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I have not read the links above. But I thought adjusting thdebars of the 4 link to create a different effect on one side was the way to keep the front level. And also ensure that on launch the rear wheels actually move away from the body eg the rear body rises.
I have probably got this all totally wrong but I am happy to show my ignorance in the face of such understanding forgiving readers 😬
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Last Edit: Oct 1, 2024 20:14:13 GMT by ivanhoew
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mk2cossie
Club Retro Rides Member
Posts: 3,060 
Club RR Member Number: 77
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Hi James, Jacking the front wheel - I jacked up the front left corner to simulate the car lifting under load, but this is far more powerful as its a direct force under the front wheel and as its a hydraulic jack - unstoppable. In real life the car is twisting around the prop so the leverage is far less and hopefully the extra bumpstops will be enough to avoid the tyre hitting the inner arch and taking all the paint off. PS, It's not cluttering the thread - it's really nice to actually get a comment rather than just likes  I always click the like on posts I like or find informative (Or in some way comedic) I don't often post, as I'm socially awkward. And suffer with foot in mouth quite a bit  But pleased to see you are still improving the pop, blackpopracing  |
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its a complex problem with lots of variables, for twist if the wheels were not touching the ground it would be pretty simple, the propshaft torque (engine torque x torque converter ratio x 1st gear ratio) would be reacted by the engine mounts at the front and axle mounts at the back twisting the chassis , this is what happens on a IRS.
with a live axle one wheel some is still taken via the suspension into the chassis, the rest is imparted into the road lifting the the other wheel by a roughly equal force.
but you have other effects as Robert mentions the suspension geometry can push the wheel into the road or lift it, the acceleration also causes a weight transfer to the rear (C of G comes into this) then there is what happens when the front wheels leave the ground and the wheelie bars come into play, and of course there are also tyres to consider.
Unless you plan to invest in a supercomputer and software like Adams. realistically all you can do is as you are and try to limit the travel, you might also look at off setting the axle to one side slightly if wheelarch clearance on one side omly is an issue.(as long as is parralel to the front one tbis won't have any significant effect)
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Last Edit: Oct 2, 2024 9:06:58 GMT by kevins
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In recent years rear anti roll bars have started being used in addition to loading the links. More rabbit holes...
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Proton Jumbuck-deceased :-(
2005 Kia Sorento the parts hauling heap
V8 Humber Hawk
1948 Standard12 pickup SOLD
1953 Pop build (wifey's BIVA build).
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I have not read the links above. But I thought adjusting thdebars of the 4 link to create a different effect on one side was the way to keep the front level. And also ensure that on launch the rear wheels actually move away from the body eg the rear body rises. I have probably got this all totally wrong but I am happy to show my ignorance in the face of such understanding forgiving readers 😬 All true Robert but I believe Mark is running his rear links parallel or close to. This puts his instant centre at infinity so there is no induced axle separation or loading. |
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Proton Jumbuck-deceased :-(
2005 Kia Sorento the parts hauling heap
V8 Humber Hawk
1948 Standard12 pickup SOLD
1953 Pop build (wifey's BIVA build).
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Paul is correct above.
Robert, I do have a bit of pre load in the top right 4 bar but it does not appear to be doing much. Running it on the street will just wear the bushes out faster.
Kevins,
It's not sideways rubbing - the car drops so much on the drivers side that the inner arch sits on the tyre tread. I'm not too fussed about limiting the front wheel lift - but I do want to stop the tyre removing all the paint every time I launch hard.
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Hi James, Jacking the front wheel - I jacked up the front left corner to simulate the car lifting under load Ah, ok... Sorry, I may have been over thinking it a little. Over thinking it quite considerably actually. crockpot , thanks for posting those links. I'll have a good read and see if I can make some sense of it all. An understanding of suspension geometry always eluded me. That and geography. James |
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I have not read the links above. But I thought adjusting thdebars of the 4 link to create a different effect on one side was the way to keep the front level. And also ensure that on launch the rear wheels actually move away from the body eg the rear body rises. I have probably got this all totally wrong but I am happy to show my ignorance in the face of such understanding forgiving readers 😬 All true Robert but I believe Mark is running his rear links parallel or close to. This puts his instant centre at infinity so there is no induced axle separation or loading. Ah cool , i wonder if theres a row of holesfor the mounting points of each arm .. mark could move the arms up and down to vary the instant centre from infinity to beyond ? I'm imagining that would be moving the bottom arms front mount upwards and the top arm front mount downwards , and do it different on each side to get ou the twwist and give an even launch . i can see mark right now slapping his forehead and bleating "yes yes i know all this... omg! " |
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I had a four bar link system on the Super B.....it still did this!  Mind you - I did later discover one bracket on the axle had broken at the weld so it was only a three bar link!! |
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The problem(?) for me is it's trying to be good at everything.
It would be dead easy to cure the lift if it were a race car only, but then it would not suit the road.
One of the big issues is the rear is quite softly sprung - it needs to be as the tyres are so big - if I go stiffer springs then the tyre sidewalls then become the suspension. So it only has 200Lb springs on the rear. I have 250lb and 300Lb springs but neither ride nicely on the road.
Robert,
Ideally the lower front link would come upwards but I only have the one hole for the lower link. The upper links have several holes I could drop the link down into but from a (rusty) memory that would not help.
Adding preload into the top right bar 'ought' to decrease the torque twist but the amount I added so far has not helped. Again - for the street this is not good as it means the rose jounts/bushes are fighting each other giving premature wear.
It's a big can of worms once you start getting into it.
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What about (thinking totally outside the box) some form of air bag on the side that compresses that you could pump up when needed and leave deflated in normal use. If it would alter the suspension even when deflated then have one each side but only ever pump one up.
Would probably cause some strange handling characteristics with one pumped up but would it matter on a drag strip?
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The easy solution (for the dragstrip) is to just make a diagonal link between the lower front chassis mount on one side and the lower axle mount on the opposite side of the 4 bars. This will stop it almost completely.
I had a look under the car for this the other night, but the propshaft occupies the same space so it would need a 'bump' in the middle of the tube to clear under the prop - not sure if this would affect it or not in use.
As I said, I'm not looking to stop it lifting the front wheel, I just want to stop it rubbing on the inner wheeltub as it removes the paint - and on the dragstrip that rubbing is costing me time/accelleration.
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sounds like a new winter project mark , creating more holes for the front of the bottom arms... then you can have th back of the car rise on launch and a much better 60 ft |
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That's not possible Robert, the lower mount is slightly below the chassis line so going much lower would get into scrub line territory and look a bit pants. I did find out something quite interesting last night though, I had adjusted my shocks for racing to stiffen them up. But before I reassembled them yesterday I thought I'd test the stiffness and found that prior to racing they were at maximum stiffness and I'd actually softened them up by mistake! That would explain a lot then! With this in mind I might go back to the 250lb springs and run the shocks a bit softer as I was under the impression I was only on a midway setting with them. That will have to wait a week though as I'm currently in Greece Cheers everyone!  |
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i thought that spring sounded v soft mark , it will be intersting to see how it works with a siffer rear.
i wonder what wound happen if you fixed the bottom link forward rose joint to the top link chassis point as well ?
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I'm not quite sure what you mean there Robert, but it sounds dodgy.
If I go stiffer springs it just gets bouncy, that's the problem with a light car and tyres that are 3 times too wide for the weight, lol.
As I said before, stiffer springs just make the tyre sidewall the suspension instead.
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Hi Blackpop
I think you should keep it pretty much as it is, It will spend most of its life on the street after all. Chasing the last tenth by making it undriveable is not good - despite the temptation.....(you can see on my BGT picture, I ran very low tyre pressure as well! Too low and it squirmed, too high and it bounced).
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Agreed, as long as I can tame it enough to stop the tyre rubbing the bodywork I'll consider it a job well done.
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