Robbie
Robbie PowerDork
9/1/18 9:52 p.m.

Looking for a double check here. Want to add some camber in preparation for the challenge. Car is a 1999 Saab 9-3. Front suspension is macstrut, but the front knuckle is a single solid piece with the strut body (boo). Factory camber spec is 0.8 deg +/- 0.8 deg, and basically you get what you get.

Underneath, there isn't a great way to move the lower suspension mounting points outward.

So I'm left with slotting or drilling new holes in the body at the top of the strut.

My trig is rusty but is telling me that 0.4 inches inboard at the top would be an additional degree of camber. (I have about 23.5 or 24 inches from strut top mount to middle of axle).

Is slotting the tops the best option? Is my math right? I may be able to get 1/2 to 3/4 inch of inboard movement at the top before the spring hits the body, so that could give me 1.5 degrees extra camber, right?

DeadSkunk
DeadSkunk PowerDork
9/1/18 10:08 p.m.

24 sin 1 = 0.418 inches ,so your math is right. Slotting the tower will certainly help. I'm not familiar with Saab suspension, but on my Challenge Miata I was able to buy extended ball joints that added about 1 degree. If I were doing it again I'd save the money and cut and weld the A-arm to make it a little longer. You may be able to do that.

flatlander937
flatlander937 HalfDork
9/1/18 11:22 p.m.

Look at adding caster too if you'll be drilling the holes anyway... think about what happens when you turn the wheel 30 degrees.

Ransom
Ransom PowerDork
9/2/18 12:04 a.m.

Not sure how far it is from the axle to the lower ball joint, but it's the whole strut you should be looking at in trig, not just from top to axle. Because you lean the whole thing, not just from the axle up. I don't think this probably changes what you should do, but it probably does meaningfully change the degrees/inch you can expect.

DeadSkunk
DeadSkunk PowerDork
9/2/18 7:20 a.m.

I looked up pictures of the lower control arm. Appears to be aluminum, so that would prevent me from cutting and welding to lengthen it as I suggested earlier. A steel facsimile might be a possibility, and that could be made a few millimetres longer to add camber. If you can TIG aluminum well, or have a buddy that can, then you could build longer arms from two pairs.

Stampie
Stampie UberDork
9/2/18 7:31 a.m.

We just drilled new holes 1.5 inches inboard on the Q45. My math says that gives us ~3 degrees. Just drilling new holes was much easier than slotting.

Robbie
Robbie PowerDork
9/2/18 10:14 a.m.

Good thoughts all. Yes, aluminum lower arms. Apparently some opels in Europe use the same lower arms except they are steel, so people have gone that route. I'm not going to work that hard at it.

Caster is low too from the factory, like 1.5 degrees. If I can add some I will.

I'll measure the whole strut today, good call.

And I will also probably just drill new holes, you're right, it does look easier!

Unfortunately the Saab 9-5 has slightly different bore axles, otherwise it would be a simple swap I think to get some struts with camber adjustment ability. Oh well.

I think I have just proven why you see so few Saab 9-3s at autox...

Robbie
Robbie PowerDork
9/2/18 10:16 a.m.

Although, making new lower arms actually wouldn't be too hard. Just need a ball joint that fits... Need to extend the distance from the ball joint to that stanchion arm bushing (and push the ball joint forward for more caster at the same time).

GameboyRMH
GameboyRMH MegaDork
9/3/18 2:52 p.m.

For adding camber, it's better to slot the holes at the bottom of the shock where it bolts to the upright than to slot the holes in the shock tower. This way you can change camber without affecting SAI - it is more tricky to adjust though. If you go this route, you could then slot the shock tower holes longitudinally for caster adjustment.

Robbie
Robbie PowerDork
9/3/18 4:30 p.m.
GameboyRMH said:

For adding camber, it's better to slot the holes at the bottom of the shock where it bolts to the upright than to slot the holes in the shock tower. This way you can change camber without affecting SAI - it is more tricky to adjust though. If you go this route, you could then slot the shock tower holes longitudinally for caster adjustment.

I wish I could, but on the 9-3 the shock and upright are a single piece. No holes to slot. The 9-5s are more standard however, so they would work in a swap but as mentioned they have different bore so the axles wouldn't work.

Appleseed
Appleseed MegaDork
9/4/18 1:53 a.m.

Never thought you'd go stance-bro on us.

Robbie
Robbie PowerDork
9/4/18 9:24 a.m.
Appleseed said:

Never thought you'd go stance-bro on us.

You should be telling me that in order to get 15 degrees of camber I'll have to make 8 inch slots in my strut towers.

GameboyRMH
GameboyRMH MegaDork
9/4/18 10:40 a.m.
Robbie said:
GameboyRMH said:

For adding camber, it's better to slot the holes at the bottom of the shock where it bolts to the upright than to slot the holes in the shock tower. This way you can change camber without affecting SAI - it is more tricky to adjust though. If you go this route, you could then slot the shock tower holes longitudinally for caster adjustment.

I wish I could, but on the 9-3 the shock and upright are a single piece. No holes to slot. The 9-5s are more standard however, so they would work in a swap but as mentioned they have different bore so the axles wouldn't work.

Whoops, my mistake for skipping through the thread...well then the only advice I have is to slot or redrill the holes diagonally from the stock location so that you can increase negative camber and caster at the same time.

iceracer
iceracer UltimaDork
9/4/18 12:51 p.m.

when you increase the SAI it will go to positive camber when turned so an increase in caster is needed.

Robbie
Robbie PowerDork
9/4/18 1:16 p.m.
iceracer said:

when you increase the SAI it will go to positive camber when turned so an increase in caster is needed.

Interesting, why? If I think about the two 'end points' of the movement being wheel pointed straight ahead and wheel turned 90 degrees, I can see how at straight ahead your static camber equals your wheel's camber, and at 90 deg your static caster equals your wheel's camber. So if caster was less than camber then you would reduce the effective camber during the movement. But I don't see how it goes positive unless the caster is negative.

What am I missing?

GameboyRMH
GameboyRMH MegaDork
9/4/18 2:53 p.m.

It is hard to visualize but he's right:

http://www.super7thheaven.co.uk/glossary/steering-axis-inclination/

Worse yet, SAI and caster don't directly counteract each other, in one direction of steering they'll complement each other, so you can't really counteract more SAI with more caster. The only way to win is to keep SAI low. Plenty of race cars are running around with more SAI than stock though.

Stefan
Stefan MegaDork
9/4/18 3:03 p.m.
GameboyRMH said:

It is hard to visualize but he's right:

http://www.super7thheaven.co.uk/glossary/steering-axis-inclination/

Worse yet, SAI and caster don't directly counteract each other, in one direction of steering they'll complement each other, so you can't really counteract more SAI with more caster. The only way to win is to keep SAI low. Plenty of race cars are running around with more SAI than stock though.

Basically, the reason why so many race cars avoid strut based suspension where possible, their limitations are known and ultimately require adjusting them to work quite well in a very narrow range at the expense of a lot the rest of the range, or make them work across a wider range at the expense of ultimate performance.

So more caster and camber until it slows down and back off to where it was fastest.  This generally results in poor initial turn-in response due to the small static tire contact patch and poor acceleration due to the same, but steady state cornering and understeer will be greatly improved.

Appleseed
Appleseed MegaDork
9/4/18 5:24 p.m.
Robbie said:
Appleseed said:

Never thought you'd go stance-bro on us.

You should be telling me that in order to get 15 degrees of camber I'll have to make 8 inch slots in my strut towers.

Stance-bros love slots.

iceracer
iceracer UltimaDork
9/4/18 6:08 p.m.

We've brought up the bad effects.   In reality it is not so bad.  Adding 2or 3 degrees to the SAI will not make a huge difference when only turning the wheels 15 degrees or so.

My ZX2SR had an SAI of 12*51"   I know it's FWD but strut is still strut.

GameboyRMH
GameboyRMH MegaDork
9/5/18 9:45 a.m.

I thought of a good way to visualize the SAI problem. Imagine you have a vertical pole with a disc mounted to it tilted down at an angle. The disc can spin around the pole, tracing a roughly inverted conical path. If you alter the angle of the disc you alter the angle of the "cone."

Now imagine you tilt the pole over by the same angle as the angle between the disc and the pole. At some point in its rotation, the disc will be vertical.

That pole is your steering axis and the disc is your wheel, and when the disc is vertical your steering is centered. The SAI is the angle between the pole and disc. Now you can see how it causes positive camber as it moves away from center, and the greater the SAI, the greater the positive camber gain.

iceracer
iceracer UltimaDork
9/5/18 1:26 p.m.

Good example.   

Steve Smith uses something similar in a book.  For KPI.

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