Custom titanium frame questions...
Moderator: robbosmans
The only thing T47 supports that BSA doesn't is short spindle BB30 cranks. Anything that fits a BB386 type frame will fit on BSA. If you go T47 you will be limited to a small handful of boutique BB manufacturers. If you go BSA, there is support from all the compnent manufacturers for their 24mm systems, and BSA30 bottom brackets from a number of manufacturers. Consider also that weight savings from BB30 will likely be partially negated by the larger BB shell and possibly heavier BB. T47 should only be seriously considered if you are running a short spindle BB30 crank for the purposes of low U factor which external bearing systems will not match or you have a SiSL2 crank you really want to use. T47 will probably see boutique support in the forseeable future, but adoption also seems limited to boutique frames. BSA continues to be the dominant standard, cheap to manufacture with plentiful parts availability and found even on Walmart bikes.
Consider that the primary purpose for the increased diameter of ST, BB, and HT is to provide a bigger surface area for frame tubes. A 34.9mm seat tube is required for a non ovalized 34.9mm top tube. An ovalized 34.9mm top tube to join to a 31.7mm seat tube will be vertically stiff and laterally flexible, generally the opposite of what people want from a top tube. A tapered HT can allow for a larger diameter round downtube, which is optimal for the torsional loads the downtube sees. A larget BB shell also allows for a larger downtube, but the miter with the seat tube and/or ovalization for better lateral stiffness negates the need for a larger BB shell. These features are helpful to stiffen up aluminum which has the lowest modulus of elasticity of the metal frame materials, and carbon to keep stiffness with thin walls of high strength fibers, but you won't see any signifigant gains in stiffness if you aren't using bigger frame tubes to match, and the advantage is less so on titanium (and even less for steel)
The ST-BB joint actually sees substantial loads and is one of the more highly stressed joints on a bike, and the ST sees a moderate amount of lateral load even on the well trangulated rear triangle, so a larger ST isn't pointless, but neither is it needed. I view having to use a larger diameter seatpost or a shim as a downside, as there is almost no case in which I would prefer a larger diameter seatpost to a 27.2mm one.
BB shell diameter has no effect on chainstay size, which is usually the limiting point of stiffness on a titanium frame, as titanium neither lends itself to hydroforming conplex shapes like aluminum, and the chainstay is dimentionally restricted by the need for chainring and tire clearance. A chainstay bridge should have little effect on vertical compliance considering it does not brace against such loads, but it should have a minor improvement on bracing the driveside chainstay for torsional loads and a minor improvement for lateral stiffness. Considering that titanium frames tend to be chainstay challenged, I would say a chainstay bridge, although minor, helps compensate to some small degree, but since the effect is small, it is again, not needed. It also has the advantage of protecting your from wedging your rim into your chainstays when trying to remove a rear flat, something that is probably neither good for the frame nor the rim. It has the problem of introducing another weld, and titanium frames tend to crack at welds. Non-tapered chainstays can also improve stiffness, but are not only heavier because of the tube, but they require larger dropouts.
There's nothing wrong with a plate dropout, but they are easier to bend. Breezer dropouts are more resistant to bending, but they interfere with some skewer setups.
I never got the big fuss over the difficulty of internal cables if you're just diligent about using a liner to change cables. I can only imagine most of the complaints were started by a clumsy mechanic turning a 5 minute job into an hour job because he yanked the cables without a liner, then complaining about how bad internal cables are. I know external cables are easier to do periodic lubrication, but internal cables are better shielded from road grime in the first place. That being said, drilling holes into tubes doesn't increase their strength, and fatigue cracks from stress risers usally only show up many years down the line.
Consider that the primary purpose for the increased diameter of ST, BB, and HT is to provide a bigger surface area for frame tubes. A 34.9mm seat tube is required for a non ovalized 34.9mm top tube. An ovalized 34.9mm top tube to join to a 31.7mm seat tube will be vertically stiff and laterally flexible, generally the opposite of what people want from a top tube. A tapered HT can allow for a larger diameter round downtube, which is optimal for the torsional loads the downtube sees. A larget BB shell also allows for a larger downtube, but the miter with the seat tube and/or ovalization for better lateral stiffness negates the need for a larger BB shell. These features are helpful to stiffen up aluminum which has the lowest modulus of elasticity of the metal frame materials, and carbon to keep stiffness with thin walls of high strength fibers, but you won't see any signifigant gains in stiffness if you aren't using bigger frame tubes to match, and the advantage is less so on titanium (and even less for steel)
The ST-BB joint actually sees substantial loads and is one of the more highly stressed joints on a bike, and the ST sees a moderate amount of lateral load even on the well trangulated rear triangle, so a larger ST isn't pointless, but neither is it needed. I view having to use a larger diameter seatpost or a shim as a downside, as there is almost no case in which I would prefer a larger diameter seatpost to a 27.2mm one.
BB shell diameter has no effect on chainstay size, which is usually the limiting point of stiffness on a titanium frame, as titanium neither lends itself to hydroforming conplex shapes like aluminum, and the chainstay is dimentionally restricted by the need for chainring and tire clearance. A chainstay bridge should have little effect on vertical compliance considering it does not brace against such loads, but it should have a minor improvement on bracing the driveside chainstay for torsional loads and a minor improvement for lateral stiffness. Considering that titanium frames tend to be chainstay challenged, I would say a chainstay bridge, although minor, helps compensate to some small degree, but since the effect is small, it is again, not needed. It also has the advantage of protecting your from wedging your rim into your chainstays when trying to remove a rear flat, something that is probably neither good for the frame nor the rim. It has the problem of introducing another weld, and titanium frames tend to crack at welds. Non-tapered chainstays can also improve stiffness, but are not only heavier because of the tube, but they require larger dropouts.
There's nothing wrong with a plate dropout, but they are easier to bend. Breezer dropouts are more resistant to bending, but they interfere with some skewer setups.
I never got the big fuss over the difficulty of internal cables if you're just diligent about using a liner to change cables. I can only imagine most of the complaints were started by a clumsy mechanic turning a 5 minute job into an hour job because he yanked the cables without a liner, then complaining about how bad internal cables are. I know external cables are easier to do periodic lubrication, but internal cables are better shielded from road grime in the first place. That being said, drilling holes into tubes doesn't increase their strength, and fatigue cracks from stress risers usally only show up many years down the line.
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The only thing I'll add is that match the seatpost with the seat tube diameter. 27.2mm posts on 34.9mm tubes is an eyesore.
Also, see if your builder is willing to do removeable cable stops like Litespeed does on its current frames.
Also, see if your builder is willing to do removeable cable stops like Litespeed does on its current frames.
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Personally I really like my 27.2mm seatpost. It’s a special seatpost designed to flex. I have 1.25” OD ST so it works well with the slim seatpost. I want comfort and looks is not a priority.
I have the Deda tapered chainstays. My builder recommended them over round seatstays. The tapered design also allowed me to use the lighter 1-1/8” Breezer dropouts. They look tiny on my bike but I’m a small rider with low power output. I wonder if Deda makes larger stays for larger riders.
As for QR I have mine set parallel to the ground for as long as I remember. To me it looks better and probably more aero by the tiniest amount.
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I have the Deda tapered chainstays. My builder recommended them over round seatstays. The tapered design also allowed me to use the lighter 1-1/8” Breezer dropouts. They look tiny on my bike but I’m a small rider with low power output. I wonder if Deda makes larger stays for larger riders.
As for QR I have mine set parallel to the ground for as long as I remember. To me it looks better and probably more aero by the tiniest amount.
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With the advent of vertical dropouts 30 years ago, I'm not sure getting the tire wedged in between the chainstays is much of a concern.
As explained before, it's only one of the few small benefits of a chainstay bridge, which happens to increase durability. I never said that it was a common occurance. As I already stated, having a chainstay bridge is not a big issue either way, in fact most of these descisions often result in fairly minor actual functional differences. On most carbon frames it is a complete non-issue because the chainstays form a U-shape at the BB or the U shape is essentially an integrated bridge.
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This guy might disagree He cannot run a 25mm tire because the builder placed the bridge too far from the BB. If you place the bridge very close to the BB then it defeats the purpose of having a bridge. Hence my statement earlier about not using a bridge if the chainstays are very short and when one intends to run wide tires.RussellS wrote: With the advent of vertical dropouts 30 years ago, I'm not sure getting the tire wedged in between the chainstays is much of a concern.
https://youtu.be/FRX98HXQz10
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There are very few, if any, truly “vertical” dropouts but that’s the name given to them. You could consider a thru axle as a truly vertical dropout.
In that video, there’s two issues... the placement of the bridge is not helping things for sure, but the placement of the hanger is even more problematic. They really didn’t take into account the fact that the diameters of the skewer nut and the derailleur Mount knuckle at that point have to pass each other. That’s a frame design issue and a very annoying one which just shouldn’t happen. At least he can seem to get it past the knuckle with a smaller tire. Sometimes it’s so bad that even with absolutely no obstruction up front the skewer nut will still not easily clear the derailleur knuckle. Shame on the builder when that’s the case.
@pdlpusher1: did you ever get a replacement hanger for your bike? Even in the picture you posted earlier in this thread, the position of your rear derailleur would I guess make it impossible to get your derailleur optimally adjusted. That’s the second point I was making in my earlier post in this thread. Makes quite a difference in shift quality when you get it to wrap the cassette while simultaneously being as close to the cogs as possible throughout the entire cassette range.
In that video, there’s two issues... the placement of the bridge is not helping things for sure, but the placement of the hanger is even more problematic. They really didn’t take into account the fact that the diameters of the skewer nut and the derailleur Mount knuckle at that point have to pass each other. That’s a frame design issue and a very annoying one which just shouldn’t happen. At least he can seem to get it past the knuckle with a smaller tire. Sometimes it’s so bad that even with absolutely no obstruction up front the skewer nut will still not easily clear the derailleur knuckle. Shame on the builder when that’s the case.
@pdlpusher1: did you ever get a replacement hanger for your bike? Even in the picture you posted earlier in this thread, the position of your rear derailleur would I guess make it impossible to get your derailleur optimally adjusted. That’s the second point I was making in my earlier post in this thread. Makes quite a difference in shift quality when you get it to wrap the cassette while simultaneously being as close to the cogs as possible throughout the entire cassette range.
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If you watch the video til the end he showed that the frame is spec’ed to clear up to a 23mm tire. So the fact that a 25mm tire didn’t work for him isn’t the builder’s fault. A lot of older frames can’t clear a Conti 25mm tire that measures an actual width of 27mm wide. Would you call all those bikes defective? The problem really isn’t Lynskey but rather running a wider tire than what the bike is spec’ed for.
Personally I’m an advocate for longer chainstays. Longer stays will let you run very wide tires, provide a smoother ride, and increase stability and confidence on fast descents. I know some of you will disagree with me because the general thinking has always been that any bike geometry that is not a ‘race’ geometry is a slow bike
As to my derailleur hanger, no, I never got a replacement from Paragon. They told me they will make a version for the Road. I haven’t had any issues with shifting so I will check back with them later. I’m not in a big hurry. By the way on my tandem I run a long cage Shimano road Shadow rear derailleur along with a 11-40 cassette. I have the B screw adjusted at the extreme end so that the upper jockey wheel will clear the 40 tooth cog. On the higher gears the jockey wheel is very low and far from the cassette. Despite this the shifting is perfect on all gear combinations. I’m running a 11-34 cassette on my half-bike, hence the jockey wheel will look far from the cassette on the higher gears. The pro bikes are running a much smaller cassette and hence their jockey wheels will appear much closer on the lower gears. The B screw on the Shadow derailleur has a wide adjustment range to allows for a wide range of cassette sizes.
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Personally I’m an advocate for longer chainstays. Longer stays will let you run very wide tires, provide a smoother ride, and increase stability and confidence on fast descents. I know some of you will disagree with me because the general thinking has always been that any bike geometry that is not a ‘race’ geometry is a slow bike
As to my derailleur hanger, no, I never got a replacement from Paragon. They told me they will make a version for the Road. I haven’t had any issues with shifting so I will check back with them later. I’m not in a big hurry. By the way on my tandem I run a long cage Shimano road Shadow rear derailleur along with a 11-40 cassette. I have the B screw adjusted at the extreme end so that the upper jockey wheel will clear the 40 tooth cog. On the higher gears the jockey wheel is very low and far from the cassette. Despite this the shifting is perfect on all gear combinations. I’m running a 11-34 cassette on my half-bike, hence the jockey wheel will look far from the cassette on the higher gears. The pro bikes are running a much smaller cassette and hence their jockey wheels will appear much closer on the lower gears. The B screw on the Shadow derailleur has a wide adjustment range to allows for a wide range of cassette sizes.
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No, that's not a problem if it simply wasn't designed for larger tires, but the lack of clearance on some bikes where the skewer nut and derailleur knuckle have to pass each other is, and should not be. I even stated the scenario where sometimes it's so bad that no matter what the clearance up front is, that pass between the skewer nut and the derailleur knuckle is still an issue. And it simply shouldn't be. It's not a "defect", just an inattention to the details during design and/or build.pdlpsher1 wrote: ↑Tue Jun 05, 2018 2:41 pmIf you watch the video til the end he showed that the frame is spec’ed to clear up to a 23mm tire. So the fact that a 25mm tire didn’t work for him isn’t the builder’s fault. A lot of older frames can’t clear a Conti 25mm tire that measures an actual width of 27mm wide. Would you call all those bikes defective? The problem really isn’t Lynskey but rather running a wider tire than what the bike is spec’ed for.
Nothing wrong with longer chainstays, for the reasons you state. But don't confuse that handling with "race bike" handling because it is without a doubt "slower handling" geometry. Finding your sweetspot is always the challenge. To each his own. And different bikes are intended to do different things well; this "all in one" notion is mostly a compromise at best.pdlpsher1 wrote: ↑Tue Jun 05, 2018 2:41 pmPersonally I’m an advocate for longer chainstays. Longer stays will let you run very wide tires, provide a smoother ride, and increase stability and confidence on fast descents. I know some of you will disagree with me because the general thinking has always been that any bike geometry that is not a ‘race’ geometry is a slow bike
Well, while you may think it's perfect, but if it's that far away from the cogs I would say it could be much better. We hashed this out months ago. The B-screw on the Shadow derailleurs does have a large range of adjustment and in the other thread some months ago I showed that for any cassette all the way up to the 11/34tooth with the ultegra derailleur and the gs cage, or the regular cage in the case of cassettes up to 30teeth with Dura-Ace, I was able to have that upper pulley right next to both the largest cog and the smallest cog, provided the hanger places the derailleur in the correct place in space. I've tested the shifting with the pulley's farther away... it is not as good.pdlpsher1 wrote: ↑Tue Jun 05, 2018 2:41 pmAs to my derailleur hanger, no, I never got a replacement from Paragon. They told me they will make a version for the Road. I haven’t had any issues with shifting so I will check back with them later. I’m not in a big hurry. By the way on my tandem I run a long cage Shimano road Shadow rear derailleur along with a 11-40 cassette. I have the B screw adjusted at the extreme end so that the upper jockey wheel will clear the 40 tooth cog. On the higher gears the jockey wheel is very low and far from the cassette. Despite this the shifting is perfect on all gear combinations. I’m running a 11-34 cassette on my half-bike, hence the jockey wheel will look far from the cassette on the higher gears. The pro bikes are running a much smaller cassette and hence their jockey wheels will appear much closer on the lower gears. The B screw on the Shadow derailleur has a wide adjustment range to allows for a wide range of cassette sizes.
Last edited by Calnago on Tue Jun 05, 2018 4:03 pm, edited 1 time in total.
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I just had a custom steel frame made and one of my requirements was a threaded BB. They recommended a bigger shell to fit the tubing and the builder made what I thought was a fair point that I was thinking of moulded carbon issues where what he was suggesting was a press-fit shell which was then machined after welding so they could be sure of the right size.
I went with T47 though as I couldn’t get the idea of a creaking BB on a custom bike out of my head.
I went with T47 though as I couldn’t get the idea of a creaking BB on a custom bike out of my head.
I'm left handed, if that matters.
^exactly... the T47 shell is based on the larger (than BSA) PF30 shell of 46mm in diameter. By just adding threads to a PF30 shell it becomes... voila... T47 and has all the benefits of the smaller threaded BSA shell with the additional size (both in width and diameter) for which to make it easier to join oversized tubes to it. I’d prefer it to BSA at this point simply because it’s bigger, allows oversized tubes to be easily used, and is compatible with basically any crankset you may care to use without the need for teensy bearings in the case of 30mm spindles and BSA shells. If I was getting a steel, or ti, frame today it would have to be T47.
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BSA can already fit DOS 34.9mm downtubes tubes, and even larger bi-oval tubes. You can even join a 38.1mm tube to it. Some of the larger tubes in excess of 40mm height, especially the oval/teardrop ones that are also narrow, can still be joined to BSA by mitering them off center to the BB and running the excess into the seat tube miter. You have to get very very large down tubes like in excess of 44mm round tubes that are both tall and wide, paired with a standard 28.6mm seat tube, for BSA to be a problem. A shaped 44mm tube won't be a problem, if it's teardrop shaped, it gets taken up by the seat tube. If it's bi-oval, it's not tall enough to overshoot the BB shell. And I think columbus is the only one making a 44mm round steel tube.
I really don't see the application of T47 for steel except for the following bikes:
1) You need a true BB30 crank for U factor
2) You really want both a 44mm+ round downtube and a 28.6mm seat tube.
I really don't see the application of T47 for steel except for the following bikes:
1) You need a true BB30 crank for U factor
2) You really want both a 44mm+ round downtube and a 28.6mm seat tube.
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