WISIL Solid Airless Tire page
Fun with Airless Tires
Some time ago Dan Fritzenger e-mailed me and asked if I would like to test out some airless tires that he was prototyping. These tires were to be designed with super low rolling resistance, for use in .Decimach or Battle Mountain racing scenarios. I told him I would be happy to test the tires and provide feedback to him about them. He proceeded to make a series of prototype 406mm Polyurethane (PU) tires. Note that these are not the Air Free brand tires, but are a similar idea. 
 When the tires arrived my first impressions were that they were a bit heavy (a couple pounds each), and that they had an interesting ridge running down the center of each tire. After e-mailing Dan, he said I could leave it on or remove it. The idea for leaving the ridge on the tire is that it would provide a very narrow track for the vehicle to run on, which in theory should be very low RR. 

The tires are a nice shape, and are very low profile.


I mounted the to my spare set of wheels with the tool that Dan provided. Take a look at the AirFree tires site for details here as their tool and method of installation is practically identical to Dan's. I had to use both hands, and both legs to pry the tires on the wheels, but other than the strength needed to install them, they went on easily. The tires were custom made for the width of the rims and fit nicely. Dan says that you could probably remove the tires by prying them off, but there's less chance of rim damage if you cut the tires off.

Here's a close-up of the tire, showing the ridge. 

I went on a New Years day ride with Ed, Larry & Co. Before the ride I rode up and down the street trying out one of the tires on the front of the 'Cuda street bike. This is definitely a solid tire. It felt fast but I could feel all the minute rocks in the asphalt surface. I was thinking about using it on the ride until I braked medium hard and the tire skidded.  The ridge was worn off in that spot making the tire lumpy. Sean Costin tried it a couple times with similar results. 

Apparently because these prototype tires are so hard, they are a bit slippery, do not hold the road well, and would not handle a high speed turn. Also if used on a streamliner at high speeds, a breeze which would normally be handled by leaning into the wind may be enough to cause the bike to lose traction and crash. After further correspondence with Dan, he says he will make another set of prototypes based on a different PU formulation that will address the issues of traction.

As these tire are designed for high speed straight line racing runs, tire wear is not an issue at this time.

I put the rear PU tire on my trainer and removed the ridge with a razor knife. It's fairly smooth, but should really be cut on a lathe in a manner similar to how race car tires are cut to ensure the roundness of the tire. It does appear to roll much easier than the Tioga Comp Pool I was previously using on the trainer.

Dan sent a set of reformulated tires, which were based on a softer PU. They look nice, with yellow sidewalls and black tread area. Recently I had a chance to do some testing. I did a coast down test on a section of my road with a good downhill, and then a nice run out. All tests were conducted with the same bike/rider and with similar wind conditions (barely any wind). In each case I started in the same spot and recorded where I stopped.  The first test was with the hard black PU tires, which were my "reference" tire. Bike weight was lighter with pneumatic tires, which should have given an advantage to the PU tires. Results below:
The yellow PU tire felt a lot better in terms of ride, and was not slippery, put pedaling effort was noticeably harder (as shown by the massive difference in roll down. The black PU tires had the ridge removed, but I did not remove the ridge on the the yellow ones. I'll remove it when I get some time and try again, I suspect it will roll better without the ridge. I had to cut the black PU tires off the wheel to mount the yellow ones. The 300ft was an estimate as I didn't have a tape rule that long.

Coastdown 1 Results

Hard black PU tires Reference - 0
Yellow/Black PU tires Reference -300 ft
Comp Pool tires Reference +114 ft
Ford Contour (Goodyear) Reference -60 ft

Conclusion: The black PU tires rolled better than I thought they would, but those tires would not have been useable in an actual racing environment.

Dan is working on another formulation for the tire, and machining a new mold to make tires without a ridge. More samples and testing will to come!

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