Polyurethane or rubber?

[Luckyone]

I’m going to be stripping all the suspension for paint, so I guess replacing the bushes at the same time would be an idea. Although I’ve no reason for thinking there is anything wrong with the old ones from the way the cerb drove, would the general consensus be to just replace as it’s in bits any away?

Assuming replacement is the way to go polyurethane would seem to be the obvious choice, but I’ve just been getting some new bushes for my other car & it seems the new trend is for harder rubber bushes rather than poly. The reason being poly goes very hard with age then wears, so the holes get elongated & you then get the arms banging about in the over sized holes. I’ve got some 8 year old poly bushes from another car & sure enough they are rock hard now, but it’s been off the road of a long time so I can’t testify to the wear. The harder rubber will go soft with age just like the OE (I think that answers the question of just leaving the originals in) but you won’t the knocking with it.

As far as I know harder rubber isn’t an option for Cerbs, so it’s just OE rubber or poly. As I said I never found the cerb to be in any way sloppy, so I’m thinking of new rubber rather than poly, anyone want to tell me I’m wrong?!

[Ireland]

Poly.

Oh, and the Powerflex ones now come with a lifetime guarantee (according to Steve Heath post on FaceBook earlier) so that should put your mind at ease.

[a1rak]

when my cerb was at Raceproved Julian was of the opinion that unless its strictly a race car then stick with rubber as the cerb is not particularly hard on he bushes. The rubber gives a better ride. Just make sure they are all in good condition. I think getting the suspension correcctly set up is the most important thing to do after the rebuild.

[shpub]

The Cerb is quite hard on bushes in my experience. I fitted a mix on the LS Cerbera 4 years ago. The poly ones are OK... the rubber ones need replacing as they are just starting to go.

Details of the Powerflex warrenty are here

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Edited by shpub on Saturday 2nd October 18:01

[itiejim]

I'd definitely keep OE. If you look at the size of the rubber part of the bush compared to many mdern euroboxes, they are very slim leaving very little room for movement even on a soft, older bush. So long as they are in good condition rubber bushes will give excellent location a far superior resistance to NVH and a longer life.

I think there's a good argument for poly on the diff mounts as there have been proven to be problems there, and they will be easier to change again in the future. However, the suspension I would leave as TVR intended.

[shpub]

I would make your decision after you have spent many hours/days getting the old ones out in the first place. Most people say never again.

The bush movement is interesting as there are some designs where I actually prefer rubber bushes. e,g the TVR Wedge front suspension where the movement offered by the bush is essential because of the way the suspension arms move. The rubber bush gives the best movement. Equally it also demonstrates how much movement you can get even with a slim bush when you have forces applied at the end of a 12+inch long arm!

[shoggyraminator]

I had an Alfa GTV with poly and a Spider with rubber (pretty well the same car) and found the Spider a lot more pleasant to drive. The GTV was really hard especially when hitting any pot holes.

[jammy_basturd]

Is there an merit to the idea of using poly for the front suspension to keep the steering feedback optimal and tight, but keeping the rear suspension on rubber to try and sustain a bit of a comfortable ride?

[shpub]

jammy_basturd said:

Is there an merit to the idea of using poly for the front suspension to keep the steering feedback optimal and tight, but keeping the rear suspension on rubber to try and sustain a bit of a comfortable ride?

Not really as the Powerflex bushes are designed for road use. There are other poly suppliers that offer bushes for other cars with different grades and some of them are sponsored by your local dentist as they are very hard indeed. And yes I do know of some sprinters who mix and match.

If you want a comfortable ride, keep 16 inch wheels on the car. The sidewall compliance does far more for comfort than trying to have sloppier bushes.

I was forced into a mix because of supply problems at the time rather than any clever deep down suspension set up tricks.

[Luckyone]

Thanks for the replies, spilt consensus then?!
Our Cerb was more of a track car, but with the baby seat in the back I think I’d like to keep the ride as smooth as possible, so rubber is better there.
I guess the abuse the bushes get can only really be related to how it’s driven & then to a degree the road surface you normally drive over. After 12 years of track days, always with two of us in the car & bumpy London roads the originals have stood up very well, so more of the same can’t be too bad.

itiejim said:

I'd definitely keep OE. If you look at the size of the rubber part of the bush compared to many modern euroboxes, they are very slim leaving very little room for movement even on a soft, older bush. So long as they are in good condition rubber bushes will give excellent location a far superior resistance to NVH and a longer life.

I thought that was going to be the case, the bushes alone, I’d got for my other car were, much bigger than the width of the Cerbs suspension arms. So yes much less scope for movement there.

itiejim said:

I think there's a good argument for poly on the diff mounts as there have been proven to be problems there, and they will be easier to change again in the future. However, the suspension I would leave as TVR intended.

This is other thing I was wandering about, I only changed the diff bushes about 4 years ago & the very nice guy Mole Valley parts place (when TVR was still alive) said the bush rubber had been changed because of the problems with it to a tougher type, the problematic upper being different to the lowers now. They are still in excellent condition so I think I will leave them.
Assuming you go galv you won’t have much choice about taking the upper out of your chassis! I wouldn’t like to try getting the new one back in after the glav though

[shpub]

shoggyraminator said:

I had an Alfa GTV with poly and a Spider with rubber (pretty well the same car) and found the Spider a lot more pleasant to drive. The GTV was really hard especially when hitting any pot holes.

Bet they had different wheel/tyre sizes and spring/shock set up though...

[kevin63]

My Cerbera is just coming up to 60k and the first rubber bushes have just been replaced with rubber ones, my thought is if they managed 60k on the original ones then they will do me. (only a couple of bushes have needed replacing)

[shpub]

Luckyone said:

Thanks for the replies, spilt consensus then?!

On a very limited sample...

I think the important point is that not all poly bushes are the same. There are types that are basically a rubber bush where the rubber is replaced by a poly substitute which is usually harder that the original. The Powerflex bushes are a different design where an actual bearing is created for the arm to pivot on. It is this that helps with tightening the movement without causing the harshness that is often associated with poly bushes.

[Luckyone]

shpub said:

Luckyone said:

Thanks for the replies, spilt consensus then?!

On a very limited sample...

I think the important point is that not all poly bushes are the same. There are types that are basically a rubber bush where the rubber is replaced by a poly substitute which is usually harder that the original. The Powerflex bushes are a different design where an actual bearing is created for the arm to pivot on. It is this that helps with tightening the movement without causing the harshness that is often associated with poly bushes.

True, hardly what I'd call a survey.
I hope your recommendation for them isn’t based on you selling them I did just spot your bolt kits though hmm….

I’m sure I saw a thread where someone said they had to knock the nitrons back a few clicks (when was the last time the search actually worked on here?) after they fitted poly bushes – if you are out there do pop in!

Steve – do you think I could get as smother ride as I have now after fitting Powerflex bushes by just knocking my nitrons back a few clicks? I would then obviously then have the option of tightening it right up for the track with a few clicks, which would be nice.
And one last silly question, what is a life time warranty? Is it my life or the cars, if the cars is there a defined term for expected life of a car it's based on?

[gruffalo]

itiejim said:

I'd definitely keep OE. If you look at the size of the rubber part of the bush compared to many mdern euroboxes, they are very slim leaving very little room for movement even on a soft, older bush. So long as they are in good condition rubber bushes will give excellent location a far superior resistance to NVH and a longer life.

I think there's a good argument for poly on the diff mounts as there have been proven to be problems there, and they will be easier to change again in the future. However, the suspension I would leave as TVR intended.

+1, this is what I did earlier this year after getting advice from a couple of ex factory chaps. They both said no way to Poly for the suspension bushes, they wear out really quick so I was told.

[shpub]

Luckyone said:

shpub said:

Luckyone said:

Thanks for the replies, spilt consensus then?!

On a very limited sample...

I think the important point is that not all poly bushes are the same. There are types that are basically a rubber bush where the rubber is replaced by a poly substitute which is usually harder that the original. The Powerflex bushes are a different design where an actual bearing is created for the arm to pivot on. It is this that helps with tightening the movement without causing the harshness that is often associated with poly bushes.

True, hardly what I'd call a survey.
I hope your recommendation for them isn’t based on you selling them I did just spot your bolt kits though hmm….

I’m sure I saw a thread where someone said they had to knock the nitrons back a few clicks (when was the last time the search actually worked on here?) after they fitted poly bushes – if you are out there do pop in!

Steve – do you think I could get as smother ride as I have now after fitting Powerflex bushes by just knocking my nitrons back a few clicks? I would then obviously then have the option of tightening it right up for the track with a few clicks, which would be nice.
And one last silly question, what is a life time warranty? Is it my life or the cars, if the cars is there a defined term for expected life of a car it's based on?

I've been using poly bushes for years - my first set went on my Wedge rear suspension around 1999 and are in fact still there.

I only started selling them because people were buying the bolt kits and then asking if I could supply poly bushes as well. This is why I don't sell poly bushes for the front suspension of the Wedge because I don't think they are really suitable. Having had a lot of TVRs with both rubber and poly bushes, I would go with poly everytime (except for the wedge...). I wouldn't sell them If I didn't think they were best. If you go rubber then fine... I'll still sell you the bolts

Part of the problem with poly bushes is that there is a lot of hearsay about them: I've even been told that they wear out on car X by people when the only bush available was rubber! So a lot of "advice" is based on dubious sources. There are also several types and manufacturers and this causes problems as some are too hard etc and all these experiences get lumped together as "poly". The case of a harsher ride is often the difference between driving for years on a sloppy worn bushes and then on new ones. The tightness then gets interpreted as "harshness". This can be especially true if the suspension has been stiffened to compensate.

All I can say is that after 16k miles, I have considerable movement in the front drag-link bushes and top wishbone ones. These are OE rubber ones.
The thing that I am dreading is their removal as it is a real pain.

If you want a softer ride then these are the options:

• Ditch the 18 inch spiders so that you can get a bit more compliance in the tyre wall. I will understand if you don't want to do this but tyre compliance is an important part of the suspension setup. It might be worth experimenting with tyre pressures as even a 1lb change can make a difference.

• Fit my rose jointed ARB drop links and then soften the Nitrons.

The Nitrons are usually set up stiff to compensate for the fact that the ARBs are not working correctly and the suspension has to be stiffer to compensate. The reason why the ARBs are not working are the rubber bushes used in the OE drop-link design which compress and move rather than transfer the corrective load from the ARB. This means you can have a softer ride without introducing more body roll.

• Soften up the Nitrons will work on the own but at the expense of a more wallowing ride.

Details of the Powerflex warranty are here.

[shpub]

Ireland said:

Oh, and the Powerflex ones now come with a lifetime guarantee (according to Steve Heath post on FaceBook earlier) so that should put your mind at ease.

Yes, I've recently set up a Steve Heath Engineering page on facebook to complement the occasional newsletters I send out.

[Luckyone]

shpub said:

I've been using poly bushes for years.....

& lots of other good stuff.

Thanks for the detailed explanation, I think you have alleviated my fears of wear now

I don’t want a softer ride than I already have, it's actually a better ride than my other half's M Sport BMW over our rubbish roads, which means it’s much better at getting the power down than it was before I’d softened it up, with the rears actually staying in contact with the road! I just don’t want to fit Powerflex bushes & find it’s got much harder & then run into problems trying to get it back to where it was to start with.
I removed the rear ARB back when I fitted the Nitrons on APM Andy's advice, to help with the short fallings of the hydratrack diff & it does seem better at going sideways at speeds below the diffs locking speed. As you said the idea being the stiffer springs there to counter act the extra body roll. (incidentally I did the opposite with my drift car by stiffening the rear ARB, but that has a "proper" locking diff so it helps to get the inside wheel spinning up to get the diff locked up early).
So if I increase the effectiveness of the front ARB with out having a rear I guess it may have some other effects. I’ve forgotten which way round it is now, when you aren’t trying to go sideways! I think it was that stiffing the ARB on one end makes that end grip more by making the outer tyre dig in more, or was it that stiffing the ARB on one end makes the other grip more as the other ends inner tyre stays in contact more than the stiffened end

Oddly the ride actually got smother when we changed from the original RL 17"s with their (I think) 235/40/17 SO2s to the 18" spiders with the much lower profile 225/35/18 Michelin Pilot Sports, so there is more to it than just the aspect ratio of the tyres. The problem I find with lowering the tyre pressure is wear on the edges, I find I have the same problem with three of our cars (the Cerb, MSport BM & 200SX), they all run 225 fronts & 255 rears but all have the same width (I think 8") rims front & rear. I’m assuming the 225 is stretched over the larger rim a bit so it pulls the edges round a bit, they all wear both the inner & outer edge evenly so I can’t think it’s the tracking. It’s odd that all three different makes of car have the same problem, which makes me think it's the rim width. The BM has never been near a track to it can't be that & the tyre place bloke said all BMs do it.

Anyhow I'm rambling massively, all I really want to know is will fitting rose jointed ARB drop links when I only have the front ARB have an adverse rather than positive effect, with or with out Powerflex bushes?

[shpub]

You are not stiffening the ARB at all - just getting them to work better. A good analogy is steering a supermarket trolley: you can steer it by kicking it but it will need several kicks to finally get it in the right direction or you can gently apply a force and it will move in a straight line. By taking out the rubber bushes, the system goes from a kick the trolley to a smooth glide. The amount of correction is determined by the ARB dimensions and that has not changed. All that has changed is how that correction is applied - from a rough kick it to a smooth application.

PS I have not been running with a rear ARB for 3 years now but I do run Tuscan S shocks and springs which have lowered the car a bit and my own drop links. Still testing the idea mind you. Passengers have said that the car feels really planted.

[Luckyone]

shpub said:

You are not stiffening the ARB at all - just getting them to work better. A good analogy is steering a supermarket trolley: you can steer it by kicking it but it will need several kicks to finally get it in the right direction or you can gently apply a force and it will move in a straight line. By taking out the rubber bushes, the system goes from a kick the trolley to a smooth glide. The amount of correction is determined by the ARB dimensions and that has not changed. All that has changed is how that correction is applied - from a rough kick it to a smooth application.

PS I have not been running with a rear ARB for 3 years now but I do run Tuscan S shocks and springs which have lowered the car a bit and my own drop links. Still testing the idea mind you. Passengers have said that the car feels really planted.

Ah excellent analogy, something else to add to the shopping list then! Just have to decide about the bushes now...