Limited run GTA Knuckle risers.

[Barryh]

Hi all,I have run this past Simon and have had his blessing to post this here..

I have made,or am busy making a very limited run of 50 sets of the original GTA Knuckle risers.
These are exact copies of the originals,made from EN36B case hardened steel,one piece construction.
The tapers are 7 deg. as per original with radii at the base for strength.
This is a one piece component,with the offset as per original.

Price per pair is R1800.00 (Approx. 250 USD) depending on exchange rate..EXCLUDING SHIPPING from South Africa.
Shipping will be quoted on an individual basis.

Interested parties can e-mail me at alfaengines at gmail dot com.

This is not a business venture or likely to be repeated,this is a once off only.
Thanks,Barry

[jcorbs]

Flaunting my ignorance of GTAs folks, but what do these knuckle risers do, and do they have value for a GTA replica based on a later model GTV.

I guess the other question is whether any of the "mainstream" (sorry Barry) Alfa suppliers have these or are we talking "unobtanium"?

Thanks

John Corbs

[genericwood]

John, the knuckle-risers raise the upper ball joint where it attaches to the upright. This changes the front roll center to some degree and gives you more negative camber change in roll. The later 2L style uprights were lengthened from the factory. So you really don't need knuckle-risers on a later car.

Erik

[jcorbs]

Thanks Erik. I had read about the later cars having different uprights.

I was hoping that these might be some sort of compensation to keep the steering arms in the same plane when the car is lowered.

John Corbs

[Alleggerita]

Quote:

Originally Posted by genericwood John, the knuckle-risers raise the upper ball joint where it attaches to the upright. This changes the front roll center to some degree and gives you more negative camber change in roll. The later 2L style uprights were lengthened from the factory. So you really don't need knuckle-risers on a later car. Erik

[velocedoc]

Quote:

Originally Posted by Alleggerita That's a matter of opinion. Alfa certainly used the knuckle risers together with the later uprights on late GTA's, GTA juniors and GTAm's in combination w/ the late spindle.

[Alleggerita]

Quote:

Originally Posted by velocedoc I have a set of knuckle risers stored in a box somewhere around here that are originals. Question: If I put these on my 105 spider will it improve the turn in on the corner or will it cause an over steer condition?

[60sRacer]

Quote:

Originally Posted by velocedoc ....If I put these on my 105 spider will it improve the turn in on the corner or will it cause an over steer condition?

[RossoGTV4Me]

I thought for late spindle cars such as 115 type AR made the adjsutment for no need of knuckle risers?

I would be interested if anyone who has a 2L with the longer spindled if they have used knuckle risers on the car with success?

[genericwood]

Rosso, I cannot answer your question directly, as I don't have experience with knuckle-risers on a late "long-upright" car. However, I can tell you that most of the race Alfas in the U.S. with modified uprights retain the stock overall length (of the later uprights). The typical modification is to lengthen the lower portion of the upright, and then shorten the upper portion an equal amount. Most modified ones were probably done in Jack Becks shop. I asked Jack why he didn't just lengthen the lower part of the uprights and leave the top alone to get a taller upright. His reply was that it the suspension software he uses showed some strange roll center changes with extra length. Of course this would vary depending on ride height and other things, but I also found some strange movement of the roll center in combinations of bump and roll with my roll center software, at least with my cars setup. On the contrary, a car I recently bought had uprights modified on the bottom only, so they were an extra inch long. It had apparently been raced successfully in that configuration. So go figure.

So what does it all mean? IMHO, the later uprights seem to have sufficient length to get decent camber gain, without causing other problems. If you want to spend money on the front suspension beyond adjustable uppers. It's hard to beat the modified uprights. They allow you to lower the car an inch without screwing with the suspension geometry.

I played around with the idea of making some upper control arms that would allow you to adjust the upper ball joint position. You could do some fine tuning that way. Looks like it would be pretty easy to just knock out the ball joint and machine the receiver for a spherical bearing. I bought the pieces, but never got around to trying it.

Erik

[Alleggerita]

The negatives Eric is referring to is, I believe increased sideways movement of the roll center under roll. The positives are an aggressive camber curve which allows the running of less static camber which is advantageous under braking. The significant increase in front roll center height also increases front roll resistance without increasing front spring rate, making the car more suitable for rough roads and tracks. Further the longitudinal roll axis inclination changes in a direction desirable for an Alfa.

On a friends car (GTA junior w/ stock rear suspension) I had the chance to try it before and after. The car had a lot more front end stick with less roll and seemed to sit slightly higher in the front when using the same springs. Bumpsteer issues were evident after the change.

My own car came from the factory set up with late (tall) 1600 spindles and 2.25" knuckle risers and rear sliding block. It was great on smooth tracks but had definite bumpsteer issues to the point that it was almost undriveable on the street w/ Dunlop Racing on it. Bumpsteering transformed the car. There are no perceptible geometry issues now at all and the car handles sublime.

I wouldn't want to miss knuckle risers on any street driven/dual purpose Alfa w/ springs on the slightly soft side. With really stiff springs and a full race set-up the drop spindles may be preferable, but I cannot really comment on that as I haven't driven a car with drop spindles.

[60sRacer]

I think the rebuilding of the uprights - lengthen the lower portion and shorten the upper equally - is to preserve the stock geometry while lowering the car.

If you just lower the car by shortening the springs, you get a lot of bump steer because the lower arm is angled upward from its deign point. The above mod of the upright allows the car to be lowered but keep the designed angles and steering geometry.

Adding The knuckle riser to this configuration would increase the camber-on-roll - not necessarily a good thing with wider racing tires. Getting the roll geometry right without tilting the outside tire will give better traction overall. The newer spindles, or the lowering-modified ones have enough camber effect for modern tires.

Robert

[genericwood]

I didn't mean to suggest that modified uprights are a substitute for knuckle risers. The modified uprights are as Robert suggested good for lowering the car without sending the roll center subterranean. The knuckle risers are primarily to increase negative camber gain. As Allegerita explained, this allows less static negative camber which is a good thing. The only question is what is the ideal height of the upright. If a 2.25" knuckle riser is good, wouldn't 3" be better? I suspect it all depends on the other elements of your set up.

I highly recommend a good roll center program if you are going into this in-depth on a race car. It will calculate the exact dynamic camber of each wheel under different bump and roll conditions. Besides that, it's fun!

Erik

[60sRacer]

Erik has it sorted out right. Using knuckle risers is just a part of a broad set of changes in suspension for fine tuning a race set-up. I don't think they matter much for a street car other than the cool factor. Maybe for a XC-TT-street set up like Murray's that swaps roll bar, seats, brakes, and tires for XC and TT.

But the best alignment - caster, camber, toe - depends on the tire (a lot) and the track layout (some), so a tire swap would need other adjustments. Knuckle risers - or other mods for increased neg camber on roll could easily make street handling with street tires worse.

It'd be fun to test all the adjustments. But then I love to test and gather data anyway....



Robert

[Barryh]

I have an update on the final product.They were completed today and Im posting a pic. of the knuckle risers..

To those persons who showed interest,thank you and Ill e-mail you guys individually..

Barry