15 & 20mm axles?

[Oracle]

Seems there's a lot of press regarding the new 15 and 20mm front wheel setups over the old/standard quick release setups. From what I understand from it all, the larger axles are stronger, thereby making the lower of suspenion forks less prone twisting.

However, for general everyday trail riding, I'm wondering how much abuse would front wheel cop compared to the rear wheel? I've always thought the rear wheel/axle holds greater percentage of riders weight (especially when you consider most riders hang back behind the seat for gnarly decents), so wouldn't the rear axle be the more important of the two to upgrade from standard 9mm quick release to the newer 15 or 20mm setups?

Or have I got the whole concept wrong and the new 'standards' are simply about making the front forks less prone to twisting and not much else?

 

[RangaRMX]

Firstly, the rear doesn't have these sizes (15, and 20mm) the biggest you can get on a MTB, to my knowledge, is a 12mm axle, which is stiff enough for anything.

Secondly, generally the rear wheel is connected to a 'triangle' or whatever design or shape your bike has, a fork only has two legs, which aren't that far apart form one another, and is usually about 500mm away from the point of support, that being the crown of the fork and head tube of the frame.

A rear end, even with a QR skewer, isn't that prone to flex as there is a lot more structural rigidity factored in via the frame or suspension linkages. Some rear ends on dual suspension bikes can flex a bit, but this is generally because of the suspension design, not the type of axle used.

Back to the question, the reason they're better, and are becoming more common, is due to the increased strength and stiffness achieved by using a larger diameter axle.
There's less fore/aft movement, which is when the actual fork and wheel flex in a back/forward direction, greater lateral rigidity which is where the fork flexes less in a side to side fashion, you'll especially notice this when in a tight corner where you're leaning the bike over and the brake disc can sometimes rub on the caliper on QR forks. There is also much better torsional rigidity, which is where the fork legs can 'twist' so one can kind of move a bit forward and one can move a bit back, you'll notice this on hard hits where the front wheel deflects a little bit from a straight direction and can hinder steering response.
Hopefully I got all that right, feel free to pull me up anyone who knows more or knows if I'm giving false information.

Generally speaking however, unless you're really hammering it and you are prone to feel these differences (which will generally only occur once having ridden a stiffer setup) then you wont really have much of a problem, and can generally factor in a bit of rider caution to avoid some instances of the above occurring.
Personally I never had a problem with QR forks, that was until I got a bike with 20mm bolt thru axle, but now I probably wont own a QR equipped fork on a trail bike again, it does make that much difference once you're privy to it, and once you reach a level that you're giving your bike a bit more than it likes.
Some people don't ride that rough and may never really benefit from the increased stiffness and strength.

 

[Wiffle]

Seems there's a lot of press regarding the new 15 and 20mm front wheel setups over the old/standard quick release setups. From what I understand from it all, the larger axles are stronger, thereby making the lower of suspenion forks less prone twisting.

However, for general everyday trail riding, I'm wondering how much abuse would front wheel cop compared to the rear wheel? I've always thought the rear wheel/axle holds greater percentage of riders weight (especially when you consider most riders hang back behind the seat for gnarly decents), so wouldn't the rear axle be the more important of the two to upgrade from standard 9mm quick release to the newer 15 or 20mm setups?

Or have I got the whole concept wrong and the new 'standards' are simply about making the front forks less prone to twisting and not much else?

You're right on both counts-sort of. Thru axle forks are stiffer both laterally (ie legs compressing to different degrees) and tortionally (wheel/legs twisting relative to the crown) than a QR, and whilst that is all, it is difficult to exaggerate the importance of this. Bear in mind that in order to steer you either turn the wheel, or lean the bike. If the fork allows these things to occur independently of rider input, the bike doesn't go where you tell it to, and in rough terrain is easily misdirected in directions you're trying to avoid. Also bear in mind that a suspension fork, due to the very fact that it needs to be able to move freely, is very difficult to make stiff, so any improvement is a good thing and thru axles (and to a lesser extent thru bolts) make a significant difference.
As for the rear end of the bike, yes it does take the lions share of the hammering (as a general rule), but it is also much easier to make stiff (think square-section stays, big weld areas, cross bracing, etc) than the fork, so they tend to get left with a QR. Having said that, I think that given the ease of use of the RS Maxle 12mm rear "dropout", you will see more and more bikes in the next few years adopting a TA rear. In fact I don't know why ALL bikes with 140+mm of rear travel don't use a TA/TB rear end, it is such a simple way to gain stiffness without any real weight penalty or expensive manufacturing processes. Just my thoughts, hope it helps.

 

[Wiffle]

There's less fore/aft movement, which is when the actual fork and wheel flex in a back/forward direction.

Sorry Ranga, can't agree with you there. Stiffer stanchions and a better stanchion/crown interface can help reduce fore/aft flex, but a TA has no way of influencing the forces that cause this type of deflection. All they do is "tie" the ends of the lowers together better so that they both move simultaneously, not separately. When the fork flexes backward, the ends of the fork keep their position relative to each other, just not to the crown.

 

[RangaRMX]

Sorry Ranga, can't agree with you there. Stiffer stanchions and a better stanchion/crown interface can help reduce fore/aft flex, but a TA has no way of influencing the forces that cause this type of deflection. All they do is "tie" the ends of the lowers together better so that they both move simultaneously, not separately. When the fork flexes backward, the ends of the fork keep their position relative to each other, just not to the crown.

Ah, that's what I was trying to say, but couldn't get it out. I had trouble enough as it was, I generally don't say what I think as well as I think it.

I understand what you mean though, my mate has a set of Manitou Stances on his bike which are QR triples, which to me is not a good idea! Anyway, they do flex a bit less, fore and aft, than my forks (66s) due to having a more reinforced crown area, obviously because they're triples, but they distort a fair bit more and their torsional rigidity isn't anywhere near mine.
That being said though most forks that are single crown and have a fair amount of travel have a little fore/aft movement anyway I've found. It's just finding a good middle ground of what type of flex and how much of it a fork will exhibit.

 

[Oracle]

Great replies thanks guys. Realised I forgot to mention in my initial post whether the 15/20mm hub options were designed as being stronger (e.g. reduced chance of snapping/shearing) than a narrow 9mm quick release axle. Although, I can't say that I know anybody who has ever snapped a quick release axel as yet.

Hence why I was wondering why if the new 15/20mm axels are stronger you woudn't want to run them on the rear. But from your posts it appears they were designed specifically to stiffen the fork lowers. Cheers!

 

[madboy]

Well from what ive been told the 15mm axels are meant for lighter use I.e cross country. Were as the 20mm axels are meant to be the big beefy strong mf's which can handle DH and freeride.

 

[Wiffle]

Well from what ive been told the 15mm axels are meant for lighter use I.e cross country. Were as the 20mm axels are meant to be the big beefy strong mf's which can handle DH and freeride.

Yeah, but no. Whilst 15mm is designed primarily for XC and AM applications, 20mm can be everything from XC (think Maxle light, Magura 60-less) to DH/heavy freeride (standard Maxle, FOX 20QR, et al).
PS stop listening to Guns'n'Roses, its affecting your spelling...

 

[the tuck]

Could not help this, but I wish i had a bear in my mind wiffle LOL

 

[Wiffle]

Could not help this, but I wish i had a bear in my mind wiffle LOL

Sort of like a bird in the hand, but somewhat more invasive although maybe not as bad as "keep" in mind (seeing as how a keep is part of a castle). English is such a twisted language...