Came across a triban 500 sora cycle on ebay snag is on riding the crank is rough in lower gears it has 9 the se uk model has 8 the cy

[Nightjar]

Secured a triban 5 sora cycle ebay snag is sora has 9 speed cassette the cranks grinds noticeabley in Lower gears the cycle has a bottom bracket of 8 speed I'm thinking replacing BB should rectify however why was 8 BB installed

 

[Cycleops]

Hello and .

Never heard of a 8 speed BB, or do you mean 8 speed chainrings or chain? BB is the spindle and bearings the cranks are attracted to, they are not speed specific.
Grinding could be due to any number of things. Can you feel play in the BB if you rock the cranks from side to side? Could be worn chain rings or chain, Any chain slip?
Could you post a pic of the bike from the drive side?

 

[Ming the Merciless]

Bottom brackets are neither 8 or 9 speed or any speed.

 

[neil_merseyside]

Bottom brackets are just bearings and care not about gear numbers.

 

[sleuthey]

Before we continue, @Nightjar please confirm which part of the bike you believe the Bottom Bracket is?

 

[Ajax Bay]

Agree with @sleuthey
However this crankset is H2 with (obv) BB to match. V easy to replace BB (if that's the issue).
9sp cassette; 9sp STIs. Chainset speed 'doesn't matter'.
"Grinding" only in lower gears? Chain fouling FD cage?
For example: https://www.ebay.co.uk/itm/385289740151? (This is a random B'twin Triban 5 with Sora)

 

[bikingdad90]

Something about the bb/chainset doesn’t look right, it’s overlapping the HT2 bearing cups (or is that’s because it’s a triple), spacer on incorrect side?

 

[Ajax Bay]

Something about the bb/chainset doesn’t look right, it’s overlapping the HT2 bearing cups (or is that’s because it’s a triple), spacer on incorrect side?

Have another go, old chap.

 

[notmyrealnamebutclose]

Does he mean the smolest cog as that would make some sense?