Skyway 6” Polyurethane Wheels

[gganio]

I have found these 6” Polyurethane wheels.
They are the closest thing that I have found to provide the comfort of pneumatic wheels and the low rolling friction of polyurethane (PU) wheels. Almost perfect. The problem is side drift and the fact that they last about 500 km as rear wheel. The above pic is after 250 km.

Frog Legs http://www.froglegsinc.com/ wheels didn’t work out as rear wheels. They can be used only as front wheel.

I think the Sky Way wheel http://www.skywaywheels.com/ can be easily used on an A-Bike. It would require some adaptation for the brake drums. Since it is soft, it should not break apart the front fork assembly.

If anybody is thinking about building a “trick” A-Bike, I think this wheel is a good starting point. It comes in several colours, I bought it here: http://www.wheelchairparts.net/CATALOG_c267354.html

[Job]

Interesting post, gganio!

I'm looking to change the pneumatic tyres for solid ones, because:
+it will save me from punctures
+i won't have to carry the pump anymore
+i won't have to check the tyre pressure
+i won't have the risk of tearing off the valve from the innertube

The trouble is finding a tyre that has the right hardness:
Too hard and the ride will be unbearable, and the a-bike will probably break from vibration.
Too soft and the pedalling will be tiresome, and i'll loose out in travelled distance per pedal stroke.

I am looking at the greentyre option: they seem to have developed a foam-filled semi-rigid tyre that could be suitable.
see:
http://www.greentyre.co.uk/w6inch.html

But I have no experience with these kind of tyres whatsoever..

Your mini125rd bike looks very interesting!
I looked up your blog and really enjoyed reading about your design and experiments.
What became of the very elegant chain guard experiment?
It seems the mini125 could do with that!
see:
http://mini125rd.over-blog.com/article- ... 07856.html

I also wonder how well the mini125 will negotiate a brick road. It has suspension in the front fork and beneath the saddle, so despite the non-pneumatic tyres i suspect it could do well.

Job

[gganio]

Me too realized that pneumatic tires, even though comfortable, would require to be inflated perpetually to 6 bar or more otherwise it would have been too much rolling friction. The result was that I was using the portable bicycle to save 5 minutes but I was spending 5 minutes to pump the tires!!!!!
I did benchmark greentyre, froglegs and skyway.
The calculation said that it was necessary to have polyurethane with rebound above 70% , otherwise the rolling friction was too much and hardness around 65A. Greentyre rebound less then 50% and hardness is 60A. Themselves talked me out of testing them on my bike. Froglegs would be the best but the polyuretane is not connected with the rim, and that makes it unusable as rear tire. That sucks, because otherwise it is kind of the perfect thing. Skyway 6" is 65A and 70% rebound.
My winter setup will be a frogleg in the front and a skyway in the back (I'll switch to inline skate wheels during the summer). That setup tends to be somewhat similar to pneumatic tire on cobblestone, but it is not quite the same. Riding on cobblestone with these bikes is feasible, but always some sort of "limping out of it" mode. If the PU wheel would be designed on purpose, then it would be better then pneumatic also on cobblestone..... but we are not yet there.

The difference between the A-Bike and the Mini125RD is very similar to the difference that there is between the Brompton and the Birdy. The A-Bike being the Brompton and the Mini125RD being the Birdy. All in all, it rides a little bit better but it is a little bit bigger.

I have already given up on the floating chain guard idea. If made on purpose it would have worked, but..... I am thinking right now to couple a chain cover idea with a purpose made bag idea. Purpose made bags are way easier to make then strange chain guards.

[Artefex]

Coincidentally, I just got a PU/foam tire to test on the ABike from this supplier of wheelchair parts in the netherlands: http://www.berghspecialproducts.nl/
They have a good selection of wheels and tires.
There was no information on the rebound or hardness but they where advertised as 'low rolling resistance'. Dropping the new tire and inflated Abike tire next to eachother they rebound about the same. My main concern is how long the tire would last compared to rubber.

Just one problem... anyone have experience of the best way to get this kind of tyre onto the rim?? As it cant be deflated, just using tire levers is extremely difficult.

[Job]

I can imagine putting a solid tyre on a rim will be difficult.

On the greentyre site they give some tips:
http://www.greentyre.co.uk/fitting.html
So for small tyres it seems a benchpress with a cone is the only option.
They don't show a picture of the cone, but i guess it's needed to get the tyre over the outside rim.

Alternatively you could try something like this:
http://www.skywaywheels.com/products_005.htm
That's a split wheel!

Now you need to find it in 6"!
And you need to find a way to attach the sprocket to the wheel, or you can only use it on the front..

Job

[Artefex]

Was not so difficult actually. Put the PU tire in hot water first and it became much more elastic.
Although I tested it today on my way to work and it is too soft, it was noticeably more difficult to ride. I will have to try some other alternatives.

Interesting point about fixing the tire to the rim on a driving wheel. To avoid the hub slipping inside the tire?
On my test ride today I marked the tire to see if this would happen but there was definitely enough friction with the hub. If the tire is a good fit I dont see this being a problem. (The inside width was slightly larger than the hub width so I trimmed it into a sort of wedge shape. The tension of the tire forces it against the insides of the hub channel, just like a pnuematic tyre)

On the basis of todays test ride I would say that a tire that is too hard (Small risk of damage, less comfort) would be a better choice than one that is too soft (Not practical as riding is less efficient).

[Job]

Your observation that a warmer solid tyre is softer than a cold one could spell trouble:
When riding the A-bike the tyres do get quite warm, especially the rear tyre.

When pneumatic tyres heat up, the pressure gets higher, so it will deform less, and roll better, automatically countering the heating process (theoretically!)

When solid tyres heat up from use, they go softer, thus deform even more, thus heat up even more, go even softer, and so on! (also theoretically)
In practice this process will also stop/level out.
Do the solid tyres heat up as much as the pneumatics during use?

So it seems wise to search for the right tyre hardness at the expected tyre operating temperature.
This will differ according to:
-front or rear wheel
-driver weight
-cruising speed
-season

So it might be interesting to test the currently too soft solid tyre on the front in winter conditions.
Hopefully it all doesn't matter too much!

Btw, i meant attaching the sprocket to a different type of wheel might be a problem.

Job

[gganio]

In my case I did tested the PU wheels at -8C and +33C (asphalt at +65C).
I have noticed that the 6" PU tires (Skyway, Froglegs, Microscooter in my case) would heat up almost nothing compared to pneumatic tires. I guess it is due that they are more efficient????
Rolling friction stays withing acceptable levels also at -8C. Pneumatic tires pick up a lot more of rolling friction at cold temperatures.
Sooner or later I will setup some roll up tests to measure what it is really going on.
My final judgment is that shore 65A is the right hardness, even though it will wear off during the summer. Harder then that will make the bike unpractical on cobblestone. Rebound should be the highest possible. Rebound below 60% would roll as pneumatic tires (well inflated) and therefore should be avoided.
Rollerskating and roller skis people are well informed about the hardness and rebound of their wheels. Unfortunately the people that have 6" PU wheels are the wheel chair caster people that are not well informed about hardness and rebound of their wheels. That is too bad and makes the quest for the ideal 6" PU wheel kind of difficult.
Sooner or later I hope a purpose made for the A-Bike 6" wheel will show up. I am sure a lot of people will prefer that wheel.
So far I am pretty happy with the Skyway wheel, however it is not yet the perfect wheel.
For tech info I had some luck with this site : http://www.airfreetires.com/

[Stevbike]

Here are some pictures I took of the tire wear on my 8" wheeled A-bike copy. This at the 300 km mark.