What Chainrings to use, Mtb to Gravel conversion

[Wannabe]

I am looking for advise as to what chainrings to use to complete my Mtb to Gravel Grinder conversion, AT A BUDGET, as this is a complete budget build.

I'm currently using a Sram/Truvativ GXP crankset, which I would like to keep. It is a 104 BCD 4 hole crankset with a 38/24 teeth chainrings. Cassette is a 10 spd 11-36.

I'm using this bike as a runaround not to overuse my Mtb and Roadbike (maintenance is expensive) thus I'm using it on road and for gravel when on training rides.

I procured another crankset with 50/36 chainrings on, but the spindle/axle is too short as it's a roadbike crankset and the Mtb frame BB cup area is wider (silly oversight from me, as I knew this.)

So, Hub Gurus, after this lengthy and rather clumsy introduction, what is my options out there to adjust my gearing to a bit more road/gravel bias whilst not breaking the bank. As said, I'm trying to keep cost down to a minimum. 

I would like to keep it 2x, to be able to use my current cassette, otherwise I'll have to source a 10spd 11-42 Mtb cassette to pair with a 42t chainring if I go the 1x route. 

[droo]

I've got a MTB based commuter hackaround thing with 650 x 42 tyres, a 38T chainring and an 11-36. I did cannon challenge on it (170km / 2800m) and didn't feel under geared at any point except hacking up the front of Signal Hill at 20% gradients, and held on on the flats at 50km/h+ without spinning out.

Chances are you'll need a new RD as well if you go to a 42T cassette, so start on the chainring and see how you go.

To keep it 2x you'll probably still find some 44/32 3x chainrings lurking in someone's parts collection, but you'd need a 3x crank to make them fit since they're both 104BCD and the SRAM 2x sets only have space for one.

[Wannabe]

Thanks droo.

I have an X9 Mtb rear derailleur on, so it should handle a 42 t at the back?

My problem is that I'm more of a natural "grinder" with my avg cadence hanging around 80 rpm on my Roadie. I feel that I'm spinning out at 40 km/h on the flats with the GG. (Guess I'll have to work at upping my cadence, or just get fitter. Lol....)  

[droo]

In my experience with overextending RDs a SRAM 10sp will do 40T max. Even with a longer B screw you'll destroy your upper pulley on a 42T. You can use a hanger extender but the shifting will suck.

I eventually reverted to the 36T and cup of cement approach. But then again I did ride the same bike SS for 10 years, so YMMV.