21 Inch Wheels - Handling issues? + Shifter question

[G5FTW]

I have a few question and would very much appreciate some suggestions, experience, or recommendations.

Let me start with some background. I first purchased a 2012 2SS L99 A6 with standard 20's on it. Car always seemed to handle fine from what I can remember. This car did not have electronic steering.

A few years later I sold it and purchased a 2014 Spring Special Edition LS3 M6 with 21's on it, this car has the new electric steering that was introduced in 2013 I believe. The car now has 10K miles on it and it just seems to handle like shit compared to my 2012 that had 20's. Now I am not sure if it's it's just in my head but I really feel like the 21's negatively effect the car. Not only in turns but at higher speeds too, car seems/feels like it's "not going to make it" and a tad "shaky" and unsteady. Shouldn't it be smooth at 75-85mph?

I remember doing 145 in my A6/20's without much concern, however in the M6/21's it's quite sketchy.

I am also not sure if it's because I am now having to shift, as I am taking one hand off the wheel at times to do that. So I suppose that could give the driver the impression of instability at times.

Can anyone with experience with both 20's and 21's and the electric steering chime in on this matter, I would greatly appreciate it.


I also have a question regarding my shifter. It is very grindy at times. 3rd is very bad and "clunky/chunky", I swear I remember reading something about this on the forums awhile back and that it is common/normal?

I am definitely not grinding gears, it will do this with the car off and sitting, it's definitely in the shifter/transmission itself. Also sometimes if I am in 1st and making a turn (say 15-25mph+), it's like the body is flexing and is moving the transmission, it's sometimes very difficult to put it into 2nd until I have completely made the turn. I really feel like the shifter is totally out of wack, is this common? Can it be re-calibrated or tuned? It also vibrates a lot at higher speeds 65+, but I would assume that's normal?

[JimE]

Should handle the same, regardless of wheel/tire size. The only major difference between the two are the tire brand/type. Different tires can feel different. There will also be a difference in the ride between the 20 and 21 as the sidewall is smaller, thus the ride will be rougher and impart more road feel into the car. Smooth ride will be a byproduct of the tires being properly balanced and the road surface. The same road can feel different between different types/sizes of tires.

As for the power steering, there is a different feel with the electric unit over the belt driven unit. But it's consistent

The "not going to make it" is typically a driver issue. Are you actually turning the wheel so sharply that the tires are slipping/squealing and the car isn't turning? Or are you simply expecting the car to turn more based on the wheel input that you using? Most likely the latter. In which case, you need to learn how the car reacts. It does have variable input steering which changes based on speed.

Shifting can be affected by temp (ie: cold vs hot fluid). Try changing/upgrading the tranny fluid.

[Snoman]

Originally Posted by G5FTW

....
I remember doing 145 in my A6/20's without much concern, however in the M6/21's it's quite sketchy....
.....
I also have a question regarding my shifter. It is very grindy at times. 3rd is very bad and "clunky/chunky", I swear I remember reading something about this on the forums awhile back and that it is common/normal?

I am definitely not grinding gears, it will do this with the car off and sitting, it's definitely in the shifter/transmission itself. Also sometimes if I am in 1st and making a turn (say 15-25mph+), it's like the body is flexing and is moving the transmission, it's sometimes very difficult to put it into 2nd until I have completely made the turn. I really feel like the shifter is totally out of wack, is this common? Can it be re-calibrated or tuned? It also vibrates a lot at higher speeds 65+, but I would assume that's normal?

These wheels look great and were a pure profit item for GM. These tires absolutely suck balls for performance. Before my strut tower brace, I could not go past 120 MPH without feeling the vehicle was about to lose control as the vibration starting at 75MPH become too violent. I absolutely will not be replacing the rubber when they wear out. Will be buying a set of 3-piece custom 20's that weigh 75% less with rubber, for half the cost.

The flaky clutch and transmission feel is the hydraulic fluid pump that needs replacing. Not to even mention it shares fluid with the brake system, it's actually one and the same. Under hard performance, the fluid drops out of the clutch and grinds like a 12 yr old learning how to drive for the first time. Forget 0-100 wrapping the red line 1st through 3rd, it's impossible to do and you will die in 2nd gear, if you are even able to get out of 1st. There are arguments talking about "wait for the car to warm up", it will lesson the issue like a band-aid but will not fix the root cause at all.

I've had 2 dealerships in Houston confirm this so far (Parkway and Classic) and both refused to fix the problem as "nothing is wrong with your car".

Strut Tower Brace: Will fix the vibration and frame twisting, I suggest Maureen@RogersChevrolet. Should be under $170 with mounting bolts.

Clutch/Transmission: Separate the Brake system from the Clutch system. Upgrade the hydraulic clutch pump and switch to braided steel brake lines at the same time since your down there. I haven't done mine yet, initial research seems to be $500-$750.