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.

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.

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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

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.

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?

-bobo

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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.

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.

chuckle

yup :)

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There is something to be said about chip and seal and none of it is good. Not very scientific but you can feel a quick pick up in speed and your legs having to work less when you are rolling down a section of road recently chip and sealed and then run into a section that was done the previous year.

We train on mostly chip and seal but our tt course are all laid out on asphalt roads. This Sunday our state tt championship will be held on our 40K course. Beautifully flat road with one 180 degree turn at the half and one overpass otherwise completely pancake flat.

Interesting, thanks for sharing all your Crr work. I suspected that chipseal is one of the reasons that the Muskoka 70.3 (and now Ironman Muskoka) course is so remarkably slow. Great to see some data.

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Northern Indiana has a lot of it.

One of the primary reasons I gave up with 23mm tires and 19mm wheels.

i'm a firm believer in the 23mm wheels with 25mm tires and chipseal has ceased to be a numbing issue. It also makes Doc happy as he told me to avoid too much vibration after I lost a kidney.

So the shoulder feels as smooth as previously, just has a new (sticky?) topcoat? If your CdA (or air density) was underestimated for the day, both numbers would be closer to previous, but with a similar delta? It will be interesting to see if time changes the values. Is there a suitable section without chipseal that could be used as a sanity check if you do a repeat test?

Yes, the shoulder is smooth... actually what the whole road was like previously. It didn't sound or feel tacky, but something was going on.

I got the temperature and density and all that stuff down, and I've done a bunch of tests out there previously. Although I have been tweaking my position slightly, I'd be surprised if I was off by more than .005 CdA. And the added drag was equivalent to a CdA increase of .038 and .052.

There's another road close that I can use for CdA testing, so that is what I'll use instead.

Hello,

Since they have been chip sealing a lot of roads around me, and I am wondering if you have re-tested this after some traffic as "smoothed" it out some.

Thanks.

Not actual testing, but I did TTs on that course for a couple years after and was always >1 min slower on similar power. 24 min vs 23 min, so ~4-5%. That was mostly on the shoulder too, but some of it has no shoulder. It may have improved a little, but not a lot.

You can test it yourself! It would be good to get more data on this...

I am wondering if one can test it with a Notio. Thanks for posting this. I was trying to come up with a “factor” to compare older times to a “chip adjusted” course. In looking around 3 to 6 percent looks about right. It’s complicated as some chip is done relatively well compared to the nightmare picture you posted.

The CdACrr app seems quite good for Crr testing, but you have to be at slow speed. I no longer believe that low and high speed Crr are the same... especially on this kind of surface.

have you had a chance 6 years later to to test this on wider tires at low pressure? You originally did this at 120 psi.

Nope, haven't done it. I ran 100spi after the test and was still >1min slower on the course. I run 23mm at 80psi for surfaces like this now, but I don't race on that course anymore.

For rough chipseal I think the fattest and fastest tires that will fit on your bike, at the lowest pressure where you can still avoid flats/damage is a good bet. Tricky though. If I'm sure that there are no potholes or large cracks I might try 60psi with 23s. Fat tires and low pressure might even be best for smooth chipseal.

I would be interested in your original test at 120 psi and then do the exact same test on same sets of road with 28mm in same brand of tire at 60 psi and compare the 4 sets of runs.

Also assume that the course is fairly flat so flexing of the the low pressure tire does not factor in.

The Notio has no estimation for Crr as part of its current features. You could do it with the Chung known elevation method that is described in the slide set that defines and explains the method and the Notio would probably help correct for any non-zero wind conditions.

The Notio does have a built in accelerometer/vibration sensor and it does output a summary graph. We have lots of new chip-seal where I live (yeah) so I will put doing some chip seal testing on the list of things to play with. You couldn’t estimate a Crr, but I would assume that there is a correlation between the amplitude of the “buzz” and Crr. If that is true, you could maybe use that to “tune” for an optimum tire pressure. My guess would be that the tire impedance effect really increases rapidly at some pressure and the optimum pressure is just below that point

Well...the "breakpoint pressure" for a particular setup is a function of road roughness, rider mass, AND speed. Roughness and speed work together to determine the amount of energy being "put into" the system.

So, yes...the losses due to energy making it through the tires and being dissipated in the system can vary by quite a bit, depending on the speed.

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Hey Ron- At last year's CA state championships I tested that exact combination on a roughish chip seal road and got 93psi as the optimum for my front tire -- rear was wider rim and tire. I weigh about 170 (body only) and on my TT rig I'm pretty close to 50-50 weight distribution. Not sure how much you weight but, unless you're a clydesdale, based on my testing experience I'm quite sure that 120 was costing you a fair amount on that road.

Oh, I'm sure. As I stated earlier I dropped down to 100 psi with those tires later. We weigh the same. How did you arrive at 93 psi?

Last race I did in early March was on rough chipseal and I ran Pistas (23mm) at 80 psi. Definitely would have liked more cushion, but there were some sketchy broken patches.

One nice thing about the chipseal around here is that the roads tend to not get large potholes or cracks, so you can lower the pressure quite a bit and still survive. There were some big potholes on the Nationals course in CO Springs though! And I found a really bad one in practice. Tires survived (80 psi there too), but my fork didn't.

Chipseal is really hard to gauge since the mix seems to vary so much. The size of the aggregate, how soft the tar is, how well it is leveled and smoothed, etc. Nationals seemed pretty fast except for the potholes. The north side of Moriarty was refinished a few years ago, with asphalt first, then rough chipseal, then another smooth layer on top. It feels great and seems decently fast. Last summer they refinished the south part. I don't know what the eventual plan is, but it was rough chipseal for the race! Hopefully they finished it like the north side...

Ya, so many good tests *could* be done. Lots of work to do it right however. I don't even have a bike that I can run 28mm tires on. On my old TT bike 23s are close.

That can depend on the tire as well. I don’t know what Conti did to their 700x20 GP4000, but that was an incredibly slow tire compared to the 700x23. Too bad. That tire looked great on the old Specialized and HED trispokes, but it was almost Gatorskin slow.

Rough *ish*? Parts of that course are damn near cyclocross. :) Fwiw, at the same weight as you, I also arrived at about the same pressure you did.

I did what you did -- took my known CdA that I've tested a zillion times and then ran a section of the course over and over at different tire pressures. I found that below about 93 the CRR was pretty flat but above that it went up quickly (was just looking for the exact data but haven't located it). Because that tire is so narrow I wanted to keep it at 93 to avoid pinch flats. FWIW I was very fast for the watts compared with everyone else, and I think part of that was getting the tire pressure right. [Unfortunately I was less than a month off a serious crash so I was far from great form and got 2nd :-(. ]

Ah, nevermind, by CA you meant the other California. Much nicer roads up there.

That's great! I guess you lived close? And trail got the same result (edit: different course I guess...); very nice to have confirmation. How low a pressure did you try and was it significantly smoother?

Adjusting tire pressure to find the optimum isn't so tedious as adding in different sizes. I may get ambitious enough to try that.

I doubt the GP4000 was as good aerodynamically anyway in real conditions vs the wind tunnel. We still have a very good small tire in the Supersonic 20mm. The Veloflex Record 23 isn't much bigger.

I don't worry about flats in TTs. Just stay off the shoulders...

I actually just went there the day before and did tire testing during my openers ride. I know I have the data somewhere but didn't find it in a quick search to get you the exact numbers. I honestly don't remember how low I went other than it was lower than I thought was safe to run in the race, just to see what would happen. I do remember that lower pressure made hardly any difference -- ~0.0001 higher CRR. I presume there was a tradeoff where it was better in some parts and worse in others. Higher pressures (than 93) were a lot worse. It's different from rollers where lower is predictably slower at any pressure. The road was pretty rough though.

At least at testing on a wooden track and on a smooth drum „our“ GP4000II in 700x20 are not that bad. And in the velodrome the aerodynamics were good.

" 'Tis far better to err on the side of too low of pressure, than too high" - me ;-)

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This is really great work and fun to read!!

We have a bit of a file on this topic, if you search 'bituminous asphalt' in the research journals you can find some pretty great info on the different strategies employed by different municipalities, private contractors and even countries that can have some really big effects on Crr. I've talked to a lot of civil engineers and some course contractors over the years in an effort to better understand and here are the basics:

In an attempt to maintain flexibility at cold temperatures, this stuff is generally modified with plasticizers, rubber, and other stuff that makes it very high hysteresis when warm or hot. Some formulations are still pliable at -20C/-5F and have the consistency of a gummy bear at 90F. Different strategies are also applied in terms of thickness of the coating, I've seen it nearly 2mm thick in some applications, and when thick, it behaves very visco-elastically with damping coefficient in the 0.8+ range.

The rate of hardening is dependent on chemical makeup and heat, but it will continue to harden asymptotically approaching some maximum over it's lifetime.. it's likely 95+% hard at 1 year according to most.

Ironically, you are seeing the benefit of the roughness of the coarse stone chips on that part of the road.. the seal cannot build on top of the stone chip and rather drains into the gaps, leaving a much thinner effective coating that you are riding one.. so effectively you are decreasing surface hysteresis at the expense of increased surface impedance. The rather thick coating on the side of the road will be due to the large fill size of the stone (which is cheapest) and then needing more bitumen to fully fill the negative space and best stick it all down.

The strategy for both of your surfaces is to present a larger contact patch with lower pressures at the interface.. so yeah, bigger tires, lower pressures!

There were some surfaces laid down/sprayed/repaired for Tokyo that presented challenges in this area and were not this bad, but presented some challenges/opportunities to exploit...and now with the delays will be quite a bit faster as the games will be run 14-15 months after the work was complete!

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So your summary was roughly "bigger tires lower pressure" (which was what I was getting at since the OP's original test was 23's at 120 psi). While I understand it is all rider plus pavement specific dependent, I guess the hard part is knowing how wide to go and how low to go, because in most cases we cannot field test before our race (we just show up and the pavement is the pavement). So with really wide tires you are trading off aero vs Crr so you're stuck having to guess the tradeoff, not really knowing what the pavement is really like, and you're also maybe limited by rim and cutout issues too. So then it boils down to gut feel before the race since you don't have all the data before (you pick tire and width and then if you can pre ride some of the course on a Saturday before a Sunday race you then guestimate the best psi for the tire installed on you rims).