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Fighting understeer - looking for ideas

Old 10-17-2018, 01:59 PM
  #16  
yoramw
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Originally Posted by Cloud9...68 View Post
You didn't mention how experienced a driver you are, so I'm not going to make any assumptions, but before making any adjustments to you car, I would take stock of your technique. For example, could you be overloading the front tires by turning too abruptly into the corners? I thought I had an understeer issue which was mysteriously only manifesting in a particular corner, when an instructor recommended I be a little more patient in that corner and delay my turn-in slightly, based on his observation from the side of the track. That simple adjustment made a big difference. I can also provoke power oversteer if I mash the throttle too abruptly on corner exit, which tells me my car is pretty well balanced. It's odd to me that a car that comes with a staggered set-up from the factory that you've converted to a square set-up (which I also have, by the way), would understeer.
I have about 20 track days done with my 944 in the two and half years of ownership. a couple with an instructor.
I get good feedback from instructors, so I would say I am at least intermediate if not better.
I do work on two things at the moment that can help. one is heel and toe work with barking into the corner (instead of finishing the braking and gear shift if need before turning the wheel).
The second skill I am focusing on is apply more gradual steering input going into the turns.

I do feel mainly in 3rd gear long corners that once I am set with the steering input I cannot accelerate even slightly mid turn without suffering significant understeer. Even maintaining speed keeps me in a slight understeer.

The two scenarios that I can get oversteer with the car are:
1. braking/downshifting without proper rev matching into a turn or mid turn.
2. accelerating in hairpin type corners in 2nd gear

From what I know and even from what I felt before some work on the car, our cars love some light acceleration through these type of corners after the car is set in the turn.
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Old 10-17-2018, 02:09 PM
  #17  
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Originally Posted by jerome951 View Post
To Yoramw, can you describe in which stage of the corner it understeers? Entry? At apex under neutral throttle? Exit? Are you trail braking when you experience understeer?
Even with really stiff springs all around, my car will understeer when I go WOT after the apex because the front gets light. I'm OK with that as I can anticipate and adjust my line accordingly and not lift.

I'm also a firm believer of focusing on the end of the car that is loosing grip to achieve balance, rather than adjusting the opposite end for less grip. Adjusting the opposite end may yield balance but reduces overall cornering ability. So, in your case, you could consider in the front: more aggressive negative camber; reduce spring rate; switching back to the stock sway bar. Or adjusting your driving style depending on when the understeer occurs.

Also what tires and pressures are you running? With some tires, a 3-4 psi change makes a big difference in grip.
When I brake properly into the corners, turn-ni is fine and no understeer there.
a little before the apex when the car is already set in the turn and under neutral throttle, it understeers. If I try to slightly accelerate at that point, obviously the understeer becomes more significant.
I tried attacking the same corner with different level of steering input to try to bring traction to the front wheels, but no matter which line I try and how much steering input I apply, I either have to decrease speed or enter the corner slower to eliminate the understeer.

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Old 10-17-2018, 02:15 PM
  #18  
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Originally Posted by 951and944S View Post
Put the car on scales, until you know the weight each corner is carrying, everything else is moot.

A properly corner balanced car is the base you should be starting from.

T
That makes total sense to me.
My alignment show has only axle scale so I just measured the front to rear weight with me in the car.
It was about F:51% R:49% with ~1/2 tank of fuel the last time I paid them a visit.

Is 50/50 really the ideal for our cars?

Last edited by yoramw; 10-17-2018 at 02:48 PM.
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Old 10-17-2018, 09:53 PM
  #19  
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Originally Posted by yoramw View Post
That makes total sense to me.
My alignment show has only axle scale so I just measured the front to rear weight with me in the car.
It was about F:51% R:49% with ~1/2 tank of fuel the last time I paid them a visit.

Is 50/50 really the ideal for our cars?
F/R won't really tell you all..., what you need to know is what amount of weight each corner is carrying.
If, for example RF spring is carrying +10-20%, it also loads the LR, you can envision the effect of this by imagining a table with unequal legs, if you place 200# on the table, not all legs are equally supporting the weight.
That's a static example.
In a car that has to transition left to right, it handles better in one direction than the other.
Turning left (with above ex) will be immediate and responsive, where turning right will be delayed as in rocking the table onto the shorter leg before the car can change direction.
Changing bars, settings, ride height, pressures, spring rates etc., etc are band aiding an improper foundation.
Your aim for F/R matching wheel width is sound and 245 is a stretch for 7" wheels.
Keep your eyes peeled for some 8" dials.

T
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Old 10-17-2018, 09:59 PM
  #20  
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BTW, which rear torsion bar....?
What's the effective rate of the rear stock torsion bar you have...?

You only really added around 165# effective rear coilover spring, depending on rate of your original torsion bar, you could very well be under sprung at rear.

T
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Old 10-18-2018, 02:16 AM
  #21  
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Originally Posted by 951and944S View Post
BTW, which rear torsion bar....?
What's the effective rate of the rear stock torsion bar you have...?

You only really added around 165# effective rear coilover spring, depending on rate of your original torsion bar, you could very well be under sprung at rear.

T
As far as I can tell I have the original Turbo torsion bar (23.5mm according to Clarks Garage site).
I am not sure how the math is done for balancing the springs. My front springs are 350 and rear are 275. Does that seems balanced with the original torsion bar?

Yoram
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Old 10-18-2018, 09:43 AM
  #22  
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Originally Posted by yoramw View Post
As far as I can tell I have the original Turbo torsion bar (23.5mm according to Clarks Garage site).
I am not sure how the math is done for balancing the springs. My front springs are 350 and rear are 275. Does that seems balanced with the original torsion bar?

Yoram
According to chart at Paragon Products,

23.5mm has effective rate of 126#

Your rear coilover spring at 60% effective = 165# (275 x .60)

SO your rear should be 126 + 165 = 291

This car is set up to be biased to understeer.

You need a 350# rear spring + the current torsion bar , would yield 336R to match the current front at 350 x .94 = 329F

T
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Old 10-18-2018, 02:12 PM
  #23  
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Thanks.
This makes sense to me.
I will get stiffer rear springs and test how it feels.

BTW, the setup was suggested by Gaz when I purchased my Gaz Gold coilover set (I asked for a set to give the car natual handling).
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Old 10-18-2018, 04:19 PM
  #24  
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Originally Posted by yoramw View Post
Thanks.
This makes sense to me.
I will get stiffer rear springs and test how it feels.

BTW, the setup was suggested by Gaz when I purchased my Gaz Gold coilover set (I asked for a set to give the car natual handling).
What's your approximate location...?

Which tracks...?

Which GAZ version do you have...?

T
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Old 10-18-2018, 05:29 PM
  #25  
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I have Gaz Gold F & R coilovers.

I am based @ Israel.
We currently have three tracks in Israel.
Two are short, very technical/low speed (less than a mile long. I get there up to 70-75 MPH top speed) - Arad & Fatzael.
The third one is longer (although in USA terms still short - about 1.4 Miles) with longer straights. (I get there up to 100-110 MPH) - Motorcity

The first two also have more vertical elevation changes and asphalt is not very smooth, so there are a lot of shocks movements

Arad

Fatzael

Motorcity


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Old 10-18-2018, 07:57 PM
  #26  
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Nice, after I posted, I remembered that I think we traded some PMs..?

Never would have thought Israel would be so big into tracking cars (not sure why), so it's nice to see you even have multiple options.
That turn at lower right in the jpeg of Motorcity looks open to 20 different racing line interpretations....
A 944 should do fine there and the sweepers at Fatzael.

SO yes, up those rear springs.

If you have the shocks with remote canister, + xpsi = x increase in spring rate but no way you'd ever get +75# to the 350 Rr you need.

T
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Old 10-19-2018, 03:31 AM
  #27  
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That's right. I know remember too. Thank you for taking the time to contribute to this thread.

The 944 loves the Sweepers at Fatzael.
As for that turn on Motorcity, it is quite tricky and I can't say I nailed it yet.
I come at almost 110MPH to it. just before the turn there is an elevation gain of about 3-4 feet and then right after it, a similar drop.
At the moment, I still struggle to find the best line for it.

I am aiming at a very late braking into the corner (~110 => ~35) staying on the outside as long as it allows me and then do a tight turn still with trail braking to a very late Apex which makes the next turn almost a straight line downhill.
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Old 10-23-2018, 06:52 PM
  #28  
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Quick update,

The 350 springs arrived yesterday and I just finished installing it and did a quick test drive in my area.
It feels much better, but the real test will be when I get it back to the track.

I scheduled a track day for next week and I am sure it will be a blast.

Thanks!
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Old 10-23-2018, 07:15 PM
  #29  
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Sounds good, I remember you don't have the 30mm F bar but hole in the middle of the Rr 19mm is as good a place to start as any.
Car should be neutral even in a 4 wheel slide.
Good luck,

T
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Old 10-25-2018, 08:25 PM
  #30  
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225 on a 7x16 wheel is part of your problem.. you are getting into the sidewall too much and it is too soft on a 16" tire. drop to 205 and you will see a huge improvement.
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