Well, after my last round of roller testing, and the quite good performance of the Conti Terra Speed, I was curious about how the seemingly only slightly more "knobby" Terra Trail would perform. So, I bought one to test out. At the same time, an acquaintance from the Slowtwitch forum, Rob Pickels, informed me that he had a pair of the new tubeless-ready Challenge Gravel Grinder Pro HTLR (that's a mouthful!) tires that he decided not to use and would send to me if I was interested in testing them out. I had been curious about the GG Pro HTLR since it had come out, since some of the reports were that the coating used by Challenge to make the tire more air-tight was butyl...and if that was the case, I didn't have high hopes that it would perform as well as their non-TLR GG Pro. I was especially discouraged when I found out they were listing it as having 2 puncture resistant layers ("2xPPS"), which is what the non-TLR version had. It didn't make sense to me...if the tire is intended to be run with sealant, then a reasonable approach would be to eliminate one, or even both, of the puncture protection strips since they aren't as critical for a tubeless w/sealant approach, and all they do is slow down a tire.
So, once I got my hands on Rob's tires, here's what I found: to my "feel", the coating used on both the outer sidewalls and inner surface of the appears to be more like a latex coating, rather than butyl (thank science!). Additionally, it looks like the HTLR beads have an additional "rub layer" coated with a black rubber (THAT could be butyl...and is there to address the cutting issues with rims like ENVEs). Lastly, on the inside of the casing there is NOT a red material layer like there is on the non-TLR models. I always assumed that was the PPS layers...and now I'm wondering if, in fact, the HTLR models actually eliminated the PPS layers? Take a look here: the tread and inside of the new HTLR is shown on top, while a well-worn non-TLR version is shown below (which had actually been run tubeless with sealant...shhhh...don't tell anyone ;-)Well, that got me curious, so I poked around the Challenge website a bit and found some things out. Apparently, when one of their tires is listed as having a single "PPS", that layer is installed BETWEEN the tread and the casing layer. When a tire is designated as "2xPPS", that means an additional layer is installed on the inside of the casing, so that it would be between the casing and the tube. Aaah...so, that must mean that despite the sidewall labeling being marked as "2xPPS" on the new tire, they must have eliminated at least the inside layer.
With a bit more digging on the Challenge site, I then came across this graphic, and I think it explains what's going on:
I think I see what's going on...the original HTLR tires must have been mis-labeled...OK, that makes sense.
Anyway...finally, here's how these 2 tires fared in the roller tests (again, full spreadsheet is located at the link to the right, or here):
TIRE CRR POWER (pair @30kph)
So, the Challenge GGPro HTLR tire basically rolled identically to the non-TLR GGPro. Seems like any additional rolling resistance from the sealing layers was offset by the elimination of one of the 2 PPS layers. That's a fair trade...
On the other hand, I was slightly disappointed in the Terra Trail performance. I was hoping that the only change was to the outer tread blocks, but I have a feeling additional rubber was also added on the sidewalls. I was hoping it would roll somewhere in a slot ~halfway between the difference in what they actually rolled, but alas, that was not to be. To be fair though, I'm currently using that tire as a front, and I really appreciate the extra grip in loose dirt from the larger side knobs...it's just quite "buzzy" on pavement.
I still wish both of these tires were actually slightly wider...more like 42-43mm measured, rather than the 36mm measured for the Challenge, and 39mm measured for the Terra Trail
What'd be the implication of Challenge GG HTLR at 36mm roll just 1w faster than Continental Terra Speed 40mm that measure around 38mm on real gravel?
ReplyDeleteWould 2mm wider rubber float better on Gravel at lower pressure or knobby of the Terra Speed rob more of its speed once we reduce the tire pressure to smooth out the gravel?
Well, I measured the difference in width on those to be just over 1mm (37.8 vs 36.7) so the pressures one would run will be pretty comparable. That said, whichever one a person would prefer is, like always, going to be highly dependent on the course and the user's comfort in the tire's handling properties. Personally, I think it's pretty much a wash.
DeleteTom, will you take tires from anyone? I have a Schwalbe G-One Allround 38mm with a worn center, a pretty much new WTB Resolute and a couple of other tires I did not particularly like that would be useful to throw on the database. Plus, I would love to get accurate numbers to see if a slick-centered Conti Race king was faster than a new one (I have both). And a G-One Speed in 2.0.
ReplyDeleteGreat work. Thank you.
ReplyDeleteHave you tried the tubeless tubulars yet? I just picked up a pair of strada biancas at 30mm. Curious what data there might be about them out there.
ReplyDeleteHave you tried the tubeless tubulars yet? I just picked up a pair of strada biancas at 30mm. Curious what data there might be about them out there.
ReplyDeleteHave you tried the tubeless tubulars yet? I just picked up a pair of strada biancas at 30mm. Curious what data there might be about them out there.
ReplyDeleteShould I find it ironic that your name has the word "echo" in it and your question was posted 3 times? :-)
ReplyDeleteI have not tried the "tubeless tubulars" yet, but based on previews testing of tubulars, I would expect them to be slightly slower than the clincher version of the same tires due to the additional hysteresis losses in the glue joints. Of course, running those also means your repair strategy would be only plugs, short of an entire tire swap (i.e. no option for boots and/or tubes for field repairs).
Thanks. No idea how that happened. My other wheels have snoqualmie passes on them. Maybe I will find a hill somewhere and do an amateur roll down test.
DeleteTom, is there anyone using the Chung method to test gravel Crr? Would this be accurate (would a non uniform surface over the test course (rough then smooth then rough again) alter the virtual elevation?)? I have some great gravel test course candidates and would love to validate Silca's tire pressure calculator and Zipps new tire pressure recommendations. Maybe later investigate how rim internal width affects ideal tire pressure or is it purely volume driven. Just not sure how clean the data would be if testing on rough surfaces.
ReplyDeleteYes, changes in "resistance to forward motion" due to different surfaces would show up as VE changes in those portions. If one knows the CdA for that condition, then one can back out the Crr in those sections. There's a paper out there where a group did Crr measurements of MTB tires on dirt using VE.
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