Now that I have a power meter in the rear hub of my road bike I can compare not only my own efforts, but how much various bits of kit slow me down. In this case, I have compared a tough fast-touring Schwalbe Marathon Greenguard 25mm tyre with a Michelin Pro 4 Endurance 28mm. The latter should have lower rolling resistance by some 7W if the laboratory results from bicyclerollingresistance.com are to be believed.
However, those tests are done on a checker plate drum in controlled conditions. In some ways that's good because it removes a lot of noise from other factors that you'd get in the real world. However, I'm interested in getting some real-world data, that applies more directly to me and the bumpy roads I normally ride.
So I ran my own rather inexact experiment as follows:
Route: 3.2km climb up "Road hill climb" through Ditteridge. I didn't measure the descent as it depends more on wind resistance.
Power: 200W average. A power I can consistently and repeatedly produce for the time it takes to climb this hill.
Wheels: Front wheel only changed. I could've changed the rear as well, but that would've taken all day.
Measurement: The total lap time for climbing the hill. With consistent power this should show any differences in the drag of the set up.
With those caveats out of the way, here are the results.
|Tyre||Pressure (PSI)||Lap power||Lap time||Relative drag (Watts)|
|Schwalbe Marathon Greenguard 25mm||95||200||00:13:21||13|
|Schwalbe Marathon Greenguard 25mm||80||199||00:13:31||16|
|Schwalbe Marathon Greenguard 25mm||70||199||00:13:27||15|
|Schwalbe Marathon Greenguard 25mm||60||199||00:13:14||12|
|Michelin Pro4 Endurance 28mm||85||199||00:13:08||10|
|Michelin Pro4 Endurance 28mm||70||199||00:13:12||11|
|Michelin Pro4 Endurance 28mm||65||200||00:13:14||12|
|Michelin Pro4 Endurance 28mm||58||199||00:13:05||9|
* Had to brake due to a turning vehicle.
|Av. Marathon Greenguard this||00:13:23|
|Av. Pro4 Endurance||00:13:09|
|Time diff per 100km (uphill) per tyre||00:07:01|
The raw data copied from my Strava ride. Recorded on a Garmin Edge 500 using a PowerTap hub. "Relative drag" is based on my dodgy reverse-use of the Bike Calculator and is only useful for comparison within this table, if at all.
The results aren't as clear as I'd hoped, but I think the technique roughly works. Climbing at a consistent power and measuring the time did show some consistent results. The Michelin Pro 4 endurance tyre with a plain Shimano 105 hub was faster every time than the Schwalbe Marathon Greenguard on a SON Delux dynamo hub (disconnected). However, the difference is only a few seconds and multiplying this up to a 100km for two wheels would result in a longer ride by less than 15 minutes.
That number only really makes sense if the whole of that 100km was uphill, like my test. Downhill, tyre rolling resistance is small compared to air resistance. Perhaps a better estimate for a real 100km would be an extra ten minutes per 100km using the tougher Marathon tyres. On second thoughts, multiplying up like that would also multiply up my errors and confounding factors, so I ought to run a better experiment before declaring such a difference.
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