Cycleops
Legendary Member
- Location
- Accra, Ghana
Pedal fell off AGAIN!
- Thread starter Willam
- Start date
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OP
OP
Willam
Über Member
I bought a mtb bb it came with 3 spacers , I bought a road bb it didn’t come with any, trust me I have been digging into this for hours, mtb need 3 as mountain bikes tend to have 73mm bb, road bikes tend to have 68 so don’t need any.
Your pic is probably in reference to mtb not road, I could post similar for road.
I do appreciate the help, not trying to come across as rude here.
fossyant
Ride It Like You Stole It!
- Location
- South Manchester
Nope - doesn't work like that.
Yes they are compatible, but with gravel, you'll have bikes with 73mm and 68mm. Think about it, you are fitting the crankset to a 68mm BB, you'll have 5mm MORE axel sticking out. This doesn't give you 'more' axel to grab onto as they are designed to tighten into the tapered splines and will only go on so far. If you fit a spacer, it's allowing the crank to tighten and pre-load the bearings better. This is the issue, it's allowing too much space.
fossyant
Ride It Like You Stole It!
- Location
- South Manchester
But GRX will most likely have a longer MTB length axel. The BB cups are identical BTW.
Really need to dig into the instructions, I know it's a bloke thing (i.e. not reading them) but I've never had a crank fall off, square taper, GXP or hollowtech.
You are doing something wrong.
fossyant
Ride It Like You Stole It!
- Location
- South Manchester
Probably best waiting for someone on here with GRX that's fitted it to a 68mm BB
OP
OP
Willam
Über Member
You sound convincing, I will give it a go but I really can’t see it working as it would surely mean less sticking out not more! But I’ve tried everything else so here’s hoping.
OP
OP
Willam
Über Member
Oh I know I am doing something wrong lol…the reason for the new crank is because the last one fell off too and that was fitted by the manufacturer! So something is not right here.
OP
OP
Willam
Über Member
I read that the threads are longer on mtb? But read also they are the same, strange shimano (thanks) label one as road and the other as mtb if they are the same?
What instructions, I would gladly read them lol
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Cycleops
Legendary Member
- Location
- Accra, Ghana
All I can say is that diagram I posted was from the Shimano dealers manual. I rest my case.
fossyant
Ride It Like You Stole It!
- Location
- South Manchester
GRX isn't a specific crankset (road or MTB only) - it's designed to use on any bike. MTB cranksets (Deore etc) usually require 73mm shells, so if fitting to a 68mm BB shell you'll need spacers, not if fitting to a 73mm BB.
You generally can't fit road cranksets to 73mm BB - e.g. 105/Ultegra.
You generally can't fit road cranksets to 73mm BB - e.g. 105/Ultegra.
fossyant
Ride It Like You Stole It!
- Location
- South Manchester
Get on google and put in GRX Chainset fitting manual.
OP
OP
Willam
Über Member
Mtb page 11 3 spacers mentioned. https://bike.shimano.com/en-EU/product/component/zee-m640/BB-MT500-PA.html
Road page 10 no spacers mentioned https://si.shimano.com/pdfs/dm/DM-RCFC001-01-ENG.pdf
Page 12 under “notice” says for Road BB a spacer is not needed. https://si.shimano.com/api/publish/storage/pdf/en/dm/FC0002/DM-FC0002-14-ENG.pdf
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OP
OP
Willam
Über Member
They give a bit more info in the dealers manual page 11 mentions a spacer but doesn’t say what size bb it is going in and page 15 talks about fitting the crank but is very basic.
https://si.shimano.com/pdfs/dm/DM-RCFC001-01-ENG.pdf
the snail
Guru
- Location
- Chippenham
I think you need to know the exact model number of the crankset, and find the tech docs for it, and the bb. The model number is usually stamped on the back of the cranks, it should be FC-something. It definitely looks like you have 5mm too many spacers fitted somewhere though.
figbat
Slippery scientist
- Location
- South Oxfordshire, UK
Is there a spacer on the driveside crank (not behind the driveside BB, but on the crank itself)?
