Hobbies Cars & Motorcycles Before Top-Dead-Center (BTDC) Share PINTEREST Email Print John H Glimmerveen. Licensed to About.com. Cars & Motorcycles Motorcycles Motorcycle History Buying & Selling Restoration & Repairs Cars Used Cars SUVs Trucks ATVs & Off Road Public Transportation By John Glimmerveen John Glimmerveen is a former competitive motorcycle racer. He later worked as a race technician for several international race teams. our editorial process John Glimmerveen Updated March 01, 2017 Definition: A common term used to indicate the amount of ignition advance. For instance, 10 degrees BTDC indicates the ignition timing is set 10 degrees before top-dead-center. Examples: Setting the ignition timing, so that the spark is initiated before top-dead-center, is necessary because of the time delay before the explosion reaches maximum force. The objective is to ensure the piston has begun its downward (power) stroke as the expanding gases reach their maximum pressure.