MTB & Road Disc Brake - Caliper Mounting Specifications - Bolt Length Specification

Nov 2, 2026

Document provides mounting specifications for MTB and road disc brake calipers, covering required bolt thread engagement ranges for different mount types, and the selection of correct bolt length to ensure safe brake attachment. It includes guidance warnings about improper bolt engagement and potential disengagement leading to crashes. The material also supplies rotor size recommendations by rider+bike system weight, plus compatibility notes by riding type and rotor system (HS2, Paceline, Centerline). It further outlines how to identify fork and frame mount types and related caliper configurations.

LanguageEnglish

CategoryTechnology

FormatPDF

Pages17

Reading Time43 min

AccessFree to download

Bolt Length Specification

Rotor Size Recommendation Chart

SRAM Caliper Type Identification

Fork Mount Identification

Frame Mount Identification

Flat Mount and Thru Bolt Standard

Post Mount Standard

International Standard Mount (IS)

MTB & Road Disc Brake CALIPER MOUNTING SPECIFICATIONS GEN.0000000005232 Rev V © 2025 SRAM, LLC Bolt Length Specification ............................................................................................. 3 Rotor Size Recommendation Chart ............................................................................. 4 SRAM Caliper Type Identification ............................................................................... 5 Fork Mount Identification ............................................................................................. 6 Frame Mount Identification .......................................................................................... 7 Flat Mount and Thru Bolt Standard ............................................................................. 8 Flat Mount and Thru Bolt Standard ............................................................................. 9 Post Mount Standard .................................................................................................. 10 Post Mount Standard ................................................................................................... 11 Post Mount Standard .................................................................................................. 12 Post Mount Standard with CPS Washers ................................................................. 13 Post Mount Standard .................................................................................................. 14 International Standard Mount (IS) ............................................................................ 15 IS Standard ................................................................................................................... 16 For SRAM Trademark information, [visit:](visit: www.sram.com/website-terms-of-use)[ ](visit: www.sram.com/website-terms-of-use)[www.sram.com/website-terms-of-use](visit: www.sram.com/website-terms-of-use). 2 Bolt Length Specification Bolts and brackets may need to be purchased separately. ⚠WARNING Choose the correct bolt length for proper thread engagement. Riding a bike with improper bolt engagement can allow the brakes to disengage from the bicycle, which can lead to a crash and serious injury or death to the rider. For forks and frames with thru bolt or flat mounts, with or without brackets, there must be 5-7 mm of mounting bolt thread engagement when mounting brake calipers. For forks and frames with post mounts, with or without brackets and/ or spacers, there must be 9-13 mm of mounting bolt thread engagement when mounting brake calipers. Flat Mount Frame and Thru Bolt Fork 5-7 mm Post Mount Fork 9-13 mm 3 Rotor Size Recommendation Chart | System Weight (Rider + Bike) | Recommended Rotor Size (Rear/Front) (mm) 1
| | | | | | --- | --- | --- | --- | --- | --- | | |
Road, Gravel, Cyclocross 2
| Cargo/E-Cargo, E-Commuter 3
| Cross-country 3
| Trail 3
| Downhill 3
| | < 140 lbs (63 kg) | 140 | 160 | 160 | 160 | 180 | | 140-170 lbs (63-77 kg) | 140/160 | 160/180 | 160/180 | 160/180 | | | 170-200 lbs (77-91 kg) | | | | 180/200 | 180/200 | | 200-230 lbs (91-104 kg) | 160 | 180 | 180 | | | | 230-260 lbs (104-118 kg) | | | | | 200 | | 260-290 lbs (118-132 kg) | 160/180 | | | 200 | | | 290-320 lbs (132-145 kg) | | 200 | 200 | | | | > 320 lbs (145 kg) | 180 | | | 220 | 220 | | 1 | If riding styles conflict, it is up to the user to size up or size down based on necessary braking power. | | --- | --- | | | | | | Road, Gravel, Cyclocross--Consult the fork or frame manufacturer’s specifications before installing a 140 mm or 180 mm rotor. These rotor sizes have compatibility limitations on many forks and frames. | | 2 | | | | | |
3 E-bikes--Consult the appropriate riding style column and select rotor size based on system weight. | | | Rotor Type | Intended Use | Compatibility | | --- | --- | --

FAQs

What thread engagement length is required for thru bolt or flat mounts?

For forks and frames with thru bolt or flat mounts (with or without brackets), there must be 5–7 mm of mounting bolt thread engagement when mounting brake calipers.

What thread engagement length is required for post mounts?

For forks and frames with post mounts (with or without brackets and/or spacers), there must be 9–13 mm of mounting bolt thread engagement when mounting brake calipers.

How can you identify the fork mount type?

Consult the fork manufacturer’s instructions or measure the distance between the center of each bolt hole to determine whether the mount is flat (70 mm), post (74 mm), thru bolt (34 mm), or IS (51 mm).

Nov 2, 2026

Uploaded by putri.kecil17