The difference between 42 & 46T chainrings

[Patrick10am]

I’m thinking about changing my 46T for 42T chainring on my BBSO1. Chainrings available at Brighton Bikes cost £75.00 do you think the difference I will feel is worth the money spent?

 

[Fordulike]

You'll probably find the Bling Ring will improve your chainline somewhat. Plus, the 42T will put less stress on the BBS01's internal gears, and give you more torque for hillclimbing through the gears.

I run one on my BBS02 and wouldn't fit a kit without one!

 

[Patrick10am]

Great it’s kinda of what I thought but it’s great to get someone that’s used 42T
Thanks very much.

 

[sjpt]

There seem to be plenty around for much less than that. eg

Electric Bike Bicycle Chainwheel Chainring 40/42/44T For Bafang G340 BBS01B-02B | eBay

Find many great new & used options and get the best deals for Electric Bike Bicycle Chainwheel Chainring 40/42/44T For Bafang G340 BBS01B-02B at the best online prices at eBay! Free delivery for many products!

www.ebay.co.uk

goes down to 40 tooth.

Not sure of the quality ...
Or get a spider, there seem to be lots on ebay for around £10, and then a higher quality standard chainring.

 

[Fordulike]

There seem to be plenty around for much less than that. eg

Electric Bike Bicycle Chainwheel Chainring 40/42/44T For Bafang G340 BBS01B-02B | eBay

Find many great new & used options and get the best deals for Electric Bike Bicycle Chainwheel Chainring 40/42/44T For Bafang G340 BBS01B-02B at the best online prices at eBay! Free delivery for many products!

www.ebay.co.uk

goes down to 40 tooth.

Not sure of the quality ...
Or get a spider, there seem to be lots on ebay for around £10, and then a higher quality standard chainring.

I might be wrong, but it's my understanding that the improved chainline benefits only apply to the 42T (Bling Ring), as it wraps around the motor housing. A spider and chainring could create chainline problems.

As for quality of the Bling Ring, I have reprogrammed my BBS02's controller, which now runs massive amounts of torque through the drivetrain. I haven't had any issues with wear over the last 5k miles. Expensive yes, but IMHO worth every penny!

 

[sjpt]

I'd certainly go for Fordulike's advice rather than mine. I don't have a BBS so don't know how details such as chainline work out.

 

[Woosh]

if you have more teeth on the chainring then the same amount of torque is spread onto more teeth.
You transfer some more of the stress and wear from the ring to the internal gears.
A 46T ring has an easier life compared to a 42T ring.

 

[Fordulike]

if you have more teeth on the chainring then the same amount of torque is spread onto more teeth.
You transfer some more of the stress and wear from the ring to the internal gears.
A 46T ring has an easier life compared to a 42T ring.

I am definitely not questioning your expertise, or trying to cause an argument, but I assumed the following.

Because a 46T chainring is larger in diameter, then to create the same amount of torque at the same point on the outer tooth edge as the 42T, the motor has to work harder. Hence the motor gears experience more load. Have you got any reference links, as I need to get my head around this before I go bonkers

 

[Woosh]

https://en.wikipedia.org/wiki/Torque

You can see that for a fixed amount of torque, if the radius r increases, then the force F decreases.
A bigger ring has less force applied to its teeth.

The wear is proportional to the force applied to the teeth.
If force F decreases, then wear of the teeth also decreases.

 

[Fordulike]

https://en.wikipedia.org/wiki/Torque

You can see that for a fixed amount of torque, if the radius r increases, then the force F decreases.
A bigger ring has less force applied to its teeth.

The wear is proportional to the force applied to the teeth.
If force F decreases, then wear of the teeth also decreases.

I can see how the relationship puts less stress on the actual chainring teeth in a bigger diameter chainring, but I can't get my head around how it would put less stress on the motor. I would have thought the motor internals would have to produce more torque with the 46T, than the 42T, to achieve the same force.

Am I missing something here?

 

[Woosh]

I can see how the relationship puts less stress on the actual chainring teeth in a bigger diameter chainring, but I can't get my head around how it would put less stress on the motor. I would have thought the motor internals would have to produce more torque with the 46T, than the 42T, to achieve the same force.

Am I missing something here?

I said

You transfer some more of the stress and wear from the ring to the internal gears.

I agreed with you. Bigger chainring, less wear on the ring, more stress and wear on the motor.

 

[Fordulike]

I said


I agreed with you. Bigger chainring, less wear on the ring, more stress and wear on the motor.

Sorry, my bad

 

[Patrick10am]

Interesting thread learnt quite a lot. I’ve predicted for the 42 T chainring more ware on the ring less on my legs. The bling ring looks like a preferably choice as it covers the motor keeping the chain in line. We will see how it goes .

 

[Fordulike]

Interesting thread learnt quite a lot. I’ve predicted for the 42 T chainring more ware on the ring less on my legs. The bling ring looks like a preferably choice as it covers the motor keeping the chain in line. We will see how it goes .

Whilst we're on the subject of Bafang BBS gear, can I just point you to a thread which shows other useful BBS stuff:

https://www.pedelecs.co.uk/forum/threads/after-market-bbsxx-crank-drive-gear.32691/