On the topic of front axles and forks.

Currently running 07ish reba at 115mm travel, 9mm qr drop, standard qr front hub.

I have a 9mm thru axle on’t way and superstar wheels.

I was molesting my front end in the kitchen seeing how much i could distort the forks/front wheel, it turned out i could distort them quite a bit, particularly when applying the front brake, the front wheel flexing to the side. I did the same to my other bike with lyriks, 20mm axle and taper steerer, virtually zero detectable movement.

I’m trying to be cheap, got the reba for free, keep on being tempted to splash out on some pikes with a 20mm axle, persuade me i don’t need the extra stiffness.

I know the 9mm thru will be stiffer than my current qr set-up, but a lot of stiffness with 20mm forks actually comes from the closed dropouts, so no matter how big of a axle you have in an open dropout, it can’t compete.

The bike is being used for xc, peaks, trail centres, bmx track, jumping.

Surely i don’t need 20mm axle on a relatively stiff short fork?

Am i just looking for reasons for better?

I wouldn’t touch QR with a 10 foot barge pole after seeing some of the horror stories.

of course you don’t “need” a 20mm thru axle
going from QR to bolt up 9mm will be barely noticable in terms of stiffness and neither will be anywhere near as a stiff as 20mm.

What you really need is a Fatbike, eh Bruce?

20mm is better but there’s still a lot of flex going on in the steerer and the slider brace.

Have some 20mm Rev Teams and you can see the sliders flex outwards on bigger hits.

i couldnt go back to QR now be honest after running 15mm qr – i love the extra security as my mates current 9mmQR keeps unding itself on some pretty rocky stuff – not good!!!

its not just that though its noticeably more stiff – if you live on a flat area with singletrack doubt you’ll notice any difference, however if you ride a lot of peak district stuff ala rocky – then yes you will notice a huge difference as did i….

what is this flex you all talk of?
the hub is there and i dont see how you get the hub to deflect due to the size of bolt you use- if it is flexing it is the fork that is doing it

Again I dont see what difference the size of bolt you use matters in this respect
I cant tell whether i am using my 20 mm maxle or QR fork tbh whether rocky or not rocky

The way a Thru axle is clamped/threaded into the dropout allows it to become part of the structure adding to rigidity/stiffness, they only really need to be oversized to achieve a stiff enough interface to be worthwhile.

You wouldn’t change the forks just for the axle, you might change the forks because you wanted the Pikes. You have 15mm bolt though option as well.

i found that my 9mm thru axel did reduce torsional ? flex, especially on drops and rocks, gnarly terrain etc

however i did notice more ‘fore and aft twang’ *
not sure if it was there before just didnt notice it

either way it did make the forks stiffer for ridding aggressively my 20mm 66s are rock solid though and not much of a comparison with my weedy 32mm floats

and my 9mm thru qr has never come undone!

* thats a term i read in a mag once

the 9mm superstar axles are steel, and pretty thick tube. 10mm helped on my back end, think i’ll try on front too. i get that back/forward twang but what can you do..
what i don’t like is they are slightly loose in the hope adapters. seems silly.

edit: no GW is right i think. a normal 5mm QR basically just holds the dropouts onto the hub. a thicker axle has more of its own strength to prevent the hub “parallelograming” between the drop-outs like this |//|

The way a Thru axle is clamped/threaded into the dropout allows it to become part of the structure adding to rigidity/stiffness, they only really need to be oversized to achieve a stiff enough interface to be worthwhile.

I am no engineer but i am sure when you clamp a QR it becomes part of the structure of the fork..anyway to get “flex” here you would need the hub to “flex or move” relative to each side. This ownt be happening

have you people heard of these two words

Placebo

Marketting

I am not trolling i genuinely cannot tell between forks

I am not trolling i genuinely cannot tell between forks

stop riding canal paths and hit up some gnar

rocketman – Member

Have some 20mm Rev Teams and you can see the sliders flex outwards on bigger hits.

Pretty rare that I’d be staring down at my fork sliders when taking a “big hit”.

Neither are me – that drop looks much much smaller on the bike tbh.


To the max [ well within riding distance of my house ] 8)

oh i’m scared

9mm forks caused that erosion?

dont need to be sacred i just need to be convinced there is any truth to the claims re maxle.

Insulting me may be fun but it wont change my mind 😛

Pretty rare that I’d be staring down at my fork sliders when taking a “big hit”.

Am familiar enough with some of the obstacles on my local loop to use them as test beds.

I replaced the 9mm QR on my jump bike with a solid cromo axle (nutted at both ends) a) because it broke, and b) be cause there was noticeable sideways flex in the front wheel on corners. The result is an axle which will be much harder to break. Didn’t really cure the flex completely though, which is likely to be coming from the wheel/tyre.

After having problems using qr’s and bolted sqewers with my DMR swop-outs,which are much fatter than normal drop-outs[lots of break squealing and judder going through the frame], I phoned mMR and they advised getting a thread tapped into the axle and using 6mm bolts directly into the axle.

End of problem! feels so much more solid than before , no squeal or judder and the brake feels so much more precise.

Done with qr’s now, going to do the same to front wheel and both wheels on the other bike, [which is running bolted skewers currently]

Apparently is something trials and dirt riders have been doing for ages,

unless you’re racing, whats the point of qr’s anyway?

Junkyard – Member
I am no engineer but i am sure when you clamp a QR it becomes part of the structure of the fork..anyway to get “flex” here you would need the hub to “flex or move” relative to each side. This ownt be happening

No, you’re not 😀 It does happen.

The skewer can stretch slightly (and only a small movement is needed to allow movement between the hub/qr clamping surfaces and the dropouts.

The 20mm design is fundamentally much stiffer.

Of course, that all said, I ride QR forks and they’re still fine but I would go for 15/20mm by preference.

unless you’re racing, whats the point of qr’s anyway?

Convenience mostly. Same reason lots of people have QR seat clamps or dropper seatposts.

I phoned mMR and they advised getting a thread tapped into the axle and using 6mm bolts directly into the axle.

What a brilliant idea!

that’s Bolt-in.. not sure it’s better than bolt-through through for stiffness.. (cue mass-debate). def. not for convenience (have to undo both sides to get wheel out!).

as my mates current 9mmQR keeps unding itself on some pretty rocky stuff

tell him to get some shimano QRs then – it is a well known problem with other designs of QR, especially when the QR lever is on the same side as the disc brake.

Given that it’s an ’07 Reba, and you’re riding trails, XC and suchlike, I’d say yes, 9mm is ‘sufficient’. The Rebas are going to flex a little anyway, regardless of axle.

Also, interestingly, I once had a ride with a guide who said he swapped back from 20mm to QR, because he found he just didn’t get enough ‘feel’ from the 20mm.

On the other hand, if you want some Pikes, and can justify the cost, why not?! 🙂

i couldnt go back to QR now be honest after running 15mm qr – i love the extra security as my mates current 9mmQR keeps unding itself on some pretty rocky stuff – not good!!!

He wasn’t using Hope QRs was he? That used to be their USP – self undoing!

Shimano QRs are 100x better.

QR deflection reasons-

1. The qr skewer is thin, is under tension, metal is springy, turn the wheel, moment is applied via rim/tyre to axle/skewer, the skewer stretches, this allows the hub to shift.

2. The dropout is open, when ever a load is applied to the axle to twist it, you essentially only have one half of the dropout preventing deflection, the droput will deform and allow movement of the hub.

3. Plates are poor structures for supporting loads, this is what a QR dropout is essentially, an open ended plate.

Reason for 20mm and 15mm stiffness-

1. The maxle is thick, there is more material to resist against stretching resulting in less stretch, less stretch constrains the hub better, resulting in less hub deflection.

2. The closed dropout, with the open dropout, there is a split in material, both sides of material can deform independently. with closed dropout, ALL material at the interface is sharing the load, not just one, flimsy side.

3. A closed dropout is essentially a tube, tubes distribute load very efficiently, think bike frames. Or else we’d be riding bike frame cut from flat plate if it made no difference.

A 9mm axle sorts 1, but doesn’t help with 2 or 3. There are other reasons for the stiffness too such as 20mm hubs, large bearings and many others.

I also want to add, you can equally argue at times you do actually want flex.

take the scenario of a rocky descent, take a 140mm+ full sus and a 100mmish hardtail.

The technique for the full sus is quite likely to be direct, straight, monster trucking, your wheels will hit into stuff, but it don’t matter, you got suspension to soak up the kinetic energy that may throw you off the bike.

Imagine the same on a hardtail, everything is 100% rigid, you hit something, it will seriously knock you off course or off your bike. Now imagine you have some flex, you encounter the same hit, it won’t impact on you to the same degree, material suspension as it were, who’s to say what is better? No doubt a design judgement the likes of Cy at cotic and brant at on-one have to make all the time.

normal QR skewer works in tension, force is transmitted from dropout through the bearing inner races, central tube to the opposite dropout.

ignoring the actual cam lever mechanism

5mm skewer has an M5 thread which can take the equivalent of about 7 nm in tourque.

9mm through skewer have an m9 thread which should take around 30nm (20 ish for an aluminium skewer)

maxles don’t work in tension, they are a pinned joint and incur bending forces. they are an axle, not a skewer (that only provides tension)

the superstar 9mm though skewer has the same cam lock lever as a 5mm
QR skewer, and thus transmits no more tension, would give no improvment in stiffness. (unless you have a very big thumb)
a 9mm through skewer with nuts at both ends would be better if you carry a spanner.

jono – design engineer.

a 9mm through skewer with nuts at both ends would be better if you carry a spanner

Oooh, now you’re talking. You wouldn’t happen to know anywhere that offers that in similar-to-Hope blue?!

Jono – Unless i have this seriously wrong, you say you can only tighten a regular qr and superstar qr to the same tension (i agree with this bit), you’ll have the same tension load, but different deflections in tension and bending due to cross section resisting deflection.

So you may have the same amount of “fixing load” in both scenarios, but each case will yield different deflections.

In my mind it isn’t the “fixing” load that is the issue, it’s the resistance to deflection or “stiffness” that is keeping everything straight.

deanfbm is surely right. imagine a thread of kevlar put under huge tension, being used instead of a metal skewer. same force holding dropouts together, obviously less stiff though. perhaps some are forgetting the benefit of simply filling all the dropout space with a single piece of whatever – the drop-outs cannot move as much relative to each other without bending said piece, so if you’ve used something that is itself stiff like a steel tube… job done right?

the 9/10mm is substantially stiffer in practice than 5mm, you can feel it. also worth noting that it’s cheap (if you already have suitable wheels + superstar QRs) so imho a great value for money upgrade, if you want to keep your old frame/forks.

But sometimes flex is good.
🙂

IMAG0420 by pten2106, on Flickr

i wanted to add to above, even open 9/10mm dropouts are quite thick/wide on alloy and magnesium frames and forks. maybe less so with steel, so whole thing less effective there. just not sure if you engineers above were factoring dropout width into this, that’s probably key. i mean length of each dropout along axle/skewer, not span between dropouts.

the 5mm and 9mm thru skewer should incuur no bending stress / force, only tension.

unless you have an interference fit between the dropout slot faces and 9mm skewer / hub boss. (you would struggle to remove the wheel in this case)

the 9mm boss on the standard qr hub only locates the wheel in the correct place, it should not provide any structure. if you measure the dropout slot it should be 9.0-9.2 ish and the hub boss/ 9mm skewer 8.9 ish. a good clearance, so the wheel can drop in and out in a jiffy!

get a good old steel threaded axle and 15mm chrome nuts on there for max stiffness!

so are we saying that the hub must flex as well with the smaller axle that QR uses, to allow the fork legs to move independently of each other?

If the hub is not flexing, and the smaller axle remains in the same place in the dropouts, then what is flexing?

If the smaller axles are moving in the dropouts because of the lower tensions from the QR lever, then why do we not see a lot of wear on the dropouts where the QR is clamped?

clamp a 9mm front axle facing outwards in one QR drop-out as tightly as you can. grab the fork leg and the axle end that’s not attached to see for yourself just how much movement there is.and more importantly how much the axle moved away from perpendicular to the fork leg.
Do the same with a Maxle inserted in the threads the wrong way and pre-loaded tight enough that it doesn’t rotate, the fork leg will still twist but the axle will remanin far clkoser to perpendicular to it.

Has this forum got even more stupid recently? Pinkbike users hove more of a clue these days.

no one’s denying 20mm is stiffer than any skewer. the question is where does 9mm skewer fall on the range from 5 to 20. this isn’t obvious at all, we’ve got responses from an engineer saying no better (!) to users saying loads better. it’s also about value, you might be able to go from 5 to 9 for about £20, but a whole new wheel and fork…
or what about 15mm, if i was buying a new fork i’d get that.

@TurnerGuy, i doubt chunky alloy hubs are bending. it’s mostly the “parallelogram-ing” between hub and dropout that i was talking about before: /||/