Setting up ride height
10-31-2012, 11:02 AM
#17
Burning Brakes
Join Date: Oct 2005
Location: FL
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I just tried, and to be honest I can't do it yet and be 100% precise. I tell you this though. When my car was set on sport, and I bring it into the garage for tire chnage, I can't get the jack under the car without using my ramps to bring the car up. However, when the car comes into the garage from a short drive and I had PSAM in normal mode, the jack goes under just fine. I am not imagining this crap, so let's try it at the track this weekend.
10-31-2012, 11:28 AM
#20
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Why did they go with soft springs is unknown to me. The downforce difference from the 3.8RS (374 lbs at 186mph) vs 4.0RS (410 at 186mph) would require just 0.75 mm (0.03") of rear ride height increase, basically nothing.
10-31-2012, 11:30 AM
#21
The ride height and rake on these cars is a function of many things. On the race cars some engineers will run a higher than normal rake (raised rear) because they assume considerable downforce at speed which delivers a "dynamic" rake closer to what we are measuring as static. Under braking the downforce comes off and the weight transfers forward, yielding a rake even higher than what you started with. Great for rotating the car but you better know what you are doing otherwise you are going to spin on turn it. On top of that, the dampers do most of their work on turn in phase (vs springs and ARB in mid corner) so the combination of the two working properly is what matters. Fiddling around with the RH or rake is fine, and maybe the car will feel easier to drive (and therefore deliver a better laptime) to a particular driver but don't mistake what you're doing for making the car faster.
Furthermore, your fuel load makes a significant difference to your rake if you want to get pedantic about it. On full fuel you will have more rake and a heavier front end, while on low fuel you'll have a light front and less rake, which incidentally will result in competing forces on the car when you're on track.
Furthermore, your fuel load makes a significant difference to your rake if you want to get pedantic about it. On full fuel you will have more rake and a heavier front end, while on low fuel you'll have a light front and less rake, which incidentally will result in competing forces on the car when you're on track.
10-31-2012, 11:34 AM
#22
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PET is, the Workshop manual is, and so are the few resident engineers.
Sport PASM only applies to the wannabe Aero Beetles, 10mm lower than standard PASM which is 10mm lower than non-PASM, in the wannabe Porsche and wannabe Aero Beetles (meaning Cayman/Boxster and Carrera).
10-31-2012, 11:44 AM
#24
Race Director
10-31-2012, 11:51 AM
#25
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The springs in the 4.0RS are softer, so at speed, the additional downforce will make it squat and produce front lift (the nose washes away, or as explained in the DE Cup driving school workbook: understeer).
Why did they go with soft springs is unknown to me. The downforce difference from the 3.8RS (374 lbs at 186mph) vs 4.0RS (410 at 186mph) would require just 0.75 mm (0.03") of rear ride height increase, basically nothing.
Why did they go with soft springs is unknown to me. The downforce difference from the 3.8RS (374 lbs at 186mph) vs 4.0RS (410 at 186mph) would require just 0.75 mm (0.03") of rear ride height increase, basically nothing.
The ride height and rake on these cars is a function of many things. On the race cars some engineers will run a higher than normal rake (raised rear) because they assume considerable downforce at speed which delivers a "dynamic" rake closer to what we are measuring as static. Under braking the downforce comes off and the weight transfers forward, yielding a rake even higher than what you started with. Great for rotating the car but you better know what you are doing otherwise you are going to spin on turn it. On top of that, the dampers do most of their work on turn in phase (vs springs and ARB in mid corner) so the combination of the two working properly is what matters. Fiddling around with the RH or rake is fine, and maybe the car will feel easier to drive (and therefore deliver a better laptime) to a particular driver but don't mistake what you're doing for making the car faster.
Furthermore, your fuel load makes a significant difference to your rake if you want to get pedantic about it. On full fuel you will have more rake and a heavier front end, while on low fuel you'll have a light front and less rake, which incidentally will result in competing forces on the car when you're on track.
Furthermore, your fuel load makes a significant difference to your rake if you want to get pedantic about it. On full fuel you will have more rake and a heavier front end, while on low fuel you'll have a light front and less rake, which incidentally will result in competing forces on the car when you're on track.
This matches my experience driving the 3.8 VS 4.0.
Some major bumps like the passing line on the inside exiting T1 get really smoothed out in the 4.0. It is a lot more stable over bumps in T17 also.
I noticed that the nose washed wide exiting T1 and Bishop bend (Both at around 100-120MPH, I guess), when there was no understeer anywhere else.
Than again, Juan's 4.0 did the same thing without taller uprights and 3.8 springs...
My 4.0 came setup a bit higher then OEM even and that in combination with the taller Baron uprights and wing at max angle gave me a lot of downforce. I now have my car re-alligned to match my 3.8RS setup and dropped the wing to the lower position. So we will see how that feels driving both back to back this weekend. Maybe I can get some decent data to compare but the cars will have different data systems..
10-31-2012, 01:18 PM
#26
10-31-2012, 02:16 PM
#28
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I set my height at 98mm front, 120mm rear. For some reason, .2 gt3's have more aggressive rake. Clarke has a secret setup....
10-31-2012, 02:18 PM
#29
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Both Orbit and Juanito 4.0 confirmed they are softer, but I don't know the rates. Now, if Juanito 4.0 sends me his old stock springs, I can get this info in 2 days.
10-31-2012, 04:34 PM
#30
FYI,
Most cup cars run at 77mm F & 115mm rear, that is about what is the lowest allowed in alms gtc and imsa gt3 cup.
Most track cars I know run pretty close to those numbers if you have adjustable suspension bits to get geometry in the rear right
Most cup cars run at 77mm F & 115mm rear, that is about what is the lowest allowed in alms gtc and imsa gt3 cup.
Most track cars I know run pretty close to those numbers if you have adjustable suspension bits to get geometry in the rear right