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Disc brakes go into wind tunnel at Specialized
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Check out the video here: https://www.youtube.com/watch?v=HXQuSnKkS-I

8 seconds over 40 km, I expected the delta to be much higher.


My other thread about disc brakes.






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Re: Disc brakes go into wind tunnel at Specialized [Ironwimp] [ In reply to ]
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I'm surprised by how small the delta was. Perhaps with a bit of optimization (such as where they placed the caliper on the rear dropout) this could be workable for tri bikes.
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Re: Disc brakes go into wind tunnel at Specialized [GreenPlease] [ In reply to ]
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GreenPlease wrote:
I'm surprised by how small the delta was. Perhaps with a bit of optimization (such as where they placed the caliper on the rear dropout) this could be workable for tri bikes.


That doesn't match the Culprit data.

Apparently Velo has a test just published (Jan. issue not available online yet) on this as well...will be interesting to compare.

Edit: it also doesn't match reports from Damon Rinard as well.

http://bikeblather.blogspot.com/
Last edited by: Tom A.: Dec 9, 14 19:16
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Re: Disc brakes go into wind tunnel at Specialized [Tom A.] [ In reply to ]
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One thing to note, it appeared that the disc tarmac was DI2 where as the non-disk was mechanical.
External cable routing around the head tube could be a factor.

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Re: Disc brakes go into wind tunnel at Specialized [Ironwimp] [ In reply to ]
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Ironwimp wrote:
Check out the video here: https://www.youtube.com/watch?v=HXQuSnKkS-I
8 seconds over 40 km, I expected the delta to be much higher.
My other thread about disc brakes.

I wonder if the drag penalty is the same when they yaw the disc brakes away from the wind (assumed they only yawed in one direction for the test as the video shows). This would expose the discs to dirty-turbulent air passing through the spokes/hub/fork.

I am all amazed at how close the results are.
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Re: Disc brakes go into wind tunnel at Specialized [Tom A.] [ In reply to ]
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Tom A. wrote:
GreenPlease wrote:
I'm surprised by how small the delta was. Perhaps with a bit of optimization (such as where they placed the caliper on the rear dropout) this could be workable for tri bikes.


That doesn't match the Culprit data.

Apparently Velo has a test just published (Jan. issue not available online yet) on this as well...will be interesting to compare.

Edit: it also doesn't match reports from Damon Rinard as well.


I find this strange too. After spending a few hours in the San Diego Low Speed wind tunnel. Culprit data can be trusted. Rims were the same, only disadvantage was the front wheel was slightly out of true. Keep in mind, croz blade ran an integrated aero brake front and rear, whereas speciialized ran normal rim brakes versus disc. This will create a bigger disparity.But most other factors remained the same. Maybe the cable routing on the Croz Blade for disc brakes, (Generation 1) wasnt as fast. We are now on Generation 3. Which we havent taken back to the tunnel. But yes, it does not match my data. It is strange. data can be found here
http://road.cc/content/feature/83327-disc-brakes-v-rim-brakes-which-are-more-aero


I was using same hoods and using an Ashima brake caliper, since no one had road Hydraulic ready at this time when testing was done in 2013.


Will be curious to see Velo Data. I hope drag gets closer to this claimed 8 seconds if true. If so. there is no reason for anyone not to ride road disc.
Last edited by: culpritbicycles: Dec 9, 14 21:58
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Re: Disc brakes go into wind tunnel at Specialized [Tom A.] [ In reply to ]
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Tom A. wrote:
GreenPlease wrote:
I'm surprised by how small the delta was. Perhaps with a bit of optimization (such as where they placed the caliper on the rear dropout) this could be workable for tri bikes.


That doesn't match the Culprit data.

Apparently Velo has a test just published (Jan. issue not available online yet) on this as well...will be interesting to compare.

Edit: it also doesn't match reports from Damon Rinard as well.

This isn't the first test by Spesh that does not match earlier data.
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Re: Disc brakes go into wind tunnel at Specialized [Tom A.] [ In reply to ]
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Couple big surprises coming out of the Win Tunnel. This, shaved legs - anyone corroborating these results in the field or other tunnels?

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Re: Disc brakes go into wind tunnel at Specialized [xtrpickels] [ In reply to ]
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xtrpickels wrote:
One thing to note, it appeared that the disc tarmac was DI2 where as the non-disk was mechanical.
External cable routing around the head tube could be a factor.

I believe superdave quoted something around an 8 watt difference between Di2 and mechanical setups. If this holds for these tests, then disc brakes are still allot worse.
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Re: Disc brakes go into wind tunnel at Specialized [Cajer] [ In reply to ]
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That was actual frame differences between mech and di2 ar frame sets. Still not sure that's the number but it's not just the wires.
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Re: Disc brakes go into wind tunnel at Specialized [Ironwimp] [ In reply to ]
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We (November Bicycles) ran the same test at A2 in August, using a rim brake Tarmac and a disc brake Tarmac that were otherwise as identical as they could be. They have some inherent differences - hood shape is different because of hydro reservoir, the brake lines are different, the front wheel has four more spokes laced 2x instead of radial, the disc bike wheels have discs - but they were as equivalent as possible. Velo arranged the bikes with Specialized, we brought the wheels and booked and paid for the tunnel time. Velo has published the results in their January issue, which just dropped Monday. The results were sent directly from A2 to Velo, and we had zero input on the article, having seen it only on Monday after it was published.

Our results were a little different than what Specialized shows. They tested with a rider, we tested without. This is entirely my faulty, as apparently I move around all over the place and an a terrible tunnel test dummy rider. With or without rider, the general directionality and magnitude of the results are similar (just a lot fuzzier in the case where I'm the rider). The lack of a drive side test in Specialized's test is the big difference between ours and theirs. I have to leave it at that for the moment.
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Re: Disc brakes go into wind tunnel at Specialized [Ironwimp] [ In reply to ]
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These are the same guys who found that shaving your legs is worth 15 watts, right???

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Re: Disc brakes go into wind tunnel at Specialized [November Dave] [ In reply to ]
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Can you ask Velo why the digital edition isn't available yet? One would think that would be ready to go well before the hard copies are printed :-/

http://bikeblather.blogspot.com/
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Re: Disc brakes go into wind tunnel at Specialized [November Dave] [ In reply to ]
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Oh...and did the Velo test have the same Di2 vs manual shifting difference?

http://bikeblather.blogspot.com/
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Re: Disc brakes go into wind tunnel at Specialized [Tom A.] [ In reply to ]
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We were provided with bikes that did have the Di2/mech difference. We removed cabling such that the only remaining differences were the shape of the shifters (disc shifters are always different from rim shifters, Di2 or no) and the other parts that are inherent differences between rim and disc setups. We went so far as to rewrap bars so that both bikes used the same bar tape. The bikes were net equal in our test.

I'm sure they'll have the issue ready for download today or tomorrow.
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Re: Disc brakes go into wind tunnel at Specialized [Runless] [ In reply to ]
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Runless wrote:
That was actual frame differences between mech and di2 ar frame sets. Still not sure that's the number but it's not just the wires.


No, it was for just the wires (7w @ 25mph.) The Felt AR runs the di2 cable into the top tube on both electronic only and mechanical frames which is slightly more aero than downtube routing such as the Tarmac.
Last edited by: Dunbar: Dec 10, 14 9:30
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Re: Disc brakes go into wind tunnel at Specialized [November Dave] [ In reply to ]
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Was Dave still there when you ran the tests?
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Re: Disc brakes go into wind tunnel at Specialized [Tom A.] [ In reply to ]
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Tom A. wrote:

That doesn't match the Culprit data.


This scenario doesn't seem unusual, unfortunately. I had a conversation with an engineer from a prominent wheel manufacturer who said they couldn't replicate wheel test results between A2 and LSWT. And that was a much simpler test. He concluded that one of the tunnels was "wrong," but I'm not sure he had any conclusive evidence to base that on.
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Re: Disc brakes go into wind tunnel at Specialized [James Haycraft] [ In reply to ]
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I was there for his last day, in fact.
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Re: Disc brakes go into wind tunnel at Specialized [Tom A.] [ In reply to ]
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Tom A. wrote:
GreenPlease wrote:
I'm surprised by how small the delta was. Perhaps with a bit of optimization (such as where they placed the caliper on the rear dropout) this could be workable for tri bikes.
That doesn't match the Culprit data.
Apparently Velo has a test just published (Jan. issue not available online yet) on this as well...will be interesting to compare.
Edit: it also doesn't match reports from Damon Rinard as well.

Keeping things as "similar" as possible closes the gap, but of course making the difference as large as "best" or currently optimized designs reveals a different "truth".

It is not unlike the guys quoting the weight difference between Ultegra Di2 w/ caliper brakes and rim brake wheels and Ultegra Di2 with R785 hydro brake calipers + disc brake rims. This gap will be smaller than the lightest rim brake set up vs. the lightest discs.

-SD
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Re: Disc brakes go into wind tunnel at Specialized [SuperDave] [ In reply to ]
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Differences in tunnels shouldn't count for that much here, since we aren't trying to compare what happened in one tunnel directly to what happened in another tunnel. We're trying to capture what happened in one tunnel versus another thing that happened in the same tunnel.

Just testing the disc side, and only out to 10 degrees, is a big shortcoming. Willful misrepresentation? Not for me to say.
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Re: Disc brakes go into wind tunnel at Specialized [November Dave] [ In reply to ]
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November Dave wrote:
Differences in tunnels shouldn't count for that much here, since we aren't trying to compare what happened in one tunnel directly to what happened in another tunnel. We're trying to capture what happened in one tunnel versus another thing that happened in the same tunnel.
Just testing the disc side, and only out to 10 degrees, is a big shortcoming. Willful misrepresentation? Not for me to say.

Ok. If the differences in test data collection has an error of 10% vs. 1% I might suggest that they do in fact count for much.
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Re: Disc brakes go into wind tunnel at Specialized [SuperDave] [ In reply to ]
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Sure, but I don't think they do. The focus seems to be on the Specialized test showing a smaller difference. That is explained in one shot by knowing that they only tested disc side, out to 10*.
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Re: Disc brakes go into wind tunnel at Specialized [November Dave] [ In reply to ]
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November Dave wrote:
hat is explained in one shot by knowing that they only tested disc side, out to 10*.

Was it out to 10 deg. or *at* 10 deg? I had assumed one angle, but could be wrong.
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Re: Disc brakes go into wind tunnel at Specialized [trail] [ In reply to ]
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Out to. They talk about them being the same at zero - they show side by head on shots at that point in the vid.
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