SRM
Geplaatst: 14 jun 2005 13:02
Ergomo Sport
Polar S-720i/710i
PowerTap Standard
PowerTap Pro
PowerTap Pro SL
SRM Professional / Amateur
Measurement location
Bottom bracket (Campagnolo or Shimano OctaLink)
Chainstay and rear derailleur
Rear hub (130 or 135 mm; 24, 28, and 32 hole drillings)
Same as Standard
Same as Standard
Crank (Shimano OctaLink or Campagnolo; 167-182 mm lengths in 2.5 mm increments)
Method
Photointerrupter circuit
Chain speed and vibration frequency
4 strain gauges
Same as Standard
Same as Standard
4 strain gauges for Pro, 2 for Amateur
Claimed accuracy
± 2
10 at any one instant, but 2-5 or less on average SPAN
± 1.5
Same as Standard
Same as Standard
± 2.5 for Pro, ± 5 for Amateur
Recording interval
Averaged values recorded every 5 sec.
Current values recorded every 5, 15, or 60 sec.
Current values recorded every 1.26 or 2.52 sec.
Current values recorded 1.26, 2.52, 5.04, 10.08, or 30.24 sec.
Same as Pro
Averaged values recorded 0.01-30 sec.
Memory capacity
11 hr.
1 workout file
4:57-76:37 hr.
Up to 99 workout files
4 or 8 hr. depending on recording interval,
1 workout file
7.5-180 hr. depending on recording interval.
1 workout file
Same as Pro
0:45-225 hr. depending on recording interval.
Numerous workout files
Calibration
By manufacturer only; accuracy can be checked via static ‘stomp test’ described below
No; but accuracy can be checked on hill of known grade
No; accuracy can be checked via static ‘stomp test’ described below
Same as Standard
Same as Standard
Slope setting is user adjustable; manufacturer calibration now available in U.S.
Mass (grams)
BB w/bolts & wires = 344 g
Computer & mount =168 g
Sensors = 118* g
Computer = 53* g
Mount/wiring = 71* g
Hub = 579* g (w/o skewer)
Computer =39.5* g
Mount/wiring = 36* g
Same as Standard, plus slight added mass due to crank-mounted cadence sensor.
Hub = 416 g (w/o skewer)
Remaining compo-nent masses are same as Pro
Pro = 560 g
Amateur = 640 g
Computer = 120 g
Mount bracket/wire = 30 g
Advantages
1. outstanding software (CyclingPeaks) with many useful analysis tools
2. third-generation design
3. fully hard-wired system is not affected by electronic or radio interference
4. easy installation
5. rechargeable computer battery lasts 5,000 hr., is good for ~30 hr., recharges in 2-3 hr.
6. almost no limit on component choice
1. least expensive of all options
2. feature-rich software, and extra hardware features like altitude
3. allows use of any wheel or crank that you want
4. large memory capacity, stores many workouts
5. incurs the smallest weight penalty
6. not affected by temperature
7. does not require calibration
1. easiest to move from one bike to another
2. affordable and accurate
3. compact, readable, easy-to-use display
4. most hub internals (axle, freehub, and drive side bearings) are all user-serviceable without disturbing strain gauges and electronics
5. easiest to install, and easiest to remove for racing – just swap rear wheels
Same as Std., plus:
1. expanded memory (up to 180 hr.); can store only one file but can create unlimited number of intervals
2. display has time of day, and rolling average capability for power, speed, and cadence data; can be customized for these functions
3. can display “pedaling power” (excludes 0, i.e., coasting values)
4. can be used with fixed gear
5. measures actual cadence (more accurate than the Standard model’s “virtual” cadence)
6. easier operation of interval feature
7. mileage is programmable
8. faster downloading with Link software v. 1.04
Same as Pro, plus:
1. improved hub internals (4 sets of sealed cartridge bearings), but not user serviceable
2. hub is 162 g lighter than Pro or Std.
3. available in fixed gear and Cam-pagnolo freehub versions
4. improved software is also Java-based and Mac-compatible
1. excellent software
2. time-tested, reliable design
3. can display rolling average for current wattage
4. large memory capacity, can store multiple workouts
5. no limit on wheel choice
Drawbacks
1. large/heavy computer
2. bearings must be factory serviced ($300) every 15-20,000 mi.
3. not easily moved from bike to bike
4. cannot accept 2004 Dura-Ace cranks
5. averaged data can be accessed only by download (cannot be viewed during interval)
6. not useful on tandems
1. most difficult to set up properly
2. difficult to move from bike to bike (to the point that it will likely never happen)
3. small display is hard for some to navigate
4. the least “clean” installation (multiple sensors and cables)
5. averaged data cannot be viewed during intervals (or ‘laps’), only at the end of the ride
6. accuracy questionable on stationary trainers, possibly from harmonic vibrations effects
7. not practical on MTB, and cannot be used with fixed gear
1. mediocre software interface (also not Mac-compatible
2. limits wheel choice
3. wheel-based system (not hub itself) is more likely to be damaged in crash
4. no disc version; requires a cover (not USCF-legal after 1/1/07) to be used as a disc
5. no disc brake version for MTB
6. not available with Campagnolo freehub
7. drive-side bearings and cone are substandard quality
8. cannot be used with fixed gear
9. “virtual” cadence only (limited to 40-140 rpm)
10. reliability problems in wet weather with original version; Graber version has better seals and coated circuitry
11. limited memory (7.5 hr.), stores only one workout
12. no rolling average or “pedaling power” capability
Same as 1-7 for Std., plus:
1. hub requires modification to be used with fixed gear
Same as 1-5 for Std.
1. expensive
2. not made to be moved from one bike to another
3. some find display more difficult to read
4. daily calibration (takes ~30 sec.) recommended
5. user-serviceable, but factory service recommended every 1500 hr., and replacement interval for cranks (not including power measuring unit) is once yearly
6. crank is slightly more flexible than other models; Dura-Ace version available at significant extra cost
7. not useful on tandems
8. accuracy of Amateur deteriorates outside a ~100W range, and may drift significantly over the course of a season
Pedal analysis
No
Yes
No
No
No
Extra option
MSRP
$1,200
720i, $575; add-on kit only, $315
$700 without rim and wheel build
$900 without rim and wheel build;
$1,000 with built wheel
$840, hub only;
$1,200 without rim and wheel build;
$1,300 with built wheel
Pro, $2,650; Amateur, $1,770
Other
Display and software give average power for pedaling time only.
Display and software give only average power for with 0 (coasting) values.
Original grey case changed to yellow in 2004.
Data transmission is through carbon fiber “windows” in hub shell. Electronics are completely contained inside hub; only batteries are accessible from cap.
Average power display obtained only from pedaling time, but non-zero values (i.e., when coasting) included by SRM software.
*Actual mass; all others are manufacturer’s claims.
For comparison, the mass of a Shimano Dura-Ace FC-7700 rear hub is 312 g, while Campagnolo lists the Chorus at 260 g, and Record as 248 g (all masses without skewer). A Dura-Ace FC-7700 bottom bracket is 201 g; an FC-7410 right crank and chainrings are 395 g; an Avocet 45 computer and mounting bracket are 20 g and 16 g; and a Polar Coach heart rate monitor (HRM) and mounting bracket are 40 g and 26 g, respectively.
http://midweekclub.ca/powerFAQ.htm