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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?
Last edited by: rruff: Jul 28, 14 11:11
I would just add that I've seen a bit of evidence on myself that chipseal that bad reduces your sustainable power too :(

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I did a long ride that was nearly all chipseal last week and I believe it. I had to stop a several times just to let my hands and feet de-numb. And that was with 80psi in 23mm Gp4000s.
jackmott wrote:
I would just add that I've seen a bit of evidence on myself that chipseal that bad reduces your sustainable power too :(

I found fresh chipseal on a regular route for me this weekend. I'll use this excuse.
I would be curious to hear what riding on the white line does for your Crr. I know it would be hard to hold that line all the time, but I would guess that you don't have to worry about the paint being tacky.
They haven't painted lines yet. They probably won't until it is fully cured... which will probably be a good time to try again.
With all the chipseal around here, but no formal testing I believe your results. I've always told riding friends smooth pavement feels a solid 1 mph faster than chipseal.

This weekend I rode my (by far) fastest bike split in a tri ever. Guess what....zero chip seal and all very good pavement.

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Would have been interesting to do some runs at 90-100psi to see if the Delta decreased.

By "smooth seal" you mean simply painting sealer over the existing surface? Crazy that it caused that much of an increase in crr.
Nice. The results when you go back will also be interesting.
Looks smooth compared to some of the shit we have here :) I don't see any bomb craters in the road
Since the other chipseal thread started I have been keeping my eye out on all the roads around me.

So far I must say that WV seems to have done something right because I haven't seen a single chipsealed road in the past week. Honestly kind of shocked because even when I lived in NJ I knew of chipsealed roads that were basically like if you made a gravel driveway on top of some flypaper.

Granted half the roads around here the white line is painted in the dirt or the brush on the side completely missing the road surface but they are pretty smooth!
>I would just add that I've seen a bit of evidence on myself that chipseal that bad reduces your sustainable power too :(

You just need wider wheels, wider tires, and lower pressure. :)

I'm not really kidding all that much, though. I know you believe you "can't feel the difference," but trust me, try it again. You can. I know you can do it. Run a Vittoria-cotton-like 23-25mm tire at lower pressure with latex on Firecrest-wide rim, and it's like a magic carpet ride on chipseal. That's not hyberbole. Get the damned Turbo Cotton, and you're covered on all fronts! And I don't mean stupid low pressure. I'm 175lbs, and I run it at 90PSI. Vs. 105 for standard asphalt. Probably giving up a bit of Crr, but, as you point out, when your junk has been turned to mashed potato-like consistency over hours of that stuff, it's time to talk about trading in some Crr.
By "smooth seal" you mean simply painting sealer over the existing surface? Crazy that it caused that much of an increase in crr.

It's sprayed on. I think it is the same stuff they use to seal asphalt roads.

I wasn't expecting that either. The shoulder seemed very nice. I reduced the smooth data first and had a wtf?! episode for a minute before I realized that the sealer must have been causing a lot of drag. It's possible that something else has happened to increase the drag numbers, since I didn't have a control. But I doubt it.

I tried the Challenge Pari-Roubaix tires (27mm, 30mm actual) on another road last fall, inflated to 60 psi. It was a subtle improvement compared to GP4000 at 80 psi. It still sucks. Nothing like a "magic carpet"...

Not all chipseal is equal. Some is pretty decent, especially if they do a layer on top with smaller aggregate.
Beyond the comfort I would love to see the Crr of something like your 20mm Supersonic at 120psi, a GP4000S at 90psi, and a Pari-Roubaix at 60-70psi.

My guess is that on a rougher surface, a larger tire w/ lower pressure is faster - and would absolutely make up for the aerodynamic disadvantage. Maybe a 25mm tire around 80psi would be the sweet spot. But I could be way off.

The tough part is that there are a few races around me that have mostly good pavement with a few to a few dozen miles of REALLY rough chipseal - Vineman and Wildflower come to mind. Lots of math involved when you get into weight, Crr, CdA when making equipment choices.

/kj

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>. It still sucks. Nothing like a "magic carpet"...

I found it to be, but then I was coming off a 19mm HED3 with 130PSI tubulars.
Based on this, I'm going to hypothesize it's the ultra smooth roads that make Challenge Roth have such a fast bike course.
First, thanks for testing and reporting, I can't believe you made that many chip seal runs, talk about taking one for the team.

They chip seal a lot here in SW Idaho and are currently chipping and sealing like crazy on a lot of my routes. It is like being a rat in a maze when trying to avoid the graveled but not yet sealed roads. They seldom fill the little divet holes and then you can't see them with the fresh black seal coat.
I am not sure if they are doing our weekly TT course this year but remember the last time they did it. They just did the top 7 miles to the ski area here and the annual hill climb is in 2 weeks. You can really feel it when you get past the half way point.
They usually use smaller rocks then the ones in your photo and it is not as bad. There are a few roads in the next county west of here that use the giant chip rocks like yours and they are really bad.

Rob
rruff wrote:
(20mm Supersonics and latex tubes, 120 psi). The air was 85F and the pavement was 125F.

interesting stuff.

i've been meaning to dig up some articles from a few years back. a local town chip-sealed a road and they were able to work with the paving company to do it in a 'cyclist-friendly' way. it helped that the owner of the paving company is a cyclist.

there were some interesting observations. i believe they found a way that didn't materially increase the costs or time to complete the project. i also believe it had something to do with the size of the aggregate (perhaps combining multiple sizes) and with the order of laying down the layers.

i ride chip seal all the time (northwestern wyoming). maybe i'm just used to it, but at 95psi on 23s (i'm about 150) i don't find any issues. 75psi on 28s is pretty dreamy, though.

120psi on the supersonics? do you find that to be fastest? i'm a little surprised by that.

PS i've been reading all your posts and the subject made me recall a situation i faced a few years ago. a local route was being chip sealed. it was a 25-mile stretch i'd incorporate into almost all my rides. i rode it the day before they sealed it and the next day it was available. it went from being my favorite stretch of road to unbearable (for me). i was riding an aluminum orbea at the time. i was SO bummed as it is 1/2-mile from my garage.

i demo'ed a roubaix (same wheels, saddle and tires/pressures) and found myself doing that stretch of road twice...and loving it. i no longer have that roubaix but the frame really did something for me. to be fair, it could have been the different geometry or the bars and tape contributing to the ride quality.
Last edited by: tetonrider: Jul 28, 14 19:13
What states are you seeing chipseal? I have not seen any in NH where I live and I wonder if they can plow snow on roads with chipseal?
Anyone know offhand the length/severity of the chipseal sections on the IMTX course?

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"What's good for me ain't necessarily good for the weak-minded."
Quote:
What states are you seeing chipseal? I have not seen any in NH where I live and I wonder if they can plow snow on roads with chipseal?

Last year they chipsealed some roads in my old neighborhood in Minneapolis. And they definitely plowed them last winter.
That's a pretty big dip in time for chip seal. You can definitely feel it being slower, but to put a number to it is just depressing.

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I've been meaning to dig up some articles from a few years back. a local town chip-sealed a road and they were able to work with the paving company to do it in a 'cyclist-friendly' way. it helped that the owner of the paving company is a cyclist.

there were some interesting observations. i believe they found a way that didn't materially increase the costs or time to complete the project. i also believe it had something to do with the size of the aggregate (perhaps combining multiple sizes) and with the order of laying down the layers.

What I saw being done was a layer of black goo, a layer of gravel, then a layer of black goo (maybe not the same stuff or as thick). There is a double layer process where they use smaller aggregate for the last layer, and that is much better. There is also a process where they add a layer of goo that is thick enough to cover all the gravel and fill in gaps. Both cost at least 50% more but are supposed to last longer.

Browsing through the cost studies I could find online, not a one of them considers higher fuel consumption. It's like a 10% increase. One study mentioned that fuel consumption would take a big hit, yet completely ignored it in their analysis!

A big selling point for chipseal is better traction. I haven't seen any measurements, but it is always cited as a plus. How would you like to experience that traction if you crashed your bike?

120psi on the supersonics? do you find that to be fastest? i'm a little surprised by that.

They are 20mm on narrow rims. I typically run them at 130psi on smooth roads. 110psi on rougher ones.

Last edited by: rruff: Jul 28, 14 21:12
My guess is that on a rougher surface, a larger tire w/ lower pressure is faster - and would absolutely make up for the aerodynamic disadvantage. Maybe a 25mm tire around 80psi would be the sweet spot. But I could be way off.

Schwalbe claims that with MTB tires on gravel, 20 psi is faster than any higher psi. My very unscientific rule of thumb is that the sweet spot for rolling resistance is where the level of vibration ceases to be annoying.

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