fietsbob

Why Does Portland Oregon, Not have an indoor Olympic Caliber Track?

700wheel

Because no person or group has come up with ten to 20+ million dollars needed to build such a facility.

carleton

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?

carleton

Yeah, that's where I started over-thinking things, too.

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).

bartek. 

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?

carleton

There are several reasonable options. Some get eliminated based on "deal-breakers" based on the features you absolutely have to have. SRM seems to have fewer deal-breakers than the others. The main one you mention...price.

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.

bartek. 

I use Garmin Edge 810 unit for now, and yeah I think I will keep it and sacrifice data resolution. I am sure it won't be a problem for a long long time.

OK. I was rather referring to 7710 compatibility than specific model here, however as BB-7710 costs between $50-70 in local martket I would go with the DA version.

I'm thinking to purchase a new brand SRM Science Track power meter (wireless), so I think all limitations are beyond me.

Great! So, yeah. I think this is a way to go. Glad, I didn't buy the Sugino yet!

Oh, ok. So only SRM crank arms are compatible with these spiders? I thought that as long as it's Octalink I am good to go on both sides. I am OK with the standard SRM crankarms then. 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.

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?

carleton

Yes, only SRM track crank arms are compatable with SRM track spiders. OR the ROTOR crank arms when the ROTOR SRM spider (a fairly new offering).

Yes, they will take off SRM for big events to save weight. By the time they go to the big event, they are 99% sure what the TT time will be because they will hit that mark in training. It's rare to go faster in an event. It happens, but most likely, the best performance will happen in training.

Medals and Jerseys are won in training. You just go to the event to pick them up

No, I do not believe that SRM pays for shipping. A battery will last years, but if you are cautious. It's good to send the cranks and head unit in for service every off-season so it's fresh for the next season. It's like a Porsche...it performs well, but needs care


For SRM Power Cranks, Cadence is calculated in the crank spider and the Cadence data is transmitted when the Power data is transmitted. Speed data is transmitted via a standard ANT+ fork sensor.

carleton

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/

bartek. 

From the SRM website:
So what this magnet stands for? I wouldn't say it's for attaching to the rear wheel as it's not in the line for the spider but I may be wrong.

carleton

OK, that's not an ANT+ Cadence sensor. It's just a "dead" magnet that's designed to trip the Reed Switch. You could put a magnet from your refrigerator down there and do the same job.

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):

bartek. 

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

carleton

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.

carleton

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.

bartek. 

Thanks for clarification. It's all clear to me now.

carleton

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 "

bartek. 

As long as Garmin unit knows how to calculate it, I am ready to go ;D

carleton

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.

bartek. 

How much time the SRM can idle? I am wondering why this "activation" process is so important here. My Garmin cadence and speed sensors idle for long time. Even coffee break usually don't put them into standby mode.

I understand you used a past time by purpose? This is not valid anymore?

carleton

The problem is that the head unit can be awake, but the cranks may not be awake.

They stopped doing this back in 2011 or 2012 I think. I think when they went ANT+. My guess is that it was because 2 reed switches would not work with a Garmin or other ANT+ head unit because the Garmin (or other) did not expect 2 reed switches.

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.

bartek. 

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.

carleton

The idle timeout for the cranks is shorter. I don't know why. Maybe because there is no way to set the timeout or recharge the crank batteries.

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.

bartek. 

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.

carleton

Let's pick this conversation back up after you buy the SRM and use it for a while

Also: Manuals & Documents

bartek. 

Does anyone know where can I buy the 5bling gloves? Seems like velodromeshop.net stopped to offer them.