TORSION BAR QUESTION?
09-01-2010, 11:12 AM
#46
Addict
Rennlist Member
Rennlist Small
Business Sponsor
Rennlist Member
Rennlist Small
Business Sponsor
I think I have found the proper way to pass the guy in front of you in your video.
http:// www.youtube.com/watch?v=mzFgGcfgjZ0
http:// www.youtube.com/watch?v=mzFgGcfgjZ0
09-02-2010, 02:45 AM
#47
Three Wheelin'
There is some difference when running combined t-bars w/ helper springs vs. straight t-bars, vs straight springs. Some depends on how the t-bars are indexed when used with helpers. As once the t-bar passes the neutral index point, its spring rate becomes subtractive to the helper instead of additive. Inside wheel in a corner, as the car body is lifting off the suspension, the coil spring is pushing upward and the torsion bar will be trying to pull the trailing arm back to neutral (if the t-bars are indexed neutral at ride height).
To put it another way, the slope of the spring rate graph (force versus displacement) remains the same whether the spring is in compression or in tension.
Best regards,
Mike Spence
09-02-2010, 07:19 AM
#48
Three Wheelin'
09-02-2010, 09:15 AM
#49
Rennlist Member
Thread Starter
The passenger seat is a nice feature. What are the two red nuclear missile launching switches on the center console, ABS reset and/or?
You are fighting the steering wheel a little to get the car turned in, but not bad. I have seen worse. I don't hear the front tires squealing. What tires are you using?
Pretty technical track, and a lot of tight/slow turns.
A couple thoughts:
Track is quite wide and allows some choice in line thru several of the turns and series of turns, which does give you some options and ability to adjust your driving style and line to the car's handling. Would be helpful to do a lot of comparison with data (now that you have it).
Is your car at or near full stock weight? The heavier it is, the more inherent push it will have in tight turns.
Looking at the video (which is difficult to assess), I certainly would consider setting the car up to rotate well (more rear spring/bar to be able to induce and control some mild oversteer). And also play with the adjustable dampers. The jounce and rebound adjustments allow some ability to play with turn-in characteristics independent to track-out. In theory, you would like to get the tail to rotate on turn-in but then tuck back in on track-out when you get back on the power.
You really want the front to turn in well, and I can see why you are concerned about push; too much understeer would hurt the car on this track.
Likely some option to do some deep trail braking in some to many of the corners. If the car gets too tail happy for the high speed corners, you may have to use a later apex those turns.
A lot of shifting required. Almost seems like a regular 951 3.375 R/P would be better suited for this track?
You are fighting the steering wheel a little to get the car turned in, but not bad. I have seen worse. I don't hear the front tires squealing. What tires are you using?
Pretty technical track, and a lot of tight/slow turns.
A couple thoughts:
Track is quite wide and allows some choice in line thru several of the turns and series of turns, which does give you some options and ability to adjust your driving style and line to the car's handling. Would be helpful to do a lot of comparison with data (now that you have it).
Is your car at or near full stock weight? The heavier it is, the more inherent push it will have in tight turns.
Looking at the video (which is difficult to assess), I certainly would consider setting the car up to rotate well (more rear spring/bar to be able to induce and control some mild oversteer). And also play with the adjustable dampers. The jounce and rebound adjustments allow some ability to play with turn-in characteristics independent to track-out. In theory, you would like to get the tail to rotate on turn-in but then tuck back in on track-out when you get back on the power.
You really want the front to turn in well, and I can see why you are concerned about push; too much understeer would hurt the car on this track.
Likely some option to do some deep trail braking in some to many of the corners. If the car gets too tail happy for the high speed corners, you may have to use a later apex those turns.
A lot of shifting required. Almost seems like a regular 951 3.375 R/P would be better suited for this track?
The two switches are so we can go between pump and E85...dare I say, at the flick of a switch. Well that's the party line. Actually they're missiles set on Boxters and GT3s...but keep that to yourself.
Car is about 2860lbs with full tank, no driver. I'm about 185lbs. No cage though. That is still to come. Just a harness bar, but there's still a bit of weight to come out of the car too. I would like to take out at least as much as the cage going in.
Tyres are Nitto NT01 275x18 all 4 corners. I like 'em very much. They almost feel as fast as R6s.
Yes there is still some tuning to be done regards the suspension and dampers. On that video I am still on my old setup of the softer front springs and rear T bars / helpers. With the new setup as mentioned previously (stiffer coils all round) this will change things. Did a trackday yesterday and in general the car felt better through pretty much all the turns. I took a couple of different lines as well, but perhaps was 'allowed' to with the new stiffer springs. They certainly seemed to take a set earlier in the turn.
In as far as tuning the car as 2 separate halves, I'm in two minds about this. (Did that just sound a tad ironic). I have always felt like I didn't want to 'fool' the nose in coming around by stiffening up the rear too much. Thinking that this would have some negatives like snap oversteer under trail and exit...but both you and Chris seem to advocate this. Not to say we haven't screwed up the rear sways or shocks to try before. Perhaps it's just a symptom of going faster and coming into corners quicker. A certain amount of patience is needed.
Having said that, I had a pro drive my car yesterday and very quickly found the limits. I learnt a few things too which is always great. One thing that seems constant amongst them (especially those with Cup Car history) is that they seem to grab an early entry and just try and hug the apex with the talent they possess. He definitely showed me some new ways of taking on some corners and just the way they brake with a more solid first push rather than a gradual application. Unfortunately I'm about 5'10" and he's probably 6'4" and couldn't fit into the car properly so had some issues changing gears a couple of times. Left it in 3rd sometimes. The wheel getting his left leg stuck a bit so not great.
This was just a mid week DE sort of day so you get all standards out there. Some quick cars and some beginners on street tyres.
http://vimeo.com/14636523
So overall it felt like some of the turn in issues had dissipated with the new springs. Plenty more work to be sorted. Not sure about the stock R&P. I'd like to try it, but overall I still think the shorter S2 is advantageous.
Last edited by 333pg333; 09-02-2010 at 09:33 AM.
09-02-2010, 09:25 AM
#50
Rennlist Member
Thread Starter
09-02-2010, 09:29 AM
#51
Rennlist Member
Thread Starter
I was just at Watkins Glen with Ross last week….! Interesting guy, I like some of his driver ideas…but some are a little too far out there for me.
So – on to the video –
1) The non Porsche guy is quite the ‘tosser’ (non driving technical term)
2) Nice ‘secret’ contraption!
3) Do most Aussie track go counter clockwise? Almost all US tracks are clockwise. Seems weird since it both favor the nonstandard (for the country) driver position!
4) One of my favorite driver quotes may help – “it is amazing how many drivers, even at the Formula One level, think that the brakes are for slowing the car down”
5) Once you get to the real upper levels for track driving you do most of the balancing in the corners with your right foot. Your set up will change a great deal as you master this.
There are some turns at Watkins Glen where the fast way through the corner is a abrupt turn in followed by lots of power to evoke a some oversteer and then manage the throttle, if you don’t you will understeer. The set up of the car for power though the corner is totally different than the ‘gentle’ method.
Of course the set up for racing vs time trial is different too….
So – on to the video –
1) The non Porsche guy is quite the ‘tosser’ (non driving technical term)
2) Nice ‘secret’ contraption!
3) Do most Aussie track go counter clockwise? Almost all US tracks are clockwise. Seems weird since it both favor the nonstandard (for the country) driver position!
4) One of my favorite driver quotes may help – “it is amazing how many drivers, even at the Formula One level, think that the brakes are for slowing the car down”
5) Once you get to the real upper levels for track driving you do most of the balancing in the corners with your right foot. Your set up will change a great deal as you master this.
There are some turns at Watkins Glen where the fast way through the corner is a abrupt turn in followed by lots of power to evoke a some oversteer and then manage the throttle, if you don’t you will understeer. The set up of the car for power though the corner is totally different than the ‘gentle’ method.
Of course the set up for racing vs time trial is different too….
2)Shhh....or they'll all want one!
3)No real pattern to the pattern.
4)Mario Andretti, no?
5)Steering with the right foot is pretty standard fare, but as you get better you just do it at a faster speed.
6)err...I'll get back to you...
09-02-2010, 09:34 AM
#52
Addict
Rennlist Member
Rennlist Small
Business Sponsor
Rennlist Member
Rennlist Small
Business Sponsor
Mario Andretti, yes.
09-02-2010, 09:38 AM
#53
Rennlist Member
Thread Starter
09-02-2010, 10:51 AM
#54
Rennlist Member
Hi Jim, this ain't so. Spring rates remain additive. The indexing/preload only affects the ride height. If you graph this (in Excel, for example) you'll see.
To put it another way, the slope of the spring rate graph (force versus displacement) remains the same whether the spring is in compression or in tension.
Best regards,
Mike Spence
To put it another way, the slope of the spring rate graph (force versus displacement) remains the same whether the spring is in compression or in tension.
Best regards,
Mike Spence
Think about it again. Define the coordinate system about the neutral axis/index point of the torsion bar. Positive spring rate slope when displacement is positive, negative spring rate slope when the displacement is negative.
In theory, same would be true of a coil spring in tension or compression, but in reality the coilover cannot act in tension as installed in the 944 rear suspension.
Picture the car on the lift with the rear suspension at droop (t-bar at unloaded neutral index point). Pushing up on the trailing arm creates a reactive downward force from the t-bar. Pull down the the trailing arm and the t-bar resists that motion with an opposite upward force.
So, when the suspension is loaded, it creates a combined/additive spring rate of the coil and t-bar. When the suspension is unloaded, once the suspension travel passes the neutral index point of the torsion bar, the torsion bar acts against the coil spring.
Some believe it is important to take advantage of this when setting up 944s. They intensionally leave the t-bars in, indexed neutral at ride height. Their belief is that this reduces rear end rise under braking and rear inside lift in hard cornering.
I have done plenty of charting and graphing of effective spring rate setups, including index angles of the torsion bars. Have also swapped and indexed plenty of sets of torsion bars. And I am not convinced that it makes a noticeable improvement in the car's handling, compared to indexing the t-bars with a preload at ride height. And for what its worth, there are factory notes burried in some of the Cup literature that states the t-bars on the Cup cars were indexed at a 9 deg preload when used with the coilover shocks.
I only made reference to that setup effect because Patrick commented that his car felt different when removing the t-bars, although having the same effective rate balance.
09-02-2010, 07:35 PM
#55
Three Wheelin'
Hi Jim, I agree that the FORCE can be additive or subtractive, however the rate remains constant. F=-kx for a linear spring, whether in compression or tension. The slope remains the same.
Put more simply: Hooke's law states that the rate of a linear spring remains constant, independent of the displacement - whether positive or negative. For linear springs in parallel, k(eq) = k(1) + k(2), irrespective of displacement.
Where I see that torsion bar preload would make a difference, is where there is a non-linear component to the rate. This would be the case for a torsion bar supported in rubber bushes, as the rubber has a non-linear rate which would create a "wobble" in the force/displacement chart about the crossover point. This effect is exacerbated by any play in the system.
Cheers,
Mike
Put more simply: Hooke's law states that the rate of a linear spring remains constant, independent of the displacement - whether positive or negative. For linear springs in parallel, k(eq) = k(1) + k(2), irrespective of displacement.
Where I see that torsion bar preload would make a difference, is where there is a non-linear component to the rate. This would be the case for a torsion bar supported in rubber bushes, as the rubber has a non-linear rate which would create a "wobble" in the force/displacement chart about the crossover point. This effect is exacerbated by any play in the system.
Cheers,
Mike
Last edited by mikey_audiogeek; 09-02-2010 at 07:46 PM. Reason: typo
09-02-2010, 09:51 PM
#56
Drifting
David Wall can really drive, i counted 2 laps at 1:46 with traffic. I can see time there for both of us
09-02-2010, 10:47 PM
#57
Rennlist Member
Thread Starter
Yes the amazing thing is how quickly he gets up to speed and the limits of all these different cars they just hop in and out of all day at these events.
Sure there is a 1.45 in the car, maybe a 1.44...if he's driving it. I'll work on a 1.46 for the time being. You'd better do the same!
Oh, this was on the Hoosiers with 295s out back so he should have had a bit more grip than my 1.47 on R spec, although I do like these Nittos a lot.
Sure there is a 1.45 in the car, maybe a 1.44...if he's driving it. I'll work on a 1.46 for the time being. You'd better do the same!
Oh, this was on the Hoosiers with 295s out back so he should have had a bit more grip than my 1.47 on R spec, although I do like these Nittos a lot.
09-03-2010, 01:28 AM
#58
Rennlist Member
I had a pro drive my car yesterday and very quickly found the limits. I learnt a few things too which is always great. One thing that seems constant amongst them (especially those with Cup Car history) is that they seem to grab an early entry and just try and hug the apex with the talent they possess. He definitely showed me some new ways of taking on some corners and just the way they brake with a more solid first push rather than a gradual application.
So overall it felt like some of the turn in issues had dissipated with the new springs. Plenty more work to be sorted. Not sure about the stock R&P. I'd like to try it, but overall I still think the shorter S2 is advantageous.
So overall it felt like some of the turn in issues had dissipated with the new springs. Plenty more work to be sorted. Not sure about the stock R&P. I'd like to try it, but overall I still think the shorter S2 is advantageous.
09-03-2010, 02:57 AM
#59
Rennlist Member
Thread Starter
Not anything revealing. He mentioned that it felt a little laggy coming out of a couple of corners in 3rd and replied to me stating that you needed to wait a moment in some of the tighter turns before being able to power on, by saying that you just had to wait and get the nose in before applying power. Simple stuff, but funnily enough I reckon he did this mostly through braking, not steering.
I went out after he drove and started to try a couple of different things. Unfortunately I flat spotted the front left Hoosier to death coming into T2. I figure I must have been going faster than before and got caught out. Good lesson.
I went out after he drove and started to try a couple of different things. Unfortunately I flat spotted the front left Hoosier to death coming into T2. I figure I must have been going faster than before and got caught out. Good lesson.
09-03-2010, 06:23 AM
#60
Addict
Lifetime Rennlist
Member
Lifetime Rennlist
Member
