The problem it solves
A throttle blip raises engine speed to match the lower gear you're about to select. If the ECU blips while the drivetrain is still connected, you get a lurch instead of a smooth downshift. So before blipping, the Nexus needs to know whether the engine is actually connected to the wheels. The Throttle Blip Gear channel answers that question, and Gear Tolerance sets how strict the answer is.
How it works
With the car in gear and the clutch engaged, engine RPM and wheel speed are locked together at a fixed ratio for each gear. The ECU compares the live ratio of road speed to engine speed against the ratios you've stored for each gear. If the live ratio lands close enough to one of them, Throttle Blip Gear reports that gear. If it doesn't match any gear, the engine and wheels have separated, which means the clutch is in and a blip is safe.
Gear Tolerance is "close enough", expressed as a percentage either side of each stored ratio.
A worked example
Say third gear is stored as 20 mph per 1000 RPM and Gear Tolerance is 4%. Four percent of 20 is 0.8, so any live ratio from 19.2 to 20.8 mph per 1000 RPM counts as third gear.
- At 5,000 RPM and 100 mph, the ratio is exactly 20. The car is in third, so no blip.
- Clutch in, revs drop to 3,000 RPM while the car still does 98 mph. That's about 32.7 mph per 1000 RPM, well outside the band. The drivetrain is disconnected, and the blip can go ahead.
Choosing a value
Too tight, and normal tire growth, wheel-speed noise or a little clutch slip can make a car that's still in gear look like it's out of gear. That risks a blip at the wrong moment. Too loose, and the bands for neighboring gears can overlap, or a slipping clutch still reads as "in gear" and the blip is held back when you want it. Start in the middle, then log Throttle Blip Gear during some deliberate downshifts. It should read the correct gear whenever the clutch is out and drop out cleanly as soon as you press the pedal.
This table only shows up once Gear Tolerance Enable is switched on in the Flat Shift function. Accurate gear ratios matter too. If the stored ratios are wrong, no tolerance setting will fix it.
Related settings: Throttle Blip Amount and Throttle Blip Duration.
