Has anyone gone from new rubber bushes to poly bushes (or similar)?
 

So my bushes are old and crap, and I am thinking of replacing them, but I am torn between new OEM rubber ones, or getting poly (or similar) bushes. I know that poly bushes are supposed to be better for handling, and you can get the offset ones, but I've heard they need to be re-greased and all that jazz, so require more maintenance than the rubber alternative. So I was wondering if it is really worth the hassel?

I know there are a million other threads on this topic, but I am asking if anyone has driven a car with brand new rubber bushes, and then driven a car with poly bushes? Is there much of a difference?

"Bushes"

https://www.miataturbo.net/attachmen...ine=1346051986

Those things

Bushings. Can't help you otherwise, I'm still on OEM bushings from 1993.

Edit: I can say however, that the difference between old and rubber is going to be roughly the same as new and poly. Or you'll have a giant leap in performance from old to poly.

AFAIK, poly bushes (I like it, we're keeping it) are great most of the time, except when they transmit road noise, bumps, and jolts through the chassis that rubber bushes would normally absorb.

As for the noisy and bumps aspect; a friend has poly bushes in his car, and it is actually more comfy and less jolty/noisy than mine, and he has stiffer swaybars and springs than me!!

There's too many variables within a suspension to isolate the 'bushes' as the cause.

In my limited experience driving a number of cars with and without poly 'bushes' lead me to draw the following conclusions:

1. A reasonable durometer poly bushing almost always improves NHV over old shitty bushings. Why? ...beyond general tolerance change from wear or tearing, the rubber hardens effectively increasing the durometer. A lot of spec guys actually seek out old hardened OEM bushings for this reason (less 'slop' due to less compression). The increased durometer translates to increased NHV. I've held old bushings out of an Arizona/New Mexico NA which felt like Delrin (minus the lubricity)

2. If you daily drive your car in any environment with lots of water/snow/salt you HAVE to install grease fittings. There are few things as annoying as a squeaky poly bushing. It also means it's not freely rotating in the control arm which is bad news bears.

3. New Rubber vs. New Poly bushings ... NHV is primarily dependent on the durometer of each. They are functionally different, so poly should provide a more predictable (and tune-able) suspension (since rubber pre-loads). This being said, if both have the same durometer there shouldn't be a significant difference in NHV so general driving will feel essentially the same.


For a year round daily driver I'd go with OEM rubber or graphite empregnated poly with grease fittings.

For a track car, I'd go with poly with grease fittings (so long as the rules allow for it)

Ultimately, your shock dampening/rebound is going to have a far greater effect on NHV. It's the reason why 400lb springs can feel 'plush' when used with the proper combination of shock and why <200lb springs can feel like total sh*t on OEM Bilstein HDs. Bushings play a small part in over all 'harshness' ... unless of course there's something critically wrong such as a tear of rot.

-Zach

...and to clarify: NHV = Noise Harshness Vibration


I work with so many engineers, I forget the world doesn't operate solely in acronyms :giggle:

-Zach

Ha! I'm on OEM bushings from 1990. I just received a compliment from a fellow forum member on how nicely my car rides and handles. He wanted to know the brand of bushings I was using so he could install the same thing!

Also, the grapevine says that some Spec Miata types prefer old rubber bushings to new. The theory goes that the older rubber has hardened. Have no idea whether this is good information or gibberish. The question I would ask is what do the race winners run?

To go along with that, part of the grapevine swears by poly, while the other part swears that they would never do poly again (maintenance and noise).

Don't you just love the grapevine?

Anyway, with all the conflicting information and all the compliments I get on my ride quality, I think I'll just stay put.

One other option, FM is selling a harder rubber bushing kit -- similar to the Mazdaspeed bushings but at a much better price.

Hey Curly...would it be worth replacing my 1990 bushes? I have all the suspension torn down because I am going to paint it and I inspected the bushes and to be honest they look fine. The steel sleeves are still nice and solid, nothing is sloppy. I am going to be tracking the car and I am just trying to figure out if it is worth doing it now since it is all torn apart. If I were to replace them I would be using Energy Suspension polyurethane bushes.

Oh I have no idea. I have plenty of track time and it sounds like our bushings are in similar shape.

It's just $300 and way too many hours and lots of frustration. It's well documented how much life sucks with some types of bushings and street driving, but you'll be hard pressed to find the facts about them decreasing your lap times.

Will they be faster? Probably. I doubt it's enough to justify the price, time, and frustration. Then again I'm lazy, so I've made enough of these decisions to probably add up to a lot of lap time sacrifices.

Thanks for the honest input. I think I am going to go ahead and do them, just because the suspension is already torn down. Just another piece to the puzzle I suppose.

I got my set of prothane bushings from ebay and if I didn't get sick during the middle of the swap I would have had them done in a couple of days.

I drilled and tapped in a set of zerk/grease fittings as well just to make sure I could service them easily.

It's not that hard to do, and I got my set for 130$ AND my car became more crisp and connected but better over harsh bumps.

fyi: my car's bushings had 95k on them and still not very hard.

My personal subjective opinion is that the poly bushes ride BETTER than rubber because they allow the suspension to move instead of having to twist a block of rubber.

I used Energy Suspension grease and have had no squeaks after 2 summers and 20k miles. I admit, though, that I did use A LOT of grease; 1/2 of a large can from 949racing.com

you could always get rid of the "bushes" completely ;)

https://www.miataturbo.net/attachmen...ine=1346519251