A brake disc is not a lifetime component.

On the R1100S, there is very little material available between a new disc and BMW’s wear limit. The rear disc starts at 5.0 mm and must be replaced at 4.5 mm. That is only 0.5 mm of permitted wear.

The front discs are similarly unforgiving: 4.5 mm when new, with a 4.0 mm minimum thickness on the early 305 mm setup shown in BMW’s workshop data. Some later R1100S variants use different front-disc specifications, so always confirm the correct disc by VIN, model and ABS configuration before ordering parts.

This guide covers replacement of the rear brake disc, including the ABS sensor ring, the factory thread-locking procedure and the checks that matter before the wheel goes back on.

Why Rear Disc Wear Deserves Attention

The rear disc is easy to overlook because it does less visible work than the fronts.

That is not always true on an iABS-equipped R1100S.

On the later partially integrated brake system, applying the front brake lever also activates the rear brake. That can create more rear-pad and rear-disc wear than owners expect, particularly on bikes used heavily in traffic, mountain roads or touring. R1100S owners have reported unexpectedly quick rear-pad wear on linked-brake bikes.

Check the rear disc regularly. Do not wait until the pads are changed.

A disc below its wear limit, heavily scored, cracked, badly corroded or visibly uneven should be replaced.

Factory Wear Limits

BMW also specifies a 276 mm rear disc diameter for the R1100S.

The important point is simple:

There is only 0.5 mm of usable wear on the rear disc.

Do not estimate this by eye.

Use a proper micrometer.

What You Need

• New rear brake disc, correct for your R110S specification
• New disc bolts if the old ones are damaged, corroded or questionable
• Loctite 2701 or the specified high-strength thread locker
• Micrometer capable of measuring brake-disc thickness
• Heat gun
• Torx or Allen tool matching your disc bolts
• Torque wrench
• Brake cleaner
• Thread-cleaning tap or suitable thread chaser
• Clean rags
• Rear-wheel stand, centre stand or workshop lift

The factory manual specifies clean threads, Loctite 2701 and 21 Nm for the rear brake-disc bolts.

Before You Start

Support the bike securely.

Remove the rear wheel and remove the rear brake caliper from the final-drive housing. Do not hang the caliper by the brake hose.

On ABS-equipped bikes, be careful with the ABS sensor and the toothed sensor ring mounted behind the disc.

BMW specifies an ABS sensor gap of 0.45–0.55 mm. This must be checked after the new rear disc is fitted.

Step 1: Measure Before Removing Anything

Measure the disc thickness at several points around the braking surface.

Do not measure on the outer lip where the pads do not sweep. Measure in the working area of the disc.

Check for:

• Thickness below 4.5 mm
• Deep scoring
• Heat marks
• Cracks
• Excessive corrosion
• Visible step or ridge
• Uneven wear across the disc surface

A disc can still look acceptable while already being below BMW’s minimum thickness.

Step 2: Remove the Rear Wheel and Caliper

Remove the rear brake caliper and place it safely aside.

Then remove the rear wheel.

This gives proper access to the rear disc, ABS ring and disc bolts.

Do not pull the brake lever or pedal while the caliper is removed unless you are prepared to push the pistons back before refitting.

Step 3: Heat the Disc Bolts

The original disc bolts are installed with high-strength thread locker.

Do not simply force them loose.

Heat each bolt to approximately 120°C before removal. This softens the thread locker and greatly reduces the risk of damaging the bolt head or threads in the wheel.

Use a heat gun, not an open flame.

Apply heat only to the bolt area. Work one bolt at a time and use the correct tool fully seated in the bolt head.

Owners working on Oilhead rear discs regularly report that heat is the difference between a controlled job and stripped fasteners.

Step 4: Remove the Old Disc and ABS Ring

Once the bolts are loose, remove them evenly.

Lift off:

1. Rear brake disc
2. ABS sensor ring, where fitted
3. Any spacers or washers in the original order

Lay the components out carefully.

The ABS ring must return in the correct orientation.

Step 5: Clean the Bolts and Threads Properly

This is where many brake-disc jobs become careless.

The old thread locker must be removed from:

• The disc bolts
• The threaded holes in the wheel

Clean the bolts thoroughly. A thread chaser or tap is the easiest way to clean the threaded holes in the wheel so the bolts can be installed smoothly and fully by hand.

Do not force a bolt into a dirty threaded hole.

If the bolt will not screw in easily by hand, stop and clean the threads again.

Step 6: Install the New Disc

Clean the new brake disc with brake cleaner before installation.

Brake discs are often supplied with an anti-corrosion coating or handling residue. Do not install one without degreasing it first.

Position the ABS ring correctly, then fit the new disc.

Apply Loctite 2701 to the cleaned bolt threads and install the bolts finger-tight first.

Tighten them progressively in a diagonal pattern.

BMW specifies:

Rear brake disc to rear-wheel drive: 21 Nm
Clean threads + Loctite 2701

Use a torque wrench. Brake-disc bolts are not a place for judgement by feel.

Step 7: Check the ABS Sensor Gap

On ABS-equipped bikes, refit and check the ABS sensor.

BMW specifies a sensor gap of:

0.45–0.55 mm

Use shims if adjustment is required.

This is not optional.

A sensor gap outside specification can create ABS faults or unreliable wheel-speed readings.

Step 8: Refit the Caliper and Rear Wheel

Reinstall the rear brake caliper and rear wheel.

BMW specifies:

• Rear brake caliper to rear-wheel drive: 40 Nm
• Rear wheel studs: 105 Nm

Before riding:

• Pump the rear brake pedal until it feels firm.
• Confirm the wheel rotates freely.
• Check that the brake is not dragging.
• Check the disc bolts visually.
• Confirm the ABS sensor wire is routed correctly.
• Confirm the ABS warning lights complete their self-test on the first ride.

Bedding In the New Disc

New discs need a short bedding-in period.

For the first 100–200 km:

• Avoid repeated hard stops from high speed.
• Use firm but progressive braking.
• Allow the disc to cool between heavier applications.
• Avoid holding the brake pedal on hard immediately after a heavy stop.

The aim is to transfer an even layer of pad material onto the new disc surface.

If the old pads are worn unevenly, glazed or contaminated, replace them with the disc. A new disc paired with damaged pads is a false economy.

Common Mistakes

Forcing thread-locked bolts cold

This is how bolt heads get damaged.

Use heat first.

Reusing dirty threads

Old thread locker can prevent correct bolt seating and torque.

Clean everything properly.

Fitting the disc without degreasing it

Brake discs are not ready to use straight from the box.

Clean both sides with brake cleaner.

Ignoring the ABS sensor gap

The disc and ABS ring are part of the wheel-speed sensing system.

Check the gap before final assembly.

Measuring only once

Measure the disc at several points. A disc can wear unevenly.

Forgetting to pump the brake pedal

The caliper pistons may be pushed back during removal. Pump the pedal until firm before moving the bike.

When Should You Replace Front Discs?

The same general rules apply:

• Measure properly.
• Check for scoring, cracks and thickness variation.
• Replace below the wear limit.
• Use the correct disc for your exact model specification.
• Clean threads and follow BMW torque data.

But do not order front discs simply by searching “BMW R1100S”.

Early, ABS, non-ABS, Sport and BoxerCup-related configurations can use different front-disc dimensions and part numbers. Owners have repeatedly found that front rotor listings can be confusing, especially around ABS and 320 mm-disc variants.

Confirm fitment against VIN and the actual parts on your bike.

Bottom Line

A rear brake-disc replacement is not difficult, but it is not a job to rush.

The important points are:

• Measure accurately.
• Replace at 4.5 mm.
• Heat thread-locked bolts before removal.
• Clean bolts and wheel threads properly.
• Use Loctite 2701.
• Torque disc bolts to 21 Nm.
• Check the ABS sensor gap on ABS-equipped bikes.
• Pump the brake pedal before riding.

The R1100S has only 0.5 mm of usable rear-disc wear.

Check it before it becomes a problem.