15mm vs 20mm axles

ok, there are 2 aspects of bike design that generate remarkable interweb debate time, stunning really. chain stay length (fracking endless debate, i'm sure there are many guys out there actually losing sleep) and 15 vs 20mm axles.

unfortunately, i'm not a bike shop guy, a mtn bike journalist, nor remarkably wealthy and unemployed, so i only have a limited amt of experience on a few bikes. i've had no opportunity to ride identical bikes, with identical forks back to back, with only different axle diameters to isolate and critique. i do have 20mm axles on an otherwise basic xc fork on a 29er (reba 29er, 20mm axle), and a Totem fork on a freeride bike. clearly the one is insanely stiff compared to the other, but the bikes are apples and oranges.

anyhow, the local guru at the LBS says only in DH type forks would it even matter or be noticeable given the forces and speeds, but otherwise it's a wash for 6" forks. i have no idea, but if you think you have real insight and/or first hand experience as to how and why it makes a genuine difference please do chime in. if your expertise is something like "20MM RULES 4EVER FTW", etc, don't waste my precious time.

Betcha on a blind taste test nobody could tell the difference. As long as the hub itself doesn't flex, and as long as there is a decent clamping force onto the fork. I think that is where traditional qr can fall down, poor clamping force.

I haven't been able to conduct said test though.

ok, there are 2 aspects of bike design that generate remarkable interweb debate time, stunning really. chain stay length (fracking endless debate, i'm sure there are many guys out there actually losing sleep) and 15 vs 20mm axles.

unfortunately, i'm not a bike shop guy, a mtn bike journalist, nor remarkably wealthy and unemployed, so i only have a limited amt of experience on a few bikes. i've had no opportunity to ride identical bikes, with identical forks back to back, with only different axle diameters to isolate and critique. i do have 20mm axles on an otherwise basic xc fork on a 29er (reba 29er, 20mm axle), and a Totem fork on a freeride bike. clearly the one is insanely stiff compared to the other, but the bikes are apples and oranges.

anyhow, the local guru at the LBS says only in DH type forks would it even matter or be noticeable given the forces and speeds, but otherwise it's a wash for 6" forks. i have no idea, but if you think you have real insight and/or first hand experience as to how and why it makes a genuine difference please do chime in. if your expertise is something like "20MM RULES 4EVER FTW", etc, don't waste my precious time.

Opinions are like assholes, everyone has one, etc etc.

Having said that I have owned both a 5" 9mm Revelation and a 5" 20mm Revelation and the difference was huge. I have ridden my friends 15mm Revelation a few times and when you brake hard on a steep corner or come in to a corner hot you can feel it. Much the same way the 9mm flexed.

Now back to the back to the OP. The difference between 15mm and 20mm is not huge but it is noticeable. For the minute weight savings the 15mm axle offers it is not worth the loss of performance and another useless standard.

I am all for new ideas and standards when they move our sport forward.
I am not for new standard for the sake new standards and profit.

I run a DT350 20mm hub attached to a 36 Talas RLC 160mm 26er [HTML_REMOVED] a DT240 15mm hub attached to a 34 Talas RLC 29er.

I doubt with my weight and my riding style I can tell the difference between the two forks. Feel that wheel size, build quality and tire selection will attribute to more front end flex felt trailside than any loss of stiffness from a fork by either smaller diameter stanchions or axles.
I'd like to see some lab testing done though to see what the differences would be.

I will say this the Fox QR20[HTML_REMOVED]Fox QR15. Mentally I don't feel like the QR15 is as secure of a system, with how the axle threads into the adjustable nut on the fork lowers, plus the system doesn't allow for the QR lever to be placed in any direction like Maxle.

With the RS Maxle being the same system, there seems to be no point in the 15mm Maxle

This whole BC riding scene is a pretty small picture in the entire mtn bike industry

I'm searching around because I remember that Rock Shox posted some great data at one point on why they were not going to make a 15mm axle based on weight loss vs stiffness loss. I remember it was something like 15mm thru was 50% stiffer than 9mm QR and 20mm thru was 20% stiffer than 15mm thru. But there was only a 10g difference or something. Funny how they stood their ground for a while, then started making 15mm stuff.

I agree with ceebee though, I'm betting it would be really hard to perceive on the trail. I went from a 32mm talas with 15mm thru to a 36 talas with 20mm thru, but that's a pretty apples to oranges comparison. I think that 35/36mm fork chassis make more of a difference than axle diameter. That being said, I've got three sweet wheel sets built up on 20mm hubs that I would rather not have to convert back and forth to use on different forks. Gotta love bike industry "standards"…

I've been spending a lot of time on a 110mm 29er (same a-c as a 140mm 26") with a 9mm QR and big cones on the hub which claim to increase the stiffness of the archaic system. I wanted to hate it, and I do still think it's a weird spec choice, but to be honest it works just fine. 8" rotor, smashing descents, it's not a problem.

The 15QR vs 20QR debate is really based in the fact that 15QR systems don't have an external clamping function. It is an obvious, physical, perceived difference. But, the companies making the products and the elite athletes testing them have approved these changes. Conspiracy theories aside, these guys also like riding bikes with appropriately stiff front ends.

What we need is Giant to come in and debunk this like they did the road bike chassis stiffness argument. Yup.

It's a non issue. Crown flex is the only real stiffness issue with SC forks. See the 32.

Now chainstays length, that's a real argument. I think the industry is wrong. 450mm is perfect for a medium trail bike and should increase/decrease in proportion to the front centre on other sizes. All this chainstays as short as possible crap is a weight distribution disaster.

20MM RULES 4EVER FTW

plus the system doesn't allow for the QR lever to be placed in any direction like Maxle.

That ability exists. You can adjust the clocking of the QR lever with the indexing ring on the left side of the fork.

To me, there will always be 20mm for DH bikes. There will always be 9mm for road bikes. Do we truly need a third size? I don't think so.

Morgan, we need to test ride our Rebas back to back.

I switched from 9 to 15 mm Reba and honestly didn't notice much difference riding it XC. Really, how "stiff" can something be that has 100 to 160 mm of upwards travel designed in. I agree the hub, wheels and tires make a much bigger difference in ride ( which was my reason for the switch).

Sure, call me a hack. I'm fine with that ;)

Cunning stunts, I wish I could have bought your 20 mm Reba. I would have gone that way just to keep a common "standard" in my fleet.

15mm axles can only be used on flowing berm type trails. Recommended for XC and trail riding, can be used in some cases for AM riding.

20mm axles are for slow, chundery, old school trails with skinniess and drops to flat. Can be used for XC and trail riding but are way overykill. Recommended for AM, FR (but FR is dead), and DH.

DJ is just for punks so they can use what ever kinds of axles they choose, hell even a 9mm qr will work.

This should end the debate on axles standards and trails on the shore.

Damn I should have also tried to integrate headset and real axles standards as well.

Switching between forks and wheels is a pain, just pick one! God damn adapters :swearing:

That ability exists. You can adjust the clocking of the QR lever with the indexing ring on the left side of the fork.

To me, there will always be 20mm for DH bikes. There will always be 9mm for road bikes. Do we truly need a third size? I don't think so.

10mm through axles for road bikes is coming.