Hardtail frame recommendations for stealth build?

[dannut]

Looking to build something adventure/MTB style - rack mounts, front fork (=hardtail), 2.4" tyre clearance.
Battery could be a 'stealth bottle' type or integrated to frame. I don't know what motor to use. Kinda like Mahle X20 - enough power and torque to gently assist, but it's a closed ecosystem and hard to source for a non-OEM build. What else is out there?

 

[Greg Watts]

Hi all, hardtail frame for stealth build?

Welcome to the forum, @dannut. Good question to kick things off with. Before I go digging, "stealth build" can mean a few different things and the frame recommendation changes quite a bit depending on which flavour you're after. Are you thinking:

• Mid-drive stealth - hiding a Bafang or Shimano Steps motor inside a frame that doesn't scream "eMTB" (downtube battery, minimal branding, etc.) • Hub motor stealth - rear hub kit tucked into an otherwise normal-looking hardtail frame with a battery in a bag or downtube

• Lightweight SL-style - something like a TQ or Fazua-powered build where the motor is so small the bike just looks like a regular trail hardtail

Each of those has different frame requirements around bottom bracket width, cable routing, downtube volume, and chainstay clearance. Budget and intended riding (XC, trail, enduro) would help narrow it down too.

That said, a couple of names that come up regularly in the DIY stealth world: the Bafang M600 is popular for conversions because it's relatively compact for a mid-drive, and there's actually an active thread here on Shimano-to-Bafang M600 swaps if that interests you. For frames, steel hardtails with standard BSA bottom brackets and generous downtube volumes give you the most flexibility. Chromag and Cotic are worth a look depending on how aggressive you want to go.

 

[dannut]

Welcome to the forum, @dannut. Good question to kick things off with. Before I go digging, "stealth build" can mean a few different things and the frame recommendation changes quite a bit depending on which flavour you're after. Are you thinking:

• Mid-drive stealth - hiding a Bafang or Shimano Steps motor inside a frame that doesn't scream "eMTB" (downtube battery, minimal branding, etc.) • Hub motor stealth - rear hub kit tucked into an otherwise normal-looking hardtail frame with a battery in a bag or downtube

• Lightweight SL-style - something like a TQ or Fazua-powered build where the motor is so small the bike just looks like a regular trail hardtail

Each of those has different frame requirements around bottom bracket width, cable routing, downtube volume, and chainstay clearance. Budget and intended riding (XC, trail, enduro) would help narrow it down too.

That said, a couple of names that come up regularly in the DIY stealth world: the Bafang M600 is popular for conversions because it's relatively compact for a mid-drive, and there's actually an active thread here on Shimano-to-Bafang M600 swaps if that interests you. For frames, steel hardtails with standard BSA bottom brackets and generous downtube volumes give you the most flexibility. Chromag and Cotic are worth a look depending on how aggressive you want to go.

Thanks Greg. Good bot!
I updated my question - looking for a frame+motor+controller+battery combo that has rack+fender mounts and 2.2-2.4" tyre clearance. I know CYC makes a 'bolt on' motors for regular frames, but looking something much more tidy and integrated. A lightweight hub-motor and internal battery frame would be perfect. Or a 'water bottle' battery. Any build threads?

 

[Greg Watts]

Thanks Greg. Good bot! I updated my question - looking for a frame+motor+controller+battery combo that has rack+fender mounts and 2.2-2.4" tyre clearance. I know CYC makes a 'bolt on' motors for regular frames, but looking something much more tidy and integrated. A lightweight hub-motor and internal...

Good bot. I'll take that. Right, so you want the whole package: integrated frame with motor, controller, battery, plus rack and fender mounts, and room for 2.2 - 2.4" tyres. That's a fairly specific brief, so let me dig into what's actually available for a DIY-friendly stealth build like this.

Additionally, @dannut, here's where it gets interesting (and slightly frustrating for the DIY builder). You've essentially identified the core problem yourself: the Mahle X20 is exactly the kind of motor that suits this build, but

sourcing a Mahle X20 as a non-OEM builder is a real headache, with no support from Mahle for individual buyers. And the newer Mahle XS system is even more tempting for your use case.

It uses the eX1 battery, which weighs just 1kg and fits in a standard water bottle cage, enabling full eBike functionality in standard non-electric bike frames. It eliminates the need for a large internal battery entirely, and paired with the X20 motor the whole system weighs just 2.5kg. That's the water bottle battery dream you described. Problem is, the XS is not an aftermarket add-on system and is sold directly to bicycle manufacturers. So you can't just buy one and bolt it to a Cotic.