Component check help - BB, Head tube, Seat tube

[ArborVelo]

I’ve got my build log post over here: I'm Building a Wooden Bike!

The way wooden bikes work is that you epoxy in metal (or carbon) inserts for the BB shell, the head tube, and the seat tube. See pic here:

I’m at the stage in design where I want a sanity check on the inserts I intend to put in. I’m a total framebuilding NOOB here so appreciate any advice or warnings that I’m an idiot.

Overall bike will be a gravel bike, going for the ability to put some wide tires on it (50mm). Was going to do a simple 1X group set.

Bottom Bracket
This one is the most confusing. I’ve read the excellent posts by @Daniel_Y : [Standards] Road and Gravel Drivetrains - Cranks and BB's but even then I still feel like an idiot.

My plan was to use a 73mm BSA bottom bracket like this: 73MM X 41MM Ø BOTTOM BRACKET SHELL 7005 THREADED BSA — BICYCLE FABRICATION SUPPLY

I’m leaning BSA as it has the smallest diameter and thus will give me more “meat” around the bb for a wood wrapper. I’m leaning wider given the tire width I want to be able to run, and the clearance issues presented by thicker wood chainstays.

Any objections?

Heat Tube
For simplicity, I was going to go with a non-tapered head tube like this: 50MM Ø X 200MM HEAD TUBE STOCK FOR 44MM HEAD SETS — BICYCLE FABRICATION SUPPLY

I want to put a nice carbon gravel fork on this. Will I be able to find one for non-tapered head tube?

I could make a tapered head tube work, but for V1 it will take more effort. Let me know if my plan is dumb or if I should really make the effort to put a tapered head tube in.

Seat Tube
I was looking at something simple like this: 35MMØ DEDA FIRE SEAT TUBE TUBE 31.6 POST - 35MM X 1.65 X 650MM MTV350E313 — BICYCLE FABRICATION SUPPLY

I would trim it down as I don’t need that much length. I could also actually use carbon, but I don’t know where to find it.

Any recommendations for a carbon seat tube insert? Overall, am I looking at the right diameter?

Thanks in advance guys!!!

[Daniel_Y]

@ArborVelo

I’m leaning BSA as it has the smallest diameter and thus will give me more “meat” around the bb for a wood wrapper. I’m leaning wider given the tire width I want to be able to run, and the clearance issues presented by thicker wood chainstays.

I think BSA (1.5in diameter) is a good choice.

73mm BB is mountain bike width, so you are constrained to MTB cranks. It will make the construction a bit easier, but at the cost of a wider Q-factor and a Frakenstein drivetrain.

To clear a 1x 40t and 50mm tire, the chainstay needs to be ~10mm thick at the pinch point.

@ArborVelo

I want to put a nice carbon gravel fork on this. Will I be able to find one for non-tapered head tube?

Even though the 44mm headtube is straight, the headset that you put into it are “tapered” (1.125 to 1.5). the 44mm headtube will work for everything.

@ArborVelo

Seat Tube
I was looking at something simple like this: 35MMØ DEDA FIRE SEAT TUBE TUBE 31.6 POST - 35MM X 1.65 X 650MM MTV350E313 — BICYCLE FABRICATION SUPPLY

You don’t need an entire seat tube, only 100mm of the top portion. For example, you can just et this topper from paragon: Titanium Seat Collar, 1-1/4" OD x 27.2 mm, 1/2" Step: Choose Length

I would not recommend that route since Paragon toppers are undersized to accommodate warping from welding. You will need to ream it, which is not required for your application.

This is the carbon fiber tube you would need:

45304 | Tube - Unidirectional - Bicycle - Seat Post - 1.072 x 1.244 x 37 Inch...

That carbon fiber tube is 27.2ID and 31.8OD. As mentioned above, you only need 100mm of the tube to constrain the seatpost correctly.

[ArborVelo]

Hero of the revolution! Thank you!

@Daniel_Y

73mm BB is mountain bike width, so you are constrained to MTB cranks. It will make the construction a bit easier, but at the cost of a wider Q-factor and a Frakenstein drivetrain.

Wrestling with my model so we will see if we can get it there on the 68. Agree would be better to be conventional.

Will I have the same issue with facing / reaming on these frame builder BB shells as you identified with the seat tube? I guess facing not as bad as I could just sand them down? (I don’t really want to buy the reaming tools for this if I can avoid it - although I’m sure I could get my mechanic to help me.)

@Daniel_Y

Even though the 44mm headtube is straight, the headset that you put into it are “tapered” (1.125 to 1.5). the 44mm headtube will work for everything.

Mind blown. Followed through on the research with this and that’s great! Thank you.

@Daniel_Y

That carbon fiber tube is 27.2ID and 31.8OD. As mentioned above, you only need 100mm of the tube to constrain the seatpost correctly.

So maybe a dumb question: ID is 27.2, and the OD of carbon seat posts is 27.2… PERFECT fit… should I be worried that I’ll be sanding down a seat tube ?

Also - WOW these carbon tubes are note quite the same price as gold, but it feels like it!

[Daniel_Y]

@ArborVelo

Will I have the same issue with facing / reaming on these frame builder BB shells as you identified with the seat tube? I guess facing not as bad as I could just sand them down?

Facing is quite involved, you won’t be able to do it with sanding. Your best bet is to see your BB supplier has access to a lathe. If they do, its a 2min job.

Alternatively, there is this option, which is designed to be glued into carbon frames:

BB4039: Aluminum T47, 1.937" OD x 68 mm

@ArborVelo

ID is 27.2, and the OD of carbon seat posts is 27.2… PERFECT fit… should I be worried that I’ll be sanding down a seat tube ?

Most seat posts are undersized. But most is not all, which is why you see a lot of stuck seatposts. The convention is to keep the seat tube at the nominal diameter. You can always ream it larger, but you can’t do the opposite!

[Spencermon]

@ArborVelo

@Daniel_Y

73mm BB is mountain bike width, so you are constrained to MTB cranks. It will make the construction a bit easier, but at the cost of a wider Q-factor and a Frakenstein drivetrain.

Wrestling with my model so we will see if we can get it there on the 68. Agree would be better to be conventional.

One small addition to consider is whose cranks you plan on using. Sram DUB wide road cranks can fit into a 73mm BB shell. I know because I did that once when I needed the extra space for a really weird project. This will limit you to only being able to use the SRAM Dub Wide road cranks though. (there may be other options out there from smaller manufacturers like Appleman, Engin, etc. but that would require a little more research)

[ArborVelo]

Thanks @Spencermon! After an hour or two in the SRAM spec sheets, the DUB wide is what I’ve landed on for the first prototype to try and make my proposed geometry work with wide tires. I think a wood bike qualifies for a “really weird project” too

[bushtrucker]

You can also pair some road cranks with MTB spindles. White Industries A30 setup is one option. The 49mm chainline will still work great with a road drivetrain. Just a bump up in Q-factor over the SRAM DUB wide setup mentioned above (163.5 vs 150 mm).

Easton EA90 cranks (149mm Q) share a spindle with Race Face MTB cranks so can mix and match there too. Stock Easton spindle is 129mm and the next size up with RF is 136mm so a 7mm increase in Q factor to clear a 73mm BB. Easton/Race Face isn’t as forthcoming as WI with this info but they would be my pick of the bunch. Cheaper and far more options with spiders/rings.

[ArborVelo]

@bushtrucker - thank you! Good info to have in the kitbag - I’ll have options when I get there. Going 73.

[PineCycles]

Here’s list of all the Gravel WIDE Cranks on the market I’m aware of. You can use any of the labeled “MTB” in the "BB Standard Column. Sram’s are great but if you run into crank arm clearance issues, there are several other good alternate options.

[ArborVelo]

Christmas keeps coming - thanks @PineCycles !