I presume I’m correct, I want to put a bash ring on notepad of 3rd cog. I never use the top cog, is it jus a matter of buying a bash ring and sticking it on?

yeah pretty much – make sure the bcd is correct
do you hit lots of stuff with your chainrings currently ? If not, just stop using the big ring and leave it there

Yep. However, you may need some longer chainring bolts, especially if you get a plastic one. Good news is some come with the chainring bolts. I got a plastic blackspire c4 last year and I’ve given it some good bashes into rocks and logs and it’s still going strong.

Yeh Iv been hitting it a few times. What is BCD?

I have a raceface crank does that make my difference to the BCD?

BCD (Bolt circle Diameter) is the distance between the bolts, Measure from the centre of one whole to the centre of the next one round the circle. I would expect it to be 110mm as this is fairly standard now but worth checking.

do you hit lots of stuff with your chainrings currently ? If not, just stop using the big ring and leave it there

Good idea to fit a bashring IMHO, just Google chain ring injury on Google images to see why… 😕

I just checked the measurement from one hole to the other and dent get what I expected, so I presume I measured it wrong. On my 3rd cog it has written on the top 104 is this the size I would need?

yes and it is the standard size

Yes, sorry my bad, 110 is the BCD for most touring cranks and 104 for mtb, so you are bang on. As stated above if you choose a thick plastic bash then you will require longer bolts as well.

Great thanks, now il try and find one

Measure from the centre of one whole to the centre of the next one round the circle

That’s not BCD. For a four-arm crank (assuming it’s symmetrical…) it’s the distance between the centres of the two opposite bolts.

Ive got a standard SLX bash ring, with bolts and 104 BCD you can have for 8 quid posted? see it here – bash

Perfect, il take that off you

Don’t mean to get in the way of you guys trade, but thought I should warn you the SLX M665 bash doesn’t fit on a standard three ring crankset without a bit of filing – about 1mm or so off the bash at each of the spiders. It’s not a question of BCD which is the same, but that Shimano made the spider a bit shorter on the M665 so the bash could be thicker and stronger round the crank arm bolts. You’d be better off with the E13 which will fit a standard spider without any modification.

its really easy done it last week!

went from 3×10 to 2×10 with a bash.

at the same time i put new chainrings on with different teeth so now am running 22/36 instead of 26/34/44, helps with getting up the hills.