Saturday, April 17, 2010

Surprising Tire Results

I've always believed burly knobby mountain bike tires were slow. You could hear the slowness. Anything that buzzed loudly on pavement has to be slow, right? Likewise, tires that feel smooth and make more wind noise than tread noise must be fast, right? I put these assumptions to the test in a semi controlled experiment.

I tested four different tubeless tires, shown in the chart below. All the tires have Stan's sealant in them.  I meticulously adjusted the break calipers to ensure no rubbing, as even a nuisance amount could skew this test. All tires were inflated to exactly 30psi. The test consisted of rolling down a 1-2% grade from a dead stop, then recording the instantaneous speed on the computer after a run-out on nearly flat pavement. Total distance, slight descent plus run-out, was about 100m.  Max speeds attained were in the 9-11mph range, so wind resistance, while significant, would not totally dominate this test. The pavement is smooth, sheltered in a forested, dead-end culdesac behind my house. Wind was negligible. It was lightly drizzling, temperature around 40F. Kitted up, I weighed 170.8 lbs.

First up were the Panaracer Fire XC Pro's on my Dean Singlespeed. These are 26" UST tires, 2.1" wide.  Tread is about half way worn down. I've always believed these to be slow. You can hear the soft, squishy knobbies scrub on pavement. They grip superbly well in slimy rock and root conditions however. That is why I like them. There was some variability in the speed at the mailbox where I noted it. Average was 7.77mph.

Next up were the Kenda Nevegal's on my Titus Racer-X. These too are 26" UST tires, about 2.2" wide, with tread half worn.  These look burlier than the Panaracer's. The knobs are spaced further apart and buzz noticeably on pavement. I didn't expect these to be faster than the Fire XC Pro's, so I was surprised by how much faster they were. They averaged 9.10mph. I took four initial measurements, then two more at the end of the test just to make sure wind wasn't affecting the result. It is interesting to note how consistent these measurements were, all within +/-0.1mph.

Next up were the Bontrager 29-3's on my Gary Fisher Superfly. These tires are 29" tubeless-ready, about 2.2" wide, and almost new. They are fairly quiet on pavement. I expected these to be faster than the Nevegal's, but they weren't. Note that the Nevegal's and 29-3's are both mounted on wheels with Shimano XTR hubs. Not all hubs coast the same, a variable I didn't want to "control out" in this experiment. At least they were faster than the Fire XC Pro's, and they had similar handling characteristics on dry trails.

Last up were my favorite tires, the WTB Mutanoraptor's. These are 26" UST tires, 1.95" wide, with tread about three quarters used up. I fully expected these to be fastest. They roll very quitely on pavement. I've been riding these for at least five years now. So I was dismayed to see they were the slowest of the bunch. I took an initial four readings, came in to check for brake rub and even removed the chain from the cassette so I would not have freewheel resistance. This made no difference in the final two readings. The rear wheel has new bearings and cassette body in it, but it spins very nicely on the bike stand. I'm pretty sure it is all tires.

Just as a sanity check, I brought my winter beater road bike out for comparison. It has Michelin Pro 2 Race 23mm tires inflated to 115psi. Assuringly, it rolled faster than the fastest MTB tires. The table below summarizes all the results. Note that I use corrected average. I double checked the rollout circumference of each tire against the calibration setting in each computer. There were some minor discrepancies, so I mathematically corrected for that.

Fire XC Pro




Pro 2 Race

Raw Data

8.3, 7.9, 7.4, 7.7 mph

9.2, 9.3, 9.3, 9.2, 9.2, 9.1 mph

8.2, 8.8, 8.6, 7.7 mph

7.7, 7.1, 7.5, 7.6, 7.2, 7.1 mph

10.2, 10.2 mph

Bike Weight

24.5 lbs

26.9 lbs

24.1 lbs

27.1 lbs

22.5 lbs


Dean SS






Mavic Crossroc

Shimano XTR


Mavic Crossmax


Tire Wear






Corrected Avg

7.77 mph

9.10 mph

8.35 mph

7.35 mph

10.15 mph


New bearings in rear


The shocker here is what I thought would be one of my slowest tires was in fact the fastest, and likewise, what I thought to be my fastest was my slowest. I suspect the Nevegal's use a harder durometer rubber than the other three tires. I suspected this before the test in fact, as they don't stick nearly as well to slimy surfaces as the Fire XC Pro's or Mutanoraptor's do. Thus there would be less knob scrub on pavement with this tire.

DaveP actually rode this set of Mutanoraptor's in Tucson, while I rode the Nevegal's tested here. I wonder if my ability to keep up with Dave this time was due to loaning him slow tires? He's going to hate me now. Just because the Nevegal's were rolling 24% faster and the measurement mailbox does not mean they have 24% less rolling friction than the Mutanoraptor's. Far from it. There is way more going on here. There is an integration effect on the initial slight grade that accumulates rolling friction effect. That's partly what makes this test work, so you aren't measuring tiny differences in speed. I expected to measure tenths of a mile per hour difference, not whole miles per hour differences.

So what can you conclude about the performance of these tires on trails? Obviously, in certain conditions a paved roll-out test would not predict at all which tire would provide the best performance on varied terrain. The closest condition to my test here would be dry hardpack. Sometimes we get this in New England. Some of the tires here would be poor choice in muddy conditions. Different course conditions demand different tire pressures too. Dropping another 5psi could shift the results.

The 29-3 was the newest tire in the bunch. I speculate after the tread wears in a bit, it's speed could approach that of the Nevegal. Thus in terms of this test, it seems like a decent tire. My road bike control is the upper limit. No MTB tire will exceed this.  There's not a whole lot of room for improvement for the fastest rolling MTB tire.

One of the biggest take-aways for me from this experiment is that I can easily be influenced by how a tire sounds and feels on pavement in judging its rolling friction. I need to do more experiments like this. The MTB tire industry certainly doesn't. There is good data available on road tires, maybe because most road tires ride over very similar surfaces, so the data is meaningful. Performing a repeatable performance test with MTB tires in a variety of conditions would be difficult at best, if not impossible. Rolling friction is one valuable metric though. I would dare conclude that my Nevegal's will roll with less loss in most conditions than my Mutanoraptor's. This doesn't mean I can race faster with them in all conditions, as the two tires handle very differently in different conditions. I'd like to take this test a step further sometime. All the tires should be tested on the same wheels and bike. I stayed away from swapping tires this go-around, as I didn't want to deal with all that Stan's sealant in the tires.


PyZahl said...

very interesting test, thanks for sharing -- but the story can (and possibly is more thread depending) be vice versus on dirt...? Would be interesting to test as well on a reasonable reference moderately packed gravel road.

Anonymous said...

now you need to get yourself a set of Maxxis Ignitors.

SteveS said...

Interesting stuff, Doug, thanks for doing this. I spent a lot of time last year trying to prove (to myself at least) that the improved rolling resistance of a 29er more than makes up for the added weight of a comparably equipped 26in mtb. Actually, I was trying to calculate the grade at which the added weight canceled out the benefit of the reduced rolling resistance. Unfortunately, as you noted, there really isn’t any published data on the coefficient of rolling friction for mtb tires out there. Schwalbe does have a nice little article though,

Also, if you want to go crazy with the math, you can follow this approach for doing a roll down test that allows you do distinguish between the wind resistance and rolling resistance.

As for your results, I’d just hate to draw too many conclusions. Other than your weight and the run that you made, everything else was different with each test. Take the weights of the bikes for example. A 2% grade over 100 meters is a 5 meter drop. Just the difference of 2 ½ pounds between bikes can account for almost a 0.3mph difference (with the heavier bike being faster) given the data you provided. Combine that with your position on the bike, resistance of the wheels or even how much Stans is in the tires and you’re probably not telling the whole story.