Quote:
Originally Posted by Redd
@dogbone, why are you against full spherical for the rear? Just curious. I for one think you will really benefit and appreciate the extra grip and feedback from sphericals, and now is the right time to do it since you're getting new arms.
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A few reasons based on my experiences over the years.
1. Reliability. The stock arms may not be the lightest. They may not be the most adjustable. But they are 100% reliable. You virtually never hear of an OEM control arm failing [when torqued properly]. When I approached the idea of building this car, the top item on my list was reliability. I didn't want to be chasing stuff all the time. Some things high on the list were to leave the control arms stock and don't touch the wiring.
I know I've had a lot of trouble with my car this year, but prior to 2021, my car was SUPER reliable. I could go a whole season with just basic maintenance and replacing consumables. I truly believe the problems I've had this year are age related----meaning I've basically used up the effective lifespan of a lot of the parts on the car. Over the years, other fancy control arms seem to have more question marks surrounding them. I just didn't need that. Also, along my journey, I talked to a pro racer who had $300k into an E92 build. They still used stock control arms for the reliability.
2. Stress. Years ago, when I was very new to all this stuff, a very experienced tech and I stood under my car while on the lift. We were talking about the concepts behind making everything solid. Yes, putting solid stuff can make your settings more constant. Yes, there are some benefits to reducing flex/play in those joints. But, there's always another consideration on a production car. In this case, we were talking about the idea of----if you don't allow a part designed to absorb energy to do its job, where does the stress go? Obviously, there are very high stresses on the bottom side of the car. The rubber bushings are there to absorb those stresses. If you go solid in a certain spot, you are pushing the energy elsewhere. It's not a free lunch. The stress/energy has to go somewhere. And can the spot receiving the added stress take it? A good example of this kind of conversation would be the rear shock tower mounting point. When moving to true coilovers in the rear, the debate has raged on for years about whether or not you need to reinforce the top shock mount.
Now, you could argue that some of the rubber bushings in the control arms and sub-frame are simply for comfort since it started its life as a street car. Well, I don't design cars, so I don't know how strong they made all those contact points. But, after looking at it for some time years ago, I decided I was comfortable with solid aluminum subframe bushings because that area is beefy with big bolts, but that I'd leave most of the control arm joints stock. In essence, I took some of the flex/movement out of the system, but not all.
The other thing that doesn't appeal to me a whole lot is that the accepted solution for going more solid on the rear arms involves tack-welding sleeves into the OEM holes.....well, this feel a bit permanent to me. If I don't like it, it sounds like a pain in the ass to revert back.
3. Is everything locked down and solid really better? Ah, this one is tough. Some people will tell you that any play/movement in the system is bad----you need to go full stiff at every joint to get maximum grip. Others will tell you a little bit of compliance actually helps you. I think the answer lies in the tracks that you drive. I think if you run on super smooth perfect tracks, then yes, removing play in the joints would be good. But, I live in the USA. The reality is that most tracks in the USA are not smooth. Most of the time, the track surfaces are not super awesome. Buttonwillow, Willow Springs, Chuckwalla, Auto Club Speedway----these tracks have a lot of---ummm shall we say---"irregularities" in the pavement, not to mention tall berms you must attack for a fast lap time. The only track I've encountered that has super smooth perfect pavement all the way around the circuit is Watkins Glen (and Laguna Seca is pretty good, but the pavement is aging there and getting some waves in it in certain braking zones). So, I think a bit of absorption is not a bad thing.
fsmtnbiker has been going through this all year while setting up his car. While going through many spring changes and alignment settings and swapping suspensions, he has been saying over and over that he can't get on power the way he wants. He went full solid and started to wonder here on the forum if a mixture of solid and flexy might help in his answer. So, I think the answer to #3 is situational. If you live in Europe and see smooth tracks all the time, you can lock the car down more and remove compliance. But on a bumpy track, I think you could benefit from a bit of compliance.
Another example that comes to mind is a Porsche Cup Car. The accepted setup on an older Cup Car was 1500lbs springs on all four corners(!!!). Think about that for a second----a 2600lbs car with 1500lbs springs on each corner. Sounds like a nightmare to me. How the heck do you attack a berm with that setup? Ok, well think about where the Cup Car was setup----not in the USA. My friend has a 996 Cup Car and it came with that "stock" setup. He finally couldn't take it anymore and has had the spring rate dropped on the car. USA tracks just aren't as smooth. So, I think the answer lies in where you drive, and you could make good arguments for both something that's super stuff and locked down versus something that has some compliance in it.
Anyway, these are some of the ideas that have guided my actions over the years. Again, I'm not a race car designer, so I'm no expert here. But my car seems to move nicely over a variety of track surfaces and track features. Could it be better? I'm sure it can. I have REALLY been eager to put some hot laps at Buttonwillow to compare the MCS setup to the old JRZ setup, but my tech issues have prevented me from going for it. From what I've sensed so far in my warm up/practice laps, the car feels really good. In the future, I might do some experimenting by swapping rear bushings one pair at a time. But whoever does the work will have to assure me that I can revert to the old setup if I want.