Forbidden Chain Guide

I created this using Fusion 360.

This is the Forbidden Lower chain guide DIY.

I believe with this mod you can increase pedal efficiency by lowering drag created by the bad undersized lower chain guide pulley.

MRP recently released the MXg SL, this mod adapts the E13 guide to function like the MRP.


Print using 80% or greater infill for durability laying flat on build plate.
I printed with PETG for strength.


1. **Materials needed:**
- M4 Nyloc nut
- Shimano or Sram derailleur jockey wheel (with bearing shims, if applicable)
- M4 washers 4-5 of these to use as spacers
- 2 printed chain re-tension sides (attached)

2. **Preparation:**
- Flip the bike so it's resting on the saddle and handlebars.
- Remove the rear wheel.

3. **Modify the lower chain guide:**
- Loosen the torx bolt in the center of the E13 LG1 chainguide a few turns.
- Push on the bolt so the rectangle logo on the back side of the chainguide pops out.
- Remove the