This is an interesting way to look at the data. I compiled the events done on my dropbar MTB and compared the relative placing to my gravel bike. These are the same events year after year, many years I would use the MTB for a race I did the prior year on the gravel bike or vice versa. I went into this with an experimental mindset. N for MTB Tires is 13, N for Gravel Tires is 24.
Being cognizant of my relative placing while using the dropbar MTB is what motivated me to change back at the end of 2020, but this is the first time Iāve compiled the data this way.
This thread has rekindled my desire to experiment and after looking through many of the events I did in the past I think positioning and gearing selection, as well as using above average gravel tires and below average MTB tires; were the main contributors to my overall lower relative performance.
I donāt have the budget for a gravel bike that will fit MTB tires - When this thread started I had an old MTB frameset that I had outgrown, sitting under my porch with plans for the scrapper. Since then Iāve pulled it out, rebuilt it as a dropbar bike and have spent the past two weeks experimenting with gearing and tires. Right now running 700cx42 Pathfinder Pro in the rear and 29x2.35 Mezcal in the front. Both average tires in their respective class.
I have ordered Thunder Burts (super ground) and once it dries out and gets closer to the season Iāll switch over and race a few events and see how it shakes out. Right now the bike seems very fast, Iām working on getting the gearing exactly the same range as my gravel bike, my estimation is that I donāt need the low-end gearing in the 20s but I do need the high end gearing around 115-120 gear inches. One of the major speed losses was getting dropped from the front group(s) in gravel races trying to spin 38x11 against 50/48/46x11 geared gravel racers. As well I was loafing up longer strenuous mountain climbs in 26x36 when I should have been at 1x1/@30 gear inches limited since I am fit enough to handle that gearing and possible higher on the climbs in our events. 42/28 right now but I expect to be able to use 46/32 once I swap cranksets, 11-32 cassette.
Not sure if Iām going to do anything position wise, the bike handles very well and while it seems possible to use a -25Ā°/-35Ā° stem to get 11mm/22mm lower I donāt think thatās going to make much difference for aero considerations. This bike has 0cm saddle to bar drop, my regular gravel race bikes have 6-7cm bar drop. And not expecting to run fenders, for dry events.
Thanks to everyone who posted in this thread, itās been both motivating and extremely informative.
Yeah, the geometry of the drop bar MTB is longer (the wheelbase), taller and slacker. I was worried that would make it less agile through tight corners, but surprisingly itās been fine, seemingly no slower than my cyclocross bike. Perceptions can be misleading, so I use the speed of my regular competitors relative to my speed as my gauge for whether Iām slower or faster through corners. Bar width is similar for both bikes at 42cm.
The most noticeable difference is the BB and saddle height, which are both almost an inch (22mm) higher for the MTB. It needs more of a jump to remount the MTB after any running sections. In comparison, the CX bike feels like I barely need to jump, casually throwing my leg over the saddle to remount.
Very nice. Thatās a good sample size, which helps statistically, as long as your fitness and level of your competition has stayed fairly consistent over that period.
I think these analyses of race results are interesting, because thatās ultimately what we care about. I still think though, the best way to make decisions is to do a controlled tyre test to determine the fastest setup. Virtual elevation tests are my preference, but admittedly it takes a lot of time and not everyone has the inclination to do that. It would be interesting to see any results of any more experimentation you do, if youāre happy to share them.
Iām doing Rock Cobbler, 80+ Miler in Bakersfield, CA on Feb 10th, on my Scalpel HT this year. So Iām here for this thread.
So far for that race itās looking like Nano 2.1 (52mm) or Maxxis Ramblers 50mm.
Both roll very well on tarmac, Nanoās have a leg up on dirt, but Ramblers in 60TPI have Silk Shield, Nano 2.1 only comes in a 60Tpi, but no reinforcement at all.
Got an email from the organizer today with this nuggetā¦which as me leaning toward, Ramblersā¦
While the IRC Double Cross is a plug for a Race Sponsor (Not so sure how āsmallā The Rock Cobbler is, nor that other race they sponsor, Unbound, really are.)
Double Cross is āokayā for gravel, but no go on an MTB as 42 is as wide as youāre gonna get. Iāll run 1.9"/50mm on an MTB, I raced a 2.1 front/1.9 rear for YEARS, so while 1.9 isnāt odd for me, 1.65 is right out.
I wrestled with this question for a while and ended up on the gravel inserts. From how it reads, the MTB is meant to allow you to run ultra low pressures, and makes regular contact w/ the ground (through the tire, of course), whereas the gravel is more a safety item for when you really hit something hard.
I ran gravel inserts most of the time, I didnāt really test its runflat capability though.
Another new wrinkle is the Vittoria Air-Liner Light, which was launched sometime this year and is only 8g more than their gravel insert. From how it reads, itās supposed to function more like the gravel insert (i.e. not run with ultra-low pressure and only there as an emergency), but let me know if you find out different.
Just chiming in on the super race vs super ground discussion. I had a chance to run the Kenda SCT casing (feels like super ground) vs. the TR casing (feels like a road bike sidewallā¦super thin) and didnāt find a difference. I really expected the TR to be measurably faster but itās a little more info that makes me think SCT or super ground is probably the way to go vs super race or TR.
I think I was at Unbound last year and the folks at Vittoria said they were going to make an Air-Light liner for Gravel, but that hasnāt seen light of dayā¦
Earlier this week, I did a re-test of the Race King versus Thunder Burt test that I did last year (see results in post #74 of this thread). As the original question from @oldandfast was about the Race King, I thought my latest test results might be of interest here.
I used the roller technique again, which is a kind of poor manās version of drum testing that organisations like BRR do. Iāve made a couple of improvements to my testing though. Firstly, I used a Power2Max power meter, which measures total power now, whereas previously my Stages single sided PM was subject to variability coming from potential L/R leg imbalances. Secondly, I now have a spare set of wheels, so ABAB type testing was easier to do, with less hassle and delays between changes.
Results are shown in the plot below. A few notes:
For reference, my previous tests results are shown in grey/lighter colours (numbered 1-3 in the legend). Note that those were performed with a butyl inner tube though.
The new tests were done tubeless. The BRR values (open square symbols) are also updated to showed their latest tubeless rolling resistance coefficient results.
The new Race King data is shown with the solid blue symbols and solid blue trend line. The Thunder Burt data is shown with the green symbols and trendline.
I did an ABABA test (A=T.Burt, B=R.King). Repeatability seems to be good, with the exception of one rogue data point for the T.Burt.
Annoyingly, I mounted the Race King in the wrong rotation direction for the first two runs (#5 & #7) before realising my error. I repeated the test the day after, which gave similar results, not only for the tyre mounted in the wrong direction (#9) but also, surprisingly, once I had remounted it in the correct rotation direction (run #10 - darker blue symbols).
Note that both tyres are old (2020 for the RK, 2022 for the TB), but had little wear. Probably 100-200 miles of usage for both. There is an uncertainty coming from aging though.
Overall though, this test once again shows that the Thunder Burt I tested is a faster tyre than my Race King. The gap is bigger than seen in the BRR results, although the BRR tests used the Super Ground version of the TB (not the Super Race), and with a 2.25ā width.
Good post, 20-28psi is about my window for 2.25/2.35 tires so itās nice to see more āreal worldā pressures compared to BRR.
Perhaps you already know or recall better than I do? IIRC the smaller roller diameter would overstate the crr by a greater degree for stiffer and/or thicker tires. Being that the Race King appears to be 30% thicker than the Super Race Thunder Burt this may explain the relatively larger difference given the BRR test is a 77cm drum?
I had thought Tom Anhalt had a post specifically discussing but couldnāt find it.
This is something I think about often riding singletrack and rougher gravel. Rollers are what - 3 to 6 (8?) inches in diameter? I ride over quite a lot of roots around that diameter and although not much actual loose stone in that range there are quite a few braking bumps, embedded rock outcroppings, terrain features and so forth that are in that range and I would theorize produce similar deformation to the tire.
I think there is validity here, outside of pure comparison sake. Rough terrain and small obstacles require huge relative wattage during events and the marginal difference between tires, that is small on the road, or smooth gravel but very large on rough gravel can change the outcome significantly. Iāve been dropped by a few hundred yards of washboard and probably had a slower finishing time losing that group by 10-12 minutes over a 3 hour ride.
