flatchat(Chris)
Supporter
Your first para sounds like it dives under braking which means you need to dial in some anti dive - achieved by raking the lower control arm -i think?
"just my thoughts anyhow"
"just my thoughts anyhow"
How much static rear caster & toe-in are you running?Chris, I had considered "anti-dive" geometry as a source of investigation but this is a very momentary, transitionary, and very high-speed specific thing I am feeling. I still believe my setup values are the source and it's not a deeper foundational chassis design issue.
Once I have eliminated the toe change idea I will go to what I think is the real problem. I still am running 900-pound springs on the rear, 750F, and the original QA-1 shocks. The shocks are at the functional limit of their adjustable damping range with both compression and rebound settings almost at the full hard limits. I think more R rebound and F compression would be my first thing to do if I could.
AND I really can't add any rear wing (I'm at 8-9 degrees of AOA ) because of high-speed download suspension compression. Again too light springs. The reason I have not done this is the car is really good on slower tracks with 110-120mph straights and slower speed corners.
So in the end I will need to more than likely, re-valve or replace shocks, go to about 1050R/ 850F springs, and add rear wing AOA. Maybe I need two sets of shocks and springs. Then just swap them out for the track I will run at. Lots of work and money but, it is what it is.
Rodger, I don't think my car makes anything like the downforce that it would take to cause F1-style porpoising. It's not an up and down thing, it's more of a rear-steer side-to-side feeling as the suspension aero unloads. And it is a feeling and it only lasts a second or two. Not a real controllability problem that requires a lot of steering correction. But it's there and it does bug me a bit.
I'll get it.............I like this stuff and it's why I bought my SLC in the first place, so I could enjoy the journey of the development of the car. Kind of a poor man's version of what it must be like to learn how to race a real prototype.
How much static rear caster & toe-in are you running?
Whether it's possible or not depends on your type of suspension. I used Porsche 996 rear uprights and a slightly modified 996 5-link system.Oh now.... that question strikes a cord.
Neil, I have been searching for intelligent discourse on the effect of rear caster. Please enlighten us (me) on the benefits (or not) of rear caster.
On a properly set-up rear suspension is it even possible to generate active rear caster (camber alteration)?
Thanks
I think it comes down to what the hub is doing in compression and rebound. This is independent of toe link effects on bump steer with compression and rebound. Depending on the geometry of the upper and lower control arms (ie rear caster), different toe curves can be resultant, I'm assuming much less pronounced than bump steer but nevertheless detectable and noticeable at performance limits.Thanks Roger (will watch as time allows)
My question specifically pertains to double wishbone on the rear of an SLC and similar chassis.
Without purposeful 'steering' input how can caster be actively altered? Or beneficially actively altered?
The street version has a rather long, slender vertical member so it is not surprising that it flexes under load.Howard I think you are spot on.
1) There was a reason Fran changed the rear toe link from the street version to the race version. The street version under high loads flex.
Street version:
View attachment 126232
Race version:
View attachment 126233
2) The suspension has anti-dive built in. So that is not the issue.
View attachment 126234
Bushings are unacceptable in my application. Porsche used rubber bushings in their 996 rear suspension and I found that using spherical rod end bearings required a slight modification of the inner pick-up points to cure bump steer. I ascribe this as to Porsche taking into account the expected rubber bushing deflection in their original design. Maybe...?Flexes far less than you may think Neil, much less than oem bushings used in oem sports car (Porsche/Ferrari/Maclaren etc )suspension components
yes, as long as both ball joints are in a plane 90 degrees to this. Fran could answer this based on CAD data. To clarify, you are only looking for it to be 0 degrees in the fore/aft direction, you can ignore camber.If the top of the rear upright is completely horizontal, does that get us 0 Caster?