New gravel build - standards questions

964cup

I'm planning my next build - another custom Enigma. This time a gravel/off-road touring type build, so based on the Escape but to my geometry and in 6Al4v. I'm trying to work out the drivetrain, and discovering that all this mountain-bike derived stuff is somewhat confusing. The thought is to go 1x, using a mix of Eagle AXS eTap XX1 and Red 1 AXS eTap. So the Eagle rear mech, 10-50 cassette and chain, and (maybe) the Red 1 power meter chainset with something like a 44t. Apparently this stuff is all inter-compatible.

Questions:

1. Rear hub type - boost 148 or normal 142? 148 gives a stiffer wheel, but might bring a bigger chainline problem. I also don't want a lumbering artic of a bike, so need to keep the chainstays at some reasonable length.
2. Front hub type - 110 or 100? I don't know if reasonably light gravel forks exist in 110. I've always thought flange spacing on disc front hubs is a bit anaemic, so 110 appeals on principle.
3. Chainline. Red 1 is apparently 45mm. Eagle AXS (MTB) is either 49mm (142) or 52mm (boost). Yet Sram suggest using a road 1x chainset with the Eagle RD and cassette. 4mm is a lot, in chainline terms. But I want a road Q-factor, not MTB bandy legs. (See here at the bottom for Sram suggesting the pairing).
4. BB - it's a custom frame, so within reason I can have whatever I want. Sram's new Dub system accommodates, apparently, everything. I'd like to go external threaded BSA for ease of maintenance: they have 68mm (standard); 73mm (Italian, but English-threaded), 83mm (whut?) and 100mm (double whut?). I'd normally assume that wider=better because stiffer, but does it matter? It can't affect Q-factor, surely, since the spindles are the same in all cases. Does anyone else support these 83mm and 100mm threaded BB "standards"? Are they a mountain bike thing?

Thanks in advance for all helpful suggestions.

...and yes, I know it's pointless and indulgent etc. I know I could buy an off-the-shelf build for some fraction of what this is going to cost, and that it would work as well etc etc. And that I will once more be guilty of too much bike not enough man and all that. But it will be fun. And shiny. I like shiny.

cycleclinic

I dont get boost for gravel bikes. Boost exist on mtb for more tyre clearance given you can put 2.2" 29er tyre and up 2.4" tyres in a 100/142 spaced mtb I dont get why gravel bikes need boost. The stiffer wheels arguement is real but larger bracing angles are not needed. Disc brake wheels dont suffer from poor hub geometry.

If your going to fo boost it can make some sense for the rear but mtb like chainlines are needed. For the front wheel you dont need a 2.6" tyre so 100mm spacing is fine.

Bb shell for toad us 68mm. 73mm is mtb chainlines. 83mm and 100mm are mtb standards for down hill bikes , dome plus bikes and fat bikes I.e not for gravel bikes.

If it's going to be a trendy gravel bike you have 650b wheels and front bag carrier, a hip flask carrier and bread trimming kit in stowed down the steerer tube.

964cup

thecycleclinic wrote:

If it's going to be a trendy gravel bike you have 650b wheels and front bag carrier, a hip flask carrier and bread trimming kit in stowed down the steerer tube.

Now you're talking. And a beer bottle opener on one of the mounts under the down tube. One of the guys at my shop has one of those, and if he was any more woke he'd be getting up before he went to bed.

I'm not hip enough for any of that. I doubt I'll ever go beyond a 38; I'll always use 700c wheels. I like discreet bling, but i also like sleek, so it won't have loads of stuff bolted onto it, although I confess I'd quite like to do some wilderness touring at some point, so it'll have rack mounts.

So from the sounds of it a 73mm shell would give a road chainset exactly the 49mm chainline they suggest for 142mm Eagle 1x. That sounds like a plan, but I'll check it with the Sram rep.

alan_sherman

I'd base standards decisions around the shimano GRX groupset because that will probably be the mass market and so be the stuff available in 10 year's time. I'm not sure what you'd gain going for mtb standards, but you might lose component options, especially if you stray from 68mm threaded bottom brackets!

I think the Reilly tempest is the nicest Ti gravel bike at the moment, but the enigma escape looks good too, especially the flexible cable options. I'm not a fan of internal cables, I prefer exposed inner cables with down tube or head tube barrel adjusters so I can adjust indexing whilst riding.

Are you planning on painting it?

964cup

Following a chat with Enigma, looks like it's going to be an Excel GR, with custom geometry based off my current Excel and the custom SS Excel they made for me last year, increased tyre clearance and some additional braze-ons for rack and extra cage etc. 12x142 rear, 12x100 front. T47 BB (there's a Wheels Mfg T47 Dub BB that will suit the Sram crankset). CK headset, 45D hubs; I'll build the wheels using 38mm carbon tubeless rims and CX-Rays. It won't be painted - all my Enigmas (this will be the 4th) are bare Ti. Just need to decide whether to bling it up with an interesting anodised colour for the hubs, headset and seat-collar. Either navy or possibly matt orange.

veronese68

I meant to post earlier after cycleclinic but I think this point still stands. Rather than going to 142 for the rear hub why not stick to 135 and use offset rims? Better spoke angles and I think they look cool.
Whatever it is I’m sure it will be a thing of joy and I’ll probably be more than a bit jealous.