The acro bike is used to clear obstacles but can't clear mud slides, the mach bike is for pure speed and for getting past mud slides. If anything choose the acro bike.
acro bike
You can get it in the bike shop in Mauville City.
It is mach bike because it travels fast unlike archo bike.
the stuntbike in ruby is called an acro bike and you can get it in mauville city
Get an Acro Bike and hold down B while moving.
You can get up the mud slopes using the Mach Bike at full speed in Pokemon Ruby. You can get the Mach Bike by talking to Rydel in the bike shop of Mauville City.
your right but you need the mach bike not the acro bike because i do it with the mach bike and works for me.
maville city farthest regular building on the right called ridells bike shop
in mauville city after you have helped rydel
get on bike and jump ofer the hedge
Next to the pokemon center in Mauville
in mauville city your choices are a mach bike (very fast but hard to turn) acro bike (a bike that is not very fast but easy to turn and you can do stunts with it)