The rolling resistance vs aerodynamics is a tricking line to walk. The rule of 105% is “only” valid if you are running a fast tire. If you are running a slow tire that conforms to the rule of 105 you might be gaining 4 watts in aero, but throwing away 10 watts of rolling resistance.
That is why you see so much reference to Cdr, because as much as Cda matters, rolling resistance is important too.
It would be nice to see what the different stall angles are going from say 35mm to 42mm to 47mm.
Also, if the 47 only costs a few watts, that might added up to a minute or so over a 100 miles, but if it saves you a flat it could save you 10 minutes plus whatever effort of having to chase solo.
This is the point at which you have to become subjective (or at least rider/course specific) IMHO. It’s incredibly helpful to know all of the aero vs RR tradeoffs, but ultimately this is the consideration loads of us end up making when we finally decide to put on a fatter tyre than might be ‘optimal’ for a particular course.
I think it adds to the fun of making an equipment choice - you look at all the data available and narrow down your choices as much as possible based on science, but in the end the final call is still alchemy - a decision based on some combination of firsthand experience and gut feeling.
I’m guessing these tires all would stall pretty much immediately since they’re so wide that the rim will never be deep enough to have the proper aerodynamic cross section. I could be wrong but I have a suspicion that aero wheels with gravel tires aren’t a thing. The narrower the tire though, the more aero it will be and higher likelihood the flow could attach to a rim…
This is one other thing I’m really curious about: how is tire performance affected by gravel roads like the one below? Aerodynamics would be a factor, rolling resistance to some extent, but how does the rollover effect factor into the equation, i.e. the ability to roll over large chunky areas and washboard sections? Has that been quantified yet?
Crr scales just like slope, so if you go down into washboardy bits and then have to come up out of them, it’s like lifting yourself up each time. So, yeah, as long as the tire keeps rolling (as opposed to sliding) it’s quantified as a part of Crr for that surface.
I think rollover typically falls under the rolling resistance discussion (right or wrong). The published resistance tests (by tire) don’t cover real world surfaces, but Dylan’s comments make me think this is part of what Silca would be looking at. Some form of rollover is a big part of any rolling resistance discussion. Whether it’s a difference between a track surface and smooth tarmac, chip seal vs gravel, etc. how a tire conforms to any imperfection on the surface is a huge factor to rolling resistance. Getting into performance over wash board feels like it’s stepping well beyond rolling resistance, but there is certainly overlap.
Are you saying this is good or bad gravel? Asking because it looks like about 50% of the gravel I ride on. I’m always curious about what different places think of as gravel.
Pictures can be deceiving, but that looks like a hard packed dirt road to me. If I were racing only on that type surface, 32mm GP5000’s and an aero road bike would my choice. I don’t want to get into a “the gravel around here is so tough” discussion, but that’s not a gravel road. We certainly have sections of road like that (and also tarmac) in many gravel races, but those aren’t the sections dictating tire choice.
Maybe, but I personally don’t find that tire choice makes a big difference on washboard. The only way I’ve found to deal with heavy washboard is to power through it, unweight your saddle, and shift your weight back a bit. Even when I’ve raced over washboard on my full suspension MTB, I find technique is more critical than tire/suspension on that stuff at speed. Not saying tire choice doesn’t matter at all, but you will still be ejecting bottles if you don’t roll it properly. And the last thing I’m worried about when banging through washboard is the rolling resistance.
Thanks all. We have a lot of hard clay with loose over top that gets washboarded really badly. Especially on our XC trails. There’s a lot of that in Colorado too.
We also have a lot of sand and loose gravel in the Houston area. Sand sucks when it gets so deep you can’t maintain traction. The worst is when they lay fresh gravel and it gets heavily washboarded. You can’t get any traction AND are bouncing all over the place.
That was a random picture I grabbed after an internet search, but it’s pretty close to the standard road where I live and is probably ~60% of my riding. I spend maybe 10% on pavement overall, and the remainder is chunkier gravel and Class IV roads like this:
I’m having a blast with my 700x50x Maxxis Ramblers I bought for the chunkier stuff and I’m wondering how much of a penalty I’ll be paying for it on hardpack. Is there less of a penalty on hardpack dirt with some loose gravel compared to pavement?
Bigger picture - I guess I’m trying to get a better sense of energy loss on uneven surfaces that aren’t pavement. Which, to be fair, it sounds like it’s on the docket for Dylan at some point.
Isn’t his math off on the aero bars vs. non-aero bars?
You shouldn’t be comparing aero bars to upright hoods position and subtracting time lost from 4.5watts of aerobars drag in the rest of the race, you should be comparing aerobars to parallel forearms position (which is only 10 watt difference), since that position (or puppy dog arms) should be able to be held easily on any section you would be in the aero bars.
AND aero bars only really help achieve 40 watt savings if you’re solo or taking long pulls on the front which the majority are not doing.
With that math it seems like it’s probably much more break even or net loss than we think. Especially if you factor in that they weigh an extra 1lb and you gotta haul that up every hill.
Seems like adding padding to your inner bars to comfortably achieve UCI illegal position while on pavement or super smooth gravel would be most effective, and then alternating between that and hoods with parallel forearms as terrain dictates.
This will be my first year at unbound, but all the advice/guidance I’ve got is that there is a good possibility of riding solo for multiple hours before it’s all over. That’s pretty rare for me in shorter races and I’m finding the trend toward finishing in larger groups over the last couple years (becoming more like road racing and folks understand the benefits of keeping a group together).
That said, I was with one other guy for the last couple hours of gravel locos last year (155 miles) and it was the first race I had used aero bars and I was happy I had them even when trading pulls. Just having the different riding position is worth something once you get into the long races. I’m still debating for unbound, but I’ll probably run them.
While possible, I’d say it’s a massive failure strategically if this happens (unless you’re off the front solo, or forced to chase an attack solo or with a small group). You should be doing everything in your power to pace with other people…even if that means riding well above your capabilites to close a gap or riding below your capabilities until people catch up. That drafting benefit is going to drawf the choice of aerobars or not.
Oh for sure. Forearms on bars is sketchy for anything but pavement and smooth dirt with no washboard/potholes.
You can wedge your hands/forearms against the hoods to be a lot more stable though, but that widens your elbows some. And I think my point still stands that it’s incorrect to compare aero bars to upright position when the comparison should be aero bars to a combination of on hoods with flat forearms, in the drops, and forearms on bars.
Edit: while on the topic of crazy gravel aero hacks…does anyone make a disc gravel rear wheel? Even weekend warriors at triathlon event have them. Theres gotta be a couple watts savings there.
I would lean towards a wheel cover vs. a disc……a disc would be too stiff for gravel, IMO. A wheel cover won’t add any structural stiffness. Or maybe a disc that is essentially a fairing over a spiked wheel like FLO or HED Jet disc.
(And we can skip the discussion about John Tomas’s Tioga disc wheel back in the day….it was not for aerodynamics and was supposedly about ride quality)
All that said, there was a guy at Big Sugar last year on a full-on TT bike with a disc….suffice I say I couldn’t get away from him fast enough before the gravel.
Also saw a guy with the new super-deep rim HED wheel that they introduced before the IM WC in St. George this year. Supposedly just as fast as a disc.
Disc wheels are “always” faster, but their biggest advantage on a TT or Tri bike is that they add stability in cross winds, however counter intuitive that may seem.
