Right some will have followed that I have changed my rear toe arms and eccentrics. I need to get it back in for geo but at the moments it's virtually undrivable. The back wanders at every deviation in the road and over heating the tyres more in the inside edge it would seem. I thought that was due to excessive toe out symptoms but when I sight down the car it definitely looks like the rears are towing in. I just need to dial in a bit of opposite toe to what I have to get me to the geo place but don't want to knacker my tyres in the process. Is the sighting just an optical illusion and I have classic excess toe out symptoms as I thought toe in made the car more stable but wore the inner tyre edge excessively. Any help or pointers appreciated. Need to drive 20 odd miles to the geo place????
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Rear toe settings and wander?
- Thread starter IanG1
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Alex
Nordschleife
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- 6 Mar 2014
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Just get a straight length of wood and hold it against the rear wheel and line it up with the sill on the car. Adjust your toe until it's virtually parallel with the sill. Also put a spirit level vertically up the wheel and set your camber so the bubble's in the middle of the spirit level.
Martin996RSR
Montreal
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- 8 Dec 2016
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If it's undriveably unstable and the rear is the only thing you have touched, and the inner edges of the rear tyres are looking scrubbed/overheated, then you've definitely got toe out at the rear*. All things being equal, toe out will wear the inner edge and toe in will wear the outer edge, though this is normally compensated for by negative camber, which favours wearing the inner edge, meaning a little toe in and a little negative camber will balance out to give even tyre wear.
*-Assuming the wondering isn't in fact due to a loose bolt somewhere back there.
Use the eccentric bolts on the lower main links to dial out some camber and use a spirit level app on your phone to get the camber closer to -1 deg than it is now. You'll find the phone accurate to at least 0.5 degrees. Saw a piece of wood to the diameter of your alloy, then tightly tape two blocks of the same size to the ends to allow you to put your new straight edge against the rim, blocks side in. The blocks allow the middle part of the length of wood not to be fouled by the spokes & centre of the wheel. It's really pretty easy, and you just reverse the orientation of your stick to check for any errors from warped wood/innacurate taping etc.
That gives you you camber, to set toe you need a second one of these camber woods, and you cable tie them to your wheels horizontally, making sure they're firmly held. You then cable tie something you know to be straight, 10mm carbon fibre tubing being ideal, but you probably don't have that lying around, so go the the autosport department of B&Q and use your imagination. You cable tie the straight poles to your wooden wheel pieces so that they project behind the rear bumper at least 1 metre. You then measure the space between them at the bumper, and at their ends to determine the amount of toe you have. You don't need to translate it into anything, you just adjust your toe arms until you have zero toe, or a little toe in.
This won't give you sorted total toe (front and back toe corrected for each other to make the car drive straight) but it will give you a rear end you can drive, secure in the knowledge it's not going to try to throw you off the road.
If this sounds like too much hassle, then just turn the toe bolts to full toe in and see how it drives.
*-Assuming the wondering isn't in fact due to a loose bolt somewhere back there.
Use the eccentric bolts on the lower main links to dial out some camber and use a spirit level app on your phone to get the camber closer to -1 deg than it is now. You'll find the phone accurate to at least 0.5 degrees. Saw a piece of wood to the diameter of your alloy, then tightly tape two blocks of the same size to the ends to allow you to put your new straight edge against the rim, blocks side in. The blocks allow the middle part of the length of wood not to be fouled by the spokes & centre of the wheel. It's really pretty easy, and you just reverse the orientation of your stick to check for any errors from warped wood/innacurate taping etc.
That gives you you camber, to set toe you need a second one of these camber woods, and you cable tie them to your wheels horizontally, making sure they're firmly held. You then cable tie something you know to be straight, 10mm carbon fibre tubing being ideal, but you probably don't have that lying around, so go the the autosport department of B&Q and use your imagination. You cable tie the straight poles to your wooden wheel pieces so that they project behind the rear bumper at least 1 metre. You then measure the space between them at the bumper, and at their ends to determine the amount of toe you have. You don't need to translate it into anything, you just adjust your toe arms until you have zero toe, or a little toe in.
This won't give you sorted total toe (front and back toe corrected for each other to make the car drive straight) but it will give you a rear end you can drive, secure in the knowledge it's not going to try to throw you off the road.
If this sounds like too much hassle, then just turn the toe bolts to full toe in and see how it drives.
Martin996RSR
Montreal
- Joined
- 8 Dec 2016
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- 613
It may help if you post a picture showing the positions of you camber and toe eccentric bolts.
Only got images of my rear toe eccentrics. When I first took it in for alignment I had 3 deg of negative camber I presume due to the H&R springs on my M030 dampers. They adjusted this to 2 deg but then came across the seized toe eccentrics so left it there till I sorted it. The car wandered on the way back so I have now changed the offending parts but returned it to its previous toe setting as I marked the bolts as a baseline. When I had 3 deg of camber it drove fine but I was weary of excessive inner edge tyre wear hence the geo.
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Martin996RSR
Montreal
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Three degrees negative is a colossal amount. Two is better, but unless you have very specialist requirements then I think you need to be at 1 degree or so. I use 0.75 degrees and that works for me.
Those toe bolts are set slighty toward toe in, but without knowing where the camber bolts are, it's hard to say what the cumulative effect of the camber and toe bolt positions is likely to be.. The lower ride height is very evident from your photo showing the camber arms not parralel with the ground, meaning the range of effective adjustment is much reduced. The more of an angle they are at, the more they are effectively shortened, and the more toe out you will be getting. Add to that the effect of bumps effectively shortening them much further and you have the cause of your lively rear right there.
Good aftermarket rear toe arms allow the outer end of the arm to be adjusted up or down to get the arms horizontal and thereby dial out the bump steer on a lowered car.
You should wind the toe bolts around until they are as far out-board as you can get them, and wind the camber bolts until they are as far inboard as you can get them. The excessive lowering will be giving you more negative camber than you would get with the camber bolts alone.
Those toe bolts are set slighty toward toe in, but without knowing where the camber bolts are, it's hard to say what the cumulative effect of the camber and toe bolt positions is likely to be.. The lower ride height is very evident from your photo showing the camber arms not parralel with the ground, meaning the range of effective adjustment is much reduced. The more of an angle they are at, the more they are effectively shortened, and the more toe out you will be getting. Add to that the effect of bumps effectively shortening them much further and you have the cause of your lively rear right there.
Good aftermarket rear toe arms allow the outer end of the arm to be adjusted up or down to get the arms horizontal and thereby dial out the bump steer on a lowered car.
You should wind the toe bolts around until they are as far out-board as you can get them, and wind the camber bolts until they are as far inboard as you can get them. The excessive lowering will be giving you more negative camber than you would get with the camber bolts alone.
Martin996RSR
Montreal
- Joined
- 8 Dec 2016
- Messages
- 613
Yes, that's correct. Set the toe bolts to that position first and take it for a drive, then if it's still terrible, adjust the camber bolts.
These are the kind of toe arms that you need in order to allow the arms to be horizontal with a lowered car:
https://www.design911.co.uk/fu/prod12921/Porsche-996-RSS-Adjustable-Toe-Steer-Kit-REAR-312/
The conical bits that go at the outboard ends can be adjusted up or down to get the arm horizontal.
These are the kind of toe arms that you need in order to allow the arms to be horizontal with a lowered car:
https://www.design911.co.uk/fu/prod12921/Porsche-996-RSS-Adjustable-Toe-Steer-Kit-REAR-312/
The conical bits that go at the outboard ends can be adjusted up or down to get the arm horizontal.
Right update for those interested. The combination of reducing the original camber had actually created excess toe in so after some measuring and lenghts of timber and a spirit level I have now managed to reduce this to something like acceptable to drive without cooking tyres etc. Now tracks in a straight line and doesn't skip and jump about. Thanks for all those who commented and I have certainly learnt a lot from playing about. In for geo tomorrow so interested to see what that brings?
Alex
Nordschleife
- Joined
- 6 Mar 2014
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- 22,176
:thumbs: Good stuff.
It'll be also interesting to see what you set it to with your 'rack of the eye' settings. Also helps for future setting (ie. if you fit a new coffin arm and it's slightly different in length).
I recently fit 2 new track rods on the front and set them just using a plank of wood and also the steering wheel position after fitting each one. Took it down the next day for tracking and one side was bang on in spec and the other just a couple of minutes out. Lads doing the setting thought I was having them on when I told them I'd set it myself on the drive using a plank of wood. :grin:
It'll be also interesting to see what you set it to with your 'rack of the eye' settings. Also helps for future setting (ie. if you fit a new coffin arm and it's slightly different in length).
I recently fit 2 new track rods on the front and set them just using a plank of wood and also the steering wheel position after fitting each one. Took it down the next day for tracking and one side was bang on in spec and the other just a couple of minutes out. Lads doing the setting thought I was having them on when I told them I'd set it myself on the drive using a plank of wood. :grin:
It wasn't that scientific but it worked. I took a length of timber and lined the upper edge to the wheel centre and a spirit level on top to check level. The end made contact with the flat end of my aero side skirt so I marked its position. I then sited down the car (other half held the timber) and marked the second position that looked straight as a second reference point. I now had a measurement between the actual and desired points. I then jacked up and took off the wheel and used the timber against the hub face and caliper and marked that against the end of the side skirt. I loosened the eccentric lock nut and wound the bolt constantly checking until I achieved the same measurement between my marks as achieved at the first step and then tightened the nut in this position. I put the wheel back on then rechecked against my original marks and it was pretty much bang on. I then replicated the eccentric nut position on the other side (I also measured the distance from the bottom of the eccentric skirt and the lower edge of the subframe as a second check) Siting down the car the wheels look bang on parallel so plenty good enough to get me the 20 miles to the geo place tomorrow.
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