I (think I) need more caster, (lowered spindles) Options

[Optimusglen]

Hey all, I know that almost none of you would have any experience here, but I wanted to pick your brains.

As a refresher, the caster of the front end is the angle of the steering axis front-to-back. 0 degrees is straight up and down, +5 degrees has the top pointed back toward the windshield. Lower caster makes the car turn quicker, higher gives you straight line stability and makes steering inputs a little harder.

The factory slots in the strut towers give enough adjustment when the car suspension is all in-spec. But what if it's... purposefully out of spec?

Case in point, I have a 914 that I've gone the ORV route with. The spindles are dropped, effectively giving me more ground clearance and room for the larger tires. (215/75R15)

(IMG:http://www.914world.com/bbs2/uploads_offsite/live.staticflickr.com-19709-1779110937.1.jpg)

Now, of course, when one part of the geometry changes, that means everything changes. I did get an alignment when I finished putting it all together, and it's technically "in-spec" but it does feel a little squirrely at higher speeds, like on the highway or long backroads sweepers.

My thought is to give it more high-speed stability and give it more positive caster, but the struts are already at the full extent of the adjustment window up top. Not only that, but the portion that protrudes through the sheetmetal also is a limiting factor.

I'm hesitant to trim the sheetmetal. The slots would be simple enough, but the center hole for the strut has a lip bent up. If a portion of that is cut away, I imagine it could/would compromise strength?

This might be a similar issue many of you track racers have when trying to maximize camber, does anyone have any insight?

[sixnotfour]

https://tarett.com/products/monoball-strut-...dBoCc0wQAvD_BwE

[mlindner]

I did open my slots up to have more negative camber....Make sure you have 1/8 inch toe in. If your 0 or toe out the car will be twitchy at speed. Mark

[Superhawk996]

Your handling problems are not likely to be solved simply by adding more caster but obviously it won’t hurt.

Because of the lift you’ve got a lot of things going on that have changed roll centers and have probably given you a pretty ugly set of toe curves both front and rear. In addition to geometry, you’re going to get a lot more aero lift due to the raised ride height that won’t help at high speed either.

I’m going to drop a link

https://www.youtube.com/watch?v=7QZ5z66PhdU?si=nrVv6Q0spN53Hxfd


To a series of vehicle dynamics videos that are good because the professor uses examples that include the 914 and his overall discussion is aimed at helping the mini-Baja team develop a suspension that is aimed more at off road use. I.e high Cg and high roll centers.

There is no one place in this series of videos to point you to for a quick solution to settle down your car but you will need to understand the implications of what has been done by lifting

Note: There are more videos than this intro video that can be accessed by his channel on YouTube

[East coaster]

I did similar mods to mine, but the alignment is in spec and doesn’t seem to have any ill habits. I’m running the same size tires too.

[Optimusglen]

Because of the lift you’ve got a lot of things going on that have changed roll centers and have probably given you a pretty ugly set of toe curves both front and rear.

Thanks for that video link!

Agreed, I have some other revisions cooking, but I didn't want to muddy the waters of this post. I think my next area of attack is the bump steer, but all the bump steer kits are designed around raised spindles, not lowered ones.

And to calrify a bit more... I don't expect this to handle like a race car, that's not the purpose. "Squirrely" is maybe an exaggeration; I never felt it was unsafe on the highway. "High speed" in my case means standard speed limits on a highway, 65-70mph.

[Superhawk996]

Nice car BTW - someday I may do a similar build now that I’m way out in the woods. (IMG:style_emoticons/default/popcorn[1].gif)

[sixnotfour]

bump steer #1 check out wrightwood racing they do lowered / lifted ..bump steer solutions..

[Jack Standz]

We run both lifted (Cayenne S) and lowered (914) Porsches.

The 914 has its spindles raised 19mm which doesn't present the same issues as your lowered spindles, but we did have to address both a bump steer solution and proper alignment, especially toe-in. It's OK now, but for a street driven 914, it's not ideal and we wouldn't raise spindle height again, it's just too problematic with crappy streets, potholes, etc. The car' drivability with it sitting so low is not always enjoyable on streets that are not smooth/even.

Maybe adjust the toe-in (both front and rear) and see if things improve, then move on to more exotic solutions to address the caster issue?

[Ninja]

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What are your alignment specs now?

Strangely squirrely at speed would make me look at toe in, especially in the rear.

Was the alignment guy really good? (and familiar with the 914)

Young or old?

I prefer the ancient crusty guy; normally they have an "attitude".

The rear on a 914 is especially difficult to align properly. The toe adjustment shifts the entire rear trailing arm.

Someone on here ( @Brant maybe) had a turnbuckle fabbed into each mount plate. This is a wonderful idea IMO. Bunch easier to adjust toe incrementally AND it triangulates the plate which should improve strength.

I would align, actually drive car, and then re-check rear alignment. As the toe adjustment actually moves the tire quite a bit I don't think "jouncing" the car will work as it does on almost everything else.

The bump steer issue might be hard to address. It does need to be checked/plotted just to see where you are at.

I'm with the others. I don't think adding caster to the front is going to help you much.

My money is on rear toe being out of whack.

The "Drift" crowd actually sets up "toe out" to make the car twitchy as it is easier to chuck it into a slide that way.
Rear toe works better at this than front, but toe out seriously eats up tires (on either end).

What are you running now?
Show us your specs!

[Optimusglen]

(IMG:style_emoticons/default/agree.gif)

What are your alignment specs now?

Strangely squirrely at speed would make me look at toe in, especially in the rear.

Was the alignment guy really good? (and familiar with the 914)

Young or old?

I prefer the ancient crusty guy; normally they have an "attitude".

The rear on a 914 is especially difficult to align properly. The toe adjustment shifts the entire rear trailing arm.

Someone on here ( @Brant maybe) had a turnbuckle fabbed into each mount plate. This is a wonderful idea IMO. Bunch easier to adjust toe incrementally AND it triangulates the plate which should improve strength.

I would align, actually drive car, and then re-check rear alignment. As the toe adjustment actually moves the tire quite a bit I don't think "jouncing" the car will work as it does on almost everything else.

The bump steer issue might be hard to address. It does need to be checked/plotted just to see where you are at.

I'm with the others. I don't think adding caster to the front is going to help you much.

My money is on rear toe being out of whack.

The "Drift" crowd actually sets up "toe out" to make the car twitchy as it is easier to chuck it into a slide that way.
Rear toe works better at this than front, but toe out seriously eats up tires (on either end).

What are you running now?
Show us your specs!

All good info! You guys definitely have me looking at toe now.

Mark had mentioned above to make sure it's 1/8" of toe in up front. Anyone know what that equates to in degrees? With the bigger tires, 1/8" for me maybe isn't the same as 1/8" for others.

For rear toe in, should that be 1/8" total toe too?

I had the alignment done by a new shop near me, a larger chain with a "state of the art" system. I was a little hesitant going there, but the guy doing it seemed competent, probably 40's. He knew what to do. I did get a printout of the before/after, but for the life of me, I cannot find it. I went back in but they don't hold their records for more than a couple of weeks. It was done last fall, then I drove it out to Chicago (about 6-7 hours) and back.

On the rear toe, I used the string method at home before bringing it in, to get it in the ballpark at least. I also used camber spacers to get it to a good point. They checked it, and it was within spec, so they did not loosen the rear mounts at all. They knew enough that they knew I'd need other spacers to change the rear camber.

For bump steer, my monkey brain was thinking that I could just shift that pivot point up the same amount that the spindle was shifted down, or anything closer to that from where it is now. I've been digging on that, and it looks like I can reverse ream that tapered hole from the other end, halfway down or until the joint seats properly. I talked to Leh Keen on that, and the Safari cars typically end with the pivot point right on that side of the steering arm, so flipping the joint is probably a closer ballpark than where it's at.

[Ninja]

The rear trailing arms MAY be causing another issue...

It is very common to remove camber when you are going low.

Chris Foley used to offer this service (and he may still!).

It involves cutting the trailing arms in half and welding them back together with a little less "twist". Chris also "boxed" each chunk which improved strength.

You went the other way!

Camber and toe on the rear is important.

When you sweep the suspension for bump steer adjustments also check camber sweep.

You might need camber "adjusted" in much the same way.

Chris Foley (Tangerine Racing) is the guy I'd want back checking my project regarding major suspension angle changes.

[sixnotfour]

(IMG:style_emoticons/default/beer.gif)

[Optimusglen]

(IMG:style_emoticons/default/beer.gif)

Yep! $$$$$$$

[sixnotfour]

(IMG:style_emoticons/default/beer.gif)

Yep! $$$$$$$

yes, notice the bump steer provision...