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Older MTB Looking for Newer Chainring Guard Solution

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Older MTB Looking for Newer Chainring Guard Solution

Old 05-24-22, 08:22 PM
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Entropy_S
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Older MTB Looking for Newer Chainring Guard Solution

Let me preface this by saying that I’m a complete newbie when it comes to bikes in general, and feel dumb asking the following question.

So, I have an old Diamondback mountain bike that I purchased back in 2007. This bike has three gears in the front, and I want to install a chain ring guard to protect the gears. The largest gear has 42-teeth with a BCD of ~135mm; can anyone help me select the appropriate guard for my use case?

I’ve attached a photo of the front gears of my bike for reference, areas marked in Green.

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Old 05-24-22, 08:52 PM
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I'm not sure those are bolt holes, and 135mm isn't a 4-bolt BCD standard that I know of.

https://www.wolftoothcomponents.com/...e-diameter-bcd
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Old 05-25-22, 07:40 AM
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Originally Posted by Rolla
I'm not sure those are bolt holes, and 135mm isn't a 4-bolt BCD standard that I know of.
I can't see any other holes other than the ones marked in Green; the holes are countersunk which leads me to believe that they could be used for something, if not a chainring guard?
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Old 05-25-22, 07:58 AM
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I just did a quick search and turned up a bunch of possibilities. If you check some of the ebay, etc. cheaper versions than the Truativ OEM's they may list the guards bolt hole distance. Shouldn't be hard to find one that works. Avoid the plastic versions if you want real chainring protection. (1) chainring guard for truativ cranks - Search (bing.com)
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Old 05-25-22, 10:47 AM
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Originally Posted by Crankycrank
I just did a quick search and turned up a bunch of possibilities. If you check some of the ebay, etc. cheaper versions than the Truativ OEM's they may list the guards bolt hole distance.
The problem I am running into with my crankset (besides being old) is that a) it uses a four-bolt design, and b) the holes are so far apart. If I find a chainring guard with a four bolt design, nine times out of ten, the BCD is 104mm, much smaller than what my crankset is calling for. However, I have noticed that with the five-bolt crankset design (which my MTB does not have), there are chainring guard options which offer larger BCD's.
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Old 05-25-22, 12:21 PM
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Curious: what kind of obstacles are you encountering, and how often are you bashing the chainring into them?
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Old 05-25-22, 12:27 PM
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Look for an 80s BMX frame-mounted guard?

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Old 05-25-22, 01:28 PM
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Originally Posted by Rolla
Curious: what kind of obstacles are you encountering, and how often are you bashing the chainring into them?
Wellll, admittedly none (yet). The reason for my need of a chainring guard is to prevent crap from inadvertently getting caught in the large front gear.
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Old 05-25-22, 01:38 PM
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I'm pretty sure those aren't bolt holes; the countersink appears to be the wrong way, towards the inside of the rings, as opposed to the face.

Generally, "bash guards" mount to the chainring bolts, which are much larger than those little holes around the edge of the rings themselves. They either mount like a 4th chainring, or in place of the existing big ring.

The only guards I've come across that mount to the edge of the ring itself are the plastic "protectors" that you find on hybrids ad recreational bikes; which are really there to protect your pants leg from the chain, than protect the chain from obstacles.
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Old 05-25-22, 01:41 PM
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Originally Posted by Entropy_S
Wellll, admittedly none (yet). The reason for my need of a chainring guard is to prevent crap from inadvertently getting caught in the large front gear.
IMO, getting stuff (branches? leaves? squirrels?) caught in the gear isn't really an issue. I think chainring guards are helpful if you're riding through boulder fields, climbing ledges, or scrambling over a lot of tree trunks, but for most situations I've rarely found them necessary. I don't know if I've ever had a non-bmx bike that had one.
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Old 05-25-22, 02:11 PM
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Those are not bolt holes. If you put bolts in them, they will get caught on the chain. If you don't think so, put a bolt in one of the holes, put the chain in the middle chainring and turn the crank.
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Old 05-25-22, 02:21 PM
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Originally Posted by Ironfish653
They either mount like a 4th chainring, or in place of the existing big ring.
Ah, okay! Thank you for that clarification.

So, from what I gather, this essentially means that the "BCD" I originally posted is incorrect, and the actual measurement I should be taking for the BCD should be the bolts that are holding all three of my gears together. I've attached a photo of the new BCD measurement; is the manner in which I have measured the real BCD of my MTB correct?

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Old 05-25-22, 06:52 PM
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Originally Posted by dsaul
Those are not bolt holes. If you put bolts in them, they will get caught on the chain. If you don't think so, put a bolt in one of the holes, put the chain in the middle chainring and turn the crank.
They are screw holes, for counter sunk phillips screws. They install from the back of the ring and thread into the OEM style plastic pant guard. Definitely not a bash guard though.

https://www.ebay.com/itm/32517806140...MAAOSwZoZidP10
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Old 05-25-22, 07:23 PM
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Originally Posted by dsaul
Those are not bolt holes. If you put bolts in them, they will get caught on the chain. If you don't think so, put a bolt in one of the holes, put the chain in the middle chainring and turn the crank.
Yup, you’re absolutely right! I did as you said, and there is very little clearance for a bolt without impacting the chain, although a countersunk screw may work.

Originally Posted by wesmamyke
They are screw holes, for counter sunk phillips screws. They install from the back of the ring and thread into the OEM style plastic pant guard. Definitely not a bash guard though.
Huzzah! Thanks for the link my friend. Gonna try this out.

Last edited by Entropy_S; 05-25-22 at 07:30 PM. Reason: Grammar
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Old 05-26-22, 02:08 AM
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Originally Posted by Entropy_S
Yup, you’re absolutely right! I did as you said, and there is very little clearance for a bolt without impacting the chain, although a countersunk screw may work.


Huzzah! Thanks for the link my friend. Gonna try this out.
You may need to measure the holes differently for a chain guard, it spacing may noy be symmetrical
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