This is oriented for road bikes. I have had a couple guys who are good road racer types tell me that they feel through axel system are noticeably more stiff than conventional skewer’d bikes. Anyone with insight or thoughts please chime in.
FWIW: I don’t have any recent basis for comparison. Have a 2015 Domane disc and I’ve done plenty of 40+ mph descents in the Sierras and it’s rock solid at ~95kg loaded weight. I ride a lot of crappy roads and have double flatted and been handed more than my fair share of sidewall blowouts.
The through-axles create a more rigid system, especially at the front fork. The front forks themselves are often stiffer also to deal with the additional forces of disc braking.
The cyclingtips article at (https://cyclingtips.com/2015/10/road-bikes-are-headed-towards-through-axels-but-why/) goes into more detail as to why.
Always had skewers until my latest bike (system six) so I’ve got about six months on through axles now. It’s still a tough comparison because this bike is my first for lots of things and it’s hard to compare just that one aspect of it
That said - the bike does feel very stable and handles like a dream - I just can’t tell you how much of that is the frame vs the through axle
The main reason for through-axle on road bikes is to resist the higher forces generated by disc brakes. As the brake pads are about a quarter of the way from the axle to the rim, you need approximately 4x the force to generate the same braking moment as a rim brake - and get 4x the opposite reaction on the axle/frame interface, often in the wrong direction as well (i.e. pushing the axle out of the frame). So the answer to your question is - it’s not so much about stiffness as about keeping the wheels on the bike. This said, it does create a more rigid frame/axle interface than skewers, as the interface is larger and the axle stiffer.
Thx all. I rode with some more guys last night. What I’m generally hearing:
- Stiffer for sprint acceleration.
- Back end was stiffer.
- Front end was stiffer.
- Noticeably faster descending…meaning through the turn (not braking).
No objectivity to this so YMMV I reckon.
I understand the reasoning for the design with disc brakes…this stiffness (mainly what I’m after) is a byproduct of the design. I don’t think anyone designed the disc/through axel to aid in sprinting or corning. More it’s just what guys/gals are experiencing as an extra bonus if you will.
Tldr: marginal stiffness differences between 12mm and QR non suspension forks. Only noticeable with suspension and 15-20mm axles.
How are they comparing directly to QR disc brake bikes with the same firm stiffness though?
Like I said 100% subjective. I assume they are comparing a previous bike with skewers to a current bike with through axels…but, I didn’t ask.
For the 2018 race season I rode a rim brake Specialized Allez Sprint, and in the fall, I built up a 2019 Allez Sprint Disc bike. When I first rode the bike, I was overwhelmed with how much feedback I was getting while riding (bumps were more jarring, no brake rub whilst out of the saddle). I do believe the disc brake model is stiffer with the addition of thru axles (12mm front and rear)
the fork has to be stiffer to account for the disc caliper forces though. You’d have to compare a QR vs a TA disc but I can’t think of any bikes that made the transition within the same model generation. Maybe comparing a CAAD10 disc vs CAAD 12 disc but there were also substantial changes made there going from post to flat mount etc.
From a mechanical engineering/materials science standpoint the two benefits of the through-axle design over the skewer are: 1) wheel alignment and 2) resistance to torsional forces. Wheel alignment is not the the subject of this thread, so I’ll skip my view here.
Regarding (2), there are 3 forces acting on a bike - horizontal, vertical, and torsional (rotational). Impact (flex in frame) due to horizontal and vertical forces at either the front or rear wheel are likely to be extremely small (unnoticeable) due material choice, wheel/skewer-axle interface differences, or shape (thinner skewer vs wider through axle).
Regarding torsional forces, the greatest noticeable impact would be at the crank/bottom bracket interface. Other points of rotational impact are at the wheels and seat/seat-post (to the extent there is flex available). At the wheels due to the frame/skewer-axle interface there is significantly less opportunity for flex due to rotation from a through-axle design vs a skewer design. The 2 two applications mentioned above (sprinting and descending) can be narrowed to sprinting while using a widely swaying action (i.e. not seating sprinting) and on sweeping technical descents (i.e. not straight line).
FWIW: My Roubaix uses skewers and my Tarmac uses a through axle design. Both have the S-Works bottom bracket/cranks. There is a noticeable stiffness and performance difference in both applications I mention above, but truthfully I couldn’t separate the differences attributable to frame design, wheels (CLX 40s vs 50s), or wheel-to-frame connectivity.