How much can you fudge chain line with a spacer on the crank?

BOXKARS
Bike Wall
shop deals on amazon
Rat Rod Bikes Bicycle Forum

Help Support Rat Rod Bikes Bicycle Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
bunnyman666

bunnyman666

Joined
Oct 23, 2020
Messages
434
Reaction score
601
Rating - 0%
0   0   0
So, being the tightwad I am, I bought a set of 48 spoke mid-school with flip flop hub (for metric freewheel) for my new build. The kicker: smallest freewheel available is 13 tooth.

This is a modern microdrive frame; however- if I use a 1/2mm spacer, it doesn’t scrape on the chain stay. It barely clears, but it clears. The question is this: will I maintain a good chain line with that 1/2mm, or am I going to have to get a smaller chain wheel?
 
hamppea said:
You'll be flyin' with that gear setup @60 gear inches. The old bmx stranded 44/16 ratio is ≈55.

Nice triple wall Supra font wheel you got.
Click to expand...

That was my hope! It’s a neighbourhood cruiser build. I may jump a kerb, but that is about it!

I am glad the LBS is not sentimental about those wheels! That front has an awesome GT hub, as well. Thanks, that front wheel is very cool from so many aspects!
 
Not happening. Put on the metric free wheel and my chain line is WAAAAAAAAYYYYY off :mad: guess I need to find a 33 tooth, which should be small enough; a 30 tooth would be safer.
Back to the drawing board...
 
bunnyman666 said:
Not happening. Put on the metric free wheel and my chain line is WAAAAAAAAYYYYY off :mad: guess I need to find a 33 tooth, which should be small enough; a 30 tooth would be safer.
Back to the drawing board...
Click to expand...

You could add 30mm spacers before installing the freewheel as well. Something wasn't quite right. 0.5mm is negligible and 39t is giant for a microdrive frame.
 
hamppea said:
You could add 30mm spacers before installing the freewheel as well. Something wasn't quite right. 0.5mm is negligible and 39t is giant for a microdrive frame.
Click to expand...
Yeah- chainline is a lot harder on modern BMX than on a road bike. I think if I go 30 (asking mfr what that largest I can go), I will be good.
 
You may continue to have chainline issues because the Mid shell is 2.5mm wider on each side than the American BB. The rear hub you have is meant for the old 68mm BB size. Modern bmx bikes use wider tires. You could get by using about half the threaded area for the freewheel. 8mm is typical. 3X 30mm by 1mm spacers made for cranks to shim a M30 freewheel can work.
 
hamppea said:
You may continue to have chainline issues because the Mid shell is 2.5mm wider on each side than the American BB. The rear hub you have is meant for the old 68mm BB size. Modern bmx bikes use wider tires. You could get by using about half the threaded area for the freewheel. 8mm is typical. 3X 30mm by 1mm spacers made for cranks to shim a M30 freewheel can work.
Click to expand...


6383080-0-image-a-11_1542638458883.jpg


Me......

d8p19a4-8b9b6558-6432-4897-95e6-f34272fde990.jpg


:rofl:
 
Update: chain line is fine, even with the mid-school hubs. It looks like 30t sprocket is the max :( . I should be okay using a 30/13, as it is close enough to the 25/9 on my O.G. Rat rod Fitbike, which is now passed to my wife.

I will take pix when it’s built!
 

Latest posts

Back
Top