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Speed vs Power
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JaRok2300




Joined: 01 May 2014
Posts: 388
Location: Worcester, UK

PostPosted: Wed Aug 29, 2018 1:03 pm    Post subject: Speed vs Power Reply with quote

I did the Tri relays in Nottingham at the weekend and it's about as flat a course as you're ever likely to get, 3 laps of the rowing lake.

It was pretty windy and seemed to be blustery an changeable in terms of direction as I never really seemed to work out where it was coming from.

I averaged 20.4mph on 217W for 15km from a standing start/stop (NP 225W) (6'2", 16st, Litespeed Blade with USE Tulas and HED 40/60s)

Just wondered if other people had a ballpark speed to power figure on the flat for comparison.
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Jorgan




Joined: 12 Nov 2007
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PostPosted: Wed Aug 29, 2018 1:45 pm    Post subject: Reply with quote

There's a long thread on this on Slowtwitch.

Not quite like-for-like, but over an almost flat HIM bike (271m) I averaged 21.4 mph on 181w NP (169w Average) 72kg/182cm. I took it pretty easy tbh, and therefore had the first cramp free HIM/IM run in years Cool I should also note that I *probably* have an excellent aero position which helps, and use a full aero helmet & disc.

But it gives you an idea just how much harder you have to work to overcome your size; the impact of being 16st on an undulating or hilly course would be huge vs someone like me who's nearly 5st lighter than you.

Wind conditions notwithstanding.
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JaRok2300




Joined: 01 May 2014
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Location: Worcester, UK

PostPosted: Wed Aug 29, 2018 1:58 pm    Post subject: Reply with quote

Thanks Jorgan,

I remembered some data I'd collected on a flat stretch of road I frequently ride and that power should put me about 2mph faster. Maybe the wind and the rough surface (it was proper filling loosening in places) had more impact than I thought. (Plus sitting up for the tighter corners on each lap)

You're absolutely right though, that extra weight is a killer on the hills and running but is obviously a factor on the flat too. Just making a bigger hole in the air than necessary.
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Doca




Joined: 27 Feb 2014
Posts: 222

PostPosted: Wed Aug 29, 2018 2:04 pm    Post subject: Reply with quote

I also did the relays, you never got benefit of the tailwind as it was on the turn near transition where you had to slow so much for the turn.

I'm 184cm, 72 ish kg and averaged 42.1kph on 317NP (Specialized Shiv, Giro Advantage 2, Flo disc & flo 60 front, GP4000's with latex tubes & Tririg brakes & cockpit, Nimbleware speed suit).


Last edited by Doca on Wed Aug 29, 2018 2:40 pm; edited 2 times in total
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Jorgan




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PostPosted: Wed Aug 29, 2018 2:07 pm    Post subject: Reply with quote

Good to see someone else is still using the venerable Giro A2 Cool
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Doca




Joined: 27 Feb 2014
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PostPosted: Wed Aug 29, 2018 2:10 pm    Post subject: Reply with quote

Jorgan wrote:
Good to see someone else is still using the venerable Giro A2 Cool


Bought it on your recommendation actually & because it was cheap. I am wondering whether to upgrade to the Aerohead or P09 though which seem to be today's favorite go to.
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stenard




Joined: 04 Sep 2013
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PostPosted: Wed Aug 29, 2018 2:25 pm    Post subject: Reply with quote

Yeah, slowtwitch have a mammoth thread on this subject.

But to offer up some alternatives of mine, based on the "flat" races I have done this year... (I've added images where poss as the ST thread does that, and I find it helps put things in perspective - they're thumbnails you can click to enlarge)

Thames Turbo Sprint (early May BH)
21.7km, 36.4km/h, 213 AP, 220 NP

Southport Olympic (late May) - closed roads, but 4 dead turns
40.0km, 36.0km/h, 195 AP, 198 NP (only 7 days after a 70.3 and I was too tired)


100 mile TT (late July)
161km, 34.1km/h, 177 AP, 185 NP

IM Copenhagen (mid Aug)
179km, 33.6km/h, 163 AP, 170 NP


There was a position change between Southport and the 100TT/Copenhagen, but it was minor with a slight rotation forward and (I think) 10mm of spacers coming out of the arm rests. That said, I almost look more aero in the early picture as I was more focused on position, whereas I imagine I was just more relaxed in the IM.

I've slightly trended down weight wise over the season. But only fractionally. Probably from about 71.5 to 69.5kg. As Jorgan says, even on a flat course, in terms of "aero-ness" and the hole you punch in the air, weight can make quite a difference. As can kit, and the rolling resistance of the applicable roads.
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Last edited by stenard on Wed Aug 29, 2018 3:25 pm; edited 1 time in total
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stenard




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PostPosted: Wed Aug 29, 2018 2:38 pm    Post subject: Reply with quote

I've made a few references to it elsewhere, and I know Jorgan has commented on it recently, but best bike split is amazing for this kind of analysis.

If you ran your file through there, it would come out with a simulated cda, which you could then compare with others. That would be more interesting potentially, as it might highlight some significant things that could be changed, whereas getting more watts is obviously a much harder thing to do.
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JaRok2300




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Location: Worcester, UK

PostPosted: Wed Aug 29, 2018 3:03 pm    Post subject: Reply with quote

Cheers guys, I've seen the ST thread but that seems to be full races (IM & HIM) so there'll be some climbing even on a flattish course.

These are really interesting so far. I'd always thought weight didn't really matter on the flat but a very rough fag packet calc says 1W per kg.
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JaRok2300




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Location: Worcester, UK

PostPosted: Fri Aug 31, 2018 7:20 am    Post subject: Reply with quote

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JaRok2300




Joined: 01 May 2014
Posts: 388
Location: Worcester, UK

PostPosted: Fri Aug 31, 2018 7:39 am    Post subject: Reply with quote

Just snipped these from the website whilst waiting for rest of team to sort themselves out.

It's interesting that my position in these is a bit different to any static pictures I've done on the turbo. It looks like I'm sitting further forward on the saddle and have slid my hands almost off the front of the extensions.

When I fitted the Tulas they moved the cockpit back a bit compared to the Heds I had on previously so I fitted a longer stem to compensate. I'm now thinking longer extensions and get by elbows right forward on the pads as still looks a little scrunched.

I really want to keep the Tulas but may have to go back to the Heds if that doesn't work.
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JaRok2300




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Location: Worcester, UK

PostPosted: Mon Sep 03, 2018 8:11 am    Post subject: Reply with quote



Soooo, I loaded my file from the relays into BBS and got the attached. I don't profess to know much about aero values but that looks way too low to me.
The actual graphs it produces seem tk have disappeared now and just left those values in the bike profile.
Any idea what I might have done wrong?

Edit: Not sure if that snip has come out clear enough but it's in the 0.18/0.19 range at all yaws.
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stenard




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PostPosted: Mon Sep 03, 2018 8:30 am    Post subject: Reply with quote

Yes, I'd say 0.18x cda values are way too low.

What settings did you choose when you set up your bike? Things like your weight, bike weight, wheel choice for it's CRR estimations etc, can all have an impact. I'm always generally conservative with the road surface option too ... for the UK I'll never pick anything above "average", often selecting "poor".

For ref, my flat numbers are 0.23x down to high 0.22x numbers. Climbing is c0.37x type numbers. You'll only get a true figure for the latter on a hillier course however. Those numbers have predicted some pretty accurate estimates of my real longer course performances. I tweak them every now and again as well, if I change kit, or change position. I try to avoid letting the analyser make big shifts to the numbers though, as I know that's unlikely in reality.

Ultimately, the software is taking a lot of variables, attempting to fix those it can, and ideally just fill in the gap being cda. So it will need to know power data, course profile, weather, bike and rider info, and then infer cda. So anything that's "incorrect" data in the other things will cause the cda number output to be off. So if your PM misread, or you've underplayed the CRR of your tyre choice, or the road surface, then cda will be super low to compensate.

You only get two or three chances to run the aero analyser on the free trial, so if you still can't get it to work, I don't mind quickly setting up a new bike profile and running your file through it will some data you provide to figure out what might be going askew. There's definitely something not right, as the simple speed and power numbers we were sharing at the outset show that your cda should be quite a bit higher to result in lower speed numbers for similar power outputs.

EDIT - my rolling resistance of the bike is listed as 0.005380. What's yours? To be honest, I have no idea if that's sensible, but as I say, my cda numbers and predicted times have been reasonable with that number having been determined by BBS
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JaRok2300




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Location: Worcester, UK

PostPosted: Mon Sep 03, 2018 9:17 am    Post subject: Reply with quote

Yeh, I was expecting something nearer 0.3 than 0.2.

My rolling resistance is the same as yours and Mechanical Loss 0.032/

I was pretty cautious on all the values, put the surface in a cracked pavement, position as recreational etc.

I'm wondering if it's elevation related as although it was pretty much flat the graphs did show some elevation changes from both my Garmin and the corrected elevation data from BBS.

Given my weight if it thinks I'm going uphill more than I am it's going to think I'm as aero as a bullet to make up for it!
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Jorgan




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PostPosted: Mon Sep 03, 2018 9:34 am    Post subject: Reply with quote

Did you upload the workout file from the desktop Connect or Mobile app? Can't see a way to do it on the App, and desktop site is filtered at work.
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