Tongsheng crank arms are for riders of height 5'9" - where can we get smaller cranks?

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xtinctionRebeller   10 W

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Tongsheng crank arms are for riders of height 5'9" - where can we get smaller cranks?

Post by xtinctionRebeller » Mar 17 2020 1:33pm

According to case studies, these are the optimum crank arm lengths given a rider's height:
[table]
[tr][th]rider height[/th][th]optimal crank length (mm)[/th][/tr]
[tr][td]6’0" (1828mm)[/td][td]177.5[/td][/tr]
[tr][td]5’11" (1803mm)[/td][td]175[/td][/tr]
[tr][td]5’10" (1778mm)[/td][td]172.5[/td][/tr]
[tr][td]5’9" (1753mm)[/td][td]170[/td][/tr]
[tr][td]5’7" (1702mm)[/td][td]165[/td][/tr]
[tr][td]5’5" (1651mm)[/td][td]160[/td][/tr]
[/table]

Most vendors don't state the length of the crank arms. After some probing, a vendor (I think Luna Cycle) told me Bafang crank arms are all 175mm. I need 165mm. Is it true that all kits are 175mm or are there exceptions? Does anyone sell smaller cranks that are compatible with Bafang?

I'm not necessarily fixated on Bafang. And I noticed that there exists 165mm crank arms for Bosch. I'd like to find a mid-drive kit for a 100mm bottom bracket (fat bike), and I guess I'd rather not have a seperate chain like a Cyclone has.

update:

I've decided to favor the Tongsheng TSDZ2 motor over the Bafang. The Bafang is heavier, draws more power, and wears out chains and sprockets faster. I just want some light assistance on climbs, so I think the TSDZ2 is better suited. I've consequently changed the subject line of this thread:

original subject: Bafang Tongsheng crank arms are for riders of height 5'11" - where can we get smaller cranks?
new subject: Tongsheng crank arms are for riders of height 5'9" - where can we get smaller cranks?

Since the TSDZ2 also has oversized cranks from the factory, I would prefer to find a kit that excludes the cranks so I buy the correct cranks separately without being wasteful.
Last edited by xtinctionRebeller on Mar 19 2020 4:02pm, edited 1 time in total.

Joe King1   10 mW

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Re: Bafang crank arms are for riders of height 5'11" - where can we get smaller cranks?

Post by Joe King1 » Mar 17 2020 6:39pm

The study you listed refers to non-assisted road bikes. This topic has been discussed ad nauseam for years & to my knowledge hasn't been definitively proven.

Regardless, ebikes don't need as long cranks as pedal bikes & if you are using your's off-road, the shorter arms (I use 155 & I'm also 5'11") are a major plus avoiding pedal impacts. Miranda make quality reasonably priced Bafang compatible cranks

https://mirandabikeparts.com/en/

I have no interest in fat-bikes so I never looked to see if they make any for steam-rollers.

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Re: Bafang crank arms are for riders of height 5'11" - where can we get smaller cranks?

Post by Rassy » Mar 18 2020 12:24am

The standard crank arms shipped with BBS02 units are 170mm.

Sick Bike Parts has some different length cranks that would be compatible with a BBS02. Here is a link to some that are 152mm long:

http://sickbikeparts.com/cranks-152mm-f ... crank-set/
-Rassy-

Two Delta Trikes equipped with a Bafang BBS02
viewtopic.php?f=28&t=88536&p=1291260#p1291260

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Re: Bafang crank arms are for riders of height 5'11" - where can we get smaller cranks?

Post by xtinctionRebeller » Mar 19 2020 4:18pm

Joe King1 wrote:
Mar 17 2020 6:39pm
The study you listed refers to non-assisted road bikes. This topic has been discussed ad nauseam for years & to my knowledge hasn't been definitively proven.

Regardless, ebikes don't need as long cranks as pedal bikes & if you are using your's off-road, the shorter arms (I use 155 & I'm also 5'11") are a major plus avoiding pedal impacts. Miranda make quality reasonably priced Bafang compatible cranks
Apart from the study I'm hearing that road cyclists my height tend to benefit from 165mm or shorter cranks. Since it's common for people to favor smaller cranks on e-bikes due to the man/motor power sharing, and also common to favor smaller cranks on mountain bikes for better clearance, I'm convinced I'm better off avoiding anything longer than 165mm. I'm short and in the end it'll be a fat mountain e-bike.

I appreciate the referral to Miranda. They mention Bosch but they don't mention other motors as far as compatibility goes. I think Tongsheng is compatible with Bafang. Are Miranda cranks compatible with Tongsheng?
Rassy wrote:
Mar 18 2020 12:24am
The standard crank arms shipped with BBS02 units are 170mm.
I was told 175mm by Luna Cycle, but either way it's too large. I'm now focused on Tongsheng but those are also too large (170mm). It's a bit annoying that all the kits come with cranks without a size option (yet Luna Cycle gives color options).
Rassy wrote:
Mar 18 2020 12:24am
Sick Bike Parts has some different length cranks that would be compatible with a BBS02. Here is a link to some that are 152mm long:

http://sickbikeparts.com/cranks-152mm-f ... crank-set/
Thanks. I hear Bafang cranks are compatible with Tongsheng. But I think 152mm is too short for me. I intend to only use electric for climbing, and I'm not going to have serious clearance issues. I'm after ~160-165mm cranks.

It's a perfect storm of weirdness because Tongsheng kits have an absurd Q-factor, and also the right crank is pushed out more by the motor, so some people get a lower Q-factor on the right crank than the left so things are centered. I think it'll be hard for me to find a TSDZ2 kit without cranks, and then to also find separate but compatible cranks with different Q factors.

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Re: Tongsheng crank arms are for riders of height 5'9" - where can we get smaller cranks?

Post by Balmorhea » Mar 20 2020 8:34am

Any unicycle cranks for a square taper type bottom bracket should work.

Crank length is a matter of taste. People are versatile about it, and the cycling industry tends to furnish either 170mm or 175mm cranks for the entire size range of adult bikes. I think it’s dumb, but on the other hand it seems to work well enough in practice.

I am tall, and I like the feel of long cranks, so my muscle-powered bikes have cranks of at least 185mm up to considerably longer than that. But when I used a Bafang crank drive kit, I wanted a faster cadence to match the motor’s most efficient speed range. So I used 152mm unicycle cranks to make it easier to maintain a high pedal RPM. Those cranks also had the advantage of putting the pedals closer to the bike’s centerline, without affecting mechanical operating clearances.

Now I use a hub motor, so I have long 190+ mm cranks again.

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Re: Tongsheng crank arms are for riders of height 5'9" - where can we get smaller cranks?

Post by Deafcat » Mar 20 2020 10:18am

Crank length according to rider height is a sham! (except with really tall riders, sure. Kinematic/ergonomics and what have you)

The truth is, shorter cranks are simply better, on assisted bikes especially, and I would recommend switching all your bikes to cranks between 150-160mm length. Miranda components in EU is where you'll want to source em from, they have a huge selection.

Benefits to short cranks: increased ground clearance, less pedal strikes, more toe and heel clearance, reduced offset requirement usually on plus/fat tire bikes.

Downsides: none, except for tall folks.

I run 152mm on my Ultra bike and will never go back to longer cranks, even though I've been cycling with 170mm for the past 15 years. Even riding the 50lb fat bike with no battery and no assist, it's a superb ride and no issues climbing, although for acoustic bikes on steep mountain climbing there may be some challenges from reduced momentary torque from stand still.

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Re: Tongsheng crank arms are for riders of height 5'9" - where can we get smaller cranks?

Post by cavi » Mar 20 2020 2:21pm

I have the Lekie buzz bars in 165 mm on both my e-bike and my wifes and they are awesome!!! If your BB uses the square fitting it will work

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Re: Tongsheng crank arms are for riders of height 5'9" - where can we get smaller cranks?

Post by xtinctionRebeller » Mar 20 2020 4:59pm

I appreciate the advice so far. I've looked at these suggestions:
  • Miranda - they have a huge number of options that seem ideal for addressing Tongsheng's cockeyed asymetric and large Q factor. I think I can get whatever crank arm length I want and perhaps with a reduced Q factor on the right to compensate for the asymetry of Tongsheng. But they're in Europe. And their website is broken. If I "add to cart" I just get redirected to an empty cart. The map under the "distributors" tab is broken -- I can't get it to list N.America distributors. Their contact page is also broken. I wrote a msg and got no acknowledgement that it was sent.. just continues to show my original msg after submission. Guess my next move is to search for a North American distributor of Miranda cranks -- but might be tricky to find one offering all the Q-factor/size options.
  • Lekie buzz bars - lekkie.bike is in New Zealand and their website is CloudFlared (which means they give problems for Tor users). I'm normally a bit reluctant to patronize a CloudFlare shop.. but I guess I'd buy from one of their distributors anyway. There are still a couple of practical issues: the Lekie buzz bars are symetric, as most cranks are, but if I'm going to install a Tongsheng TSDZ2 the right pedal is further right than the left one is to the left, if I understand correctly. So I'd rather have a right crank with a lower Q factor so my right and left foot are equidistant from the center. The price is $99 in CA, which I find a bit steep. I have no idea why crank arms reach these prices but for 3 figures I'd want Q-factor perfection.
  • Sick Bike Parts - the price is decent ($28). Maybe I'll put up with the fact they're ~8mm smaller than what I'm after, and symetric. Some riders say they don't notice the right-shifted position of the pedals.
I really wish a Tongshen reseller would bundle in some sensible cranks. Consumers shouldn't have to buy a kit with bad cranks and then immediately spend a lot at a different vendor to replace them.
cavi wrote:
Mar 20 2020 2:21pm
I have the Lekie buzz bars in 165 mm on both my e-bike and my wifes and they are awesome!!! If your BB uses the square fitting it will work
I'm curious about your square fitting comment, because bottom brackets are all cylindrical and the Tongsheng and Bafang motors entail replacing all the guts of that with their own -- or so I thought. In which case, isn't it just a matter of being compatible with the motor kit? The buzz bars are claimed to be compatible with: Bafang BBS01/BBS02/BBSHD/Maxdrive, Bosch Performance/Active, Yamaha, Brose, TTIUM, Shimano Steps E6000. Which leads me to believe that all cranks designed for any one of those motors are likely compatible with with any of the others. Lekkie doesn't mention Tongsheng, but I've read in other places that Tonsheng TSDZ2 crank arms are compatible with Shimano Steps E6000 and Bafang.

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Re: Tongsheng crank arms are for riders of height 5'9" - where can we get smaller cranks?

Post by Waynemarlow » Mar 21 2020 8:23am

Both the Tongshen and the Bafung use an old fashioned " square taper " crank arm.

From the standard Tongshen 170mm as supplied some of us have replaced the right crank with a Shimano I think by memory E600 BMX crank which has almost no offset which then brings the Q factor back into the normal range. To be honest most people including myself, don't really notice the offset pedal, the human body seems to compensate OK.

So any square taper crank arm, typically from the BMX ranges are the ones to look at. Some of the unbranded ones are ridiculously inexpensive so you can mix and match two sets with a varying offset at not a lot of cost.

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Re: Tongsheng crank arms are for riders of height 5'9" - where can we get smaller cranks?

Post by cavi » Mar 22 2020 4:21pm

the Lekie Buzz bars come in both the straight and the offset, I have the offset for my bike


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Re: Tongsheng crank arms are for riders of height 5'9" - where can we get smaller cranks?

Post by xtinctionRebeller » Mar 22 2020 5:26pm

Thanks Cavi. It says the offset introduced by BBS (Bafang) motors is 18mm. Does anyone know if it's the same offset for Tongsheng motors?

After watching this video, I might be a bit more open to the idea of 152mm crank arms:
http://qklhadlycap4cnod.onion/watch?v=7GlIu0Znfcs
Would be useful to be able to incorporate off roading into my habit.

Miranda shows some crank sizes are for fat bikes. What's the difference between cranks for a fat bike and cranks for a thin bike?

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Re: Tongsheng crank arms are for riders of height 5'9" - where can we get smaller cranks?

Post by Balmorhea » Mar 22 2020 7:47pm

xtinctionRebeller wrote:
Mar 22 2020 5:26pm
Miranda shows some crank sizes are for fat bikes. What's the difference between cranks for a fat bike and cranks for a thin bike?
Only the width if the bottom bracket. Normal bikes have 68mm bottom brackets, some MTBs have 73mm, but fatbikes have typically 100-120mm BBs. The arms themselves usually do not differ between one and the other.

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Re: Tongsheng crank arms are for riders of height 5'9" - where can we get smaller cranks?

Post by torker » Mar 22 2020 7:57pm

I ended up using 155mm. Bmx cranks on mine for pedal strike. Also good for bad knees. Most non powered riders prefer longer cranks for more leverage.
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