I'm wanting to build a carbon road bike with disc and thru axles. The frame has 142x12mm rear dropout and I'm trying to work out getting wheels that have hubs that I can use a shimano road groupset with. It seems very convoluted as to whether 142mm hubs are even compatible with road cassettes. I'm wanting to use dt swiss hubs and run 25c tires. also will this effect chain line and type of rear mech hanger? I have some mechanical abilities, but this is really confusing me. It seems that there are many road bikes with disc and thru axles on the market, and alot have 142mm dropouts?
Please advise

142mm is the standard dropout spacing for 12mm thru axles, and any hubs I'm aware of that are made to this standard with Shimano compatible freehub body will accept a road cassette.
Note that there is now something called the Boost standard which has 148mm dropout spacing, but so far, that is only found on mountain bikes.

The '142mm' is indeed the distance across the hub mounting faces but for all intents and purposes, the true spacing is 135mm. The ends of the hub axle engage pockets in the frame that are 3.5mm deep on both sides (142 - 7 = 135).

For hubs, you need to understand that MTB 11 speed systems for the most part still use the same 8/9/10 speed freehub at roughly 35mm long. The eleventh cog overhangs the rear of the freehub but due to its high tooth count does not interfere with the receding spokes. Standard road cassettes use much smaller eleventh cogs and require the longer ~37mm freehub. So long as you pick a hub that a. matches your rotor choice and b. matches your cassette choice you are good to go.

Chainline is slightly affected by the 135mm effective spacing (2.5mm). In practice, it won't make a difference for most because it is rare to find a road disc frame with ultrashort chainstays.

The rear derailleur hanger should only play into what type of thru axle you need. The two most common systems are where the hanger itself is threaded (Syntace) or where it uses a replaceable nut (Shimano e-thru).

For hubs, you need to understand that MTB 11 speed systems for the most part still use the same 8/9/10 speed freehub at roughly 35mm long. The eleventh cog overhangs the rear of the freehub but due to its high tooth count does not interfere with the receding spokes. Standard road cassettes use much smaller eleventh cogs and require the longer ~37mm freehub. So long as you pick a hub that a. matches your rotor choice and b. matches your cassette choice you are good to go.

thanks joejack. I see you have an fm079-f. I'm waiting for an fm088. did you build the bike frame up? so if i find hubs with a road freehub I can use an ultegra 11 speed groupset? any advice on building the bike? thanks for your time.

btw I grew up in Hockessin, DE in the late 70's-early 80's

sorry i screwed up the quote

I did build my bike and the wheels on it: Chinabomb Disc Brake Road Bike Build

Unless you plan on using the Ultegra 11-34 cassette, you need wheels with a road freehub, i.e.
one that is 11 speed compatible. Of course, I think you'd be hard pressed to find road rims built with a MTB hub but it could happen. And you can still use the 11-34 on a road freehub by adding a spacer.

As far as advice building the bike, do you have a build list? I believe I gave some prior advice for thru axles which was one of the things that took me some time to figure out on mine. Everything else was fairly straightforward other than things I did that added complication like mixing Campagnolo mechanical levers and TRP calipers.

I grew up in Hockessin as well! Born in 1978. Where'd you go to school?

thanks, my list is not quite as organized as yours, but I have most of it sorted out. I have the trp website saved and once the frame arrives I will confirm exact size and order axles, thanks for your help there. I was thinking of going with an entire groupset, possibly the new Ultegra 8020, but it appears no one has it available right now. I did read that shimano now offers 11-34 road cassette, though not what I'm interested in. I am grateful for you sharing your experience. I've built a fixed gear from a bare metal 70's Sears and Roebuck frame my dad rode all over Delaware/PA when I was a kid, but this is much more involved.

I lived in Hockessin from 1970-1983 and would have graduated from Thomas Mckean High School in 1985 had we not moved out of state.

Definitely buy a full groupset as the savings are worth it. Just sell off what don't need. Let me know any other questions specific to your build. I'm happy to help.

I grew up close enough to Mckean that I could hear their marching band from my bedroom. If you had been at St. Mark's then you might have known my oldest sister.