DOES THE HDK SUSPENSION K-MEMBER HANDLE BETTER THAN A T-BAR SUSPENSION?
on the tie rod end, you could call it luck. Amazing how persistence can turn into ....luck.
Maybe I misunderstood, but from your description it didn’t sound like you calculated the roll center, saw a need and identified a change of tie rod ends to make adjustments to improve it, and then carried that out.
It sounded more like you were forced to change the tie rod ends because of a supplier change and are mostly speculating it made the roll center better. If the new parts had been worse for geometry, then what?
First, I love your Duster Demon, it was an inspiration for my build. I think I said before Tim's car and my car are as close to a match for HDK coil over and torsion bar you will find. I also run the taller UBJ and the SPC fully adjustable UCA with a stock boxed LCA, Bilstein shocks the big Helwig sway bar made for 18" wheels. I'm sure Tim runs more spring in the front than my 1.08" bars. Our rear suspensions are also virtually the same. My car weighs more than Tim's because of the insulation and sound system. We also ran 114.95MPH, Tim to my 114.49MPH in the 1/4. The biggest difference is tires, I run 245/40-18x9 and 275/35-18x9.5 Falkin RT660s. This year Tim stepped up to 265/40-18x9.5 and 295/35-18x10.5 Bridgestone RE71s which has been the standard go to autocross tire for several years.
I remember when Tim called me and told me about essentially extending the wheelbase to get more caster by simply changing the spacers per a conversation with Denny. I called him a cheating bastard if I remember! He presented Denny with a question, and Denny had a very simple fix. We all run power steering, and the more caster we can tune in allows for quicker steering inputs thru a slalom. So Tim wanted big numbers. I'm currently at 5.5/5.6 caster. Pretty much the most I can run without hitting the back of the fender. So Tim runs a more aggressive alignment than I do, but I like driving my car during the summer, so I backed off the numbers a bit.
Anyway, the other big difference between our cars is the driver. I just started autocrossing in August of 2023 when my car was a handling mess until this year. So I'm getting better now so I hope to close the gap. But nothing in racing or life for that matter is static, but we'll see. I believe with a good driver, our cars would be very close on the autocross and 3S. Which is better? Flip a coin. I kind of like old school stuff, so torsion bars and external shift linkage with my 855 5-speed. It's not the smoothest, but if I want that, I can shift my Mazda6 manual with my fingers. We both autocross a lot. Of course the STL-SCCA has the most competitive CAM-T cars in the country, including the SCCA National Champion, so I always have a great yardstick to measure against. We also both drive our cars to the track and enjoy driving them. I wished this post hadn't turned into a **** show. HDK has it's place, and it proven. If you decide to go that way, know that the winner of MoParty 2025 has that system under his car and will be back next year to run again.
I’m sure you already know the tire difference is massive. Increasing the amount of available grip, especially in the front, from going to a 245 to a 265 or 275 will have a huge impact.
The wheel rate is also important, and will be more important if you go to larger tires in the front because you’ll need added rate to handle the increased grip. It’s crazy how much the tires have changed in just the last decade, the wheel/spring rates I was running on my Duster were more than enough when I choose them. But even with just the Falken 660’s I’m at a place where the rates probably need to be higher.
The alignment differences aren’t that extreme. The caster is nice because it increases your camber on turning, so you can run more static caster, get more dynamic camber, and not wear out your tires with extreme static camber. But that’s a fine tuning thing, it wouldn’t be a big change compared to going to 275’s square.
One thing I think a bunch of ya'll talking about my initial roll center being terrible is I chose to use the spindle I have due to the ability to run the beefy corvette hub. It's a standard height M2 spindle. At the time, my knowledge of suspension dynamics was lack luster. I didn't know a short spindle would be such a detriment. However, I stand by my choice because I like the hub vs. the old school bearing setup I would have gotten with the TALL Wilwood spindle. I do think that TALL spindle would have prevented some of my issues early on, but I was ignorant at that point in time. So what have I gained, besides a giant trophy? I've given myself an education on suspension dynamics because I was determined to find the right ADJUSTMENTS to make it the best performing suspension the car has ever had. Knowledge is king and you should never stop learning. I enjoy helping people when they come to me for advice. I wouldn't be able to help if I didn't have real world experiences and the knowledge gained over the last year.
And that’s huge, and why your efforts are so valuable. No suspension system starts out perfect for anything, and as much as the geometry and physics will tell you, you do have to put it on the road and see what you get and make changes. And we can all learn, and should strive to do so. Which is why I keep asking questions.
I can't express how badly I want the naysayers to get their car on an autocross, wherever you live. See how you compare to the fast guys out there. It isn't easy in a new car let alone something that's 50 years old. And I would love it even more for them to come jump in the car at any of the events I do. You will be holding on to something and pressing a brake pedal that doesn't exist. I don't care how many hills or curvy roads you have near your home. You aren't driving your car like you will on an autocross. At best I'd say 5/10 on the street and you would only know this if you actually did it.
And that’s your pride. I get it, you’ve worked hard. But just because you did a thing doesn’t mean other people don’t understand what it took to get there, or can’t get there themselves if they had the time.
One of the most important factors in AutoX is knowing you car, it’s a precision event. Seat time. Yes, it’s true you’re not gonna push as hard on any road as you do on an AutoX course. Or at least you shouldn’t! But if you know you’re at 50% on the road, well, you know what you need to do. The physics is the physics.
I know I’d have a learning curve driving AutoX again, I wouldn’t be nearly as fast as my car is capable of. Maybe I’m not the fastest driver, but, that doesn’t mean I don’t know what I’m talking about either.
Oh I love the "I don't drive around traffic cones in a parking lot, I'm an oval track racer". Again, come on out. I bet you get lost on course. Many road racers and oval track racers have said autocross is more complex than big tracks. Sure you don't get the door to door adrenaline, but who cares. Things are happening so fast you wouldn't want a car next to you. It's also a known fact that autocrossers make better road course racers. But this is a whole different argument that I'm sure will go off the rails.
Shoot man, when are you going pro then? Going to get a national SCCA title first?
I’m not trying to diminish what you’ve done, I’m truly not. But I think you’re making claims you can’t back up when you talk like that.
Have you been on a road course? Yeah AutoX has fast transitions, but life comes at you pretty fast at 140+ mph too.