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What do you use a chainring diameter gauge for exactly?

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What do you use a chainring diameter gauge for exactly?

Old 04-12-17, 09:02 AM
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bikerbobbbb
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What do you use a chainring diameter gauge for exactly?

Is it worth getting if you're replacing chain rings, at least just to check specs?

CDG-2 Chainring Diameter Gauge | Park Tool
CDG-2 CHAINRING DIAMETER GAUGE
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Old 04-12-17, 09:08 AM
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"The CDG-2 easily and accurately measures bolt circle diameter (BCD) in millimeters for a wide variety of four- and five-bolt chainring patterns"
There you go.
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Old 04-12-17, 09:22 AM
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No
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Old 04-12-17, 10:26 AM
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Originally Posted by leob1 View Post
"The CDG-2 easily and accurately measures bolt circle diameter (BCD) in millimeters for a wide variety of four- and five-bolt chainring patterns"
There you go.
Which can be done this way-
Sheldon Brown's Bicycle Glossary Bo - Bz
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Old 04-12-17, 11:07 AM
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https://www.wolftoothcomponents.com/...e-diameter-bcd
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Old 04-12-17, 11:12 AM
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Useless tool unless you don't own a small ruler, and/or can't do simple math.

For 5 bolt chainrings, measure between 2 adjacent bolts (on center) and multiply by 1.7.

Or you can do an inline search for charts that cover this.
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Old 04-12-17, 11:32 AM
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Originally Posted by bikerbobbbb View Post
What do you use a chainring diameter gauge for exactly?
Apparently, it is usually used by attaching a fishing line and dragging it behind a boat.
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Old 04-12-17, 01:10 PM
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Originally Posted by AnkleWork View Post
Apparently, it is usually used by attaching a fishing line and dragging it behind a boat.
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Old 04-12-17, 01:20 PM
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Originally Posted by AnkleWork View Post
Apparently, it is usually used by attaching a fishing line and dragging it behind a boat.
personally... I'd advise a stout rope being attached to any Boat Anchor.... unless you choose some REALLY big fishing line...
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Old 04-12-17, 01:45 PM
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Originally Posted by maddog34 View Post
personally... I'd advise a stout rope being attached to any Boat Anchor....
Perhaps one big enough to sink the entire "boat"?
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Old 04-12-17, 02:03 PM
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So for when you would use this info....

http://www.parktool.com/assets/doc/p...structions.pdf

If I was buying a new chainring, I'd need to know the number of bolts and the BCD? (Along with the number of teeth I would imagine but that might not be required to connect the chain ring to the bike.)
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Old 04-12-17, 02:38 PM
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Originally Posted by bikerbobbbb View Post
So for when you would use this info....

http://www.parktool.com/assets/doc/p...structions.pdf

If I was buying a new chainring, I'd need to know the number of bolts and the BCD? (Along with the number of teeth I would imagine but that might not be required to connect the chain ring to the bike.)
Correct
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Old 04-12-17, 02:54 PM
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What's it for?

Selling to bicyclists.
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Old 04-12-17, 08:46 PM
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mostly for shops during the intake process to quickly identify the bcd and get an accurate estimate
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Old 04-13-17, 12:34 AM
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It's a handy tool for determining the bolt circle diameter (bcd) of chainwheels. What is easily discernible ie. measurable is the linear distance between chainring bolt holes center to center (c-c). However, chainrings are sized according to the "circle" size of the bolt holes NOT the linear distance between two bolt holes.

It's a great tool to carry to a bike swap to get great quality rings like TA cheap. There are many bcd "sizes" that can't be discerned just by looking with the eye test. Only a broke fool walks around a swap with vernier calipers and a slide rule to convert bolt hole distances to bcd. If he can't afford the tool he can't properly afford to stock up on chainrings at a swap, regardless of his measuring and math skills.

Any shop that can't afford a BCD gauge is wasting productive time. A lot of bike mechanics in this industry are stoned out of their minds, and can't effectively make the calculation manually, at any given moment. It's just the right tool for the job to ensure a quick, convenient and failsafe way to ENSURE identifying the actual BCD standard. Destitute and covetous internet trolls who can't afford bike tools will post as apologists that it's not a "needed" tool. Most of them are tools. Any tool that prevents a mechanic from wasting valuable productive time grabbing the wrong size chainring out of spare stock and bringing that to the repair area wasting time/steps is cheap insurance. The primary operational expense of a repair department is labor. The customer pays for neeeded parts/bits. Think of the BCD gauge as being a quality tool to keep the mechanics productively efficient. Considering how low paid most wrenches are and the poor skill level and quality of their work, versus the value of the repair ticket to the shop, it's a necessary tool. Think of it as a Poke-yoke or "idiot proofing" of making sure the right size gets identified, the FIRST TIME. Allowing the shop to leverage that $12/hr wrench into billing more repair invoices in the accrued payroll period.

Last edited by mtnbke; 04-13-17 at 12:42 AM.
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Old 04-13-17, 12:56 AM
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Originally Posted by FBinNY View Post
Useless tool unless you don't own a small ruler, and/or can't do simple math.

For 5 bolt chainrings, measure between 2 adjacent bolts (on center) and multiply by 1.7.

Or you can do an inline search for charts that cover this.
It should be mandatory for E-Bay sellers to buy one of these
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Old 04-13-17, 02:48 AM
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Originally Posted by FBinNY View Post
Useless tool unless you don't own a small ruler, and/or can't do simple math.

For 5 bolt chainrings, measure between 2 adjacent bolts (on center) and multiply by 1.7.

Or you can do an inline search for charts that cover this.
Not true

There are Campy five bolt cranks that have identical distances between adjacent bolt holes 64.7 but different BCDs (110 or 112)
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Old 04-13-17, 06:57 AM
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If you have to ask then yes it is.
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Old 04-13-17, 07:42 AM
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Originally Posted by mtnbke View Post
Not true

There are Campy five bolt cranks that have identical distances between adjacent bolt holes 64.7 but different BCDs (110 or 112)
If the holes are the same distance then the tool's indicator arm will not move. So you will not see it move from 110 to 112. It is mathematically impossible to have same distance but different BCD.

The Campy holes are not identical distances. Only four of the five are like that. The fifth is further out, so not all holes are 64.7

For swap meet, all you need is small steel pocket rule. Everyone has phone with calculator so the math can be done quickly.
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Old 04-13-17, 10:31 AM
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Originally Posted by mtnbke View Post
Not true

There are Campy five bolt cranks that have identical distances between adjacent bolt holes 64.7 but different BCDs (110 or 112)
Sorry, True, but with a catch.

First the math. For ANY pentagon, which is what the 5 bolts form, the points can only lie on a circle of a single diameter. Increase the diameter, and the points would move apart.

So, the math is OK, but the assumption isn't. On the crank to which you refer, the bolts don't form a pentagon. One bolt is is off the circle and has a different BCD. The difference in bolt to bolt difference is small, but it's there. In any case, you're not any more likely to notice it with a bolt diameter tool than with a ruler, and even then ONLY if you measured all the distances and spotted the two that were off.


Sorry for repeating what was said above, I responded to the quote and didn't see it.
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Old 04-13-17, 11:26 AM
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Old 04-13-17, 05:26 PM
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Originally Posted by bikerbobbbb View Post
Is it worth getting if you're replacing chain rings, at least just to check specs?

CDG-2 Chainring Diameter Gauge | Park Tool
CDG-2 CHAINRING DIAMETER GAUGE
OK, people, if you're still questioning whether this is a "troll" or not, this post should answer it once and for all.....
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Old 04-14-17, 05:56 AM
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Originally Posted by AlexCyclistRoch View Post
OK, people, if you're still questioning whether this is a "troll" or not, this post should answer it once and for all.....
WHAT, Bikerbobbb a troll? Please tell me it's not true! He always has such amusing posts.
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Old 04-14-17, 06:10 AM
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He got the C'dale fanboy to bite, that's always fun....
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Old 04-14-17, 04:07 PM
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....as if the BCD on your chanrings is gonna shrink while in storage........
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