thinline
Posts:323
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| 06/11/2018 09:35 AM |
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So, went to put a friend's brand new Trek Domane SL 5 in my car to go to a ride spot yesterday. I have a Ford Escape and have a 2x4 with two fork clamps mounted on it and just put bikes inside instead of on the roof. I went to pop off her front wheel, and well, couldn't. The release lever was closed up against the fork and was shut so tight I just couldn't pull it open and couldn't get my fingers around it because of the fork.
Then, I noticed it wouldn't have mattered. The bike did not have the typical skewer I am used to. The fork didn't have the upside down "U" for the axle to rest in. It had a hole that the axle fed into. So, it would not have mounted on my clamp anyway.
I got on line to try and understand these things and searching on "skewer" did not turn anything up.
I know someone out there can point me in the right direction!
Hope y'all are well and enjoying the miles.
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Cosmic Kid
Posts:4209
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| 06/11/2018 09:38 AM |
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It is a "thru-axle" and is now standard spec on bikes with disc brakes. There were incidents of wheels coming out of traditional QR dropouts when using disc brakes.
This is one of the reasons that limits adoption of disc brakes in professional road racing....there is still no "standard" for thru-axles and it significantly slows down a wheel change. |
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| Just say "NO!" to WCP!!!!
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Cosmic Kid
Posts:4209
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| 06/11/2018 09:40 AM |
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Good primer video here....
https://www.youtube.com/watch?v=4w6uqN_Pips |
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| Just say "NO!" to WCP!!!!
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thinline
Posts:323
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| 06/11/2018 10:01 AM |
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| Many thanks! I was puzzled. |
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79pmooney
Posts:3180
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| 06/11/2018 10:57 AM |
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I never "got" why the disc calibers had to be behind the fork with the resulting forces trying to lift the wheel out of the fork. Turn the assembly around, forward of th efork (and just like the rear wheel) and regular bottom opening drpouts like we have been using for 120(?) years work just fine. (Maybe not for the accuracy needed to avoid brake rub, but just fine for both safety and quick wheel changes.
This always struck me as one of those "duh!" moments except it seems that insight hasn't happened and won't. Everybody is way too invested in the in the caliper aft to pull their heads out of the sand.
Ben |
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Orange Crush
Posts:4499
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| 06/11/2018 11:07 AM |
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Ben - I'd venture to guess that's a matter of aerodynamics and aesthetics.
Thinline - thanks for the Monday morning laugh. |
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79pmooney
Posts:3180
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| 06/11/2018 11:30 AM |
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OC, UCI could have mandated the caliper be in front and they could have cited two safety reasons - the above and the calipers would now be (partially) shielding the hot and sharp rotors from frontal contact with fallen riders. UCI could have mandated that 5 years ago and let manufacturers scramble before anyone had a lot invested.
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Cosmic Kid
Posts:4209
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| 06/11/2018 01:38 PM |
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IIRC correctly from my product development days in the bike biz, it is primarily a rotor cooling issue. If you put the caliper on the front of the fork, you shield a significant portion of the disc from airflow around it, thereby reducing cooling forces around it.
This is an issue across all types of disc brakes, not just road bikes.
I believe superior braking forces also factor into it, as well, but could be wrong on that point... |
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| Just say "NO!" to WCP!!!!
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longslowdistance
Posts:2881
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| 06/11/2018 08:56 PM |
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| Motorcycles put the calipers behind the fork to protect the calipers and hydraulic lines from direct whacking and also wind driven stuff. Same logic applies to bicycles, at least mtb and cross.
Calipers in front might get a bit more wind (well maybe a little on a road bike), which would enhance cooling rather than impede. |
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Orange Crush
Posts:4499
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| 06/11/2018 09:17 PM |
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If you put them in front of fork they face the wrong way to get proper airflow for cooling (open part facing back).
And agreed with CK torque forces would probably be all wrong. |
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79pmooney
Posts:3180
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| 06/11/2018 11:59 PM |
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Hmmf. So the design challenge is a little stiffer. in cars, they shield the whole assembly with a car body, then add a whole bunch of weight for the brake to stop. Do ing as I suggested might have slowed the discs a couple of years. And allowed faster wheel changes, freedom from yet another standard.
This is something that if UCI had thought out, everyone would have figured a way to get on board. (They could also have said that they were not going to allow discs until there was one standard for all disc wheels; disc size and location and axle standard.) What we have now is a mess. I predict that a grand tour will be lost on a disc related slow wheel change.
Ben |
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Cosmic Kid
Posts:4209
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| 06/12/2018 08:30 AM |
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How is the current situation any different than when there was no cross-compatibility between Shimano & Campag? When Campag had 10 speed and Shimano was still 9 speed? Each team makes their equipment choices....there is no mandate to run discs. If someone loses a race because of a slow disc wheel change, that is on their equipment choice, not the UCI.
You can't really compare the discs in cars to the discs on bikes because there are massive differences, most notcieably the amount of fluid in the systems. With that much volume, it is much harder to get the braking fluid to overheat / boil. |
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longslowdistance
Posts:2881
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| 06/12/2018 10:08 AM |
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| Caliper in front: The open part would face down and slightly forward, matching the rotor, and get good airflow. Motorcycles tried this a few times during the transition from drums to discs back in the day. You may see it on a vintage moto.
I'm not a mechanical engineer, so I may have this wrong, but I don't see how it would make much difference regarding force applied to the fork: pull from the front vs. push from the back, but with a similar lever arm. |
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79pmooney
Posts:3180
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| 06/12/2018 10:48 AM |
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CK, I see the issues of brakes, especially front brakes as being quite different from the choices of gearing. The front brake is the most important safety feature on a bike by quite a lot. It seems to me to be entirely proper that UCI dictate a well thought out set of criteria to make both the safety aspects and the ability to change wheels cleanly (an item they provide through neutral service and therefore reflects on UCI).
And the cooling of the brake fluid? Well this is a system being designed from scratch. Once the parameters are set, it is up to the engineers to design a system that works. But a huge part of good design is setting the parameters. First look? We are looking at a machine that has evolved over more than a century and works really well. As a racing machine, one key element is the ability to change wheels fast since the tires so crucial to speed puncture so regularly. Vertical fork ends and quick releases accomplish this really well.
In races, crashes happen; usually involving more than one rider. Discs get very hot. Putting the calipers in front of the disc shields it a little.
So the design challenges get a little bigger? Isn't that what the engineers are paid to solve?
Now the horse is out of the gate. We are going to have to live with these poor choices a long time. UCI had its chance to get things off to a good start.
Ben |
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Cosmic Kid
Posts:4209
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| 06/12/2018 10:59 AM |
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As you note, they supply wheels through neutral service....but teams that made their own equipment choices that did not align with wheels available through neutral support were kinda SOL. I see no difference to the issue of teams wanting to use discs...there are performance advantages to them that also entail some risks. You evaluate the performance gains vs. the risks associated with that choice.
Even if the UCI set a standard for discs re: thru-axles, etc it doesn't change the fact that it takes longer to make the change...and thru-axles are essential to safety with discs. So your hypothesis that someone could lose a race because of a disc wheel change still holds true regardless of a universal standard.
There is no mandate from the UCI to ride discs.....those that wish to opt for the convenience and speed of QR's are still free to do so.
The reality is that discs for road have evolved pretty quickly (I noted several years ago that the lynchpin to this whole thing would be hydraulic brifters). Rarely are things "right" upon introduction. Refinement and adaptation are the hallmarks of product development as much as innovation.
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