Converting a '12 Trek Slash to 1X with OneUp 42T?

I've been contemplating engaging in a little wrenching, and as I'm vaguely mechanically inclined I've been intrigued by this add-on. You're probably more knowledgeable on this subject than me so your input is appreciated.

-My current all-purpose mountain bike is a 2012 Trek Slash 8. Running an XO RD with an X7 11-36 cassette and an X7 FD with an X9 38-24 crank.
-I'm a almost-middle aged guy who doesn't ride as much as I want or need. Consequently my fitness has taken a hit this year…but I also find shifting between the rings, well, annoying, clunky and generally soul-sucking.

My plan is to make the following changes:
-Add the OneUp 42T/16T sprockets to my rear cluster.
-Replacing my deformed/slightly mangled X0 RD with a new X0 Type 2 with the clutch.
-Replacing the rings with a Race Face 32 tooth Narrow/Wide ring.

My questions:
1. Any red flags/potential idiocy/things I should be cognizant of?
2. For you gearing math wizards, how much am I losing on the top end here? More importantly, on the bottom? As I am slowly increasing in mass with a corresponding decrease in fitness, should I be thinking of a RF 30 ring, instead?

Many thanks.

Dont be fooled by the hype, the One-up conversion is definitely a compromise. The 32 (or 30)/42T wont be quite as easy as your current 24/36T and you will lose a whole lot on the bottom end. If you need to pedal along streets or flats to get where you are going, you will definitely find the 30 or 32T front ring lacking. I have done the conversion on our big bikes, and love the added bonus of the bail out gear for climbing fire roads etc. It definitely isn't something I would do on my AM or trail bike though, as there are often sustained tech climbs that call for granny (at least for me).

Just my .02

The conversion is worth it in my opinion. I can still spin to or from the trail head in my 30-11 combo at a modest 25-30 km/h without issue. Climbing is pretty damn close in the 30-42 or 30-40 combo depending on which conversion cog you choose. The simplicity is what appealed to me and I wasn't disappointed. I would definitely recommend the 30T front ring for all around riding.

you guys running 30 t chainrings,dont you run out of gear and spin out?

I spin out with a 38 and wish i had more from time to time.

….or are these bikes meant more for up/down noodling around in the bush at lower speeds?

just curious….

2. For you gearing math wizards, how much am I losing on the top end here? More importantly, on the bottom? As I am slowly increasing in mass with a corresponding decrease in fitness, should I be thinking of a RF 30 ring, instead?

Your current lowest gear:

24x36 = 0.667

Lowest gears with 1x10:

32t: 32x42 = 0.762
30t: 30x42 = 0.714

You can try how a 32x42 feels: it's more or less like a 24x32 (0.75)… just do a couple of rides without using your largest cog!

I say go for it, but it depends on the terrain you ride on.

I run 1x10 11-36 with a 32 up front and I find it perfect on a long travel bike on technical terrain. The only time I would want lower gears is on long sustained steep fire roads, but that's when your 42t comes in. You need to carry some momentum when things get a more technical, so spinning in a very low gear wont help you much. Actually, I now climb stuff I never could climb on a 2x10. Same thing for spinning out, you might miss the higher range when on the road or going down a fire road, but on BC trails, not so much. I never ever wanted more, exception being in the bike park with smooth manicured trails, but you can switch to a bigger chainring for those few occasions.

You WILL struggle a bit the first few weeks, be warned, but you will get used to it quickly. It's a great training tool, it gets you fit fast, because it forces you to pedal a little harder instead of spinning a bailout gear. I know I woudn't go back.

I don't find my 1x10/42 shifts 100% perfect but it's close enough.
I love not dealing with front shifts.
I can climb everything now that I did before even though at the low end it's technically not quite as low.
I don't have to do extended road pedals to get to my rides.
The 30t chainring was an important choice (on my 29er).

you guys running 30 t chainrings,dont you run out of gear and spin out?

I spin out with a 38 and wish i had more from time to time.

….or are these bikes meant more for up/down noodling around in the bush at lower speeds?

just curious….

I don't get up to hyper speeds on my local trails. Too tight and twisty.

In Moab I ran out of gears a few times, but really at that point I was going pretty fast and it wasn't a big deal.

I can spin at pretty high RPM so that might mitigate the issue for me as well.

I say go for it be it a 30T or 32T narrow wide. I would even say not to go for the one up and just run a stealth granny ring sans dérailleur. If you know a long steep climb is coming just kick it down with your foot. Weighs nothing and is nice for emergencies.

I say go for it be it a 30T or 32T narrow wide. I would even say not to go for the one up and just run a stealth granny ring sans dérailleur. If you know a long steep climb is coming just kick it down with your foot. Weighs nothing and is nice for emergencies.

I have gone to the 42 on up and a 30t RF front. I wish I had lower gears some times. I can think of a few rides that I will not be able to ride up with this combo. I am thinking of doing what Tmack says. If you like dropping more than a hundred bucks on one ring go for it. I wish I didn't.

most the guys around here i know running 1x are running a 28t up front..one guy has a 26..they are telling me ultimately they don't feel they have the same gearing range as the 2x systems.. i haven't tried 1x yet..

I had a friend go 1x10 on his ride (no oneup or anything just 11-36) and he actually found it detrimental to his fitness. He didnt ride that much and found the 1x10 so lacking that he ended up walking more climbs and stuggling more with fitness.

Im just about to go with a 32front and 11-36 but with the ghetto granny that Tmack suggested. I know i wont use it often but for some of the steep climbs in whistler and long days in chilcotins there is no way i could live without it..

Ensure that what you are trying to do will actually improve your riding before you drop that much cash on it is what i am trying to say…

I had a friend go 1x10 on his ride (no oneup or anything just 11-36) and he actually found it detrimental to his fitness. He didnt ride that much and found the 1x10 so lacking that he ended up walking more climbs and stuggling more with fitness.

Im just about to go with a 32front and 11-36 but with the ghetto granny that Tmack suggested. I know i wont use it often but for some of the steep climbs in whistler and long days in chilcotins there is no way i could live without it..

Ensure that what you are trying to do will actually improve your riding before you drop that much cash on it is what i am trying to say…

That's funny. Going 1x10 has had the opposite effect on my fitness. I used to hate climbing in the granny ring and now find the 30T chain ring just feels "right" for all types of climbs, and if anything I am climbing better now.

Like any training, you need to ride several times a week for a few weeks to build that type of fitness. Of course, it you ride once a while and walk as soon as it gets a little hard, it's not going to work for you. You need to push yourself a bit.

It basically forces you to do interval training. Sprint once a while instead of taking the low gear. It's not easy at first, but you quickly see results and it makes a big difference in your overall riding, it's not just about climbing.

EDIT: Re-reading the OP's intro, it doesn't look like the best choice for him, you need to ride fairly regularly. I guess the solution is then to put a 30 ring while keeping the granny, and see how it feels. That's a 50$ investment. If it feels like you could deal with it given a few extra gears (42t), then go for it, but if it's nowhere near, just keep your double.