No one was injured in the attack on the Season Max Tyre shop belonging to Azison Musor, 36, on Siroros Road in Tambon Sateng of Muang district.
Witnesses told police they saw two men arrive on a motorcycle. The pillion rider then hurled the home-made bomb into the shop before they sped off.
The blast shattered the shopfront window and damaged tyres and alloy wheels on display.
Police believe insurgents were behind the attack.