Why 15mm fork axles for AM/ENDURO are the DUMBEST THING IN THE UNIVERSE

[Damian Sanders]

Which would you rather have, the 15mm axles that are common on XC race bikes, or the 20mm axles common on downhill bikes?

The bike industry is run by a bunch of morons who only want your money.

[grabtindy]

You're totally right. Excuse me while I run down to the patent office to register a new 17.5mm axle standard.

[RootSkier]

Have you broken a lot of 15mm axles?

[Damian Sanders]

Have you broken a lot of 15mm axles?

I've never been dumb enough to run one.

[D(C)]

Axle diameter is just one design parameter that affects the torsional stiffness of a fork.

Aside from attaching the wheel, the axle has a similar function to the arch: resisting the legs from trying to twist around each other. If you think about the legs twisting around each other, there are a couple things going on with the axle: bending and torsion.

In terms of bending, while some bending may occur within the axle itself, I wouldn’t expect going from 20 mm to 15 mm to make a huge difference on a section as short as the axle. My bet is that the bulk of bending deflection happens at the axle-dropout interface. So if you make a more rigid connection at the dropout (longer axle-dropout overlap, thicker dropout walls), you minimize deflection.

For torsion, the axle is trying to twist on itself, and also within the dropout. While a thicker, larger diameter section better resists torsion, my guess once again is that the majority of the torsion happens from the axle twisting within the dropout. A larger diameter axle means more clamping surface area, and less clamping force needed to achieve the same degree of restraint. But assuming you could get enough clamping force, this extra surface area won’t matter.

The main advantage of through axles over standard quick release is that the clamping achieves additional bending and torsional fixity, but I don't imagine the diameter of the axle alone varying by 5 mm matters that much.

TL;DR – while multiple “standards” are annoying, you’d have to run the numbers on the fork as a whole before getting your panties in a bunch about performance.

[zion zig zag]

TL;DR – while multiple “standards” are annoying, you’d have to run the numbers on the fork as a whole before getting your panties in a bunch about performance.

Try and keep up. DS getting his panties in a bunch without reason is what he does.

[Damian Sanders]

Axle diameter is just one design parameter that affects the torsional stiffness of a fork.

Aside from attaching the wheel, the axle has a similar function to the arch: resisting the legs from trying to twist around each other. If you think about the legs twisting around each other, there are a couple things going on with the axle: bending and torsion.

In terms of bending, while some bending may occur within the axle itself, I wouldn’t expect going from 20 mm to 15 mm to make a huge difference on a section as short as the axle. My bet is that the bulk of bending deflection happens at the axle-dropout interface. So if you make a more rigid connection at the dropout (longer axle-dropout overlap, thicker dropout walls), you minimize deflection.

For torsion, the axle is trying to twist on itself, and also within the dropout. While a thicker, larger diameter section better resists torsion, my guess once again is that the majority of the torsion happens from the axle twisting within the dropout. A larger diameter axle means more clamping surface area, and less clamping force needed to achieve the same degree of restraint. But assuming you could get enough clamping force, this extra surface area won’t matter.

The main advantage of through axles over standard quick release is that the clamping achieves additional bending and torsional fixity, but I don't imagine the diameter of the axle alone varying by 5 mm matters that much.

TL;DR – while multiple “standards” are annoying, you’d have to run the numbers on the fork as a whole before getting your panties in a bunch about performance.

Wow, a bunch of handwaving. I'm thrilled. Do you even know how tube diameter relates to stiffness?

http://theteamrobot.blogspot.com/201...solutions.html

[shirk]

Did you just crawl out from under a rock??? The whole "get upset about 15mm" was a couple seasons ago.

[Damian Sanders]

Did you just crawl out from under a rock??? The whole "get upset about 15mm" was a couple seasons ago.

No, but I see no reason to stop being upset. I'm pissed I need to spend $700+ for a Fox 36 to stay with 20mm in a modern high end fork.

[D(C)]

Wow, a bunch of handwaving. I'm thrilled. Do you even know how tube diameter relates to stiffness?

http://theteamrobot.blogspot.com/201...solutions.html

Yeah, a bunch of handwaving. Sorry, slow day at work. But you get what I'm trying to say.

No question a larger diameter tube is stiffer. But if that stiffer tube is poorly clamped, you will still get a ton of deflection.

IMO you should be getting indignant about the lack of pinch bolt dropouts on the market, but not necessarily about axle diameter.

[kidwoo]

Did you just crawl out from under a rock??? The whole "get upset about 15mm" was a couple seasons ago.

Moral of the story: when something sucks just give it long enough and although it doesn't quit sucking, we're ADHD enough to just forget about it

[JeffreyJim]

Damian, I understand you are upset.

That said I've run both. On the exact same bike. On the exact same fork. On the exact same wheel. Guess what? I couldn't tell a damn difference.

And this is coming from a guy who is big and routinely complains of flex. You are whining about something that doesn't matter.

Sponsel is right, we picked the wrong standard. But what SRAM is really trying to do is get rid of 20mm all together. And with their boost shit they can get the stiffness they desire out of the 15mm interface.

Yes, that's right - don't be surprised when 20mm (for all applications) goes the way of 1.5 headtubes.

J

[kidwoo]

No question a larger diameter tube is stiffer. But if that stiffer tube is poorly clamped, you will still get a ton of deflection.

well first off that makes the 20mm forks WITH pinch bolts that fox is making look a lot more appealing in this realm than that new lyric

But that touches on something else that's pretty important. Bolt on bmx hubs are pretty damn stiff so yeah, it's not just a bolt diameter. But with the RS maxle stuff, you're not getting as good as a clamping interface. My front wheel between a new fox 36 and my pike is pretty significantly different flex-wise at the hub interface. You can see it. But like you point out, I'm not saying that's entirely the axle diameter. But if RS is going to use that pinner axle, they should at least get it clamped better. I'm more in the "RS sucks for this" camp more than the 20mm fo life camp.

[shirk]

Moral of the story: when something sucks just give it long enough and although it doesn't quit sucking, we're ADHD enough to just forget about it

Ohh hey look a squirrel.

[TahoeJ]

It's like the same thread over and over with slight variations...

[markcjr]

I thought my 2015 pike was stiffer than my past few years fox 36's. Maybe that had to do with the rest of the fork but it seemed to track better. I also had better wheels so maybe that helped too

[JeffreyJim]

I thought my 2015 pike was stiffer than my past few years fox 36's. Maybe that had to do with the rest of the fork but it seemed to track better. I also had better wheels so maybe that helped too

Interesting. I felt the opposite but just by a hair. New 36 is *absolutely* stiffer than the Pike. Lyrik though? That should be pretty close.

[grabtindy]

Yes, that's right - don't be surprised when 20mm (for all applications) goes the way of 1.5 headtubes.

J

Shit, my bike has both. No wonder I'm not getting any cover shots.

[Anospa]

Maybe I'm not sensitive enough or I haven't gotten my bike onto anything rowdy, but I just switched from a 2010 Lyrik to a Pike and I haven't noticed any real big negatives in terms of stiffness. I'm headed to VT for an enduro this weekend, that'll hopefully be a good sample point in the extreme noodle-ness of a 15mm axle.

My complaint is that they are switching to boost under the argument that its stiffer than a regular 15mm axle, yet is the same width as a 20mm axle! The reasonable part of me is into boost because that allows for 1 standard to hold true for regular and plus sized bikes for the next few years. Of course, when everyone realizes that riding around with heavy tires isn't super fun another new standard will come out.

[Damian Sanders]

http://theteamrobot.blogspot.com/201...solutions.html

Great comment from the above link:

"fuck undoing 5 bolts each time you want to take the front wheel off and load your bike in the back of a 2001 honda accord.

good thing about torque caps is that your old shitty wheel still works in there..." -dcamp


My old perfectly good 20mm wheel won't fit in there. And BTW, if we want the "advantage" of the "Torque caps"' added stiffness we have to buy a SRAM torque cap hub and build a new wheel, thus rendering the new gimmick not worthwhile even if we had our 15x100mm "old wheels from 2014". Is it that hard to make shorter Boxxers lowers with the 20mm axle and put them on a longer stanchioned Pike crown-streerer assembly + damper ? The Marzocchi 66 an 888 shared the same lowers (except for the QR/bolts) with different travel and it worked. But I get it, SRAM wants to make more and more proprietary stuff that works as a kit. More parts to switch = more money for corporations, this is how it works. This was not made for the customers, this was made to get money in the business.

You work for TREK don't you ? The company that asked SRAM to make BOOST 148 hubs instead of using 150mm and making it wider already. I had already ruled out Specialized for their corporate practices, now SRAM and Trek joined the blacklist for future purchases with their damn axle shit. (And shitty warranty service at SRAM.)

By the way, I have 150x12 axle and a 68mm BB on my Socom running a 1x10 drivetrain without any issues with chainline or q factor. Race Face has me covered with adjustable chainline cranks. I guess you're just waiting another 2 years to release BOOST 153 ? Fuck this. I'm not against change for better products (like dampers, tires, etc), I am against change for change. There was no stiffness (and weight now with torque caps) to switch from 20x110 to 15x110. As for the flanges width, they could have widened the flanges on a 20x110 hub and we could live in a better world.

End of rant.

[Damian Sanders]

Of course, when everyone realizes that riding around with heavy tires isn't super fun another new standard will come out.

Guess what? Modern light 26" wheels with 2.3" tires work the best for 99% of technical trail riding. They are the stiffest, strongest, accelerate/brake the best, are the most manuverable, roll over everything very well, allow long suspension travel without unnecessarily complex frame design, allow a stiff frame, and allow a wider tire with less mass. It truely is the superior wheel size, don't let anyone tell you it's not. Why would I want to pay lots of money to downgrade to an excessively large wheel or tire?

[bagtagley]

Are there no step-down axles available? As long as the face is large enough for the end caps to press against, that could work, no?

[Anospa]

Haha, we're just gonna go full on rant mode in this thread, and that's just fine with me!

I've only ridden a few 29er bikes, two 650b bikes, and a fat bike in a parking lot, so my opinion is a bit narrow I guess. But why do all these reviews keep gushing over traction for fat and plus bikes? I haven't wanted for much more traction than I'm getting now. Only times I've been in dire straights losing traction are flat out on ski slopes, and I think a fat bike would be running into a whole mess of different problems at that point.

Maybe I need to go faster, that's usually the answer.

[JeffreyJim]

Great comment from the above link:

Just so we are clear...

DCamp (David Camp) is an engineer at SRAM. He used to be an engineer at Trek. That may add up to "david camp loves introducing new standards" when nothing could be further from the truth. He's anti-new standard unless it really makes a material difference.

David is also faster/a better rider/smarter than any of you (when it comes to bike engineering). I promise. Watch for a top 20 in this weeks EWS if not better out of the pinner. Google him if you want a bit more background on who is fighting the good fight over there at SRAM

This whole axle thing is silly. I complained about the 15mm axle the day it was introduced. I still think we should have just kept the 20mm standard and called it a day. But the gram pinching XC guys want something as stupid light as they can get it, the lawyers (and riders) all want QRs gone and the engineers are plenty smart to make a 15mm interface stiff enough for any of us. What we don't need is two axle sizes when they are this incredibly close to each other. Its stupid. Ideally we can all agree on a few wheel sizes and one rear hub spacing/axle size and one front hub spacing/axle size. I realize we all think "man it was good as it was, why keep changing it"...current spacing came from...road bikes....30 years ago. What we are doing is a bit different.

I just hope smart guys think this one through so we can leave it be for at least 5-10 years!

Whoever said something about lack of pinch bolts is right. That's a real way to add stiffness over the current RS system.

[toast2266]

But the gram pinching XC guys want something as stupid light as they can get it ...

In lots of cases, the 20mm setups are lighter.