2009: Wheel Size Locked?

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PeteCress
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Joined: Tuesday, December 1, 2009 - 16:53
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2009: Wheel Size Locked?

I posted this question to BionX's web site two days ago and no answer.

Called NYCEWheels and put it to whoever answered the phone, but they accompanied their answer with the assertion that different size wheels for, say a BionX 350 unit, contain different motors - which I think undermined her credibility.

The question: If I buy a 2009 BionX 350 with a 26" wheel and then put it in a 20" wheel, can I reprogram the system so that it knows about the bigger wheel? How about the other way? Can I decrease the wheel size?

Anybody know for sure?

My real agenda is defeating the 20 mph cutoff.

I don't really want to go much over 20, but if I have tail wind or something, I don't want it doing sudden things at, say, 19.5 mph. I keep hearing the phrase "Hitting a wall".

Instead I want smooth response/activity for a few MPH over 20 - so I can do 20/21 or even 22 without it getting weird.

alan in tempe
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Re: 2009: Wheel Size Locked?

The question: If I buy a 2009 BionX 350 with a 26" wheel and then put it in a 20" wheel, can I reprogram the system so that it knows about the bigger wheel? How about the other way? Can I decrease the wheel size?

Anybody know for sure?

[Second try; no idea why my previous post is not showing up hours later.]
I don't know for sure, but I have an educated (EE) guess...
It is likely Bionx uses the same basic motor with different windings for different wheel sizes. The number of turns of wire in each stator coil can easily be varied from model to model (all the same number within any single motor!) to vary the motor's Kv value. A higher Kv will give a faster motor with no load on it, but with reduced torque (keeping the power/voltage/current more or less the same). If this is what Bionx does, then re-lacing a 24" Bionx motor to a 26" wheel (all else the same), will give a faster maximum assist speed, but with less assist torque. Your top speed may go from 20 MPH on the 24" wheel to 22 MPH on the 26" wheel, but the increased wind resistance and reduced torque may actually reduce your top speed, or only increase it a tiny bit. It will also cause you to accelerate from a stop less quickly, and slow your maximum hill climbing speed. Conversely, putting a 24" wheel on a 26" Bionx motor would reduce your top speed, but get you faster acceleration up to the reduced top speed, and stronger hill climbing ability.

-- Alan

nycewheels
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BionX motors ship with different speeds

This is still correct as per your earlier phone call when you spoke to Shoi in shipping.

BionX motors are wound different for different wheel sizes.
A 20" motor has much higher rpm's than a 26" motor to compensate and run at the same top speed. I nice high speed system that actually works better than a 500 watt BionX (in my opinion) is a 20" motor laced into a 26" or 700C rim. It will do about 24 mph and be somewhat efficient, not sucking your battery empty like the BionX PL 500 does at 27 mph.

Bert, www.nycewheels.com

Regards, Bert (first guy in, last guy out)
(212)-737-3078 | (800) (692-3943)
www.nycewheels.com | Bert [at] nycewheels.com
NYCeWheels | 1603 York Avenue | New York, NY 10028

fastlane
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Re: BionX motors ship with different speeds

This is still correct as per your earlier phone call when you spoke to Shoi in shipping.

BionX motors are wound different for different wheel sizes.
A 20" motor has much higher rpm's than a 26" motor to compensate and run at the same top speed. I nice high speed system that actually works better than a 500 watt BionX (in my opinion) is a 20" motor laced into a 26" or 700C rim. It will do about 24 mph and be somewhat efficient, not sucking your battery empty like the BionX PL 500 does at 27 mph.

Bert, www.nycewheels.com

The Bionx motor for the 20 in wheel runs to 385rpm the one for the 26/700c wheel runs 300rpm So if you re-lace the 20 inch motor to a 700c wheel you will go faster from 20mph top to 24/25mph top speed, but will you lose torque, and do you have to set the controller to a 20 inch wheel setting even though you are running the 700c wheel to get the higher speed and not lose the torque. If you leave the setting on the proper wheel size will the controller even allow the rpm to go over 300rpm and up to the 385rpm. And if you need to set it to the 20 inch wheel setting to get to the higher 385 rpm how do you correct your speedometer and odometer in the controller.

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