Chainring for the Hydra

[biruja]

I was looking for opinions on the Hydra chainring. The medium frame comes with a 39T front chainring. (I thought 1x chainrings had to be even numbers.) On my current BBSHD, I have the Bafang 46T chainring and a top speed of around 35 MPH. This top speed is super-fun on paved paths. Curious if folks have an opinion about a larger chainring on the Hydra. And will the Kindernay have any impact on the chainring choice? I do want to use the Hydra for trails including some steep hills. Seems like with the X1, I don't need to worry about low-end torque and can get a faster (top-speed) bike. Opinions?

 

[scrambler]

I posted an excel sheet earlier that allows you to check different chainrings on derailleur and IGH for the bike and see the various cadence at various speed and gears.
Hydra - Kindernay vs. Rohloff? | Page 2 | Electric Bike Forums - Q&A, Help, Reviews and Maintenance (electricbikereview.com)

 

[biruja]

When I fill in the spreadsheet with a 27.5" x 3" wheel (0.6985 m) and leave the cadence at 80 RPM, your spreadsheet shows a max speed of 37 MPH. This is good (excellent), however, the spreadsheet shows a rear sprocket / front sprocket values of 22 and 70 respectively. So if I input a front sprocket of 39T and leave the rear value at 22T, this shows a (top) speed of 21 MPH (80 RPM) or 26 MPH (100 RPM). This feels low for paved trails or roads (fine for forests). Switching to the the 46T shows a top speed of 25 MPH (80 RPM) and 31 MPH (100 RPM). If I'm understanding the spreadsheet values, it seems a no-brainer to pair a 1000W or 2300W X1 with 'at least' a 46T front chainring. I haven't seen anyone make this point on the forum. So don't most of us want a 46T or 48T front chainring to have the option of both trail riding (emphasizing low end torque) and reasonably quick on-road riding.

 

[scrambler]

Just to clarify.
When you say 0.6985 m is that the rim size you entered or the resulting wheel diameter you got?
My understanding was that 27.5 rim for 3" tires was a 0.584m rim but I may be wrong. This is the one point I had a hard time confirm...
If I leave the rim at 0.584 and enter a 3" tire I get 0.736 m for the overall wheel diameter.

Next, If you are using a derailleur, use the sheet named derailleur in the Excel file.
There the default front sprocket is 39, and the rear sprocket go from 11 to 46 (can be changed, these numbers are the variables, so should be in red, I corrected the spreadsheet...)
In the "speed from cadence" if I enter 80, then I get 12.8mph with gear 6 (21T -39T), or 24.5mph with gear 11 (11T-39T)
with 46T in the front, I get 29mph with 11T rear.

These seem to match the online calculator found at BikeCalc.com - Speed at all Cadences for any Gear and Wheel

But so if you want to do 10mph at an 80 cadence, yes you would want 46T

 

[reed scott]

I was looking for opinions on the Hydra chainring. The medium frame comes with a 39T front chainring. (I thought 1x chainrings had to be even numbers.) On my current BBSHD, I have the Bafang 46T chainring and a top speed of around 35 MPH. This top speed is super-fun on paved paths. Curious if folks have an opinion about a larger chainring on the Hydra. And will the Kindernay have any impact on the chainring choice? I do want to use the Hydra for trails including some steep hills. Seems like with the X1, I don't need to worry about low-end torque and can get a faster (top-speed) bike. Opinions?

Wait till you get the bike. My chain ring is a 40. In tenth gear I can do way faster than safe with a cadence of about 70 or 80. But I'm riding dirt roads. I guess if keeping up with traffic is a thing maybe a 44 ring could be handy.

 

[biruja]

@scrambler The 0.6985m is 27.5 inches. That's the Google inch to meter conversion entered into Rear Rim Diameter (cell F5). The total calculated diameter is 33.5" and .851 m. I'm looking up the speed in the Kindernay table with adjusting the pedal cadence for 80 (normal) and 100 (hard) in cell E21. In this table, the default Front Sprocket (cell D16) value was 70 so I changed it to be 39 (puskar's default chainring) and 46 (which I believe is the upper limit of the frame). The rear sprocket is fixed on a Kindernay and I kept your default value of 22T. This gave a max speed of 31 MPH@100 RPM. See the attached picture. You see why this sounds slow, and this is with the 46T larger chainring.

 

[scrambler]

Unfortunately, converting 27.5" into a RIM size does not appear to be the proper way to do that as depending on the tire you use it appears 27.5" wheel can be different things.
It would be nice if @pushkar could confirm the exact diameter of the 27.5" Rim used on the Hydra.

If you will have a Kindernay, your Sprocket will be 22T in the rear, and 55T in the front. I don't believe there are any other options available for it that would fit the Hydra.
But if you are using a derailleur, you need to use the derailleur sheet and adjust the Rear sprockets choices that match your derailleur available rear sprockets.
If you re download the sheet the rear sprocket values of the derailleur sheet will be in red as variables you can change

 

[TomW]

On my current bike with the Archon X1 1000w I use a 44t up front with a shimano cassette 11-42, 27.5 wheels with Fat Maxis Minion rubber this gives me the range I need and allows me to hit 35mph. It seems to be the sweet spot for me
I am theory building a Hydra myself at the moment and I plan to start out with the same ratio's as I am using at the moment as it should be comparable.

 

[scrambler]

Regarding my last remark about the Kindernay, this was with a Belt in mind (22T minimum in the back, and 55T maximum, may be 60T in the front).
Kindernay with a chain does not have this limitation.

 

[biruja]

Ok, I've learned a few things: (1) A 27.5" tire has a rim diameter of 23" or .584m: Source (very interesting). (2) The Kindernay is usually used with rear cog of 14T: Source. It can be run with a 15T or 16T. (3) If @pushkar is using the standard 14T rear cog, then this provides a virtual 9.5T - 51.5T cassette (Source: see previous). (4) Plugging these numbers into @scrambler's calculator, the top speed in gear 14 at 100 RPM is 35 MPH. This is almost exactly the top speed of my BBSHD and I would not want any faster. My conclusion: this is as close to perfect as I can imagine-- a beast for trails and a super-exciting top speed.

 

[biruja]

I should mention: This is with the 39T chainring that @pushkar is providing standard. I don't think there is a need to go bigger.