I kind of want to set it and forget it. Unless something is seriously unstable on track.
Sorry, didn’t see this until now.
Remember, there are multiple parts to a corner. At the most basic, it’s entry, middle, and exit. Each phase requires different driver inputs if you want to go through the corner as fast as possible. That said, if we are focused on addressing the entry phase, then you want more bump stiffness. There are a few reasons:
-
When you turn your steering wheel, the suspension will react (read: roll), and roll is what slows down weight transfer. The slower the weight transfer takes to occur, the longer it takes for your car to change direction as a result of steering input. In other words, if the front end of the car is soft, then when you turn your wheel, the soft front end must roll slowly first…and then only after the roll has completed will the car change direction.
-
Camber deflection. Factory cars all have rubber bushings. These deflect for the sake of nvh. But are no good for keeping a proper wheel alignment. As a result, when you begin cornering, your front outside wheel will gain some positive camber (that is, it isn’t necessarily becoming positive, but it is less negative than when it was going straight). This reduces outside front tire grip–which is the most important tire for cornering (as it takes the most load).
So when you have a firmer front end (more bump stiffness), your front end will not roll as deeply–meaning it takes less time for weight transfer to occur (read: faster). This will increase responsiveness of the front end…aka, make the car more pointy–greater initial steering response. Faster reaction time. This, combined with the fact that a firmer front end resists camber deflection more (if the suspension is less prone to rolling, there are less geometric forces acting on the suspension to influence camber), then your tire is in better contact with the ground. Thus, you have more front end grip + less roll = faster turn-in response.
You are correct in your next post in identifying that a firmer front end transitions more weight rearward, so you get more rear-end grip. You’ll find many rwd race cars prepared this way on purpose. It’s generally going to be the fastest setup for a front engine, rear drive car. With a firm front end, you have a pointy car that can get directed to the apex of a corner rapidly. Then, you have lots of rear-end weight transfer to weight the rear wheels (drive wheels!) so that you can get on the gas sooner and harder to blast out of the corner. This is why you see rwd cars lifting the front inside tire upon corner entry. Massive front end stiffness…
The suspension designer at PSi is chiding me for having a 650 spring rate at the rear. He personally feels 400 is the right number, citing the motion ratio of the B8. I cited much higher rates in the B7 RS4 rear like 1000 and he pointed out a different motion ratio. My dampers are valved such that I could go down to 550 without an issue. Will have more data soon.
Motion ratio of B8 is 0.6 rear. With a 650lb rear spring, it puts you at a wheel rate of only 234lb/in.
For the record, stock wheel rate at the back (based on S5 spring rate) is 158lb/in
It is less than 100lb/in increase. Not certain it is a huge deal. But also, depends on what you are looking to address from a handling perspective. Upping the rear rate this much may allow you to remove the rear sway all together. You get the same/similar effective wheel rate, but less mass, and more independant suspension action.
Also, according to stasis, “most audis are 0.8 in the rear” for motion ratio.
If that is true, B7 is even stiffer out back compared to the b8.
And for the record, an E36 M3 is 0.65 motion ratio in the back. And the PSS9 rear spring on the E36 is about 600lb/in.
Still not seeing the problem.
Running a big rear bar I’d be concerned, as you don’t want to pick up the inner rear wheel bc we have the sport diff! But stiffer rear springs? And being approx #230… is ok. You can play with alignment to compensate other areas.
What were your front rates again?
Quoting this for RS4nightmare incase he misses my response from the previous page 
I have some data. I suppose I’ll start with the adjustment in the middle (12/24) for lack of a better starting place. Any advice @boro?
Front JRZ RS1 (at 0, 4 and 22 clicks, out of 24 possible)
http://i58.tinypic.com/2v16alw.jpg
Rear JRZ RS1 (at 0, 4, and 23 clicks, out of 24 possible)
WOW those shocks are SO PROPER!
Those are by far the best dyno’s I’ve seen. They look doctored 
Really clear digressive curve, distinct rate changes with each adjustment and progressive jumps in the curve to correspond with the clicks. That almost never happens!
Also really nice to see that the max curve on both front and rears are similar.
Honestly though, not easy to say where to start without driving the car first.
I actually would not put the fronts in the middle as a start, as the difference between each adjustment is very distinctive with your JRZ’s. I would be tempted to start near the lowest and go up from there to get the rebound you require to suit the springs/pace of the car/corner(s) on the circuit.
Put the fronts at #4 and go from there.
For the rears, you’ll need more to go with your spring rate (more rebound–plus, it’ll address some of the chassis balance “issues”). Rears I’d start with #9 or so. It looks like the base curve is roughly 50% less than the fronts, that’s why I’m suggesting such a big jump in the back.
The best $60 I ever spent was getting your advice in exchange for the data. We won’t know how proper it truly is until I go back and put the OEM’s that I beat up on every apex curb of every track in California.
PSi is a big Ohlins shop so they pretended to be nonplussed by JRZ, or Moton, or TPC Racing. Completely dismissive of any mass market coilover like a Bilstein. I think JRZ is a good compromise.
Sorry to bomb this thread with charts from a different car, but could help but notice how similar the rear chart was to mine.
http://tapatalk.imageshack.com/v2/14/12/04/0243d64b3234cda7b52b2b4253585440.jpg
Ehh… Maybe not that similar.
Are there any B8 platform concerns with using a 2" hole saw to drill holes in the shock towers so I can access the adjustment knobs? Getting the JRZ installed today.
So it’s pretty simple to drill the front shock towers. For the rears it is not possible because it’s some double hulled construction. Instead in the rear you poke a 3" hole in the wheel lining and slice flaps into it. Technically you could wrap your hands up around there and make an adjustment. Although it only takes about 10 minutes to pull the whole shock assembly out.
I set it 8/24 front and 12/24 rear. EDIT: this is probably too aggressive. Will revert to 4/24 in front and 6/24 rear.
http://tapatalk.imageshack.com/v2/14/12/12/89c7ee81e83c888b86186ac3f721b943.jpg
Looks good, very clean. So you aren’t planning to change the damping in the paddock? What about ride height?
I think it’s fair to say you have the most track ready s4 on the boards, maybe qua77ro being the only equal. How comfortable is your car on the street?
Adjustment sounds like a pain in the ass.
In emails with Bryan Hise at JRZ, I requested he design the system to stay at OEM ride height. I really didn’t believe it until I saw it. It’s probably 10mm lower than I had though visually it looks the same. We’re roughly at 25.9" to 26.2" fender height all around. I have a full 6.0" of ground clearance rocker panel to ground. The springs are still settling and I haven’t corner balanced it yet. I’m anticipating a 3700 pound empty weight, and low 39xx with the driver and fuel in it (track weight). The tech working on the car is an expert and the craftsmanship in this custom job is all his. He even made nice caps for the front towers out of recycled BMW gaskets (that’s Berkeley for you). He made mention that this ride height didn’t move the roll center (or else it would dive excessively under braking). He also mentioned the wheels have over 7" of droop when the car is raised, which means the suspension can travel freely.
Setting these dampers on 12/24 (which I now know is a race setting), I can say they’re in an entirely different league than a Bilstein/KW/HR street kit. I honestly might revert the front to 0/24 and the rear to 4/24. I want to leave it at one tuned setting. Finding the balance where I like the low speed rebound and I like the high speed rebound is going to be key. Obviously I only have one adjustment, with the ability to bias it front to rear. It’s enough rope to hang myself with for now. I can’t imagine starting with 2 way or 3 way if you hadn’t gone through this beginner’s exercise.
If I’m right this will be one of the most track ready S4’s. If I’m wrong it will be expensive for me to inch my way there. I have 3 track weekends scheduled in Jan/Mar/May. We’ll find out. Though I’ve put a bit of cash into this I feel it’s less expensive to keep my low miles S4 than purchase a 2015/2016 sports sedan, which runs over $70k at least.
http://tapatalk.imageshack.com/v2/14/12/14/83d63dd7ff2832c6b2c9afd3303e18f3.jpg
http://tapatalk.imageshack.com/v2/14/12/14/953726d822b2ae80528bb904b7243bc7.jpg
This isn’t specifically about the B8, but shows what a next level suspension has in terms of componentry: http://www.elephantracing.com/tool-box/specs/991/Cup/991-GT3-vs-991-Cup-Car-Suspension-Comparison.htm
I read through that and some of it is pretty cool to see the differences. Certain things have been out for a long time either with other OEMs or with aftermarket companies.
I like the adjustable caster link. Most cars have caster locked in place from the factory and the only time that it is off is when you get into an collision or something bends the control arms. Don’t see why the GT3 needs a rubber bushing there since a solid adjustable puck probably wouldn’t transfer much NVH to the driver.
They use spherical bearings basically every where instead of rubber bushings. Certain people like me want to do that anyways just to not have rubber bushings.
The sway bars have blade ends that allow much finer adjustments compared to the normal two to three hole adjustable sway bars that are sold now. Very cool.
I haven’t seen so many double shear bolts/nuts. Never seen a single shear end break but apparently it happens enough that Porsche felt it was worth the time and aggravation.
My final settings on the JRZ are 0/24 front and 4/24 rear, which is close to “maximum soft”. It’s highly competent both at low speed around town and stable/connected at high speed over expansion joints in the highway, drainage grates, and other obstacles. You can be more confident than stock on almost any surface.
Now it’s a question of how many miles these will last. If I can get 14,000 miles and 2 years out of them before a rebuild I will be very happy. If I could get a second set of the dampers for $2400 I’d consider doing annual rebuilds, to keep them at peak performance and avoid having them leak or blow out when they naturally expire. I’ve seen some Stasis/Ohlins kits go at 8000 miles and a dozen track days - they start seeping fluid.
@boro92 - I dropped off the OEM dampers with 39,500 miles and 30 track days on them (!) for a shock dyno. I won’t get the results until next week. I had to double check my track calendar but it is actually 30 days. Obviously I’m going to discard those dampers as they have exceeded their useful service life.
August 2014 Hooked On Driving Laguna Seca 1
July 2014 HOD Thunderhill-West 1
May 2014 Audi Thunderhill 2
March 2014 Audi Laguna Seca 2
Jan 2014 Audi Thunderhill 2
Oct 2013 Audi Sonoma 2
Aug 2013 BMW Laguna Seca 3
June 2013 BMW Buttonwillow 1
May 2013 Audi Thunderhill 3
Jan 2013 Audi Thunderhill 2
Nov 2012 BMW Thunderhill 2
Oct 2012 Audi Sonoma 2
May 2012 Audi Thunderhill 2
Apr 2012 BMW Buttonwillow 1
Feb 2012 BMW Laguna Seca 2
Nov 2010 BMW Thunderhill 2