" lower than stock at the optimum setting and will adjust up and down from there about 1.5""

"The track is stock."

"There is approx 3" compression/rebound."

"Bump steer is minimal due the layout of the steering parts, we are particularly happy with what we have achieved in this area."

[kdf]

Hello Fastbacker, it's nice that you have gotten in contact with the sellers.

"Its built with full ackerman and the usual toe gain at 20deg. So its works like as a normal car."

Doesn't look like it is. I did a quick model of the steering geometry and this is what it spitted out:


According to the model the inner wheel steers just a bit less than the outward wheel. The model has margin of error, but nowhere enough for me to consider the steering geometry being full ackermann. This graph should be interpreted from the bottom up. At steering value 17 both front wheels steer 17 degrees, for 100% ackermann the inner wheel should turn approx 23 degrees, which is 6 degrees more.

Rule of thumb is that in a front steer car, the tie rods usually go forward from the steering rack to the spindle. Usually in a rear steer rack the tie rods also point forward from the steering rack to the spindle. You can play with the geometry a little like they have done, by moving the steering arm on the spindle as far out as possible, but in this case it hasn't been enough.

It doesn't make a big difference if the steering has full ackermann or not in normal driving, because you can't get the steering system to follow the ackermann curve at low steering angles anyways. The difference will be more noticeable if doing steep turns like on the parking lot or in autocross.

EDIT: added a curve for 100% ackermann to the graph.