Lemond Revolution - increase in speed for the same power over time?

Triathlon Forum
1

I’ve had a Lemond Revolution for 2 months now.

On 4th July, 240W (SRM) was 33.8kph. 2 months later, 240W is 36.8kph.

Has anyone else seen this increase in speed for the same power over time? A side effect of it is that the Wattbox is almost useless for any sort of long term power monitoring, though it’s okay for day to day comparisons as the change each day is quite small. I’m speculating that the source of this increase in speed for the same power is a reduction in bearing drag, and wear on the belt. Even so, it now requires over 40W less power to do the same speed compared to two months ago, and that seems like a huge amount of drag to lose from the system.

I contacted Lemond about this, and their response was that the user can’t calibrate the Wattbox as it is factory calibrated. And re my speculation about belt wear, they said they will make replacement belts available online. This doesn’t help much as it would just put it back to where it was 2 months ago and it would presumably still change by the same amount each day as the new belt wears, and we really shouldn’t have to fit a new belt every 2 months anyway.

If other people have seen this effect, can you tell me if it eventually stabilised? It’s hard to imagine that a new unit could have an awful lot more than 40W of drag to lose as it wears in!

2

I have not, but I have the original Revolution with a Power Pilot.

3

One way to tell would be to do exactly that… ie put a new belt on back to back with old belt and re-test…

Also are you confident the SRM cal has not drifted? through either ramp or environmental conditions??

As an aside… it doesn’t matter… you train off watts not wheel speed on a trainer… 240w now is just the same as 240w 2 months ago right ? (provided the power meter has stayed consistent of course)…

Interesting though… especially re the belt power loss…

4

40W is way too much to be from belt break-in. I’d double check whatever you’re using to check the power against. The majority of the drag at that power level is aerodynamic (from the fan), and that’s not going to be changing that amount.

I find it odd that the Wattbox has no coast down calibration procedure. That was added to the Power Pilot firmware to address unit to unit variances, along with small amounts of changes from belt wear.

5

As an aside… it doesn’t matter… you train off watts not wheel speed on a trainer… 240w now is just the same as 240w 2 months ago right ? (provided the power meter has stayed consistent of course)…
The reason it matters is I want to use the Wattbox as a consistent reference to check the calibration of multiple power meters against, in addition to static torque tests. This problem doesn’t stop me using it for that, because the Wattbox power is very consistent relative to SRM if you only do low intensity training sessions, the relative power reading only increases by around 0.1% per day. So provided I don’t try to compare power meters across days when I’ve done some high intensity training (which can cause a much bigger upwards movement in the Wattbox power relative to SRM power, approx 1%), I can cope with 0.1% drift per day. Obviously it would be preferable to have longer term stability, though.

More importantly, some people may want to use the Wattbox as their only source of power data while using the Lemond, e.g. if they don’t own a power meter at all, or if they own a PowerTap. It would be extremely misleading for such a user to think that their power has improved by tens of Watts when all that has happened is the Lemond is running faster for the same true power.

Another issue is that if it carries on much longer the high speed could present problems for higher intensity sessions, e.g. not having long enough gearing.

I don’t believe the SRM’s slope has changed in that time because a static torque test says it still has the same slope that it left the factory with, which has been the case every time I’ve tested it since I bought it several years ago. My power at max efforts in TTs is unchanged. And I have also used my first Power2Max as a comparison, which a static torque test says reads 0.4% lower than the SRM, and the Wattbox gave the same figure of 0.4% lower than the SRM. Again, this particular Power2Max has always given a very similar result to that every time I’ve tested it over several years.

Tom, I agree it’s puzzling where such a large loss of drag could be coming from, as you’d expect the aerodynamic drag of the fan to dominate. Am I right in thinking that the power to overcome bearing drag is likely to be roughly related to speed squared, so the bearings on the flywheel axle would have ~64x the drag of wheel bearings? If that is the case, maybe they are the most likely source of the change, and it should eventually stabilise.

6

Just thinking out loud, could a build up of dust be causing this? I know, for example, that a concept2 rowing machine alters the drag on the flywheel by changing the amount of air flowing around it, less flow = lower drag. Perhaps dust is reducing airflow, therefore reducing drag?

7

Have you done any disassembly to see if there is any rubbing/wear marks? I’d guess that a pulley or rotating component was rubbing, and now its sufficiently worn. I dont think that there is any way that it would be bearing or belt break in. Also, how “in control” has the temp (air density) been? If you’re comparing dry cool temps to wet hot temps, the density change may alter fan resistance by a substantial amount.

8

I’ve just taken the cover off to have a look - no sign of anything having been rubbing.

Dixie, I can’t see any significant dust on anything, it has a gale force wind blowing through it every time you use it, so I think that keeps it fairly clear of dust.

The Wattbox is supposed to account for air density by having sensors to measure temperature, humidity and pressure. If anything, the air density has increased over the 2 months I’ve been using it, due to gradually falling temperatures, which would cause the opposite effect of what I’ve seen.

I still think the bearings are quite a likely source of the change. It says here that a rear wheel bearing can have 0.5W of drag at 25mph:
http://velonews.competitor.com/2014/03/bikes-and-tech/technical-faq/technical-faq-much-drag-can-eliminate-dropping-two-bearings_321169
If the drag is related to speed squared (still not certain about that assumption), that would be 32W per bearing at the fan/flywheel, which spins 8x as fast as the rear wheel. Looking at it, I think there may be 4 bearings spinning at that speed inside the Lemond - 2 on the fan axle and 2 on the belt tension adjusting pulley, so they could create as much as 128W of drag at 25mph, and losing 40W of that over 2 months of use starts to look quite plausible.

But what I was really hoping was that some other people might have speed data spanning a long period of time to see if the same thing has happened with their Lemond.

9

As an aside… it doesn’t matter… you train off watts not wheel speed on a trainer… 240w now is just the same as 240w 2 months ago right ? (provided the power meter has stayed consistent of course)…
The reason it matters is I want to use the Wattbox as a consistent reference to check the calibration of multiple power meters against, in addition to static torque tests. This problem doesn’t stop me using it for that, because the Wattbox power is very consistent relative to SRM if you only do low intensity training sessions, the relative power reading only increases by around 0.1% per day. So provided I don’t try to compare power meters across days when I’ve done some high intensity training (which can cause a much bigger upwards movement in the Wattbox power relative to SRM power, approx 1%), I can cope with 0.1% drift per day. Obviously it would be preferable to have longer term stability, though.

More importantly, some people may want to use the Wattbox as their only source of power data while using the Lemond, e.g. if they don’t own a power meter at all, or if they own a PowerTap. It would be extremely misleading for such a user to think that their power has improved by tens of Watts when all that has happened is the Lemond is running faster for the same true power.

Another issue is that if it carries on much longer the high speed could present problems for higher intensity sessions, e.g. not having long enough gearing.

I don’t believe the SRM’s slope has changed in that time because a static torque test says it still has the same slope that it left the factory with, which has been the case every time I’ve tested it since I bought it several years ago. My power at max efforts in TTs is unchanged. And I have also used my first Power2Max as a comparison, which a static torque test says reads 0.4% lower than the SRM, and the Wattbox gave the same figure of 0.4% lower than the SRM. Again, this particular Power2Max has always given a very similar result to that every time I’ve tested it over several years.

Tom, I agree it’s puzzling where such a large loss of drag could be coming from, as you’d expect the aerodynamic drag of the fan to dominate. Am I right in thinking that the power to overcome bearing drag is likely to be roughly related to speed squared, so the bearings on the flywheel axle would have ~64x the drag of wheel bearings? If that is the case, maybe they are the most likely source of the change, and it should eventually stabilise.

Back when I did the “virtual CdA and Crr” of the LeMond (http://bikeblather.blogspot.com/2013/01/whats-virtual-cda-and-crr-of-lemond.html), I came up with an equivalent Crr of .0051 (85kg bike+rider). This would basically represent the belt and bearing drag.

Anyway, using that, I calculate a TOTAL non-aerodynamic drag of 40W at an indicated 34 kph.

Something still doesn’t sound right with your setup…

10

When you did this test, you had 222W = 34.1kph:
http://bikeblather.blogspot.nl/2013/01/whats-up-with-those-funky-rings.html

Mine started off needing ~240W for that speed, and now only needs ~200W for that speed, so it’s not completely out of line with yours, yours was in the same state mine was after a month of use when you did that test. How much have you used it since that test, and what power does it need now for 34.1kph?

11

When you did this test, you had 222W = 34.1kph:
http://bikeblather.blogspot.nl/...ose-funky-rings.html

Mine started off needing ~240W for that speed, and now only needs ~200W for that speed, so it’s not completely out of line with yours, yours was in the same state mine was after a month of use when you did that test. How much have you used it since that test, and what power does it need now for 34.1kph?

Actually…the one in my possession had been used quite a bit before I received it (Thanks Matt!), so it should have been quite well “worn in”.

IIRC, it was quite noticeable (but only in the range of 5-10W IIRC) in comparing some of the data with the factory “coast downs”…I’ll have to wade through some old emails to figure that out…

edit: Oh, and I’m letting a friend borrow it right now, so I can’t tell you what the current value is.

12

Longshot, but since it’s a wind trainer (all resistance is aerodynamic), has the air density decreased significantly over that time? Primary determinants of air density are altitude and temperature. If it has gradually drifted (and you’ve stayed in the same place), then that rules out altitude, but has temperature gradually increased?

13

I didn’t get my Lemond Revolution new, but it was very lightly used. It came with the cassette and it barely showed any wear.

I’ve been using it with the Wattbox 2-3 times a week since February, and mine has been pretty constant over that time.

Last week: 240W at 22.3 mph (35.9 kph)
March: 239w at 22.15 mph (35.6 kph)

Small differences in temperature/humidity between those two data points, but not much.

Cheers!

14

As an aside… it doesn’t matter… you train off watts not wheel speed on a trainer… 240w now is just the same as 240w 2 months ago right ? (provided the power meter has stayed consistent of course)…
The reason it matters is I want to use the Wattbox as a consistent reference to check the calibration of multiple power meters against, in addition to static torque tests. This problem doesn’t stop me using it for that, because the Wattbox power is very consistent relative to SRM if you only do low intensity training sessions, the relative power reading only increases by around 0.1% per day. So provided I don’t try to compare power meters across days when I’ve done some high intensity training (which can cause a much bigger upwards movement in the Wattbox power relative to SRM power, approx 1%), I can cope with 0.1% drift per day. Obviously it would be preferable to have longer term stability, though.

If it is related to higher power sessions is the belt slipping? If so it will wear the belt down and slip more with more use.

15

Longshot, but since it’s a wind trainer (all resistance is aerodynamic), has the air density decreased significantly over that time? Primary determinants of air density are altitude and temperature. If it has gradually drifted (and you’ve stayed in the same place), then that rules out altitude, but has temperature gradually increased?

Apparently, the Wattbox is supposed to have sensors to account for that (temp, humidity, pressure), so it’s probably not that.

16

When you did this test, you had 222W = 34.1kph:
http://bikeblather.blogspot.nl/...ose-funky-rings.html

Mine started off needing ~240W for that speed, and now only needs ~200W for that speed, so it’s not completely out of line with yours, yours was in the same state mine was after a month of use when you did that test. How much have you used it since that test, and what power does it need now for 34.1kph?

The test I linked to above was from one of the very first tests I did with the trainer, and the virtual Crr and CdA would predict a power of 219W @ 34.1 kph. I’d call that within the margin of error as compared to the test you linked to with 222W @ 34.1kph, which was one of the LAST times I used the trainer…

17

I didn’t get my Lemond Revolution new, but it was very lightly used. It came with the cassette and it barely showed any wear.

I’ve been using it with the Wattbox 2-3 times a week since February, and mine has been pretty constant over that time.

Last week: 240W at 22.3 mph (35.9 kph)
March: 239w at 22.15 mph (35.6 kph)
Are those figures Wattbox power or power from a separate power meter? The Wattbox power will remain fairly constant relative to speed, what I’m describing is the Wattbox power changing over time relative to SRM power, or equivalently speed relative to SRM power changing over time.

18

As an aside… it doesn’t matter… you train off watts not wheel speed on a trainer… 240w now is just the same as 240w 2 months ago right ? (provided the power meter has stayed consistent of course)…
The reason it matters is I want to use the Wattbox as a consistent reference to check the calibration of multiple power meters against, in addition to static torque tests. This problem doesn’t stop me using it for that, because the Wattbox power is very consistent relative to SRM if you only do low intensity training sessions, the relative power reading only increases by around 0.1% per day. So provided I don’t try to compare power meters across days when I’ve done some high intensity training (which can cause a much bigger upwards movement in the Wattbox power relative to SRM power, approx 1%), I can cope with 0.1% drift per day. Obviously it would be preferable to have longer term stability, though.

If it is related to higher power sessions is the belt slipping? If so it will wear the belt down and slip more with more use.

It’s a timing belt (i.e. toothed). If it’s slipping…well, you’ve got bigger problems :wink:

19

Are those figures Wattbox power or power from a separate power meter? The Wattbox power will remain fairly constant relative to speed, what I’m describing is the Wattbox power changing over time relative to SRM power, or equivalently speed relative to SRM power changing over time.

Ah, gotcha. Yes, those are from the Wattbox power. Sorry, I missed the “SRM” in your initial post.