I am trying to estimate rolling resistance and subsequent expected range for different sets of wheels, from early research I have stumbled mostly about papers on cycling rolling resistance and found some very interesting/counterintuitive facts, for example a softer wheel can have LESS rolling resistance due to bounce, and a wide contact patch can also have LESS rolling resistance due to a contact distribution that induce less hysteresis.
Now, I don’t know exactly where to start to be able to quantify this properly for urethane wheels, it sounds like the easiest would be a bench test (expensive) or simply test rides (time consuming), does any one have any data or pointers that may help me get ahead on this?
I think rolling resistance is directly related to rebound and that can be tested with a sample you bounce something against and simply see how high it comes back… why companies don’t do simple rebound tests to show and tell I wonder. its not everything though and I hear it doesn’t go well with durability. rubber bouncing balls aren’t so durable but have awesome rebound.
It can be complicated, on a track bike in a velodrome 23/21mm wheels are often faster than 19mm but sometimes the bounce combines with pedal stroke frequency and can rob lots of power, either adding or taking away pressure can fix it on a practical level. I always felt better (#faster) riding slightly over gear and over pressure if that means anything.
But I think the efficacy of a thane wheel is in part to it’s suspension like characteristics, it takes up the hit quickly but then there is a level of rebound control as that energy is returned, this prevents the bounce and wasted energy… of course those fluent in the dark art of thane formulation could manipulate this to deliver ride quality/performance…
I think the more “bounce” the better for rolling resistance. if youre on a bike then you can have your pedal stroke energy robbed and it can be complicated but if you’re just riding along not adding any energy and trying to get as far a roll as possible I think it comes down to the more bounce you have the better. if you bounce a rubber ball on the ground and it comes back to 90 percent of its dropped height then 10 percent has gone to heat and wasted. when your wheel hits something in the road it deforms and you want it to spring back as much as possible.
if youre rolling along and you hit something in the road, a crack or even a big rock, and your wheel is hard enough that your momentum is now being directed up into the air, then I think the tires are too hard and they could even still have a great rebound but not for such conditions. Id think you’d want to have the wheel soft enough to deform around a bump and then reform after the bump and with a rebound that losses as little energy as possible in the process. so hardness of the wheel would have to be matched to the rolling surface as well as have a good rebound. a guess
Just want to clarify, the data I found indicate that less bounce for a uneven road induce less rolling resistance. Less bounce means that either a tire is inflated to a lower pressure or for a urethane wheel I would assume a softer durometer – within certain limits. It basically needs to match the pavement texture.
The bounce is how much the rider and vehicule bounce upward upon meeting pavement texture, I am not sure if it’s the correct term, I have seen “sprung weight” also used.
generally if we are talking about a motorcycle, the sprung weight is the upper forks legs back to the rear shock shaft…
& the un-sprung weight would be for example on the front: the front wheel, brake assembly and lower fork legs. If you imagine it is the weight not being carried by the suspension
on a traditional bicycle though the tire is you suspension though so…
and here I was just relating my personal experience which is counter to the data and it is as much about the feeling and having a more responsive bike under me when racing in the velodrome.
Here are three big myths about urethane skateboard wheels:
Myth #1. “The harder the duro, the faster you go.”
We have to make a distinction between shortboard/trick/vert wheels and longboard wheels. Skaters tend to use hard wheels on smooth surfaces (concrete, ramps) when traction isn’t needed as much. Think of the wheels as the balls in bearings. Steel balls on steel races is super fast but soft urethane balls on steel races would be dog-slow. Harder is faster up to a certain point. After about 94a, the compound is more important than the hardness alone. Even when the duros are very hard, it’s best to have the highest rebound as possible for running over imperfections on the surface.
When it comes to rougher/asphalt surfaces however, the fastest (longboard) wheels I’ve tested are typically between 72a and 77a. It’s not just having a soft urethane, you need to have a super high-rebound urethane as well. These wheels tend to gobble up the imperfections and spring back in a way that reduces vibration and maintains momentum. Given the same wheel and hub, increasing the durometer and/or reducing the rebound tends to slow the wheel down.
Myth #2. “The bigger the contact patch, the more rolling resistance you have.” Don’t look at bikes and cars and pneumatic tires for the answer here. We are NOT a road bike with thin rubber tires inflated to 110 psi. We are skaters who need to support 150 to 250 pounds on 4 smallish urethane wheels. We started in the '70’s with wheels that were only about 30mm wide, and have slowly moved toward wheels that better suit our needs. I tell skaters to think about what you’d want if you had a car that had to drive on grass or sand. The LAST thing that you’d want is a narrow and highly inflated tire. You want to let the air out of some big wide tires. Wider urethane wheels better support the average weight skater and his deck on asphalt.
Myth #3. “Smaller wheels roll up to speed (accelerate) faster than bigger wheels.” I always loved racing against skaters who believe this myth. Their wheels were typically shorter and narrower and given the same core, felt harder. Small wheels may be nice for tight slalom where “nimble” is needed instead of high speed, but that’s about it. If you want to go fast (without a motor) I recommend having a soft high-rebound wheel that is at least 75mm tall, 58mm wide, and that has a small to medium hub in it. The best example of debunking the small wheel theory is when Mischo Erban and I were up at GMR both using Lime (80a) Centrax wheels. I had SIX 83mm x 78mm Centrax and he had FOUR 77mm x 68mm Centrax on his board. We decided to do a “rolling resistance” test because there were many people there believing that I was giving up a lot of acceleration at the start of the run and when coming out of the turns because I had 6 giant wheels that I had to get up to speed. From a dead stop we’d hold on to each other for a few feet and then let go. We traded decks and repeated the process several times. Whoever was on the board with the six bigger wider wheels started to pull away every time. We weighed about the same and aerodynamics was not a factor. The bottom line is that big fat deep soft high-rebound wheels haul ass and can handle turns better as well. Adding a motor typically just means that you’ll benefit from having wheels that are nice and fast under gravity, and that you can roll over crap better when the wheels are taller.