Urethane subframe bushings?

[mtrhed]

Has anyone replaced their subframe bushings with urethane units? I'm thinking of going with the AKG 90A ones when I R&R the stock ones but am undecided between urethane or solid aluminum. My car is a weekend/fun roadtrip on the twistiest back roads I can find car but the wife does come with me sometimes

[GuidoK]

Why would you want solid aluminium?

[mtrhed]

That's what I'm trying to decide on. 0 deflection but unsure of added NVH on this car. I have the Vibra-Technique competition motor mounts and love them! Have had urethane and delrin mounts on other BMW's and have been happy with them. Was just wondering if anyone had gone this route on the Z4 and been happy with them. Mostly interested in longevity and performance. My old 1988 E30 325i with delrin mounts was awesome and is still being enjoyed by my friend who I sold it to at 247K miles. Over 100K miles on those mounts. Am more likely going to go with urethane.

[GuidoK]

I'd never go for solid mounts on anything that bolts directly to the chassis. We all know what kind of horrors the e46 has in the rear.....
A motor mount is bolted to a subframe; this is directly bolted to the chassis.
For that reason alone I even didn't go for 90A (although all the rest of the rear suspension bushings on my car are 90A or stiffer).

The subframe bushings are the bushings that transmit all the suspension&driveline forces to the chassis itself.
So to prevent the e46 horrors I went with shore80A stiffness (my engine produces a lot of torque: 342 lb-ft)
Shore 80A is already stiffer than stock. Shore 80A still feels like hard rubber. Shore 90A already feels more like plastic; you can compress it with your fingernail, but not anymore with your finger itself.

[mtrhed]

Ok, that's the kind of feedback I'm looking for! Looking for something stiffer than stock that doesn't cause any issues and hopefully lasts longer. My daily driver is a Volvo V70R wagon so I don't mind my weekend sports car to be a little stiffer but not cause problems.

[Beedub]

these seems to be the latest thing the e92m3 members are doing, basically going solid Diff and subframe mounts because the F series ///M models and the GTS are now/was(GTS) solid mounted, my issue with this is the new f series ///M car will have been designed with this in mind, the z4m , e92 m3 wasn't, so all those m3 owners doing so may create issue down the line, however the manufacturers of these solid mounts believe this will actually cause LESS chance of subframe mount cracks as the stock mount is deflecting and causing a tearing motion. Now this argument is all and well but what about CONs for such as mod, and I'm not talking NVH, this MUST place additional stresses, i has to surely.

[GuidoK]

Originally Posted by Beedub

however the manufacturers of these solid mounts believe this will actually cause LESS chance of subframe mount cracks as the stock mount is deflecting and causing a tearing motion.

There's your objective pov

Stiffer mounts mean bigger forces. It's as simple as that. Especially metal fatigue is created by short stiff forces.
A more complient mount will spread the total sum of the energy over a larger motion range and therefore a larger timespread, thus reducing the peak force significantly.

If spreading the same energy over a longer timespread would increase the chance of tearing the subchassis mounting points, a car sitting still would be a disaster, as that is a maximum timespread

The bolts that hold the subframe are pretty whimpy if you take in consideration there are only 4 and their position increases the torque on those points compared to all other suspension components.

[Beedub]

Originally Posted by GuidoK

There's your objective pov

Stiffer mounts mean bigger forces. It's as simple as that. Especially metal fatigue is created by short stiff forces.
A more complient mount will spread the total sum of the energy over a larger motion range and therefore a larger timespread, thus reducing the peak force significantly.

If spreading the same energy over a longer timespread would increase the chance of tearing the subchassis mounting points, a car sitting still would be a disaster, as that is a maximum timespread

The bolts that hold the subframe are pretty whimpy if you take in consideration there are only 4 and their position increases the torque on those points compared to all other suspension components.

you don't need to convince me buddy, I'm with you all the way.....

[Beedub]

take a read guys, this is what ALOT of these guys are doing...

http://www.m3post.com/forums/showthread.php?t=925690

im NOT convinced this is a good idea.

[mtrhed]

Yeah....I'm now thinking I'll scratch the solid mounts off of my list and probably just go with the 90A AKG mounts when the time comes(soon).May add a touch more NVH but I'm not worried about them causing any issues.