Tomsl923833

From what I've read the 4130 tube frame is more desirable then the 1020 tube. Why? Is it durability or, quality? Or both.... I have both... I guess I'm more concerned with durability. To honest even though weight is a concern at 280 5 or 10 lbs of extra bicycle weight isn't going to slow me down that much...

oddjob2

Carbon steel without the alloys is less stiff or strong, 50,800 psi tensile strength, vs 97,000 psi for chromoly, hence heavier gauge tubing required.

Full discussion here:
https://www.bikeforums.net/bmx/608667...ten-steel.html

At your weight, nothing to be concerned about. Wheel strength is more of a factor.

uncle uncle

(Slightly veering off topic here)... Those look like ultimate tensile strength values... I would think yield tensile strength values would be more applicable in this case, since you don't really want to take your frame to the point of deformation? Really, compression strength of tube would be the best, but those numbers seem hard to obtain.

fietsbob

A 4130 tube will have the same strength as a 1020 steel tube structurally,

without needing to be as thick a tube wall to do so. (so lighter)

nfmisso

For iron and it's alloys, compression strength is close enough to tensile strength that they are assumed to be the same for Engineering calculation purposes. In compression, what gets you is buckling. Buckling is extremely geometry and load dependent, so each critical case needs its own detailed ($$$$$) analysis.

matweb.com is a great source of material information.

Lascauxcaveman 

There was a noticeable difference between similarly sized frames of CroMo and the one and only 1020 frame in my fleet. Both in weight and "liveliness." Suffice it to say I no longer own the 1020 frame. I have enough bikes that there was no way a significantly inferior bike was ever go to get ridden anyway.

For a big guy like you, @Tomsl923833, you might consider aluminum too. Cannondale has made a ton of touring and racing bikes over the years that are quite a bit stiffer and a little bit lighter than the steel frames of their era.

cdmurphy

They're both the same stiffness for a given wall thickness, but the 4130 (Chrome Molybdenum steel) can take about 2x the stress before it yields compared to 1020 (High carbon steel). Because of that, 4130 frames can be made thinner and lighter for a given target strength. That thinner and lighter frame will be more flexible than the 1020 frame, due to the thinner tubes. This flexibility is generally regarded as desirable -- it takes some the edge off bumps and road vibration, and seems to make pedaling easier. (Much of this is debatable -- some riders don't like the flex, so it may be personal.) Some ultra light / thin bikes may be too flexible for very heavy or strong riders, so don't think of it as an absolute. At the extreme, you can get tire rub or ghost shifting due too too much flex, and the handling can get somewhat imprecise as the bike flexes when you steer.
At your weight, you would probably want to stay away from the lightest of racing frames, but many of the sport touring frames from the late 70s - early 80s would be great. (Tange #2 or #3, Columbus SP or Tenax, or even straight gauge Cr-Mo would probably hold up just fine, and give a nice ride.)

cdmurphy

I forgot to add, that 4130 is quite a bit better than 1020 in fatigue strength, so if both frames were of equal thickness, the 4130 would last much longer. This is kind of moot, as 4130 frames usually aren't as thick, so real world durability will probably be similar, if not less if the 4130 is particularly light weight. Most production frames, as long as they aren't super light race only models, will last for at least tens of thousands of miles of riding. Essentially forever for most owners. 100,000 miles isn't uncommon (except very few riders stick to just one bike for so long).

Tomsl923833

No wonder the toe clamps don't fit!!!! They aren't made for size 14!!!!! I guess I might need to look for bigger tires and rims!!! Thanks everyone!!!#

79pmooney

No. All steel has the same stiffness. All. (Until you bend that steel beyond recovery.) Yeah, the picky ones will say there are differences, but those differences are so small the reference handbooks used by engineers to build ships, bridges, etc. just use 30,000,000 as the stiffness for all steels. Rarely do you see the actually stiffness even listed. Looking through my old Materials textbook, I see a table that shows most steels at 29 million, spring steel and hardened ball bearing steel at 30 million and stainless steel at 28 million. Granted, these are rounded off numbers, but that is a 7% difference between the highest and lowest. 7% gets lost in the feel of a bicycle frame.

Now, higher strength is a different matter. That is all over the place in different steels and can make a big difference - if you draw larger diameter tubing to take advantage of the higher strength. If you don't, like say you reproduce your Peugeot UO-8 exactly with specially drawn Reynolds 753 (probably 3X as strong as UO-8 tubing), specially drawn to exactly replicate the tube diameters and wall thickness, you will have the worlds strongest UO-8 by far; that you can drop off a cliff and the frame will stay straight, but it will be exactly the same slug going up a hill, just a slug that will survive and stay straight for many more crashes.

The tensile strength that oddjob is referring to is the pounds of pulling force it takes to pull a 1" cross section rod of steel until it stretches permanently. The stiffness or modulus of elasticity is a dimensionless number that describes how much a material deflects when a force is applied to it - as long as that force causes stresses that never exceed the tensile strength. When that force is removed, the material returns to its original shape. (Think a spring, say a leaf spring for a car. Any steel can be used for that leaf spring and will behave the same - until you hit the big bump! Then the high strength steel will just go on like nothing happened and your mild steel spring will collapse and leave you car a bottom scraping low-rider. But on the rough chipseal you can use the world's best instruments inside the car to measure vibrations and you will not be able to tell if the springs are mild steel or the world's best.

The easy way to sum this up - for metal bike frames, stiffness depends on shape and the basic metal. Steel, aluminum, titanium. The quality of the metal only matters in how it allows the maker more leeway in the shapes he can use.

Ben

FBinNY 

This is a very popular mythconception.

All steel alloys fall within a very narrow band of stiffness or flex properties (Youngs Modulus) except for stainless steels which cluster about 10% lower.

However, as pointed out, the tensile strength varies greatly, both based on the specific alloy and processing. So, frames built with weaker steels require mare steel, ie. thicker tubes, and end up proportionately heavier and stiffer than their better counterparts.

However, when considering frames, the specific material matters less than the details of the tubing's design and assembly. Butted tubes add strength where it's needed most, allowing stronger frames that are not unduly stiff, and the wall taper of better forks and seat stays greatly affect the ride characteristics.

The above notwithstanding, it pays to consider design priorities.

Better frames are designed with weight savings having a high priority, and tend to be built nearer the minimum acceptable strength. OTOH - those building cheaper frames tend not to care so much about weight, and know their clients are more likely to abuse the bike, so they tend to overbuild. So, the cheaper frames are more likely to be stronger and more durable, ie. more like a truck or SUV than a sports car.

uncle uncle

To the original posters query... Most steels have a "fatigue limit", which is the load that you can apply to them, and if you don't go over that load, the steel will never fail in fatigue, no matter than cycles of loading you subject it to. (This is not the case with aluminum tubing.) This would be one measure of durability. Another would be how dent resistant a steel tube might be; 4130, with it's typically thinner walls when compared to most 1020 bicycle tubes, is mostly likely going to be susceptible to more dent damage, even though in the charts, it's going to be the "springier" steel.

Quality is a hard term to quantify... both 1020 and 4130 have industry standards, which if adhered to, mean both meet their respective "quality" levels. Most C&V enthusiasts seem to feel that 4130 gives them a better "quality" riding experience.. though I think it's always subjective to the individual, and the almost infinite other variables that make up a frame (or bike), like wheel quality and material, play just as important a roll. And to throw more kerosene on the fire, I think early 70's French and Japan entry level steel frames feel differently, but I'm not so sure the material (again) has as much to do with it as the typical geometry.

I think a great quality of C&V bikes for me personally, is given their affordability, and the fact that I have the space, I can experience both 1020 and 4130 frames.

ryansu

Right there with you brother, Carbon bikes cringe when I walk by, I chuckle when I hear fellow Clydesdales bragging about how they lightened their bikes with frame/component/wheels, I think really? that's where you're focused? My daily rider is 4130 (09 Handsome Devil) with 700x47c tires, I am the one holding it back lol

[IMG]Patton by Ryan Surface, on Flickr[/IMG]

oops wrong photo

Sunday mkt plus by Ryan Surface, on Flickr

BigChief 

+1 Well said.

T-Mar

There is lot of misconception about the endurance limit of steels. The performance is pretty impressive on a properly prepared lab sample. Unfortunately, a bicycle frame is far from that and variations in manufacturing processes can cause fatigue failures at well below expected loads.

It can argued that a higher end frame with a good grade tubeset is less likely to suffer fatigue failure because more highly skilled craftsmen typically build these frames and take greater care in the construction. Still, I've seen lots of fatigue failures on frames of all levels.

repechage

If I could only afford a bike with a basic tube set, I would get one of the smaller Brand production French frames, when have seen them without paint, from what I see, they went in fast, overflowed the brass and got out. No gaps, no overheating. Decent geometry even for the lower end bikes.