how would lowering a beam change the toe in? the wheels will still be the same angle relative to each other when looked at in plan view. I'd say if you want to centre the wheels in the arch, move the whole lot backwards at the beam/shell mounts and avoid potentially bendy flappy unsprung weight increasing plates
you dont lower the beam you raise the height of the stub axle which means the beam does not travel into such an acute angle and remains totally horisontal.
Further to what's in post 1 off the Mk3 TDI car, it's only been sat in the Mk3 Kit Car homologation papers all along. Takes a decent picture and it all makes sense!
Okay-doke...so all that extra work was to raise the engine, so the bags could drop the whole car further (relatively) with the net result being the subframe was back on the floor, yeah? Kinda proves my point...
when you think 2 dimensionally - yes it would your spot on, but its a 3 dimensional movement 5 minutes toe in for example & 1'30 mins (half) camber what happens if you flip it 90' though the axis ? yes fixable, with shims but most setups have an offset stock axle bushs I could go more in depth if I'd actually done any reseach, as well it could also account for lowering COG, retaining close to OEM for the regs??
My god Im just seeing this now. So Ill add some. Im going to start a thread soon with these drawings Ive talked about but Ill fire these in here right now. The drawings are of the rear beam cross section. All dimensions are taken by me, off a 90> spec gti rear beam. So Ill say Im happy that they are correct. There is two drawings on the drawing. The first is standard height and in dark pens. The pink highlighter is of the car lowered 30mm and is shown directly ontop of the standard height drawing. Notice what changes. The body is lowered 30mm, obviously. The wheel centre moves forward 8.5mm. The roll centre drops from 62mm to 52mm. I have all drawings done in plan view too showing toe change(minimal)Very Minimal) But they can wait. The front roll centre which I have also calculated sits 40mm from the ground. Giving the ideal roll axis angle from front to back of I cant remember what. (Ill look later) The main points on drawing are Beam pivot Torsion centre(the centre pivot axis of beam u section) The wheel centre And, the ground. They are simple drawings, just spend a while looking and all will become clear. Ill present them a bit better once I kick them all off in a thread, but they may be food for thought for the time being. Ill draw in what happens with a yellow marker later if the plates are used as discussed earlier. You may have noticed I dont watermark anymore, takes too long. So a sloppy signature will have to do, sorry if its a bit out there. BG
Ill explain how to calculate theoretical roll centre for a torsion beam later. Its very simple.(But very hard to find out as to how you actually do it!)
are these just simply to retain the correct wheelbase, which will shorten as the rear beam arches upwards? i'm sure there is an advantage to keeping the beam horizontal also, kinda the same principle as keeping the track rods and wishbones flat at the front
No - the purpose of them is appearance: to centralise the position of the wheel in the wheelarch on a lowered car, solely for aesthetics. The purpose of this thread though is to say 'stuff that - how can these be used from an engineering perspective?' !!
sorry, worded that wrong, i'm commenting on the reason the works beams have these modifications. Stuff the aesthetics!
Right! The Mk3 TDI beam on page 1 is done for geometry reasons, not the same principle as wishbones, but I know what you mean. If they merely wanted wheelbase, they'd extend backwards only, so the fact that they extend upwards tells us something about the behaviour of the beam around its pivot. The Astra beam is simply lengthening of the wheelbase, but I don't know an Astra beam from a Cavalier beam, so it may be sturdier too, other reasons etc.
its probably the case of keeping the beam horizontal so there is minimum geometry change when the wheel raises into the arch, similar to minimising bump steer on the tie rods. Its an interesting mod though!
By keeping the beam horizontal with the plates you gain suspension tarvel, isn't it best to have a softer back end with more travel so that you are less likly to cock a wheel, I have heard of keeping the rear end supple to help gain control and turn in... We dont have indendent rear suspension so it is harder achive this when dropped. Adding an anti-role bar to what already is a large anti role bar (the beam) can cause it to be too snappy and edgy.
Agree with that, but I can't help feeling there is something else at play here, I can't put my finger on it. Axle behaviour under braking, as the body rises.
As you brake the front dips, the rear rises, short travel rear shocks will I supose 'lock out' and loose their travel - back end becomes edgy? More travel on the rear allows the beam to still ride bumps, corner etc when braking without the edgyness, or at least make it less?
The extended travel at the rear of my current setup certainly helps with stability and cornering . Gurds
It's not so much short dampers I'm thinking of as there is only so much forward lurch to extend them. I'm more thinking of the starting point under braking, with the axle pointing upwards. The comparison is an OE ride height where the axle extends downwards below the horizontal as the rear simultaneously lifts.
