Power meter for GRX cranks and flat pedals?

Does anyone know of a power meter that would work with GRX cranks and flat pedals? I’m 67 yrs old and, after 30+ years on road bike with SPD-SL clipless pedals, switched to a ‘do it all’ dream bike that I ride all year round (multiple tires & wheelsets) including Wisconsin winters (650b 2.25” studded tires). 

I’ve REALLY started slowing down the past few years (never was all that fast). So, for the 1^st time, I’m trying to train instead of just ride. Did my 1^st interval ride and discovered what they say is true, heart rate doesn’t work well. Takes way too long for my HR to respond to changes in effort, and it stays constant even when I can tell I’m working less hard (e.g. on a slight downhill). 

Would appreciate any ideas.

I would think a left crank arm power meter from Stages or 4iiii would work. I couldn't find one for my wife's Warbird with GRX last year and ended up getting a Stages Ultegra arm that someday I'll change out to get the correct offset, but it is very small at 2.5mm. 

stu wrote:You could use a simple speedometer or GPS app to compare your speed to previous efforts.

BTW my speed fell off a cliff about the time I turned 70 and I wasn't all that fast before.  I'm into optimizing my acceptance as much as my training 😉

Thanks for comment re “fell off a cliff” because that’s what it’s been like for me. Glad to know I’m not alone, I just it just happened a few years earlier for me. I’ll definitely work on the “acceptance” piece 😊

bender16v wrote:I would think a left crank arm power meter from Stages or 4iiii would work. I couldn't find one for my wife's Warbird with GRX last year and ended up getting a Stages Ultegra arm that someday I'll change out to get the correct offset, but it is very small at 2.5mm. 

Thanks much, I’ll check into left crank arm power meter from Stages or 4iiii.

chas wrote:

Yep, true.  In theory.  I tried to work through Stages last year, and then through my LBS, and had zero luck.    I wanted to have them install a power meter on my crank.   Finally, I gave up.

4iii might be more responsive.  If you can just buy a left crank arm and install it on your bike, that would be the way to go, IMHO.

I train mostly with HR.  I got a polar HR monitor, because others (especially optical) were not that accurate (especially doing velodrome intervals).

Still getting used to the power thing.   The benefit is that power readout is instantaneous, so it in effect tells me what my heart rate will be in a few seconds.

But the one thing I need HR for is recovery.  If I'm doing intervals (or simple hill climbs) there is no point in pushing myself a second time until my HR has recovered.  It does not matter what I'm capable of (in theory), if I don't get my HR down below my threshold, I'm not going to be able to generate power for very long.

Thanks for the comment on HR recovery. I’d never considered that.

jonjkruse wrote:I've seen various clip on platforms around that convert a clipless pedal to a platform.  Presumably if you can find such a product for Look KEO clips, you could make yourself a set of flat pedals from Assioma power meters. I have a dual set of Assiomas and while I clip into them, I really like them.  

Thanks much, I’ll look into that option.

reqvkq wrote:

Thanks much, I’ll check into left crank arm power meter from Stages or 4iiii.

clarksonxc wrote:Stages factory install on that GRX crank arm might be your best bet; if you can go without it for a couple weeks.

chas wrote:

I tried to do that for a year, stages didn't respond to me or my LBS (not that my LBS really cared about me).    I'd try 4iii   

graciejohn wrote:I have a Stages GRX 810 Left Crank Arm available for sale.  172.5mm.  I changed cranks on my gravel bike and don't have a need for it anymore.  Works great and in pretty good condition as well. Ignore the photos of the crankset itself, that has been sold already.