Chainring diameter gauge tool ???

[Fatmat]

Hi guys, does anyone know where I can get a chainring diameter gauge? I’ve only just find out that park tool did (still do!) make/supply these but I can’t seem to find one in stock!

 

[foz]

just use a ruler?

 

[vcballbat]

just use a ruler?

I always carry a tape measure in my pocket but I don't tend to use it as a rule

 

[grantoury]

Clever toolmaking by Park tool. I never knew there was such a thing. Probably because a caliper or a tape measure does the same thing and I always have those lying around

 

[Guinessisgoodforyou]

Go here.

"Sheldon Brown's Bicycle Crank/Chainring Bolt Circle Diameter Crib Sheet"

Identify bicycle chainring bolt-hole patterns to deterimine compatibility

sheldonbrown.com

 

[Fatmat]

Thanks for you’re feedback guys, I’ve attached a pic, its easy with a 4 bolt but it’s guess work with a 5, how do tell that it’s not 138 or 140? I could print out some circles to help follow the line but it’s still slightly guess work, there must be a better way, ie the tool

 

[Fatmat]

I appreciate it’s a branded crank so I could google it but I have this issue all the time with obscure chainrings / cranks

 

[foz]

Just measure between the holes and calculate or use Sheldon to get the bcd. Or print out the sheets from Sheldon (I hadn't seen them before, I think they're fairly new)

 

[Fatmat]

Yes, that’s fair enough, I can use the formula to calculate, looked a bit complex, maths never my strong point, am just being lazy! Thanks for your help appreciated