SMG for racing and everyday use: A Brit View
I'm a refugee from BM3W. As my first post (= reveille? sorry, bad anglo-french joke) can I help answer the original query? Note that it is possible that anything I say might not be true for the US market (what is US model equivalent of E46?).
There is strictly no such thing as an 'auto' M3. SMG stands for Sequential Manual Gearbox. It is a normal manual gearbox (same as on manual cars, with a clutch, no torque converter) but it is controlled electronically. In auto mode it will change automatically, at various degrees of 'ferocity' according to taste. However, in manual mode it is almost totally under your control, changes being made by the gear stick (forward = down, back = up) or by pulling the paddles (left = down, right = up). Note that the name sequential does not mean you are limited to shifting one gear at a time: two pulls = 2 gears.
In auto mode it can be driven much like an auto, but it does not 'creep'. It can give smooth slurred changes but also quite quick ones depending on setting. Many drivers use auto 2 or 3 for heavy traffic, though I don't feel it necessary.
In manual mode it is sheer brilliance - lightning changes (in 5 or 6) which may be a bit jerky, though if correctly adjusted not too bad, or you can operate at a lower more gentle setting (anyway you learn to feather the throttle marginally, just a 'think' really, when wife in car). You have total fingertip control (except it changes down to avoid labouring if you forget, and also double declutches for smoother down changes!). It has clever add-ons like 'launch control', great for racing.
The SMG-type gearbox was developed for F1 racing (Indy with right turns!). The lightweight M3, the CSL, which BMW designed specifically for racing was ONLY MADE WITH SMG !!! Oh yes, and the change at 80ms is faster than just about any driver can possibly achieve, and without fluffing/missed gears (they say it won't change down if it would over-rev) and you stay on the throttle! And there are change lights that allow you to get your up-shifts spot on at max revs. Oh, and two hands on the wheel at all times (unless crossed up). Need I say more?
A test drive is NOT sufficient to appreciate the wonders of this gearbox, and most dealers haven't a clue. It does take learning, but as with all the best things in life it is worth it. Best to get someone who knows it well to demonstrate its brilliance. (I have owned mainly stick shift, but also several auto, and this beats both. By the way, my wife has a DSG Golf, also very good.)
If your friend wants more info, the best source for user experience (though not racing) is the brilliant website of a German guy called Leo. If you can't find him I'll try to locate.
Last edited by Helix; 03-18-2007 at 04:28 PM.
Reason: added section on racing, plus clarifications