Most Vettes are driven on flat, straight roads where the worst thing that can happen to you if you slide off of it is that you end up in a pasture, corn or soy-bean field, a parking lot, front lawn, sandy beach or desert. For these people, a great suspension "upgrade" might be to simply weld the suspension components directly to the frame and eliminate all springs, shock absorbers, sway bars, bushings, etc. Driving a Vette in these regions is a total waste since the capabilities of a sports car are not needed, and you might as well be driving a dump truck, combine, tractor, school bus, race car or family van to your nearest suburban shopping center. However, for a small percentage of Vette drivers who actually negotiate windy, bumpy roads at speed where sliding off the road means meeting a three foot diameter tree or granite ledge head-on or dropping hundreds of feet into a ravine, such so-called "up-grades" make no sense whatever because a stiff, less compliant suspension will cause you do skitter and dart right off the road to a certain death.

 

How much additional roll stiffness do you get from going from rubber bushings to poly bushings? And how much additional road noise and vibration do you get as well?

I added Z51 sways to my base coupe with F55, and after increasing the downward rake and running a PSI higher in front than rear, find the handling balance to be just on the understeering side of neutral even with the stock front spring. I'd like a bit more roll stiffness, but not as much as I would get from a thicker set of sways like the JOC's. Would the poly bushings do that for me?

 

My guess would be the additional road noise and vibration would be far more noticeable than any additional roll stiffness. Their is a reason the OEM bushings are rubber rather than poly, and its not cost, the poly bushing are no more expensive to manufacture. But of course anyone with poly bushings will claim they are better. But just think about it, and how a sway bar works; the type of bushings they pass through have little or nothing to do with their effect on the suspension.

 

Poly bushings reduce suspension deformation under load, providing more precise cornering. They also transmit road vibration and create ride harshness.

Ride harshness is often blamed on the hard-compound of polyurethane bushings. Though partly true, that is not the primary cause of harshness.

In fact, there is another process in play - friction. Friction is the primary cause of ride harshness with polyurethane bushings.
Rubber Bushing

Rotates via Deformation

Rubber bushings - how they work

For all their faults, rubber bushings allow suspension movement with very little friction. Rubber bushings do not slide in their mounts, they accommodate movement by deforming in a twisting motion. There is no friction surface hence the friction is very, very low. Rubber bushings resist movement due to the spring rate of the rubber, not friction. Their behavior is similar to a torsion spring though the spring rate is small.

Polyurethane bushings - how they work

Aftermarket polyurethane bushings are completely different than the rubber bushings they replace. Instead of deforming, the polyurethane forms a friction-surface that slides around the steel suspension member or mounting point.
Polyurethane Bushing

Rotates on friction surface

Unfortunately the polyurethane-on-steel friction coefficient is significant causing them to "grab" the steel liners. With the weight of a vehicle resting on the polyurethane the friction becomes substantial. The problem is compounded under high speed cornering loads or heavy braking. The problem is further compounded if the polyurethane bushing fitment is not precise or bushing alignment is poor. Grease will help reduce the friction but doesn't last long, as demonstrated by the many cars with squeaky polyurethane bushings.

 

Just for the record the base rear spring is slightly stiffer than the Z51 rear spring.... 657 lbs on base ..... 645 lbs on Z51...

 

Wheel hop is associated with conventinal longitudinal leaf springs, not traversly mounted ones like on the Corvette. Handling tight curves is one thing, and your tires play the major roll in this capability; handling tight and curvey roads with washboard surfaces, frost heaves, sudden bumps or dips, is another thing, and a stiffer, non-compliant suspension (i.e. one with heavier than necessary sway bars) is a detriment under these conditions. Don't confuse negotiating closely spaced pylons on a flat, smooth parkiung lot or runway at speed with handling curves under less than ideal real road conditions.

 

Just why I went with Koni FSD shocks. Added the thicker sways too.

The base suspension set up is horrible for a sports car....bouncy...the FSD's take the bounce out yet still smooth the road roughness without being stiff.

Maybe not the best set up for track but for street it is pretty sweet.

It is all I need!!

 

Use the grease that Pfadt provides. Even in rainy Seattle I have only re-greased once and that was after 2 years of use as an everyday driver. And everything in my setup is poly.

 

Bought a set of z51 bars tonight, next step Bilstein HD's and Michelin PS2 ZP's. Thanks for all the input!

 

The only thing poly will do is make the sways work a little better by reducing deflection. With poly on sways only you will not really increase any noise, or at least that was my experience. Now going to poly bushing on all suspension component and the ride is both harsher and you will have more noise.

 

Thanks. A little bit more is what I was looking for, and all the better if it doesn't generate a noticeable amount more of NVH. The front bars seem to have the bushings mounted too close to the bend, causing the outer hole to ovalize pretty badly and that seems to let in a lot of grit. Hopefully, the poly bushings won't do the same.

 

The poly's have the same problem up front, it is just the design of the system. This is one reason I would like to go to the Pfadt Light Racing Bar, but price is just to much. But the Pfadt grease keeps it pretty clean. Also it is very easy to re-grease the sway bushing once a year if you are worried about it.

 

The difference is so small that the engineers must have been splitting hairs that day. Changing just the front spring seems to work fine for most people.

Since springs and sways work together as a package, installing just the Z51 sways has caused some people to experience what they considered to be exesssive or dangerous oversteer. Others have been happy with that setup. The problem is that it's hard to safely test the various conditions you might encounter out on the street, I would take the safer combination and install the Z51 front spring along with the Z51 sways.

Our 2009 Coupe has the Z51 system, I got tired of being beat up by the horrible roads in Illinois and installed base model shocks. The rest of the system remains stock Z51, I find the ride to be significantly more comfortable but the handling is still great. Each person's conditions and wants are different.

 

IF I didn't have the F55 Magnetic Adjustible Suspension I would go with the Koni FSD shocks, kind of a poor man's F55 if you will. Of course the base suspension with the F55 option is hardly "bouncy", since F55's greatest attribute is keeping tires in contact with the road.

 

Jim I agree that there is most oversteer with the Z51 setup but it is very manageable if you understand what is happen, IMO it is mostly driver error.

With base sways the car will tend to understeer if you enter the corner to hard or pickup the gas to soon. The same holds true for Z51 sways if entering the corner to hard but when picking up the gas you can get either condition and it can be hard to balance. A lot depends on the road surface.

If you are at basically max turning capability and you pickup the throttle a little the car starts to push. Pick it up a lot and it will snap on you. This is where I think autocross really helps with understanding the dynamic's of the car. This year I will probably give JOC's a try if I can work it into the budget.

 

This is what ive tried to inform people about


the base car rolls and dives too much - you dont even need to be speeding to take a turn hard enough on the street to get the car to start leaning or for the front end to compress too far.

As far as understeer, its definitely there, but i think it was dialed in with the anticipation that you could use the throttle to turn the vehicle - the problem is that then youre dealing with all the other issues of an understeery suspension. Any good driver can deal with this, but if you overcook a turn, guess what? you wont be able to turn in, which to some peopel is scarier than having the rear end tryign to breakaway. COmpanies like pfadt make very understeer oriented sways, and this is what some racers like, but as I said the more understeer, the less turn in and the more youll need to have the course or sector memorized - this isnt really always possible, especially on backraods, so having the extra turn in makes it much easier to keep carrying speed and recover if you brake at the wrong time or take the wrong initial line

the base rear is supposed to be stiffer than the z51 rear, using the z06 spring up front will give a similar balance as the z51, but slightly stiffer overall.

as far as oversteer issue with the z51 sways, the base model and z06 models have a more oversteer oriented spring package but the base sways are very understeer oriented. z51 gets more understeer oriented springs with more oversteer oriented sways. combine the z51 sways and base springs and you get more oversteer. Its very fun and controllable - it makes the car easier to drive to an extent, but you end up not getting it to its maximum limit because the rear does want to breakaway a little sooner than it should. I want to emphasize that it isnt some scary oversteer, its easy and gradual - very controllable.

As far as the tire go, they may contribute to harshness, but the one thing that really cleared up the bumping during turns was putting understeer oriented springs (were talking understeer compared to the other springs) and redoing the shocks with z06 units. I believe the main reason the shocks helped was because of the increase in rebound.

as far as jacks comment on upgrades causing the car to become unstable on rough roads, thats true but its exaggerated. The base suspension is much softer than necessary. doing mild suspension modifications makes the car handle much better on rough crowned backroads.

One thing people do all the time as a suspension upgrade, which I am against is lowering the car with leaf springs and cut pads. keeping all the original suspension travel really helps when youre going on crowned roads and transitioning from one section of a turn into another.

this is all from my personal experience with modifying the suspension and testing the modifications on very rough surfaces including a few dirt/gravel runs.

last note - the gs gets the z51 springs and z06 sways with z06 shocks up front and gs specific rears. This car could have gotten the z06 springs and shocks, but instead got more understeer oriented springs - I believe this was because the car was less likely to be used on flat racetrack surfaces, and more likely to be used on the street with bumps. Just something to keep in mind...

i hope this information helps!

 

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Thanks for that info pettvette.

 

I just received my Bilstein HD's and installed them. That was fun. I got the Z51 bars in the other day and just for fun I measured them against the ones on my car..... They are the same I checked against a spring and sway bar list I copied from another forum member and I indeed do have Z51 bars on my car already. Previous owner must have already done that mod. I was wondering how much better the car would corner, as it cornered pretty good before. I did score a zo6 front spring and mine is a base so after I put the tires back on and record the ride height, I will take the front suspension back apart and change the front spring. Now if someone would just buy my rims and tires I could upgrade to the CCW 505a's with the z06 sized PS2ZP's.

PS Anyone need a set of Z51 sway bars?

 

Wow, that's all I have to say! What a difference. This thing feels like it is clamped to the road. Zero body roll, no more brake dive, nice ride. This thing handles! This is hands down the best handling car I have ever owned!

Base car, base rear spring, Z 51 front and rear bars, Bilstein HD shocks, and Z06 front spring. This is a formula anyone can duplicate, $550.00 out of pocket all in. Next week some new Michelins and I'm done.....for now