OK, this may be a bit bonkers, but I figured out how to play Ramps with a racing wheel, with proper analogue steering and acceleration/braking.

It's a little involved and only works on Windows.

Mouse input

First, you need a version of Ramps (or whatever game you plan to play) edited to accept mouse input. Like this version:

WARNING: Attempting to drive with an actual mouse may cause high blood pressure and throwing things.
Also I've only tried this in PICO-8 itself - not sure if it works when running in a browser.

Joystick -> mouse

Next, you need a utility to convert game controller input to mouse movement.

I couldn't find one that did exactly what I needed, so I ended up making my own here.
Tip: If you try it out remember F12 toggles it on/off - as you can't use the mouse when it's enabled.

Race

So basically run the utility, run the mouse-input version of Ramps in PICO-8, switch to full-screen, and go :-)

ramps joystick wheel