I ran the SK+ in the Unbound 100 last year. No punctures, which was job 1, but really question the value of the micro knobs to do much more than blast the down tube with tiny pebbles & grit. I’m almost 99% sure I’ll be on SS+ this year.
It’s more a texture that wears off almost instantly. i have a set right next to me. They have smaller dimples than my Gp5000 tires.
GK SK’s knobs are especially useless. I’ve used them on sand climbs (West Michigan dunes - Barry Roubaix Segar “Road” ) and the 43c were able to actually great.
Why anyone listens to this clown is beyond me
Not trying to be pedantic but since grains of sand are so small I’d imagine all those treads could provide a significant amount of reaction force in the direction of travel compared to a completely slick tire.
Maybe the tires cost 50% more than competing tires because of the labor involved in shaving down those side knobs.
1 Like
I read his aero study. He used 15 and 30 second tests. WTF can you tell from a 15 second test?
What duration do you consider acceptable?
AFAIK, these shorter sample rates are relatively common in this type of testing. It’s about getting drag values in a state and comparing to others in that same set of variables.
Those short times are extrapolated into longer ranges like 40k or longer to relate more to specific event distances as needed.
1 Like
Extrapolating is fine but I don’t see how his measurement could be precise enough when taking 15 and 30 second samples.
It’s been nearly 10 years since I was in the WinTunnel at Spesh for my testing, but they did some short window of testing as well. It was no longer than 1 minute per position between our test cases. Their equipment at least, is sensitive enough to get force/drag data in that duration, to which they dump right into their formula to get the longer projections.
I have no idea what RH does, but this process can and does work in this basic small measure to large estimation process for whatever equipment and setup Spesh made. I can only presume other tunnels take a similar approach.
1 Like
Indeed, you only need sufficient time for any transient flow behaviour to have stabilised. If this happens within that short a duration, then you have your test condition.
As working section size or flow velocity gets larger, the energy costs can become sizeable so you don’t want to run any longer than necessary. I chatted to a researcher at university working on transonic flows, and for that wind tunnel at that speed, you’d get a useful test window of well under a second!
3 Likes
I agree with the article. I think some are losing a central point. Jan is not saying knobs are not beneficial, he is saying SIDE knobs are not beneficial. If knobs help with all around traction, use them. I do this in the winter riding in the mountains because all the gravel roads are mud and snow strewn. In the summer I have only used slicks properly aired for the conditions. If I can stand on the pedals and accelerate with my slicks, I run the slicks. If I can stand and accelerate only with knobs then I run my knobby tires. I have run side knobs in the past and they feel terrible when they “hook up” and cause as many issues as they prevent in my experience. I have found high volume file treads/slicks to be better in traction and better all around when riding gravel but I live in the PNW where it is dry when I do my gravel rides. On the rare occasion I do a winter gravel ride in the hills, I will consider knobbies if the roads are muddy. I have multiple sets of semi slicks (side knobs) hanging in the garage I never use anymore because they are slow for slicks and don’t help when I need it.
4 Likes
This is really interesting context — thank you for sharing. I knew RH has done wind tunnel testing in the past and it’s interesting to see them using similar timeframes for the tire testing!
1 Like
They are measuring CDa right? It doesn’t take an hour of wind tunnel time to test for that.
This is the wider tires are not slower article:
First, Herse is trying to sell his stuff. His testing methods are not super scientific. I just take what he writes with a grain of salt. He states contradictory info like on one hand ‘wider tires are faster’ than then ‘wider tires are NOT slower’. He completely discounts the more rigorous work of BRR.
I have a set of GK SS, GK SK+, Pirelli Cinturato Gravel M, and Pathfinder Pro in both 38 and 42. So I can now overthink it and guarantee that I have wrong tire for Unbound! 
4 Likes
Just close your eyes and grab a random set from the bin. Introduce a little chaos into your life! 
3 Likes
So I read the article. The main argument seems to be that most people don’t lean the bike enough in gravel corners. I don’t know how you ride your bikes, but I (still beginner) lean the bike quite a lot (like a MTB, bike steeper than the body). This gives me more stability and body weight is deeper, also more weight on front tire.
Of course it depends on the length of the corner. In long enough corners my knobs (pathfinder pro and some newer schwalbe tires) catch the dirt/gravel. I see that they are dirty after riding.
The whole article however reads a bit like a marketing text. And they also sell tires with knobs.
This is why I loathe gravel. Just stick a pair of conti 5000’s on the road and be done with it.
Listeners/readers are less likely to respond respond to qualified, well reasoned statements. This thread wouldn’t exist if he had said what is actually true: side knobs won’t help with cornering for 90% of rides purely on gravel roads.
For rides where I ride a bit of tarmac to gravel and then stay on gravel, I am very rarely leaning bike enough to need them. When I do lean enough, I would not crash due to lack of grip, but because the gravel is sliding beneath me (as was commented above).
However, one of my favorite routes is a gravel ride out to some single track and back. When it has been dry, the side knobs 100% help on the areas of single track that aren’t too sandy for knobs to go through.
2 Likes
I didn’t get the base data shared in my example (just the time saved for quick comparison) but everything I’ve seen from the WinTunnel and similar testing starts with CDa at the root, then extrapolates to the distance values commonly compared.
Having re-read the aritcle, I have additional thoughts re: the claims…
As you can see in the photo showing Inno traversing a technical section, this year’s Mid South course wasn’t just smooth gravel. Why didn’t the lack of side knobs put these racers at a disadvantage?
The problem with this statement is that he is taking a small section of the course and extrapolating it into the general conditions, which was not the case. From my understanding, Mid-South is a pretty fast course with packed dirt roads for the majority of the course. You generally make your tire choice based on the entire course, not just one (or a few areas). For Mid-South in dry conditions, a slick would be a great choice.
Again, “gravel” is not universal so using the conditions at Mid South to make a general claim re: gravel tires is flawed, at best.
In the photo above, you see me countersteering to catch a slide. I’m absolutely on the limit yet the lean angle doesn’t look that impressive—because it isn’t.
Again, he is taking a snapshot (literally and figuratively) and expanding it into a full-length motion picture. For those conditions pictured, a slick may have been a better choice…but just becuase he could not lean much on that turn doesn’t mean you can’t lean more in other turns. YOu also have to ask if leaning more in that picture was even necessary.
He also uses images of riders and bikes with mud splatters and says “See? They rode slicks and were just fine!” 2 things re: that logic - 1) You cn get mud splatters from one area of a course. Splatters don’t mean the entire course caused those splatters (see my comments re: Mid South this year above), and 2) these riders have greater skills than the layperson…they can use that to ride a faster tire which may not not be a good choice for riders of average ability. Pros / Experts are more comefortable with things like tire slide, loss of traction, etc. In short, they can compensate for the lack of control that a slick may bring, but could be challenging for other riders.
2 Likes