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Old 03-28-08, 11:48 AM   #1
csown
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Need help with PowerTap selection

Hi folks,

I've decided it's time to move to a PowerTap. I've been using a Garmin Edge 305 and it fits me well but I'm finding I need better data than HR and velocity.

I've been looking at the specs on the Saris website and it's a little confusing which one I need. For some background, I train on my commute of 30mi/day a few days a week, a longer ride or two on the weekend, and I do some work on rollers. I commute on a heavier cross bike, and on the trainer I use my race bike which has a shorter wheelbase. I want to be able to move the PT between the two bikes easily without having to wire a ton of crap up. With the 305, I just keep cadence units on both bikes and I move the computer between bikes. In the archives I found some useful info this post but don't have answers to everything.

...so, my questions for you wise guys out there:
1. If I go with SL 2.4, can I just move the wheel and head unit between bikes without needing a fin unit on both bikes? If I go with SL, is all I need an extra fin unit?
2. How the hell does the thing measure distance? Does it use a rotating magnet with the fin unit, or is it all done inside the hub?
3. Is the cadence pretty accurate even when you're applying constant power throughout the stroke?
4. When racing, do you use the PT wheel or just for B/C races when you want data? If you don't use the PT wheel, what do you do about measuring distance/cadence? Do you have another cheapo computer for that?
5. Does not having a coded HR strap get annoying? If you're at a race, does it record someone else's HR sometimes?
6. Does it suck not having other info like elevation gain, or once you have power nothing else matters?

Thanks in advance!

-Chris
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Old 03-28-08, 11:56 AM   #2
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1a yup
b you need a $75 wired mount for each bike you want to use with the SL
2 hub measures each revolution multiplies by circumference and vouela
3 Cadence is alright, I'd prefer to have mine wired, but it's all good in the hood
4 power tap for training races, race wheels for A races
5 never
6 the internet is a wonderful thing (i.e. look up the route you just rode)
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Old 03-28-08, 11:58 AM   #3
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Quote:
Originally Posted by csown View Post
... I want to be able to move the PT between the two bikes easily without having to wire a ton of crap up.
...so, my questions for you wise guys out there:
1. If I go with SL 2.4, can I just move the wheel and head unit between bikes without needing a fin unit on both bikes? If I go with SL, is all I need an extra fin unit?
2. How the hell does the thing measure distance? Does it use a rotating magnet with the fin unit, or is it all done inside the hub?
3. Is the cadence pretty accurate even when you're applying constant power throughout the stroke?
4. When racing, do you use the PT wheel or just for B/C races when you want data? If you don't use the PT wheel, what do you do about measuring distance/cadence? Do you have another cheapo computer for that?
5. Does not having a coded HR strap get annoying? If you're at a race, does it record someone else's HR sometimes?
6. Does it suck not having other info like elevation gain, or once you have power nothing else matters?
Thanks in advance!
-Chris
Go wireless.

1. Newer (current) PT 2.4 SL models (wireless) don't have a fin. Hub. Computer. That is all.
2. Inside hub.
3. I don't have the optional cadence sensor on my PT. That said, the PT calculate a virtual cadence, but I don't pay much attention to it. I kinda know what my cadence is - power readings help me know this.
4. PT every race. No power information is as valuable. Open pro rims for me.
5. Never had a problem with HR strap from someone else...can't say.
6. My Polar unit has elevation. PT doesn't. I never use the Polar, but ride EVERY ride with the PT. I miss the elevation at times, but never felt like I needed it. Power data is just too interesting.
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Old 03-28-08, 02:38 PM   #4
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Thanks guys. Useful answers. Not being a randonneur type I think I'll be able to live without the route/elevation data. I'm also sick of the Garmin wiping out trip data if I forget to push the end lap button before powering off.

I'm sold. I have a feeling this wheel is going to get a heck of a lot of use.

Now what's a good price for this stuff? I seem to remember WaterRockets said $700-$750 for the SL is what to look for. Quick look on eBay shows SL 2.4's are going for something like $1250. Anyone seen better?

How much weight do I lose without the fin? 150 grams or so?

Should I go for 24 spoke? I'm 150lb and my stuff tends to last. Though when I dial it up to 400 WATTS after a couple months of training with power that may change.

-C
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Old 03-28-08, 03:26 PM   #5
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If I had the money to go wireless, I would. Instead, I bought two full Ptap pro Kits-two hubs/wheels, one head unit, three fins/sensors. I have one fin on my Cx bike, one on my tt bike and one on my race bike.
I have the fins/sensors on the same spot on each bike so I can use them without power when I am doing an A race or just out for a ride.
In the winter I set up one wheel with a CX tire for outside riding/cx riding. I keep one wheel with a road tire and put that on the trainer.
In the summer I put road tyres on the CX bike and use it as a rain bike-it is 9 speed.
The other ptap stays on my 10 speed road bike.
I don't like changing cassettes and I definitely don't wanty to be changing tyres before every ride, hence the two hubs/wheels, one computer and three harnesses/sensors/fins.
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Old 03-28-08, 03:49 PM   #6
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Quote:
Originally Posted by csown View Post
Now what's a good price for this stuff? I seem to remember WaterRockets said $700-$750 for the SL is what to look for. Quick look on eBay shows SL 2.4's are going for something like $1250. Anyone seen better?-C
Tough to beat eBay's prices. If you go Pro (same except for axle/freehub) you can find them for ~$600, But you can find used SL's for that, so, your call.
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Old 03-28-08, 03:49 PM   #7
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A (hijack) question of my own - will the wireless head unit work in a harness-d bike cradle?
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Old 03-28-08, 03:49 PM   #8
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$700-$750 would be for a used wired SL wheel.

Dunno much about used wireless prices, but It seems that new PowerTaps can be had for $1050-$1150, and wheel parts for $80. Most builds cost $30.
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Old 03-28-08, 05:08 PM   #9
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power >> elevation data if you're training
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