Slow down or slow up?

[purplepoppy]

Driving along a narrow road you find yourself behind a tractor doing 10mph. Do you say it'll slow you down or slow you up?

Another example. You're trying to do some work but the kids keep interfering. Are they slowing you down or slowing you up?

[Lliam]

"Slow 'down'" or "speed 'up'" are sensible phrases.
"Hold up" means wait, stop, or "Hang on a minute".
I think "Slow up" is a malapropism derived from combining "slow down" and "hold up".
But "slow up" really doesn't make any sense

[bean2k21]

Ain't nobody getting behind no tractor. What? You think I'm going to stand there shucking the damn corn they throw at me? Oh yes, Master, let me shuck your corn for you for free. You better slow up with your racialism.

[FreyaRed]

Down. Slow up sounds like drinking sober or colorful black-white.

[AviatorTom]

"Slow down" is what I hear more often than "slow up". The inverse "Speed Up" is vefy common.

[Chazmatazz269]

I say “slow down” but the argument for “slow up” is equal in every conceivable way.

[SnowedIn]

This is such a great question. Both slow me down.

[DJB72]

It depends if I'm in Devon or Yorkshire.

Down in the Westcountry, up in the Dales

[NathanDavis]

is this about speed versus velocity... scalar versus vector? American versus British...

[purplepoppy]

Nothing complex, I just noticed both get used

[Havthrills]

I've always said slowing down. Haven't heard slow up that much.

[goaded]

Down. Do-be-do down dowwwn.

[Sparkie460]

I say slowing me down

[Charliefretz329]

Slowing me down is how I’d say it

[Msputiton]

Slow me up

[Andres77]

Down

[Old_Golden]

Slown down, hold up

[jimmy2]

Slow your down