Adjusting the chainline

Giraffoto

If I want to convert a triple crankset to single by just taking off the outer and inner rings, is the middle ring perfectly lined up to the middle of the cassette? And if I wanted to do the same thing with a double, how much would I need to space the big ring inwards to get the ideal chainline?

I’m building up a bike for my seven-year-old and I want to make it a 1x9 for simplicity, lightness, reliability, and availability of parts (i.e., I’ve got all of the parts except the crankset), but I can only find double or triple cranksets with the required short cranks – so I’m going to have to get one of these and convert it.

cooldad

Use the triple, the middle ring should be just about perfect.
Double will need the width of the gap to line up nicely, which is quite a lot of adjustment.

lpretro1

Why faff about removing rings etc. Why not just stop the front derailleur down so it can only be used in the middle ring? Then as he gets older and more used to gears it will be dead easy

The Rookie

Given how many bikes are now going 1x, why does he need to get used to front gears?

benpinnick

Triple is good, double is 2.5mm out, which may be resolvable if its a BB that uses spacers, which are handily 2.5mm each. Move one from the drive to non dive side and you're sorted.

Giraffoto

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19627864#p19627864]lpretro1[/url] wrote:

Why faff about removing rings etc. Why not just stop the front derailleur down so it can only be used in the middle ring? Then as he gets older and more used to gears it will be dead easy

I'm taking a punt that 1x is the way of the future. More seriously, if I start him off on a 1x setup he won't have to think about double shifting at any point, he'll just get a feel for when he needs to change up or down. You don't really need a very wide range around my neck of the woods (I said in another thread that if I were building my own bike right now, I'd go 1x11) and the 11-32 rear, 32T front that we're starting with should be fine.

Also, they're steel rings, so it's a quick and easy weight saving

FishFish

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19628082#p19628082]benpinnick[/url] wrote:

Triple is good, double is 2.5mm out, which may be resolvable if its a BB that uses spacers, which are handily 2.5mm each. Move one from the drive to non dive side and you're sorted.

I think that would move the line by 5mm because:

removing from the drive side would adjust the line in by 2.5mm
adding to the nd side would pull it in by another 2.5mm

It took me a long time to work this out but it is logically quite simple!

Chunkers1980

Er, no

The Rookie

Absolutely er no, someone didn't think!

Antm81

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19629161#p19629161]FishFish[/url] wrote:

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19628082#p19628082]benpinnick[/url] wrote:

Triple is good, double is 2.5mm out, which may be resolvable if its a BB that uses spacers, which are handily 2.5mm each. Move one from the drive to non dive side and you're sorted.

I think that would move the line by 5mm because:

removing from the drive side would adjust the line in by 2.5mm
adding to the nd side would pull it in by another 2.5mm

It took me a long time to work this out but it is logically quite simple!

Obviously not that simple, put it this way you remove from the drive side and essentially it moves 2.5mm closer to the shell. However as the bottom bracket is still the same size you now have a 2.5mm gap on the non drive side where it doesn't touch the shell. The spacer you removed now fits in this gap. You still haven't moved the drive side crank more than 2.5mm closer to the frame.

Chunkers1980

So your Q factor is moved 5mm left not the chainline

benpinnick

Some doubles (sram s1000) are just a triple without the big ring fitted.

Most arent though. For example current S1000 doubles are 3 mm out of line on the big ring.