Alignment tools for derailleur hangers and brake discs

A bicycle frame hanger straightener and a brake disc straightener are part of the basic equipment of a bicycle repair shop.

A bicycle hanger straightener is a specialized tool used in bicycle maintenance and repair to properly align the derailleur hanger – the small component that holds the rear derailleur to the bicycle frame. The hanger plays a key role in the precise shifting of a bicycle. If bent or misaligned, it can lead to poor shifting, misaligned chain, and even possible damage to the drivetrain. A derailleur hanger straightener is an investment that pays off, especially if you need to do more maintenance or after a fall. Instead of replacing components due to poor shifting, you can often just straighten the derailleur hanger.

A disc brake straightener is a specialized tool used to adjust and align brake discs. Disc brakes on bicycles can sometimes become misaligned due to a variety of factors, such as impacts, rotor warping, or normal wear and tear. Aligning a brake disc ensures that it rotates smoothly and evenly in the caliper, preventing friction between the brake pads and ensuring effective braking performance.

How to use a derailleur hanger straightener?

Place the bike on a mounting stand (ideal), or stabilize it so it doesn't tip over.
Remove the rear wheel - it will give you better access to the heel.
Remove the derailleur.
Screw the derailleur hanger straightener into the thread where the derailleur is attached.
Make sure that the straightener is screwed firmly, and the tool can rotate around the axis of the foot.
The leveller has a measuring stick or indicator that rests on the wheel rim.
Turn the tool to 3, 6, 9 and 12 o'clock (positions like on a clock face) and at each position measure the distance from the bar to the rim.
If there are differences in distance (e.g. 5 mm on the left, 15 mm on the right), the derailleur hanger is bent.
Gently push or pull the tool in the opposite direction of the deviation.
Straighten gradually and carefully – repeatedly check the distances in different positions.
The goal is to keep the distance between the bar and the rim the same or nearly the same in each direction (±1 mm).
Unscrew the tool.
Put the derailleur and rear wheel back in place.
Try the shifting and fine-tune if necessary.

How to use a brake disc straightener?

Watch to see if the disc wobbles as it rotates – moving closer and further away from the brake pads.
If so, it is bent and needs to be straightened.
Place the bike on a mounting stand or otherwise stabilize it.
You don't have to remove the disc - the work is done directly on the bike.
Slowly spin the wheel and listen for friction against the pads, or watch the disc move through the brake caliper.
When you find a spot where the disc is deflecting, stop the wheel.
Insert the tool (straightener) through the groove into the appropriate place on the disc.
Gently pull or push the disc in the direction opposite the bend.
Make small, gradual adjustments – then always turn the wheel and check the result.
You may need to adjust several places around the circumference of the disc.
The goal is for the disc to pass evenly and without contact with the plates.

Check out our video "Rescuing a bicycle frame and derailleur - hanger"