Effects of 25lb spring change on push?
02-09-2010, 09:30 PM
#31
Three Wheelin'
I would be careful about specific set up advice on the internet unless from someone in my area that undertsood my tracks and had an identical car and/or pro experience. I remember back in the day one of my buddies took some advice on set up from someone that spent 80-90% of his time at Willows Springs. And the advice was for Sears Point. Hmmm....
Back in the day, folks like Milledge, the guys at KMR and many others had good set ups for many tracks on the pro circuits... and many were willing to share. Sure, there are ranges for things like camber for a specific tire, but to get a specific number on line and expect it to work... probably a longshot.
Don't take the safety stuff lightly. Wheel failures = bad. Spindle failures can be ugly. Control arm failures too. My two control arm failures were about 3 weeks apart, one at Candlestick Park in an AX, the other at Thunderhill. The latter was a failure of a freshly rebuilt Turbo S arm from a famous Porsche parts place (they are still in business). They knew what I was using it for as I discussed it with them when I arranged for the rebuild. At the time I was running a front Weightmeister bar and some hefty springs in the 350 - 400 range I think.
I had taken my fellow instructor, Scott, out for a ride that am. He had a nearly identical car, but with Fabcar arms he bought used. He had sheered a pin in one of those arms under braking in the corkscrew at Laguna Seca in the weeks between my two failures. No one got hurt. He spoke to Dave Klym about it, and Dave's theory was that the used arms Scott bought had counterfeit pins.
So here we are at Thunderhill and after I gave Scott a ride, I went out and got with the program. On the second or third lap, I felt vibration under braking in turn 1 (fast lefthander). Thought it was maybe a warped rotor... but I had huge rotors and big reds, so...??? Then car was fine in 2, a left hand sweep. Car had weird push in 3, a slow right hand turn. I thought something was wrong with the left front tire. Then fine through 4 and up the little hill. A left hand turn at the top, turn five. In a 951 you get the car pointed straight in 3rd gear and floor it., and wait for the boost to kick in going down hill as you start heading right toward turn 6.
Then kabloom on the way down the hill after 5. Left front wheel folded under the car (tore up the fender on the way). Spindle ripped from strut. Ripped the brake line open (so no brakes) and into the dirt. Big project to load on the flatbed and about $4k worth of damage.
The ball had torn out of the freshly rebuilt arm.
Called the famous Porsche parts place to warn them that they probably made an assembly mistake and to check their procedures so no one would get hurt. I was thinking about fellow drivers and the business' interests and giving them a heads up. Inquired about $$ for damage to my car. They got nasty and said there was something wrong with my car.
Eventually had to take legal action. Turns out my friend Scott, who had been in the car that am and who had a nearly identical car, is a pretty good lawyer. Settled short of court. $$ fell short of costs, but things could have been much worse. Still have the parts. Pasha came over and took pictures but never got them into Excellence.
I had decided on rebuilds after thinking about it for a long time. Made the wrong decision. After the big accident, I decided to pursue Charlie Arms which I heard about from Jeff Stone at KMR. So at his suggestion I called Jon Milledge... the first production units weren't ready yet from Charlie. So I called Dave klym... discussed stuff with him for a while... then bought a set of Fabcar arms. They were on the car for 2-3 months, then I got the first set of Charlie's. Sold the Fabcars as good used parts.
I bring all of this up because with the 944/951 family, it is important to consider some of this stuff in parallel with changes to suspension intended to improve handling. And for many, these can be competing budget items. 911 cars don't have the same type of failure prone front control arm/ball joint set ups but... mine busted a rear hub and stub axle under load at Thunderhill last June. Took the wife on one hell of a ride.
Be aware. Take care.
Back in the day, folks like Milledge, the guys at KMR and many others had good set ups for many tracks on the pro circuits... and many were willing to share. Sure, there are ranges for things like camber for a specific tire, but to get a specific number on line and expect it to work... probably a longshot.
Don't take the safety stuff lightly. Wheel failures = bad. Spindle failures can be ugly. Control arm failures too. My two control arm failures were about 3 weeks apart, one at Candlestick Park in an AX, the other at Thunderhill. The latter was a failure of a freshly rebuilt Turbo S arm from a famous Porsche parts place (they are still in business). They knew what I was using it for as I discussed it with them when I arranged for the rebuild. At the time I was running a front Weightmeister bar and some hefty springs in the 350 - 400 range I think.
I had taken my fellow instructor, Scott, out for a ride that am. He had a nearly identical car, but with Fabcar arms he bought used. He had sheered a pin in one of those arms under braking in the corkscrew at Laguna Seca in the weeks between my two failures. No one got hurt. He spoke to Dave Klym about it, and Dave's theory was that the used arms Scott bought had counterfeit pins.
So here we are at Thunderhill and after I gave Scott a ride, I went out and got with the program. On the second or third lap, I felt vibration under braking in turn 1 (fast lefthander). Thought it was maybe a warped rotor... but I had huge rotors and big reds, so...??? Then car was fine in 2, a left hand sweep. Car had weird push in 3, a slow right hand turn. I thought something was wrong with the left front tire. Then fine through 4 and up the little hill. A left hand turn at the top, turn five. In a 951 you get the car pointed straight in 3rd gear and floor it., and wait for the boost to kick in going down hill as you start heading right toward turn 6.
Then kabloom on the way down the hill after 5. Left front wheel folded under the car (tore up the fender on the way). Spindle ripped from strut. Ripped the brake line open (so no brakes) and into the dirt. Big project to load on the flatbed and about $4k worth of damage.
The ball had torn out of the freshly rebuilt arm.
Called the famous Porsche parts place to warn them that they probably made an assembly mistake and to check their procedures so no one would get hurt. I was thinking about fellow drivers and the business' interests and giving them a heads up. Inquired about $$ for damage to my car. They got nasty and said there was something wrong with my car.
Eventually had to take legal action. Turns out my friend Scott, who had been in the car that am and who had a nearly identical car, is a pretty good lawyer. Settled short of court. $$ fell short of costs, but things could have been much worse. Still have the parts. Pasha came over and took pictures but never got them into Excellence.
I had decided on rebuilds after thinking about it for a long time. Made the wrong decision. After the big accident, I decided to pursue Charlie Arms which I heard about from Jeff Stone at KMR. So at his suggestion I called Jon Milledge... the first production units weren't ready yet from Charlie. So I called Dave klym... discussed stuff with him for a while... then bought a set of Fabcar arms. They were on the car for 2-3 months, then I got the first set of Charlie's. Sold the Fabcars as good used parts.
I bring all of this up because with the 944/951 family, it is important to consider some of this stuff in parallel with changes to suspension intended to improve handling. And for many, these can be competing budget items. 911 cars don't have the same type of failure prone front control arm/ball joint set ups but... mine busted a rear hub and stub axle under load at Thunderhill last June. Took the wife on one hell of a ride.
Be aware. Take care.
02-10-2010, 12:27 AM
#32
Three Wheelin'
I might even suggest to the OP that adding MORE spring will help dial out the push. 400 is "soft" and you've gotta be at an optimal point before you can be assured that reducing/increasing spring rate will have the effect that all of the tuning books say it will. You may need MORE spring rate to control roll and keep the tire happy. If less spring rate was always the answer to increasing grip, we'd all be running 50 pound spring rates.
Do the 951's use Mac struts up front? If so, raising the front ride height to help put the front suspension in a better portion of the camber curve may be the answer. If it's anything like BMW's, you also actually increase roll tendency by lowering the front suspension (due to relationship between roll center and center of gravity...yes, it's true no matter what you've read about lower always being better), so without going to a much higher spring rate to help control the additional roll, raising the ride height up may actually help the front to roll over less, keeping the tire happier at it's current alignment setting.
Do the 951's use Mac struts up front? If so, raising the front ride height to help put the front suspension in a better portion of the camber curve may be the answer. If it's anything like BMW's, you also actually increase roll tendency by lowering the front suspension (due to relationship between roll center and center of gravity...yes, it's true no matter what you've read about lower always being better), so without going to a much higher spring rate to help control the additional roll, raising the ride height up may actually help the front to roll over less, keeping the tire happier at it's current alignment setting.
Mike
02-10-2010, 12:27 AM
#33
Burning Brakes
Thread Starter
Wow. Thanks Mahler. Sobering story.
BTW - agree with your thinking on internet advice. I take it as way posts to help guide my own plan. There are a lot of really smart folks out here and I appreciate their advice. But agree, you need to be able to sort the wheat from the chaff.
BTW - agree with your thinking on internet advice. I take it as way posts to help guide my own plan. There are a lot of really smart folks out here and I appreciate their advice. But agree, you need to be able to sort the wheat from the chaff.
Last edited by Jeff N.; 02-10-2010 at 12:45 AM.
02-10-2010, 10:20 AM
#34
Race Director
Jeff,
There is alot of good advice, but it also can be overwhelming.
There are 50 things you could do to the car, but you need to decide what fits in your budget and with the way you run the car.
The hard part is most of us don't know how hard you drive or the details of the tracks you drive.
There is alot of good advice, but it also can be overwhelming.
There are 50 things you could do to the car, but you need to decide what fits in your budget and with the way you run the car.
The hard part is most of us don't know how hard you drive or the details of the tracks you drive.
02-10-2010, 11:42 AM
#35
Burning Brakes
Thread Starter
Hi Joe, this is all really helpful as it gives me some idea of the available ***** I need to consider. My driving background is that I'm running DEs in the pacific northwest primarily at Pacific Raceways, Bremerton Raceways (airfield), with an occasional run at Spokane and, hopefully later this summer, Oregon Raceway Park. I'm a PCA and CCA instructor and will typically run A group. Get out to maybe 6 to 8 track days each season.
Had this car a couple years now. First efforts were focused on reliablity and am now trying to get smarter about the setup. Not much background in suspension setup details so I thought I'd ask here.
I think it's pretty clear the right way to do this is start a log, work from tire temps and do a series of planned adjustments. The value and trick has been to determine what adjustments to make.
Had this car a couple years now. First efforts were focused on reliablity and am now trying to get smarter about the setup. Not much background in suspension setup details so I thought I'd ask here.
I think it's pretty clear the right way to do this is start a log, work from tire temps and do a series of planned adjustments. The value and trick has been to determine what adjustments to make.
