I run two bikes - SL8 with Quarq Dfour and SL7 setup for RBTT with Stages dual sided - the fit at the backend of the bike is identical, same crank length, seat height and setback, the RBTT bike just has a longer stem and narrow bars.
The whole reason I bought the Quarq Dfour in the first place was that the stages seemed a bit like a RNG at times. I have endless examples of it clearly not being consistent. I thought keeping a good battery in would mitigate the worst of it, but I’ve had a few hints that even then it’s not quite right, despite it only making it down to 98% by the end of the season.
There’s a correlation starting to form between my bad days and the days I ride this bike (I don’t use it for all RBTTs, mostly just the faster, flatter ones), latest was today’s 40km TT and out the gate I’m struggling to maintain 20w under my normal 16km TT power. So I’m assuming my legs aren’t good today - ride to feel for the rest of the ride and end up averaging 20w under my FTP, for 1hr, feeling spent at the line.
All until I see the MyWindsock CdA estimate 0.02 lower than the fairly consistent 0.245 I’d hold for a 20 min effort, despite absolutely holding my position worse, particularly after 40 mins. I know it’s just an estimate, many factors etc. but this is just a long way around of saying I think these seeds of doubt are unsustainable.
As an aside, if I model the course for today’s conditions with my usual CdA, I get my exact FTP within 1w.
TL;DR: What’s the best way to achieve power parity between bikes?
I can’t really go with pedal power meters - I use Speedplay and require a wide Qfactor (~61mm)
Is another Quarq likely to be consistent with my existing one?
Or am I better buying something like an Xcadey/Sigyei or other chinese spider meter and relying on it’s adjustability to match the Quarq?