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16 Oct 2010

Tire testing

I'd been thinking about a new and improved rolling test for quite a while. I'd done one once before and actually, I was far from satisfied with that David had found a good location and I new what had to be improved in my way of testing. The rolling distance was enlarged from 50 or  so to 260 metres and the time between different tires was greatly reduced. Top speed during all tests was between 17 and 20kph.

The location is a quiet old viaduct with rough asphalt. To me, in a test, rough asphalt is a realistic mixture of smooth concrete and brick roads. Tires should also perform good on less than perfect roads. Call it a more realistic form of testing if you like. I can't tell you the rolling resistance coefficient of the tires. But such numbers don't represent the actual difference in speed.

I measure the time it takes to roll the distance. From that I calculate the average speed. The result of that is that I can see what the actual speed advantage, or disadvantage, of a tire is. The rear tire is my usual Racer at 5 bar. The rear carries about 30% of the total weight.

Schwalbe Kojak
My current choice with 1000km experience. Reasonably comfortable, good grip, easy to mount, puncture resistant enough (thus far, winter is coming), last long enough, fast, and tested with Schwalbe 6a inner tubes.

Schwalbe Durano
My previous choice with 1000km experience. Little comfort, enough grip, easy to mount, does not wear fast, rolls good, puncture resistant enough, and tested with Schwalbe 6a inner tubes.

Continental Grand Prix
A request from David. This set of tires is brand new and that usually makes a tire less fast. They give a rough ride. Mounting them went a lot easier than expected. They look really fast. Also tested with Schwalbe 6a inner tubes.

Avocet Fasgrip
A exotic tire which is out of production. They have no grip and very little puncture resistance. They are wide and very comfortable. Presumably very fast, especially with 6000km of rubbing in. Tested to see how good it'll be against narrow racers like the Durano and the GP. David's idea. I used different inner tubes for this set.


(click for larger table, V+ should be V-)
Conclusion
Hard and skinny doesn't work for me when it comes to tires. Under normal conditions the wider Kojak is faster and a lot more pleasant to ride. Front tires and 8.5bar do not sound pretty in a velomobile. The GP seems to suffer from being new. My feeling tells me that it's something like a Durano. Possibly faster, but that hard to judge without having ridden it. The Fasgrip is the fastest, but has the previously mentioned disadvantages.

In the end it was nice to see that the control run turned out good. That tells me I have done a proper test with reliable results. I know that testing like this leaves room for error. But the differences between tires are consistent. I'll keep on using Kojaks.

Next idea is to see how the Kojaks compares to something I'd like to use during the winter, the Supreme. Some say it's awfully slow. I like the idea of not getting a puncture in the cold and wet winter. We'll see how things go.

2 comments:

  1. I've worked on the GPs with sandpaper, changing this, as you tested them, to this much smoother tyre. They're still new, but hopefully this will make them faster. A few days ago I switched to Marathons for winter, but I've put the GPs (and an Avocet Fasgrip on the back) on the Mango for tomorrow.

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  2. Peter

    Great testing you have done here. My Quest came with the 1.35 Kojaks and I have just ordered my third pair to go on the front. I got 4,500 kilometers out of the first pair and about 5,800 kilometers out of the second pair. I would attribute the longer milage of the second to rotating the front tires from side to side just a couple of times. If I were to rotate every 1,000 kilometers I bet I could get even longer use out of them. What lead me to go with the new tires was the showing of the casing through the tread.

    Many Thanks for you time and effort into this.

    David

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