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 2017-04-26, 09:35 PM #31 johnfoss North Shore ridin'     Join Date: Apr 2002 Location: El Dorado Hills, CA Posts: 16,357 Yes, a fatter tire/low pressure generally means greater rolling resistance. But I think we get the idea: Smoooooooth rolling with no tread noise or vibration! I imagine if you have long cranks and poor spinning skills, i.e. an inefficient spin of the pedals, you could end up bouncing all over the place while trying to ride in a straight line... __________________ John Foss www.unicycling.com "The "impending disaster that never quite happens" is the the Eureka moment of unicycling. Everything that follows is just refinement." -- Engineer on a Unicycle
2017-04-27, 12:24 AM   #32
lightbulbjim
Unicyclist

Join Date: Jan 2015
Location: NSW, Australia
Age: 32
Posts: 263
Quote:
 Originally Posted by johnfoss Yes, a fatter tire/low pressure generally means greater rolling resistance. But I think we get the idea: Smoooooooth rolling with no tread noise or vibration!
Actually wide tyres have less rolling resistance at a given pressure than narrow tyres. Put another way, to achieve a rolling resistance of X with two otherwise-identical tyres of differing widths, you will need to inflate the narrow tyre to a higher pressure than the wider tyre.

Of course a wider tyre might be heavier, harder to steer (depending on pressure) etc.

Pressure and rolling resistance is a bit weird too. On smooth surfaces more pressure means less rolling resistance. But offroad more pressure can often increase the rolling resistance.
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2017-04-27, 03:27 AM   #33
johnfoss
North Shore ridin'

Join Date: Apr 2002
Posts: 16,357
Quote:
 Originally Posted by lightbulbjim Actually wide tyres have less rolling resistance at a given pressure than narrow tyres. Put another way, to achieve a rolling resistance of X with two otherwise-identical tyres of differing widths, you will need to inflate the narrow tyre to a higher pressure than the wider tyre.
The pressure difference necessary to ride on a tire that's actually narrow compared to a super-fat one makes it impossible to compare them realistically at the same pressure. In other words, higher pressure as the tire narrows should be a realistic assumption.

That said, I don't know if rolling resistance is the same as friction. I was thinking in terms of friction in my previous post.
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John Foss
www.unicycling.com

"The "impending disaster that never quite happens" is the the Eureka moment of unicycling.
Everything that follows is just refinement."
-- Engineer on a Unicycle

Last edited by johnfoss; 2017-04-27 at 03:27 AM.

2017-04-27, 04:05 AM   #34
lightbulbjim
Unicyclist

Join Date: Jan 2015
Location: NSW, Australia
Age: 32
Posts: 263
Quote:
 Originally Posted by johnfoss The pressure difference necessary to ride on a tire that's actually narrow compared to a super-fat one makes it impossible to compare them realistically at the same pressure. In other words, higher pressure as the tire narrows should be a realistic assumption. That said, I don't know if rolling resistance is the same as friction. I was thinking in terms of friction in my previous post.
You're right that it's not practical to compare them at the same pressure, but the principle still stands. As an example, a 25mm wide tyre at 100 PSI might have the same rolling resistance as a 50mm wide tyre at 60 PSI. There are many other factors at play, of course, such as tread, tyre material, wall thickness and probably shape.

source
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 2017-04-27, 06:31 PM #35 johnfoss North Shore ridin'     Join Date: Apr 2002 Location: El Dorado Hills, CA Posts: 16,357 Good chart! A reminder that tire pressure is always going to be a factor in how much energy it takes to move a wheel, regardless of width. A 5" tire with really high pressure might be pretty interesting to take on a bumpy trail. You might bounce like a basketball! __________________ John Foss www.unicycling.com "The "impending disaster that never quite happens" is the the Eureka moment of unicycling. Everything that follows is just refinement." -- Engineer on a Unicycle
 2017-04-28, 08:55 AM #36 Vee The Unsung Uni-Hero     Join Date: Dec 2010 Location: Moscow, Russia Age: 40 Posts: 56 I have seen some pictures of the Hatchet with a Snowshoe 2XL on them but I cannot tell what size rims they are. I have a couple of Clown Shoes lying around from a fat bike and want to put one in my hatchet with a Snowshoe 2XL. I need to order the hub from UDC US and want to make sure everything is going to fit before I do. Has anyone put a 100mm rim with a Snowshoe 2XL in a Hatchet yet (with pictures)?
2017-04-28, 09:00 AM   #37
Vee
The Unsung Uni-Hero

Join Date: Dec 2010
Location: Moscow, Russia
Age: 40
Posts: 56
Quote:
 Originally Posted by johnfoss Good chart! A reminder that tire pressure is always going to be a factor in how much energy it takes to move a wheel, regardless of width. A 5" tire with really high pressure might be pretty interesting to take on a bumpy trail. You might bounce like a basketball!
Indeed.
I have the Vee Apache at about 15 PSI and it feels solid. It takes very little energy to get it rolling. I cannot imagine a thinner tire at 15 PSI rolling as easily.

The Apache says it can go to 40 PSI but I cannot imagine the person that would want to do that. At 15 I feel every bump and have to hold on tight on a bumpy road.
I took the wheel out of my uni and tried to bounce it like a basketball and perhaps a new sport is to be had. Once I got it going it was very easy to dribble.

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