speccing a custom gravel/travel frame

[Discodan]

After looking for the right new gravel frame, with the intent of swinging most of my current running gear across, I couldn't settle on anything so have decided to take a different path with a custom frame. In a leap of faith I've found a titanium frame specialist in China that will make pretty much anything you want, including a break-away style travel frame that will let the front triangle come off. The idea is for it to have the ability to act as my primary gravel bike, but also be a decent road bike for traveling by putting on my road wheels. I wanted to get your thoughts on how to spec this to get the features and usability I want.

The key requirements, I think, are:
• 700c x 45mm tyre clearance minimum, ideally 50mm with 650b
• external cable routing around the headtube entering on the downtube,
• both seat-stays meeting on the seattube (not a Y piece inbetween), slightly dropped stays
• tapered headtube,
• 142x12mm through axle,
• threaded english BB,
• flat mount brakes to suit 160mm rotor
• UDH
• Mounts for bottle on seattube, bottle on inside of downtube, bottle on underside of downtube, top tube bag

To be able to brake the frame easily I'm thinking the rear deraileur and brake cables would need to exit from the downtube in front of the coupler, route under the BB shell, and then use external guides to hold the cable and hose to the chain-stays with zipties so I can remove the rear caliper and derailleur from the bike, cut the zip ties, but leave them attached to the cable/hose. Is there a better way to do this apart from etap of course, but I'll probably re-use my 105 mechanical groupset? There are options with quick-disconnects for hydraulic lines and cable disconnects but I think just taking off the RD and brake will be easier, the one downside being realigning a flat-mount caliper which can be a pain.

In terms of geometry, I'm no guru so will likely just copy geo from an existing gravel bike. I'm going to borrow as many of my mates gravel bikes for a few weeks and make sure I'm happy with it but I think something that's not gravel race but also not super lazy and long long my current G bike is. Something like the Grizl might be a good compromise.

So, any thoughts on this plan? Anything I've missed I should spec to avoid a mess?

thanks in advance
d

[satanas]

After looking for the right new gravel frame, with the intent of swinging most of my current running gear across, I couldn't settle on anything so have decided to take a different path with a custom frame. In a leap of faith I've found a titanium frame specialist in China that will make pretty much anything you want, including a break-away style travel frame that will let the front triangle come off. The idea is for it to have the ability to act as my primary gravel bike, but also be a decent road bike for traveling by putting on my road wheels. I wanted to get your thoughts on how to spec this to get the features and usability I want.

The key requirements, I think, are:
• 700c x 45mm tyre clearance minimum, ideally 50mm with 650b

^ This is trivially easy to achieve

• external cable routing around the headtube entering on the downtube

^ Why? Running internally will just complicate things, especially with splitting the frame

• both seat-stays meeting on the seattube (not a Y piece inbetween), slightly dropped stays

I've no odea what the first part above means...

• tapered headtube

May be problematic as these only come in a few lengths; 44mm headtubes can be made to suit

• 142x12mm through axle,
• threaded english BB,
• flat mount brakes to suit 160mm rotor

These are normal...

• UDH
• Mounts for bottle on seattube, bottle on inside of downtube, bottle on underside of downtube, top tube bag

To be able to brake the frame easily I'm thinking the rear deraileur and brake cables would need to exit from the downtube in front of the coupler, route under the BB shell, and then use external guides to hold the cable and hose to the chain-stays with zipties so I can remove the rear caliper and derailleur from the bike, cut the zip ties, but leave them attached to the cable/hose. Is there a better way to do this apart from etap of course, but I'll probably re-use my 105 mechanical groupset? There are options with quick-disconnects for hydraulic lines and cable disconnects but I think just taking off the RD and brake will be easier, the one downside being realigning a flat-mount caliper which can be a pain.

If it was me I'd run the cables externally and use splitters on the derailleur cable(s), easily available from various sources. There's IMHO no ideal solution for the rear brake hose, but I'd most likely just unbolt the caliper from the mount and cut the zip ties. Bear in mind that getting the bars off to box the bike can be a PITA with hydros, so something like the Formula quick disconnects near the bars could be very helpful - and are another reason not to try to hide the cables/hoses. Running the front brake hose through the fork blade can also be problematic in this regard; it'd be way easier just to cut the zip ties and take the front caliper off sometimes, so I wouldn't write off forks which don't have internal hose routing, i.e., Ritchey.

In terms of geometry, I'm no guru so will likely just copy geo from an existing gravel bike. I'm going to borrow as many of my mates gravel bikes for a few weeks and make sure I'm happy with it but I think something that's not gravel race but also not super lazy and long long my current G bike is. Something like the Grizl might be a good compromise.

So, any thoughts on this plan? Anything I've missed I should spec to avoid a mess?

thanks in advance
d

I presume you're thinking of Waltly, based on some of the comments above. Back in 2019 I ordered a custom gravel/touring frame from them, and was very pleased with how it turned out. However, the reason I did so was because I couldn't get a good enough fit from anything off the peg, not so much because of details. Bear in mind that you need to be able to read and understand an engineering drawing, and you must know enough to understand and check *EVERY DIMENSION* on it befire signing off as they will build *exactly* what's on the drawing, and say themselves that they are not bike designers or fitters. Getting this all straight can take a lot of emails(!), and some patience, but they are responsive and helpful.

Waltly were also, understandably I suppose, quite keen to avoid butted tubing (because they didn't think the extra cost was worth it) and smallish diameter tubing, presumably to ward off any potential problems. However, the one thing I'd substantially change on the next frame is to use smaller (and maybe butted) tubes in some places to get a bit more flex and comfort - I'm not heavy, aggressive or hard on gear though, so YMMV.

PS: If going for a separable frame (with S&S or Breakaway style couplers) it's worth considering how you're going to be able to lock it up when travelling. It'd be very annoying to come back and find half the bikr missing...

[olnow]

I've done exactly what you propose, but with external hoses and AXS. Post mount brakes with IS rear, which unbolt to pack. I use reusable cable ties, which have a little release lever to hold the hoses..Walty were great, bike currently weights about 9kg all in (with guards). I'll add a pic when I've worked how too....

[satanas]

Reusable cable ties are a great idea - thanks. AXS does indèed simplify some things, but unfortunately the FD battery limits tyre clearance significantly and I have no interest in 1x. Rumours suggest GRX 12 speed Di2 might appear mid-year, so it'll be interesting to see what happens there, otherwise I'll most likely stick with GRX mechanical for the next bike as it's both cheaper and easier to fix; I'm in no hurry...