cloudshe

thanks to papadoc for providing the link to John Giovanni's 6 link mod
(Corvette Fever http://www.corvettefaq.com/c3/6link/index.html ). the article makes a good case against the C2/C3 IRS's geometry being prone to unintended toe changes with rear spring compression & release.

previously i had considered the rather pricey Guldstrand setup, which eliminated the toe instability, but still used the rear axle as part of the camber equation.

so now i'm thinking the Dragvette 6 link might be the trick. although it doesn't provide the progressive camber change that unequal length struts give you (because that's not what drag racers want or need), it is adjustable for establishing an acceptable constant camber for different uses (drags, street, performance handling), and it eliminates the understeer caused by toe instablity resulting from the off-parallel angle of the OEM strut. and with the 6 link i can still use my worn stub axles, a 30% savings on the price of the Dragvette setup.

i've seen some complaints about frame clearence with the upper strut
connection, i'll have to check with Dragvette on that. any comments or suggestions out there?

TheSkunkWorks

The Dragvette 6-link does NOT eliminate rear toe-steer, which remains a function of track width variation during suspension travel relative to the C2/C3 TA's "fixed" forward attachment point. Also, many variables (power, tires, road/track...) effect what will be the optimal amount of camber gain. Until/unless you are able to improve on the camber and toe-steer curves resulting therefrom, and proven thru testing specific to your application, I'd highly suggest that you work from the baseline John Greenwood recommends of setting rear ride height so as to position the inner u-joint CLs 1/2" above the outers and to lower your inner camber strut links to 1/2" below their stock location relative to the diff. (You can raise the diff in the chassis to lower rear CG.) My $.02



TSW

professor_speed

Spend all the money you want but this ^^ Works, lots of fast c2/3's doing exactly this. (multiple suspension kits follow that basic formula.) Also unless the axles have a slip joint there going to be a binding problem unless you get everything adjusted perfectly. Without a slip joint the upper link is virtually useless, the lower appears to move 1/2" down as suggested. The same geometry can be accomplished for a lot less.

cloudshe

thanks for the reply! this is exactly why Dragvette requires you to remove the C-clips on the stub axles, thus creating a slip joint and removing the axle from affecting the camber geometry.

my problem at the moment is my stub axles are worn to the point that my rear end is quite squirelly on the street. i've got about 1/8 to 3/16 in of play. i was impressed by the Giovanni 6 link article about how his geometry minimized the understeer problem caused by toe change when the trailing arm suspension is flexed in a turn.

i guess since i'll never seriously race my '65 i'm looking mostly for better street manners. if i get the autocross bug again, that's a great way to wear out those stub axles quickly, with the 6 link that doesn't appear to be a problem, and it looks like it can be tuned for some pretty good handling, although not approaching Greenwood track perfection.

again, thanks prof for your input!

cloudshe

good point! if you note what happens in a turn when the outer spring is compressed and the inner spring is in rebound, the toe is increased on the outer and decreased on the inner. the net effect is the track is changed little, but both tires end up pointing slightly to the inside of the turn, causing some amount of understeer.

this is because the OEM lower strut angle is set to maximize desired camber change. when the strut(s) are located so as to be parallel to the ground/frame at rest, as in the DV 6 link, toe change is minimized as the suspension deflects. unfortunately, camber change is also minimized, which is why the Greenwood setup is proven to work a lot better on the track

hope i got this right, thanks skunkworks for your reply!

TheSkunkWorks

Bearing in mind that toe is measured level with the hub CL, the C2/C3 rear toe-steer curve is a constant determined by effective half-shaft length as the hub end moves about its arc during suspension travel into bump or droop. As we're dealing with a cosine error, the further from level with the chassis in either direction is the half-shaft, the more progressive will be toe-steer for a given amount of travel. Where the rears are pointing when they're relatively unloaded does matter, but the big nasty fly in our soup is rear instability due to toe-steer moving towards or into toe out once the half-shafts go below level (at the diff end) during squat or bump while one or both rear tires are most highly loaded. Hence the reason for setting rear ride height to where the half-shafts are that recommended 1/2" above level.

Rear camber gain is eliminated when the camber struts are repositioned so as to be parallel with equal length upper links. Any deviation from this relationship will induce some degree of camber gain (whether positive or negative). Tho track width variation can definitely be minimized by reducing or eliminating negative camber gain, toe-steer remains a separate matter. That said, other than strictly for drag racing, it would be a fundamental mistake to conclude that any amount of camber gain is always and necessarily a bad thing.

terrys6t8roadster

I'm running the Drag Vette setup in the 6t8 and really like how well the rear end feels planted in the car and the security of the half shaft loops. Also running the VP&B dual mount, which means you can't run the inner half shaft loops. Kind of a PITA to get the heim rods set so the stub axels don't bottom out inside the carrier. Also not running the clips. This year I'm going to be playing with camber settings, got a cool digital guage from Longacre, now all I need is a toe guage. T

cloudshe

wow, you bring up a good point. with the camber change, the TA is rotating around the axle attachment point, not just being pushed outward by the lower strut. so that would minimize the toe change, even though the track change measured at where the tire meets the ground is significant with the change in camber

now i'm thinking i just need to eliminate the play from the worn stub axle ends. i've tried the cheap method before, using shims between the C clips and the diff wall (don't forget to realign the toe), worked okay but not certain how it held up. this time new stub axles i'm sure. thanks again for the greenwood numbers!

cloudshe

good thought about the axles bottoming. when increasing the camber, since the struts are equal length, it would be a good idea to make sure that when the upper strut is shortened, the bottom strut is lengthened the same number of turns to maintain axle end clearance inside the diff

DaveL82

Going with a 6 link type setup with taking out the drive shaft as the upper link or even changing the stock strut rod inner mount are a big help with camber and handling. The newer/wider tires don't need a much camber gain as the old tires so the stock setup isn't the way to go (too much camber gain). This does not fix the toe change as mentioned.

To address toe you either need to go with a setup that lets the trailing arm pivot (hinge point in control arm in front of hub assembly) and uses a toe link at the rear to maintain toe link the Guldstrand setup or go with an even more complicated double a-arm arrangement.

Hey guys used to race with near stock type setups and over the years morphed into real exotic double a-arm tube frame cars.

cloudshe

i'm starting to believe that the main handling gain with the Dragvette setup is the elimination of the rubber bushings in the strut rods and the predictability that comes with minimal camber change. if i were on a racing budget i think i would go Guldstrand, for the reason you mentioned.

as it is, for the '65, looks like i'll go from 15x6 wheels to 17x7, replace the stub axles, and try out the Greenwood geometry for improved street performance. thanks mucho for your thoughts!

TheSkunkWorks

FWIW, the Greenwood inner camber strut link height tip is with respect to the C3 bracket. The C2 bracket has even higher inner links, so on a '65 you'd need to update that piece to get there with a 1/2" spacer.

cloudshe

i'm guessing i could use a C3 bracket. hope it doesn't interfere with the exhaust pipe ground clearance, but seems that not an issue with the C3 chassis. it looks like the new geometry reduces the rate of camber increase, maybe because of tire technology improvements, as you mentioned before, if my memory serves

let me give it a try, i'm planning on keeping the stock setup (instead of the dragvette one) but fixing the stub axle wear problem, going to 17x7 wheels & tires, and using your Greenwood adjustments. Thanks amigo!