Mk.4 suspension question

[Nigel Allen]

Hi Guys,

My Roadster suspension appears to be too soft, but I would appreciate some guidance as it is not an area I know much about. I occasionally have a problem with the front tire rubbing on the guard. This occurs when all of the following 3 conditions are met:
- Braking heavily
- Turning
- Hitting a bump in the road

The front springs are 500# and the collars are pretty much wound down to the bottom of the threads.

150971

The shock absorber rod is wiped all the way to the bump stop. Do I need a heavier spring?

The rear springs are 450#, but as can be seen from the photo, the collar is almost all the way down.

150972

I do not have any torsion bars.

Weights are as follows:
Front: 1146 (520kg)
Rear: 1389 (630kg)
= 2535 (1150kg)

That includes me, 198 (90kg) and ~1/2 tank of fuel - The above weights were measured by our local testing station and had to include driver and fuel)

Current ride height is around 4 1/2 inches. Tires are Nitto NT05-255-17 / Nitto NT05-315/17. The handling is decent and passengers comment on how plush the ride is. Any advice on addressing this issue (apart from going on a diet) would be sincerely appreciated.

Cheers,

Nigel

[CraigS]

First I am not sure what the 'guard' is so I don't know how serious a problem this is. But, you have a few of choices.
1- Ignore it as it happens infrequently
2- Raise the ride height which at 4.5 inches now, I wouldn't want to do
3- A stiffer spring. I'd go to 550 as a first experiment.

[Nigel Allen]

Whoops, sorry Craig, guard is short for mudguard (Aussie term), I should have said front fender. Specifically the outer edge of the tire touches the outer edge of the fender flare.

Is it common to have so much preload on the spring? There is hardly any thread remaining.

I don't recall others reporting this issue. My car is not any different to others on this forum. Just has me a little perplexed...

[rich grsc]

Whoops, sorry Craig, guard is short for mudguard (Aussie term), I should have said front fender. Specifically the outer edge of the tire touches the outer edge of the fender flare.

Is it common to have so much preload on the spring? There is hardly any thread remaining.

I don't recall others reporting this issue. My car is not any different to others on this forum. Just has me a little perplexed...

You're correct, thats not common. I think you have the shocks assembled incorrectly? My ride height is about the same, maybe just a little lower, and my adjuster is near the middle of the threads. When the car is on jack stands and suspension is at full drop, the springs should be free of the adjuster.

[Jeff Kleiner]

Nigel,
Your spring collars show that your adjusters are a little farther than I'm used to seeing but your 4 1/2" front ride height is higher than I commonly see as well so that will definitely play into it.

Now we we've been educated and know that "mudguard" is what we'd call "fender" let me ask...was the excess flashing trimmed from the wheelwells of your fenders/mudguards when your body was prepped? They start like this:

https://thefactoryfiveforum.com/attachment.php?attachmentid=150994&d=1626611753

And then I trim them like this:

https://thefactoryfiveforum.com/attachment.php?attachmentid=150993&d=1626611690

And finish them out like this:

https://thefactoryfiveforum.com/attachment.php?attachmentid=150995&d=1626611787

If they haven't been trimmed it isn't unusual for the tires to make contact, especially if some of these apply
---using '96 or later Mustang spindles
---running larger tires with "square" shoulders (I'm going to assume that your 255 Nittos are 40 series aspect ratio and not 45; 255/40-17 is ordinarily not a problem)
---running zero or very little negative camber along with a low level of positive caster
---running a very low ride height (which you are not)

Are any of these pieces fitting into the puzzle?

Cheers,
Jeff

150994
150993
150995

[Nigel Allen]

Craig, Rich, Jeff,

Thanks for taking the time to reply. It is really appreciated.

Craig - Your option 3 is likely the easiest solution. Although finding parts in Australia might not be so easy.

Rich - Good question. Pretty confident in the assembly and fitting of the shocks. I also have the damping at the lowest setting. I think Jeff might have worked out where things are going wrong...

Jeff - Your point about the flashing is right on, It wasn't taken away by my painter. I knew I should have flown you down here!

151015

Also, he had to stretch the right hand flare slightly, as it didn't quite cover the tire (a definite fail at our testing station) The 'stretch' was put into the angled section of the flare, therefore slightly lowering the outer edge. Bummer. The tire only just touches on big bumps / heavy braking. I will order heavier springs.

As mentioned earlier, fronts are 500 and rears 450. If I increase to a 550 or 600 on the front, I guess I could move the current 500s to the rear?

Cheers,

Nigel

[CraigS]

I 'think' front and rear springs are the same free length so yes put them in the rear. Sorry about my recommending 550 as a test. Somehow I only remembered the 450 but that is your current rear. So, I would recommend going to 600 if you go that way. Now that Jeff has figured the real problem is with the flares I would look at fixing them. It will take some careful work w/ sander but I suspect you could get rid of that lip, or leave just 1/8 inch of it, and touch up the raw edge w/o needing to re-do the entire front fender. If you were to sand the lip off at a vertical angle the raw fiberglass would not be very visible even w/o touchup so a standard paint stick or a modelers brush could cover it.

[Jeff Kleiner]

Man Nigel, that thing looks TALL! That's 4.5" in front? I run 3 3/4"-4" in the front and the front tire to body gap between yours and mine looks like a whole lot more than 3/4" difference.

https://thefactoryfiveforum.com/attachment.php?attachmentid=151036&d=1509280517

I find it very surprising that with that much gap between the tire and fender (mudshield ;) ) lip that'd you'd get enough deflection on anything less than a massive bump to make contact, but as the saying goes "It is what it is". Keep in mind that if you opt to go to a stiffer front spring without making a corresponding change to the rear stiffness it will induce understeer (more understeer actually because with the factory spring rates they already have a moderate push).

Cheers,
Jeff

[Avalanche325]

If it is just touching, you might try adding a little camber.

I agree that it looks like it is sitting high. I wonder if you have something else gong on. I would certainly investigate.

"This occurs when all of the following 3 conditions are met:
- Braking heavily
- Turning
- Hitting a bump in the road"

That's a combination that can cause a LOT bigger trouble than tire rub in one of these. Be careful how much you trail brake in a Cobra.

[Nigel Allen]

Man Nigel, that thing looks TALL! That's 4.5" in front? I run 3 3/4"-4" in the front and the front tire to body gap between yours and mine looks like a whole lot more than 3/4" difference.

https://thefactoryfiveforum.com/attachment.php?attachmentid=151036&d=1509280517

I find it very surprising that with that much gap between the tire and fender (mudshield ;) ) lip that'd you'd get enough deflection on anything less than a massive bump to make contact, but as the saying goes "It is what it is". Keep in mind that if you opt to go to a stiffer front spring without making a corresponding change to the rear stiffness it will induce understeer (more understeer actually because with the factory spring rates they already have a moderate push).

Cheers,
Jeff

G'day Jeff,

Sorry, it's the second time I have created confusion, first with mudguard reference and now with a bad photo. Doh! I feel like a bit of a stooge. The photo was to show the profile of the lip of the fender. The reason there is such a gap between the fender and tire is that I had just put the car down off jack stands and hadn't settled the suspension. The gap is around half of that shown.
By the way, love the photo of your car.


Avalanche,

Thanks for your comment about camber. I checked the print-out from my wheel alignment. it is as follows:
Camber: -0.20 degrees
Caster: 3 degrees

What camber is recommended for a street driven car? I have a great selection of winding, hilly roads where I live, but not likely to do track days.
The car has a manual rack as supplied by FFR. I recently fitted the Epower steering conversion, so looks like I should increase the caster as well.



When I originally built the car, I was under time pressure and didn't do as much research in this area as I should have. Before the body was mounted, I took the car to the best wheel aligning shop I could find locally. I feel the guy got out of his depth with the T-bird IRS. Realistically, I probably need to do the IRS alignment again, before I get the front done.
Car currently drives quite well, but is a little quirky at times. I feel like I need to do the alignment and suspension settings from scratch.

This time I will be researching and picking the great minds on this website. :)


Many thanks,

Nigel

[J R Jones]

Nigal, You originally mentioned turning as a rub factor and no torsion bars, which I interpret as anti-roll bars.
A front anti-roll bar would potentially cause understeer in high speed cornering. https://suspensionsecrets.co.uk/anti-roll-bars/
On the other hand, if you like the ride quality of the 500 lb springs, the anti-roll bar would reduce squat on the outside and retain current ride characteristics.
BTW, I assume everyone is measuring ride height at the same reference point.
BTW -0.2 degrees camber is not much. I expect the FFR spec is more negative.
You do need a competent alignment technician with insight, not a numbers guy "on the clock".
jim

[Jeff Kleiner]

Nigel,
For primarily street cars I go .5 to .75 degree negative camber (going to the more negative range could help your situation). Manual steering gets 3 to 4 degrees if positive caster; power steering 6 to 8 degrees positive. Toe in I like 3/32”—make sure that it is toe in, not out (toe out can make the car kind of darty at speed).

Cheers!

Jeff

[rich grsc]

Yep Jeff is on the money. The camber setting you have now is causing much of you clearance issue, and if you're adding power steering you'll need to increase the caster, that too could help.

[phileas_fogg]

Hi Nigel,

CraigS and I did the alignment for my T-bird IRS following these instructions from Mark Dougherty, a.k.a. the Traveling Builder:

“The best way I have found to set the do the initial setup of the FFR Version 1 IRS.

1)screw the jam nuts all the way up the heim joints.
2)on the front side screw the heim all the way in and bring it out 3 full turns
3)turn the back heim all the way in and back it off 4 full turns.
4)install the arm in the frame at the front leg put as many washers as possible in front of the heim joint leaving enough room for 1 washer behind. Install the washers and tighten the bolt.
5) on the rear leg just install the bolt no washers yet. put the nut on by a couple turns but do not tighten it down. After the alignment later the rear washers go in.
When the alignment is done they should not adjust the front heim joint.
they will adjust the rear first to set the toe in.
then they will move the upper arm in or out to set the camber.
no castor setting.

you will find if doing it this way the rear leg should come out almost in the middle of the rear tabs.”

After following Mark’s instructions to the letter, the front leg looks like this (seven spacers in the front; one spacer in the back):

https://farm5.staticflickr.com/4299/36249005816_da31a3be9b_k.jpg (https://flic.kr/p/XecCwU)IMG_1385 (https://flic.kr/p/XecCwU) by jhsitton (https://www.flickr.com/photos/91016165@N07/), on Flickr

And the rear leg looks like this (no spacers yet, but the rod end is roughly centered between the tabs):

https://farm5.staticflickr.com/4308/36123288752_ca0093eea4_k.jpg (https://flic.kr/p/X36iej)IMG_1387 (https://flic.kr/p/X36iej) by jhsitton (https://www.flickr.com/photos/91016165@N07/), on Flickr

Nobody tells you how tight to make the jam nuts on the rod ends. I’m guessing 1/8 turn should be plenty.


John

[phileas_fogg]

After 1000 miles, I decided to re-align my Roadster. I started by verifying the rear, and then moved to the front.

First of all, I spent a couple of hours pulling what’s left of my hair out because I couldn’t get repeatable measurements. Turns out the right-hand bay of my garage is WAY more level than the left-hand bay (CraigS & I did the initial alignment in the right-hand bay, so everything was good). For reasons I won’t go into here, I decided the Roadster should be parked in the left-hand bay, which led to my initial difficulty.

With that lesson learned, I used a couple identical-length sockets, my toe bar, and a level to figure out how much tilt there was to the floor. I placed the sockets in the center of the contact patches, spanned the distance with my toe bar, and used the level to figure out how much plywood to put under the low spot. I used a couple of strips of painter’s tape to make sure I got the wheels in the same spot as the sockets.

[Need picture]

With that sorted, I made some initial measurements using the Longacre toe bar (http://www.longacreracing.com/products.aspx?itemid=2445&prodid=7212&pagetitle=Toe-Bar) and Longacre digital camber/caster gauge (http://www.longacreracing.com/products.aspx?itemid=2446&prodid=7215&pagetitle=Digital-C%2fC-Gauge-w-AccuLevel™-and-Quick-Set™-LW-Adapter).

I discovered that I had too much toe in at the rear (3/16” total), and not enough camber at the left rear. Working at the left rear, adjusting the upper control arm fixed the camber, and adjusting the rear leg of the lower control arm fixed the toe. The latter was a real PITA; I had to drop the fuel tank to get enough room for my socket, ratchet, & torque wrench.

I also measured the thrust angle. I used some blocks of wood to raise the toe bar over the side pipes, and pressed one end of the toe bar firmly against the rear tire (I made some witness marks on the bar so that I could repeat the placement of the bar).

https://live.staticflickr.com/65535/46902498925_c77f0fb4fc_k.jpg (https://flic.kr/p/2esBySz)IMG_5535 (https://flic.kr/p/2esBySz) by jhsitton (https://www.flickr.com/photos/91016165@N07/), on Flickr

https://live.staticflickr.com/65535/47818907511_38a622cb2c_k.jpg (https://flic.kr/p/2fRApdB)IMG_5538 (https://flic.kr/p/2fRApdB) by jhsitton (https://www.flickr.com/photos/91016165@N07/), on Flickr

At the front, I used a couple of carpenter squares to measure the distance from the toe bar to the 4” round tube.

https://live.staticflickr.com/65535/47818907121_81a5ca1094_k.jpg (https://flic.kr/p/2fRAp6T)IMG_5541 (https://flic.kr/p/2fRAp6T) by jhsitton (https://www.flickr.com/photos/91016165@N07/), on Flickr

I couldn’t get the two squares next to each other due to interference with the body, so I used the small ruler to span the small distance between them.

I was able to get the two sides to within 1/16” of each other while maintaining camber & toe in.


John

[phileas_fogg]

My target specification for the rear is camber to 1* (both sides), and total toe-in to 1/16".

When setting camber, one full turn of the rear upper control arm heim joint = 0.4 degree.

Hopefully this will get you (or your alignment guy) a leg or two up on the learning curve.


John

[Nigel Allen]

Hey guys,

Thanks for all the help so far. We have just gone into a weeks lock in South Australia, so perfect timing to work on the alignment without continual interruptions. Today I put the car on jack stands and leveled the rear up side to side using a laser level. I figure if I remove the rear coilovers, I should be able to put blocks under the rear wheels to simulate 4.5inch ride height. Then I can start working on the various steps of the alignment. I am hoping I can pull off the toe-in succesfully.

Nigel

[Nigel Allen]

Rear end:
Well I made some progress over the last couple of days. I re-aligned the T-bird IRS that was not done too well originally and got it within spec. Was a lot of work to do on jack stands, but I got there using John's tips, laser plumb-line and parallel string lines. Got totally filthy. It amazed me how much road grime builds up on the underside of a car.

Front end:
Went looking for some 600lb springs from Koni, but couldnt find any. So I ordered some https://www.summitracing.com/parts/eib-08002500600 to replace the 500lb springs currently on the front. Hopefully they will fit the Koni coilovers OK...?

My plan is to move the 500lb springs to the rear to replace the 450lb springs currently fitted. Hopefully this will allow me to reduce the preload on the coilovers both front / rear, and get a 4 / 4.5 inch height, with a bit firmer ride.

I am learning as I go, so feel free to add comments / suggestions or links to information.

Cheers,

Nigel

[Nigel Allen]

Update:

I received 600# coilover springs from Summit in 5 days! That is impressive. I fitted these to the front and the 500's that were in the front got shifted to the rear. Set up the ride height to 4" front, 4.5" rear. Now the spring collars are nowhere near the maximum pre-load. The handling is vastly improved, without degrading the ride at all. Took the car to a wheel alignment shop (owned by a Superformance driver) got the front set up to spec for power steer (I had recently converted to Epowersteer) and that was it. The car is now officially outstanding.

I made many changes all at the same time, without testing in between. This was mainly because our winter has been very wet, preventing any decent driving after each change. As such, I cannot say with certainty what change made the the greatest improvement, but likely switching to the Nitto tyres was top of the list, closely followed by the slightly heavier springs.

I just want to thank everyone in the thread who took the time to provide support. I am a two finger typist and I know it takes time and effort to post. It is sincerely appreciated. I just got the car back on the road this week for the good weather that has finally arrived, and just in time too; Our Cobra club, which is tiny, had a lady make contact looking for a ride for her friend who has terminal cancer. All the stars aligned, he was having a 'good day' the weather was perfect and I was able to surprise him with a spirited 4 hour ride he had always dreamed of. These cars get thumbs up and shout outs everywhere. At a cross road, one huge fella leaned so far out of his Kenworth window to get our attention, I truly thought he was going to fall out onto the pavement!

It's terrific that others get such a kick out of these cars as we do. We both had a great day out in the Adelaide hills and to have a guy you only met a few hours before, hug you was most humbling.

Thanks to everyone who contributes to this forum.

Nigel

[GFX2043mtu]

I have mine dialed in for road racing and I’m running a solid rear with 750 Eibach springs up front and 400 rears with the FFR front roll bar and vpm rear bar with 1.9 deg negative camber, 3 deg caster with 3/32” toe in. I’m not giving away the shock settings but I can tell you that is great for road racing. Super controllable, you can understeer over steer what ever you want. I would go 750 fronts and go up 50 lb/in in the rear springs. Fronts spring changes you won’t notice a increase in harshness as you sit over the rear. What this does is cause the nose to keep down and balance the car out as with 500 springs they nose lift a lot if you make any power. Now for a street car I would do 1.25 deg negative camber, 3 deg caster with 3/32” toe in. Also make sure your brake master cylinders are the correct size for your brake package. Rear tires tend to do good with .5-1.0 negative camber and zero toe in. Toe in on rear tires make the squirrelly if you get in the wet ever.