Would you rather a 6061 or 7075 stem?

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Beamex

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11/12/2017 8:22 PM

The majority of the high end stems are still made from milled 6061 Aluminum. I've got a Colony Squareback 7075 but I think I read somewhere that 6061 squarebacks also exist. Just wondering if this is because of cost of they slip more or what.

What is the very best stem in your opinion?

Spenlard

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11/12/2017 8:37 PM

7075 is the preferred material i suppose. 7075 is better than 6061...but as long as it's cnc machined not forged it's not a huge deal or really a deal at all for that matter

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11/12/2017 9:44 PM
Edited Date/Time: 11/12/2017 9:46 PM

I put 7075 on both my bmx's.

Colony official front load on my main and a primo anhilator top load for my dirt/cruise bike.

I know its stronger overall not really positive its better for the stem application but I trust it more mentally so it helps.

7075 is more brittle so its prone to cracking and snapping with less warning than a 6061 series but it would take more force to get it to snap than it would a 6061 to bend or break.

sundaybmxRR

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11/12/2017 9:59 PM

this was brought up in a recent thread in regards to clamping power... 6061 was arguably deemed the better choice since it's softer than 7075 so the knurling on bars bite into it more decreasing the chance of slippage, although when I had my Primo stem which was 7075 it never slipped either way. I've cracked both 6061 & 7075 aluminum stems (not cracking the face plate due to improper tightening or something stupid like that) but I've only ridden 1 7075 stem so I'll say I'd rather 6061 since my track record is better with them and less chance of slipping

grumpySteve

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11/12/2017 10:33 PM

6061 because that's the industry standard for a reason. It clamps better. And the strength difference in a big chunk of material isn't greatly noticeable.

GCBMX69

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11/12/2017 11:15 PM

7075
Never had one slip with it and haven't crushed my bars either

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Cellmember

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11/12/2017 11:58 PM
Edited Date/Time: 11/13/2017 12:01 AM

Ive run both 6061 and 7075, 7075 from personal experience is better because it's stiffer, and steerer clamp area does not tend to close the gap making for installation easier on/off, 6061 is a little to soft I have the clamping area almost touch and even with it being fairly far away, the stem would grab the steerer making it harder to install and most likely most have gone through the same thing at a certain degree, where the heads of the stem bolts sits can cause a mushrooming making the bolt harder to remove and thats with using the correct torque on all bolts. Most use 6061 because there is a price difference and of course it also depends on how it's made, cnc'd, forged, molded etc. But typically a 7075 will outlast a 6061.

Edit: I don't get the same problems compared to 6061, not 1 problem with a 7075 I use colony official, variant and squareback. Love em.

Mishinn_Control

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11/13/2017 4:52 AM

Spenlard wrote:

7075 is the preferred material i suppose. 7075 is better than 6061...but as long as it's cnc machined not forged it's not a huge deal or really a deal at all for that matter

Actually, forged Aluminum (actually most forged materials) is stronger than billet.

Mishinn_Control

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11/13/2017 4:55 AM
Edited Date/Time: 11/13/2017 4:59 AM

& to answer the original question, 7075 is a stronger aluminum (assuming that was your concern).It handles stress better than 6061. 6061 is really more for welding (when it needs to be welded). That is not to say that 6061 is bad. I don't know the exact strength difference, especially as it pertains to what is & is not adequate for a stem & BMX street/park/trail riding.

ggallin422

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11/13/2017 1:47 PM

It's more prone to cracking just like 7000 series rims. More likely to slip too. I'll stick with 6000.

elytron

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11/13/2017 7:09 PM

I would get real upset if my Colony Official cracked on me. So far they haven't, and my bars haven't slipped yet.

Wasn't aware that there was debate over this. I just assumed the stronger aluminum was superior when I purchased mine. I also have a set of 7KA rims, have ridden them for years. Have held up well so far.

SoCalShreds

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11/15/2017 9:39 AM

Mechanical engineer here:

When you compare the stress strain curves for 6061 and 7075, you can see that 7075 has a much higher yield, and ultimate stress; almost 150% higher.

However, its not all about strength, because when taking a part (like a stem for example) all the way to yield, you get twice the strain out of 6061. So, increased strain, means increased ductility.

6061 is more ductile, but yields and fractures at a lower stress than 7075. As far as the argument with clamping being better with a softer material, I highly doubt the force from the bolts is sufficent to yield the aluminum, (plus why would you want to?) So that argument isn't worthwhile.

So, why does industry mainly use 6061? Since it is softer, it is easier, and quicker to machine. Plus, when it comes down to it 6061 is good enough for little kids bikes.





Bulletpup

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11/15/2017 10:12 AM

SoCalShreds wrote:

Mechanical engineer here:

When you compare the stress strain curves for 6061 and 7075, you can see that 7075 has a much higher yield, and ultimate stress; almost 150% higher.

However, its not all about strength, because when taking a part (like a stem for example) all the way to yield, you get twice the strain out of 6061. So, increased strain, means increased ductility.

6061 is more ductile, but yields and fractures at a lower stress than 7075. As far as the argument with clamping being better with a softer material, I highly doubt the force from the bolts is sufficent to yield the aluminum, (plus why would you want to?) So that argument isn't worthwhile.

So, why does industry mainly use 6061? Since it is softer, it is easier, and quicker to machine. Plus, when it comes down to it 6061 is good enough for little kids bikes.





Nice!

I always trust 7075 over 6061

Its just a lot more expensive and a bit harder to machine so most companies dont bother.

I got 7075 rims and i think hubs too...

p1p1092

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11/15/2017 10:37 AM
Edited Date/Time: 11/15/2017 12:53 PM

SoCalShreds wrote:

Mechanical engineer here:

When you compare the stress strain curves for 6061 and 7075, you can see that 7075 has a much higher yield, and ultimate stress; almost 150% higher.

However, its not all about strength, because when taking a part (like a stem for example) all the way to yield, you get twice the strain out of 6061. So, increased strain, means increased ductility.

6061 is more ductile, but yields and fractures at a lower stress than 7075. As far as the argument with clamping being better with a softer material, I highly doubt the force from the bolts is sufficent to yield the aluminum, (plus why would you want to?) So that argument isn't worthwhile.

So, why does industry mainly use 6061? Since it is softer, it is easier, and quicker to machine. Plus, when it comes down to it 6061 is good enough for little kids bikes.





On the clamping point:
You do realise how much compression a bolt is capable of at relatively low torque, right? If not, have a look at this: [link]

What do you mean by "I highly doubt the force from the bolts is sufficient to yield the aluminum"? I don't quite understand the context.

My main argument for 6061 as stem material, besides the availability, price and ease of manufacture would be that it's quite a bit softer so the knurling can bite in to almost the full depth of the knurl and get a better grip. 7075 is 53.5 on the Rockwell A scale whereas 6061 is 40. That's quite a difference, more than enough for there to be a difference in clamping ability.

SoCalShreds

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11/15/2017 5:32 PM

Valid point with the hardness. I understand what you mean now. I honestly don't know if it would make a noticeable difference for clamping force, that is a good point though.
I haven't have much issue with clamping that I can relate back to the stem/stem material, I feel that amount or knurling on the bars is a bigger player in that game.

p1p1092

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11/16/2017 2:40 AM

SoCalShreds wrote:

Valid point with the hardness. I understand what you mean now. I honestly don't know if it would make a noticeable difference for clamping force, that is a good point though.
I haven't have much issue with clamping that I can relate back to the stem/stem material, I feel that amount or knurling on the bars is a bigger player in that game.

I'd agree with that; the style, sizing and density of the knurling along with the width of the clamp area would have a far more significant effect but I think material hardness does make some difference.
If you made a stem from 4130, as suggested in a recent thread, you'd sooner crush the bars than make it grab and yet you'd barely scratch the surface of the stem. An extreme example but it does kind of illustrate the difference hardness makes. The other extreme would be a very soft material, say lead. If you clamped on the bars with a lead stem, it'd grab the knurling really well but it'd strip out and the bars would move with very little force.

am-shaegar

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11/16/2017 9:17 AM

Guys, I'm telling you, a 4130 stem would be awesome!

To solve the crushing of the bars issue, you can add a small filling in the bars, like this:




grumpySteve

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11/16/2017 10:03 AM

am-shaegar wrote:

Guys, I'm telling you, a 4130 stem would be awesome!

To solve the crushing of the bars issue, you can add a small filling in the bars, like this:




And it would weigh a ton.

The reason these ideas never go into production is because someone a lot cleverer than any of us has already thought about it and found reasons it won't work

p1p1092

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11/16/2017 10:11 AM

am-shaegar wrote:

Guys, I'm telling you, a 4130 stem would be awesome!

To solve the crushing of the bars issue, you can add a small filling in the bars, like this:




As I said above, the knurling wouldn't dig in to the stem at all. It'd weigh a ton and would have no worthwhile advantages over aluminium. It would be at very best, a great exercise in pointlessness.

Mishinn_Control

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11/16/2017 10:23 AM
Edited Date/Time: 11/16/2017 10:27 AM

am-shaegar wrote:

Guys, I'm telling you, a 4130 stem would be awesome!

To solve the crushing of the bars issue, you can add a small filling in the bars, like this:




p1p1092 wrote:

As I said above, the knurling wouldn't dig in to the stem at all. It'd weigh a ton and would have no worthwhile advantages over aluminium. It would be at very best, a great exercise in pointlessness.

While I agree, 100%, with p1p1092... you COULD possibly make a cr-mo clamp with serrations that could be matched to serrations in the bars to allow for micro-adjustments to the bar position while also minimizing slipping of the bars. That would keep the weight down. Again, doing so may just shift the stress point elsewhere on a crash & end up being catastrophic to a frame, etc..; You could also incorporate a "key" on the fork tube facing forward with a matching "keyway" in the aluminum stem block to take the guesswork out of alignment. It's all possible. For me, it's more a matter of "need". Does anyone really need these things or is the current setup perfectly fine?

Xxohioanxx

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11/16/2017 2:02 PM

am-shaegar wrote:

Guys, I'm telling you, a 4130 stem would be awesome!

To solve the crushing of the bars issue, you can add a small filling in the bars, like this:




"Hey, guys, I have a great idea. Let's try to solve these problems we don't have by introducing new problems."

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eskimojay

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11/16/2017 3:57 PM

I’ve never actually paid attention to the metal my stem was made from

ggallin422

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11/16/2017 5:03 PM

A chromoly block that size would weigh like literally 10 pounds. Get over the cromo stem. There's a reason things are the way they are. They would slip like crazy too. Until profile starts making stems out of 7075, I'll stick with 6065. I think they know what they are doing.

buttmeate

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11/18/2017 9:35 PM

grumpySteve wrote:

6061 because that's the industry standard for a reason. It clamps better. And the strength difference in a big chunk of material isn't greatly noticeable.

"And the strength difference in a big chunk of material isn't greatly noticeable." until you start driving holes and milling off edges of that piece of aluminum

wallride a bus everyday

grumpySteve

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11/18/2017 11:33 PM

grumpySteve wrote:

6061 because that's the industry standard for a reason. It clamps better. And the strength difference in a big chunk of material isn't greatly noticeable.

buttmeate wrote:

"And the strength difference in a big chunk of material isn't greatly noticeable." until you start driving holes and milling off edges of that piece of aluminum

I've never cracked a stem. I'm pretty sure the good manufacturers out there know where stress points are. They tend to break where the bolts are generally, and stems aren't machined out loads like they were 10 years ago