Trying to work out what my options are for the boys cross bike groupset, based on what I've got lying around in the house.
Currently got to hand......
1x 38T crankset.
1x 105 5700 10sp groupset with medium cage mech.
1x Tiagra 10sp (exact model unsure) groupset, on a bike but could be stripped.
Ideally I want to run 1x with the 105 but I don't think the range will be enough for a 12 year old to cope with, nor sure if a lack of clutch mech makes dropped chains more likely?
The Tiagra seems to be running a 36T largest sprocket on his old Islabike so could swap that and have reasonable range but can't be arsed swapping stuff out unless I have to!
What are my options? Seems mixed opinions about whether I can put a 10sp MTB mech on the 105 5700? Maybe need to find a 9sp but then lose range and clutch? Alternatively just suck it up and go 2x at the front with a new spider for the cranks, might be the easiest option but he would certainly prefer 1x, as would the mechanic (me!)
The easiest option if you want a clutch is 10 speed grx setup a 1x. Or if your tiagra is the newer type that had a different pull ratio to older Shimano 10 speed then you can use the grx mech with it. Range wise 11-34 cassette with a 36t ring works for my 13,yo daughter, younger daughter has a 34t. We mostly leave the clutch off as shifting is nicer without. It gets turned on for bumpy courses.
10 speed GRX on the 105 shifters? My understanding was pull ratio on the GRX different wouldn't work as this was definitely my first option!
You don't mention brake type. Discs are much better for them and hydros much better for the mechanic as they don't require the same level of fiddling as cables.
If he races, I think there are rules about gearing on kids bikes? So they can't damage themselves. Just to add to the confusion.
You don't mention brake type. Discs are much better for them and hydros much better for the mechanic as they don't require the same level of fiddling as cables.
Cable discs will be fine.
If he races, I think there are rules about gearing on kids bikes? So they can't damage themselves. Just to add to the confusion.
No gearing restrictions in CX, he has a seperate road bike with restricted cassette.
10 speed GRX on the 105 shifters?
No, 10 speed GRX and new tiagra use the same pull ratio as 11 speed road. 10 speed 105 is the old pull ratio, I don't think there is a viable clutch mech for this (unless one of the microshift options works with 10 speed road pull ratio).
I meant easiest option is 10 speed grx shifter and 10 speed grx mech, though obviously this does not use what you have (I did see the first line but was trying to offer context/options). I would check what version of tiagra you have. If it's the newer type (4700 updards IIRC) then use that with a GRX mech of any flavour (10 speed is the cheapest).
You can mitigate dropped chains to an extent with a narrow wide ring and cheap top chain guide. For the gear range there is the very strong argument that if they are heading into very low gears then they will likely be as quick on foot anyway.
10 speed GRX on the 105 shifters?
No, 10 speed GRX and new tiagra use the same pull ratio as 11 speed road. 10 speed 105 is the old pull ratio, I don't think there is a viable clutch mech for this (unless one of the microshift options works with 10 speed road pull ratio).
I meant easiest option is 10 speed grx shifter and 10 speed grx mech, though obviously this does not use what you have (I did see the first line but was trying to offer context/options). I would check what version of tiagra you have. If it's the newer type (4700 updards IIRC) then use that with a GRX mech of any flavour (10 speed is the cheapest).
You can mitigate dropped chains to an extent with a narrow wide ring and cheap top chain guide. For the gear range there is the very strong argument that if they are heading into very low gears then they will likely be as quick on foot anyway.
Thanks, clear. Which model of Tiagra has the right pull ratio do you happen to know?
Yes agree to some extent on range but the standard 105 will only give 11-32 and I think this is too limiting especially for a younger rider. 11-36 would be fine, doesn't need some crazy big modern range.
I think its Tiagra 4700 and newer (including the rs405 hydro units). If you look closely these are basically the 11 speed units with a 10 speed mechanism instead of 11. You can actually convert them to 11 by swapping the ratchet 😀 (I did this with a 10 speed GRX shifter to convert to 11 speed as had a broken shifter and 11 speed cassette).
1x 105 5700 10sp groupset with medium cage mech.
1x Tiagra 10sp (exact model unsure) groupset, on a bike but could be stripped.
It is worth figuring out what flavour the Tiagra actually is if it's 4600, you might as well use the 5700 (both will be the 'old' pull ratio) if it's 4700 though it would be worth using that as you have a comfortable upgrade path to bigger cassettes with GRX (e.g. RX400) mech compatibility. But a Clutch mech matters far less than using a N/W ring for retention (IMO/IME)...Â
Failing that though you should still be able to stretch an older tiagra or 105 mech over an 11-34 or 11-36t 10speed cassette without too much drama.
The biggest benefit might actually come from crank choice, anything that can have rings changed easily on a small enough BCD might help Jnr more, if you're stealing the cranks from an older bike 110 BCD road cranks will go as low as 34t, 104 BCD MTB cranks will go as low as 32t. That said the arm length might not be ideal?Â
You can probably do more to help him with crank choice (and having multiple rings to choose from) than by providing a bigger cassette.Â
Of course 12 year olds come in a variety of sizes and can grow quite quickly, I'd be on standby to rebuild it all on a new frame before next winter...Â
Ok looks like the shifters are 4700 not 4600, in which case happy days I have my easiest upgrade path. Just a bit of faff switching back and forth over bikes but worth it! Thanks all.