- I'm currently rehab-ing from a serious crash and have limited flexibility in my neck (amongst other issues). I've had to install a fork with longer steerer and put several inches of risers under my stem to elevate it (that I can gradually remove as and when my neck allows me to get lower again). I can't yet get onto the drops at all, even with those risers installed, so I'm riding very upright on the elevated tops all the time, pretty much in a MTB position. Added to that I'm 6'4" and wearing relatively loose jerseys. Using the photo technique, I estimate I have a projected frontal area of 0.57m^2 in this position and my Cd must likely be towards the high end of reported ranges (ie. c.0.8, I think that would be) as neither my shape nor surface is at all 'aero'. I estimate that would result in a CdA of about 0.550m^2 at sea-level pressures, yet the CdA that my cal ride files are giving me is 0.386m^2 - which sounds to me more like the figure I, as a long-armed 6'4" rider, might have gotten on the drops (no TT bars) of my road bike before my crash. It doesn't seem realistic for my current circumstances as described but its what my PP is saying.
- Having recently re-located, I am also riding on different roads than before - around the coast here they are mostly very rough chipseal with plenty of cracks, bumps, poor patching and loose chips, plus short sections of of dry gravel on some of my routes. I'm now running Rene Herse Babyshoe Pass ExL 650B 42s at 45psi front and 50psi rear in winter/spring (my frame gives a 45:55 weight split and the bike/rider package is 213lb) and planned to swap to Hutchinson Sector 700c 28s at 90psi in summer. I know these are low-ish pressures and I hope I will get the pressures up a bit too as the rehab comes along but for now too many bumps at high pressures are a pain in the neck (!) I can certainly feel the extra road drag compared to the decent surfaces I rode where I lived pre-crash, but my cal ride files are giving a Crr of 0.0136 for this setup, which sounds to me way too high - isn't that more like a figure for running MTB tires off-road in mud ? It doesn't feel like mud when riding on these and bicyclerollingresistance.com produces a Crr result of 0.00432 for the very similar Rene Herse Snoqualmie Pass ExL 44s. Admittedly, that Crr is when tested on brr's smooth steel drum (and at slightly lower per tire loading but at the same 50psi as I have). But should I really expect Crr to triple from 0.00432 to 0.0136 for the different road surface as described ? Is bad chipseal as bad as mud ? (I haven't yet swapped to the Hutchinsons, so don't have a cal ride figure with them as I want to get this setup profiled right first and have some chance of tracking my rehab progress across setups.)
The ride starts and finishes in the same spot, and within it are three segments ridden as O&Bs plus some connecting mileage. In case it helps for anyone trying to assist me, I can't see how to mark them as 'laps' or similar, so I've split these three individual O&B segments within the overall file out into 3 separate files; there are 4 files in total and the three O&B splits are attached to a follow-on post. Each O&B segment is 5-8 miles total. The first was selected because it is almost entirely straight, with side-wind at 90° for both O and B, and with a lot of wind-shelter from dense trees. The second and third O&Bs both start from the same beginning and turn round at the same endpoint but get there by different routes - the second one has cross-head/cross-tail wind on O and B respectively; the third one has a stretch with 90° side-wind and another stretch with direct headwind (O) and tailwind (B). Both were more exposed to the wind than the first O&B segment but the day's wind was unusually light and stable for my location, blowing at 10mph (according to the pre-ride local forecast and to post-ride records) with gusts of only 13mph. These are atypically calm/stable conditions here but I understood this is better for cal rides. The road surfaces were on average a little better than typical - there were some stretches with chipseal that's been throroughly worn down smoother, there was no recently-laid new chipseal, and there was no gravel. One thing I saw straightaway is that something upset the tilt towards the end of O&B #2. From the spot indicated that it happened I don't recall any particular event that did this. The PP didn't appear to notice it live as the watts shown on my head unit never stopped displaying, which is what I understood they would if the PP is spontaneously re-calibrating mid-ride. There are also a couple of points spuriously shown as braking - I think these are actually on the worst road surface sections.
To confirm the ride conditions, I know that I was not passed by more than a single vehicle on any of the O&B segments; they've each been exactly O&B around 3-4 miles each way; and were ridden with pretty consistent but light winds throughout the duration as far as I could tell. Given they're on rural roads without traffic, I've even been able to ride down the center line most of the time to make them as close as possible to literally O&B and to ensure that both surface inconsistencies and any wind-break from trees is more or less the same between O and B legs.
For each O&B the Isaac software shows the 'check calibration' needle in the green, so I assume that my PP does think the combination of these CdA and Crr figures consistently aligns with its sensor measurements, such that the calibration is correct and the calculated wattages are accurate. Is that what the needle means ?
I'd be really grateful if anyone can explain why/how the existing cal figures of 0.386 and 0.0136 and the wattages are actually likely to be correct despite the discrepancies with my estimates and expectations ? Or alternatively how to set starting values in a PP profile and calibrate it to come back with more plausible figures than those ?
Many thanks for any help and advice - much appreciated in advance.