Larry's Tailbox testing on V20 & Magic

[LarryOz]

I have been busy the last month acquiring and building some tailbones for the Vendetta.
Today I tested:
#1 - Stock V20
#2 - V20 with standard Cruzbike racecase
#3 - V20 with M5 (21 ltr) tailbox
#4 - V20 with M5 tailbox and water bottle pod

All tests were conducted at the same avg power output of 2.3 Wt/Kg
Strava link: https://www.strava.com/activities/6347926513
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As you can see the biggest gain is adding the Cruzbike racecase, then an additional 0.16 mph for adding the M5 case with a bottle pod on it.
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Tomorrow I am hoping to test out a couple custom tailboxes I built.
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[JerseyJim]

I like how you got the M5 case to fit so well. The Cda reduction is significant for such a small change. Do you think filling the space behind your helmet and bottle pod would decrease the Cda further?

 

[vosadrian]

Great data Larry! The CdA suggests there is a bigger difference between the cases than the mph difference suggests.... maybe the wind changed between runs? Also, would love to see a test of the race case with vs without bottles fitted. I'm trying to workout if I should add something to mine up high behind the neck/helmet. Looks like the is some benefit between the 2 M5 case variants in your testing.

 

[Henri]

The CdA suggests there is a bigger difference between the cases than the mph difference suggests

I think, the CDA is just calculated from speed and power. So if wind changes, calculated CDA would change fitting to the speed. If the, seemed to drift, I would guess, it might be because average power was not not consistent power and there were differences in when and how the work was done. If my guess about how windsock works is correct, then that would be taken into consideration to calculate the CDA, but we can't see it in the figure for average power.

 

[vosadrian]

Mywindsock uses the local weather as part of the cda calculation. So if the local wind changed, it will factor into the calculation. But the wind it uses is not necessarily accurate for the exact location of the bike.

 

[Frito Bandito]

Those are great looking boxes Larry. They are actually big enough to hold stuff without being too large. Are you thinking of making and selling a few of them? If so, I'd definitely want to be on the list.
I have been kicking around the idea for a custom box similar to the one in your 3rd pic, but a bit shorter and taller that just reaches snugly up to the top of the head rest bars.

 

[LarryOz]

I like how you got the M5 case to fit so well. The Cda reduction is significant for such a small change. Do you think filling the space behind your helmet and bottle pod would decrease the Cda further?

It was not a simple task:
I reinforced the area where it attaches to the headrest by laminating CF on both sides. I had to build a special jig to hold pressure against both sides while the resin set.
I also had to fabricate an adapter.
In all, many hours of labor
You can see it below if you look closely.

The M5 box is not cheap though! $700 which included shipping from the Netherlands.

 

[LarryOz]

Those are great looking boxes Larry. They are actually big enough to hold stuff without being too large. Are you thinking of making and selling a few of them? If so, I'd definitely want to be on the list.
I have been kicking around the idea for a custom box similar to the one in your 3rd pic, but a bit shorter and taller that just reaches snugly up to the top of the head rest bars.

- I did buy an extra M5 tailbox in case someone else wanted one - but they are not cheap - $700 including the shipping from the Netherlands.
email me separately if you are interested and I will try and figure out what I can do the adapter and bottle pod for (larryoslund@gmail.com)

 

[ccf]

I have been busy the last month acquiring and building some tailbones for the Vendetta.

How about testing a Bacchetta Brain Box?

 

[LarryOz]

How about testing a Bacchetta Brain Box?

Send me one and I will test it!

 

[vosadrian]

I have a brain box you could test.... but would cost more to send it to you than sourcing one locally to you!

I look forward to seeing what you work out to be best Larry. I'm up to try a V2 of the box I made. First attempt was trying to keep it simple and learn working with carbon. I'm up for something more complex now, but not really sure how to make it the most efficient. It takes a lot of time and effort to build prototypes and test them as you are doing. Thanks for doing that for the benefit of us all.

 

[ed72]

Great testing. It does not surprise me the M5 box is only 0.08 mph faster than the Cruz box. Probably within the margin of error.

Was there any side wind?

Asking because I know my M5 box is not very good in side winds but I have nothing to really compare it to other than estimates of CdA on out and back routes. I don't trust the windsock CdA values, your average speed if power was constant is a good measure.

 

[LarryOz]

More testing with the 2 CF tailboxes I recently made on the V20

It looks like the bottle pods slow the bike down a tad.
The 11" box I built look to be just a little slower than the M5 with the bottle pods.
Note: These boxes were specifically designed to be attached to the Magic and are not really as aero as they could be (wind under seat) See next post showing how much more aero they are ont he Magic.
I will have to experiment with tipping the boxes to align the bottom of the box to the underside of the V20 seat and see what kind of difference is seen
pics:

 

[LarryOz]

Here is the data and testing from the Magic with the same boxes. In these tests too the pods on top are slowing that without.

note: 15" with bot pod - pos came loose and was flapping = reason for sign slower speed than expected
The 15" wide box increased the speed by 0.90 mph over the stock Magic
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pics:

 

[RojoRacing]

Didn't you have a thor seat with a dolphin box? or did the extra shoulder and head high of the thor make it a no go for you?

 

[vosadrian]

Now I am definately not an aero expert.... but is it possible that the curved edge on the back of the bottle pod is two sharp and causing the air to release in a turbulent way. Perhaps a vertical pointed trailing edge with the sides curving in at a more shallow curve to the point would release the air more cleanly? Actually vertical is not really the point. Just bringing it to a point curving it in from the rear most bottle? Kind of like a TT helmet.

 

[jond]

Gee whizz larry. Dedication . Great stuff. Thanks for sharing. You really are a cruzbike scientist mate.

 

[LarryOz]

Didn't you have a thor seat with a dolphin box? or did the extra shoulder and head high of the thor make it a no go for you?

I did Jason - but as you noted the seat is too large and stuck me farther up in the air than I like to when mounted on the V20 frame - so not as aero for me
The box was too large and did not meet the qualifications to keep the bike in the "unfaired" category. Still a great choice for someone who want a "ton" of room and likes the THor seat. I still have it if anyone is interested in buying it.

 

[LarryOz]

Now I am definately not an aero expert.... but is it possible that the curved edge on the back of the bottle pod is two sharp and causing the air to release in a turbulent way. Perhaps a vertical pointed trailing edge with the sides curving in at a more shallow curve to the point would release the air more cleanly? Actually vertical is not really the point. Just bringing it to a point curving it in from the rear most bottle? Kind of like a TT helmet.

Perhaps - I have about a dozen other bottle pods roughed out, but it takes a ton of time to carve out the bottle wholes for them . I will probably eventually test them, but I think I will build my wind tunnel first, as I think that perhaps the slight changes may not be that perceptible due to the route I have.

 

[jond]

Perhaps - I have about a dozen other bottle pods roughed out, but it takes a ton of time to carve out the bottle wholes for them . I will probably eventually test them, but I think I will build my wind tunnel first, as I think that perhaps the slight changes may not be that perceptible due to the route I have.

okay cruzbike ultra mad scientist 9 years in a row award. They pretty much broke the mould (British English spelling oem) with yourself larry. America has no mould lol. Gaol bird aussies can spell.