I will be converting one of my bikes to a single ring set up starting with a 42 tooth up front and a 3rd eye. I have a 105 long cage and a 11/32 cassette I was considering mounting to give me a wide range. Do you think chain rub or slack will be an issue ? Anyone running a long cage with a cassette this big ? Thoughts ?

Anyone running a long cage with a cassette this big ? Thoughts ?

just about every geared mountain bike uses this setup.

I will be converting one of my bikes to a single ring set up starting with a 42 tooth up front and a 3rd eye. I have a 105 long cage and a 11/32 cassette I was considering mounting to give me a wide range. Do you think chain rub or slack will be an issue ? Anyone running a long cage with a cassette this big ? Thoughts ?
Are you just asking if it has ebough capacity? I believe the capacity of a 9-speed, Shim, long cage, road RD is 37 teeth. You have 42-nothing + 32-11 = 21 teeth. Even a short cage (31 teeth capacity) would work. - TF

That set-up will function no problem.
However, in a race situation you will find that the gap between gears is too big, your gear will always be either too big or too small. A tighter cassette will be a better option for racing, like a 12-25 or even 12-27.

The cage length doesn't determine what size cassette you can run. It only determines how much chain slack you can have. You might still need an MTB rear derailleur to run an 11-32 cassette. I think the max for Shimano road derailleurs is 28 (although you can get lucky on some frames and run a 32 with lots of noise).

The maximum cassette size is determined by the size of the derailleur's body (parallelogram). The MTB derailleurs have a bigger body so they can handle bigger cogs.

You could try it but don't be surprised if it's not optimal.

If you only have one front chainring, you don't need a long-cage rear derailleur, road or MTB. The reason is you will never have a lot of slack chain, unlike, for example, you would if you had a triple crankset with a long chain, and shifted into something like a 32 front x 13 rear combo.

If your largest cog is 27 or smaller, best to use a short-cage road rear derailleur.
If your largest cog has more teeth that 27, best to use a short-cage MTB rear derailleur.
I'm talking about Shimano here.

My long cage shimano road derailleur fits an 11-32 with no problems. Personally, I prefer to race a smaller cassette, but the 11-32 is great for trail riding.

You might be better running an 11-27 for racing. 11-34 is really low and possibly not very useful for cross racing.

If the hill is that steep, you would be better off to get off and run at that point. Trying to spin/push that gear might take more energy than running.

If the course is really hilly, going with a 39 tooth front chainring might be a better option instead of 42.