Slighly technical question
I just got my bike back from the LBS, they installed a quarq for me. My bike will stay on the trainer for the most part. Will the quarq be affected by how much resistance I put on the trainer wheel? Does it matter? I noticed in last years eagleman, I did the race based on avg. mph. (don't beat me up) and I was 2-3 mph faster than what my trainer speed was indicating. I might have had the resistance too high.
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No, it won't affect the Quarq. However, now that you have power on the bike, completely ignore the speed on the trainer and especially don't compare that speed to what you may see outdoors. There is no relation, at all.
I just have to not listen to my friends on the rare occasions we "spin" together. I "go" 20% slower than they do on our respective trainers, but am faster outside.
Two things play into this:
1) The resistance curve is different from one trainer to another and depends on other things like tire pressure too. You might just have a "stiff" trainer like me.
2) Speed on the road is related more-or-less to W/kg (at least on flats), but speed on a trainer is strictly watts. It doesn't matter if you're wearing a parachute on a trainer. :-)
Wm
I figured it wouldn't matter just wanted to make sure. thanks
@Tucker - I got my thong on and I am ready to start crushing!
Oh and I think William may have slightly mistated above. W/kg is the big factor on hills while watts are the biggest factor on the flats, aerodynamics aside.
It's more complicated than that.
Here's an explanation that makes (gross) simplifications:
Assume you are climbing a 100% grade, and that you have no mechanical friction loss on your bike. In that case, your velocity would be very low, and wind resistance can also be neglected. In this case, you are STRICTLY governed by W/kg.
Now assume you are at a zero grade, again with no frictional losses. Then you have only rolling resistance (linear with velocity) and wind drag resistance (cubic with velocity). At low speeds, resistance is effectively linear with V, and at the speeds most of us go, it's closer to the square (neither linear nor cubic dominate), and at very high velocity the cubic term dominates.
Each of the two resistances is proportional to a separate lumped contant that contains information about your mass and tire pressure and quality (rolling resistance) and your effective "aeroness" (wind resistance).
The rolling resistance is generally assumed to be strictly linear with mass, i.e., W/kg is the term that matters (not absolute W)
For the wind resistance, you need something to stand in as a proxy for "aeroness", which is often called proportional to "effective frontal area". If you think about it, all other things being equal, there's a relationship between how massive you are and your "area". Unfortunately, it's not strictly linear (or square, or whatever). If frontal area and kg were directly proportional, then we could use W/kg as a direct stand in. If frontal area were unrelated to your mass, then we could use absolute watts as a stand in. Neither is the case, but W/kg is a BETTER stand in than absolute watts...
Thus, generally, W/kg works better as a handy approximation tool than absolute watts, with the following provisos:
1) We have been assuming no mechanical loss in the bike, but there is a mechanical loss of a few %.
2) We have been assuming that the bike has no mass, but the bike DOES have mass. So for rolling resistance and gravity, it's really W/(kg of body + kg of bike)
Both of these tend to make W/kg fail because we don't include the ~8 kg of the bike, and they make the term look closer to just absolute W (which would be the case if your bike weighed a LOT more than you, instead of the other way around).
The other place that it makes it look more like W than W/kg is that there is a minimum velocity required to keep the bike going (and not topple over), so if that's below some fraction of your FTP, you have to use a proportionately higher fraction of your FTP than your heavier, more powerful rider next to you sometimes.
Anyway, that's a very long explanation, but no... I didn't mean "absolute W" on the Flat... unless the "extra" kg are making you ONLY longer and not wider at all. :-)
Cheers,
Wm
I realize it is more complicated than my generalization above. I was merely pointing out that watts are the determining factor when it comes to speed on the flats.
It seems you are saying that is not the case and W/kg are a better determinant. So are you saying on a flat, assuming we are basically the same aerodynamically, you will always ride faster than me because you have a higher W/kg? I was always told, and have read here a bunch of times, that the people with higher FTP will go faster on the flats. And on the hills W/kg would be a bigger factor. You are telling me that is not correct. Is that what you are saying? Am I misunderstanding?
What William is getting at is that it's more than just W, but not as simple as W/kg. It is really watts per cross-sectional area, and cross-sectional area goes up as kg goes up. So W/kg is the best way of describing it. If you are talking about vey big differences in weight, then it's a good way of comparing. Small differences in weight, and it's pretty much just about watts.
The best way to learn this stuff is to experience it by riding with a variety of different people. Big, small, fat, skinny, strong and not so. You'll instinctively learn where w/kg is more important that absolute watts, witness how some folks pay a penalty for not being aero, etc. You'll also learn to sorta ballpark someone's FTP as you ride them more often. Very convenient for long climbs and other hard rides, as you can tell when someone is working too hard and it's only a matter of time before they come back to you.
But to answer your question specifically:
If you and I have the same aerodynamics, then whoever has biggest watts wins....making the further reasonable assumption that we are talking about realistic bike velocities where the air resistance is much more important than rolling and mechanical resistances.
But the supposition that you and I have the same aerodynamics is a huge one...and the W/kg is kind of an imperfect stand in for Watts/cross-sectional area.