Height Adjustment & Travel, Why parallel? Options

[Joseph Mills]

My 914 goes to the shop next week for alignment: 1.5 to 2 degrees neg camber front, 2 to 2.5 neg rear with 1/16" toe-out front, 1/16" toe-in rear. Tires are Hoosier A3S03's.

I have found a few posts that seem to indicate that when the A-arms and trailing arms are parallel to the ground, you have maximized your cars height. Is this in fact, correct?

If so, why is this level preferred? If you go below this height is suspension geometry adversely effected? How much wheel travel is left at this point?

Joseph
'75 914 2.0L AX bound

[ChrisReale]

I dont think yo have maximized the height when the arms are parrallel, youve minimized it, meaning it as low as you want it to go. Does that make sense, or did I misread your post? Beer in my gut... (IMG:style_emoticons/default/beer.gif)

[Brad Roberts]

Answers will very...but. I feel its important because of bumpsteer. Most people dont/cant correct for the bumpsteer by using anything more than the typical rack spacers. I have personally found the best bump with store bought spacers is having the control arms parrallel to the ground. Anything beyond that and you have to start experimenting with stacked washers or spend the big bucks and buy the bump kits that adjust out at the steering arm.


B

[Joseph Mills]

Chris,
Sorry. Poor choice of words (brainfart typo). I should have said "Optimized" (as in optimized handling). Think I'll go have a beer.
Joseph

[Brad Roberts]

I knew what you meant.


B

[airsix]

Sorry, no answer. Just extending the question a bit. I hope someone with experience and figures can jump in.

If you observe the geometry of the front suspension you will note that there is camber change throughout the range of suspension movement, with the greatest degree of negative camber when the lower conrtol arms are horizontal. As the suspension moves further from this point in either direction the camber goes further possitive.

My problem with the whole idea of arms-level-at-rest is that means you have maximum negative camber when everything is at rest. When you load up a wheel it will compress the suspension and reduce negative camber (I'm ignoring body roll - I'm just talking about the strut angle relative to the body). Does that make sense? This is why I'd really like some raised-spindle struts like the Bilstein RSR's. Using a raised spindle to lower the car and then having the static possition of the control arms below level - the amount of negative camber increases as the wheel is loaded up - at least until the travel passes horizontal - but with the right spring/shock combo you can probably keep from passing that point under most conditions. Is this making any sense?

If you start with the control arms level at rest then you are losing more negative camber with each additional pound of weight transfered to that wheel which is just the opposite of what you want. So you throw the car into a corner and you start losing negative camber as the strut compresses and the control arm moves past horizontal. Add to that the possitive camber being induced by body roll. Double wammy. You really want the suspension geometry to increase negative camber as load increases to counteract the possitive camber being induced by body roll.

Now maybe the camber you conserve due to reduced body roll from lowering the car is of greater benefit than the camber lost by having the control arms "going past the half-way point" under load. Maybe that's why people are advocating the "arms at horizontal" spec. I don't know. Ok Brad, speak up. Or anyone else for that matter.

-Ben (IMG:style_emoticons/default/confused24.gif)

[Brad Roberts]

Raised spindle is the way to go.. but its very very difficult to do this with a 914 strut or early 911 strut. The Koni and Bilsteins are the easiest to raise. You have the idea nailed down. Now. With 23mm torsion bars and a "race shocks" there wont be much suspension travel. This is a inherit design flaw in the rear and front of 914's. You deal with it the best you can and try to limit the amount of change during travel.

B

[Dave_Darling]

Limiting the camber change is one of the reasons for putting the A-arms parallel to the pavement. The smallest changes in camber occur when the A-arm movement is near where the arm is horizontal. Ditto the changes in toe, I believe. The suspension seems to be in the heart of its working range at that point.

I actually prefer a little bit of droop in the at-rest position of the A-arms. The tire that is having load taken off of it will have more camber/toe change that way, but the one that is being loaded will have less. Which I think outweighs the larger change on the other side. But how much "a little bit of droop" is depends on a whoooooooole lotta things. Spring rates, driving style, the pavement you're driving on, and on and on.

I'm not nearly enough driver for that to make a real difference, so I just eyeball it...

--DD

[drew365]

Joseph; I'm curious about the numbers you posted because I had my car aligned yesterday by a Porsche only mechanic. He set it at: Front 0 toe and -2 camber, Rear 1/16" toe-in and -1.3 camber. He said that was all the neg. camber he could get in the rear. These settings are quite a bit different than your going for. Did my guy screw up or is each car going to be different?

[Brad Roberts]

Each car is going to be different. Bent arms tweaked tubs... you name it.

I just barely got 1.7 in the right rear of the last 914 I built while the left rear had NO problem getting 2.0


B

[airsix]

Joseph; I'm curious about the numbers you posted because I had my car aligned yesterday by a Porsche only mechanic. He set it at: Front 0 toe and  -2 camber, Rear 1/16" toe-in and -1.3 camber. He said that was all the neg. camber he could get in the rear. These settings are quite a bit different than your going for. Did my guy screw up or is each car going to be different?

Don't forget, the more you lower the rear ride height the more negative camber you get, so if your car sits taller you'll have less negative camber you can dial in. (use adjustable spring plates to change rear ride height)

-Ben

[J P Stein]

He,he.....this is great stuff.

Prior to my mods, bout -.25 was all that was available at the front. Dropping the ride height bout an inch gave me -.9 deg.

At the rear, I had about the same as the front. Dropping the ride height .75 and pulling all the shims(6mm worth) gave me -4......oops (IMG:style_emoticons/default/blink.gif)
4mm went back in and now there is about -2.2.

The front is about ready to re-check....dunno there, yet. Shooting for -2+.

Off hand, I'd say there is a "bit" of variation from car to car (insert tounge in cheek smiley here).

Drew:
Stick your haid under the back of the car and see if there are any shims in there (above the outter suspension mount). If there are some on both sides
I'd find a new alignment guy. If there are none, I'd drop the ride height a bit, .5 inch or so.

[Joseph Mills]

Drew,
My settings are the initial settings I hope to be able to do to set my car up for autocrossing. 2.5 degrees negative camber should suit the tires I am using (they like a lot of camber). However these would not be great street settings if that is what you're looking for (would result in poor tire wear and car wandering over bumps in a straight line). As Brad has pointed out, each car will have possible restrictions for various chassis/component reasons.

It seems that usually you will want more neg. camber in the rear than the front. You have just the opposite. If you can only obtain 1.3 in the back, maybe you should consider setting the front at 1.3 also. You would certainly have better street tire wear. It could also lessen a tendancy for your car to oversteer. But others may have other opinions.

Joseph
'75 914 2.0L AX bound

[Brad Roberts]

I have NEVER set a car up with more negative in the rear than the front.


Tidbit of info for people reading this thread:

Newbies in first time AutoX or Time Trial scenerio's do NOT need a ton of negative camber for your first alignment. You will not use the tires to their full potential no matter how Ricky Racer you think you are. I see this all the time, where an alignment shop sets your car on FULL KILL and you THINK your driving it 9/10ths and the first tire temps you do show inside (210) middle (180) outside (140) Your not using the whole tire and wont until you learn to drive.

My point. Start conservative and save your tires. It wont be until AutoX or Time Trial number 4-5 before aggressive alignments will help you out and you will only know when its time by doing the tire temps. When you start seeing outside temps higher than inside (add more negative camber)

B

[drew365]

J.P.; No shims were used in the rear. He corner balanced the car so I assume he balanced the need for good corner balance and more negative camber.

Joseph; I'm setting the car up for track only. It really only gets driven on the street to and from the shop.

Brad; Thanks for the info, I'm not Ricky Racer yet but I'm turning respectable times and think I get the tires up to temp.

[airsix]

Brad; Thanks for the info, I'm not Ricky Racer yet but I'm turning respectable times and think I get the tires up to temp.

Speaking of tire temps...
We've talked about cheap flares, cheap corner weights, cheap other stuff. How about a cheap pyrometer? I for one am tired of wondering about tire temps. Anybody got a killer cheap & effective trick? (please don't say shoe pollish)

-Ben

[Jeroen]

do some searching on Pelican
there's an article on how to make your own, using a regular voltage/auto meter, a big nail a bic pen and a cheap part from radio shack...

cheers,

Jeroen

[seanery]

C'mon Jeroen!

a bic pen?

It's getting deep here guys!

[drew365]

Didn't you ever watch McGeyver? I think he'd use some bubblegum too. (IMG:style_emoticons/default/tongue.gif)

[Jeroen]

hey, he's asking for cheap and if it works... who cares
I guess you could always upgrade to a fountain pen later (IMG:style_emoticons/default/biggrin.gif)

cheers,

jeroen