I am thinking about installing polyurethane bushings on the front suspension members of my 2005 XKR coupe. Has anyone had experience with these materials? Does the ride/handing firm up markedly? Is there more road noise conveyed to the cabin? How do they affect front end suspension geometry, if at all? Overall, are they worth the cost to change?

Thanks in advance for the help.

Tim

 

Hi Tim, I'm about to start a thread regarding this very subject; I changed my stock bushings out last night for some polys. I'll try to answer your questions there. Check later this evening, I have a few threads to start regarding my latest 'projects' on the ol' girl.

 

I'll be waiting too as I've got to do at least my sway bars front and rear then others till I can find the noises and 'Kill!" them.

 

Taking a page from my 20 years of playing with Corvettes, poly bushing are one of the dumbest ideas around- the absolute perfect marketeer's solution for a non-problem. I regret using them.

 

Could you expand on that? I know the rubber OEM bushings have a tendency to deteriorate. I think mine will probably need replaced soon, and I was thinking about using poly, just because they are supposed to be much more long-lasting than rubber.

 

Much like us senior men with our grizzled looks and receding hair lines, exterior appearance has nothing to do with what's going on inside. I removed the majority of the bushings on my Corvette when they were almost 30 years old simply cause they looked like crap. The replacements were zoomy swoosh leap tall building poly that promised to make me much more attractive to the opposite sex and the envy of all my peers.

This was before a far wiser and greyer car nut sat me down and explained how a standard rubber bushing works, how the advantages of a pinned flexible rubber sleeve were sacrificed with a non-flexible unpinned poly bush and in fact I had effectively downgraded the car. He was right and I learned a lesson on just how persuasive marketing can be particularly when the complete function of the stock piece is not understood by the average hobbyist. Stupid me.

Being a pack rat, I had kept the old bushings from the front and rear suspension. I cut a few of them open and lo and behold the inner material was just as good as the day they were made three decades before. The outer checking of the rubber simply bore witness that the bushings were doing their job as explained by my mentor. I had wasted my time and money on replacing them.

The secret to understanding how a rubber bushing works is knowing that the inner and outer surfaces are each pinned in place- they do not move with respect to the component they are attached to. Actually suspension movement is accomplished by 'twisting' the rubber inside the bushing. This torsion is beneficial in two ways- it acts as a rising rate spring to resist suspension deflection (this resistance is accounted for during factory design) and more importantly the 'twisted' rubber eliminates the ability for the bushing to be deflected axially, to a higher degree than the equivalent aftermarket poly bushing.

The net result of a rubber bushing is a is slight compliance under normal conditions that dampens road vibration and minor bumps, but a hard bushing that keeps the wheels aligned perfectly under severe driving conditions.

The poly bushings being absolutely rigid, cannot be pinned to the outer or inner sleeves. They must be allowed to pivot at the outer and/or inner contact points requiring grease to avoid the famous poly squeak. The fact that there is now relative motion were there was none in the factory design may mean fasteners will loosen themselves up. I have to re-tighten my A-arm arm bushing bolts at least once a year. The constant rate rigidity means that I feel every little pebble the tires go over and expansion joints in bridges almost knock my teeth out.

But, aside from that they're great!

 

Thanks Mikey! That's definitely something to think about. And since I'm planning on selling the car soon, I'll never need to replace them again anyway.

 

This makes sense given your detailed description of who the bushings are supposed to work. My question for you would be on sway bar bushings. These operate differently than control arm bushings or even the end links, so my question is, wouldn't the poly bushings actually perform better in this one application? I have never used poly in the past, and I too have been influenced by the marketing hype.

I have a package of poly sway bar bushings that I will be putting on today, yet I'm very curious of your opinion / experience on this specfic subject.

 

Sam, I see you are looking to sell your car soon! You have put so much time and energy into it!

Are you just going to look for another, but in the color combination that you really wanted or maybe a XKR so you get the additional performance?

 

I really wanted a carnival red car with the light tan interior. I bought this one because I couldn't pass up the price. And now I also notice the styling differences between the 2005/2006 models and the earlier ones. I want to buy an 05 or 06 in carnival red. When I bought my silver one, my wife and I were planning our trip out west and we needed to get something soon. I had been looking for a couple of months and prices were going up, up, up because summer was coming. I'm going to try to sell mine now while there's still time for the buyer to cruise around with the top down, then this fall/winter buy my preferred car when prices are hopefully a tiny bit cheaper.

And strangely enough, on the way to Myrtle Beach this afternoon I passed a car lot that had a newer XK sitting out front. It was an 07/08/ or 09, and I really didn't like it as much as the older ones. It was a nice looking car, but I just really like the looks of the 05/06 model years.

Now I'm at the Embassy Suites on the beach in Myrtle Beach and what am I doing? I'm sitting in my hotel room surfing the internets! I really need to get a life. My kids are down at the beach having fun at least.

 

Again, from Corvette only experience, the bushings that hold the bar to the frame are the torsion type so the same rules apply as A-arms. The end bushing act in compression (and not torsion), so the harder the bushing the sooner the sway bar will do it's thing. I'm not convinced an effectively stiffer sway bar is desirable.

 

I'll stick with the poly for the sway bars, mainly because of the resistive nature of the poly over the OEM rubber. A power steering leak ate my RF bushing. The OEM rubber just gets fatigued way too quickly. TBH, I haven't noticed any difference in performance gain, loss...and it may just be my mind playing tricks, but there may be some truth to vibrations being more easily transferred to the driver. Then again, I was 'trying' to notice a difference.

 

Interesting. I'd like to know what you end up doing to your '05 R coupe and how you like it since that's the same as I have.

Sam from all of your contributions on the forum, I'm surprised to hear you say your selling. But, I must admit that the carnival red with cashmere interior is gorgeous. My '98 coupe was that combo and I looked and looked and looked for an R coupe with those colors. Never found one. Interesting though, the guy I sold mine to wanted to add it to his '97 carnival red convertable so he'd have matching coupe and vert. I never thought I'd like another color, but I like the jaguar racing green as much or more. PS, through my looking, I don't think they made any '05 or '06 in carnival red. I could be wrong, but I was told that by a dealer and I have never seen one. But that doesn't necessarily mean anything.

 

Ok, I have to admit, I didn't like the poly bushings after 4 days of driving with them. EVERY single bump is felt. I also did not get the 'custom' fit set, and had to modify a universal set to fit in our XK8 notch where it resides. Since I did not notice any increase in roll, I put my 6 month old OEM rubber back in. It is much smoother now. I'd rather spend 1 hour every 1-2 years putting new $15 each bushings under her as they fatigue and fall apart.

 

Well thanks to everyone for the replies. Given the density and rigidity of the poly bushings I suspected that there was likely to be an issue regarding road-feel and noise. I am also inclined to use the OEM bushings and enjoy the ride quality. Perhaps someone will come up with a little better rubber formulation that will provide the same ride quality coupled with greater resistance to degradation.

 

I'm going to have my 2000 XK8 checked, and if it has polies then I'll have OEM's reinstalled. I like the softer ride of the 16in OEM wheels and higher profile tires, vs the ride of my old 2002 I had before this one with the 17in wheels. OEM bushings would definatly complement my current set up.

Mikey, thanks for your evaluation of the poly bushings. It's the honest sharing of information like that which really powers forums like this.

Rusty

 

...And since I'm planning on selling the car soon...

Whoa! Sam, this doesn't have anything to do with the water in the fuel problems in the Four Corners area, does it? That's all behind you now!

Rusty