Camber/caster settings

[Bob 5.0]

Hey all,
I know this topic has been discussed before but I'm having steering issues on my Mark 1. Going straight down the road it wants to jump left and right like a grass hopper. I just had it in for a front end a line and it's at -1.5 degree camber and +3 degree caster this is what I have read to be the correct settings for my car with manual steering rack ! Can I get some input from others as to what they are running .
Thanks in advance
Bob

[GoDadGo]

Hey all,
I know this topic has been discussed before but I'm having steering issues on my Mark 1. Going straight down the road it wants to jump left and right like a grass hopper. I just had it in for a front end a line and it's at -1.5 degree camber and +3 degree caster this is what I have read to be the correct settings for my car with manual steering rack ! Can I get some input from others as to what they are running .
Thanks in advance
Bob

Bob,

I've got a manual rack in a MK-4 and my settings are .5 Degrees Camber, 3 Degrees Caster, and 1/16" tow-in.
From what I've been told by several experts, these cars must have a little tow-in or they get twitchy.
Mine tracks just fine and doesn't do any dancing.

Hope This Helps!

Steve

[weendoggy]

Variables: manual or p/s rack, ride height, tire pressure, rack alignment (bump steer) etc.??

[GoDadGo]

Variables: manual or p/s rack, ride height, tire pressure, rack alignment (bump steer) etc.??

Excellent Points!

I keep my tire pressure at 22 LBS and my ride height is at 3.75" so my tie-rods are basically parallel to the plane of the road.

[Rdone585]

I would check all your suspension parts and make sure they are in good condition (ball joints, and all greased fittings), replace or tighten as needed. Make sure all of the suspension nuts and bolts are snug and not loose. Grease all the grease fittings. Check and set the toe. For your steering, what components are you using. There is a donor part, I think it was called a slosh module, found on the Mustang steering column. If you adopted it in your car, you could consider replacing it with a more stable u-joint. If all this is good and you still experience what you described, I'd try to make an estimation of the amount of bump steer you may have. When you test drive is it on a smooth road, bumps, or uneven surfaces (our roads are mostly bad).

[rich grsc]

A slosh module is for the fuel gauge. :confused::rolleyes:
I would be looking to be sure you have toe-in, and not toe-out.

[weendoggy]

A slosh module is for the fuel gauge. :confused::rolleyes:


I think (I'm not responsible for reading minds) that he means the "rag joint". :)

[Bob 5.0]

All good advice guys ! But everything in my suspension is new , and it was aligned by a very experienced professional! He has done my Ferarri my GT 40 and my heavily modified mustang and all good . I'd just like to know what others are using for settings !!!

[Rdone585]

weendogy - bingo, that's correct. I couldn't remember but you got it.

[nick7405]

Following, curious also

[J R Jones]

Bob, The autocross and track guys claim the Cobras are not straight line stable unless the caster is at 6-7 degrees. I have never seen that much castor on a car. The downside is the steering effort is so high they use power steering. Catch 22.

Your jumping description suggests a dynamic anomaly. If everything is buttoned down maybe it is a design issue. In a dynamic sense that could be bump steer.
Another influence is positive scrub radius. If you have positive off-set wheels on front to fill the wheel wells, road irregularities may cause them to steer. This was discussed on another thread:

https://low-offset.com/workshop/scrub-radius-explained/

jim

[Bob 5.0]

Jim,
I'll do some investigations into the bump steer and some calculations and let you know what I find !! Thanks this is good advice

[tonywy]

Bob, before you make yourself nuts, as mentioned check the toe. I see you have faith in your alignment guy but, these cars are touchy when it comes to alignment. Make sure the "total toe" is a 1/16" in.

[Bob Cowan]

These cars are perfectly stable at 3-4* of caster. I use a lot less camber, like .75*, based on tire temps.

A little bit of toe out helps with corner turn in, but can make them a bit twitchy on irregular surfaces. On the street I like about 1/16" total toe in.


Checking for bump steer is pretty important. It's is a tedious process, but not overly complicated.

https://i.imgur.com/hB9OEFg.jpg

[jwhit]

i have coupe with manual steering and the 3 degree caster made mine feel to responsive for me so im at 5 ° caster .5 ° camber with fat 1/16 toe in

[J R Jones]

Bob, If you want a diversity of alignment opinion, review GTBradley's recent thread on Autocross. Brad has MK 4 Cobra with a 500hp Coyote.
https://thefactoryfiveforum.com/showthread.php?39533-First-autocross-Round-two

For bump steer I use a laser attached to the hub, projecting on a field to the side, I trace a vertical line at ride height and measure laser line displacement at jounce and drop. Measuring is easy, fixing is not.

I recently saw a posted photo of an 818 like mine with a shim pack between the tie rod and the steering arm suggesting B/S correction. I looked at my car and indeed the lower control arm and tie rod are at differing (static) angles which I predict will cause B/S. That will add to my work in progress.
jim

[Indy Shu]

Tires can also make a big difference. A recent tire upgrade completely cured a the light, twitchy feeling i was getting, although mine is PS.

[Jeff Kleiner]

The geometry of the Mk1 and Mk2 roadsters makes them prone to bump steer (rack relocation on the Mk3 and later cars solved most of it and rack extenders on Mk4s eliminated it). Don't just blindly thow a "bump steer kit" at it---without first measuring it you're liable to just make it worse. Measure it and make the corrections based on what that indicates.

Jeff

[rich grsc]

The OP as still never said whether he has toe-in or toe-out?
I find it interesting, someone who's been here 3 months trying to school someone with 10 yrs of experience with these cars, on the street and on the track.
On a straight stretch of highway, bump steer shouldn't cause the car to jump around left and right like a grasshopper.

[Joe Campbell]

Related to all of this, does anyone know the SAI (steering axis inclination) angle on the MkIV?

[J R Jones]

Joe, I will venture out here again at the risk getting spanked for my time as a member. It has been four days since your post.
SAI is also known as KPI (king pin inclination. It is a line through both ball joint centers viewed from front or rear.
It is really a range of angle for as you lengthen or shorten the upper control arm for camber, the SAI will change. Related but not the same.

If you intend to measure SAI, you could use a digital level held against the inside of the upright/ball joint bosses. Difficult at ride height with the wheel on.

I might cheat using a laser.
Remove the wheel/tire and suspend the hub to simulate a loaded suspension.
Set-up a laser for a non-leveled vertical line. Mount the laser to a tri-pod and beam the ball joint shafts from the front.
Fix the laser angle on the ball joint shafts and hold a digital level up to the laser beam to read the beam angle.

I am not sure what you are after, the SAI is somewhat fixed, and not an alignment adjustment. It is a factor in scrub radius when measured against the wheel/tire centerline.

When you turn your steering wheel, the tire wants to pivot around the point where the KPI meets the road surface. However, if the centerline of your tire is laterally offset/away from that point, the tire is going to have to “scrub” through a small patch on the road.

The surface area of this patch that we speak of is your actual scrub radius. It is the distance between the point where the steering axis meets the road vs the point where the tire centerline meets the road.
jim

[nucjd19]

Joe, I will venture out here again at the risk getting spanked for my time as a member. It has been four days since your post.
SAI is also known as KPI (king pin inclination. It is a line through both ball joint centers viewed from front or rear.
It is really a range of angle for as you lengthen or shorten the upper control arm for camber, the SAI will change. Related but not the same.

If you intend to measure SAI, you could use a digital level held against the inside of the upright/ball joint bosses. Difficult at ride height with the wheel on.

I might cheat using a laser.
Remove the wheel/tire and suspend the hub to simulate a loaded suspension.
Set-up a laser for a non-leveled vertical line. Mount the laser to a tri-pod and beam the ball joint shafts from the front.
Fix the laser angle on the ball joint shafts and hold a digital level up to the laser beam to read the beam angle.

I am not sure what you are after, the SAI is somewhat fixed, and not an alignment adjustment. It is a factor in scrub radius when measured against the wheel/tire centerline.

When you turn your steering wheel, the tire wants to pivot around the point where the KPI meets the road surface. However, if the centerline of your tire is laterally offset/away from that point, the tire is going to have to “scrub” through a small patch on the road.

The surface area of this patch that we speak of is your actual scrub radius. It is the distance between the point where the steering axis meets the road vs the point where the tire centerline meets the road.
jim

Please continue to post J R. I have learned a lot of of the " academics " if you will from your posts. They are well thought out and always meant to be helpful. I appreciate the efforts you put into them :)

[Joe Campbell]

Good stuff JR.

I got a response from Dave Lindsey at FFR that the SAI spec on MkIV roadsters is from 11.5 to 12 degrees, depending on camber. My only interest in it was to determine optimum caster setting, and per several suspension experts I trust, caster should ideally be set at no more than about 2/3 of the SAI spec, or 7.5ish to 8 degrees positive.

It's often bounced around that if you have power assist on an FFR to put in as much positive caster as you can get, so that's what I told my alignment shop after putting in a new manual (electric power) steering rack. They were able to get the car to almost 12 degrees but were concerned that was a bit much - they said I could try it out and bring it back in if I wanted to back it off a bit. It tracks great - I could probably take a nap on a long straight with no traffic. But it feels heavy in a non-linear way and then slacks off a bit, probably because it's trying to lift the car a bit when I turn. I also found my manual rack was a slow one. I'll back off on the caster when I put in the quicker ratio rack.

[GoDadGo]

i have coupe with manual steering and the 3 degree caster made mine feel to responsive for me so im at 5 ° caster .5 ° camber with fat 1/16 toe in

Jwhit,

How much heavier did your steering feel when you went from 3 degrees caster to 5?
I've got the manual rack on my MK-4 and it feels almost neutral so a little more angle may give me the feedback I'm looking for.
I'm not auto-crossing nor road-racing, but am driving a lot of curvy back roads with mostly interstate driving on the way home when I'm done.

Steve

[J R Jones]

Joe, Thanks, but I didn't answer your question. I am pleased that Dave had the information.
By accounts I read, the MKIV is evolved in suspension geometry so you have a good platform to work with.
I never heard the 2/3 rule and never challenged it. As I have mentioned on other threads I have never driven a car with more than 4.5 degrees caster.
I like to experiment and utilize the "scientific method": A-B-A tests. I like quick/agile handling.
Visualizing your observation of lifting the front with large caster, I also see increased scrub radius which may affect steering while braking on mixed traction surfaces. Trying to anticipate any downside, and referencing a motorcycle example, it seems extreme caster could cause "flop" which you may have experienced with your "slacks off a bit" experience.
jim

[CraigS]

Caster can be too much for sure. When I try to think through things like this I tend to try to imagine an extreme of whatever I am thinking through. In this case imagine if caster was 45 degrees. Remember + caster means the upper ball joint is further back than the lower ball joint. Let's look at the left front wheel (from 5 feet away from the left side of the car) w/ 45 degrees of caster. It is fairly easy to see that, if the steering wheel were turned to the left, the left front wheel would drop down. If it were turned to the right it would move upward. This still happens even at 3 deg caster, just to a much lessor, much less visible extent. At one time I had 9deg caster in my MkII w/ power steering. I happened to be parked one day and needed to back up in a tight turn so I cranked the steering wheel left before letting the car start to roll. I could actually see the LF fender rise and the RF fender fall. So I started thinking what is happening when I drive through a normal corner. In a left turn the car naturally leans to the right. Well, hell,,,,,light bulb moment,,,,,my high caster setting is going to make the front of the car lean even more than it normally would. And it would have detrimental affects on dynamic corner weights as the outside front tire would lose corner weight and the inside would gain corner weight compared to an identical car w/ less caster. The next chance I had the time caster went to 7 degrees. I'd like to say I could feel an immediate improvement at the next autocross but I can't. But a bit of google of alignment specs for known good handling front engine/rear drive cars like Corvettes, Miata's,etc. turned up a lot more caster specs in the 6-7 range than in the 9-10 range.

[J R Jones]

Craig, As usual you have a pragmatic approach. I tried your visualization exercise, and it did work for me.
If the "kingpin" is vertical with high caster, the difference is noticeable.
If you add camber to the kingpins, high caster makes the R&L "lift" differential more extreme.
So combining extreme adjustments add up.

Your back-up experience reminded me of a old FWD experience.
I can be irresponsible and some (Japanese?) FWD car surprised me when I nailed it in reverse. It tried to spin the steering wheel out of my hands.
I assume it was suspension geometry, but I did not look into it. I wonder what brand it was?
jim
Actually I referenced your contributions from the GTBradley autocross thread earlier in this thread.

[VIRGIN MIKE]

Too much caster , in my FFR Truck (13 degrees I was told), required so much turning force that it torqued the electric steering enough to push the tie rod bushing out of the housing - On my very first test drive the truck handled so poorly I deemed it undriveable. After finding the bushing issue ... (I will spare you the soap opera). With the third reck installed I got flat bed tow to the alignment shop, was told the caster was 13 degrees, reduced it to 7, camber and toe were correct, and drove it home with no problem. Now with 300 miles on the clock, going to verify alignment again on Tuesday.

[jwhit]

Jwhit,

How much heavier did your steering feel when you went from 3 degrees caster to 5?
I've got the manual rack on my MK-4 and it feels almost neutral so a little more angle may give me the feedback I'm looking for.
I'm not auto-crossing nor road-racing, but am driving a lot of curvy back roads with mostly interstate driving on the way home when I'm done.

Steve

at 3 degrees mine felt to quick to turn (very responive ) the 5 degrees makes it feel perfect to me

[CraigS]

at 3 degrees mine felt to quick to turn (very responive ) the 5 degrees makes it feel perfect to me

It is interesting to see all the different reactions re; steering feel. I think it is important to realize that any given caster spec will work differently for different drivers. We have variations in physical strength, rack ratios, tires, tire pressures, SAI angles of different spindles, toe-in specs, power steering assist levels, coupe vs roadster, and even our experiences driving other cars. My point is don't get too hung up on a given caster spec being ideal for you and your FFR. Any where between 3 and 9 will be OK. I even ran +1* for a couple months when I got my MkII w/ manual rack and it was too heavy for me. It took me those months to gather parts and install them to switch to power.

[Jeff Kleiner]

Craig,
About gaining inside corner weight:

https://thefactoryfiveforum.com/attachment.php?attachmentid=138308&d=1606319435

And we all know how this worked out ;)

SUre do miss him...

Jeff

[CraigS]

Me too.