# Curious about butting...



## JonathanGennick (Sep 15, 2006)

Hope I'm not out of line posting under Frame Building, but this seems a likely place to find the right expertise. I'm curious about butting, and specifically about the fork on the following bike:

2015 PROLINE EXPERT XL | Redline Bicycles

The fork is butted and tapered.

What would be the design goal of the butting? Would it be to make the ends thicker for welding, while leaving the tubing thinner in the middle?

One of my neighbors just bought that bike for her son to race. We were talking over the specs and got curious about the butting part and what that likely meant. We can't exactly saw the for in half though...


----------



## c8stom (May 19, 2015)

JonathanGennick said:


> What would be the design goal of the butting? Would it be to make the ends thicker for welding, while leaving the tubing thinner in the middle?


Single butted is when one end of the tube has a thicker wall whilst the rest of the tube has a thinner wall. Double butted is when both ends have thicker walls and the middle has thinner. Triple butted is the same as double butted but the material removal is taken a stage further to make the walls in the middle even thinner.

For most designers, the two main goals would be to
- Save weight
- Tune ride quality

In the case of steel, tubing is almost always butted as straight gauge would result in a heavy frame.

In the case of titanium which is lighter and poses less of a weight issue to designers, butting is usually chosen for ride quality tuning

My custom ti has straight gauge as I don't like so much flex and prefer greater strength. Having a frame 200grams heavier as a penalty is no big deal.


----------



## dbhammercycle (Nov 15, 2011)

You must spread some Reputation around before giving it to c8stom again.

sorry c8stom...


----------



## Walt (Jan 23, 2004)

Ok, I will quickly chime in and dispel a couple of misconceptions.

-Butting is 100% about weight. The vast majority of the stiffness (or lack thereof) of bike tubes is determined by the diameter of the tube. The wall thickness will have a VERY small effect but it's not enough to be noticed on a completed frame. So a butted tube frame will ride just like an unbutted tube frame, but weigh less. 
-"Triple" butting is just butting the two thick ends differently (so instead of a tube that is .8mm/.5mm/.8mm, it would be .8mm/.5mm/.7mm). So it's really double butting, but uneven double butting. 

All mid to high end steel or ti bike frames are made with butted tubing. You won't find straight gauge on anything but Walmart level bikes, as butted tubes are pretty cheap in the context of $500+ complete bikes. 

-Walt


----------



## JonathanGennick (Sep 15, 2006)

Walt, thank you. I get what you are saying, but then why bother to make the ends thicker? If 0.5 mm is enough in the middle, then why not throughout the entire length?


----------



## watts888 (Oct 2, 2012)

stronger welds at the end.

IMO, a butted fork does make a difference when compared with a straight gauge steel fork. Kind of like why we ride 120mm suspension forks, when 100mm suspension forks are available. Just a little bit more comfort with the right amount of controlled and predictable flex.


----------



## Walt (Jan 23, 2004)

The stresses are all at the ends, so they need to be thicker to not break. The middle of the tube is relatively unstressed, so it can be thinner.

It's also easier to weld the thicker material, but good welders could handle 0.5mm no problem. The tubing would crack near the welds, though, at least with commonly used bicycle tubing. 

-Walt


----------



## JonathanGennick (Sep 15, 2006)

Thanks all, for the explanations. Really appreciate the expert insight.


----------



## dbhammercycle (Nov 15, 2011)

Walt said:


> -"Triple" butting is just butting the two thick ends differently (so instead of a tube that is .8mm/.5mm/.8mm, it would be .8mm/.5mm/.7mm). So it's really double butting, but uneven double butting.
> 
> -Walt


So it's a gimmick? I did not know that, thanks Walt.


----------



## Feldybikes (Feb 17, 2004)

Also, a fork that's tapered and butted probably doesn't have the same thicknesses you might think. Generally the tube starts as a cylinder with the top end is thicker to start and the bottom thinner. Then, as the tube is swaged (tapered) then bottom gets thicker walls as the diameter shrinks. It's the same amount of material, so it has to go somewhere. In this case, into the wall thickness. In the end, the bottom/smaller diameter/tapered part of the fork leg is as thick or more likely thicker than the top.

As for triple butting being a gimmick, the name may be gimmicky, the benefit may be real.


----------



## iggs (Oct 18, 2007)

So I get that butting doesn't affect the frames stiffness or feel. That's more to do with tube diameter. 

But what about general robustness? Say for a mountain bikes ability to deal with knocks and bumps. Chain stays are vulnerable in crashes and top tubes can get dinged by handlebars (brake levers). Does non butted tube have advantages in some places?


Sent from my iPhone using Tapatalk


----------



## Walt (Jan 23, 2004)

iggs said:


> So I get that butting doesn't affect the frames stiffness or feel. That's more to do with tube diameter.
> 
> But what about general robustness? Say for a mountain bikes ability to deal with knocks and bumps. Chain stays are vulnerable in crashes and top tubes can get dinged by handlebars (brake levers). Does non butted tube have advantages in some places?
> 
> Sent from my iPhone using Tapatalk


Yes, thicker walls will mean much better dent resistance. But frames don't get dented *that* often that it's a huge issue. If you're looking at a custom frame, you could certainly get a very dent resistant setup by having the framebuilder use straightgauge. You could also have them use (as I do for many frames) Supertherm tubing, which is butted but slightly thicker (1/.7/1mm). Lighter than straightgauge, VERY strong, very good dent resistance.

-Walt


----------



## iggs (Oct 18, 2007)

Thanks Walt. Interesting

Another question. How much of a tube needs to be butted to get the desired strength at the weld?

1? 2? 3? 4? cm from the weld?


Sent from my iPhone using Tapatalk


----------



## Walt (Jan 23, 2004)

We're into "bunch of threads on this already" territory, but the answer is: as far as you need to keep the thin portion of the metal from being affected by the heat of the welding. For very good welders, that can mean the thick portions can be pretty short. For not so great welders/brazers who are putting more heat into the joint, it may need to be further.

In the real world, I give it a minimum of about 30mm. 

-Walt


----------



## dr.welby (Jan 6, 2004)

Walt said:


> The wall thickness will have a VERY small effect but it's not enough to be noticed on a completed frame.


Bicycle Quarterly did a double blind test of 7/4/7 and 9/6/9 frames and two of the three test riders were able to tell which one was which. So I wouldn't say it's unnoticeable. This was with standard sized road tubing which is now at the flexy end of the tubing options though. With stiffer mountain bike frames and fat tires to mask things I'd bet the difference gets harder to discern.


----------



## Velobike (Jun 23, 2007)

This is how it's done

Reynolds Technology


----------



## JonathanGennick (Sep 15, 2006)

Thanks for that link velobike. That was interesting.

So if using double-butted tubing, then you must have to buy it ready-made to the length you need, right? Never thought about it before, but I guess you can't just buy generic tubing lengths and cut them down, because you'd lose the butt. Am I thinking correctly?


----------



## Feldybikes (Feb 17, 2004)

JonathanGennick said:


> Thanks for that link velobike. That was interesting.
> 
> So if using double-butted tubing, then you must have to buy it ready-made to the length you need, right? Never thought about it before, but I guess you can't just buy generic tubing lengths and cut them down, because you'd lose the butt. Am I thinking correctly?


Sorta.

Depends how precise you're getting with your butts. For example, True Temper S3 which is made to be super light comes in 3 different lengths with longer center sections. Many times, though, a bigger bike will just end up with a longer butted section. Probably not a bad thing in most cases.


----------



## mickuk (Jul 6, 2007)

You'll probably be interested to look at the Columbus catalogues linked below to see all the different tube and butt lengths.

If you look at the second one (Zona), it shows which end the tube can be shortened from and how much can be cut (although for light riders / personal use / careful brazing I've sometimes trimmed more without disaster).

You can also see how seat tubes are sometimes butted on the outside.

http://www.framebuilding.com/acrobat files/COLUMBUS TUBES 2015.pdf

ZONA


----------

