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Possibly dumb question about Bosch bike with very small chainring

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Possibly dumb question about Bosch bike with very small chainring

Old 07-20-19, 07:21 AM
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wesmamyke 
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Possibly dumb question about Bosch bike with very small chainring

Okay, having not actually ridden a Bosch mid drive bike this might be a dumb question. I was looking at Trek and other bikes that have a very small front chainring. Some are rated to 28mph, so clearly it's not an issue under power. My question is in the case of a dead battery.

Is the bike severely handicapped if the battery dies? Even riding in a very hilly area I find anything less than a 36t chainring almost unusable in a 1X drivetrain, as you immediately spin out on the slightest downhill.

I'm currently rebuilding my only 1X bike to have a 38t ring to hopefully make it a little better than the 36t.
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Old 07-20-19, 08:10 AM
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I believe all those Bosch and Yamaha mid drives are 7 or 8 speeds. 1x removes the advantage of a mid drive, where a smaller motor can use the bikes gearing.
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Old 07-20-19, 08:56 AM
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I meant 1X front chainrings, they all have a rear derailleur. Some are 8/9spd, the nice one is 11spd.

That is the current industry term, as in 1x8, 1x9, 1x10 and 1x11.
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Old 07-20-19, 09:12 AM
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You can change the front chainring. FSA makes them from 36 to 46t. Others may make them as well.

edit: It looks like there are few different systems. Some have gearing such that the front chainring is not directly connected to the crank. I've seen mention of a 2.5x gear ratio so a 15t front chainring would be equivalent to a 37t chainring on a regular bike. Bosch's documentation on these details seems a little sparse.

Last edited by gregf83; 07-20-19 at 09:25 AM.
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Old 07-20-19, 11:28 AM
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The commercial ebike makers are selling bikes to a lot of owners who don't know how (or why) to shift, so they pick a smaller front gear so that newbie riders have a better chance of making it up a hill using the smallest rear gear. And yes, I suppose a strong bike rider will spin out at higher speeds. Anyway, you'll know more than the rest of us when you do a test ride.

You might find a larger chain wheel, but have to make sure that a bigger gear will fit the bike. On some, it might hit the frame, probably another feature to protect the motor by keeping the user from going to a 52T, It's another thing to ask the dealer when you see him. Maybe it voids the warranty?










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Old 07-20-19, 11:48 AM
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That Bosch tiny chainring spins about 2.5 times faster than the crank.
The Yamaha mid-drive rides better than the Bosch without power........(I think)
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Old 07-20-19, 12:14 PM
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Bosch has a Sclumph (sp?) drive that "magnifies" the front chainring by a factor of 2.5; ergo if it has 14 teeth, it's like a "normal" 35 tooth ring.
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Old 07-20-19, 06:03 PM
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Okay, it would seem 20t is the largest size they make. Has anyone ridden one of these Bosch mid drive bikes? Does that crank gearing cause much drag? I just read the other thread about the newer version that claims less drag and a normal chainring.

The Trek ones were totally sold out when I checked recently, so not much chance to test ride one. I could order one locally though if they become available.

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Old 07-20-19, 09:34 PM
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The info I found suggests that the Yamaha mid drive has no drag where the Bosch's does when the assist is turned off. I was looking at the Giant Quick E+ vs the Trek Verve+. I finally settled on a Bafang hub motor so there is no drag when the pedal assist is off.
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Old 07-21-19, 01:04 AM
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I've ridden many Bosch, Yamaha and Brose mid-drives, as well as Bafang DIY and the drag with the motor off seems to be the same with all of them. Perhaps if I compared them back to back I might notice a difference, but the drag is so minimal (to me) as to be of no consequence.
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Old 07-21-19, 09:59 PM
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Depends which model of Bosch. Also the year. The Active line has no noticeable drag, the old CX line does have drag. The 2020 CX is said to have practically eliminated any drag.
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Old 07-23-19, 07:06 AM
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My Trek Verve with Bosch active line has no noticeable drag.
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Old 07-23-19, 11:11 AM
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For Bosch, it's more about the generation of motor. The new generation motors, including Active and Active Plus, and the soon to be released Performance all have minimal extra drag when the motor is off. The previous generation motors (Active/Performance/Speed/CX) all had some noticeable drag when off. Brose and Yamaha are similar to the new generation Bosch motors, with some of the newer Brose even better than before.
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