Donor bike crank BCD too small for bigger chainrings

[UphillBattle]

I have a Carrera Fury (200£ on Facebook for a £650 bike that was in awful condition) that I’ve been porting my parts from my old bike (I ran it until the pedals no longer worked!) to and it’s working fine but the front chainring is WAY too small for my purposes.

I carelessly bought a new 50t chainring among all the other AliExpress parts but now find that the BCD of it (104) is too big for the tiny little 1x10 crankset on this thing. I’m measuring 75mm so I’m guessing it’s an asymmetric BCD 76. According to the Halfords spec it’s a Prowheel 32T narrow-wide crankset. Nothing I can see fits it and certainly not in the 50+ T range that I’m after. I don’t imagine I’m the first to have trouble converting an off-road-focused MTB chainring to a vastly larger ebike-friendly one. Do I just replace the crank and use the larger chainring I already have? I know nothing about cranks, is there anything to look for other than it having a 104 BCD?

 

[saneagle]

I have a Carrera Fury (200£ on Facebook for a £650 bike that was in awful condition) that I’ve been porting my parts from my old bike (I ran it until the pedals no longer worked!) to and it’s working fine but the front chainring is WAY too small for my purposes.

I carelessly bought a new 50t chainring among all the other AliExpress parts but now find that the BCD of it (104) is too big for the tiny little 1x10 crankset on this thing. I’m measuring 75mm so I’m guessing it’s an asymmetric BCD 76. According to the Halfords spec it’s a Prowheel 32T narrow-wide crankset. Nothing I can see fits it and certainly not in the 50+ T range that I’m after. I don’t imagine I’m the first to have trouble converting an off-road-focused MTB chainring to a vastly larger ebike-friendly one. Do I just replace the crank and use the larger chainring I already have? I know nothing about cranks, is there anything to look for other than it having a 104 BCD?

Why not change the crankset? They don't cost much used ones from Ebay.

I would have thought that the bigger problem would be the clearance of the chainwheel from the chainstay, which is what makes bikes like that unsuitable for a pedal assist conversion unless you want to do slow off-road rides.

 

[Raboa]

Put a small geared cassette on the back? How many gears on the back cassette?

 

[UphillBattle]

Why not change the crankset? They don't cost much used ones from Ebay.

I would have thought that the bigger problem would be the clearance of the chainwheel from the chainstay, which is what makes bikes like that unsuitable for a pedal assist conversion unless you want to do slow off-road rides.

Ah, I just looked and there is indeed no clearance for the chainwheel versus the chainstay.

Looking at options for pushing the chainwheel outwards: it sounds like spacers or a chainring with an offset are the options.

I’m not too bothered about disturbing the angle of the chain: I mostly ride in the top gear so it makes sense to bias toward those outer gears on the rear cassette.

 

[UphillBattle]

Put a small geared cassette on the back? How many gears on the back cassette?

It’s a 10x, 11-46T. I actually just replaced it as I couldnt use the previous one, shame I didn’t se this problem before I bought this replacement cassette.

 

[UphillBattle]

Hmm or maybe get a 2/3x crank and just use the one chainring.