Auto for me, every time - maybe 'coz I'm getting lazy. Advantages are:-
You have a spare leg to brace yourself with.
You can left-foot brake if you want to.
You can make your LSD lock up more by applying a little brake with the left foot, whilst still applying throttle with the right foot.
You can select a higher gear (2 or D) before a climb at the bottom of a steep hill, and if the wheels start spinning the auto box will change up to a higher gear, which will limit the spin and help maintain grip - try doing that in a manual (unless you're Jake the Peg :shock:
If you use 2 or D on a muddy surface you'll auto change up when needed, which will help maintain traction.
You don't have to worry about a clutch.
As there's less to think about, it's easier to concentrate on your line.
Failed Ascents are a lot easier to deal with.
It's a lot easier to back out of a dodgy situation quicky.
You're much less likely to stall an auto.
The downsides:-
Less engine braking.
You can't roll-start if you stall on a hill.
Increased brake wear.
I think the manual versus auto debate will carry on for ever. Bottom line is to opt for your personal preference, and sod everyone else
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