DAVISRILEY

That is awesome! Great work.

D666S

Ultralightweight carpets

So, if i understand right, the less fuel you have the more understeer the car is, so you set a harder sway bar position?

The options in a car like this seems to me almost endless, I mean, I wonder where to start from. Do you start from a basic set-up (springs, shocks, alignment, heights, tires, sway bars, etc.) and then start to change from where???

David

Geoffrey

Understeer and oversteer aren't quite that simple, you can have both understeer and oversteer in the same corner and a swaybar won't fix that. Damper adjustments (compression and rebound) and spring rate have a large effect on the transient vehicle dynamics whereas a swaybar is effective during steady state cornering. When the weight balance of the car changes such as a reduced weight from burning off some fuel, the handling will change. The cockpit adjustable bar will allow you to compensate somewhat for that. For me, I find I'm lazy sometimes and with a race schedule weekend, I am reluctant to make a change to the car and risk making it worse. In addition, I have burned my arms on the hot rotors (before I got protection) and don't really like adjusting the front bar when everything is super hot. I'm hoping this bar will allow me to experiement with setup more frequently than I currently do now.

CWay27

Great work Geoffrey. And to think that this car started life as a stock C2...... Truly amazing!!

AOW162435

Geoffrey,
Very, very slick! I'm looking forward to your impressions.


Andreas

Geoffrey

David, to answer you question about where to start with a fully adjustable car. Setting up a GT car will always be a compromize due to the street oriented geometry and unless you are willing to relocate suspension components, you'll always be fighting that. In my case, my car is not as low as one might run it, I set the ride height so there is clearance from every body panel including the inner fender liners. This prevented my car from being super low. I'm about 7mm higher than 993RSR specifications and most people run them lower than that. I also wanted my drive axles to be near parallel for longevity and of course it allows clearance onto my trailer and lift at home without rubbing or having to remove the front splitter.

I then proceeded to do a bump steer test on the front and rear so I know the bump steer curve of the suspension and that allowed me to further refine the ride height slightly to help reduce the bump steer.

I've had the car now for 3 seasons and have run basically the same tires, so through tire temp testing, I know the camber, toe, and caster settings to run for each track based on my driving style, tire, weight, etc. On some tracks like Lime Rock I run a stagered setup where the camber on the right of the car is not the same as the left.

To select the spring rate, I determined the motion ratio of the suspension, corner weights, and used that to find a starting spring rate. From there, I've changed springs several times to find what I like. "What I like" has changed as my driving skill has improved. The initially soft spring rates were not effective this past year and I doubled the spring rate to get the weight to transfer quicker in the corner which also means you have to be more "ahead of the car".

I started my 3 way dampers at the factory settings and have adjusted from there using both MoTeC suspension position sensors but mainly by how the car feels. These setting change from day-to-day, track-to-track, tire-to-tire depending on how the grip feels and how the car is balanced.

Since I have run the car for 3 years, I have a baseline setup for each track I go to and I start there.

I hope this helps...

Peter Bull

I've got these mounted on my IB

Front:


Rear:


As they are now, they are not adjustable from the cockpit. They are, however, very simple to adjust from the outside.

I don't know if they will fit a 964, but I have design drawings lying around here somewhere if you want to have something to start with.

/Peter

D666S

So Geoffrey you first calculate corner weight, ride height, then you set alignments and spring rate...

When you say "get the weight to transfer quicker in the corner" means you have quicker rear to front weight transfers in braking manouvres and front to rear in acceleration or you refer to side by side movements in the middle and the end of a corner?...

Regarding those test "motion ratio of the suspension" and "bump steer test" means you start from an "ideal" curve of those parts and then you compare them with the telemetry records during practice?

Sorry but

I'm start to think a basic telemetry sensors will be useful for me...

David

Geoffrey

The motion ratio is a test to determine the amount of movement of the damper/spring vs the wheel. Due to the design of our cars, it is not a 1:1 ratio. You can then determine the wheel rate with a given spring rate. The bump steer test will determine how much the toe changes for a given movement in compression or rebound from the static ride height. All of this is nice to know, but the reality is that you pick a starting point, test, and go from there.

When you first start high performance driving, you need a car that is not so reactive so it gives you time to build skill in understanding what the car is doing. You need a car with a soft spring rate which will move the weight around the car at a much slower rate than a stiff car. You of course also need dampers that are valved for the springs and can be adjusted for the range which you are working with. This allows you to begin to feel the weight moving so you can build your reaction skills. Driving a 911 on the edge is no different than any other car except your reactions must be much quicker, especially with the rear, so you don't get into a situation where you are past the point of no return. As an example, if you have a car with no springs and dampers, the weight transfers immediately

When I built this car, I spent the first year with a very soft setup mostly because I bought the dampers used and they came with the springs. I installed the suspension position sensors and worked with them for awhile as I was working through oversteer issues in the car. I then went even softer in the rear, which was better, however, the dampers were on the lowest settings. At a race I was comparing my data with another driver's who was faster than me and was looking at the sections where he was faster and it was areas of high speed where I wasn't confident in the car to get back on the power and was slower entering some major straights. I changed strategy and went up in the spring rate and the car was much more reactive and was easier for me to drive faster in the fast corners. I was able to drop .5 seconds off my fastest race lap during a test day later that year using an older set of tires.

Weight transfer occurs any time the car changes direction left to right, or under braking or acceleration.

There is a lot more to it than I've explained here...

First I set the ride height, then corner balance and finally alignment. The suspension geometry testing and springs would normally be selected. I did not do all of this at one time, I have been working various things out over the course of the 3 years I've driven this car.

I hope this helps.

Geoffrey

With the new bar fitted, there is interference between the drop link and the brake line. When I built the car, I installed the stock 10mm steering stops. The RSR has much larger ones, so I made a pair of 15, 17, and 20mm steering stops to install and try. I want to retain as much steering as possible without any interference.

Left to Right 10, 15, 17, and finally 20mm

Tom W

Geoffrey: I'm busy trying to turn a biochemist (me) into an engineer (not me) and looking to cheat every way possible. In looking at the MoTeC data for my car, I've been using a motion ratio of 1.0 as I've never had the true MR determined for my car. Would you be willing to share your results? I'm struggling with looking to change spring and potentially shocks and would like a bit better results with the calculations if I can get it easily.

By the way, my CV joints with Krytox and 6 hours on them look great (two 30 minute sprint races with practice and qualify = 2 hours and a 4 hour enduro). After 5 hours with Neo they were shot but the transmission was also raised about 1/4 inch to get a little better angle from the axles. It looks like the 2 changes have helped a great deal. They will be reassembling and we'll look at them again in 10 hours (unless we get prompted to do it sooner do to noises).

Ag02M5

Geoffrey...what size/offset front wheels are you running if you don't mind me asking. You have probably answered in another thread I'm sure.

Geoffrey

Tom, Call me and we can discuss.

My front wheels are 10" wide with an offset of 56mm
My rear wheels are 12" wide with an offset of 7mm