Hot Rods Suspension Magicians LOOK HERE...

OK, my self built roadster has been done for a couple of years now and I'm generally satisfied with it. BUT (there's always a BUT, right).

The ride quality sucks. On smooth pavement it rides and handles very well...on bumpy roads or going over bridge joints it will beat you to death.

Many I've talked to say, "get used to it, it's a hot rod, they all ride rough."

My response is "maybe". I'm not quite willing to admit defeat without a fight. My reason in making this post is to hopefully start a serious discussion about ways to improve the ride quality of street driven hot rods. I have lots of questions and if I can find some answers for them that make sense, my plan is to tear into the suspension on my car over the upcoming winter "down time".

Here's the specs on my current setup. The front end: 3" dropped axle with Bilstein "shorty" shocks, Posies spring, hairpins and panhard bar. The front is fine, never bottoms out and rides good. My plan would be to leave it alone.

Rear End: C notched frame, with ladder bars, Bilstein shocks and coil-over springs. The shocks have 3 inches travel from fully collapsed to full extension. Springs are 8" length, 150#. Ride height is set at 11.5 inches eye-to-eye on the shocks. These are the settings recommended by Bilstein. There is approx 2.25" travel between the axle and the frame. I have played around a bit with different spring rates and 150# seems to be the best compromise.

Now, my questions:
Is it simply a matter of shock travel? If I make the C notch deeper or do a mild Z on the rear of the frame this should enable running shocks with more travel. Will this and some appropriate tweaking of the spring rate equal better ride? I realize the rear floor and subrails would need to be modified and I'm OK with this if the fix will make a dramatic improvement in ride quality.

How much shock travel is necessary to improve the ride? I currently have about 2.5", which obviously isn't enough. What's the magic number here...3"...4"...???

I had the same problem more or less with the coupe I owned before the roadster. I tried lots of different shock/spring combinations and while some were marginally better than others, I never got it to ride as good as I wanted. I'd like to hang on to this roadster for a long time, and it sure would be great if it didn't ride like a log truck.

'Appreciate input from folks who have delt with this problem and solved it.

 

Is the rear suspension bottoming out? If so, what do you have to control the bottom out? Bumpers, size, shape, durometer?

If it is bottoming out, you may need more spring, or (different) bumpers to control the last 1/2 to 3/4" of travel.

Also, you say you have 2.25" of compression left, but how much extension or rebound do you have? Does the car sit at mid stroke on the shocks at ride height?

What air pressure are you running in your tires?

 

I wouldn't design for less than 6" total travel at the wheel: 3" bump; 3" rebound – more if you've got the room.

Most conventional live-axle damper installations have more damper travel than wheel travel. Damper valving generally doesn't like too much leverage, as you're wasting too much motion in valve compliance etc.

 

What angle are the rear coil overs installed at, when viewed from the rear?

 

QA-1 coil overs have adjustable bump and rebound. I have them on a few cars at the moment. You can control ride firmness with a couple of clicks. They even make them adjustable form inside the car. I like Bilsteins, I have them on my Roadster but I use QA-1 when I run coil-overs.

 

post pics of rear suspension

 

Tom,I'm not a magician but I can make almost anything disappear all I have to do is lay it down!

Just before the All Deuce Run I replaced my old rear coil over Shocks , they were 30 years old and technology has made leaps and bounds since then, with the QA- 1 that Several of my friends had used in recent years and they have have 18 different adjustments with the simple turn of the knob and 11 different spring rates from 95 lb to 500 lb.

When we were building Dave's deuce pickup we installed the shocke and put the softest setting and I stood on the frame and bounced and it bottomed out,we then put it on the stiffest setting and again I bounced up and down and they didn't budge,Dave & I stood on it and hardly moved.

When we left home for the all deuce run I set the adjustment on 3 and the car only bottomed out once,when we got to the motel I turned the knob on each shock 2 turns,the ride was very smooth and I never bottomed out again. HRP

 

This ....^^^^

Sent from my SM-G900V using The H.A.M.B. mobile app

 

This is not Tom's first Deuce build and the shocks are set up the way all the frame manufactures configure their angles.

I know he doesn't want it setting like a 4 wheel drive truck.

Just for S & G's how much are are you running in the rear tires? HRP

 

If it were me I would give Ohlins in Hendersonville a call. They have a suspension Dyno and you can look at what the car is doing, adjust it and put it back on the simulator.

 

The picture above that Danny posted in post #9 is of my car's rear, showing the shock angle. To answer some of the other questions: The car sits at mid stroke at ride height. The 2.5 inches referenced in my original post is the distance from the top of the axle housing and the bottom of the C notched frame with car sitting on the ground and half a tank of gas. I'm using bump stops that mount in the C notch. They are small, maybe 3/4 inch thick and hard rubber...I don't know what their density reading is.

I'm running 33 psi in the rear tires. I don't want to go too much below this due to tire wear issues when underinflated. I'm seeing a couple of votes for QA-1 shocks and will do some more research on them. It'd be great if a simple change in shocks would fix this.

Pigfluxer, thanks for the tip on Ohlins in Hendersonville. I think I'll give them a call, they are not too far from me and getting the car suspension dynoed could answer a lot of questions.

Ned Ludd, thanks, your comment re-enforces my original supposition...more shock travel would fix it.

Thanks guys, keep em coming.

 

It can be a lengthy dance between spring rate and valving/dampening.

If I had access to a suspension dyno, I would be there asap. It will likely save you money and headaches.

One pair of springs, and one pair of shock bodies can turn a car you hate, into a car you love!

 

A light car like that does not need anywhere near that pressure. Take off 10 and try it.

 

Exactly.

 

Agreed...33psi is WAY too much for a light weight car.
What's the front vs. rear weight ? What's the full car weight ?

How long are the "ladder bars" ? Are they like in the picture above ? That suspension should have a good ride if the shocks and tires are setup correctly.

I'd bet that about 26 to 28psi would go a ways toward lightening the bad ride...without...hurting the tire wear.
I'd bet that that the corners of the tread have never been on the ground at that pressure..! Unless the car weighs 3800lbs.

Mike

 

~ 18 - 20 psi may help. A friend w/a 27 T roadster ran 12 psi! (You're too low psi if the 'Payloader-at-Speed' effect happens) and tire sidewalls oscillate at speed.

 

Hard to say without testing myself but the ladder bars may be the problem or in part..

Set up my first car with and tested the articulation and immediately threw them out and installed a four link.. obviously a lot of guys don't like as they don't look trad but on a low car where there not seen I don't have a problem with them.. ladder bars are in essence a fixed mount on the rear which won't allow the bars to move in relation to.. it's the same principle as a split bone and beam car but on such the axle can twist and allow the suspension to still articulate in the chassis.. Truck arm are also of the same design and I'm assuming that's why there an I beam so they can give and allow the rear some resemblance of a working..

Never say never but I probably wouldn't run ladders on a street car if at all possible..

I've got a four link, transvers 40 ford front spring (obviously in the rear) non techy 69 nova shocks and a panhard in my A and considering I think it does pretty well.... but I view it as a hot rod so my standards may be different??

A possible "solution" might be to test the car under driving conditions without the rear sway bar.. with ladder bars the rear is acting as a sway bar of sorts and being as how it can't twist like an axle much stronger of one.. .. essentially with the sway bar rear your "doubling" up the control compared to the front, obviously this differs on how the ladder bars are set up and are affecting the chassis so this is pure speculation..

My A is fairly low and with split bone front giving the axle sway duty handles well imo and has no additional roll control and with the four link shouldn't have much roll resistance from the rear as opposed to your set up??

Also the panhard being un-level may be affecting.. especially with ladders as at rear mount points are fixed so theres no give..

my .02..

 

The ladder bars in the picture are a time-tested, perfectly valid setup. Parallel ladder bars make the rear axle a giant anti-sway bar. Ladder bars that nearly meet at the leading end do not. They allow the rear housing to rotate, through a combination of bushing deflection, and bar flex. Truck arm rear suspension works exactly the same way, but the arms are a little different in configuration.

The panhard bar in the picture is not level, because there is no body on the car to compress the suspension.

 

Interesting, never thought about the effect of ladder bars with a sway bar. May try taking the sway bar off to see it there's a difference. I'll try dropping the tire pressure too. As for the panhard not being level, it's because the photo was taken without the weight of the body on the chassis. Once the body and other components are on it levels out. Somebody asked about the weight of the car, it's 2500# with gas and my fat ass in the drivers seat. I don't know about the front/rear distribution.

 

With that setup, they don't.

@Ned Ludd, can you give an explanation of this? I am on vacation, an need to get off the board before my wife smashes a wine bottle over my head.

 

After looking at photo posted by HRP and reading what Gimpy and others have written, I gather that the angle of the panhard bar is now shallower now that cart is at ride height? The longer the bar the smaller the arc and less lateral movement during suspension cycling. Depending on how the car now sits with body on, what angle is it now on, is it close to horizontal? I'm no expert but would it work better when parallel to centreline of rear axle. Is it feasible to modify the pinion bracket to accept a longer panhard bar and alter angle to horizontal? Insofar as sway bar is concerned I wonder if that is having any adverse impact on the handling? I have one in my car with Jag IRS and I'm happy with it however I've never seen one with ladder bars before and only with parallel 4 bars and on heavier triangulated 4 bars in bigger bodies.

At ride height shock needs to be 1/3 down stroke as a rule of thumb. Others more knowledgeable than me will no doubt seek further information from you on the car, weight, set up etc etc. Based on information your shocks should be compressed 1" at ride height with an additional 2" for compression. There is not a lot of room between axle and frame, do you have bump stops? I'd be more comfortable with 3-4" clearance.




A '32 roadster with a 350/350 weighs approximately 2,600lbs; 1,200lbs over front axle and 1,400lbs over rear axle.

 

I been designing an building car kind of a long time,started in the 1950s,mostly race cars,that win a lot.
I only started with that line too set were I'm coming from!
#1;First is tire psi,lots of guys think it needs to be what it said on the tire< stop right there,and know tire is not on a stock auto!! The car is most likely a lot less lbs. then what tire was design for. So only pump up tire just enough to hold side walls from bending outword near the road more then about 1/2in.{ about same it would do on a big car of 3000lbs+ with 33psi. Know that tire is designed to flex over bumps as to load,and now the load is far less! Far better ride can be had by tire being at the right psi for load on tire{ that for your roadster is likely around 20psi or so=look at sidewall . This will be biggist thing for ride. A tire that is over filled for its load dosen't flex...............
Next is springs n shocks,I see lots both mounted wrong an springs much higher rate then needed.=hard ride. Shocks that are mounted inboard/closer to center of car ride bad*. Springs of higher rate/stiffer then needed ride hard=they are hard. How much movemint you have can be a prob.

 

Yeah, I know.. that's why I added the speculation bit.. hoping I wouldn't have to read this..

 

There is so little weight on that 32 out back, so more effort is always needed, compared to say a 40 ford woodie.

this won't help you with coil-overs...but..

I set up the buggy spring "feel" first with no shocks. That is done with the car just sitting there, push down on the back end. If it is already too stiff, imagine it with even light shocks.

So get the spring to feel decent, then go with light shocks, not some HD gas shock.. But you are stuck with coil-overs, so IMO, you are somewhat limited compared to my late 40s very wide (longer leaves make for a better ride)rear spring, with separate shocks that I can set the shock angle, as well as have choices on the different shocks "feel" by both hands, before even putting them on.

bear in mind that a short back end (short rear body & low weight) makes the unsprung weight formula tougher when we use a heavy rear end ass'y... so it is a lot of trails before you get it nice. It can be made to ride nice.

.

 

Another thought after looking at photo, if you draw intersecting lines through the front ladder bar mounting point it appears that the sway bar may be parallel to top bar, therefore they both pivot at different points. If you were to adjust the pivot point of the lower sway bar connecting rod so that it is on a similar imaginary line when drawn from front ladder mounting point to where it mounts to axle housing, triangulating everything at the same pivot point it may impact? Hopefully you won't any more strange harmonics.

 

Not sure, you're right that in a ladder bar set up the resistive forces are minimized with the chassis mount points close to the center line but there still there, which in a sound system is only an increase in spring rate effectively.. combine that with a sway bar which also increases the spring rate and coil overs that may not be tuned to the set up and you may have a problem.. if that's the case then you're right that the system could be cured with springs.... and if not manipulate the sway bar also..

 

I've put together cars with that P&J ladder bar suspension. It is perfectly fine.

Harshness comes from things too stiff: PSI, springs. If the psi is okay and the springs are not too stiff, the next bang comes from a lack of available travel room.

Coilovers make it harder to test springs. On a car with leaves or coils with separate shocks, the usual thing is to remove the shocks and give the car a bouncy-bouncy test. No bouncy-bouncy = springs too stiff.

I guess with coilovers you have to play with different coils.

Once the spring right, you can play with shocks.

A heavy diff and rolling stock doesn't help in a light car either, but you can get a decent ride in a Deuce roadster.

 

If lowering the air pressure isn't enough I would recommend moving the upper shock mounts in a little bit to lay the shock over a few more degrees. I'm not a slide rule engineer, but someplace on here was a discussion and chart about shock angles. That will give the wheel more leverage, plus you can run a longer shock and stiffer spring, but it will work better because of the leverage thing. And drilling and sleeving two holes is easier than stepping the frame and cutting the floor.

 

I ran a 32 roadster for 10 years with no harshness, rear coil Jag overs springs rated at 220lb.
One thing I always test is the ability for the suspension to actually work, pretty basic test, stand on both the front and rear spreader bars ( one after the other) and bounce the suspension, if the suspension bounces you are pretty well somewhere around the mark, if it doesn't bounce there's your problem.
As others have said, shock valving and angle etc will fine tune the system,
And no Hot Rods don't need to drive like a bucket of shit to be a Hot Rod, if they do they should be fixed.

 

Thanks @gimpyshotrods . Let me explain it this way.

The most extreme angular displacement the axle is likely to see in roll is something in the order of 6°. That's one wheel 3" up and the other 3" down – a situation you're not going to experience every day. If the ladder bar pivots on the frame are 35" apart, they'll want to move around 1¾" up or down at that angle, only they can't because they're attached to the frame. The only things that can happen is that the ladder bars rotate the frame to the same angle as the axle, or flex trying, or twist the axle. That is how the ladder bars and axle become an effective anti-roll bar.

Now suppose the ladder bar pivots on the frame are only 5" apart – which seems to be roughly your setup. Then at 6° the ladder bar pivots only want to move about ¼" up or down. That might even be within the compliance of large rubber bushings, if that's what you've got at the front of the ladder bars. In this case the anti-roll action is vastly diminished, enough so that you can pretty much leave it out of consideration.

If you go further and suppose that there is a single ball joint at the front of both ladder bars, there is no tendency to vertical displacement at the pivot no matter the angle of the axle. There would be no anti-roll action whatsoever. You've then basically replicated the original early Ford torque tube setup for all geometric purposes. In the real world a single rubber bushing would give the same result, as long as it can accommodate 6° of misalignment without a lot of resistance.

In all these cases the axle and ladder bars form an assembly which rotates in roll about an axis which runs through a point halfway between the front pivots and the rear roll centre, which in your case is the point where the Panhard bar intersects the central vertical plane of the car. You'll notice that this axis slopes up to the rear, seeing as you've got a fairly high rear roll centre. This will induce a tiny bit of roll steer, luckily in the safe understeery direction. If you've got the space to raise the front ladder bar pivots a tad, that would harden the hook on launch a bit and simultaneously reduce the roll understeer, i.e. give sharper, less Dad's-Oldsmobile responses. (And high rear roll centres are the norm, conventional wisdom coming from Nascar etc., but there is a huge amount to be said for much lower roll centres overall.)

All in all, there isn't much wrong in principle with this setup, except a lack of clearance over the axle. I'd like to see a good 1½" more.