Twitchy Cobra?

[glastron351]

So after having logged close to 500 miles on my MK4 I'm trying to dial it in a little more to my comfort level. One thing that I have noted is that the steering feels quite 'light' and a little twitchy, noticeably more as you run at highway speeds and faster. At first I wrote this off as just the nature of driving such a short wheelbase car but I have had other cars with short wheelbases and they did not have the same 'twitchy' feeling.

I've had a 4 wheel alignment and have attached the specs however I do not understand the total toe which is in degrees and I gave the alignment imperial spec (3/32). After multiple searches it appears that total toe is 1/2 of which I provided but I could very well be incorrect on this and am looking for advice. Would also like to create a more 'heavy' feel from the steering if this is possible...again my appeals to the wonderful knowledge base out there.

BTW-The car has a manual steering rack and tracks straight and true without pulling to either side...

Thanks in advance - John

[glastron351]

Apologies for the sideways alignment pic....even if I rotate it and save it and re-select it, it still pastes sidways....sigh

[GTBradley]

The picture when clicked on comes out correct. What air pressure do you run in your tires? And have you had the corner weights done?

[JIMOCO]

2x on the tire pressure. I dropped mine from 26psi to 22psi and felt a big improvement. The car feels more stable although at high speeds it does get light and it feels a bit unnerving. Not nearly as bad as it was before the pressure change. I have manual steering with 3 degrees of caster. I have been told that with power steering I can increase caster to 7+ degrees which will reduce the the twitchy feeling.

[walt mckenna]

The only thing that sticks out between yours and mine in Caster and Camber. Let's disregard Camber for now and focus on Caster. I have power steering, so I run my Caster at 7.5 degree positive. I get good feedback through the steering with no sense of twitchy. I know you have a manual rack, so I would try increasing the positive caster until you get to the point of compromise between correct feel and steering effort.

[GoDadGo]

Manual Rack:
Toe In........1/16"
Caster........3-4 Degrees
Camber......5-.6 Degrees

Power Rack:
Toe In........1/16"
Caster........7-8 Degrees
Camber......5-.6 Degrees

[glastron351]

Hi Guys...thanks for the feedback...I havn't done a 4 corner weigh in but I believe I am around 24psi in the tires....will check.

It seems increasing the caster may be the first thing to try....I feel the steering is very light right now so a little more positive caster would be a good compromise (to me) between the low speed steering and high speed lightness....

[GoDadGo]

Glastron,

I'm in the same boat as you and will likely increase my caster to 4 maybe 5 degrees.
2,000 RPM equates to 83 MPH and that's where my 383 starts to get comfortable.
My goal is to be able to cruise at 80-85 MPH and not be lugging along doing it.
Please give us feedback as you alter your set up if you don't mind.

Steve

[glastron351]

Hey Steve...yes I will keep this post updated as I progress. Will take me a few days to bet back at the car but once i do will let you know...

[glastron351]

Steve...I don't want to hijack my own thread but noticed you shortened you LCA to improve your rear wheel placement inside the wheel openings. Did you just cut and reweld your LCA's? or something else? This is something I plan to do but currently have the FF Forged aluminum LCA...may purchase some steel ones to accomplish this. If you could reply to jgguliov@gmail.com to keep this thread on track would be greatly appreciated. Thanks

[GoDadGo]

Steve...I don't want to hijack my own thread but noticed you shortened you LCA to improve your rear wheel placement inside the wheel openings. Did you just cut and reweld your LCA's? or something else? This is something I plan to do but currently have the FF Forged aluminum LCA...may purchase some steel ones to accomplish this. If you could reply to jgguliov@gmail.com to keep this thread on track would be greatly appreciated. Thanks

I had two sets of lower control arms made that were 3/4" and 7/8" shorter than stock, because I'm OCD, and doing this really didn't impact my build.
My entire driveline is off the beaten path so a lot of things had to be altered and/or reworked to do what I did with the SBC, ZF 6-Speed, and Dana 44.
Also, my driveshaft is pretty long by Factory Five Standards.

Shortening the wheelbase on the car impacts the depth that your yoke goes into the transmission so beware.
I'm not sure you can easily shorten the wheelbase because as I remember the traditional Ford / TKO or T5 driveshaft is pretty darn short.
Shown below has a good look at my driveshaft and the entire set up.

https://youtu.be/_wnHDNgnNqs

Here are some adjustable that came from the same folks that made my fixed lowers.
https://www.spohn.net/shop/Factory-Five-Racing-MK3-MK4-Roadster/Adjustable-Rear-Lower-Control-Arms-with-Del-Sphere-Pivot-Joints.html

[tonywy]

Sounds to me like a toe issue. I see what the readout says. You should be at a 1/16 total toe. Most "alignment shops/tire shops" won't want to take the time to align one of these cars the correct way. You need to find a shop to do this or buy your own gauge and turn plates and do it yourself. More caster will give you a more on center stabil feel.

[davekp]

Looks like you have toe out at the rear. Not a good thing. You want 0 or slight toe in.

[RRussellTx]

Do you think the issue might be Bump Steer?
I don't have your issue, but I installed one of these from Breeze during the build to avoid such an issue and also to get the rack to line up better:

https://www.breezeautomotive.com/shop/offset-rack-mounting-kit-for-ffr-roadster-and-coupe/

[Jeff Kleiner]

I answered on the other forum but will repeat:

Absolutely need to assure that it is toe in, not out. I measure in inches, not degrees and like to see 3/32" total. "Twitchy" with a lack of straight line stability is a classic sign of zero toe or toe out.

Like others have said check your tire pressure; 22 ish for 17s and no more than 24 for 15s. Start there, it won't cost you anything.

As has been mentioned more caster would help if you can deal with the extra steering effort (now you know why some of us always recommend power steering ;) )

Jeff

[Jeff Kleiner]

Coming back to this because as I thought about it curiosity got the best of me. Your printout shows that the alignment ended with .05 degree of toe per side. I plugged that into this calculator:

​https://robrobinette.com/ConvertToeDegreesToInches.htm​​​

The results show that converts to .0429" or roughly 3/64". For a street driven car I recommend 3/32" or .09375" of toe in which the handwritten notes indicates is what you requested. Looks like the alignment shop may have had a math error or simply wasn't following what you were asking for but in the end they only set it for about half of the 3/32" requested. This toe setting would be a contributor to the lack of straight line stability.

Set tire pressure to 22psi, correct the toe in setting and if you can tolerate a bit more steering effort at parking speeds run the caster up to 4 degrees and I bet you'll find that it drives like a different car.

Jeff

[Rdone585]

When you are setting your toe make sure you roll the car back and then forward about a foot to let the suspension adjust to the new setting. Alternatively if you are on a four post lift you can use the sway bar as a pull up bar to get the suspension resettled. Longacre has instructions (http://www.longacreracing.com/technical-articles.aspx?item=8161&article=Set%20Toe%20Properly) that come with their toe plates with many other tips for setting toes.

[glastron351]

Hey Guys - Thanks again for all the advice. GoDadGo....Thanks for the input on the LCA's. Will focus more on this in the fall as I am trying to get this thing dialed to drive on the street...aesthetics will wait till their is snow on the ground (Sigh). Looks like I may try making my own set of LCA's or buy some steel ones and shorten them like you did. Upon talking to a few vendors it sounds like they don't recommend I go heim jointed LCA's due to the 4 link set up I have. (The LCA's help keep the axle centered and triangulated in the chassis), although the addition of a panhard bar would correct this...anyways I digress.

Jeff-Thanks again for the info...your dissection of the toe in data is what I came up with originally but I don't understand it enough to know any difference. Glad to have the Pro's share their knowledge base. I will head back to the alignment shop next weekand see what they have to say. The alignment guy was a pretty decent guy (and a hot rod guy) so I'm hoping it was just a simple miscalculation.

Davekp-not sure what to do about the rear (toe out?') Will talk to shop about this. Not much adjustment options for this...possible bushing deflection?

Will try to do this one step at a time, first verifying toe settings than maybe introduce a bit more caster.

Thanks again

[GTBradley]

Well, now you have me trying to figure mine out. I wouldn't call my car twitchy or nervous, but it does definitely demand your attention and eyes on the road. So, I'd like some help understanding this better.

I gave the alignment shop what the FFR manual suggested for a car with power steering which was:

Caster: 7 degrees
Camber: -0.5 degrees
Total toe: 1/16"


For front tire diameter of a Nitto 555 G2 I got 25.03"

What the alignment shop set for total toe was 7 degrees (4 degrees LF and 3 degrees RF)

What the calculator Jeff provided tells me is that I got 0.03495' and that equates to about 1/32" not 1/16", (1/16" is suggested for power steering by FFR manual).

Am I doing this right? If I am it looks to me like what I got would make the car feel more twitchy based on FFRs recommendation or is 1/32" not that bad for a power steering car?...


https://thefactoryfiveforum.com/attachment.php?attachmentid=134330&d=1598470046 https://thefactoryfiveforum.com/attachment.php?attachmentid=134333&d=1598470195

https://thefactoryfiveforum.com/attachment.php?attachmentid=134331&d=1598470171 https://thefactoryfiveforum.com/attachment.php?attachmentid=134332&d=1598470182

[GTBradley]

Maybe I'm using the calculator incorrectly. It says "Toe angle for one wheel in degrees" for the first input, but if I put total toe angle in there it comes out to about 1/16". I'm confused.

[davekp]

Do you have IRS?

[GTBradley]

Yes, I do.

[davekp]

I guess I don't understand how a Panhard rod works with IRS. Can someone explain?

[GTBradley]

Panhard rod was only mentioned in glastron’s post. I have IRS and only posted to see why my alignment settings seem incorrect. I didn't figure I was hyjacking the thread as it seemed to come to a resolution. Probably confused everyone because no one seems to know. I think I'm going to assume that my total toe for the front wheels should be 0.14 degrees not 0.07 like I currently have.

[walt mckenna]

I guess I don't understand how a Panhard rod works with IRS. Can someone explain?

A Panhard bar is used to locate the axle in place and keep it from moving side to side. Not used with IRS.

[walt mckenna]

Panhard rod was only mentioned in glastron’s post. I have IRS and only posted to see why my alignment settings seem incorrect. I didn't figure I was hyjacking the thread as it seemed to come to a resolution. Probably confused everyone because no one seems to know. I think I'm going to assume that my total toe for the front wheels should be 0.14 degrees not 0.07 like I currently have.

Can't tell from the raw numbers whether your total toe is positive (toe-in) or negative (toe-out). I will assume positive, in which case .14 degrees would seem excessive. My static total toe is .04 positive which is more in line with your current setting and within the specified range of -.08 to +.08 set by my alignment shop. A little dynamic positive toe will enhance straight line stability, while a little dynamic negative toe will help with corner entry for those of us who go to the track, so like most everything , we must adjust to suit our purpose.

[GTBradley]

Thanks, Walt for explanation. And yes, mine is positive. I really just didn’t understand the 1/16” suggested by FFR and what it equated to in degrees.