Model A Tudor aerodynamics?

SOLUTION NEWS!!! i CAN'T TELL YOU HOW HAPPY I AM!!!. I have run into an unusual situation with handling in my 1929 Model A Tudor highboy hotrod. http://www.jalopyjournal.com/forum/showthread.php?t=394342&highlight=marmonherrington
I have since added a sway bar to the rear suspension because it feels like the car get affected by road irregularities more than it should. Now that that is "tightened up", if in a lot of traffic and above 60 mph, the car feels like the ass is wanting to bobble left and right like being buffeted by the wind. I have had to back off on passing a couple semis dragging reefers or dryboxes because the car wants to get upset, HAVE TO SLOW DOWN to get a handle again. I haven't had somebody else drive it so I can follow and watch yet. It's unnerving at 70 mph and faster.
Has anybody else experienced anything like this? I know I can tighten up some on my coil-over spring preload, might help. I have concidered stepping from 250 lb to next stiffer rear springs. Or is it something I will have to learn to just learn to drive through the experience like driving a slick road?
I realize it's not a late model vehicle and will never feel like one either.
Weebles wobble but they don't fall down.

 

Very lightweight but with a large tall profile.. ever drive an early VW bus?

How does it handle at speed with nobody near you? If it feels very stable with no other vehicles near you, I'd think you are fighting what I said about light and tall.

If it does not feel the best without other cars nearby, maybe you can get it somewhat better with suspension changes. If there is no wind at all, and no other cars near, and it still feels weird, it is not all just aerodynamics.

 

Would need to see a pic of the swaybar setup. It is possible to mount them wrong, or to mount them so that on a soft suspension with plenty of travel they are pivoting on an arc and causing side to side movement, which then becomes self-perpetuating. Sway bars are very often (incorrectly) mounted from the pumpkin or banjo, when they should be mounted as close to the wheel as possible, thus reducing the severity of the arc they travel through. A long sway bar will be more stable than a short one.

 

I have had the car in the passing lane on smooth road at ummmmmm, double double nickel with comfort but not relaxed, by myself. Not getting unsettled, but before the sway bar install. You could cruise in comfort at 80-90 if the road wasn't imperfect.
The sway bar is a universal under rearend mount type with arms that point forward about 10-12" Looks kinda like ass under my car because the 58 Ford car rearend has a slight offset center and the swaybar appears to be offset under the rearend. The swaybar is formed from 1" round bar stock correct for that application, think it was for like a 70 Ford pickup and from my stash of useless new parts. Link kits like a Chevelle or 90's Chevy pickup, urethane bushings because of in the kit, not choice. The bar is not under preload in any direction when bolted, the forward pointing arms are pretty much level with the suspension loaded.
May be useless without pics.
Yes, the thought of conflicting arcs as suspension travels has crossed my mind. I have not had the opportunity to take a short speeding ticket blast since the sway bar install. I have also put rear side glass and passenger door glass in, which changes how the car feels too. I relate this to the steering change in my 65 Chevy pickup with the stock tailgate up or down at 65 mph, you can feel it in the steering wheel if you pay attention.
The car is more fun than a barrel of monkeys! Miss Chevious because she will get you into it!

 

You might have identified a whole new species, death wobble in the rear.

 

my `28 tudor handles great at freeway speeds...passing semis , changing lanes , left lane , right lane , taking off ramps with one hand on the wheel. yes , it's pushing a lot of air , but the handling is predictable and comfortable. no sway bars , 4-bar front , 220 lb coil overs and pete & jake style ladder bars rear. there must be something we don't know about your car

 

I might have designed a rear suspension from listening to a good dirt car guy, that has inherint problems with a car that is like a billboard being pushed at a fairly high rate of speed. The design is great around the 1/4 mile clay, but not worth a ---- rolling down the road. The design would be great for a rock crawler with minor changes because the rear suspension does not bind in long travel when the coilovers are removed, therefore will not twist the frame to tear up a swiis cheese body, but also rolls with ease to make for an ill handling car at sustained speed that you will not see on a 1/4 mile dirt track.
If you're a suspension guy, you will observe on a Chevelle or like car with a triangulated four link in OEM form, they have large OD bushings and large rubber to flex for comfort and bind with correctness. I assume on that same suspension, that when you install polygraphite or urethane in that suspension, you install bind and sacrifice comfort, possibly break bolts or brackets. I assume on the extreme because of working with cement trucks, dump trucks, etc that get put into parts wearing and breaking situations, especially if not correctly spec'd for the job.
wanting to repost pic of suspension, don't know how to do without hookie pokie. Damn, that is what it's all about.

 

I have read several times that running a sway bar on one end is not a good idea.

I found the article in Street Rodders Chassis & Suspension Handbook 2000 edition.

"although many factory cars have them only on the front, using them on both ende is best.
Of course , when using roll bars fore and aft, they must be coordinated. Too much roll resistance in the front leads to understeer: too much of a bar in the rear leads to oversteer. (Thats why antiroll bars are never used on the rear only.)"

I have seen cars featured that had a sway bar on only one end and they apparently didn't have a problem with them.

I suspect that it could be problematic depending on what kind of suspension you are running.

.

 

I am a suspension guy, in fact. I suspect that the bar is too stiff for the application.

A 1" rear bar would be pretty good for a Chevelle, but probably not a A.

I suspect that going up in spring stiffness would produce make the ride uncomfortable.

 

I'm on the same page with everything you have said, including my possible intentions. I punched holes and clamped around paint I really didn't want to FU.
The car by itself on a twisted hilly road is very fun to drive. I'll say I can cut 45 minutes time on a 3 hour trip through a twisted road because of how the car handles before the sway bar and by itself in aerodynamics, ummmm, guess was mostly driving 75 in a 55 most of the time and went up a small mountain out of Buffalo River faster than I can drive my 96 pickup. Before the rear sway bar, and using the science of a Ford I-beam axle with split wishbones as a sway bar.

 

Hi Pat
What you describe here is an anti roll bar, not a sway bar. From your construction photos, you already have a sway bar mounted above your rearend.
As said previously, an anti roll bar should not be mounted on the rear only, as this will induce the rear to break away when cornering (oversteer). It could be this oversteer tendency you`re feeling when `hit` by the displaced air when around other vehicles, hence your original comment about the "ass wanting to dance left and right"...

 

Brizey, above the rearend is the panhard bar which located the chassis to the axle housing side to side. The length, location, and angle of that bar will induce handling and steering. Serious dirt late model and NASCAR racers adjust with this. The panhard bar can control body roll if designed to be in a one way turn design. In a coil spring stock Chevy pickup from 60 to 72, you can watch the body of the truck drop and push over to the left when following as the suspension goes thru it's motions because of panhard bar length and angles, two designs if you know them like I do and have modified.
Displaced air when around other vehicles, 75 mph in a 45 mph car design. Tapered turds around.

 

You need to do two things. Drive so fast there is no traffic around you. AND. Chop the shit outta that thing to clean up the air!

 

Thanks, Tman, needed that!!!! Useless parts, warp speed generator??? Got one somewhere!

 

I honest to God just shot beer out my nose when I read this thread title.
Good luck on the issue at hand though.

 

One thing I will not stand for on anything I post or start is alcohol abuse! Clean up your damn keyboard and repent! Jeez, whatcha trying to do here
!

 

A few years back, we had an issue with a brand new work rig. When you cruised highway speed in traffic, it scared the bloody hell out of you! It was like driving on a slick track. No one at the Ford dealership could find the problem. ( In their defense, nothing was broken or loose.) Finally in desperation, we took the thing in to a local shop that builds..... get this, logging truck trailers.
One of the guys there told us the rear spring rates were too soft, that someone at the factory put the wrong springs in. We let him make up and install new rear leafs........ VIOLA! Like a totally different ride!

Not saying this is YOUR problem, but maybe something to consider.

 

Back to the problem at hand. I believe F&J may have nailed. I had a conversation with a long time customer that works with garbage trucks and also races dirt cars. He mentioned Mack MR trucks having curved air foils, fairings, deflectors, whatever at the front of the cab. They were put there to take the compacted air at the front of a cabover truck and direct it down the sides of the truck. They were put there because the cab would sashay at the trucks high speed, 65 mph, over the damn near solid suspension. The cab looks like a 2x4 block over the engine and front of the frame, y'all know them.
Control the suspension under air trying to deflect a box, you induce ill handling. Light and tall. The suspension flexes and travels fine when cornering on a smooth twisty road, but gets upset feeling with larger road irregularities. A lot of things happening.
Again, I know it's not a late model car with fancy ass Corvette suspension. It's my design of suspension, NOT STORE DESIGNED. So here we go some more.
Anybody else have and experience like this?

 

if you have any pics, alot of the suspension pro's here will have more to consider.

 

The third link(upper) looks to be mounted a little low.
If your running a flexible bushing the rear could be wraping up a bit on the drivers side. At high speed that could move the back end around and that would explain why a sway bar or roll bar wouldnt help.

 

Patrick, trying to get all my thanks lined up...............it was you I bought that A wood kit from right?

 

i was going to post about this (sorta) ......at triple digits , it gets pretty noisy and stuff (from air). car isn't squirrelly , but you know your moving in the quarter. is chopping the barndoor sized windshield on my coupe the only fix to this turbulance....? would drilling the visor help...? i don't remember my old tudor being this crazy (it went 12.60's @ 112) , but it was chopped 5 1/2" and didn't have a top insert.

 

Correct with the A wood kit. Hope I reboxed it good enough to go to the Black Hills.
After today's happenins, needed laugh. Shit, you could've shot in a smartass comment about fn radial tires! Are ya slippin?

 

No, i am not a tire Nazi. I am like Don Rickles and will equally offend both side of that argument............

Wood kit is awesome. Should be installing it this winter. Gotta stain stuff one of these Indian summer nights, just becasue I can!

 

Before I'd blame it all on aerodynamics, there is a lot to check first.

Shove the car on both ends to see how it feels : compare it with other cars.

Toe check, and get a caster reading.

Make some tire pressure tests, major changes to see a difference.

Have someone follow the car to see if it's dog tracking.

Most important, put up some pics of the suspension??

 

Will double triple check with all above. Rear tire pressure check Saturday and bumped up to 35 at both sides, but also with older worn tires and they don't hop at 750rpm or so at 60 mph. Front tires shake the radiator again above 80, will need to replace and send to trailer tire heaven.
Please click on link in thread beginning, believe most suspension stuff can be seen short of the currently added rear sway bar. I'm not photobucket or computer tolerant for very long.

 

Pat, here's Scotty's thread on alignment using his non-Traditional level!
Looking at the chassis pics, the rear panhard looks short, though it could become a watt's link upper half, or lengthen it to the full rear width and use an new mounting point. If the body were to roll a few degrees, it could affect the axle's location relative to the frame. This, if the chassis behavior search eliminates any other gremlins.
http://www.jalopyjournal.com/forum/showthread.php?t=413853

 

A dead perch on the front, and stiffer rebound damping in the coil overs on the rear fixed my RPU. Felt exactly as you described before. The rear panhard bar needs to be as long as you can make it. Frame rail to center of the rearend is almost useless.

 

I drove my car to a buddy's house today. It was about a 45 mile round trip on some of Arkansas' best interstate highways in the Little Rock area. During the trip I learned something.
Watch the road for big truck short dual skidmarks. This usually means there is a certain bump in the road because the skid marks are from dump trucks running empty and having the pusher axle raised and the tires slap the ground because of the road irregularity.
Dean Lowe and I talked about his old RPU and current RPU. Dean says his current truck can be a handful on a rough section of road when driving at highway speed.
My car can be too. What we kinda figured out is the body is able to rotate easily over the rear suspension, and possibly the front suspension. We came to the conclusion of having a longer panhard bar should help the situation because having the shorter bar almost has the car on a pivot point lke a teeter tooter.
We also talked about possibly using a dead perch on the front spring because the car may be trying to roll between the shackles too, which would also contribute to the body roll.
I had added a sway bar on the rear (Brizey, you're correct on anti-roll bar) and I believe when on a rougher road, it's in like a spring loaded correction mode to each side all the time, fighting body rotation and making for another uneasy feeling in the rear suspension.
So like everything else I've done with the car, I have more learning and fabrication to do. Possibly will have to weld some more stuff to the frame. I'm damn glad I painted instead of powder coating!
My old dirt car style suspension needs to be a little different for better street and highway driving characteristics.

 

if the car drove ok b4 the addition of the anti roll bar I would disconnect it and go for a ride for comparison .