Koogar

I asked about Dura Ace compatibility some time back and they couldn't confirm one way or another but were not optimistic. Seems like that hasn't changed.

carleton

I could "measure" your power output by watching your effort. That doesn't mean it's precise, accurate, or repeatable.

Just because it has the words "Power" and "Meter" in the product name doesn't necessarily mean it does what you think it does.

dunderhi

Are you words of warning for all power meters, crank arm power meters, or 4iiii's power meter?


Does anyone know if the 4iiii power meter is a supply your own crank-arm business model. I ask this since there doesn't seem to be price differentiation for the Shimano 105 vs. the Dura Ace.

Banchad

Yeah you have to supply your own kit.

Dalai

Was designed with the intention you could self install, but at the moment you need to send in your left crank arm for a factory installation...

carleton

Just in general. Making a power meter of any sort seems to be a way to make easy money in the road cycling world.

Remember, there is a Power Meter that measures wind and calculates the power output

dunderhi

I'm new too all of this power training stuff, so I wasn't aware.

carleton

Most cycling power meters assume that you are a road cyclist riding for 2-4 hours/ride and you want to know long-term data. That's why their sampling rates are every 1 or 2 seconds. A lot of things get averaged out in that many data points.

Track events are (obviously) much shorter. So, you want more accurate data more often. This is why the SRM is the gold standard for track. It samples (or used to) as fast as twice per second, for the not tech folks. So for a Flying 200 or 1K, you get a lot better sets of data than you would with others.

Also, I don't like the 1 crank arm power meters. Yeah, on the road, you can assume that the output will average out. But, on the track, during a standing start, you are getting half of the data.

If you can afford it, get a PM that measures from the crank spider.

I'm not sure what the word is on pedal power meters these days. Are they getting better? On paper, they are superior to crank spider PMs because they are closer to the source of the power (your legs) and they are measuring left and right data independently. Plus they are easy to swap to other bikes.

taras0000

SRM is a one crank PM. What's the difference if you measure at the crank or spider? Hub based in theory should be the most accurate. Also lots of room to house internals, therefore more complex computer, therefore higher sampling rate.

Crank based ones to allow you to use any wheel you want.

carleton

Actually, it isn't. You can separate the two crank arms and the BB from the spider. It's a 4 piece crankset.

The right crank arm mates with the spider with 3-4 screws (depending on your model):




But, I see what you mean. The left crank arm moves torque through the bottom bracket then over to the right crank arm which then turns the spider.

(these aren't exactly track parts, but they work for the illustration)

SRM Crank arms:


Plus bottom bracket:


Plus SRM spider:


Equal: SRM Power Meter

Dalai

Sensors on the left crank only deforms the strain gauges when pressure is applied to the left pedal. With the sensors on the spider, pressure on both pedals deform the strain gauges on the the spider - hence measures deflection from both pedals.

Crank arm photo on the scales is my photo Carleton

Banchad

I can't, so I'm making one(for my dissertation).

carleton

Wow...the internet is a small world

Good luck! Can you talk about it? What style? Where are you placing the strain gauges?

taras0000

This just brought about a big face-palm for me. It's so obvious. I don't understand how I didn't figure this out myself. Frankly it's just as accurate as a hub based PM, it just doesn't take into account the minimal losses from the chain.

carleton

Yup. And it can be argued that being that because the crank spider is closer to the legs than the chain is in the system, then you are getting a better measurement of what the rider is doing because it's getting measured before the chain stretches and absorbs some of the torque.

This is why SRM is considered better than PowerTap (measures at the hub). This is also why the promise of pedal sensors was so high, because they were closer to the body than crank arm, chainring spiders, and hubs as a measuring point.

Then there was the PM that measured in the cleat.

I think the cleat is as close as you can get and reliably measure force in 2 directions (downstroke and upstroke).

The Power Meter shoe could work. But it would be undermined by the straps that sprinters use. Because when you use straps, the force added is applied to the bottom of the pedal. Not sure how a shoe power meter could measure that.

wens

Hmm, I need to draw the system to really think this through, but assuming negligible damping, I don't think deflection of any component changes measured power enough to matter, since everything is deflecting at the same time. The reason you get lower readings for a power tap vs crank based pm is fiction losses in the chain. Probably tiny for a track bike. Power taps do have some aliasing effects because they measure time based instead of event based. Not sure how much it matters for sprinters, but it's basically negligible for enduros.

Eta: by same time I mean the time effects are too small to matter for classical mechanics.

queerpunk

eh, it's not entirely intuitive because there are parts you don't see. a PM on the spider looks like a PM on the right crank, since it's not really visibly clear that the spider is actually (like, conceptually) located on the spindle, not the right crank - even though it's fairly obvious that it receives input from both cranks.

Banchad

I can talk about it but I'd rather not until I actually know whether I'll be able to finish it for my dissertation deadline.

Predator circles its prey with new Major Track one-piece carbon handlebar & stem - Bikerumor

What do you all think of these?

carleton

A waste of engineering and money.

They solve a problem that already has better solutions.

Why would you pay 2.5-3x the price of a comparable top-tier stem/bar setup to have no angle, reach, or bar tilt options? It's a bad idea. They introduced these back in like 2011. They are not popular for a reason.

This is the equivalent of having a fixed, rigid car seat drilled into the floor of the car. No sliding, no tilting, no adjustments of any kind.

Trackliche

+1

This seems to be the whole model of Predator, IMO.

TC

queerpunk

cool but impractical.

if i was made of money i'd be all about those, for the cool factor. but i'd want to test out the shape of the bar, first, to see if i'd be happy with the sphinx position; i'd also probably wind up having different handlebars to travel with, since those might not fit into my travel bag; i'd also probably wind up maybe not using them on my next bike, since obviously you can't tweak the stem length and angle.

i know a few custom carbon dudes who will wrap a Scatto bar to a carbon stem and smooth out the juncture. that's cool too.

but in general, there's a reason that one-piece bar/stem combos haven't really caught on.

if they were making sprint bars, madison bars, and road bars, they'd probably be a bit more successful.

Dalai

@Banchad - looking forward to hearing more about it when you are able to talk.

Banchad

https://www.youtube.com/watch?v=bgLfOrVJJMg

Trackliche

More Perko happiness:

https://www.youtube.com/watch?v=g3ri1th4dBg

TC

gtrob

Those predators will look nice, but Im sure will flex like crazy. They are aiming for 350g, when scattos are 380g for a narrow 37cm bar only. Not to mention all other issues with fit, however once you have all that set its not like it changes much.

But I bet they would look cool