DOES THE HDK SUSPENSION K-MEMBER HANDLE BETTER THAN A T-BAR SUSPENSION?
The problem is that when you start talking about things that are entirely subjective you open the conversation to opposing opinions. Saying the HDK "feels stiffer" is 100% subjective. And without some kind of analysis of the torsional resistance of the HDK, or the amount of flex in the chassis with an HDK mounted, it will remain 100% subjective.
Same goes for handling. Saying the car feels better is fine, but again that's entirely subjective. My personal opinion is that 90% of the "feels better" comments that come from installing a coil over conversion boil down to 3 things- the feel of the rack and pinion (which adds no performance), higher wheel rates than what was previously run on the torsion bar suspension, and better shocks. The latter two are easily addressed now with the torsion bar and shocks options available.
I've never heard of an RMS AlterK or a HDK with an actual structural failure. That said, the lack of a few simple gussets is surprising to me, and that goes for ALL of the coil over K's, not just the HDK. There was a tubular style K member available through DC for the circuit cars, and it had gussets. I'm still researching its actual construction, but it appears to have had a lot more reinforcement than any of the currently available coil over conversions. The application of course is something to consider.
What I would really like to see is a full plot of the toe change, camber change and roll center, like what Bill Reilly did in his "debated usage" article for the FMJ spindles. Now, that suspension was basically entirely stock except for the 1" lower ride height compared to factory. It was run with 26" tires and a rake of 1.5", which of course changes some things. We've now seen some of the camber gain numbers, but that's only part of the puzzle and @racerjoe showed that in the stock HDK configuration with 1" extended ball joints and his cars setting the camber gain on the HDK was substantially worse than the basically factory stuff here. Which he fixed with a 2" extended ball joint to get slightly better numbers than a basically stock torsion bar suspension.
Obviously the ride height makes a big difference because it changes the control arm angles. In the case of the HDK, the LCA length also has the potential to make some significant changes toward the roll center and the toe change, because changing the length of that control arm changes both the angle of the control arm AND the arc it will travel in.
Ultimately my goal is to make a plot like this for my car, because it's flatter and lower stance and adjustable UCA's will change some of the values compared to the article numbers. Probably not as much as changing the length of the LCA by a 1/2" like you can do with the HDK, but I don't have the numbers yet so that's easy to say. It's going to be a bit though because I'll need my shop finished before I can attempt it.
The problem is that when you start talking about things that are entirely subjective you open the conversation to opposing opinions. Saying the HDK "feels stiffer" is 100% subjective. And without some kind of analysis of the torsional resistance of the HDK, or the amount of flex in the chassis with an HDK mounted, it will remain 100% subjective.
Same goes for handling. Saying the car feels better is fine, but again that's entirely subjective. My personal opinion is that 90% of the "feels better" comments that come from installing a coil over conversion boil down to 3 things- the feel of the rack and pinion (which adds no performance), higher wheel rates than what was previously run on the torsion bar suspension, and better shocks. The latter two are easily addressed now with the torsion bar and shocks options available.
I've never heard of an RMS AlterK or a HDK with an actual structural failure. That said, the lack of a few simple gussets is surprising to me, and that goes for ALL of the coil over K's, not just the HDK. There was a tubular style K member available through DC for the circuit cars, and it had gussets. I'm still researching its actual construction, but it appears to have had a lot more reinforcement than any of the currently available coil over conversions. The application of course is something to consider.
What I would really like to see is a full plot of the toe change, camber change and roll center, like what Bill Reilly did in his "debated usage" article for the FMJ spindles. Now, that suspension was basically entirely stock except for the 1" lower ride height compared to factory. It was run with 26" tires and a rake of 1.5", which of course changes some things. We've now seen some of the camber gain numbers, but that's only part of the puzzle and @racerjoe showed that in the stock HDK configuration with 1" extended ball joints and his cars setting the camber gain on the HDK was substantially worse than the basically factory stuff here. Which he fixed with a 2" extended ball joint to get slightly better numbers than a basically stock torsion bar suspension.
Obviously the ride height makes a big difference because it changes the control arm angles. In the case of the HDK, the LCA length also has the potential to make some significant changes toward the roll center and the toe change, because changing the length of that control arm changes both the angle of the control arm AND the arc it will travel in.
Ultimately my goal is to make a plot like this for my car, because it's flatter and lower stance and adjustable UCA's will change some of the values compared to the article numbers. Probably not as much as changing the length of the LCA by a 1/2" like you can do with the HDK, but I don't have the numbers yet so that's easy to say. It's going to be a bit though because I'll need my shop finished before I can attempt it.
