Will These Cran Arms Fit My Bike?

[Cycling_Man]

Hi guys. I am just writing this post to ask some advice on the topic of a new chainset.

Just wanted to ask. I am looking at some crank arms https://spacycles.co.uk/m8b0s109p4710/S ... ple-Cranks that say they are tripple cranks. Will these cranks work on my bike that has a double chainring setup or will they not work. Much appreciated.

[531colin]

Well, it can't be made to work.
The cranks you are looking at take chainrings with a bolt circle diameter of 110mm https://sheldonbrown.com/cribsheet-bcd.html
In short, if the bolts securing your chainrings are 64.7mm apart, you have 110mm BCD chainrings, which will fit the crank.
Spa tell you the BB axle length you need for a triple chainset. That will put the middle ring 45mm from the bike centreline. https://sheldonbrown.com/chainline.html
Now, you want your inner (which is the manufacturer's middle) at 41mm, not 45mm........so you need a BB with 4mm less "stickout" on the right than what a 110mm BB axle has.
Which, according to Brucie's stickout guide, you ain't going to get...viewtopic.php?f=5&t=105385
....because, there is only one axle shorter than 110mm, and thats 107mm, and the right stickout is the same.
.....unless you can come across a Bb unit with adjustable chainline.

E&OE, and I need a lie down now!

[Cycling_Man]

Well, it can't be made to work.
The cranks you are looking at take chainrings with a bolt circle diameter of 110mm https://sheldonbrown.com/cribsheet-bcd.html
In short, if the bolts securing your chainrings are 64.7mm apart, you have 110mm BCD chainrings, which will fit the crank.
Spa tell you the BB axle length you need for a triple chainset. That will put the middle ring 45mm from the bike centreline. https://sheldonbrown.com/chainline.html
Now, you want your inner (which is the manufacturer's middle) at 41mm, not 45mm........so you need a BB with 4mm less "stickout" on the right than what a 110mm BB axle has.
Which, according to Brucie's stickout guide, you ain't going to get...viewtopic.php?f=5&t=105385
....because, there is only one axle shorter than 110mm, and thats 107mm, and the right stickout is the same.
.....unless you can come across a Bb unit with adjustable chainline.

E&OE, and I need a lie down now!

Thank you for your reply. Would you mind explaining this in a way that you are talking to someone who knows literally nothing about bikes haha. I am really new to cycling and literally don't know much about what you said. I can tell you that I know the measurements on these cranks match up to the bike I have I believe. The bike I have has a 110 BCD and 170mm cranks. I am just not sure if the crank arms here will fit because they say they are "Triple Cranks" which I believe would go on a tripple chainset which I don't have. I have a double chainset.

So what I am asking is will the cranks here:https://spacycles.co.uk/m8b0s109p4710/S ... ple-Cranks that state they are triple cranks fit onto my bike that has a double chainring setup? I have found these cranks that say they are for "Signle / Double Crankset" but would prefer them to be black which they don't do in the ones here: https://www.sjscycles.co.uk/cranks/sjsc ... set-170mm/

So I was just asking if the black cranks I originally listed would fit without hassle due to them stating being for a triple or will they not and I need to go for the other silver cranks I listed. Thanks, Cycling_Man.

[slowster]

On your previous thread I advised as follows:

Lastly, as jimlews has pointed out above, bottom bracket axle lengths also vary, and the Spa cranks are designed for a 110mm length axle if used as a triple chainset. In your case you would not use third inner ring position and you would only be using the chainset as a double, and consequently would need a shorter bottom bracket axle, probably 107mm. If your current axle is significantly different in length, it will affect front derailleur shifts, possibly so much that the front derailleur will no longer work. Unless you know what your current axle length is, e.g. by reference to the manufacturer's specifications for the bike or the chainset, the only way to find it out is to take the crank(s) off the axle and then measure the axle length. In other words, it would be risky to buy the Spa chainset without first finding out what your bike's current axle length is, and what the BCD is of your chainrings.

viewtopic.php?p=1600639#p1600639

It's possible that your front derailleur might be able to cope with those cranks being fitted to an axle that is shorter or longer than the recomended length, and sometimes the only way you will know is to buy the cranks, fit them, adjust the derailleur, and see if it will work.

If the front derailleur will not work because your current axle is the wrong length, you can buy square taper cartridge bottom brackets for between £10-£25 (and the one below is only £8). You would have to pay your local bike shop extra to remove the current cartridge and fit the new one, but it might still be the best/cheapest option given that the Spa cranks themselves are so cheap..

NB Before buying a new cartridge bottom bracket, measure the width of your frame's bottom bracket shell. It's probably 68mm, but MTBs and some other bikes use 73mm shells. You need to ensure that whatever cartridge bottom bracket you buy not only has the right axle length for your cranks, but also is the right width for your frame's bottom bracket shell (probably 68mm, but best to measure it and make sure).

https://spacycles.co.uk/m16b0s110p3232/ ... et-F-2001P

[531colin]

The chainrings need to be where your front mech. expects them to be. You can't buy a bottom bracket bearing for the Spa triple cranks which will do this, but for the SJSC cranks you link you can....its 110mm, as it says on the website

[jimlews]

"531colin",

Would the Spa TD2 double drive side spider be a better fit on the OP's axle?

edit: The chainset he is replacing is a double.

[531colin]

TD2 double requires 110mm BB axle......what length is currently fitted to the OP's bike?

(not currently available in black 170mm anyway)

The snag with the Spa triple is that THERE ISN'T A BB UNIT MADE which will get the chainrings where the F. mech. expects them to be.
The shortest BB unit made will get the chainrings 4mm too far to the right.

[slowster]

The snag with the Spa triple is that THERE ISN'T A BB UNIT MADE which will get the chainrings where the F. mech. expects them to be.
The shortest BB unit made will get the chainrings 4mm too far to the right.

That is a pity. The XD-2 triple is designed for a 110mm bottom bracket, and the double version for a 107mm bottom bracket. I had assumed that if the inner ring of an XD-2 triple was removed, the cranks could be used as a double on a 107mm bottom bracket. I further assumed that this would similarly apply to the TD-1 triple crank the OP is considering.

[Cycling_Man]

"531colin",

Would the Spa TD2 double drive side spider be a better fit on the OP's axle?

edit: The chainset he is replacing is a double.

The chainrings need to be where your front mech. expects them to be. You can't buy a bottom bracket bearing for the Spa triple cranks which will do this, but for the SJSC cranks you link you can....its 110mm, as it says on the website

Like I said above the measurements match up I believe. The bike has a square tapered bottom bracket with a 110 BCD and 170mm crank arms. I just wanted to know before I asked if these crank arms would fit onto a double chainring front set up since they state they are for a triple set up. I don't know much about bikes so was wondering if these arms could just replace the old ones that I currently had on my bike without any fit issues.

I spoke to a bike shop and he said that these arms would work but if it was fit I would have empty mount holes which I wasn't sure what he meant by that. He also said that this is fine but if the chain ever falls off it could get stuck under them which isn't good and he can always add a third cog so it takes the space up, even though I won't be able to use it.

It doesn't matter too much now because I think I am going to go with the second silver crank arms even though I would prefer them to be black. I just wanted to know if these arms would work on the current 2 ring front set up on the bike I currently have or if there would be fit issues due to their not being a third chainring. I wouldn't of thought there would of been much of an issue because it fits in between the outer and middle chainring which my current double setup does so thought that there wouldn't be many fit issues. Do you guys happen to know this. If you want a few pictures of the current damaged chainset I have check out the thread here: viewtopic.php?f=1&t=145466

Thanks.

[531colin]

"531colin",

Would the Spa TD2 double drive side spider be a better fit on the OP's axle?

edit: The chainset he is replacing is a double.

The chainrings need to be where your front mech. expects them to be. You can't buy a bottom bracket bearing for the Spa triple cranks which will do this, but for the SJSC cranks you link you can....its 110mm, as it says on the website

Like I said above the measurements match up I believe. The bike has a square tapered bottom bracket with a 110 BCD and 170mm crank arms. I just wanted to know before I asked if these crank arms would fit onto a double chainring front set up since they state they are for a triple set up. I don't know much about bikes so was wondering if these arms could just replace the old ones that I currently had on my bike without any fit issues.

I spoke to a bike shop and he said that these arms would work but if it was fit I would have empty mount holes which I wasn't sure what he meant by that. He also said that this is fine but if the chain ever falls off it could get stuck under them which isn't good and he can always add a third cog so it takes the space up, even though I won't be able to use it.

It doesn't matter too much now because I think I am going to go with the second silver crank arms even though I would prefer them to be black. I just wanted to know if these arms would work on the current 2 ring front set up on the bike I currently have or if there would be fit issues due to their not being a third chainring. I wouldn't of thought there would of been much of an issue because it fits in between the outer and middle chainring which my current double setup does so thought that there wouldn't be many fit issues. Do you guys happen to know this. If you want a few pictures of the current damaged chainset I have check out the thread here: viewtopic.php?f=1&t=145466

Thanks.

I don't see how I can be any clearer.
Refer to Sheldon Brown on chainlines....I linked it earlier.
The triple crank arms will put your 2 chainrings where the outer 2 chainrings of a triple are expected to be.....NOT where the 2 chainrings of a road double are expected to be.
Sheldon shows you where, how it is measured, and the whole dog and pony show.
You can't fit a shorter BB unit, because they don't exist.

[531colin]

The snag with the Spa triple is that THERE ISN'T A BB UNIT MADE which will get the chainrings where the F. mech. expects them to be.
The shortest BB unit made will get the chainrings 4mm too far to the right.

That is a pity. The XD-2 triple is designed for a 110mm bottom bracket, and the double version for a 107mm bottom bracket. I had assumed that if the inner ring of an XD-2 triple was removed, the cranks could be used as a double on a 107mm bottom bracket. I further assumed that this would similarly apply to the TD-1 triple crank the OP is considering.

Thats interesting....Brucey's stickout list (linked earlier) has the right stickout the same for 107 and 110mm

[slowster]

The snag with the Spa triple is that THERE ISN'T A BB UNIT MADE which will get the chainrings where the F. mech. expects them to be.
The shortest BB unit made will get the chainrings 4mm too far to the right.

That is a pity. The XD-2 triple is designed for a 110mm bottom bracket, and the double version for a 107mm bottom bracket. I had assumed that if the inner ring of an XD-2 triple was removed, the cranks could be used as a double on a 107mm bottom bracket. I further assumed that this would similarly apply to the TD-1 triple crank the OP is considering.

Thats interesting....Brucey's stickout list (linked earlier) has the right stickout the same for 107 and 110mm

I guess that begs the question how close a match one manufacturer's 107mm is to another manufacturer's 107mm. Brucey's stickout measurements were for Shimano UN55 cartridges, and presumably Shimano maintained the same measurements for the successors of the UN55 and UN26, the UN300 and UN100.

It would not surprise me if there were a fair bit of variation between brands in the asymmetry, the length of the taper, and/or the nominal vs. actual axle length, but which largely were not critical to front derailleur performance, i.e. I suspect a mm or two difference in resulting chainline might often be neither here nor there for some combinations of components (although it would probably be noticeable compared with the shifts of a drivetrain which uses matching Shimano components from the same groupset, especially the higher end groupsets).

Spa recommend First Components bottom brackets on the webpages for the TD-2, RD-2 and XD-2 chainsets, and previously they recommended Stronglight JP400. But that might just be because they are less expensive than the UN55, rather than because the dimensions were a better match for the cranks and gave a slightly better chainline.

[Cycling_Man]

I don't see how I can be any clearer.
Refer to Sheldon Brown on chainlines....I linked it earlier.
The triple crank arms will put your 2 chainrings where the outer 2 chainrings of a triple are expected to be.....NOT where the 2 chainrings of a road double are expected to be.
Sheldon shows you where, how it is measured, and the whole dog and pony show.
You can't fit a shorter BB unit, because they don't exist.

I know you are trying to help and be clear but you I have just started learning about bikes and getting into cycling and bikes. For example I don't even know what you mean when you say BB (I'm guessing bottom bracket). I didn't even know what LBS meant till a few days ago so just learning the basics haha.

I get the chain will be wonky a little bit, others have helped me to understand this too. The bit I don't get is the reason why. Are you saying the reason why these arms woudn't fit well is because although they have a 110 BCD they are designed for a tripple and so they would stick out just that slight little bit more to make room for the third chainring that isn't there and so placing them on a double chainring set up would technically work but would push the two chainring set up on my bike out, leaving room for the third chainring that isn't there, causing the chain to be at a slight angle? If so does that mean placing a third smaller chainring on the bike would fix this fit issue because although I woudn't be able to technically use the third chain ring it would fill up that space that is meant to be there due to the triple crank arms being that slight bit longer. I'm also guessing that is why the other user trying to help is suggesting that a 107BB would help to make these arms fit without the need for a third useless chainring to be fitted but you are saying that they don't make those so it wouldn't work.

I'm sorry if you are getting frustrated trying to help me understand that so if you don't feel like you can't explain it any clearer or are just getting frustrated at my lack of understanding that's fine. Thank you for your help, it was helpful as I just am trying to get a wider knowledge of bikes and don't have any knowledge on bikes. I have never owned a bike before so just trying to learn a little.

Thanks you for your help, Cycling_Man.

[andrew_s]

To approach describing the problem from a different angle...

Your front mech has a fixed range of movement. It will only move so far in or so far out from the frame.

If your chainrings are too close to the frame, the front mech won't move far enough in to reliably knock the chain off the outer chainring on to the inner.
Similarly, if the chainrings are too far out, the front mech won't push the chain far enough out that it catches on the teeth of the outer chainring and shifts.
(In both cases, it would probably shift sometimes, and just make scraping noises and not shift at other times. It's in the nature of things that this is most likely to happen when you are rapidly losing speed on a hill, and really need to get that inner chainring selected.)

The distance between the frame and the chainrings is dictated (in square taper) by both the design of the crankset and the length of the bottom bracket (BB) axle. You can move the chainrings out by putting in a longer BB, or move them in by putting in a shorter BB.

The normal distance between the centreline of the frame and the chainrings is called the chainline. In the case of a double this is measured to a point half way between the two chainrings; in the case of a triple, it is measured to the middle chainring.
Consequently, if you use the outer two chainring positions of a triple as a double, the half way position between the two chainrings will be where the outer chainring of a double would be, about 4 mm further out than the front mech would expect them to be.

You'd normally correct that by buying a shorter BB, but the 110 mm BB axle specified for the TD-1 Triple chanks in question is as short as is available.There is a 107 mm BB, but according to Brucey's table, it's the same as the 110 mm BB on the pedal side, and shorter on the left, so it won't help.

This leaves your options as...

a) Get the TD-1 cranks anyway, along with a 107/110 mm BB if your existing BB axle is longer (measured end to end), and hope that you can get the front mech to work properly anyway. You (or the shop) might be able to, especially if the front mech is an older model, but it's not guaranteed.

or

b) Get a Spa TD-2 triple RH crank* (£15), again with a 110 mm BB if your existing BB is longer. This is specified as 113mm triple, 110mm double, so your chainrings will be in the correct place.
One thing to check BEFORE you order is the orientation of the square hole in your existing cranks. The TD-2 has its hole set diamond fashion, with the diagonal of the square lined up with the crank arm. There are some square taper chainsets that have the square hole set square-on, with the diagonals of the hole at 45° to the crank arm. If your existing cranks have a square-on hole, and you fit a replacement crank with a diamond hole, your crank arms will be at 135° to each other, rather than opposite, which would be borderline unrideable.

* there's also a TD-2 double RH crank which is the same, but without the extra bolt holes for the 3rd chainring. Not in stock in 170 mm black though.

[531colin]

.............b) Get a Spa TD-2 triple RH crank* (£15), again with a 110 mm BB if your existing BB is longer. This is specified as 113mm triple, 110mm double, so your chainrings will be in the correct place. ..............

Where is this information, please?
113mm BBs don't appear in Brucie's stickout list. If the 3mm shorter than 110mm is all on the right side, this would work.