Autocross Performance: top up or down

[KenG]

I have a 2008 M3 convertible. I've just started soloing it in SCCA autocross. My question is about differences in handling with the top down. I know the car is pretty carefully balanced with the top up, and I'm guessing that the weight of the top is enough to alter the handling if that weight is shifted to the rear by stowing the roof. It's cool to run it with the top down, but if my cornering is significantly affected, then I don't want to do that! Thoughts/experiences?

[r53s65e90]

All the experienced autox drivers with any convertibles I have seen go top down. No exceptions. Must be the slight shift of center of gravity downwards. IMO.

[mdosu]

why don't you give it a try on a run and compare? If you're a novice, you likely wont' notice any time difference based on this weight shift, it's more up to your ability to execute a course smoothly that'll make the major difference.

Let me put it this way, shifting 200 lbs or so from your roof to your trunk, you likely won't even notice a difference given you car is 4000 lbs... it's not like you're doing this in a stripped out race car.

[LTJohn]

put it down for the visibility and feedback of the tire sounds.

The vert is not competitive anyway, so just do it for fun!!!

[Richbot]

Down, for sure.

[DARK_M3]

I doubt you will generate anough speed on an autocross to make a difference. I would focus on tire choice.

[KenG]

Originally Posted by DocJohn

put it down for the visibility and feedback of the tire sounds.

The vert is not competitive anyway, so just do it for fun!!!

Why is the convertible less competitive?

[mdosu]

Originally Posted by KenG

Why is the convertible less competitive?

the extra 400 lbs isn't exactly a performance mod, + the extra bracing needed. Think about it, the vert is like a box with the top chopped off, it'll need extra bracing to keep the rigidity. I think it's noticeable in weight and the structure. Try driving a coupe for a moment.