SRM Pro vs amateur

pcannell said:

Does anyone out there have both - I'm looking for real world comparisons of the accuracy and precision of these. I currently use the Pro on my race bike and was considering a cheaper Amateur version for my training bike - but I'm concerned that it won't give me repeatable valid numbers - or that it will differ from the pro one on the race bike.

thanks.

I've got both, and after calibrating them myself I'm confident that they give comparable and accurate results. I'd suggest calibrating them using several different masses and plot a graph which will give you confidence in the consistency of the slope for each powermeter, and make sure you re-zero them at the start of each ride and if you get any significant temperature fluctuations during the ride. Don't trust the factory calibrations, my Amateur has always been spot on but the Pro was very widely off when I got it.

I also have both and I have compared each to my Computrainer and they are so close as to be indistinguishable.
Best,
Bill Black

pcannell said:

Does anyone out there have both - I'm looking for real world comparisons of the accuracy and precision of these. I currently use the Pro on my race bike and was considering a cheaper Amateur version for my training bike - but I'm concerned that it won't give me repeatable valid numbers - or that it will differ from the pro one on the race bike.

thanks.

pcannell said:

Does anyone out there have both - I'm looking for real world comparisons of the accuracy and precision of these. I currently use the Pro on my race bike and was considering a cheaper Amateur version for my training bike - but I'm concerned that it won't give me repeatable valid numbers - or that it will differ from the pro one on the race bike.

thanks.

I've got the Amateur, FSA Pro, and Dura Ace Pro. The Amateur offset number fluctuate a lot more than the pro models, but as long as it is reset for each ride they all give very similar numbers.

Bill Black said:

I also have both and I have compared each to my Computrainer and they are so close as to be indistinguishable.
Best,
Bill Black

Hi Bill, welcome. What is this - a toe in the water from wattage land?😉

Hi there, Yes I have both cranks and would agree with all the above posts. I use my pro crank for events and specific intervals. NP from L3/4 rides with the Amateur crank is exactly as I would expect to acheve going by the 20-60min power data from workouts on the Pro crank.

Of course I calibrate them both regularly to be certain this remains true, and in my case the slope of my Am crank is very linear, not the same as some people have inferred, but I've not seen other peoples data to be sure.

The zero offset does vary more with temperature, reflected by the larger variations in the stored value on the AM crank than the Pro, something to be aware of when temperature varies more than say 5degrees C in any ride.

Be aware changing chainrings can change the correct slope - when you have 2 cranks you need to keep on top of these things otherwise it can get difficult to interpret data, if you don't have the confidence that both cranks are accurate. Especially when you look back at the end of the year!

I started on the Am crank and then doubled up with the Pro and don't find the Am crank to be distasteful now, which I guess says something!

Gavin

I have been using Polar Power for almost two years, but am thinking about upgrading to SRM, so… the amateur is only 5% accurate but I don’t really care about whether I am making 300 watts and it tells me 315 or 285 as long as that number is precise, or rather consistent. Forget about comparing the numbers between two different cranks, Pro and an Amateur (there is a 7.5% possible range difference), are the numbers for the Amateur consistent over time or should I just keep my polar since I know it is that good already… or spring for the pro. 😕

wilmar13 said:

Forget about comparing the numbers between two different cranks, Pro and an Amateur (there is a 7.5% possible range difference)

Actually if you use the same process to calibrate the cranks, then the potential difference is actually 3%.
Potential is the key word here!
If you use the same process to calibrate them it is highly unlikely that the Amateur is going to be -5% and the Pro +2% from some gold standard perfect measure.
My amateur was notoriously bad until I sent it back to Germany where they replaced a condenser. It now is as stable as the Pro.

wilmar13 said:

Forget about comparing the numbers between two different cranks, Pro and an Amateur (there is a 7.5% possible range difference)

You can compare numbers between two cranks, especially if you calibrate them the same way. At worse the potential difference between then is 3%. The key word being 'Potential'

When calibrated using a consistent methodology it is highly unlikely that an Amateur would say be -5% and a Pro +2% from some gold standard.

This is said of course within the knowledge that both your cranks need to functioning properly. My amateur when off a few years ago, but a little trip back to SRM for a condenser change fixed it, so that now it is a stable as my Pro

evanhyde said:

I've got the Amateur, FSA Pro, and Dura Ace Pro. The Amateur offset number fluctuate a lot more than the pro models, but as long as it is reset for each ride they all give very similar numbers.

Since you are lucky enough to have all 3 models, do you find there is any performance difference between the 3? And I am not specifically referring to the power accuracy but more the feel of the crankset, durability, etc. There is a substantial price difference between the amateur and say the DA - is the DA worth the extra $800 or so in your opinion ?
Thanks

power1369 said:

Since you are lucky enough to have all 3 models, do you find there is any performance difference between the 3? And I am not specifically referring to the power accuracy but more the feel of the crankset, durability, etc. There is a substantial price difference between the amateur and say the DA - is the DA worth the extra $800 or so in your opinion ?
Thanks

The biggest difference that I can see is the weight. Adding the Amateur to my Centaur eqiupped bike pushed it over 20lbs. As far as stiffness goes, I cannot tell any difference between the Amateur/FSA/DA Pro models. I am not very concious to small changes in material, however, and to me all cranks that I have ridden feel the same.

Of the three cranks, I have spent the most time on the Amateur. It has 6,000Km over 2.5 years on it and has not had any issues with durability. I take it out in all weather and it has not had any problems.

Bottom line - if the weight savings is not worth the extra several hundred $$, go with the Amateur.

decrono said:

You can compare numbers between two cranks, especially if you calibrate them the same way. At worse the potential difference between then is 3%. The key word being 'Potential'

When calibrated using a consistent methodology it is highly unlikely that an Amateur would say be -5% and a Pro +2% from some gold standard.

This is said of course within the knowledge that both your cranks need to functioning properly. My amateur when off a few years ago, but a little trip back to SRM for a condenser change fixed it, so that now it is a stable as my Pro

OK, what I am trying to get at is how do you define accuracy? Can the amateur at any time be somewhere in the range of 95-105% of actual (the reported output constantly varies between 95-105% of actual), or rather that the amateur crankset may read within 5% of actual output but is consistent... for example a specific crank outputs 97.8% of actual power, but it consistently reads 97.8% of actual???
Again I don't care if my reported # is consistently off by 5%, but if it can vary(day to day, within same ride, etc.) by 10% for ametuer, but only 5% for Pro, then the Pro becomes worth the money.

SRM amateur is sensitive to temperature changes. If you are in Bay Area and you may head out of your house in Palo Alto with a temperature of 70 and head over to the ocean (55 degrees), that will have a huge impact on your power readings.

nrhorwitz said:

SRM amateur is sensitive to temperature changes. If you are in Bay Area and you may head out of your house in Palo Alto with a temperature of 70 and head over to the ocean (55 degrees), that will have a huge impact on your power readings.

I believe the Pro is just as sensitive to temperature, and the zero-offset should be set several times in a ride with highly variable temperatures. I usually set mine 10 minutes into a ride and then around every hour after that. The values usually change by +/- 2 or 3 in that time.

evanhyde said:

I believe the Pro is just as sensitive to temperature, and the zero-offset should be set several times in a ride with highly variable temperatures. I usually set mine 10 minutes into a ride and then around every hour after that. The values usually change by +/- 2 or 3 in that time.

...which has a negligible impact on the calculated power. Indeed, even if the zero offset changes by 10 Hz (which typically requires a very large change in temperature), the calculated power only changes by ~1%.

acoggan said:

...which has a negligible impact on the calculated power. Indeed, even if the zero offset changes by 10 Hz (which typically requires a very large change in temperature), the calculated power only changes by ~1%.

Good to know. I wasn't sure what the units on the zero offset were, but I was pretty sure they aren't watts. Maybe one calibration per ride is good enough.

Is the SRM pro more precise than the amateur or merely more accurate???!!!! Why is it this seems like asking how many licks it takes to get to the center of a tootsie pop?:p Seriously, no one has an answer? 😕

wilmar13 said:

Is the SRM pro more precise than the amateur or merely more accurate???!!!! Why is it this seems like asking how many licks it takes to get to the center of a tootsie pop?:p Seriously, no one has an answer? 😕

More accurate, same precision. (I think)

acoggan said:

...which has a negligible impact on the calculated power. Indeed, even if the zero offset changes by 10 Hz (which typically requires a very large change in temperature), the calculated power only changes by ~1%.

Doesn't that depend on slope? The amateur cranks appear to have lower slope values - mine is 13.0 vs 23.0 for my Pro crank - both identically calibrated. A given shift in offset value will therefore have more impact on reported power on the amateur crank than the pro?

Gavin

gza said:

Doesn't that depend on slope? The amateur cranks appear to have lower slope values - mine is 13.0 vs 23.0 for my Pro crank - both identically calibrated. A given shift in offset value will therefore have more impact on reported power on the amateur crank than the pro?

Gavin

Yes, it would - it would also depend on your cadence. That's why I said '~1%' instead of giving an exact value (although '1-2%' might have been more apt).

BTW, I'm not sure if it is a Pro vs. Amateur difference or just a crank-to-crank difference (in slope), as my Pro track crank has a slope of 15.2, i.e., not far from your road Amateur.

Another BTW: it just dawned on me that 'gza' must be the Gavin I know!?