Is the GT3 Ride Height Adjustable?
12-14-2018, 01:35 AM
#31
Race Director
Drop front 1-2mm and the rear 3-4mm from stock and stiffen the front sway bar to one hole from full stiff as a start. That will keep rear planted and front from being too aggressive.
Personally I like the looser car set up because the rear steering negates a lot of rotation at higher speeds.
What I really dislike is a car that rolls and dives too much...the 675LT has spoiled me.
Personally I like the looser car set up because the rear steering negates a lot of rotation at higher speeds.
What I really dislike is a car that rolls and dives too much...the 675LT has spoiled me.
12-20-2018, 07:29 AM
#32
Rennlist Member
05-14-2019, 06:15 PM
#33
By angling the chassis (Rake) you control the "surge" effect of braking or the ability of the car to turn at various speeds.
General rules:
Lower nose= less air underneath the nose so it has more direct initial turn in.
Front vs rear ride height= the more rake the more the rear will rotate, for high speed stability you drop the rear 5mm or so. Very small adjustments here make huge differences
The rear steering masks a lot of the old problems inherent in track setup for a GT3/RS.
But the proper rake and nose height makes the car more reactive to the wheel. You also have to coordinate the sway bars to make sure that the rear grip is not overly compromised.
General rules:
Lower nose= less air underneath the nose so it has more direct initial turn in.
Front vs rear ride height= the more rake the more the rear will rotate, for high speed stability you drop the rear 5mm or so. Very small adjustments here make huge differences
The rear steering masks a lot of the old problems inherent in track setup for a GT3/RS.
But the proper rake and nose height makes the car more reactive to the wheel. You also have to coordinate the sway bars to make sure that the rear grip is not overly compromised.
05-14-2019, 06:47 PM
#34
I'm a bit surprised no one mentioned the risk to the front strut towers when lowering the GT3, though perhaps that wasn't as well understood over a year ago when this thread started. Both the GT4 and GT3 have proven vulnerable to catastrophic failure of the strut tower (see here GT3 and here GT4). The GT3 and 4 suspension travel is by design relatively short, and cutting that travel by further lowering the car is one of the surest ways to reduce margin and significantly increase your chances of a failure. Rubbing the front splitter is cheap and largely cosmetic; a pothole or curb encounter that fractures your tub is the opposite.
If you can get over that risk there are a couple other things to keep in mind. Lowering the front of the car lowers the front roll center height (RCH) disproportionately due to the strut suspension up front. The effect is largely what CJ mentioned- the car is more "direct" on turn in because the CG has more mechanical advantage over the suspension. Effectively the suspension gets softer, which is likely also the reason he also mentions countering this with increased front swaybar. Meanwhile the rear suspension is a multi-link, which means RCH doesn't drop as quickly when you lower it so little if any adjustment is required. However both the front and rear suspensions bring the bump stops into play relatively early, so as you lower the rear you unwittingly start to increase dynamic spring rate which can have unexpected effects.
If you do lower things I'd go easy and with a proven front and rear setup for the above reasons. I would also plan to corner balance- on softly sprung cars corner-balancing can be largely a waste of time, but the GT3's sprung relatively stiffly and thus has much less margin for error.
If you can get over that risk there are a couple other things to keep in mind. Lowering the front of the car lowers the front roll center height (RCH) disproportionately due to the strut suspension up front. The effect is largely what CJ mentioned- the car is more "direct" on turn in because the CG has more mechanical advantage over the suspension. Effectively the suspension gets softer, which is likely also the reason he also mentions countering this with increased front swaybar. Meanwhile the rear suspension is a multi-link, which means RCH doesn't drop as quickly when you lower it so little if any adjustment is required. However both the front and rear suspensions bring the bump stops into play relatively early, so as you lower the rear you unwittingly start to increase dynamic spring rate which can have unexpected effects.
If you do lower things I'd go easy and with a proven front and rear setup for the above reasons. I would also plan to corner balance- on softly sprung cars corner-balancing can be largely a waste of time, but the GT3's sprung relatively stiffly and thus has much less margin for error.
05-14-2019, 06:51 PM
#35
By angling the chassis (Rake) you control the "surge" effect of braking or the ability of the car to turn at various speeds.
General rules:
Lower nose= less air underneath the nose so it has more direct initial turn in.
Front vs rear ride height= the more rake the more the rear will rotate, for high speed stability you drop the rear 5mm or so. Very small adjustments here make huge differences
The rear steering masks a lot of the old problems inherent in track setup for a GT3/RS.
But the proper rake and nose height makes the car more reactive to the wheel. You also have to coordinate the sway bars to make sure that the rear grip is not overly compromised.
General rules:
Lower nose= less air underneath the nose so it has more direct initial turn in.
Front vs rear ride height= the more rake the more the rear will rotate, for high speed stability you drop the rear 5mm or so. Very small adjustments here make huge differences
The rear steering masks a lot of the old problems inherent in track setup for a GT3/RS.
But the proper rake and nose height makes the car more reactive to the wheel. You also have to coordinate the sway bars to make sure that the rear grip is not overly compromised.
I'm a bit surprised no one mentioned the risk to the front strut towers when lowering the GT3, though perhaps that wasn't as well understood over a year ago when this thread started. Both the GT4 and GT3 have proven vulnerable to catastrophic failure of the strut tower (see here GT3 and here GT4). The GT3 and 4 suspension travel is by design relatively short, and cutting that travel by further lowering the car is one of the surest ways to reduce margin and significantly increase your chances of a failure. Rubbing the front splitter is cheap and largely cosmetic; a pothole or curb encounter that fractures your tub is the opposite.
If you can get over that risk there are a couple other things to keep in mind. Lowering the front of the car lowers the front roll center height (RCH) disproportionately due to the strut suspension up front. The effect is largely what CJ mentioned- the car is more "direct" on turn in because the CG has more mechanical advantage over the suspension. Effectively the suspension gets softer, which is likely also the reason he also mentions countering this with increased front swaybar. Meanwhile the rear suspension is a multi-link, which means RCH doesn't drop as quickly when you lower it so little if any adjustment is required. However both the front and rear suspensions bring the bump stops into play relatively early, so as you lower the rear you unwittingly start to increase dynamic spring rate which can have unexpected effects.
If you do lower things I'd go easy and with a proven front and rear setup for the above reasons. I would also plan to corner balance- on softly sprung cars corner-balancing can be largely a waste of time, but the GT3's sprung relatively stiffly and thus has much less margin for error.
If you can get over that risk there are a couple other things to keep in mind. Lowering the front of the car lowers the front roll center height (RCH) disproportionately due to the strut suspension up front. The effect is largely what CJ mentioned- the car is more "direct" on turn in because the CG has more mechanical advantage over the suspension. Effectively the suspension gets softer, which is likely also the reason he also mentions countering this with increased front swaybar. Meanwhile the rear suspension is a multi-link, which means RCH doesn't drop as quickly when you lower it so little if any adjustment is required. However both the front and rear suspensions bring the bump stops into play relatively early, so as you lower the rear you unwittingly start to increase dynamic spring rate which can have unexpected effects.
If you do lower things I'd go easy and with a proven front and rear setup for the above reasons. I would also plan to corner balance- on softly sprung cars corner-balancing can be largely a waste of time, but the GT3's sprung relatively stiffly and thus has much less margin for error.
05-14-2019, 07:01 PM
#36
Here in the US 8mm would probably reduce the size of the bump you could hit before the failing the chassis by ~15%, and that 15% decrease might double (??) the number of road hazards you're likely to encounter that would be large enough to cause an issue? Hugely back of napkin... but if it makes you more vigilant you might not be at any greater risk?
05-14-2019, 07:32 PM
#37
Rennlist Member
You're not in Germany, I assume. There I'd say no to avoid throwing off aero balance- too much downforce in front = instability at speed.
Here in the US 8mm would probably reduce the size of the bump you could hit before the failing the chassis by ~15%, and that 15% decrease might double (??) the number of road hazards you're likely to encounter that would be large enough to cause an issue? Hugely back of napkin... but if it makes you more vigilant you might not be at any greater risk?
Here in the US 8mm would probably reduce the size of the bump you could hit before the failing the chassis by ~15%, and that 15% decrease might double (??) the number of road hazards you're likely to encounter that would be large enough to cause an issue? Hugely back of napkin... but if it makes you more vigilant you might not be at any greater risk?
05-14-2019, 10:01 PM
#38
Race Director
When i look at 991 gt3 cup cars..like the ones in the IMSA GT3 cup challenge...they seem to run a flatter lower rake. I'd love to know the height difference from front to back on these cars. I know there suspension is different than my street .2 GT3....and as CJ pointed out I have rear steer and that keeps the rear more planted...but it's interesting.
Also the GT3 and RS that set the Road Atlanta records were lowered and appeared to run a flatter rake.
Thoughts?
Also the GT3 and RS that set the Road Atlanta records were lowered and appeared to run a flatter rake.
Thoughts?
05-14-2019, 10:04 PM
#39
Rennlist Member
When i look at 991 gt3 cup cars..like the ones in the IMSA GT3 cup challenge...they seem to run a flatter lower rake. I'd love to know the height difference from front to back on these cars. I know there suspension is different than my street .2 GT3....and as CJ pointed out I have rear steer and that keeps the rear more planted...but it's interesting.
Also the GT3 and RS that set the Road Atlanta records were lowered and appeared to run a flatter rake.
Thoughts?
Also the GT3 and RS that set the Road Atlanta records were lowered and appeared to run a flatter rake.
Thoughts?
05-14-2019, 11:23 PM
#40
When i look at 991 gt3 cup cars..like the ones in the IMSA GT3 cup challenge...they seem to run a flatter lower rake. I'd love to know the height difference from front to back on these cars. I know there suspension is different than my street .2 GT3....and as CJ pointed out I have rear steer and that keeps the rear more planted...but it's interesting.
Also the GT3 and RS that set the Road Atlanta records were lowered and appeared to run a flatter rake.
Thoughts?
Also the GT3 and RS that set the Road Atlanta records were lowered and appeared to run a flatter rake.
Thoughts?
For street cars with existing aero packages rake has a more straightforward impact. Up front reducing ride height makes more front downforce (good if you can balance it with the wing) and makes that downforce more ride-height sensitive (bad).
If you could get those record run setups that’d be a very good place to start...
F1 cars are a whole different ballgame- Newey’s book goes into it in some detail, and it’s very clear how complex the interactions are. Even when what you’re doing is in plane sight it’s often the case that other teams can’t re-create it.
05-15-2019, 04:39 AM
#41
Platinum Dealership
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Originally Posted by Brian Himmelman
Would you advise a 8mm lowering of front suspension on a 991.2 GT3 for appearance ? Any warnings
03-15-2020, 09:11 AM
#42
Would it handling closer to the RS with great turn in ? Thanks
03-16-2020, 04:55 PM
#43
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