filmjay

I know somebody's done it. I just can't find much on the topic except for sway bars. Maybe I'm not searhcing the right terms.

How would Z51 springs affect the F55 system? Would it throw some kind of oddball code? Would they even fit properly?

Wouldn't a 2.73 Z51 rear swap into my 2.56-geared A6?
Having an '08, how much does that limit me for a potential swap? (ie. I know an '05 will not fit.) I'd have to find an '08+?

Thanks for any info, tips, or links on the subject.

chsmith112

Z51 springs?

vertC6

You would not change out the leaf springs they are the same, all you would need to do is add the Z51 sways. The transmission gearing is different in the Z51 so if you wanted to change up the gearing you wouldn't mess with the tranny just change out the rear end gears to 373 or 390's.

HOXXOH

No problem on the 2.73 gear, as it was an option in '08 anyway.

The rear spring rate is almost identical to the Z51, so no reason to change it. The front spring is swapable.

If you change the springs and the sways, you should also consider changing the tires to match.

AFAIK, the only codes related to the F55 are for non-function.

The F55 rate of reaction is changeable with the tour/sport switch. I would think changing the spring rate attempts to control the suspension in a similar way as leaving the switch permanetly in sport mode. Any suspension gurus here?

filmjay

I remember seeing a chart floating around that listed the various spring rates of C6 models. I do remember that the Z51 rates were only 8-12 lbs more than the F55 springs. Still if I could find some take-offs, I wouldn't mind having those few extra pounds.
I know there was an A6 Z51, but I was wondering if I had to look for a specific model year, or will any '06-current 2.73 rear work.

martysauto

I wouldn't go higher than a 3.42 gear with and a6. It's similar to a 4.10m6

filmjay

I've run the numbers in a gear calculator and a 2.73 is what I'd like. Which is why I'm interested in finding a Z51 pull-off rather than getting a whole new rear for something that came as a factory option.

...maybe if I can find a Z51 owner that's upgraded their gears....

Upgrading the sways is a no brainer...without the widebody, the Z51 sways are the way to go.

Any info or advice on composite springs? Think those spring rates would be too much for the F55 system? (I still can't find the specific info on C6 spring rates)

adam205348

I have the F55 and the 2.73 factory. I think it is a perfect combo with the gearing in the A6. So you do not have to look specifically for a Z51 take off.

HOXXOH

The 2.73 was an option in any A6 car in '08 and '09, but included in the Z51 option. For 2010, the 2.73 is the only gear for A6 GS cars and all the rest have the 2.56.

oldmansan

I have the chart but it doesn't include F55 spring rates. The front Z51 rates are higher than the base (526 Z51 versus 420 base) but the rear base springs are actually higher than the Z51 (657 base versus 645 Z51). I don't think you'd feel much (if any) difference with the rear.

San

GringosC6

Why would you want to downgrade with Z51 parts

filmjay

I can't find any info on Z51 shock rates, but I think the stiffer front spring on an F55 would help make for a sharper turn-in in the stiffer "Sport" mode.
Though part of me keeps thinking a stiffer spring on the front might also cause the opposite effect as well since the base/F55 rear spring rates are already higher than Z51.

Matched with a set of Z51 sways, I think it would be a nice upgrade to the F55 suspension. I'd like a little more handling without having to get into a full coil-over setup...which is the only "next step" for F55.

Just can't find anyone that's tried it yet....

GringosC6

I was just kidding around, seems like every thread I see with Z51 and F55 in the same sentence turns into a "mine is better than yours thread"

TLK

I've read a lot of these threads, and anecdotally I can tell you that many people have upgraded the F55 sways, but very little on changing the springs. I myself have gone the Z-51 sway bar route on my F55. Others have gone to Hotchkis, Z-06 or even T1.

How far you push it depends on your tires. With stock Goodyear runflats, Z-51 is the max you can go. With better tires, Z-06 is a possibility without fear of losing the rear end. With even better tires, T1 is possible or Pfadt (depending on your tolerance to NVH).

I now have better tires and may try Z-06 sways (sway actually since one bar is the same as Z-51) some time in the future.

filmjay

Funny you should post that about tires...I discovered a screw in my LR GY runflat yesterday, so I'm viewing it as an opportunity to upgrade the rubber.

I've had a few offers on springs. But now that I gotta buy tires, I'm going to have to wait and see how much they run me before sways/springs.

I found that chart too...


When I get the tires sorted I think I will try a Z51 front spring, leave the stock rear, and Z51 (maybe Z06) sways at both ends. Don't know about the Z06 sways though since I don't see new wheels or a widebody kit in the immediate future.

TLK

Not sure if you knew, but all the bars work on all the cars. You don't need Z06 wheels to use the Z06 bars.

The base/F55 car spring rate is substantially lower, so if you change them out, please share you experience good or bad.

filmjay

Yes, I'm aware all the bars are interchangeable. But the Z51 and lower bars were designed for the base C6 wheel size and width. While Z06 bars and up are designed with a wider, stickier wheel in mind.
It is my assumption that with too much bar, a potential snap oversteer condition is introduced. Not that anyone would ever see this without pushing the limits of the car though.

With big, fat, sticky tires I wouldn't mind more bar. But since I'm still running on the base size/width wheels, I don't want it to try and swap ends on me any faster than it normally would. I'm sure the stiffer rear spring of the Z06 helps counteract that tendency a little more too.

I've got lots of goody boxes coming in this week, so if I have time (provided tires don't kill my wallet) I want to try a Z51 front spring.

HOXXOH

If you can devise a method, other than SOTP, to compare the base front spring with the Z51 spring, a lot of us would appreciate that information. Many F55 guys have changed to Z51 sways and all have reported improved handling, but the spring is a whole nuther animal. The ZR1 has different shock programming to match it's stiffer suspension, so the assumption is that GM created the F55 programming to match the base springs.

A before and after spring swap over undulating surfaces and around bumpy curves with the F55 in both tour and sport modes would be the minimum for comparison. Just be safe when pushing the envelope.