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#4478
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Does anyone know a rule of thumb estimation of the difference in time for a 500M done at high altitude (like Colorado Springs) vs one done at sea level?
The estimated time difference for a flying 200M is 0.5s. I think it's 2s for a kilo. 500M?
The estimated time difference for a flying 200M is 0.5s. I think it's 2s for a kilo. 500M?
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I'm not sure I've ever heard a rule for the 500.
Since a 200 is 0.5s and a kilo is ~2s, I think the natural reaction would be to say 1s...although I would bet it's less than that because you spend a bigger proportion of the 500 at slower speeds where a reduction in air resistance doesn't help as much.
Since a 200 is 0.5s and a kilo is ~2s, I think the natural reaction would be to say 1s...although I would bet it's less than that because you spend a bigger proportion of the 500 at slower speeds where a reduction in air resistance doesn't help as much.
I haven't done a lot of 500s, and none at altitude. Only 1 kilo at altitude during my 1st season (none at sea level that year, go figure).
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Seems like the SRM is only reasonable option for power measurement. It's quite pricey though. In fact, that Stages is not really what I want, I started to think how much I could spend for the power meter and discovered a huge price gap between them.
Then I realized that in fact, by buying the SRM, I get also the crankarms, so basically I can "reduce" the price of the SRM by saving on the new S75DD crankset that was on a buying list for the new bike. In fact, saved money would give the SRM into reasonable price range (Stages ~$1000, SRM ~$2000, S75DD ~$500) of $1500.
Is it a good way of thinking? I guess that SRM crankarms are stiff and durable enough for training/racing?
All I need is to buy extra is a DA BB-7710?
I am also wondering, cause I can select a crankarm length on the website, but I cannot select decal and crankarm colors and I saw many options of them. Do you know how to choose it while buying?
Or maybe can I order SRM spider without the crankarms and use the DA cranks instead?
Then I realized that in fact, by buying the SRM, I get also the crankarms, so basically I can "reduce" the price of the SRM by saving on the new S75DD crankset that was on a buying list for the new bike. In fact, saved money would give the SRM into reasonable price range (Stages ~$1000, SRM ~$2000, S75DD ~$500) of $1500.
Is it a good way of thinking? I guess that SRM crankarms are stiff and durable enough for training/racing?
All I need is to buy extra is a DA BB-7710?
I am also wondering, cause I can select a crankarm length on the website, but I cannot select decal and crankarm colors and I saw many options of them. Do you know how to choose it while buying?
Or maybe can I order SRM spider without the crankarms and use the DA cranks instead?
#4481
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Seems like the SRM is only reasonable option for power measurement. It's quite pricey though. In fact, that Stages is not really what I want, I started to think how much I could spend for the power meter and discovered a huge price gap between them.
Then I realized that in fact, by buying the SRM, I get also the crankarms, so basically I can "reduce" the price of the SRM by saving on the new S75DD crankset that was on a buying list for the new bike. In fact, saved money would give the SRM into reasonable price range (Stages ~$1000, SRM ~$2000, S75DD ~$500) of $1500.
Is it a good way of thinking? I guess that SRM crankarms are stiff and durable enough for training/racing?
All I need is to buy extra is a DA BB-7710?
I am also wondering, cause I can select a crankarm length on the website, but I cannot select decal and crankarm colors and I saw many options of them. Do you know how to choose it while buying?
Or maybe can I order SRM spider without the crankarms and use the DA cranks instead?
Then I realized that in fact, by buying the SRM, I get also the crankarms, so basically I can "reduce" the price of the SRM by saving on the new S75DD crankset that was on a buying list for the new bike. In fact, saved money would give the SRM into reasonable price range (Stages ~$1000, SRM ~$2000, S75DD ~$500) of $1500.
Is it a good way of thinking? I guess that SRM crankarms are stiff and durable enough for training/racing?
All I need is to buy extra is a DA BB-7710?
I am also wondering, cause I can select a crankarm length on the website, but I cannot select decal and crankarm colors and I saw many options of them. Do you know how to choose it while buying?
Or maybe can I order SRM spider without the crankarms and use the DA cranks instead?
ANT+ SRMs will work with less expensive head units. So, that might save you some $.
You don't need the Dura Ace 7710 BB (~$100). The 105 or Ultegra BB will work fine, too. I've used them. As with all things 105, Ultegra, and Dura Ace, you are paying for fit, finish, and weight reduction.
Beware of power meters that meet the minimum requirement to be a power meter just to get in the game (like the one that measured air pressure).
The SRM cranks are very, very stiff. Actually more stiff than Dura Ace.
If you are worried about getting the decal or crank color you want, just call in your order. They are really nice. I've been to SRM HQ. They make each unit by hand after your order it (online or phone).
You can probably buy just the spider and put on whatever SRM crank arms you want (I had multiple arms when I owned my last SRM), but you will have to learn to calibrate them yourself which is what SRM does for you when you buy them. No, you cannot use a DA arm on SRM spider. You CAN use a DA left crank arm with a SRM right crank arm + spider. Team GB did that for a while. I think to save a few grams even though it wasn't pretty.
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You can probably buy just the spider and put on whatever SRM crank arms you want (I had multiple arms when I owned my last SRM), but you will have to learn to calibrate them yourself which is what SRM does for you when you buy them. No, you cannot use a DA arm on SRM spider. You CAN use a DA left crank arm with a SRM right crank arm + spider. Team GB did that for a while. I think to save a few grams even though it wasn't pretty.
BTW. Do the SRM pay for shipping costs for battery replacement? There is no distributor in my country so internal shipping can be pricely.
EDIT. I know that cadence measurement is external (and magnets are included), how about speed? Does SRM measure speed or it's totally separated thing?
Last edited by bartek.; 10-15-17 at 12:19 PM.
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I know some elites demount the SRM for the biggest events such as Olympic to save the weight. I am not in the 1/1000th of second difference in my races, so not a big deal for me.
Medals and Jerseys are won in training. You just go to the event to pick them up
BTW. Do the SRM pay for shipping costs for battery replacement? There is no distributor in my country so internal shipping can be pricely.
I know that cadence measurement is external (and magnets are included), how about speed? Does SRM measure speed or it's totally separated thing?
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CORRECTION:
You can mount the speed sensor to measure the front OR the rear wheel. I usually do fork because the position of the front wheels never change. The position of the rear wheel changes with gearing and chain tension.
Here is Shannon McCurley's (IRL) bike with an SRM and speed coming from the rear wheel. Notice the ANT+ transmitor/sensor on the seat stay. I'm guessing that there is a magnet in the disc, maybe in the valve hole?
source: https://www.momnium.com/shannon-mccurley-bt-ultra-rio/
You can mount the speed sensor to measure the front OR the rear wheel. I usually do fork because the position of the front wheels never change. The position of the rear wheel changes with gearing and chain tension.
Here is Shannon McCurley's (IRL) bike with an SRM and speed coming from the rear wheel. Notice the ANT+ transmitor/sensor on the seat stay. I'm guessing that there is a magnet in the disc, maybe in the valve hole?
source: https://www.momnium.com/shannon-mccurley-bt-ultra-rio/
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The SRM Science Track PowerMeter arms can be exchanged to fit either format.
Weight: 738 g
BCD: 144 mm
Q-Factor: 141 mm
Wireless: ANT+ Compatible
Battery Life: 1900 hours
Accuracy: < 0.5% error
Includes:
PowerMeter Spider 144 BCD
Drive and Non-Drive Side SRM Octalink Compatible Crank Arms (7075 Aluminum)
Cadence Magnet Kit
Weight: 738 g
BCD: 144 mm
Q-Factor: 141 mm
Wireless: ANT+ Compatible
Battery Life: 1900 hours
Accuracy: < 0.5% error
Includes:
PowerMeter Spider 144 BCD
Drive and Non-Drive Side SRM Octalink Compatible Crank Arms (7075 Aluminum)
Cadence Magnet Kit
#4486
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The SRM Science Track PowerMeter arms can be exchanged to fit either format.
Includes:
PowerMeter Spider 144 BCD
Drive and Non-Drive Side SRM Octalink Compatible Crank Arms (7075 Aluminum)
Cadence Magnet Kit
Includes:
PowerMeter Spider 144 BCD
Drive and Non-Drive Side SRM Octalink Compatible Crank Arms (7075 Aluminum)
Cadence Magnet Kit
Also, the way that SRMs are made using Reed Switches, the cranks ARE the cadence sensor and the Power data is actually just added to the Cadence transmission as an extra passenger
You can wave any magnet near the cranks and simulate a cadence. Some people do that to wake up the SRM before a time trial to get the first few seconds that are usually lost.
Here are the equipment options (depending on what you buy):
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Yeah, I know this is just a magnet. I actually had been using one "refrigerator" magnet for my speed sensor on fork ;D
I am more in a question on where this magnet is mounted to make a signal for the spider. I bet it's not a read wheel glued. You posted a picture of the magnet and I still can't figure it out
I am more in a question on where this magnet is mounted to make a signal for the spider. I bet it's not a read wheel glued. You posted a picture of the magnet and I still can't figure it out
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It mounts on the bottom bracket so that it can be very close to the spider:
This can be tricky since we don't have cable guides on our track bikes. So, you will need double-sided tape to hold it in place.
SRM install guide.
This can be tricky since we don't have cable guides on our track bikes. So, you will need double-sided tape to hold it in place.
SRM install guide.
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Also, it gets really bad if you have a BB shell that is not a cylinder. You essentially have to rig up something.
Install and configuration can be a pain.
Install and configuration can be a pain.
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Awesome!
More detail:
You know how a wheel speed sensor works? Every time the magnet in the spokes passes the sensor, the sensor feels the magnet and says, "The magnet passed me again. SEND_1. The magnet passed me again. SEND_2. The magnet passed me again. SEND_3. The magnet passed me again. SEND_4...."
There is a time stamp with each SEND. The head unit receives them and uses the difference in time between SEND_2 and SEND_1 to calculate speed.
A normal cadence sensor works the same way.
The SRM works differently. The magnet does not move. The SPIDER moves. The computer is in the moving spider, not the stationary part attached to the frame.
So, every rotation, the spider says, "I passed the magnet again. SEND_1. I passed the magnet again. SEND_2. I passed the magnet again. SEND_3....
The head unit calculates the Cadence based on the time between each SEND.
There is another passenger in that SEND data. Torque.
The current Torque being exerted on the cranks is measured by strain gauges inside of the spider and that value gets a free ride with the cadence data.
The head unit says, "Heyyyyyy! I can take Cadence, Torque, and Crank length and calculate POWER "
More detail:
You know how a wheel speed sensor works? Every time the magnet in the spokes passes the sensor, the sensor feels the magnet and says, "The magnet passed me again. SEND_1. The magnet passed me again. SEND_2. The magnet passed me again. SEND_3. The magnet passed me again. SEND_4...."
There is a time stamp with each SEND. The head unit receives them and uses the difference in time between SEND_2 and SEND_1 to calculate speed.
A normal cadence sensor works the same way.
The SRM works differently. The magnet does not move. The SPIDER moves. The computer is in the moving spider, not the stationary part attached to the frame.
So, every rotation, the spider says, "I passed the magnet again. SEND_1. I passed the magnet again. SEND_2. I passed the magnet again. SEND_3....
The head unit calculates the Cadence based on the time between each SEND.
There is another passenger in that SEND data. Torque.
The current Torque being exerted on the cranks is measured by strain gauges inside of the spider and that value gets a free ride with the cadence data.
The head unit says, "Heyyyyyy! I can take Cadence, Torque, and Crank length and calculate POWER "
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This is why you can't get Power (or Torque) if the cranks are not moving.
This is why cadence and power drop out at the same time in a file (usually because the sensor bumped is too far away).
This is why speed is unaffected by cadence/power issues in SRM files.
This is why you miss the first 3" of standing start data...because the cranks haven't rotated around enough for the head unit to calculate a cadence...and therefore power.
This is why SRM used to offer spiders with 2 reed switches (diametrically opposed) to make all of the above happen faster. But, you had to program the head unit to know that the cadence was being reported every 1/2 rotation and not full rotation. Otherwise the cadence and power would be doubled for any given effort.
This is why cadence and power drop out at the same time in a file (usually because the sensor bumped is too far away).
This is why speed is unaffected by cadence/power issues in SRM files.
This is why you miss the first 3" of standing start data...because the cranks haven't rotated around enough for the head unit to calculate a cadence...and therefore power.
This is why SRM used to offer spiders with 2 reed switches (diametrically opposed) to make all of the above happen faster. But, you had to program the head unit to know that the cadence was being reported every 1/2 rotation and not full rotation. Otherwise the cadence and power would be doubled for any given effort.
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This is why SRM used to offer spiders with 2 reed switches (diametrically opposed) to make all of the above happen faster. But, you had to program the head unit to know that the cadence was being reported every 1/2 rotation and not full rotation. Otherwise the cadence and power would be doubled for any given effort.
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I understand you used a past time by purpose? This is not valid anymore?
Basically, they were better than the competition and had to downgrade the product to match the others.
You can have one specially made, but I don't think the head unit software supports 2 reed switches anymore. So, you will have to manually 1/2 all of your cadence and power values in Excel before analysis. Not worth it.
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Yeah, I'm asking about idling timeout for the cranks, not the head unit. I barely can remember situations when I did a break for a lunch or whatever then jumped back on my roadbike and see "X sensor detected" or whatever unit would say. It was already detected at the beginning and the time out for the Garmin sensors (not headunit) was long enough.
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Yeah, I'm asking about idling timeout for the cranks, not the head unit. I barely can remember situations when I did a break for a lunch or whatever then jumped back on my roadbike and see "X sensor detected" or whatever unit would say. It was already detected at the beginning and the time out for the Garmin sensors (not headunit) was long enough.
Also, if you are getting speed data from GPS on a road ride, the GPS satellite will keep the head unit awake even when you are not moving. Because the satellite and Earth are moving and the head unit isn't sure what's going on. There are times when my old Garmin 500 would beep on and off when the bike was sitting against the wall because it thought that I was riding.
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Yep, but sensors are sensors. As you already mentioned, all they do is transmitting data, so it doesn't matter if my head unit is on or off.
Wondering if SRM provides idle timeout information somewhere.
Anyway, lets back to the real case. So, we have standing start, we take a bike from infield, go to the start gate. I guess time between setting bike in the gate and releasing the holder is about 60-90 seconds at maximum. It's not that much for idling. And comparable to 30 minuts or something for Garmin sensors idling.
Wondering if SRM provides idle timeout information somewhere.
Anyway, lets back to the real case. So, we have standing start, we take a bike from infield, go to the start gate. I guess time between setting bike in the gate and releasing the holder is about 60-90 seconds at maximum. It's not that much for idling. And comparable to 30 minuts or something for Garmin sensors idling.
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Yep, but sensors are sensors. As you already mentioned, all they do is transmitting data, so it doesn't matter if my head unit is on or off.
Wondering if SRM provides idle timeout information somewhere.
Anyway, lets back to the real case. So, we have standing start, we take a bike from infield, go to the start gate. I guess time between setting bike in the gate and releasing the holder is about 60-90 seconds at maximum. It's not that much for idling. And comparable to 30 minuts or something for Garmin sensors idling.
Wondering if SRM provides idle timeout information somewhere.
Anyway, lets back to the real case. So, we have standing start, we take a bike from infield, go to the start gate. I guess time between setting bike in the gate and releasing the holder is about 60-90 seconds at maximum. It's not that much for idling. And comparable to 30 minuts or something for Garmin sensors idling.
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