They recently chipsealed my TT and field testing course, but fortunately part of the road has a shoulder and that was only seal coated... no gravel. So I thought it would be a good opportunity to see just how much the chipseal slowed me down. I rode through there the day they sealed it, so I knew how old it was. I figured it would take a couple days for the seal to cure. I went back 4 days later for the testing.
It was quite a contrast. The shoulder felt very smooth with just some occasional gravel, and the chipseal was rough as hell. The picture below is a fair approximation of how it looked:
I did 16 out-back runs, alternating between smooth and rough parts of the road, so 8 runs each. I knew from previous testing in the same location that my CdA should be ~.205, so I fixed that number and allowed the Crr to vary. The Crr I'd been using before was .0035 for the tire temperature of 100F (20mm Supersonics and latex tubes, 120 psi). The air was 85F and the pavement was 125F.
Prior to chipseal, Crr= .0035
Chipseal, Crr= .0074 (111% increase)
Smooth seal, Crr= .0064 (83% increase)
Edit: In case you are wondering, a Crr increase of .0005 cost you ~.17mph on your TT bike. So the chipseal is ~1.3 mph slower, and the smooth seal ~1.0 mph. That's assuming the same power, and I'm sure I wouldn't be able to maintain that on the rough part for long.
This was after 4 days of cure, and the seal no longer felt or sounded sticky and it didn't accumulate on the tires or get thrown on the frame. But I guess it was tacky or soft enough to dramatically increase resistance. I wonder if chipsealed part was actually less sticky or soft compared to the shoulder after 4 days of traffic? If I look at the two it's a difference of .0010. If that is difference is solely due to roughness, then it would be ~30% increase relative to the .0035 of the tires. Considering how it felt that doesn't seem like that much.
Guess I'll have to try again. Anybody know how long it might take to fully cure?
It was quite a contrast. The shoulder felt very smooth with just some occasional gravel, and the chipseal was rough as hell. The picture below is a fair approximation of how it looked:
I did 16 out-back runs, alternating between smooth and rough parts of the road, so 8 runs each. I knew from previous testing in the same location that my CdA should be ~.205, so I fixed that number and allowed the Crr to vary. The Crr I'd been using before was .0035 for the tire temperature of 100F (20mm Supersonics and latex tubes, 120 psi). The air was 85F and the pavement was 125F.
Prior to chipseal, Crr= .0035
Chipseal, Crr= .0074 (111% increase)
Smooth seal, Crr= .0064 (83% increase)
Edit: In case you are wondering, a Crr increase of .0005 cost you ~.17mph on your TT bike. So the chipseal is ~1.3 mph slower, and the smooth seal ~1.0 mph. That's assuming the same power, and I'm sure I wouldn't be able to maintain that on the rough part for long.
This was after 4 days of cure, and the seal no longer felt or sounded sticky and it didn't accumulate on the tires or get thrown on the frame. But I guess it was tacky or soft enough to dramatically increase resistance. I wonder if chipsealed part was actually less sticky or soft compared to the shoulder after 4 days of traffic? If I look at the two it's a difference of .0010. If that is difference is solely due to roughness, then it would be ~30% increase relative to the .0035 of the tires. Considering how it felt that doesn't seem like that much.
Guess I'll have to try again. Anybody know how long it might take to fully cure?