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Interesting discussion. But I think its important to remember that all these cars are actually quite different despite being setup on chassis's with many of the same parts. My experiences are all with racing so I'm not sure they apply but....
For instance:
Wheelbases:

Spider: 88.6”
GTV: 92.5”
GTV6: 94.4”
Milano: 98.8”
Berlina: 101.2”

The difference in these wheelbases make for some very different handling characteristics, along with the difference in front to rear wheel loads. My vintage racing Berlina weighs 2300 pounds and has a 16mm rear bar with 250 lb./in rear springs and it was not enough roll stiffness. It slides a lot but does not rotate that well. So I am going to test a 19mm adjustable rear bar and then try more rear spring.

Alfa racing lore says disconnect the rear bar a race GTV. The in car video I have seen of well prepared- well driven GTV's makes them look pretty dam twitchy and tail happy. So that may work there, but I would like to know why. I remember reading in one of the racing prep texts about dealing with an ill handling car - it said that sometimes you have to kill the good end of a car to deal with the other ends problems - I have a feeling that is the reason why removing the rear bar on a GTV worked well in the past. But it would be better to fix the problem if it could be identified. Anti roll bars applied correctly are a great thing, they increase the roll stiffness but don't change the spring rate if the car is not rolling.

Here are the calcs for a 16mm rear bars wheel rate:
Rear ARB 105/115 Alfas

The bar that came in my 1974 Berlina is .63” Ø, has an effective length of 26.38” and the arms are 9.63” long. The motion ratio is 1.

(1,178,000 x .63”^4) / 26.38” x (9.63”^2) = 76 lbs. / inch Current bar

So, I would try the bar and then disconnect one end and see how that feels. That's my plan for the next time I get a chance to test.
 

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Ah but inducing a little more oversteer (on the road, not the circuit) balances the chassis more and in fact reduces understeer in reality. Remember on standard tyres/std suspension these chassis are controlled drifters NOT grippers.
I`ve played with my 2 litre (`74 std Euro spec but with 185 x 70 x14 tyres) and tried with and without rear anti roll bar and on a normal road understeer is reduced with the standard roll bar.
 

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1969 GTV 1750 Australia
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I have always liked the stock set up on the S1 GTV's. Lots of warning of grip loss and no dramatic oversteer. My 1968 Porsche 911, now that had oversteer!
 

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Just another 'sample' to the 'observations'. My '68 1750 GTV had the rear bar, basically stock car when i got it but springs perhaps cut a little or compressed, just seem to sit a little lower than some. It had oversteer but didn't seem excessive or uncontrollable - seemed fun. Then i sprinted it on track (Mallala) and one of the old guys pointed out I was lifting a rear wheel on some corners and I should remove the rear bar. Next sprint I did and times improved. You could feel the difference on the street, not a massive difference but yes less oversteer - didn't notice significant understeer.

About that time though I found a lsd to replace the open diff that was in it. Once again lap times down but didn't notice much in street driving.... until it rained! Fast hills driving and if you break the rear end loose under power, it wants to change ends must faster than it did with open diff - which makes sense because both wheels spin with lsd but open diff still has one wheel not spinning and maintaining traction. Not a big deal, I just had to be a bit more cautious in wet conditions. But I never tried the rear bar connected with the lsd in there, but I can imagine that might add and extra degree of difficulty in the wet.
 

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But Mad North-Northwest
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Discussion Starter #47
Well crap. I got the bar from Ed, redid the bushings, and installed it (which was quite a fight.) Problem is the top of the left drop link is hitting the body in front of the gas tank on any sort of bump. As far as I can tell there's no way to adjust this, and I'm reasonably certain I installed the bar oriented properly.

I'm wondering if the car got tweaked at some point. Anyone else seen this?
 

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Do you have the bend in the arms facing down? that is the correct way to install it. On the first go around most people put it upside down.
 

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But Mad North-Northwest
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Discussion Starter #49
I read that and I was like "OH $!#%$", but then I realized what you're saying. Yes, the bend is down, so the rear part of the arm angles up, correct?

I've also got the drop bars oriented correctly. And I was smart enough not to mix up the upper and lower bushings. So I don't think I did anything dumb, but...

Here's the diagram I was using (which is from the S4 manual.)

1629963
 

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I read that and I was like "OH $!#%$", but then I realized what you're saying. Yes, the bend is down, so the rear part of the arm angles up, correct?

I've also got the drop bars oriented correctly. And I was smart enough not to mix up the upper and lower bushings. So I don't think I did anything dumb, but...

Here's the diagram I was using (which is from the S4 manual.)

View attachment 1629963
Sanity check... you sure you got everything correctly oriented?

1630023
 

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But Mad North-Northwest
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Discussion Starter #51
It's definitely oriented correctly. There's slight clearance on the right but none on the left. I don't see any way to adjust this out.

I'm wondering if the body was tweaked at some point.

1630143
 

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Looks like one of two possibilities: Body is tweaked or the bar isn’t the correct one for your car. The latter seems the more likely possibility if there are no tell tales of prior body/chassis damage/repairs.
 

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But Mad North-Northwest
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Discussion Starter #53
Well, I wouldn't be surprised if the car had been hit, but I'd be amazed if it were that bent without other evidence.

Anyway, I thought all the rear bars were the same, but looking at the parts diagram there's a different P/N for the Spider vs the GTV. So my guess is that's the problem. I'll need to check with Ed to see what this came out of.
 

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If you need a GTV rear bar I have one in San Francisco. Could do local pick up, Or maybe I could deliver it, my work takes me to San Jose a couple times a week. If interested PM me.
 

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need to check with Ed to see what this came out of.
I think that it came off my 79 Spider but I have parted two other Spiders and two GTV's. I was not aware of differences. I apologize if you paid me to ship the wrong bar.
 

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But Mad North-Northwest
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Discussion Starter #56
Eh, don't worry about it. Not like it was expensive, and I didn't know the bars were different either. I'll pass it on to someone who needs it.

I checked with Smithy and unfortunately he no longer has the bar that he thought he did. I'll call Larry at APE on Tuesday and have him measure what he's got. Worst case I'll just leave it off, probably won't make much difference.
 

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Not to muddy the water, but interesting that the GTV rear bar has longer arms, but presumably the same mounting location, and that's why one hits the gas tank on Gubi's Spider?. If so, different length arms on Spider & GTV bars means they have different strength. Not a whole lot, but maybe enough that removing the rear bars on Spiders vs. GTV's produce different changes in handling. Or, mounting a shorter arm Spider bar on a GTV results in a stiffer bar than stock and less understeer/more oversteer.

Changing length of lever arms on the same diameter sway bar is a known technique for tuning handling on race cars. Here's my interpretation on my autocross spider but this is matched with a large diameter tubular front bar corrspondingly:
1630367


Since the GTV has a longer wheelbase, you probably have a GTV bar on your Spider.
 

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But Mad North-Northwest
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Discussion Starter #59
To clarify, this is a GTV, the bar is from a Spider. It appears the Spider bar has longer arms, but I won’t know for sure until I find a GTV bar.
 

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Ooops. Maybe got it backward. Interesting nevertheless that there are two different bars for Spider & GTV.

To clarify, this is a GTV, the bar is from a Spider. It appears the Spider bar has longer arms, but I won’t know for sure until I find a GTV bar.
 
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