38T Middle chainring compatibility with Truvativ FireX triple crank

[cocopops]

2021 sees the 3rd major overhaul of my Cannondale T2000 touring bike. The original crankset is now worn. It's a Truvativ FireX, ISIS Drive, 4-arm triple 28-38-48 104/64BCD. It's working with a SRAM 9-speed cassette 11-34 (which will be replaced with 11-32). The bottom bracket was replaced after the first year and is still ok.

The inner 28T/64BCD chainring is hardly worn and can stay. Besides, it's reversible.
I've bought a new Truvativ 48T outer chainring.
The 38T/104BCD middle chainring must be replaced, but there appear to be none left that I can find searching on the web. Looks like the Truvativ part number is 11.6215.023.000. This original middle chainring is profiled and has pins.

Pictures of the chainrings are here:
https://1drv.ms/u/s!AutFk1rG0cVxmSqJ2b- ... i?e=J8IkhC
[exp. 30/06/21]

Question is what other manufacturers' 104BCD 38T middle chainrings will work in this setup? I'm hoping to avoid a complete replacement of BB & crank set.

Shimano seem only to make 104bcd 38T as an outer ring.
I see a TA Chinook 104/38T middle ring. Assuming I can make it fit the crank arms, how well will that work with existing Truvativ rings in terms of shifting?

Any other alternatives or manufacturers of chainrings for a 4-arm 104/64 triple?

Main priority is to keep functionality and smooth shifting. As I have never used the lowest gear and I've regularly run out of top gear on downhill sections, If need to change all 3 rings, I'd be happy to change the configuration to something like 30-39-50. I don't want a middle ring less than 38T.

[531colin]

I have to say I would be riding those chainrings, happily!
Maybe file the burrs off the middle ring if you get chain suck.
Your middle ring is steel, and doesn't seem to sit on a shoulder of the crank spider; I think most middle rings will be alloy, and will expect to sit on a shoulder, so you might have difficulty in replacing it with a different manufacturers product.

[Valbrona]

Going to be one of those things where you default to buying TA or Stronglight and see how it works.

[cocopops]

Thank you both for your comments.

I had no idea what chain suck is, until you mentioned it. I've searched for, and read about it now. I've not experienced that but will obviously bear it in mind.

Interesting that you think the wear is not that significant. Great to have comments from others with more experience. In the light of that, I'll probably get a TA ring (aluminium) as a backup but put the original back in service and see how it goes. I have a Parktool chain gauge and can monitor that periodically.

I could rotate the 38T middle ring by 90 degrees to use the less-worn teeth. That might affect shifting. Might affect chain wear? I should just try it. Anything significant about 90 deg rotation that you've heard of?

The crank arm spider does have shoulders for outer and middle, assuming we're talking about the same thing.

I've posted 6 extra pictures on my cloud storage which show a crank arm and other pics of teeth close-ups. (those that I thought were badly worn)

[531colin]

I think there is going to be a lot of "suck it and see" here!
The shift between 2 rings is "designed" to work in a particular way.....features on the 2 rings are "timed" to help the chain off one ring onto the other one, so in theory if you rotate the middle ring 90 degrees then it won't shift so well.....and the same applies to a different manufacturer's chainring. However, I can't tell the difference between old-fashioned plain chainrings and modern ones with all the features, so it may not matter at all.
The shoulders for your steel middle ring look smaller than the shoulders for the alloy outer ring....fitting an alloy ring here may alter the gap between any 2 chainrings, or it may be OK, I don't think you can know without trying. You can maybe space the rings using washers.