BBSHD gear ratios

I'm wondering if my existing gear ratios would be too high with a BBShd motor.

My bike is an old Raleigh Orge 21 with a read freewheel with 12,14,16,18,21,24,28 teeth and would use the standard BBSHD 46T. The wheels are 26x2.1 these ratios come out quite fast:-

100 to 160 RPM cadence
46x12 29.92 32.91 35.91 38.90 41.89 44.88 47.87
46x14 25.70 28.27 30.84 33.41 35.98 38.55 41.12
46x16 22.50 24.75 27.00 29.25 31.50 33.75 36.00
46x18 20.00 22.00 24.00 26.00 28.00 30.00 32.00
46x21 17.11 18.82 20.53 22.24 23.95 25.66 27.37
46x24 15.00 16.50 18.00 19.50 21.00 22.50 24.00
46x28 12.81 14.09 15.37 16.66 17.94 19.22 20.50

What I'm wondering is the lowest speed 46x28 seems quite fast ? I really want to go an absolute maximum of 25MPH ish

I swapped my BBSHD to a smaller chainring. The top speed went down, and the hill-climbing ability was very improved. Motor now runs cooler under all conditions.

That's good to know, I've just came across the Shimano MegaRange rear freewheel with a 34T 'low' gear which would be better than my existing 28T low. The MegaRange freewheel would be a lot cheaper than a 40T BlingRing for example.

What chainring did you use?

The BBSHD likes low gearing. I use 30 tooth chain ring and I think 12t-42t cassette (with a few removed so the chain line stays OK).
Even with the mini 30t chain ring, the motor can reach the bike's top speed limited by wind resistance and power in the top 3 gears. But the pedal cadence is crazy fast and you can't keep up with it at top speed. With human input, I can go about 20mph, but it can reach 28mph using the throttle.

The stock BBSHD chain ring is a heavy, ugly thing.

Do you have any issues with a 30T Chainring with the BBSHD and what is the offset?

Anyone know what's the lowest RPM the BBSHD is happy with ? the spec says 130-160 RPM I think

myozone said:

Do you have any issues with a 30T Chainring with the BBSHD and what is the offset?

Click to expand...

I have not had any issues with the 30t chain ring other than the chain line. I "edited" my cassette to keep the alignment reasonable. I have not measured the offset. It is a 10 speed cassette, but now I can only use 7 speeds, which is plenty for me. I have about 2k miles on it, mostly very steep off road stuff. I have a lot more issues with my brakes.



If you don't spend too much time climbing 20% grades, you can probably do well with a larger chain ring.

Thanks @fechter that's a really good idea! :thumb:
I have a freewheel but could change that to a cassette. Working out the cadence and speeds 3 or 4 gears would really all I need. Maybe I'll start off with the stock 46T BBSHD chain ring and my 28T sprocket rather than the expense of a 40T Bling Ring. With your example there are more options than I realised. I wouldn't do much hill climbing most of the hills are <15% and the very steepest ~18% and short lengths.

What is the question exactly? You know that your gear ratio is twice the speed that you want, since you show the results.

Hayes256 Funnily enough, I'm thinking of doing the exactly same thing ! with my old Raleigh Ogre 21 (green)
I think just using to two lowest gears would be fine giving a maximum of speed of 25 MPH. You could change to 40 tooth Bling Ring and a MaxRange 34 tooth rear sprocket freewheel. The 34 tooth would have a more worthwhile ratio than the 40 BlingRing.

For the record I figured on 60-160 RPM. 60 RPM works out to be maximum torque 160 Nm and 100RPM is maximum power 1500 watts that's my working out.

I have recently installed a BBSHD on a trike, and used a 48t chain ring, pretty close to the stock 46, but a little more offset. I have a 9 speed cassette with ratios from 11-32 in the back. If you use anything smaller up front, it often has to be positioned out the the right up front and can impact chainline - anyway...

While calculations tell me I have crazy speed capability, the reality is I don't often run the motor anywhere close to full power, and the indicated speeds are significantly lower under real load - more so for my heavier trike than your application. I think the 60-160rpm makes sense in looking at available speed range. I have not much used the smaller gears at back, 11, 14t etc, so while that means I could use something smaller up front, I want a straight chainline. If anything, I'm considering a cassette at the back that has a bigger "granny", a steel one. With the bigger 46 up front, take care to start or climb in the biggest sprocket at the back. I converted this trike from hub motor to mid, so I am re-learning my tendency to let the motor assist in any gear at any time.