Custom titanium frame questions...

Discuss light weight issues concerning road bikes & parts.
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Calnago
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by Calnago

Wider tires, with shortish chainstays of significant size, surely benefit from not only the larger diameter of the T47 shell but it’s significantly greater width. There’s just more real estate to work with and attach the stays to. There is zero drawback to it when compared to BSA. I think it’s the modern day version of BSA in light of larger tubes, wider tires, etc etc. it doesn’t share any of the limitations that a BSA shell would with the current requirements of today’s frames and components, the main one being wider tires. I think it just makes a better looking frame as well since the stays can have more of a straight smooth line to the dropouts given the wider stance that the stats can be set at on the BB shell. Which is even more important if you’re considering discs as well.
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RyanH
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by RyanH

Well, this being weightweenies, the lightest affordable crankset is a SRAM Red BB30 crank at 346g with a PF30 FSA BB at 68g for a combined weight of 414g. Interestingly though, the lightest no expense spared option is a BB86 bike with 51g THM bearings and a 296g THM Clavicula SE (347g total), and second lightest being BSA/ITA at 72g for BB and 296g THM Clavicula SE (368g total). PF30 THM Clavicula SE setup comes in at 404g total.

But, unless you're running THM, there's a weight penalty with non BB30 sized cranks. I think the GXP Red crank is ~100g heavier. If you plan on running 24mm spindles anyway then you might as well go BSA but if you'd like a light option without going for THM then 68mm wide shell is the way to go. Also, while I too probably would end up speccing T47, PF30 in Ti isn't as bad as the carbon offerings. I have had Chris King cups eventually creak after a decent amount of mileage, but removing them and reapplying copper paste would've resolve (or Loctite 609). The delrin offerings work flawlessly though in my experience at least.
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by Weenie


RyanH
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by RyanH

Calnago wrote:
Tue Jun 05, 2018 10:43 pm
Wider tires, with shortish chainstays of significant size, surely benefit from not only the larger diameter of the T47 shell but it’s significantly greater width.
Are you thinking of BB386? I thought T47 is 68mm wide so technically would offer less horizontal real estate for the chainstay placement than BSA. Right?
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Calnago
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by Calnago

Ouch! Yes I think you’re right Ryan... PF30 is based on a 68mm wide shell so while that wouldn’t provide more width for welding/brazing, it certainly wouldn’t be less as BSA is 68mm wide as well. I’m not sure about this, but I think with a wider shell with a 46mm bore the process of cutting threads into it is exactly the same. So it would just be the threaded adaptors that are different, along with the length of the internal sleeve connecting them. Kind of like Colnagos Threadfit BB’s... wide shell with threaded in cups to accommodate the crank of your choosing.
Edit: I just confirmed that T47 is not limited to 68mm shells. So yes, you can have shells every bit as wide as the current widest carbon shells utilizing the T47 “standard” and thus have the extra real estate to work with. So to me it’s just a nobrainer to go with T47 if i were to have a steel or ti bike built today.
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zank
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by zank

You can do a 86.5 mm wide T47 shell and use the King internal T47 bb. Basically think of it as threaded PF41. One problem with that is there are no Campagnolo cups available. The ones Argonaut has made are for the 68 mm shell.

2lo8
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by 2lo8

@Calnago
That's somewhat true, but only applied to the wide version of T47, which means you can't run narrow U factor cranks. You also have more room to move the chainstays out on a disc bike with disc crank. But on a normal QR bike with typical ovalized straight CS road geo, there's usually no issue fitting OS CS to 68mm. Oval chainstays are actually usually narrower than traditional 22.2mm ROR CS, and very few people have the idea to make the CS less oval at the weld to increase lateral stiffness. It might have an effect on bent CS, but I think those are usually bent in the opposite direction of needing more BB real estate.

The drawback of course, is not having the availability of BSA parts, and being restricted to T47 parts and associated tools, which appears will never receive mass market adoption, simply because it doesn't do enough over BSA or PF30. I hate expensive consumables, so I see having to buy a $150+ BB a fairly big drawback to buying a $30 DA BB when I can't see any real advantage to T47 except the specific conditions I listed earlier. If cost is no issue, then there's little disadvantage, but there's also little advantage unless your frame has a fairly specific setup.

T47 very much seems like a solution in search of a problem for steel to me at least.

@RyanH
It's 52g difference between GXP and BB30 red. The 68mm BB shell weight difference is ~30g, minus whatever shavings you get from trimming tubes. The difference is there but it ends up being very small. If SRAM ever updates Red to fit wide BB386, like they have for Force and lower, then it should be able to run on BSA. If you run a 22 to 24 adapter on GXP then you can turn it into a wave washer MegaExo type crank, and should be able to run it on Shimano's especially light BB-9000. T47 also has threaded cups, so I think the BBs end up being in the typical ~100g weight range of non-DA BSA cups.
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Calnago
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by Calnago

Agreed that T47 will never achieve mass market adoption, simply because the mass market is carbon now where pressfit is the solution in the absence of some kind of alloy sleeve bonded in, but that’s more costly. Good luck getting mass adoption of more costly production methods.
But in the boutique Ti and steel market, I don’t see why T47 wouldn’t be the most preferred solution going forward. The trends towards wider tires and bigger tubes kind of dictates that me thinks. There will always be special cases I suppose favoring one method over another but on balance I’d still go with a T47 solution if I was buying now.
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Calnago
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by Calnago

zank wrote:You can do a 86.5 mm wide T47 shell and use the King internal T47 bb. Basically think of it as threaded PF41. One problem with that is there are no Campagnolo cups available. The ones Argonaut has made are for the 68 mm shell.
My god... you’re right @zank! No Campy adaptors for T47 wide shells! That changes everything. I take it all back, T47 just sucks the big one. Lol
Kidding, I still think the T47 is a good standard going forward for Ti and Steel, but I guess I’ll be sticking to carbon or opting for pressfit solutions in steel or Ti in order to be able to use my beloved Campy. Or back to BSA. Image
Last edited by Calnago on Wed Jun 06, 2018 12:15 am, edited 2 times in total.
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Calnago
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by Calnago

@zank... you’re a frame builder. What are your thoughts as to pros and cons of moving forward with T47 as a replacement to BSA for steel and Ti?
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2lo8
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by 2lo8

Calnago wrote:
Wed Jun 06, 2018 12:02 am
But in the boutique Ti and steel market, I don’t see why T47 wouldn’t be the most preferred solution going forward. The trends towards wider tires and bigger tubes kind of dictates that me thinks.
Chainstays are dimentionally constrained by both the tires and the chainrings. You can't just move the chainstays out for tire clearance without moving the chainrings out or bending and crimping the chainstay. Increasing BB shell diameter does nothing for clearance. It's also more than just BB shell width. I think that was the logic behind BBRight which only extended the BB shell on the left side, which means asymmetrical CS. Steel also doesn't need the extremes aluminum needs either since it is a more compact material.

44mm for steel is a very very large tube. A traditional DT is 28.6mm. As I said before I can only think of one tube on the market that big (which will mate to BSA with a matching OS ST). OS and DOS are 31.7mm and 34.9mm, which can already get the kind of stiffness most people want from a steel frame at a lighter weight. A 44mm 6-4-6 tube is also about the same weight as a 9-6-9 28.6mm (classic columbus SL or bottom end chomor) tube, just much stiffer, and people who tend to buy steel aren't looking at maximum stiffness. BSA is still more than compatible with tubes larger than traditional, but smaller than round 44mm. And bi-oval and teardrop shaped 44mm is fully compatible with BSA.

It's aluminum, and maybe Ti, that uses such large tubes on a regular basis. Not steel. For steel T47 only provides a solution for a handful of very niche situations.
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pdlpsher1
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by pdlpsher1

One thing unique on the T47 is the fine thread. This was a compromise to allow the new standard to work with existing tooling and bearing sizes. It also allows tapping of an alloy PF30 BB shell and turn it into a T47 BB shell. When installing a T47 cup one must be careful and avoid cross threading.


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Calnago
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by Calnago

2lo8 wrote:...It's aluminum, and maybe Ti, that uses such large tubes on a regular basis. Not steel. For steel T47 only provides a solution for a handful of very niche situations.
But would it be fair to say that there’s nothing that a BSA shell would be suited to that a T47 shell wouldn’t be just as suited to? And if there’s applications where a T47 might add some functionality if desired (30mm spindles with room for proper sized bearings for example, larger ti tubes being another), then why wouldn’t you want to adopt it going forward? It seems more accommodating to more situations in today’s world. I don’t know, the price of change I suppose. Sometimes good, sometimes not so good. I was a staunch resistor of pressfit BB’s when they were coming out and it took a long time before I would even tool up to be able to fix peoples creaks, etc. Up to then, I’d just say “I don’t want anything to do with that mess, take that noisy creak back to wherever you got it from”. But after taking pity on a few problem cranks I sort of got to like the challenge of fixing a creak when the shops couldn’t and now I just accept that pressfit is likely here to stay but I’m confident enough in my installs that creaking has not been a problem. But they’re certainly not as simple as a good old thread BB, where anyone with a minimum amount of tools and a little grease (no retaining compounds, primers, etc) could easily install, remove and maintain their own bottom brackets. And now that I know there’s very few Campy adaptations of T47, I wouldn’t hesitate to go BSA if I was getting a Ti or steel frame. So there’s that I suppose. I’ve nothing against BSA, it’s just that I think T47 might offer a few more pluses going forward.
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2lo8
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by 2lo8

Calnago wrote:
Wed Jun 06, 2018 1:18 am
But would it be fair to say that there’s nothing that a BSA shell would be suited to that a T47 shell wouldn’t be just as suited to? And if there’s applications where a T47 might add some functionality if desired (30mm spindles with room for proper sized bearings for example, larger ti tubes being another), then why wouldn’t you want to adopt it going forward?
BSA30 uses full size bearings and should still come ahead compared to T47 depending on the specific BB. T47 also offers a weight disadvantage against BSA BB-9000 in that both the shell and the BB is heavier by maybe 70-100g or so. Even though SRAM seems to still push GXP for BSA and also stuff like BB86, I don't see a reason the newer BB386 stuff isn't compatible with BSA 30. Not everyone is a RED on everything fanatic. Even in the case of RED the overall BSA GXP vs T47 BB30 weight advantage is very small and I can beleive be eliminated when adapted to a BB-9000.

If you're looking at market trends, then market trends are also heading the the direction of long 30mm in the form of BB386 or whatever instead of BB30. I think the two premier cranks that are BB30 specific are RED, for minimum list weight, and SiSL because Cdale came up with BB30. I'm having a hard time of thinking of any others. Maybe some of the frame specific cranks paired with frames.

BSA also simply has historical and market intertia. It's been around for a century or so, it works for most cases, and there's no reason for the proliferation of a new standard that is not sufficiently differentiated just to meet a few niche conditions. The elimination of threads is actually one of the advantages of a BB30 system. BSA threads aren't really for threading cups with press fit cartridge bearings in, it's just a historical quirk that they work well for that. Switching standards creates problems, so they should really be implemented only if they solve problems.

I would have liked to have seen T47 provide enough room for a cartridge unit that had bearings for both sides, perfect pressfit alignment of bearings, and a preload spacer in the middle, like square taper cartridge BBs, but without an axle, but as far as I know, such a thing does not exist.
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RyanH
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by RyanH

Is there enough room to run di2 wires inside a BSA30 setup?
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2lo8
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by 2lo8

Probably not comfortably. A bit more room is running a matching Shimano 24mm crank. The bigger diameter probably helps with trying to keep things internal for any kind of internal routing.
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by Weenie


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