The only place for a coil spring is up Zebedee's arse.
Joined: Sep 02 2016
Posts: 320

Wonder why the purveyors of these abominations don't mention why they are such *** to remove
once we have actually realised that their 'expectations' are not realised in practice ?


Joined: Sep 14 2016
Posts: 339

Its worrying how marketing buzz wins out over proper engineering.

It should be self evident that a polybush system can only work as advertised "provide improved control due to consistent steering geometry" when used as a cheap substitute for rose joints. With a bit more compliance for better NVH (Noise, Vibration, Harshness) levels. Rose joints are rough riding. Of course any significant compliance promptly interferes with the preciseness of the steering geometry. Somewhat contradictory. Time to quote Emerson.

Most road vehicle suspension systems aren't geometrically good enough to work freely over the full range of movement when rose jointed so the compliance of rubber bushes not only controls NVH but also gives that essential "give" to let things articulate properly. If you start seriously looking around car suspension systems its clear that there is some pretty serious engineering going on in the rubber bits. They don't do void bushes and the like for fun.

P38 suspension geometry is basically that of cantilevered leaf springs. Whatever your views on old fashioned, cantilever leaf springs with solid axles are a pretty good system so long as the tyres have reasonably deep sidewalls, especially when stabilised with a Panhard rod. So long as you ignore the inconsistent friction and self damping characteristics. Which is probably OK if you keep below 50 mph! P38 variant keeps the advantages and sorts the friction / damping issues but has to have controlled compliance. Rose joint it and it will pretty much lock solid in roll. Bump steer is going to be interesting too. Rigidly consistent steering and suspension geometry you don't have. What you do have is carefully balanced and compensating "compliance errors" that make the system work well. Appropriate sized tyres, deep sidewalls not boy racer rubber bands, being more than a little important too.

Given that Richards orange poly bushes worked pretty well for a decent mileage the the things clearly don't work the way the maker claims. Cheap Britpart et al blue version falling apart in pretty much nowt flat show what happens when they are sort of made to theory and hammered by 2 tons of P38 saying "I'm rolling so shut up and take it".

Not sure that I'd be happy spending money on something allegedly "better" that just doesn't work the way the makers say. Also deeply skeptical of the development abilities of "we make (aftermarket) bits for any car" firms against the real vehicle manufacturer who is going to put serious resources behind getting it right so they can make many thousands of cars and keep the customers somewhat happy. Whatever your views on Rover and BL in general the primary failings were production side, not engineering side. Bearing in mind that hitting the price point is hard and engineering compromises are inevitable. Which sometimes don't compromise as happily as was anticipated.

As the man says "sell the sizzle, not the steak". Most customers aren't equipped to analyse things properly. Especially as new "near enough to sort of work" will, initially at least, be an improvement on tired old soggy standard. Remember the instructions on all those snake oil economy devices "First give the car a full service and tune up so its running properly". Might as well have stopped there and saved on snake oil. Or the old motorcycle tuners trick. Put a decent step about halfway up the power curve to make them rev it out properly in second and third. Feels faster but why not just rev it out in the first place!


Joined: Dec 30 2015
Posts: 1359

I totally agree. There's a lot of aftermarket bits that will work. It doesn't seem to be so hard to make metal bits that are the same shape or good enough. But I've always found it worth buying the best rubber bits you can find, be that bushes, hoses* or tyres!
Polybushes are popular with the wrong sort of people ;)

*ok, not always rubber.. but rubbery.

Joined: Jan 05 2016
Posts: 869

The only time I've used polybushes (or a variation thereof) was on my E39. The rear trailing arms have pressed bushes that aren't (or weren't, it has been a while) available separately, and the arms costs somewhere in the region of £500. EACH.

Set of polybushes from some supplier in Europe specifically for these arms on the other hand was something like £80 I think. Even if they needed replacing every 2-3 years, it would have taken quite some time to justify spending a grand on two arms.

Joined: Jul 12 2016
Posts: 812

Sloth wrote:

The only time I've used polybushes (or a variation thereof) was on my E39. The rear trailing arms have pressed bushes that aren't (or weren't, it has been a while) available separately, and the arms costs somewhere in the region of £500. EACH.

A friend of mine has an E92 320D that needs new bushes for some of the arms in his suspension. I hope for his sake that either the arms are cheaper or the bushes are available!

Joined: Sep 02 2016
Posts: 320

Of course we could always 'just' make them ourselves .... https://www.youtube.com/watch?v=2_0BYvTkZ0o (FF to 5 mins or so)

...16-24 hours curing time (@23C+); His Follow-up vid shows they certainly held up to 10months/1000 miles

Note: I still hate them but this looks like fun !