Fathom E+ 2 Tuning Solutions

PLANET3 is a planetary gear set which reduces the rotation speed of the magnet used by the wheel speed sensor three times. For every three full rotations of the rear wheel, the magnet completes just one full rotation – effectively making the bike think it’s doing 1/3 the speed it is actually doing, thus increasing the pedal assist speed limit by a factor of 3. For the Specialized models sold on EU/UK market this translates into a speed limit increase from 25 to 75 km/h (15.5 to 47 mph), while the US and Canada models limit is raised from 20 to 60 mph.

VERY IMPORTANT: On 2022 Giant Fathom E+2 the spacing in the rear is decreased due to the design of their sensor carrier. This means that in order to fit the PLANET3 you will have to sand/file some of the material from the back of the sensor (let’s say around ~1mm of sensor thickness. This does not affect the operation of the sensor in any way and is not something that is likely to be noticed by any bike shop. However, it is an invasive modification into a new bike, so PLEASE do not purchase the PLANET3 if you are NOT OK with doing this. Another solution would be to simply buy a spare sensor if you’re worried as they’re always rather cheap (~20 EUR/USD).

EVEN MORE IMPORTANT: The 2021 model year Fathom E+2 features a 6-bolt rear hub with the same hexagonal nut profile of the “end cap”, while the 2022 model is a Shimano Centerlock rear hub. The difference is in the way the brake rotor attaches (but this means the PLANET3 is completely different). PLEASE walk over to your bike and take a look at the rear hub on the braking side before ordering. Sometimes people make a mistake thinking the year they bought the bike or the year the bike was produced is the model year – this simply isn’t true. To be 100% certain of the rear hub, please take a physical look at the hub and if your bike has a 6-bolt instead of the expected Centerlock (and vice-versa) – please just order the PLANET3 for the other model year (or, poke me via e-mail and I’ll send you the correct link).

For Giant/Yamaha e-bikes a dual planet configuration is mandatory and the device will ship as such. If you try to run it with a single planet there will be speed sensor errors in lower gears since the speed that the bike will be reading is very very low (real speed divided by ~3 since that’s the ratio of the single planet device). Dual planets halve the ratio of the device to ~1,513 so that the speed in low gears is kept higher and closer to “real”, but at the same time the assistance speed limit is lowered to 1,513x normal. This is usually ~38 km/h/23,5 mph for EU specification bikes and most users find it plenty. However, if you don’t really climb very steep stuff or muddy/loose conditions where you’d be likely to have some wheel spin, and you stick to tarmac or fire roads for your climbing in a gear higher than 4th; then you could be fine with a single planet and a higher speed limit of ~76 km/h.