How does a rubber tyre compare to a steel gap?

How many goathead thorns have you pulled out of a tyre? They are pretty much always the thorn only with the head part worn away. It takes many, many revolutions of the tyre to repeatedly press the thorn deeper and deeper into the tyre. Many times, this results in a slow leak later that's not easily detected. Often times, the rider will replace the tube and end up with another slow leak. That's because the thorn has worked it's through the casing and the outsid end is shaved down to the level of the tyre surface, making it hard to detect.

Jobst isn't the end-all of bike-knowledge as his abstract academic background is often at odds with in-the-field experience of Sheldon Brown and others with tonnes of shop time. Over 10 years ago, right after that post, I devised a test verify his assertion on wiping tyres. Even when presented with all the experimental data, he refused to accept it. My test went roughly like this.

1. toss 100 goatheads onto the ground (about 2 handfuls). They land in roughly a 5-ft diameter circle
2. ride a bike at 20mph through the goatheads
3. continue riding for another 12miles (I chose this distance because it was the distance from the shop to my house).
4. repeat 10x (number of same rides in a week to work and back)
5. count number of goathead spines left in tyres
6. count number of flats.
7. change a variable and repeat.

The results were as follows:

1. the tyres pick up 3-5 goatheads when running through the thorn-field, regardless of liner
2. Without liners = 2 flats immediately, 5 flats within 5-miles, 3 flats in 6-12 miles, 100% flat rate
3. with liners = 1 flat immediately, 3 flats within 5-miles, 4 in 6-12 miles, 80% flat rate
4. with liners + scraping = 1 flat within 5-miles, 2 flats in 6-12 miles, 30% flat rate

This test is easily repeatable by anyone with similar results. Most goatheads never puncture right away. Most of the time, you'll never even notice when you ran one over and by the time you get a flat or slow-leak, only the spiny thorn is left in the tyre. Liners do reduce rates of flats given the same odds of running over debris. Liners along with scraping reduces flats even further.

I have another experiment on scraping alone somewhere... Although now with advent of digital video, I should revisit this with video-analysis of the scraping action.


I agree with Panther007, tyres with built-in kevlar liners are even better. Although for the ultimate commuter wheels, I like to install Tuffy liners inside kevlar-belted tyres along with thorn-resistant tubes and Slime. I rode all the way across the US in '96 and got 2 flats. But boy, those tyres were way slower than my racing tubies.