Poly bushes - recommended or not?
Discussion
I was intending to replace the standard front wishbone suspension bushes on my 2000 Chimaera with poly bushes until this morning when i received some VERY NEGATIVE comments about them.
They came from a highly regarded company within the bible and to cut a very long story short went along the lines of "under no circumstances fit them to the car, it will handle like a bag of C**P and they do not suit the handling characteristics of the car". I was somewhat surprised by this as it appears to contradict some other views that i have researched on the previous threads.
He further commented that the people that sell these items just want a sale and do not understand the technical side of the subject.
I am very interested to hear if any one has heard anything along these lines before and views either way.
They came from a highly regarded company within the bible and to cut a very long story short went along the lines of "under no circumstances fit them to the car, it will handle like a bag of C**P and they do not suit the handling characteristics of the car". I was somewhat surprised by this as it appears to contradict some other views that i have researched on the previous threads.
He further commented that the people that sell these items just want a sale and do not understand the technical side of the subject.
I am very interested to hear if any one has heard anything along these lines before and views either way.
I've been told the same, recommended upgrading to supaflex bushes by one very reputable indie whilst another also mentioned highly in the bible said not to touch them, it will make the car too precise and skittish and to just replace worn bushes with standard TVR ones.
I'll also be very interested to hear opinions on this as the £7-800 its likely to cost is a lot of money to splash out on something that will make the ride worse and uncomfortable...
I'll also be very interested to hear opinions on this as the £7-800 its likely to cost is a lot of money to splash out on something that will make the ride worse and uncomfortable...
I don't know who gave you the advice about polybushes but they want shooting.
The blue poly bushes are *softer* and *worse* for suspension location than teh std TVR bushes .. tehy will make the car wooly and imprecise compared to new std tvr bushes. They also seem to get worn through rapidly for some reason on teh ones close to the manifolds. they are *worse * than the std tvr bush so avoid if possible, but not for the reasons your indie has said!
There's *one* place on the tvr where the blue poly bush is well worthwhile and that's on teh rear upper wishbone forward bush where the extra compliance over teh hard red version helps in lining up the top damper bolt, which can sometimes be a real PITA to line up with solid bushes.
In all other cases use the RED superflex bush which is very hard.
the do *not* affect the ride at all, the reason is that the std tvr bush has minimal rubber in it anyway, has minimal cushioning effect so the change to hard poly bushes isn't noticebale.
The poly bushes are virtualy fit and forget (they still wear eventually close to the manifolds but nowhere near as quickly as the tvr bushes do) and are an excellent upgrade to do. You can also replace them one at a time as your std bushes wear out, you don't *have* to replace the whole car set in one go.
Hope that helps a bit. I have no problem completely contradicting the advice given by your other indie .. in my experience they are wrong.
The blue poly bushes are *softer* and *worse* for suspension location than teh std TVR bushes .. tehy will make the car wooly and imprecise compared to new std tvr bushes. They also seem to get worn through rapidly for some reason on teh ones close to the manifolds. they are *worse * than the std tvr bush so avoid if possible, but not for the reasons your indie has said!
There's *one* place on the tvr where the blue poly bush is well worthwhile and that's on teh rear upper wishbone forward bush where the extra compliance over teh hard red version helps in lining up the top damper bolt, which can sometimes be a real PITA to line up with solid bushes.
In all other cases use the RED superflex bush which is very hard.
the do *not* affect the ride at all, the reason is that the std tvr bush has minimal rubber in it anyway, has minimal cushioning effect so the change to hard poly bushes isn't noticebale.
The poly bushes are virtualy fit and forget (they still wear eventually close to the manifolds but nowhere near as quickly as the tvr bushes do) and are an excellent upgrade to do. You can also replace them one at a time as your std bushes wear out, you don't *have* to replace the whole car set in one go.
Hope that helps a bit. I have no problem completely contradicting the advice given by your other indie .. in my experience they are wrong.
You can get blue (soft), black (inter) and red (hard). I've seen blue ones split after only a year or less so I'd avoid them. I have black ones and they feel excellent (but then they replaced original bushes that were 8 yrs old - so they would wouldn't they).
I think the objective is to replicate as much as possible the characteristics of the standard bush but for them to last longer. The standard bushes are great when new but degrade at a much faster rate than the poly' ones.
I think the objective is to replicate as much as possible the characteristics of the standard bush but for them to last longer. The standard bushes are great when new but degrade at a much faster rate than the poly' ones.
Hi there.
Unfortunately I've not got a full car set left, and the superflex importer is frankly dire, so have just set up an account with powerflex and am sending them some tvr bushes to copy.
bad news is they'll take 4 weeks to come through, but the sporadic supply of superflex bushes is doing my head in so much that a switch to a UK producer seems the obvious choice.
Amazingly powerflex had stopped making the TVR bushes as they had no distributor .. so I've stepped in.
Form an orderly queue
...
Unfortunately I've not got a full car set left, and the superflex importer is frankly dire, so have just set up an account with powerflex and am sending them some tvr bushes to copy.
bad news is they'll take 4 weeks to come through, but the sporadic supply of superflex bushes is doing my head in so much that a switch to a UK producer seems the obvious choice.
Amazingly powerflex had stopped making the TVR bushes as they had no distributor .. so I've stepped in.
Form an orderly queue
... 
When I decided what polybushes to fit, it was clear to me that there was too many contradicting opinions to know what was right. So I decided to have a go at speccing it myself.
The premise was simple I had to find a bush that would give the same or slightly less displacement than the equivalent TVR original bush. The original bush was rubber so the Shore A rating would be 50-70. The thickness of the polybush compared to the rubber is very nearly 2 times thicker. Therefore as all other things are equal (i.e force acting on bush), to achieve the equivalent displacement the strain has halved. This means the compression modulus of the polybush material has to be at least twice that of the rubber.
Looking at a graph of compression modulus shore 70 has a modulus of ~790 psi, shore 80 is ~1250 psi, shore 90 is ~2500 psi, shore 95 above ~5000 psi.
With all the geek bit out of the way, the conclusion is I went for the Shore 90 bush (i.e black superflex) because it would be 3 times the modulus and therefore no more displacement than the original. I personally believe that Shore 80 (blue/purple) is too soft, and the Shore 95 (red) is very hard and there maybe more shock load transfer onto the wishbone pivot brackets on the chassis. I don't know whether this would be a problem, I doubt it because those brackets are huge.
Disclaimer: This was a very simplistic analysis and have no empirical evidence to support this. If there any glaring holes in my analysis, please tell me so.
The premise was simple I had to find a bush that would give the same or slightly less displacement than the equivalent TVR original bush. The original bush was rubber so the Shore A rating would be 50-70. The thickness of the polybush compared to the rubber is very nearly 2 times thicker. Therefore as all other things are equal (i.e force acting on bush), to achieve the equivalent displacement the strain has halved. This means the compression modulus of the polybush material has to be at least twice that of the rubber.
Looking at a graph of compression modulus shore 70 has a modulus of ~790 psi, shore 80 is ~1250 psi, shore 90 is ~2500 psi, shore 95 above ~5000 psi.
With all the geek bit out of the way, the conclusion is I went for the Shore 90 bush (i.e black superflex) because it would be 3 times the modulus and therefore no more displacement than the original. I personally believe that Shore 80 (blue/purple) is too soft, and the Shore 95 (red) is very hard and there maybe more shock load transfer onto the wishbone pivot brackets on the chassis. I don't know whether this would be a problem, I doubt it because those brackets are huge.
Disclaimer: This was a very simplistic analysis and have no empirical evidence to support this. If there any glaring holes in my analysis, please tell me so.
I went for what wheeljack said but on a far less scientific basis (though I did find out what the Shore rating meant. The things you learn, eh?).
I was also told there'd been a colour change, that the 'old' blue ones were 8o, the 'new' blue (blue/black) are 90 and reds=95.
Jools, I know you don't have a full set. T'was me that wanted them this afternoon.
I was also told there'd been a colour change, that the 'old' blue ones were 8o, the 'new' blue (blue/black) are 90 and reds=95.
Jools, I know you don't have a full set. T'was me that wanted them this afternoon.
ish
wheeljack888 said:
Therefore as all other things are equal (i.e force acting on bush) If there any glaring holes in my analysis, please tell me so.
Stress=force/area but there is no/insufficient end restraint so the area changes. Unlikely to make more than a 5% error though so your conclusion appears to be valid. Thought that you'd like to know. lol
Very... 
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