Guys I’m a 3×9 dinosaur looking at building a gravel bike. Not sure I want to go compact up front or 1x so would an mtb double chainset say 26-36 be compatible with 105 or ultegra shifters and can either cassettes be used. Also can mechanical disc calipers be used.Cheers

Shimano road 10spd and MTB 9spd rear mechs share the same cable pull so will work with each others shifters but the front mechs are different. MTB chainset will have the rings further outboard but might work with a road front mech, maybe a triple version but I’m not sure.

Yes, you can use mechanical disc calipers with road levers as long as they are road discs.

Are you looking at reusing some parts from your MTB on this build?

Old 105 10 spd shifters work OK, but just beware that the current Tiagra 10spd shifters and mech are a subtly different cable pull, so Tiagra shifter and mtb 9 spd mech on 10 spd cassette won’t index properly (mtb mech lets you run 36t cassette)

There is a work around – 1mm spacer between 3 and 4 sprocket.

Hmmm. Bit of a minefield/trial error then! I was looking at buying new parts either 10 or 11speed depending on what offers I could find.

If you’re buying new then it’s not so tricky because you can choose the right things, it’s harder if you are trying to reuse older parts.

If you are buying new then IMHO it’s worth getting 11 speed for future proofing and deciding if you want to shell out for hydraulics at this point. The levers are one of the most expensive parts and they commit you.to gearing and brake choice.

I’d suggest though, if you want to build a 1x gravel bike then you should look at SRAM rather than Shimano. They have dedicated mechs for road 1×11 and it would be easier to avoid component mismatch. I was a big Shimano fan but I think they’ve lost the plot on transmission parts recently.