Mini Hiryuu - Mid power ebike

[neptronix]

And apparently the bike i was looking at is no longer listed.

Found another candidate ( $499 )
29er Mountain Bikes Up to 60% Off - MTB - Motobecane Fantom 29 EXPERT



Geometry not listed. Asked bikesdirect and they got back to me fast with this:

FANTOM 29ER HYDROFORMED AL FRAME GEOMETRY​	​	​	​	​	​
Seat tube (Center to Top)​	13”​	15.5”​	17.5”​	19”​	21”​
Effective Top Tube (Center to Center)​	22.9”​	23”​	24.3”​	25” / 635mm​	25.7” /​ 652mm​
Top Tube (Center to Center)​	22.1”​	22.4”​	23.2”​	23.8”​	24.6”​
Chainstay (Center to Center)​	460mm​	460mm​	460mm​	460mm​	460mm​
Bottom Bracket Drop​	53mm​	53mm​	53mm​	53mm​	53mm​
Seat Tube Angle​	73°​	73°​	72.3°​	72°​	72°​
Head Tube Angle​	70°​	70°​	70°​	70°​	70°​
Wheel Base (Center to Center)​	1103mm​	1102.9mm​	1129mm​	1141.1mm​	1159.6mm​
Standover Height​	28”​	31”​	32.4”​	33.8”​	35.2”​

I'd go for the 19" size.

That's the longest chainstays i've seen on a bike like this. Usually 425-440mm.
72" seat angle beats my current bike in crank forwardness by enough.
I get an extra 1.5 inches of wheelbase.
Less swiss cheese dropout factor.
Head tube angle is better than current bike but not awesome. Improvable.
Current 50mm suspension seat post barely clears, would be adequate
Might not be lighter.

Current bike ( 21" size ):



Boy, it is hard to find a bike that has old standard dropouts/etc but retains good geometry. This looks like my best option for V2.

 

[E-HP]

Is that front chain ring big enough?

 

[neptronix]

No way. Needs to be 44T minimum.
Pictured largest chainring is 42T.
Looks like it has room for additional!

 

[neptronix]

Okay, i can't get good answers out of bikesdirect, i think in actuality is that they're dropshippers. It sounds like they don't have a warehouse with product in it to give even the most basic info :/.

Photoshop to the rescue. Aligned the two prospective bikes to the seat post to observe differences in geometry.

Orange: 2024 Motobecane Fantom 29 ( $499 )
Blue: unlisted 2025 Motobecane Fantom 29 SS12' ( $688 )




On the cheaper bike, the wheelbase is effectively shorter as a function of the fork angle, not the frame.

Versus Mini Hiryuu v1, we get approx +30mm to the rear and +9.6mm to the front.
An additional 20mm of fork height ( same thing i did on v1 ) should add an additional +5mm on the front.
Reduction of rear tire size probably worth +1-2mm to the front.

So net, after modifications vs v1:
+30mm rear length, +15.6mm front length
Not bad!

MTBers online report that bikes with longer chainstays are more steady at high speed. Exactly what we want on an ebike

The 19" would accept a Thudbuster LT + pedal hack. 21" would give me 18mm more length in the front, but the seat height might forbid a thudbuster LT, which is a dealbreaker.

I think a 29er with a thudbuster LT might be equal in comfort to the 32er, considering that the 32er can't take decent suspension height in the seatpost or front fork with a 29" front wheel swap.

Looks like i'm getting the cheap 29er that has generous chainstays:

 

[Chalo]

The problem with both 32" and 36" wheels is that the components are either cheap BSO garbage or absurdly expensive fancy unicycle stuff.

I would like to build a good quality custom 36er, but I can't justify that kind of outlay for a bike with only entertainment value.

 

[neptronix]

Totally, it's so frustrating.
With 32's, i would want something like 1.25-1.75 inch wide tires ( and narrower, less insanely heavy rims ) to help exploit the speed you could develop thanks to the huge diameter. We don't need much horizontal contact patch because we're wealthy in vertical contact patch.

MTB riders seem to say 32" x 2.25" tires have a wealth of traction; yet you can't benefit from that much, the bike is oafy and can't really be pushed in a way that lets you utilize the traction.

I think this wheel size is better suited for road/cargo/hybrid/gravel bikes. But a narrower tire has yet to be invented.

I think the 750d aka 30-30.5" wheel size would be better because it wouldn't require so many compromises to a bike's geometry.
https://www.pinkbike.com/news/wtb-develops-new-750d-wheel-size.html

Look at the above white Motobecane 29er and imagine that headtube needing to be 1 inch taller to fit a 30" tire. You can take off 1 inch of front suspension travel and probably get away with it. But you can't get away with taking 3 inches off to fit a 32" unless the bike frame's size is extra large.

I think there's a better business case for 750d because a company could produce bikes from medium to xtra large sizes.

The only bike i could find with 750d wheels is a moots prototype from last year.



I think nobody could get their hands on wheels and tires for these without being a bike company, so that proposition is out. it's way too early.
29er it is!

 

[neptronix]

Thinking about motors again.

The best approximation of the lightest mid drive on the ebikes.ca simulator is the Shengyi SX2.
Imitating some flux weakening on the bafang G370 ( 1.6kg/3.5lbs ) by using 66v and using major current limiting on it to cap it at 600w results in an impressive speed with the two motors in play.



Not bad for a combined 7.5lbs of motor. The front motor is inefficient, but won't be used often enough to matter.

Might actually go this route instead of pumping up the power on the lightest mid drive. The 900w limitation also limits chain wear.

 

[neptronix]

Frame choice made.

Considered this deal, also has abnormally long chainstays ( good ) but it would require me getting another battery that's broken up into two pieces and mounted to the side. Too much extra expense to make that work :/



I got in touch with bikeisland, they had a Motobecane Fantom Expert 21" in the warehouse they were able to measure for me. The standover height at the seat tube is 33", therefore my Suntour NCX will just barely fit. If i'm wrong, i get a Thudbuster ST instead.

This bike is apparently discontinued; bikesdirect is selling them at reduced prices on ebay/bikeisland.com, so i managed to get a new one for $40 off.



Pretty excited to get a bike with closer to modern geometry, big wheels, but still compatible with hub motors..

 

[neptronix]

Bike arrives friday. I'll assemble and see if it's not too big for me. If not, sending back and getting a 19".

Excited about this +60mm wheelbase that's closer to a small motorcycle on the big size though.
Fingers crossed.

 

[neptronix]

Got the 21" bike in.
Wheelbase wise, approximately +1 inch in the rear and +2 inches in the front vs the Gravity Basecamp.
21" Gravity Basecamp v7 has the seat tube 32" from the ground, this one is 32.5". The standover height is totally wrong on this model.
Bottom bracket is a little lower than the Basecamp ( i prefer that for lower rider CoG )

Standover height is improved to the point where i don't need to undersize the rear tire to get more crank forward, so that's cool.
Basically the perfect geometry for street riding.



The longer chainstays and front end + the super wide handlebars do make it feel like a bus to turn compared to the 26er. But it's also much more stable feeling, which is exactly what i want at higher speeds.

For the mid drive, looks like it takes a 46T on the inner chainring and 56T on the outer. With some offset adjustment i think i can fit 50t almost in the center/outer position. Let's see.