Talking about technical stuff has never been part of my forte but something caught my eyes when it comes to Pocong equipped torsion twist beam axle, which has been used by VW ever since Mk1 till Mk4 Golf and now in the Pocong.
Gossiping here and there, you’ll definitely be sure that majority of people prefers independent rear suspension (IRS) in comparison torsion/twist beam. Hardly surprising because generally speaking, it offers better ride quality and handling characteristics due to lower unsprung weight and the ability of each wheel to address the road without disturbing its neighbour. Does that make torsion beam axle that much inferior? If it is, how come Megane R26R which is the fastest fwd car ever to lap Nordschleife equipped with one?
Let’s have a brief idea what is torsion beam axle. Imagine it as long metal H shaped bar which the front H attached to the chassis via rubber bushings while the rear H carries stub axle for each side of the car and the cross beam holds two training arms providing “roll stiffness”. Coil spring are in placed for both side where they sits collinear with damper to form a “coilover” unlike having damper sits inside coil spring in IRS. VW at least to my knowledge didn’t use anti roll bar for the rear.
A key difference between the camber and toe changes of a twist beam vs IRS is the change in camber and toe is dependent on the position of the other wheel, not the car's chassis. In a traditional independent suspension, the camber and toe are based on the position of the wheel relative to the body. If both wheels compress together their camber and toe will not change. Thus if both wheels started perpendicular to the road and car compressed together they will stay perpendicular to the road. The camber and toe changes are the result of one wheel being compressed relative to the other.
In simplest term, torsion beam axle is very much a semi-independent where wheels can move relative with each one but their motion is inter-linked than IRS. Given that, tuning it is very much limited in torsion beam axle where toe, camber and caster couldn’t be adjusted upon doing alignment.
Naturally, oversteer will be more apparent nature in torsion beam axle. Thus why car manufacturers dial more –ve camber and +ve toe and softer spring & damping to mask this characteristic to give more compliant ride. Balance between handling and comfort is one trade juggle. You can’t have as ideal setup as you’ll get in IRS.
So we can conclude that torsion beam sucks? Err not really. Because it fairly use less components, you’ll get less weight, and because it’s ‘fixed’, rear cambers and toe didn’t have to be realigned after going through our infamous potholes. Unless you managed to bend the torsion beam axle, which I did after suffering horror tail out in the Proton Savvy, it won’t cost you your arm & leg i.e. RM800+. Hey for that whole thing, it’s reasonable.
Adding after market shims will reduce +ve toe will get the car more neutral. Anti roll bar for the rear will resist lateral motion of the wheels as the body leans in turns. Brands like H&R, Eibach, Neuspeed and Whiteline have blade adjustable where you can opt for three settings “Soft”, “Medium or “Max”. On top of that having H&R sport spring & Bielstein sport dampers providing firmer damping all around. And because you’ve done so much on the rear, you may need to replace standard front anti roll bar with after market ones as well to get it balanced all around. Replacing hardened rubber bushings will be next if you’re really hardcore. One thing that’s tough for the Pocong, is how can you extend the front & rear tracks apart from replacing the wheels. 17” is presumably the max you can go for as beyond that scrubbing against the wheel arch will be just a start of a whole new problem. When there’s a will, there’s a way and on top of that certainly plenty of dough will go down the drain.
Gossiping here and there, you’ll definitely be sure that majority of people prefers independent rear suspension (IRS) in comparison torsion/twist beam. Hardly surprising because generally speaking, it offers better ride quality and handling characteristics due to lower unsprung weight and the ability of each wheel to address the road without disturbing its neighbour. Does that make torsion beam axle that much inferior? If it is, how come Megane R26R which is the fastest fwd car ever to lap Nordschleife equipped with one?
Let’s have a brief idea what is torsion beam axle. Imagine it as long metal H shaped bar which the front H attached to the chassis via rubber bushings while the rear H carries stub axle for each side of the car and the cross beam holds two training arms providing “roll stiffness”. Coil spring are in placed for both side where they sits collinear with damper to form a “coilover” unlike having damper sits inside coil spring in IRS. VW at least to my knowledge didn’t use anti roll bar for the rear.
A key difference between the camber and toe changes of a twist beam vs IRS is the change in camber and toe is dependent on the position of the other wheel, not the car's chassis. In a traditional independent suspension, the camber and toe are based on the position of the wheel relative to the body. If both wheels compress together their camber and toe will not change. Thus if both wheels started perpendicular to the road and car compressed together they will stay perpendicular to the road. The camber and toe changes are the result of one wheel being compressed relative to the other.
In simplest term, torsion beam axle is very much a semi-independent where wheels can move relative with each one but their motion is inter-linked than IRS. Given that, tuning it is very much limited in torsion beam axle where toe, camber and caster couldn’t be adjusted upon doing alignment.
Naturally, oversteer will be more apparent nature in torsion beam axle. Thus why car manufacturers dial more –ve camber and +ve toe and softer spring & damping to mask this characteristic to give more compliant ride. Balance between handling and comfort is one trade juggle. You can’t have as ideal setup as you’ll get in IRS.
So we can conclude that torsion beam sucks? Err not really. Because it fairly use less components, you’ll get less weight, and because it’s ‘fixed’, rear cambers and toe didn’t have to be realigned after going through our infamous potholes. Unless you managed to bend the torsion beam axle, which I did after suffering horror tail out in the Proton Savvy, it won’t cost you your arm & leg i.e. RM800+. Hey for that whole thing, it’s reasonable.
Adding after market shims will reduce +ve toe will get the car more neutral. Anti roll bar for the rear will resist lateral motion of the wheels as the body leans in turns. Brands like H&R, Eibach, Neuspeed and Whiteline have blade adjustable where you can opt for three settings “Soft”, “Medium or “Max”. On top of that having H&R sport spring & Bielstein sport dampers providing firmer damping all around. And because you’ve done so much on the rear, you may need to replace standard front anti roll bar with after market ones as well to get it balanced all around. Replacing hardened rubber bushings will be next if you’re really hardcore. One thing that’s tough for the Pocong, is how can you extend the front & rear tracks apart from replacing the wheels. 17” is presumably the max you can go for as beyond that scrubbing against the wheel arch will be just a start of a whole new problem. When there’s a will, there’s a way and on top of that certainly plenty of dough will go down the drain.
Sketches of twist/torsion beam axle
Whiteline rear bush control arm
Whiteline toe kit adjustable (Shim)
Whiteline rear ARB 20mm blade adjustable
Whiteline front ARB 22mm blade adjustable
No comments:
Post a Comment