tires vs springs
10-04-2014 | 10:10 AM
#31
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Joined: Oct 2002
Posts: 12,008
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From: Hyde Park, NY
The softer sidewalls of an under-inflated tire will give false sense of "more grip", but there actually isn't any more grip... Also, under-inflated tires tend to wear out the outside tread edge first, because of the sidewall roll-over.
If anyone has any of these symptoms, I encourage you to start upping your tire pressures. Go up a pound or two each session to give yourself time to get used to them. You'll be rewarded with longer tire life and faster lap times!
10-04-2014 | 02:58 PM
#32
Thread Starter
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Joined: Jan 2005
Posts: 346
Likes: 4
From: Seattle
As for Aero, it's a black art and it is highly undervalued and misunderstood. I've been lucky enough to have dealt with two highly regarded people and would be lucky to know about as much as they'd scrape off the bottom of their shoes, but it's well worth doing if you're serious about making massive inroads in your car's performance. In terms of return on investment it can't be beaten. There are a lot of mistakes being made out there though so it's definitely worth doing some research Or ask some other schmucks who've paid to do this themselves. 
Rich
10-05-2014 | 10:01 AM
#33
Drifting
Joined: Jan 2012
Posts: 2,883
Likes: 348
From: New York & Indiana
What 944, NA OR TURBO?
The car has over steer in braking and cornering and power on. Why???
The Koni 30 shocks have more rebound influence (harder) and more bump influence (harder) than the original Koni yellow single adjustables.
The additional help spring lets less load transfer to the rear under throttle, ie. less load on the rear tires, less friction, ie over steer.
What are the settings for bump and rebound on the rear shocks? If the rebound is too harder, higher number of clicks, then the rear under braking will not maintain sufficient tire contact patch and load, ie the car is now transferring load to the front and unloading the rear, causing over steer under braking,
IMO, the ill handling car is caused by improper suspension setup and cold tire pressures settings (to some extent)
First, I would remove the 100 lb help springs and stiffen some the anti-roll to compensate for the removal of the help springs. I would look at the settings for the F/R shocks in both bump and rebound. Make adjustments to correct the oversteer. For tire pressure influence, see Van's post.
What are the manufacturer of the anti-roll bars F and R? The diameter of the anti-roll bar has an influence on roll resistance and diagonal loading under turn-in and track-out. Shock settings can also have the same influence.
For what it is worth, I have a 944 NA with all the same suspension upgrades. The car has 944 Weltmiester anit-roll bars, 500 lb springs in the front and 31 mm hollow tube torsion bar in the rear, double adjustable Koni front shocks, Koni series 30 rear shocks.
The car is neutral under all conditions. Tires are 225/55/15 all around, either Toyo RA1 or Hoosier R6.
Tom
The car has over steer in braking and cornering and power on. Why???
The Koni 30 shocks have more rebound influence (harder) and more bump influence (harder) than the original Koni yellow single adjustables.
The additional help spring lets less load transfer to the rear under throttle, ie. less load on the rear tires, less friction, ie over steer.
What are the settings for bump and rebound on the rear shocks? If the rebound is too harder, higher number of clicks, then the rear under braking will not maintain sufficient tire contact patch and load, ie the car is now transferring load to the front and unloading the rear, causing over steer under braking,
IMO, the ill handling car is caused by improper suspension setup and cold tire pressures settings (to some extent)
First, I would remove the 100 lb help springs and stiffen some the anti-roll to compensate for the removal of the help springs. I would look at the settings for the F/R shocks in both bump and rebound. Make adjustments to correct the oversteer. For tire pressure influence, see Van's post.
What are the manufacturer of the anti-roll bars F and R? The diameter of the anti-roll bar has an influence on roll resistance and diagonal loading under turn-in and track-out. Shock settings can also have the same influence.
For what it is worth, I have a 944 NA with all the same suspension upgrades. The car has 944 Weltmiester anit-roll bars, 500 lb springs in the front and 31 mm hollow tube torsion bar in the rear, double adjustable Koni front shocks, Koni series 30 rear shocks.
The car is neutral under all conditions. Tires are 225/55/15 all around, either Toyo RA1 or Hoosier R6.
Tom
10-06-2014 | 03:48 PM
#34
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Joined: Feb 2003
Posts: 29,956
Likes: 180
From: saratoga, ca
This isn't actually true. Lower tire pressures - like 30 psi for Hoosiers - creates a lot more flexing in the tread carcass while the tire is rolling, which generates more heat, and will overheat the tire... Ever feel tires get "greasy" at the end of a session?
The softer sidewalls of an under-inflated tire will give false sense of "more grip", but there actually isn't any more grip... Also, under-inflated tires tend to wear out the outside tread edge first, because of the sidewall roll-over.
If anyone has any of these symptoms, I encourage you to start upping your tire pressures. Go up a pound or two each session to give yourself time to get used to them. You'll be rewarded with longer tire life and faster lap times!
The softer sidewalls of an under-inflated tire will give false sense of "more grip", but there actually isn't any more grip... Also, under-inflated tires tend to wear out the outside tread edge first, because of the sidewall roll-over.
If anyone has any of these symptoms, I encourage you to start upping your tire pressures. Go up a pound or two each session to give yourself time to get used to them. You'll be rewarded with longer tire life and faster lap times!
what I have seen is some of the slower guys, running the higher pressures and being very loose. the fastest guys , in WCGT , then, and our groups now, run with the tires being 30psi hot. these are the 1:29 to 1:31 guys at laguna. there is a possibility that the smaller sizes of tires, might like more pressure, but that's a guess on my part. Ive done temperature and pressure monitoring for a long time from the 35psi hot range to 28psi hot. when on the 35psi side, the centers are hottest. classic ,over pressure.
10-06-2014 | 03:58 PM
#35
Rennlist Member
Joined: Feb 2003
Posts: 29,956
Likes: 180
From: saratoga, ca
sorry for that one comment. yes, we are talking about fixing oversteer here.
i do think corner entry looseness can be helped by softer rear springs, but you really might need to get less rebound in the rear on the shocks.... if you cant do that , loosen that sway bar, but the easiest way is to get the larger tire i the back. you are undertired. coming from a guy that has raced this kind of balanced platform for many many years. funny though, you have an oversteer problem. usually, these cars push by nature.
i do think corner entry looseness can be helped by softer rear springs, but you really might need to get less rebound in the rear on the shocks.... if you cant do that , loosen that sway bar, but the easiest way is to get the larger tire i the back. you are undertired. coming from a guy that has raced this kind of balanced platform for many many years. funny though, you have an oversteer problem. usually, these cars push by nature.