SRM inaccurate readings

JohnCisco10

Not sure if this should go here or in another section, but...

Bought a used SRM, amateur model. Worked just fine on my old bike the first week I had it. Bought a new bike (new Giant TCR advanced) and installed it and on my ride my cadence was nearly double what it actually was and my power reading was off because of this as well.
I've tried positioning the power sensor everywhere I can (i'm using double sided tape to secure it) and I have some interesting readings now. If the sensor is positioned on the downtube, my cadence when pedaling forward is roughly double actual, when I pedal BACKWARDS it is fine. If I position the sensor on the chain stay behind the BB the cadence is fine when pedalling forward but about double when pedaling backwards. Power appears to be off still and also sparadically get readings of 0 on cadence and power. I've read the SRM manual about 5 times over and tried finding any info online but for the life of me I can't seem to get this positioned properly. Either that or maybe the hardware in the cranks is bad???

I contacted SRM and they told me to keep trying to reposition the sensor and if I can't get it to work to send it in. Since the only thing I've done differently is put it on a different bike, I'm so far reluctant to think the unit is bad.

I have not yet put it back on my old bike but maybe that's the next step?

The new Giants, the BB area of the frame is absolutely huge and has different geometry than my Orbea, which is making mounting the sensor difficult. With the crank off, and I run the sensor over it, the cadence appears to be fine and not wacky.

help!

John

dkrenik

I might recommend the new sensor mounting kit. The concern is that I just got one today and am having troubles with th PM picking git up.

Time to ping SRM...

Dave

JohnCisco10

I'm wondering that too. I remounted on old bike, same problems. Put back on new bike now.

It's really odd, when setting the zero offset, you're supposed to receive a signal the entire 360 degrees of the pedal stroke, I ONLY receive a signal from 3 to 9. The people at SRM said if I'm receiving any signal, there's no reason with the powermeter for me to not receive it allt he way around. They told me to keep trying to reposition the sensor and send them pictures of how it's mounted and they'll try to help. When I rode with it today it was mostly not working, but periodically would. BUT if I pedaled backwards it would pick up the cadence and power without any problems, forwards, it wouldn't and that was out riding. At least the cadence numbers are correct now when they do show up.

I may try to borrow someone else's sensors or swap cranks just to try and eliminate one of the two as a problem. New sensors look like $70 on the SRM web site.

peterpen

It sounds to me like you need to keep refining the sensor position.

I have the same frame and have my sensor on the downtube, secured with a rubber band around the BB cup (DA model) and a zip tie around the downtube - then a drop of super glue to make sure it doesn't work loose.

Hang on, just read that you remounted on your old bike and had similar problems. If that's the case, I'd send it in to SRM - sounds like something got messed up when you took it off.

dkrenik

Kind of weird replying to my own post and I thought this update apropos...

I mounted the new-style sensor kit last night and it works flawlessly. The under BB mount has a stronger signal when it's mounted a few mm's further away from the SRM disk than with the older sensor kits. I highly recommend using one - very easy to install. Just remember to get a longer screw for the cable guide.

Dave

JohnCisco10

I talked with someone that actually has the same frame I have and said they had problems with it working but bought the mounting bracket from Competitive Cyclist and it worked flawlessly. According to the CC web site, CSC and T-Mobile use this bracket on their bikes and the people at SRM recommend it.

With more playing on the position of the sensor I'm able to get a signal on 3 of te 4 quadrants on the powermeter and cadence all the time...so quite close but not quite right yet.

thanks for the input on the BB mounted sensor. I hope the mounting bracket from CC will do the job, if only I didn't have to wait on shipping

JohnCisco10

the mount from Competitive Cyclist came in today. I'm still having issues with not being able to pick up a power signal through the entire pedal stroke. Half the pedal stroke I get a good reading when setting the zero offset. The other half I get 0. Have spent almost 2 hours trying different positions, angles, distances, etc...
Does anyone have a good picture of the angle and distance the power sensor should be from the powermeter? I can't find much of anything online and the SRM users manual isn't helping.
SRM is still telling me I'm not aligning the sensor properly...