Caster vs Camber?

[teamshaw]

Hi. My POG is a dedicated track/hillclimb car. Based on Sam’s thread I rotated my front strut tops to prioritise caster over camber. The alignment guy thought that I would be better off going back to the original settings, but I’m not so sure? What do you track guys reckon?

Latest settings attached.


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[simon k]

The caster there is good but zero camber will be horrible. You should put in some TT ball joints and a set of eccentric subframe bolts and you'll get a couple of degrees.

Your back end is a bit of a mess too. I could help you with that

[teamshaw]

Great thanks. I will try and source those bits and get them in.

I’ve got some shims to go into the rear, they are next on the list. What toe/camber do you suggest?


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[simon k]

I did the TT ball joints without drilling the bottom arms, I just filed the holes in the ball joints till the I could get the bolts in, pushing them as far forward as i could

I can help with eccentric bolts if you want some.

Left-rear is good, make the right match it

[Sydneykid]

The caster there is good but zero camber will be horrible. You should put in some TT ball joints and a set of eccentric subframe bolts and you'll get a couple of degrees.

I did the TT ball joints without drilling the bottom arms, I just filed the holes in the ball joints till the I could get the bolts in, pushing them as far forward as i could

Agree

Front caster is great, needs neg camber, around 3.5 degrees for circuit work and longer high speed hillclimbs (eg; Bathurst), possibly get away with 2.5 for short lower speed hillclimbs. I'd never run toe in on the front, zero at least, up to 2 mm or so toe out each side.

Rear camber is OK, needs the same amount of toe out on the RHS as it has on the LHS.

Cheers
Gary

[sambb]

got a pic of your strut tops fitted in the car?

[Ozsko]

The caster there is good but zero camber will be horrible. You should put in some TT ball joints and a set of eccentric subframe bolts and you'll get a couple of degrees.

Your back end is a bit of a mess too. I could help you with that

I hate eccentrics for suspension adjustment as they move in two planes at the same time and this can't be avoided. I would go to extreme lengths to avoid using eccentrics but that is just my dislike of them for suspension adjustment. Truly horrible things to be avoided at any cost.

[simon k]

I hate eccentrics for suspension adjustment as they move in two planes at the same time and this can't be avoided. I would go to extreme lengths to avoid using eccentrics but that is just my dislike of them for suspension adjustment. Truly horrible things to be avoided at any cost.

interesting.. I wonder if we're talking about the same thing though - these are to take up the manufacturing clearance in the front subframe mounting points and accurately position them... discussed here -> Tramlining & Excessive Torque Steer.

[Sydneykid]

I hate eccentrics for suspension adjustment as they move in two planes at the same time and this can't be avoided. I would go to extreme lengths to avoid using eccentrics but that is just my dislike of them for suspension adjustment. Truly horrible things to be avoided at any cost.

Can be looked at both ways, sometimes I want to adjust either, for example in an inner lower front control arm installation I can adjust roll centre, up or down to the max, without affecting the camber OR I can adjust the camber, in or out to the max, without affecting the roll centre. Pretty useful for the one item cost and installation. The in betweens requiring both together is where it gets tricky, if I want an exact amount of each, that can be hard to achieve. But being realistic, they are mounted in rubber or polyurethane bushes so ~1/8 degree (of camber) or ~2 mm (of roll centre) is hardly material. There's multiples more than that in the dynamics, the deflection of the bushes, the bending of the strut, the flex in the hub, not to mention the twist in the chassis itself and even the flex in the wheels.

In the formula cars with carbon fibre tubs etc we adjust using 0.5mm shims, but in a production based road car spending time and brain power on trying to achieve exact static suspension geometry is not an efficient use of resources.

Cheers
Gary

[seangti]

Teamshaw, I'm running Kmac tops on mine that are camber castor adjustable. I'm running at max castor which I think it around 4deg, with -3.5deg camber of left and -2.5 deg on right. All the QLD tracks are right handers. I can't recall toe settings.

I've also got the rear whiteline shims. It's been too long with this set-up to know anything different, but I had progressively added camber from conservative to track centric and notice improved 'stance' during cornering. So you'll certainly get improvement going from -1.5 to -3+.

I've not done the eccentric bolts or ball joints. It rarely gets driven these days

[sambb]

Ozko the eccentrics on our cars are used on the subframes. They're not crash bolts on strut legs. The subframes like almost all the subframed VAG cars are notorious for shifting around. The eccentrics are used as a set and forget. Any tuning changes after that are made at the strut top. I basically put my subframes as far forward as they'd go on the front hole and as far out as they'd go on the back hole to maximise caster. In doing this the eccentrics didnt bind one iota because obviously everything isn't an interference fit under there. I believe the ones we use on the Polo offset each bolt relative to the frame by 2mm so there is nothing extreme going on there. As long as you use common sense ie not try to move the front eccentric forward and the back one back, and move them in complimentary ways so that they're not fighting one another, then there's no functional problem. The main benefit is that you can go some way to accurately squaring up any left/right discrepancies and once you've done it you lock it down and you know it'll never move again, unlike the factory situation where you're putting a 10mm bolt in a gaping hole that no matter how many times you spec torque it with new factory stretch bolts it WILL move again.

[Ozsko]

Ozko the eccentrics on our cars are used on the subframes. They're not crash bolts on strut legs. The subframes like almost all the subframed VAG cars are notorious for shifting around. The eccentrics are used as a set and forget. Any tuning changes after that are made at the strut top. I basically put my subframes as far forward as they'd go on the front hole and as far out as they'd go on the back hole to maximise caster. In doing this the eccentrics didnt bind one iota because obviously everything isn't an interference fit under there. I believe the ones we use on the Polo offset each bolt relative to the frame by 2mm so there is nothing extreme going on there. As long as you use common sense ie not try to move the front eccentric forward and the back one back, and move them in complimentary ways so that they're not fighting one another, then there's no functional problem. The main benefit is that you can go some way to accurately squaring up any left/right discrepancies and once you've done it you lock it down and you know it'll never move again, unlike the factory situation where you're putting a 10mm bolt in a gaping hole that no matter how many times you spec torque it with new factory stretch bolts it WILL move again.

And I still would not use eccentrics but thanks for the explanation, the best thing that can be said for them is they are a crude cheap device. I am involved in prototyping some adjusters on another vehicle at the moment to replace the eccentrics that are currently used and my dislike for eccentrics has grown as I get further into the project.

[sambb]

we are just as much using the eccentrics to anchor the subframe as we are using them for alignment reasons. In terms of the anchoring side of things go, yeah it would be much better if the subframes had tight tolerances with the bolts and were even dowelled/keyed into the body. Then for one you'd not even need to look there for a possible solution to an alignment problem and also you'd know that regardless of position that they'd stay put. There might be better ways to fix the subframes but after lots of km's, track work and a solid front end collision later, the subframes havent budged with the eccentrics whereas they were all over the place without them. Its pretty commonly accepted on the VW's that fitting subframe sleeves to fill the void between bolt and subframe hole will help in rigidly anchoring the subframe. I'll be honest with you I cant figure out how an eccentric (provided its not binding and putting sheer forces through its bolt) is any different to a basic sleeve. To the bolt, it just sees the lip on the eccentric adjuster as a washer doesnt it and puts the same clamping force down through the subframe as if it were acting directly on it? I'm happy to be schooled though if that's not the case. As an adjuster, yeah for sure they are finicky to setup if you are looking to adjust in just one plane without affecting the other. On our subframes if you think of them as a base adjustment to get you close to square before you zero in with your other adjustments, then they suffice - or if the car is basically stock (no ball joint or strut top adjustment available), and has say a significant mismatch left to right then it gives you probably the only adjustable way of remedying that.
The method you are prototyping - is it to replace subframe eccentrics with slots, or to replace eccentrics in their various uses in general? If its to do with VW subframe adjustment then I'd be super curious to see what you are working on.

[sambb]

These are yours yeah? and this is the drivers side. It looks like the slider section is biased towards one side of the strut top eg the inside two bolts in this pic. So you've oriented the tops north/south which looks like it might even add a bit of camber if you are trying to add caster which sux. Normally you'd line up the slider axis with the inside back bolt (for caster and camber) but it looks like your slider channel wont extend far in the desired direction if you do that.
Easiest fix would most likely be running different strut tops that line up the slider channel differently so you can angle them in and back. Apparently nissan S15 strut tops (check with Simon) have our bolt pattern. Maxpeeding do cheapies and these one position Whiteline ones would get you max camber/caster in a fixed position style......but then to dial it in you'd have to eccentric the subframe.

Couldnt tell you if S15 ones use the same bolt sizes or if your strut would fit into them without a sleeve/mod etc though.
This is my passenger side top looking back towards the firewall. They were east/west but I was able to change the orientation so the channel ran towards the inside back bolt. These are MCA tops but you should be able to find an S15 alternative that will give you that orientation with more range than your ones will give you.

While the eccentric designed to fit more or less into the existing subframes holes are quite good at maximising caster they dont seem to have as much impact on camber. My eccentric only needed the slightest ream for them to go in. In terms of lateral movement, front hole of subframes does camber, rear hole does caster. I think Simon floated this at one stage but for your situation possibly you could drill out the front bolt hole on the subframes so that an oversized eccentric could go in there allowing you to get say 3-4mm of lateral shift in the front of the subframes. Run them with superpro offset caster rear LCA bushes so you dont give away any caster and that may be enough to get you an extra 0.75 degree. Other than that modding wishbones to accept an alternative ball joint or balljoint position would most likely be the answer.

[simon k]

Nissan strut tops have the same bolt pattern, but rotated 180 degrees (or swapped side to side). Maybe try to find some with a longer channel, one that goes all the way across like Sam's. Those tops in Sam's picture would work, but they look pretty big, you'd have to cut the whole of the dome off - does that weaken the tower too much?