Does coast down use wind speed for instructions?

[EHB]

I had some failed coastdowns last weekend. On each occasion the display said I was at 20MPH. I'm confident I wasn't as it was way too easy and then when I was going so slow I felt unstable it still said > 8MPH. On reviewing the files I wasn't at 20MPH when the device told me to coast. What was at 20MPH was the wind speed (bike compared to air) as it was a really windy day.

I'm going to try again tomorrow evening, in the dark as the prediction is of 6MPH only winds in the evening. I'm sure the instructions say not to attempt coast downs on windy days but where I live there is rarely no heavy rain or wind when I am not at work.

Either way it doesn't explain why the device said 20MPH when I wasn't. For my repeat tomorrow I will also take a Suonto Ambit 2 to gather ANT data simultaneously.

[Velocomp]

Please post your ride file.

[EHB]

Will do. Sadly 14MPH winds so delayed till tomorrow (predicted to be 4MPH)

[Velocomp]

Coast downs can be tricky to do.

I would wait until the winds are calm.

[EHB]

I've attached one of the coastdowns. No error this time. Wind was about as quiet as it ever gets. As you can see I don't get to 20MPH, It didn't feel like 20 either. It felt like I'd only just started. Even the air speed is not 20. I promise it was telling me 20 and that was when I stopped. If you look at the DFPM you'll see the power; it isn't high enough for 20MPH either (rubbish training bike and [my usual training] baggy MTB clothes).

I can calibrate to the DFPM but would like an accurate CRR so the live aero resistance was accurate. Thanks.

[Velocomp]

Your profile shows that the total weight of bike + equipment is 41 pounds. Is this correct?

Are you using 700 x 23C wheels?

Please do a 3 mile out-and-back ride (not a cal ride).

[EHB]

sorry for the slow reply. Working away from home a lot.

Does it matter how long this cycle is as long as it returns where it started?

I have a 'zero day' on thursday and hope to go for a cycle (depends on when a delivery of xmas presents arrives relative to sunset).

Regards the weight. The total me+bike+stuff weight is correct. It maybe that much as it is crap training bike + mud guards + puncture proof tyres + pannier rack + four lights + two water bottles + big seat post bag + chest/elbow/hip body armour + off road helmet + flappy MTB clothes + phone + touring shoes/pedals. It is training so I don't mind making things a bit harder. Will double check what proportion of the total is me though. Don't think it should effect the maths too much though as the total is correct - I double checked when converting it to pounds (I use Kg).

[Pete]

41 lbs is only 18.6kg
Assuming you got divide & multiply the wrong way around, correct weight is 90.2kg
Which is actually 198.44 lbs.

[EHB]

I'm hoping we are talking about different weights now. I don't fancy much cycling up hill with a 90Kg bike. I still haven't weighed myself as I lee forgetting to take the scales back up to the bathroom. Will do so now. Here' a 10 mile ring. I've also attached a .fit file of the same cycle, although started and ended at slightly different times. Unfortunately my post was late so I didn't get to go for a proper cycle.

10 mile circle 4 upload.ibr

(439.32 KiB) Downloaded 270 times

it only seems to allow one file

[EHB]

the forum software doesn't seem to like .fit files

[EHB]

did the ibr. file look ok?

Limited to what further testing I can do at moment as have an achilles tendon injury that won't go away. Can do short runs. Also snowy outside. Dont know what effect that would ave on the numbers. It is either snow or salted sludge.

[Russ]

Hello EHB,

I took a look today, waiting for the roads to dry

I did a return to original download and then did a check cal without the DPFM,
then I cancelled that and did a check cal with DPFM and both are close to each other.
Your wind cal would seem to be close enough, unless the wind changed during your ride
or unless your wind zero was off significantly.

Your tilt correction was close enough for a start and Newton will fixup that anyway during a ride.
The questions still unanswered were wheel size and weight, if your total weight is correct, the split
between you and bike doesn't matter for the cal check, it matters for your ftp test and tss numbers.

Your CRR is possibly questionable and if it is off much will skew the CdA a bit. The estimate
for CRR choices appeared to be normal clincher on smooth pave. I believe you described tires that
may be of a higher CRR value and if the roads were not smooth then the CRR should also be pushed
upward by .001 or so for rough pavement but more for MTB off road. Search on this on the forum.

I wonder if you are in metric and confused about 20MPH during your coast downs? Your unit, in
this ride, looks to be performing speed info quite well, and for the two types of check cal to
be in close agreement says, to me, things are looking fairly good, except for the question of
the split or balance of CRR vs CdA in the total power calculations. At lower speeds this is
not as critical.

Regards,
Russ

[EHB]

Hi Russ,

apologies for the very belated reply. I had not realised anyone had replied to my post. Thanks for the advice. I will add the very small amount to the CRR as suggested.

The instructions for coast downs say 20 mph - I've checked the instructions. I am confident I wasn't doing 20mph relative to the ground when it told me to coast. 20kph maybe, but the instructions definitely use mph.

I've added some panniers to my training bike so I'll need to redo the coast downs for the new profile anyway. Hopefully tomorrow evening will not be too windy.