Tubing Diamter Advice needed

Quoted post said:

Originally posted by buffedupboy
Hi all,

I am trying to get my first custom frame built buy a manufacturer. I have limited knowledge so I will need all the advice I can get! I'm designing it based on certain bikes that I have tried and liked.

I have pretty much sized the frame. I am a 58cm frame rider, Height 185cm Weight 85kg. I want to use the frame for training and crit racing. It is going to be made with 3/2.5V Titanium tubing.

I am using a double ovalised down tube measuring 42x34mm. I am still deciding on the top tube. Do I use a 31.8mm/ 1.25" (standard) diameter tube or should I go for a slightly larger 34.9mm/ 1.375" diameter top tube? What sizes are normally used by other Titanium frame manufacturers. I really love the Vortex and Extralight.

If there are any owners out there, perhaps you could measure the top tube diameter for me?

Regards,
Sean

So why don't you let the builder decide what is best for your weight and desired results? The TT is not highly stressed and may only need the bigger diameter at the HT junction for increased stiffness there. bigger tubes are going to weigh more so your are trading some marginal increase in stiffness for more weight. The TT on my 57 cm Merlin extralight is about 35mm. but it's double butted and still very lihgt.

Thanks,

I will probably go with the 35mm dia. top tube double butted. I am having a manufacturer produce the frame for me, there is no actual frame builder to spec it and to advise me which is why I am relying on forums for help. There is no local builder to assist me in building a custom frame as well so that option is out.

Regards,
Sean

Quoted post said:

Originally posted by buffedupboy
Thanks,

I will probably go with the 35mm dia. top tube double butted. I am having a manufacturer produce the frame for me, there is no actual frame builder to spec it and to advise me which is why I am relying on forums for help. There is no local builder to assist me in building a custom frame as well so that option is out.

Regards,
Sean

So then, what does this outfit really know about building bicycle frames, and are you potentially tossing your dinero down the toilet?

Quoted post said:

Originally posted by boudreaux
So then, what does this outfit really know about building bicycle frames, and are you potentially tossing your dinero down the toilet?

Well, they have built many frames OEM for other Ti frame companies. But that's not really the point here. I want to know because I want to learn.

I like to design my own things and I also like to know what I am paying my money for. I understand the risk involved in this whole experiment of mine which is why I'm trying to limit it by posting in this forum.

What bike do you ride? Maybe you can do a measurement on you TT for me.

Regards,
Sean

Quoted post said:

Originally posted by buffedupboy
Hi all,

I am trying to get my first custom frame built buy a manufacturer. I have limited knowledge so I will need all the advice I can get! I'm designing it based on certain bikes that I have tried and liked.

I have pretty much sized the frame. I am a 58cm frame rider, Height 185cm Weight 85kg. I want to use the frame for training and crit racing. It is going to be made with 3/2.5V Titanium tubing.

I am using a double ovalised down tube measuring 42x34mm. I am still deciding on the top tube. Do I use a 31.8mm/ 1.25" (standard) diameter tube or should I go for a slightly larger 34.9mm/ 1.375" diameter top tube? What sizes are normally used by other Titanium frame manufacturers. I really love the Vortex and Extralight.

If there are any owners out there, perhaps you could measure the top tube diameter for me?

Regards,
Sean

You're getting it custom, right? I would go with a smaller diameter than that given you're weight. Top tube doesn't really make as much of a difference in stiffness as do the down tube and seat tube. Anyhow, if you ask different builders, you will get different answers. There is no right answer. Just buy two frames and pick one you like. Cause this question is showing that you are totally obsessing too much.

I will try to help but it is going to be generalities. At your weight I would go for the 1 1/4" top tube with a.035" wall thickness. I would question you on your choice of a frame for training and crit riding. A crit bike has shorter wheel base (not much) and a higher BB. A training bike would have a more normal BB drop and a little longer wheel base and not as quick handling bike. I quess that it would be good though if all your training was for crits. I quess that I would also think about maybe a butted frame because you can drop some weight on the frame. A butted headtube is a great place to loose weight on a 58cm frame. On the downtube I would maybe also think about a 1 1/2" down tube. I don't think that your weight is too much for a 1 1/2 in an .035 downtube versus a 1 3/4 down tube. The big reason they are oval is because the headtube and BB are smaller than the 1 3/4 down tube so you have to squish the tube in order to cope the joints. It is stiffer because of the larger diameter and a little given from the squish. If you think about the squish at the BB it is good position for the stiffness but at the headtube the squish causes a stiffer ride for bumps but maybe it would be better to have the squish parallel to the ground for more steering precision but you can't really build it like that. I quess that maybe I might be wrong about the last part but it is something that I have thought a lot about. I hope this helps.

Hi Bacardi,

As of last night, I thought I had made up my mind in chosing the larger diameter top tube. This was based on the fact that Airborne uses the smaller diamter but in an ovalised shape, merlin uses the larger diameter and Moots uses an even larger diameter. This shows that the smaller diameter alone was found to be insufficiently stiff.

This morning however, I get 4 similar suggestions of using the smaller one. I AM DEFINITELY OBSESSING! You are also right in that different builders will give different answers (because they have), and there is no right answer.... sadle also true. So I guess this is all a learning experience for me and I will never know if I never get them both built and tried.

The frame has been designed to be more of an all rounder capable of crit racing. It has a normal/ slightly lower BB drop and a fairly short but not extreme chainstay length.

It has been speced with a 1.5" dia. DT which is ovalised at HT and BB.

How would double butting the HT save much weight, it is so short, curious.

Thanks,
Sean

The HT is never doublebutted. Dude, you have got to just get a bike and enjoy riding it. Crit bike, so what? Stiffness is overrated and the difference between the bikes top tubes isn't going to have much effect on stiffness. Its mostly down tube and seat tube. Come on. Quit the obsessing!

Quoted post said:

Originally posted by BaCardi
The HT is never doublebutted. Dude, you have got to just get a bike and enjoy riding it. Crit bike, so what? Stiffness is overrated and the difference between the bikes top tubes isn't going to have much effect on stiffness. Its mostly down tube and seat tube. Come on. Quit the obsessing!

I know the HT is never double butted, but I thought that maybe I was wrong because the other member posted that the best place to save weight was a double butted headt tube.

I've going to spec a massive downtube but will leave the seattube standard.

I can't stop obsessing! It's ridiculous. It's my first attempt at designing something like this and I want to get it close. I'm like this in every design that I do, which is why I chose to do what I do I guess.

Stiffness is an important criteria for me, my schwinn is super light but then it is so noodly it is not funny, I can really feel the BB flex when I hit it. My Cannondale is what I call ideal stiffness, it doesn't weight as light but it will go when you floor it.

Anyways, I realised another criteria which I didn't consider was that if the TT is larger in diameter than the seattube and the headtube and I didn't ovalise it, I'm gonna get a really ugly joint... which is again something I am obsessing on as well.

You should have seen me when I was deciding on the HT extension and how it must match the ST extension and at the same time have a standard geometry without extending the ST too much.... know where I'm going with this one?

regards,
Sean

Dude this is totally ridiculous. Just buy a bike. Look at it this way. You're not going to be happy with it one way or another with all your second guessing. So, you might as well just buy one now. After all, you already know that you are going to be pyscho analyzing every little detail even after you buy it.

Quoted post said:

Originally posted by BaCardi
Dude this is totally ridiculous. Just buy a bike. Look at it this way. You're not going to be happy with it one way or another with all your second guessing. So, you might as well just buy one now. After all, you already know that you are going to be pyscho analyzing every little detail even after you buy it.

Uhhh..... thanks for the advice but I think I'll stick to my decision. I will psycho analyze it regardless whether it was stock or custom. I don't see why it is ridiculous to question decisions whether they have been made or in advance. I always believed that it is not the destination but the journey that makes us.

I think it is more ridiculous to buy something off the shelf by subjective values like Reviews and Feel of the bike. It is totally illogical if you don't know why it was different to your existing bike in the first place. Tube size, geometry and the like make for a more informed purchase. I could well buy a stock bike in the end after all my research but I would know what geometry to look for.

Now back to the original question. Does anyone else have their views to add about the diameter of a top tube for a 3/2.5 Ti frame? If not, I think I've pretty much decided ( for today anyways) that the ideal size is a 31.8mm 0.9/0.7/0.9 tube.

Regards,
Sean

Quoted post said:

Originally posted by buffedupboy
I know the HT is never double butted, but I thought that maybe I was wrong because the other member posted that the best place to save weight was a double butted headt tube.

I've going to spec a massive downtube but will leave the seattube standard.



Stiffness is an important criteria for me, my schwinn is super light but then it is so noodly it is not funny,

Mr. Bianchi likes to toss alot of hooey.The HT on my Merlin is thicker walled where the cups seat and thinner walled along the rest of it's length. Call it double butted or not but it is definaately two diffferent thicknesses. You worry about stiffness? Then go with the bigger toptube and seattube. Don't you think people who do this for a successufl living know what they are doing? My Merlin uses the bigger tubes all around and it IS light AND stiff. Why try and reinvent the wheel?

A butted frame with a butted headtube or internally relieved is a good place to loose weight. In a 58 cm frame butted tubes should reduce the weight by 1/4 pound. .9 wall thickness is the same as .035. I think that you should just go with a 11/4 seat tube and 11/4 TT and a 13/4 DT. It will be fine for you. It really does not sound like you are building a crit bike though. HT are 11/2 in dia. and the better ones are butted!!!!

I would sure find out what type of tubing this company is using. Is it comunist TI or or is it american Ti. There is a huge difference between the two. That is the big question I would be asking. Comunist Ti is deffinately sub standard.

Quoted post said:

Originally posted by pudster
I would sure find out what type of tubing this company is using. Is it comunist TI or or is it american Ti. There is a huge difference between the two. That is the big question I would be asking. Comunist Ti is deffinately sub standard.

Just more hooey, and I ws beginning to think you were better than that.🙁

Quoted post said:

Originally posted by pudster
I would sure find out what type of tubing this company is using. Is it comunist TI or or is it american Ti. There is a huge difference between the two. That is the big question I would be asking. Comunist Ti is deffinately sub standard.

And they say Americans have unsophisticated political views!

Quoted post said:

Originally posted by pudster
I would sure find out what type of tubing this company is using. Is it comunist TI or or is it american Ti. There is a huge difference between the two. That is the big question I would be asking. Comunist Ti is deffinately sub standard.

COMMUNIST TI? Dude what's up? Lost someone in Nam?

Regards,
Sean

Boy I am sorry that I said communist Ti, that was kind of rude. I guess that what I should have said is it Chinese Ti. The Chinese Ti is not what I think is good Ti. The tubes are not real round and the tubes are wavey. The reason that I would want to know is because the Chinese Ti is very cheap in price and not as good a quality. I guess that I would hate to see someone pay a lot of money for a frame that has cheap Titanium. This why all Ti bike manufactures say they use like Sandvik aerospace grade Ti tubing or another American Ti manufacturer. I guess that I just wrote more hooey!

Whatever mate.

Have you seen or tested any of these "Chinese ti" tubes? That's a very bold statement but I doubt you have any real evidence or experience to back it up.

I've seen these "Chinese ti" frames and they look the same as "American Ti" tubes. Can't tell a difference between an airborne or a litespeed if you asked me. Doubt you could either.

It's like saying all scandinavians have blonde hair, all chinese have single and slanty eyelids, all americans are fat and stupid. It just isn't true.

In fact aren't some American owned companies' planes made in China?? How did a conversation on Top Tube diameter degrade into a generalisation of chinese and their products?

Regards,
Sean