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Exactly 1/2 of 2-Epic
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Discussion Starter · #1 ·
Does anyone know of a source for rolling resistance values for 29er tires? 26" values would be good too...

Sorry if this is old news...but a search brought up a thousand irrelevant posts. I'm most interested in Nanos and Fast Traks.

Thanks!
 

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Recovering couch patato
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All else being the same, I think science says diffence should be proportional to tire diameter. It's strange no-one on here has done good DH roll-out tests yet. If only I had a rolling 26" bike, and identical tires in both sizes...
 

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Exactly 1/2 of 2-Epic
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Discussion Starter · #3 ·
Identical tires?

Cloxxki said:
All else being the same, I think science says diffence should be proportional to tire diameter. It's strange no-one on here has done good DH roll-out tests yet. If only I had a rolling 26" bike, and identical tires in both sizes...
Is there such a thing as identical 26 and 29 inch tires?? Can you think of some makes/models that are identical across sizes? That might be as close as I can get...got a little project I'm working on...
 

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And He was Not
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It might be a good idea to look to the Road Bike world to see the differences between 650 and 700 C wheels. I'm sure they analized this to death.
 

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Only dead people are old
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hairball_dh said:
Is there such a thing as identical 26 and 29 inch tires?? Can you think of some makes/models that are identical across sizes? That might be as close as I can get...got a little project I'm working on...
It would be a benefit if your project used the same tires on both...Bontrager, IRC, and WTB (I believe) all make 26 and 29" versions of at least one tread design. Identical - no; similar - yes.
 

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I think the OP is trying to compare 29" tires to each other. No one has tried a test, but the prevailing opinion is that the Nanoraptor rolls best.
 

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So if it is proportional then the 29er would have a greater rolling resistance than the 26er??

Lots of variables other than the type of tires in doing out tests:

1. Tire air pressure
2. Combined rider and bike weight
3. Type of bike
4. Aerodynamics
5. Type of terrain or surface

I always thought of doing roll out tests on different 26 inch tires including high pressure slicks but never got around to it. So many variables and so much work switching out tires. I think if a tire feels slow compared to another it probably is. Something with some sort of smoother center block seems to roll well to me. But then for off road you may not want a tire that rolls well if you give up traction.
 

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richwolf said:
So if it is proportional then the 29er would have a greater rolling resistance than the 26er??

Lots of variables other than the type of tires in doing out tests:

1. Tire air pressure
2. Combined rider and bike weight
3. Type of bike
4. Aerodynamics
5. Type of terrain or surface
I don't think you need to worry much about 1, 2, or 3 so long as they're held constant. These road tire resistance test results show that for the most part, if a tire rolls faster at one pressure, it will roll faster at another as well. The terrain may not matter much either - more bumps will cause more casing flex and widen the gap between fast and slow tires but the heirarchy should remain the same.

This chart debunks a tubular tire myth. You can read about it here: http://www.sheldonbrown.com/brandt/rolling-resistance-tubular.html
 

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Very interesting. I dig stuff like this even though it streches my miniumal comprehension skills to the limit.

But you do have to pay attention to keeping 1 2 and 3 constant which in itself would be a lot of work.

But since the test used rollers and road tires I would think it does not totally apply to offroad tires and offroad terrain. Is it more efficient to have a bike suspended and damped over bumpy terrain or have no suspension and rock hard tires which will toss the rider and biker around??

Also according to the chart presented it looks like narrower tires don't always have the least amount of rolling resistance. I heard people still use them though because there are other factors such as aerodynamics and weight to consider.
 

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I tested a pair of Mythos XC F&R and got the following values at 26 psi and 190 lbs rider plus bike weight:

mid-smooth asphalt: Cr=0.010
semi-rough gravel with some grass: Cr=0.028

I think that steel-roll or asphalt type of tire testing is partly misleading for off-road tires, since those tests don't take into account two things that only matters for off-road tires: suspension (tire height) and the ability to unrest the ground as little as necessary. A small tire will need high pressure and have bad suspension and therefore a rough and inefficient rolling. And it will plow the ground more, even further slowing down the rolling. Big knobs may also stir a soft ground more.

Because of that, I think that MTB tire rolling measures need to be done on real off-road ground, such as by rolling down a hill or having a fixed-power motor on the bike, and at various pressures. Unless it's only asphalt values you are after.

That said, I think my Nanos roll overall better than my ACX's and Mythos.
 

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Exactly 1/2 of 2-Epic
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Discussion Starter · #11 ·
cool...protocol?

anden said:
I tested a pair of Mythos XC F&R and got the following values at 26 psi and 190 lbs rider plus bike weight:

mid-smooth asphalt: Cr=0.010
semi-rough gravel with some grass: Cr=0.028
Yes, asphalt crr is certainly a misleading figure for general MTB use...but for the project I'm working on it will suffice. I think it is basically a trait specific to the casing and not so much the tread?

How did you set up the testing protocol? I may as well consider that too.

Thanks!
 

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Recovering couch patato
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hairball_dh said:
Is there such a thing as identical 26 and 29 inch tires?? Can you think of some makes/models that are identical across sizes? That might be as close as I can get...got a little project I'm working on...
Name me some 29" tires that don't also exist in 26"?

Ok, some easy ones that do come in both 29 and 26 :

WTB Nanoraptor, Motoraptor (ExiWolf not same width I think)
IRC Mythos
Maxxis Ignitor
Specialized Fast Trak (size might differ, 29"er is wide)
Bontrager AcX
Schwalbe Big Apple 2.0 and 2.35, Little Albert 2.1
Kenda Klaw
 

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hairball_dh said:
Yes, asphalt crr is certainly a misleading figure for general MTB use...but for the project I'm working on it will suffice. I think it is basically a trait specific to the casing and not so much the tread?

How did you set up the testing protocol? I may as well consider that too.

Thanks!
It's about measuring your rolling speed. It is time consuming, requires a couple of long slopes with constant angle, an accurate speed meter, and a few tools: http://forums.mtbr.com/showthread.php?t=37434

Good luck with your project. Make sure to report you findings.
 

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Exactly 1/2 of 2-Epic
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Discussion Starter · #14 ·
Very nice anden

anden said:
It's about measuring your rolling speed. It is time consuming, requires a couple of long slopes with constant angle, an accurate speed meter, and a few tools: http://forums.mtbr.com/showthread.php?t=37434

Good luck with your project. Make sure to report you findings.
You've done your homework! Quite interesting to see that for your tested tires RR was roughly 50W at 7mph - that's relevant for my first round of testing. I'll certainly test a tire or two, certainly a Nano and possibly a fast trak and report back.
 
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