Spoke gauge and wheel build question

[safasdf444]

Hi,

I have a Bafang G310 from Grin. I am about to purchase an old mountain bike, 26 inch wheels, V brakes. I would like to have a bike shop install the hub in the existing wheel.

Would they be able to use the existing spokes? Or will I need to get beefier ones for this build. When I chatted with the bike shop the other day, they said their spoke cutting tool couldn't handle thicker ebike spokes and most likely I would need to order spokes from wherever I got my hub motor.

What gauge of spokes would this setup need? Since the G310 is on the smaller side would the existing spokes be ok?

I'm trying to learn a bit so I can understand better when I go back to the bike shop.

thank you!

 

[amberwolf]

I doubt any wheel builder will reuse spokes, even if they were identical lengths for the new hub in the new rim (which they won't be). They may not even be willing to reuse the rim and require a new one to be used, becuase they can't guarantee a wheel built from unknown condition used parts.


FWIW you don't want "beefier" spokes, thicker ones are more likely to fail, not less, because they will require too high a tension for the rim's strength, causing rim nipple hole failure.

If you are willing to look around you can read about this in many many posts here on ES about wheels, spokes, etc.

But if htey are a "real" bike shop that builds wheels, they *should* already know all this, and be able to cut you (or order them from the appropriate place) the correct 14g-15g butted or 13g-14g butted spokes the wheel should be built from, and they should be able to determine the correct length spokes needed.

If they want to use thicker 12g spokes, etc., with an existing bicycle MTB rim, they probably don't know how wheels work, and you should go somewhere else to have it built, or you can learn how to do so yourself easily enough.

 

[safasdf444]

I doubt any wheel builder will reuse spokes, even if they were identical lengths for the new hub in the new rim (which they won't be). They may not even be willing to reuse the rim and require a new one to be used, becuase they can't guarantee a wheel built from unknown condition used parts.


FWIW you don't want "beefier" spokes, thicker ones are more likely to fail, not less, because they will require too high a tension for the rim's strength, causing rim nipple hole failure.

If you are willing to look around you can read about this in many many posts here on ES about wheels, spokes, etc.

But if htey are a "real" bike shop that builds wheels, they *should* already know all this, and be able to cut you (or order them from the appropriate place) the correct 14g-15g butted spokes the wheel should be built from, and they should be able to determine the correct length spokes needed.

If they want to use thicker 12g spokes, etc., with an existing bicycle MTB rim, they probably don't know how wheels work, and you should go somewhere else to have it built, or you can learn how to do so yourself easily enough.

I guess a dumb basic question from me. Do hub motors require special spokes? Or are they same spokes you would use on a regular wheel?

 

[amberwolf]

Well, I already said the size spokes you need in the post, and there are a lot of other posts you can look up that describe in detail why, if you're interested. (no point in repeating it all here yet again)

But basically, wheels built of the same rims need the same spokes, because the spokes required are first based on the rim being used.

Wheel design is more complicated than that, but you don't have to worry about all the details (if you do you can look them up in existing posts, etc), just use the right gauge spokes for the rim being used.

A qualified knowledgeable wheel builder that's going to build a wheel for you will be able to deal with anything else that's different about that particular wheel and usage.

 

[amberwolf]

Some possible searches for detailed info; they don't list all the posts or threads that have info, there are many. Unfortunately due to the nature of the search, it also includes irrelevant posts and threads.
https://endless-sphere.com/sphere/search/2232305/?q=spoke&c[title_only]=1&o=date
https://endless-sphere.com/sphere/search/2232305/?q=spokes&c[title_only]=1&o=date
https://endless-sphere.com/sphere/search/2232321/?q=wheel&c[title_only]=1&o=date
https://endless-sphere.com/sphere/search/2232321/?q=wheels&c[title_only]=1&o=date
https://endless-sphere.com/sphere/search/2232346/?q=wheel+build&c[title_only]=1&o=date
etc.

 

[Chalo]

Hub motors are usually drilled for thicker spokes than what the rims need. As a result, when you use 14ga (2.0mm) spokes, you'll have to put 2.0mm flat washers underneath the spoke heads so they don't dig into the hub holes or try to pull through.

 

[docw009]

14G spokes with washers will work per Chalo's comment, but if you look at Grin's web site, I believe they recommend Sapim butted spokes, 13G at the elbow and 14G at the wheel, Bike shops ought to have a spoke cutter that can handle 14G.

There you go, Go to the shop with either option.

 

[safasdf444]

14G spokes with washers will work per Chalo's comment, but if you look at Grin's web site, I believe they recommend Sapim butted spokes, 13G at the elbow and 14G at the wheel, Bike shops ought to have a spoke cutter that can handle 14G.

There you go, Go to the shop with either option.

I just learned something, Thank you!

 

[gromike]

Check out Grin's spoke length calculator, Online Spoke Calculator for Hubmotors and Ebikes.
And watch their motor wheel building tutorial toward the bottom of this page, Wheel Building - Learn .
I built 3 motor wheels with Grin's guidance.
Wheel building, at least single crossed spokes, isn't all that difficult. Kinda a pleasant evening thing to do. Money saving, though, it's not.

 

[glennb]

They're drilled for 13G.

 

[glennb]

Photo is two cross in 27.5 rim (584mm).

For a 26" wheel I'd only go single cross.

 

[bananu7]

Perhaps a silly question, but instead of using thinner spokes, why not use a stronger rim that can handle tension from 2.3mm spokes?

 

[Chalo]

Perhaps a silly question, but instead of using thinner spokes, why not use a stronger rim that can handle tension from 2.3mm spokes?

Because then they'd be heavy motorcycle rims, needlessly crude and chunky for the job they have to do. Bicycle parts are designed based on their requirements, not to pair with arbitrary inappropriate other parts.

If you start making bad design choices for foolish reasons, eventually you end up with a car instead of a bike.

 

[bananu7]

Because then they'd be heavy motorcycle rims, needlessly crude and chunky for the job they have to do. Bicycle parts are designed based on their requirements, not to pair with arbitrary inappropriate other parts.

If you start making bad design choices for foolish reasons, eventually you end up with a car instead of a bike.

Well yeah, but the loads the heavy hub motors put on the rim are far greater than what they experience in normal use, so it's not like you can just put a hub motor in a regular bicycle rim with regular gauge spokes and expect it to hold up fine. I am pretty sure motorcycles use spokes much heavier than 2.3mm anyway.

 

[Chalo]

Well yeah, but the loads the heavy hub motors put on the rim are far greater than what they experience in normal use, so it's not like you can just put a hub motor in a regular bicycle rim with regular gauge spokes and expect it to hold up fine.

That's exactly what you can do. The loads imposed on a wire wheel by a hub motor are at least an order of magnitude lower than the design loads for a bicycle wheel. Wire wheels are so fit for their purpose that attempts to replace them with castings or disc wheels have all failed because the results are weaker, heavier, more expensive, and less serviceable than the usual kind.

I am pretty sure motorcycles use spokes much heavier than 2.3mm anyway.

Some do, some don't. But even a tiny displacement racing motorcycle for small riders has wheels that are heavy and inefficient compared to what we're accustomed to with bicycles.

 

[E-HP]

Well yeah, but the loads the heavy hub motors put on the rim are far greater than what they experience in normal use, so it's not like you can just put a hub motor in a regular bicycle rim with regular gauge spokes and expect it to hold up fine. I am pretty sure motorcycles use spokes much heavier than 2.3mm anyway.

4 or 5 HP from a hub motor vs 10 or 20 times that for a motorcycle is a big power difference.

 

[dgc]

14G spokes with washers will work per Chalo's comment, but if you look at Grin's web site, I believe they recommend Sapim butted spokes, 13G at the elbow and 14G at the wheel, Bike shops ought to have a spoke cutter that can handle 14G.

There you go, Go to the shop with either option.

Sapim Strong single butted spokes are the one's I use and the hub motor normally take 36 spokes, not sure of the power rating of the your motor but I have laced a Bafang 500 watt hub motor into a double skin rim with these. I have used Strong spokes for wheels on my 500 watt mid drives as well.

 

[artbo]

Because then they'd be heavy motorcycle rims, needlessly crude and chunky for the job they have to do. Bicycle parts are designed based on their requirements, not to pair with arbitrary inappropriate other parts.

If you start making bad design choices for foolish reasons, eventually you end up with a car instead of a bike.

why do they have to be heavy motorcycle rims for 2.3mm spokes? i drive now a rim from DT swiss, hybrid u683 with Grins all axle and butted sapim strong spokes in 2,3mm and 2,00. i cant say that i find this spokes to be "strong" and thinking if i should switch to thicker spokes, but i am not sure yet. i think those DT swiss hybrid rims should handle higher tension from thicker spokes, unfortunately i dont see this information on their website, they only write rider weight limit of 180kg.

U 683 | DT Swiss

www.dtswiss.com

i noticed today that sapim has also E-strong spokes in 2,6mm and 2,3mm which they recommend for hub motors, here is a comparison (in german):

Welche Speiche wofür?

Hier sehen Sie eine Übersicht der bei uns erhältlichen Speichen von Sapim mit wichtigen technischen Daten und Anwendungstips. Speichen sollten…

komponentix.de

also DT swiss writes on their site for their hybrid wheels:

"Thicker spokes​

Thicker spokes are used in the Hybrid wheels in comparison to the conventional MTB wheels. This Hybrid specific spoke increases both the lateral and the torsional stiffness. As previously explained in the context of the hub flange, this helps to get better lateral stiffness, more suited to the loads of eMTBs but it also increases torsional stiffness, for the transmission of the propulsion power from the hub to the rim. Furthermore, each spoke is always loaded during a rotation. This continuous and consistent load avoids fatigue of the spoke that can lead to failure.

Hybrid MTB | DT Swiss

www.dtswiss.com

 

[Chalo]

why do the have to be heavy motorcycle rims for 2.3mm spokes?

They have to be heavy rims so the spokes can be turned up to a high enough tension that they stretch elastically enough to follow the rim as it flexes under load. A 2.34mm round spoke needs 37% higher tension to stretch the same amount as a 2.0mm spoke of the same length, and 69% higher tension than a 1.8mm spoke. But bicycle rims are usually rated for maximum spoke tension of 100kgf to 125kgf. So at that maximum tension, the thicker spokes will go slack and cause problems at lower wheel loads, making the wheel weaker even though the spokes themselves are stronger.

That's where the DT marketing claptrap you quoted fails hardest. Spokes are under continuous tension only when the wheel isn't loaded. When it is loaded, the tension drops as each spoke passes over the contact patch of the tire, and if that tension drops to zero then the spokes go slack momentarily and cause loosening and fretting damage to the rim. The thicker the spoke, the lower the wheel load at the time this happens.

If you use a rim that can tolerate proportionally higher spoke tension, then you can make thicker spokes as reliable as thinner spokes at lower tension. But you could also use thinner spokes at the higher tension and the wheel will be even stronger.

 

[dgc]

Yep, that's right regarding the Sapim E spokes, I have usually been matching a Bafang hub motor to a heavy duty double eyelet rim so have used the Strong single butt spokes rather than drilling the rims out along built with a 2 crossing spoke pattern, although a 3 crossing is stronger, but have had any problems so with the even with a rear wheel which is over 6 years old.