Rubber or Poly for a Daily Driven Corner Carving Street Machine?
Not voting but will comment based on my own experiences since I've used them all (poly polygraphite, nylon, rubber) both on street and autocross.
First, you're right to not equate corner carving to track or autocross with even moderately sticky tires. The tire temps, stick and surface makes a big difference.
I'm about to pull the trigger on a front end rebuild kit and I can't decide if I want to go with Rubber or Poly bushings for the Lower Control Arm (LCA).
This is for a '74 Duster and my goal is to build a daily driven street machine that can handle well (hopefully very well).
I'm not planning on entering any AutoX's but some spirited driving up some mountain roads and freeway on ramps would be fun.
Rubber in the lca and upper control arms will last longest if they are of any quality. I disagree with Pete on LCA being a continual failure item. Ball joints far more, and based on the TSB, probably many shops were replacing before needed because they checked wrong.
Polyurethane can permanently distort (deform) when the load and deflection gets too high. I did not have this happen, but did wear out after 50k miles, using the PST's original polygraphite LCA bushings. A more recent set, supusedly graphite impregnated (need to dig out reciept to see which seller brand) did not last as long. They deformed, however the autocross loads were higher due to other improvements including tires (Hoosier TDs and then Toyo RA1s).
During this time I switched from PST's UCA bushings to the Moog offset. I highly recommend this to get the more aggressive alignment. Occassionally a car won't need them to get the more aggressive alignment, but most will - especially earlier ones.
Nylon LCA bushings are currently installed. They transmit more high frequency vibration to the steering wheel even with tall street tires. How much you feel depends on the roads. Some highways here are smoother than others. However nylon is much tougher and while less elastic won't deform plasticly.
Here's my planned list of additional parts:
- Moog Lower Ball Joints, Moog Tie Rod Ends (11/16"), Moog Idler Arm
- PST or Reilly Motorsports Adjustable Strut Rods
- Hellwig Tubular Sway Bar
- Tubular Upper Control Arm (either PST, Reilly Motorsports, or Firm Feel - can't decide)
- PST 1.03" or Firm Feel 1.06" Torsion Bars
- Bilstein shocks all round (maybe up front first, then rears later as budget allows)
I have searched on this subject and there are quite a few old posts regarding this, but I'm still unclear.
Any reasons why I shouldn't go poly?
Use the adjustble strut rods if you use off the shelf polyurethane strut rod bushings and don't want to
measure and machine the bushings. Anything you can do to reduce for aft movement at the strut rod is a plus IMO. So poly here yes.
Front Sway bar - biggest improvement you can buy
Bigger t-bars - another excellent bang for the buck for your purposes.
Shocks - Good shocks are very worth it in autocross. Depending on your corner carving, maybe not as noticible, but my feeling is go all four even if it means not buying something else.
Poly sway bar end links and heavy spacer and washers are important and low cost. Poly sway bar bushings will squeak if not greased but worth the reduced deflection and breasable fittings are now available or can be home made.
A good, slightly more aggressive than stock alignment is a must.
Lower both ends of the car if you can and is relatively low cost. Remember the back of the car plays a pretty big role too.
Tires and road surface are the biggest determinent on how it all works.
