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Set -Up Diagnoses


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#1 gabuck

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Posted Apr 15 2012 - 05:08 AM

I can usually diagnose the simple handling problems such as snap oversteer or terminal understeer/oversteer but not the more complicated stuff. For example why if I'm getting oversteer in a corner and I lift off a fraction do I get bad understeer? Or if I go into a corner I start to get a pendulum effect? I think it's about damper settings but don't understand what is happening or what to do. And I can't really see what front toe in/out does.

I remember a long time ago seeing a really good article on a site which was about diagnosing handling problems and explaining how to set-up cars. Any ideas where it might be - but it was before 69Mod and wings.

Geoff

#2 John Woods

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Posted Apr 15 2012 - 07:35 AM

Oversteer to understeer sounds like differential.
I use 45/60/6 for big flat tracks like Monza and 45/60/1-2-3 for twisty tracks like The Ring.
If the diff is changed, brake bias likely needs some tweaking, depending on brake use and technique..
Pendulum effect sounds like ARBs and maybe shock rebound together with bad toe, (which is maybe like trimming yaw when in a small airplane).
Negative front toe causes slight understeer.
Slight positive front toe stabilizes car on straights.
Lately I have zeroed out camber and toe and only balance ARBs with shocks and tire pressure.
Many have noted using excessive ARB and toe settings provides benefits without issues because of GPL physics being not entirely accurate.
For general reference, I rely on BrunoB's Simple Setup Method.

Check www.gpllinks.org for lots more setup and driving technique advice.

And as always, anything I post is just a question and a guess.

Edited by John Woods, Apr 15 2012 - 02:50 PM.


#3 Andy Clegg

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Posted Apr 16 2012 - 08:55 AM

I've been using Paul Jackson's setups off the Speedgeezer website. John, where is Bruno B setups please?

Edited by Andy Clegg, Apr 16 2012 - 08:56 AM.


#4 John Woods

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Posted Apr 18 2012 - 11:28 PM

View PostAndy Clegg, on Apr 16 2012 - 08:55 AM, said:

I've been using Paul Jackson's setups off the Speedgeezer website. John, where is Bruno B setups please?

Hey Andy,

BrunoB published the easy setup method awhile back on blackholemotorsports, but it disappeared, so thankfully Arturo P posted it here:

BrunoB's Setup Method

Its not setups. Its about how to make your own and get the most grip, or diagnose and correct why a setup isn't working for you.

Edited by John Woods, Apr 18 2012 - 11:32 PM.


#5 Andy Clegg

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Posted Apr 19 2012 - 01:09 AM

I've got that many ways to set up a car on the computer that I get lost. I figure that a lot of it is how you drive the cars. Thanks to yourself and Arturo. I'll download this now in case I forget.

#6 Ophitoxaemia

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Posted Jul 03 2014 - 03:15 PM

I like the setup guide for tuning static state turning, but one problem with it is that a car doesn't usually understeer vs oversteer the same through an entire corner. For example, it might oversteer on entry and understeer on exit. It will likely be different on and off throttle. This is where the shocks settings come into play, controlling the speed that weight transfer occurs during the braking and transition to throttle stages. And of course, the diff has a huge effect on a starting point. It's easy to select a diff that understeers on entry, then oversteers like crazy on throttle. Do I decide that is oversteer or understeer?

Thoughts?

#7 MECH

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Posted Jul 03 2014 - 03:48 PM

I thought that the amount of understeer on corner entry relates to corner exit oversteer.
E.g. if you have less understeer entering the amount of oversteer should decrease aswell because steering input is less.
So it's cause of what you have setup for corner entry e.g. understeer. But that's just imho :)

#8 John Woods

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Posted Jul 05 2014 - 05:13 PM

View PostMECH, on Jul 03 2014 - 03:48 PM, said:

thought that the amount of understeer on corner entry relates to corner exit oversteer. :)

What the coast side might be doing may not symmetrically correlate to what the power side does?

Diffs cause push.
Here's another link to the Vari-loc Diff Tuning Guide.
There's a diff guide for GPL by Neils H that was on SRWorld.
Where is it now...?

Also, Alison Hine noted the necessity of tuning the diff and brake balance.

Edited by John Woods, Jul 05 2014 - 05:43 PM.


#9 Pete Gaimari

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Posted Jul 05 2014 - 05:38 PM

85/85/1 would certainly turn it much better than 30/30/6.

#10 John Woods

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Posted Jul 10 2014 - 07:38 AM

View PostMECH, on Jul 03 2014 - 03:48 PM, said:

thought that the amount of understeer on corner entry relates to corner exit oversteer.

The more I think about it, the more I think I agree, even tho I didn't exactly disagree, just wasn't sure.
:)
Still not so sure tho. For a given setup, reducing understeer on entry would reduce oversteer on exit? Can kindof see that making sense.
My theory is neutral during entry, (goes where toe setting points it),  and slight throttle-induced oversteer on exit, so I can steer front into track camber and still go "straight."

Edited by John Woods, Jul 10 2014 - 07:39 AM.


#11 jgf

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Posted Jul 10 2014 - 09:16 AM

One issue with determining an understeer/oversteer condition is that a strong understeer can be misdiagnosed as oversteer - you turn the wheel more and more till the lateral grip of the front tires exceeds the rolling grip and the car snaps around.  You assume an oversteer because you spun.

As for the pendulum effect, I've found increasing the front bar usually alleviates this.

#12 John Woods

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Posted Jul 12 2014 - 08:56 AM

View Postjgf, on Jul 10 2014 - 09:16 AM, said:

As for the pendulum effect, I've found increasing the front bar usually alleviates this.

Agree pendulum motion is lack of harmony between spring and bar.

The bar is not capable of sustaining its effect on outside wheel?
The spring is free to bounce around beyond the bar''s limit?
So in this example, reducing front spring would work as well?
Could this effect also be caused by messed up rear?
Or maybe shocks too soft in rebound?

If only one bar is changed, steering balance changes with it?
To maintain steering balance, bars are changed together and in opposition?
So changing front bar to eliminate pendulum will likely require rear bar redial of steering?

#13 Pete Gaimari

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Posted Jul 12 2014 - 02:16 PM

Driving style can fool you on what a setup will do too. Letting the car coast into the apex will let it turn free with no understeer, but get on the throttle too early before the apex can turn into understeer.

Some drivers can overheat the front tires from understeer while another driver with the same setup can keep the tires cool.

#14 jgf

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Posted Jul 13 2014 - 07:57 PM

View PostJohn Woods, on Jul 12 2014 - 08:56 AM, said:

View Postjgf, on Jul 10 2014 - 09:16 AM, said:

As for the pendulum effect, I've found increasing the front bar usually alleviates this.

Agree pendulum motion is lack of harmony between spring and bar.

The bar is not capable of sustaining its effect on outside wheel?
The spring is free to bounce around beyond the bar''s limit?
So in this example, reducing front spring would work as well?
Could this effect also be caused by messed up rear?
Or maybe shocks too soft in rebound?

If only one bar is changed, steering balance changes with it?
To maintain steering balance, bars are changed together and in opposition?
So changing front bar to eliminate pendulum will likely require rear bar redial of steering?

Reducing the front spring would probably exacerbate the problem.  The issue, I believe, is too much steering response - the car gets a bit out of line and you correct slightly but the front wheels overcompensate, you countersteer and the front overcompensates in the other direction.  You end up seesawing the wheel as the car does its pendulum bit until it, usually, spins.  Increasing the front bar reduces the front grip and the steering sensitivity while also making the steering more precise.  I've found this works across the board - GPL, GTL, GTR2, N2003.




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