Hello,

I'm currently using a 50/40/30 triple crankset + derailleur on a Brompton where I 1) removed the outer 50T, and 2) replaced the middle ring with a 46T.

I'd like to install a chain guard as the outer ring.

Would this product work if I chose the "use on double chainring" option? Should I order a 46T, 48T, or 50T?

Out of curiosity, how do the single/double chainring models differ? Why two models?

Thank you.

It seems that I am using the rule of 4T more for the guard than the largest ring. Note that these guard rings are relatively heavy. A lighter option would be a ring that meant to work with a plastic guard, if you can find one in your desired size. As to to a dedicated guard for single vs double crankset, it might be the issue of space for the crank. (When necessary you could always trim the ring on your own.) It could be also an issue of mounting bolts, but they mention none in their offer.

Thanks. I'll try and find one made of plastic instead.

I've seen folks grind the teeth of the outer rings on a double; making it a guard/protector.

I think this is funny but a couple of years ago I need a chain guard for on of my folders that had a broken plastic chain guard. I actually made a chain guard out of a 54 tooth chain ring that I filed the teeth off of. Roger

I used a saber saw. I bought a cheap chainring that was a lot cheaper than a chainguard ring. Cut the teeth off with a saber saw. That of course left a rough cut. Put the ring on the crank arm and hand turned the crank for about 10 or maybe 15 minutes while I held a file on the rough cut until it was quite smooth.

Saber saw, I used a fine tooth metal blade, the aluminum clogged up the teeth, I might have used two blades. But I had plenty of blades so that was not a problem.

Aluminum is not that heavy, works well for me.

Photo is old, later I decided to spray it black to match all the other black stuff. This is obviously not a folder. The chainring I cut was a 52T, the chainring behind it in the inner position on the double crank is a 44T. The guard is a bit bigger than ideal, but it is close enough that I have no desire to replace it.

I looked at a few of of the Driveline guards around the home and Litepro on-line and the formula for their diameter seems to be D=0.4cm*(No of teeth)+1.1cm. Stacking this against the 22.3cm diameter of the plastic guard that Brompton provides for their 50T ring yields 53T or 3T more than the largest ring. I.e., one should be able to go with just 3T more than the largest ring. Also looking around the home and on-line, some of the alu rings seem well lighter than other. though presumably not as a tough.

Thanks!

You meant 22.3 cm.

👍

Maybe cutting and drilling into an old frisbee would work, if it's flat enough.

I had a BCD110 50T chainring handy, and it looks like I do need the equivalent of a 52T to cover the 46T outer chainring + chain.

I'm unclear at how chain guards sit on spiders. Do they come/require longer nuts so they can sit on top of the single/outer ring?

Is it a double, with the outer ring used for the chain guard?

Yes. I have had for a long time. I think it might have been off a Campi, but I am not sure. I made one for a different bike too. As I recall, the teeth snap off and leave a little that must be filed or ground round to line and a little bit must be ground to get a better fit to where it attaches, kind of an undercut where it attaches to the crank just on the back edge.

I'll just get the 52T chain guard and see how it goes. At €20, it's not worth trying to file down a chainring.

Relative to other alu guards, this one is light. You mount it with the same hardware as regular rings. Since you should have the original bolts for the triple, you should have no problem there. The real problem is when you mount such a guard as a third ring on a double or fourth on a triple, as then you need the not very common extra long bolts.