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ARE FREERIDE TIRES FASTER THAN XC RACE TIRES?


Disclaimer: I wrote this story three years ago for VeloNews, and it was so intricate and demanding to read that even they wouldn’t run it. (Heck, I didn’t consider running it until I posted this story.)

The VeloNews editor also didn’t like the idea that, on a long trail ride, freeride tires might be faster than XC race tires. Trying to convince him that skill, cornering speed and confidence are more important than low weight and rolling resistance was a lost cause.

You’ve been warned. Now check out this action:








Mountain biking has its own brand of religious dogma. Light tires climb way faster than heavy ones, low rolling resistance is the key to fast trail riding, light wheels and tires make your bike much faster, and so on. These pronouncements are certainly popular, but are they true?

Several online calculators make it possible to calculate how various bike setups, terrain and conditions affect your power output and speed. As an example, let’s look at the effect of switching from light cross country tires to burly freeride tires. Mark Twain said, “If you torture a statistic long enough, it will confess to anything.” Well, let’s torture us some statistics!








Click for big.

Assumptions – Rider weight: 180 pounds

– Rider position: Upright – Bike weight: 26 pounds with light XC wheels and 2.0 cross country tires. 27.2 pounds with burly 2.4 freeride tires. – Added weight: Changing from 2.0 cross country tires to 2.4 freeride tires adds 1.2 pounds to the wheels. – Added rolling resistance: Hard to measure, but my neighborhood tests put it at +10 percent. – Added cornering traction: Hard to measure, but photos and race times make +50 percent seem conservative. – Power outputs: 100-watt cruise, 300-watt hammer, 800-watt sprint – All other variables: Technique, wind, sand, rocks, berms and moon phase are all ignored. Remember the movie Tron? Let’s hop on our light cycles and see what happens.

Climbs
The skinny tire leaves his fat friend in the dust, but not by much. The steeper the hill and the harder you pedal, the smaller the effect of tire weight and rolling resistance. Fatso might lose a mellow one-mile climb by 3.3 percent timewise, but on a hard steep climb he’ll stay within 1.5 percent. Heck, if the climb is really steep and loose, Fatso might actually win.

Time to hammer up a one-mile climb:

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XC

FR

Time difference

% difference

2.5% grade 100w

10:06

10:26

+0:20

+3.3%

2.5% grade 300w

4:12

4:17

+0:05

+2.0%

10% grade 100w

29:02

29:32

+0:30

+1.7%

10% grade 300w

9:51

10:00

+0:09

+1.5%

Next time you feel like you’re pulling a tractor tire up a hill, remember your macho tires aren’t slowing you down as much as you think. Keep pedaling and hope they pay for themselves later.

Flats
Air drag increases exponentially with speed, so while your buzzing knobs might drive you crazy, your real impediments are all those displaced air molecules. Keep pushing. The harder you go, the less your big tires are slowing you down.

Time to ride one mile flat:

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XC

FR

Time difference

% difference

Cruise 100w

5:08

5:20

+0:12

+3.9%

Hammer 300w

3:01

3:03

+0:02

+1.1%

Descents
Now those big meats earn their keep! Coasting down a steep descent, weight means nothing, and you push so much air that those growling knobs become insignificant. Meaty tires cost you a few seconds on gentle grades, but when the pitch steepens to 10 percent they’re just as fast as the puny ones. When your bike wants to roll at 40 miles per hour, the limiting factor becomes confidence.

Time to coast (no brakes) a one-mile straight downhill:

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XC

FR

Seconds

% difference

2.5% grade

4:00

4:11

+0:11

+4.9%

5% grade

2:20

2:22

+0:02

+1.4%

10% grade

1:32.1

1:32.4

+0:00.3

+0.3%

Acceleration
Without a doubt, lighter tires make a bike feel much quicker. In that first instant of acceleration, before the rider starts moving, the lighter tires bestow a 40 percent reduction in rotational inertia — enough to turn a hippo into a jackrabbit. But once you start pushing your body through the air, that advantage all but disappears.

Distance traveled after two seconds of accelerating from a stop.

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XC

FR

Difference

% diff

Sprint 800w

7.36 feet

7.26 feet

1.2 inches

+1.4%

Hammer 300w

2.51 feet

2.47 feet

0.5 inches

+1.6%

Mountain cross racers like Brian Lopes swear by light rims and tires because they deliver faster starts. Light wheels are indeed faster, but by only one or two percent. Lopes only needs an inch to take a world championship. If your powers are sub-Lopesian, ask yourself whether a narrow lead is worth blowing the first turn.

Corners
Cornering forces are a product of radius and speed. For a given turn, increasing your speed exponentially increases the Gs — and the amount of traction you need to stay out of the bushes. Let’s assume the skinny little XC tire will hold 0.3 Gs in a turn and the wider, side-knobbier FR tire will hold 0.45 Gs. (By the way, those forces correspond to 17- and 22-degree lean angles.)

In our imaginary world, the burlier tires save you 1/3 second in every turn — not to mention reducing the need for post-turn acceleration. On really curvy trails you never reach full speed, so you end up riding at your cornering speed, which is about 20 percent higher with the knobbier tires. Ride a mile of pure turns, and freeride tires will save you almost a minute and a half.

Riding a 90-degree turn with a 15-foot radius

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XC

FR

Difference

% difference

Speed

8.2 mph

10 mph

-1.8 mph

+22%

Time

1.96 seconds

1.61 seconds

-0.35 seconds

-22%

A virtual race
How do these tires compare over a fantasy mix of climbs, descents, flats, straights and curves? Over this 32-mile ride, the XC tires make time on the climbs and the straight flats, but they quickly lose ground on steep descents and curvy sections. Increased confidence and cornering speed make the freeride tires more than three minutes faster overall.

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XC tires

Freeride tires

Difference

4-mile 5% climb; 300w

0:23:22

0:23:49

+0:00:27

8-mile 2.5% descent; half curves

0:33:29

0:32:51

-0:00:38

2-mile flat; all curves

0:14:36

0:12:00

-0:02:36

2-mile 10% climb; 300w

0:19:31

0:19:50

+0:00:19

2-mile 10% descent; coasting

0:03:04

0:03:05

+0:00:01

1-mile flat; all curves

0:07:19

0:06:00

-0:01:19

5-mile 5% climb; 300w

0:28:26

0:29:02

+0:00:36

3-mile flat; 100w

0:13:37

0:14:15

+0:00:38

5-mile 5% descent; half curves

0:17:14

0:16:24

-0:00:50

Total: 32 miles

2:40:38

2:37:17

-0:03:21








Click for big.

Go forth and calculate
You can tweak these numbers however you like, but the fact is lighter, faster-rolling tires might not always be faster on the trail. At the very least, think about how you dress your rims. If you’re serious about optimizing your bike, run some experiments. Ride your favorite trails with a timer and a heart rate monitor or wattage meter, and find out which tires ride fastest.

If you’re feeling nerdy, you can find the spreadsheets I used for these calculations at www.leelikesbikes.com/calculators.html. These let you calculate the effects of everything you can imagine. Plug in your numbers and torture some statistics of your own.

Whew! If you made it this far, you rock. What do you think?
—Lee


November 3, 2008 : Posted In: Equipment,Skills/training : Comments (34)

34 Comments »

  1. Rob Says November 3, 2008 @ 12:31 pm

    Nice analysis Lee. You’ve been slacking on the info-graphics as of late, this makes up for it!


  2. Farid Says November 3, 2008 @ 1:15 pm

    wow! very cool. Thanks for posting.

    ...your a Mad Scientist!


  3. MW Says November 3, 2008 @ 1:18 pm

    Nice read Lee. I know that in our neck of the (sandy) woods the pinner tires and super high presures do nothing for you. Its all about big flotation to win. Its cool to see a full blown XC racer with 2.35-2.55 meats. It took a while to convert them using my Jedi DH mind tricks. Now many of them are racing on larger vloume tires stating they dont get as much deflection.


  4. Justin Says November 3, 2008 @ 1:53 pm

    Good article. Definitely makes me feel better about those knobby freeride tires I run. I ride them because I love the way they hook up when I lean my bike over.


  5. Tony Says November 3, 2008 @ 4:15 pm

    Hi Lee,

    Good article. I’ll stick with the knobblies for XC.

    What about on smoother, flatter surfaces (concrete and bitumen)? I’m about the convert my soon-to-be-old hardtail to a commuter and am considering swapping out the Maxxis Ignitors for Continental Sport Contacts (or similar). My commute’s got a few patches of off-road downhill, so thus the decision to stick with the MTB platform as a commuter rather than going with a road-bike platform.


  6. Taylor Says November 3, 2008 @ 6:03 pm

    Hey Lee,

    Awesome article, I can see why thy wouldn’t want to publish it. However, that being said, it should be taken with a grain of salt before people start spouting off siting your article in their bibliography.
    It depends tremendously on the particular tires. Your test is about Freeride tires, not DH tires. I started to do the math on a more extreme pair of setups for the sake of weight comparison.

    XC setup:
    dual 2.1 DTC folding Nevegals @ 609g each = 2.69 pounds
    DH setup:
    dual 2.5 wire bead Nevegals @ 1376g each = 6.07 pounds

    That’s a difference of 3.38 pounds, almost 3 times the difference in weight from your test.
    My point is people shouldn’t expect to run full DH tires with the same results, the weight difference is far more significant.

    To be fair, I have an 05 Enduro that I run full time with a 2.5 folding Nevegal front and 2.35 DTC non-UST Nevegal rear. Those would be considered Freeride tires in my book and I wouldn’t go with anything lighter ;)


  7. leelikesbikes Says November 3, 2008 @ 7:03 pm

    Thanks everyone.

    Tony: On smooth, hard surfaces like concrete and asphalt, smoother tires are faster and get better traction in the turns. A pair of slicks makes a mountain bike an entirely different (and quicker) machine. They’ll hold you back on dirt, but they’ll rock on pavement.

    Taylor: Great point about the weight of DH tires. It would be cool to re-do the numbers with the extra-heavy, extra-sticky meats.

    And lets not forget all of the variables, not the least of which are the terrain and the rider.

    BTW: I based this comparison on Specialized 2.0 Fast Traks (XC) and 2.4 Specialized Enduros (freeride/all mountain).


  8. Axel Says November 4, 2008 @ 12:25 am

    Hey, cool write up!

    There was a similar story in german mountain-bike magazine. They measured rolling resistances on different real world surfaces (gras, asphalt, gravel) for different kinds of tires. http://www.mountainbike-magazin.de/know-how/expertentipps/alles-ueber-rollwiderstand.35972.2.htm (well it’s in german ;) ). It was a project of The German Sport University Cologne :)

    They concluded that as long as you are not riding asphalt, fatter tires with low pressure have the least rolling resistance (deflection…)!

    Ever since the Schwalbe Nobby Nic 2,4” and the likes have been very popular here.

    Axel


  9. Vito Says November 4, 2008 @ 2:51 am

    Agreed on many points, but I don’t understand if you took into account the added energy it takes to put out the same wattage with burlier wheels.


  10. Brian Says November 4, 2008 @ 9:12 am

    Great write up Lee, I’m not too much of a bike tech geek and I thought it was easy to read and interesting. I can’t imagine why some of the MTB mags wouldn’t want to publish that, much more useful than the garbage some mags are filled with. I’ve always felt a lot faster overall with beefier, light freeride-ish tires, good to see a few numbers to back that up. Just imagine how much time they save when the going gets rocky and more technical. Looks like the 2.5 Nevegal Stick-E front and 2.4 Motoraptor rear will remain my tires of choice.

    Keep up the good work!


  11. leelikesbikes Says November 4, 2008 @ 9:51 am

    Vito:

    The rider is producing 100, 300 or 800 watts of power on both tires. The differing weight and rolling resistance are reflected in the times/distances traveled.


  12. leelikesbikes Says November 4, 2008 @ 10:36 am

    Here’s how you can read that German article:

    http://www.leelikesbikes.com/translate-web-pages-with-babel-fish.html


  13. tony Says November 4, 2008 @ 12:23 pm

    I used to run 2.5 DH dual casing Nevegal on the front and rear of my Blur LT (kinda over built as a all mountain/dh ride around 35 pounds) Slow and heavy. (did I mention HEAVY? and slow?)
    Now, i’m trying the new free ride version 2.5 Nevegal (folding bead 28psi) on the front…
    I definitely feel the difference between the two…front more lively in all ways and outrageous tracking, especially on parallel ruts (what, we aren’t supposed to rail those???). Rear feels like a big dune buggy tire (26-28 psi with dh tube)...even sounds slow. I’m thinking of going with the free ride version on rear. I know the bike will handle great, it’s just that I feel so confident with the DH beast on there…I really don’t worry about picking a line anywhere I ride.


  14. leelikesbikes Says November 4, 2008 @ 12:59 pm

    It all comes down to confidence, which is a personal thing.

    Ariel Lindsley, XC/Super D and now DH honch, told me he likes to run a normal front tire and big, sticky rear tire. It lets him put the hammer down without worrying about hookup.

    To each his own, eh?


  15. Tjaard Says November 4, 2008 @ 9:45 pm

    The big question in this is whether the FR tires give you that much more cornering traction. That would depend a lot on your trail conditions. Also, does the rider have the skill to out-corner the XC tires?


  16. leelikesbikes Says November 4, 2008 @ 9:49 pm

    Great questions.

    Lee Likes Research Grants dot com!


  17. Tjaard Says November 4, 2008 @ 9:54 pm

    Sorry to post this twice, but I read top-to-bottom.

    Here is the English version of the rolling resistance article.
    http://www.bicicletta.co.za/Downloadable%20Docs/Rolling%20Resistance%20Eng%20illustrated.pdf
    BTW a year or 2 back there was a study by Conti showing similar results going from a 23mm to a 25mm road tire.

    Lee’s calculations only center on the cornering for the advantage in the FR tires, so in his model the fastest would be a XC center with a FR sides. To put this all together the fastest tires would be:
    Large volume, supple casing and tread, hard rubber, closely spaced, low center knobs and agressive, grippy rubber transition and cornering knobs.


  18. leelikesbikes Says November 4, 2008 @ 10:08 pm

    > To put this all together the fastest tires would be:
    Large volume, supple casing and tread, hard rubber, closely spaced, low center knobs and aggressive, grippy rubber transition and cornering knobs.

    Yes!

    The 2.4 WTB Mutano Raptor dual compound was ahead of its time.


  19. Eric Says November 5, 2008 @ 10:19 am

    Great read (as always!), just a quick note to who was asking about commuting on a mtn. bike. I used to ride from Ft. Collins to Loveland about 15mi one way. I got some 26×1” slicks and aired them to 125psi. Should be way faster than my previous 26×1.5 city slicks at 90psi right??? Well, real world comparison showed the 1” had so much drag they would actually slow down when you quit pedaling. So every time I coasted it was like dragging the brakes!
    IMO, it comes down to the drag force on the tire patch. Bigger contact patch = less psi/sq. in. I know some engineer type will probably tell me I’m wrong but the way I look at it is on the skinny tire I had say 200lb psi of contact patch where as on the fatter tire the drag was only like 100psi of contact patch.

    My example #2 is riding with a friend of equal speed/fitness and with me be on a 35lb (or more) FS bike with fat tires, going down the road I was riding off the shoulder in the dirt and going the same speed and effort as my buddy with a HT and XC tires on the paved shoulder.

    Sorry for the novel! (You’re just inspiring I guess! :D )


  20. Mr. P Says November 5, 2008 @ 1:26 pm

    Great stuff Lee.

    Thanks for putting it all together, that must have been a mind bender. I never thought that cornering could have such a significant impact.

    Would rolling resistance be the ultimate factor tho? The reason I ask this is that RR is with you every part of the ride: ups, downs, flats, corners (I guess less of a factor on the downs. Your number of 10% RR over a 10 mile course would equal 1 mile).

    P


  21. leelikesbikes Says November 5, 2008 @ 1:46 pm

    Rolling resistance is only one of several limiting factors:

    – Rolling resistance – Air resistance – Mechanical friction/energy loss – Riding buddy hooking a finger on your saddle rail – Thighs rubbing the seatpost – General lack of intestinal fortitude – Etc.

    At speed, air resistance is the biggie.


  22. leelikesbikes Says November 5, 2008 @ 1:46 pm

    Rolling resistance is only one of several limiting factors:

    – Rolling resistance – Air resistance – Acceleration – Mechanical friction/energy loss – Riding buddy hooking a finger on your saddle rail – Thighs rubbing the seatpost – General lack of intestinal fortitude – Etc.

    Acceleration takes a lot of power. Once you’re up to speed, air resistance is the biggest drag.


  23. Mr. P Says November 5, 2008 @ 8:51 pm

    “At speed, air resistance is the biggie.”

    So you are recommending a skin suit? ;)

    Is it true that air resistance starts to become a factor above 17mph? I’m just figure out what is myth.

    P


  24. leelikesbikes Says November 5, 2008 @ 9:32 pm

    Air resistance is always a factor. The faster you go, the more of a factor it becomes.

    Put scientifically: The force of air resistance increases in proportion with the square of speed.

    Put practically: When you double your speed, you quadruple air resistance.

    Here are rough numbers from the “Bike forces and power” calculator I linked to above. They show the amount of power it takes to ride a certain speed on flat ground, and the amount of that power that goes to air resistance:

    – 5 mph : total 48 watts : wind 6 watts
    – 10 mph : total 125 watts : wind 43 watts
    – 15 mph : total 271 watts : wind 144 watts
    – 20 mph : total 519 watts : wind 341 watts

    In this example, wind resistance become more than half the drag at about 15 mph.

    That crossover point depends on lots of factors, including equipment, riding position and whether you’re rocking a skinsuit!


  25. marz Says November 6, 2008 @ 8:43 am

    Great article and it reminds of conversation I had a while back about deflection and its effect on the efficiency of a bike. A guy on a rigid single speeder points to my fat tyres and 6” of front and rear suspension and comments that his bike is so much more efficient than mine. I agreed with him that when the trail is smooth and flat he may have the advantage, but I mentioned that once things get rough, rocky or rooty I’ll be the one on the more efficient bike as the suspension will be absorbing more vertical deflection than his rigid bike. He disagreed saying that when he needs to absorb rough sections of trail he just stands and uses his body to work the trail. I added that while he’s standing and working the bike along the trail, I’m sitting down and just pedaling straight through it.

    Not sure who’s right here. What do you think? On a level section of trail where there are alot of 3-4” roots or rocks (a healthy rock garden) crossing the trail who’s riding more efficiently, the 20lb rigid single speeder or the 36lb full sus?


  26. leelikesbikes Says November 6, 2008 @ 8:56 am

    I think that depends on riding style.

    If you’re both sitting statically, the suspension bike will be much better.

    If you’re pumping, it comes down to who has the greater kung fu.
    —-

    I’ve been wanting to take my Intense BMX cruiser to Hall Ranch—a mix of smooth flow and big rocks—for a little experiment.


  27. Alex Says November 6, 2008 @ 5:17 pm

    The burly freeride tires look great on paper, but paper is a little bit different from dirt. Looks like it’s time for you to do some real-world experiments pitting freeride tires against XC tires and see if your theory holds up. If it does, congratulations on becoming the arch-nemesis of XC tires.


  28. leelikesbikes Says November 6, 2008 @ 7:31 pm

    Yes, it is time for real-world tests. I think, to start:

    – Set up a mixed-terrain course.
    – Several riders doing several laps each.
    – Changing between two sets of tires, in varied order to account for fatigue and learning the course.
    – See what happens.

    Of course, we’ll have to do this on lots of different courses!


  29. Anthony Says November 8, 2008 @ 9:39 am

    One more variables to consider: reliability. A sturdier casing will resist pinch flats and punctures better than an XC tire. Add the minutes it takes to change a tire to the XC tire time.
    Another point: 6” travel bikes. I don’t understand why you’d put XC tires on a bike like this, it will most likely out-run the tires very quickly if you use the bike to its potential. The way I see it if I can get away with XC tires on the terrain I am riding than the 6” travel bike is also too much for the terrain and I should be riding a hardtail, 4” or 5” bike. The capability of the tires should match the capability of the bike, then you’re optimized:)


  30. leelikesbikes Says November 8, 2008 @ 10:58 am

    Anthony, nice!

    There’s an equation out there involving skills, fitness, confidence, riding style, terrain and bike setup. Oh, and phase of the moon. ...


  31. Randy Boy Says November 12, 2008 @ 8:25 am

    Great writeup there Lee… one factor you never considered but should…. as a variable… I’d bet you a case of your favorite microbrew that those XC tires that are so light are also far more likely to get a flat which would wipe out any time gains you might get from them while you spend your time replacing the tube. They are also, in my experience, far more likely to have a sidewall tear, and with the sidewalls so paper thin, if you lower the air pressure even slightly to obtain a bit larger “footprint” from the tire for more traction, you also risk getting a pinch flat.

    When you ride skinny racing tires and you are a Clydesdale, you’ll understand very clearly the meaning of “skittish” when going fast… you sacrifice control and need to make up for it with Lopes like skills.

    BTW, I have met and talked Lopes over breakfast one morning, and most of us need to understand he’s forgotten more bicycle techniques for going fast than any of us will ever remember. Few have the skills, ability and nerve to find out and test the limits of riding equipment the way he does. I’ll take being mortal as fine, and smile with the confidence a Schwalbe 2.4 Big Betty Freeride provides up front adds. I’m with you on your findings. Volume is king.


  32. Randy Boy Says November 12, 2008 @ 8:29 am

    Dang…. I should have read the whole thread before posting… someone beat me to it. That’s why being old and riding fast ain’t safe, Senior Moments make your forget what you were doing.


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