On a parallel leaf set-up do the spring hangers need to be at the same height or can one be higher than the other? I know pinion angle comes in to play in the rear...but thats all I know! Thanks
Are you talking smae height side to side or front to back? Side to side I would think that you would want them the same height unless you were running some wierd drag racing spring preload setup. Front to rear often the front spring hanger is lower that the rear even if you account for the length of the shackles.
Remember you have to factor in the length of the shackle on the rear end of the spring. I don't believe having them at the same height is critical however your static pinion angle once it is all together is. I would be more focused on getting that right than equalising the hanger heights front to back.
The front and rear mounting points need to be the same height from side to side, but not front to rear, and the front mounting point no higher than the center of the rear housing. This will allow the spring to work properly. Speedy
Yup...helps control "roll steering" as a vehicle leans in a turn. Having the front too high or too low can do some strange things to handling!
I am a picture guy..... Side shot of frame rails, with hangers...on my F1 the hangers are at the same "elevation", like in the picture on top....I am curious of the effects of moving one or the other up like in pic 2 would cause problems.
That will give you more down angle on the pinion, which can be fixed to some extent with tapered shims between the spring and axle. If you are trying to lower it much with this method, I would suggest dropping the front eye mount the same distance.
I had to 'drop' both my rear spring mounts front and rear on my F100 as I put the 9" housing on top of the rear springs instead of under them to lower the truck. And found out it lowered it alright - by about 8" or so - and that was before I removed any leaves. So I used some box-section steel etc and remounted the spring mount downwards the amount of using the top rivet holes on the cast hanger were where the lower holes were on the frame/ch***is...if you know what I mean.
[FONT=helvetica,arial][FONT=helvetica,arial]The geometry of a leaf spring suspension has the best overall handling whenever the rear leaf eye height is mounted higher than the front eye height.[/FONT][/FONT] It is to induce "Roll understeer", when a car bodyrolls the outside wheel moves forward on an arc from the front spring eye. This causes the rear end to try and steer inwards on the corner or straighten the front up [ understeer ] The purpose of roll understeer is to load up the suspension with a little bit more bodyroll so it stabilizes the rear end. If the suspension had Roll "Oversteer" the rearend would become loose and unpredictable on corners, but the real nightmare is in a straightline when bodyroll and roll oversteer cause the rearend to sway back and forth [ the rollsteer and bodyroll work opposite to each other ] This is a flaw on most homebuilt trailers and a lot of caravans ,because people think the axle should arc rearward over bumps , if the turned the springs around so the shackles were at the front [ similar to straight axle g***ers ] they wouldnt sway uncontrollably.
I am curious to know why no caravans or trailers I see dont have such a setup then if it works so well. I am not trying to be smart, but just asking the question since from your detailed explanation it sounds practial. I would have thought from a safety point of view authorities would promote such a concept for regular use.
Most caravans that have this swaying problem are single axle [ tandems have the springs facing opposite to each other ] These single axle caravans were a nightmare on NZ roads in the 70's [ usually being towed by a near-sighted driver in a small family sedan ] Nowadays most caravans have trailing torsion axles. Torsions do not steer the axle through the range of suspension movement. Roll steer is a problem of any straight [or beam ] axle. It cannot be eliminated, but only minimised.
Sure it can... Just use the ORIGINAL torque tube and single pivot wishbone style suspension of an early Ford. Ol' Henry wasn't dumb....LOL Trailing arm setups like those torsion arms WILL move the wheels back and forth BUT they don't use a connecting axle so they keep the wheels parallel to the direction of travel. Never thought about the difference between front and rear shackles having that much effect on rollsteer...but it seems very likely!!! Interesting stuff!
The A frame beam axle is one of the simplest systems out there, But even the A frame system has roll steer [it is only minimal ]. To totally eliminate roll steer the pivot ball and the axle centerline would need to be exactly the same height at all times [as in no up/down suspension movement ] Lowering the pivot induces roll understeer and raising induces roll oversteer. If we go back to the subject of trailers for a while. On a tandem trailer with rocker equalizers [and shackles] when the suspension compresses on the outside of a corner ,that side wheelbase shortens causing roll understeer which is stable. But on a cheap tandem trailer with rocker equalizers and slippers [or sliders] on each end ,when the suspension compresses on the outside of a corner that side wheelbase lengthens causing roll oversteer which is unstable. You notice this when following one and suddenly a Semi goes past and itll start to sway [ the saving grace is the tow vehicle can usually pull the guts out of the trailer ]
In the front you have the same issue. Just replace "pinion angle" with "caster angle".... It's even more important to keep from rotating the front axle when you move the spring mounts.
I've been looking into parallel leaf suspensions a bit. On the rear, I've noticed the rear leaf eye higher than the front. From my reading it appears that this is done to try to make the front half of the spring close to parallel with the ground (within the limits of the actual spring being arched). With the fixed mount in front, this then makes the front half of the spring tend to act as a trailing link to locate the axle, and the rear tends to provide the actual suspension. That makes a lot of sense to me, but I don't know if it's an accurate representation. But I see the opposite configuration on the front. Not counting the 4x4 guys, it seems, on the front axle, the spring eye is fixed up front and higher than the rear, which tends to be the shackled end (but not always). I've read the shackle can be on either end - usually it's on the end opposite the steering link - in other words, on a front steer, you'd put the fixed leaf mount in front. On a rear steer, you'd put the fixed link mount in back. This keeps the axle located on the same half that the steering is occuring to minimize any bump steer due to axle movement. But it seems like you'd want the front mount lower on the front axle for the same reason you'd want it that way on the rear axle - so the front link is close to parallel so it acts primarily as a link. About the only thing I can come up with is that the front axle does most of the braking, so you'd want the rear half of the spring to locate the axle. But if the shackle is back there, it doesn't seem like it'd be an effective link. I've looked all over the web and haven't found a good discussion of setting the spring inclination angle on front parallel leafs. About the best I can come up with is to copy the OEMs, but I'd really like to know the "why" behind it.
On the front leafs, it occured to me that the front eye might be mounted higher than the rear to provide a degree of anti-dive on braking. Just speculation on my part though.
This is a reasonably correct ***umption. If the geometry of the steering is correct [ not to be confused with suspension ] you usually dont get any roll steer in the front. In the rear the wheels are fixed at 90 degrees to the axle,so if there is a wheelbase variation the rear will steer [ due to the arc it travels ] For example: if you had a front suspension with "cowl steering" and no bump steer ,any wheelbase variations will not affect the direction the wheels are pointing [the drag link controls this ]
The Jalopy Journal
