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Rear sway bar stiffening


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I've got a factory 21mm rear sway bar on the car. I want to try to dial out some of the understeer, so stiffen the rear sway bar. There is plenty of room on the flat ends to drill another hole each side, thus shortening and stiffening the factory bar. I've got a tame engineer who probably has the right kit to drill hardened steel, has anyone tried this before?

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@Northy tried this and had problems with the drop link angles.

More camber and toe in at the front should reduce understeer. 

Mark

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Thanks Mark.

I already have adjustable drop links on there so shouldn't have the same issue as @Northy.

Looks like I will have to find someone with a spark eroder though...

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Posted (edited)

The rear arb mounts on our cars could be stronger and are known to fail/weaken in normal use.  If you increase the stiffness of the bar you should do this same to the mount.  There are several options and some useful detail in this link

http://forums.pelicanparts.com/porsche-911-technical-forum/463007-rear-sway-bar-bracket-broken-help.html

Edited by Ian Comerford
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On 25/05/2024 at 14:07, SilverWT said:

@Northy tried this and had problems with the drop link angles.

More camber and toe in at the front should reduce understeer. 

Mark

Mark, I have been mulling this over and having a play. Front camber now gone from 0.8 deg to 1.3 deg which is as much as I think I can get up front. That should help understeer as you say.

You then say more toe-in helps. I don't understand why this would help and how much is "more". I have 1mm a side, 2mm total already which is the prescribed 0'15" total - should I double this?

Thanks for the help...

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20 hours ago, R500_WKD said:

You then say more toe-in helps. I don't understand why this would help and how much is "more". I have 1mm a side, 2mm total already which is the prescribed 0'15" total - should I double this?

Apologies my old brain got this the wrong way round. Slight toe out on the front gives better "turn in" (at the expense of a harsher front ride over bumps), which will help reduce understeer.

Rear toe out, or reduced toe in, will also reduce understeer by increasing oversteer.

My 3.2 has no understeer at all* on track/road and is not too tail happy with the following spec/settings:

  • Weight around 1,000kg, Std front T bars, Turbo 26mm rear T bar, 22mm front ARB, 21mm rear ARB, Bilstein "Club Sport" shocks (next ones up from "Sport"), lowered with a 1 degree rake.
  • 7x16 front wheels with 205/50 tyres, 9x16 rear wheels with 245/45 tyres and 6mm spacers.

 

  • Front nearside camber = -1.6 degrees (max I could get)
  • Front offside camber = -1.4 degrees (max I could get)
  • Total front toe = +1.0mm (toe out by 0.133 degrees)
  • Rear nearside camber = -2.2 degrees
  • Rear offside camber = - 2.3 degrees
  • Rear nearside toe = -1.2mm
  • Rear offside toe = -1.6mm
  • Total rear toe = -2.8mm (toe in by 0.372 degrees. The side to side difference should be less, but it was the best I could do at the time)

*I do get power on understeer in very slippery conditions if I go mad and get my LSD to lock.

 

Mark

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25 minutes ago, SilverWT said:

Apologies my old brain got this the wrong way round. Slight toe out on the front gives better "turn in" (at the expense of a harsher front ride over bumps), which will help reduce understeer.

Rear toe out, or reduced toe in, will also reduce understeer by increasing oversteer.

My 3.2 has no understeer at all* on track/road and is not too tail happy with the following spec/settings:

  • Weight around 1,000kg, Std front T bars, Turbo 26mm rear T bar, 22mm front ARB, 21mm rear ARB, Bilstein "Club Sport" shocks (next ones up from "Sport"), lowered with a 1 degree rake.
  • 7x16 front wheels with 205/50 tyres, 9x16 rear wheels with 245/45 tyres and 6mm spacers.

 

  • Front nearside camber = -1.6 degrees (max I could get)
  • Front offside camber = -1.4 degrees (max I could get)
  • Total front toe = +1.0mm (toe out by 0.133 degrees)
  • Rear nearside camber = -2.2 degrees
  • Rear offside camber = - 2.3 degrees
  • Rear nearside toe = -1.2mm
  • Rear offside toe = -1.6mm
  • Total rear toe = -2.8mm (toe in by 0.372 degrees. The side to side difference should be less, but it was the best I could do at the time)

*I do get power on understeer in very slippery conditions if I go mad and get my LSD to lock.

 

Mark

Thank you Mark. My numbers now look like this with the front camber change yesterday. Similar to you in most respects. I'm reluctant to change to toe out at the front as it's already a bit darty on poor road surfaces and I don't want to make this worse as it is primarily a road car.

  • Front nearside camber = -1.3 degrees 
  • Front offside camber = -1.3 degrees 
  • Total front toe = -2.0mm (toe in by 0.26 degrees)
  • Rear nearside camber = -2.1 degrees
  • Rear offside camber = - 2.1 degrees
  • Rear nearside toe = -1mm
  • Rear offside toe = -1mm
  • Total rear toe = -2mm

Car is 1010 kg dry, so weights are close. I have the same TB's as you but 20mm front ARB and 21mm rear. Shocks are refurbished Green Bilsteins. Rake is about 1.5 degrees with same heights to wheel arch front and back at 625mm +/- 4mm.

Tyres are 215/45/17 front and 245/40/17 rear.

Hopefully the change I have made from 0.8 deg front camber to 1.3 degrees will make the difference. I have softer front ARB than you and slightly wider front tyres which should both reduce understeer. I was thinking about stiffening the rear ARB but I might go with this set up for the moment until I can test properly again.

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