Supermoto dirt section: from tarmac to loam

A "real" supermoto track adds a dirt section - a jump, a loose loam or gravel loop, sometimes a small step - to an otherwise tarmac kart circuit. Your bike is set up firm and low for grippy asphalt, which is exactly wrong for the dirt: on loose ground a stiff, low, tarmac-biased bike skips, deflects and loses drive. The dirt section forces a compromise, because whatever you soften off for the loam, you then carry back onto the tarmac.

Soften off the tarmac base

Everything you did to add tarmac hold-up (firm compression, firm rebound, low sag, dropped front) hurts you in the dirt. Back some of it off

• Compression, both ends: softer. Open low-speed compression front and rear so the wheels stay in contact with loose, uneven ground instead of skating over it. This is the same "let the tyre follow the surface" logic as any off-road setup.
• Rebound: slower (fewer clicks out). On loose dirt an over-fast rebound makes the wheel skip and hop off bumps and on landings. Slow the rebound a little so the wheels stay settled and tracking on the loose stuff. (Note: this is the opposite of a wet-roots enduro bike, because here the enemy is skip on landings and loose ground, not packing over rapid root chatter.)
• Tyre pressure: much lower. Drop pressure well below your tarmac numbers for a bigger contact patch and mechanical grip in the loam. This is the single biggest dirt-grip lever, just as on any off-road bike.
• Sag: more. Add a little rider sag over your tarmac figure so the rear tyre presses down into the dirt and the bike is less nervous over the rough.
• Fork height: raise the front a little. Let the forks show a little less through the clamps than your sharpest tarmac setting (front slightly higher) for a bit more front ride height and straight-line stability over the jump and loose entry, at the cost of a little tarmac turn-in sharpness.
• Rear sprocket: a tooth more. A tooth larger on the rear shortens the gearing for drive out of the slow, loose dirt corners without bogging - useful where the dirt loop has a tight, low-traction exit.

Then it is a compromise back on tarmac

Everything above trades a little tarmac performance for dirt survivability. A softer, taller, longer-geared bike with lower tyre pressure will feel slightly vaguer and less razor-sharp on the asphalt sections. That is the deal on a mixed track: you set up for the part of the lap that hurts you most, and ride around the compromise on the part you can manage. If the dirt section is short and easy, bias toward tarmac; if it is long, rough or decisive for lap time, bias toward the dirt.

Change one thing at a time and do a full lap - tarmac and dirt - before judging.

Sources: standard supermoto dirt-section practice (SupermotoJunkie setup threads); supermoto gearing guides (supermoto.co.uk); off-road tyre-pressure and sag practice (MXA); LAISA supermoto-setup-guide / supermoto-kart-track-guide / gearing-guide.

Starting point, not a safety guarantee - always test it yourself.