Bicycle Flat Prevention in Goathead Thorn Areas

goathead thorn
spines pointing upwards on this goathead thorn are broken, normally there are spines in all directions

Avoiding thorns

Goathead thorns are an opportunistic species, fast to colonize and grow on disturbed ground, but unable to compete in the long run with other plants if the area is left undisturbed. My experience (in the western part of the United States) is that these thorns mostly grow on vacant lots and by the sides of roads and similar weedy areas in populated areas. Everyone hates goathead thorns, not just bicyclists, so they are not typically found in well-maintained areas, especially where children or dogs might be walking barefoot. I have never seen a goathead thorn in true backcountry, either in forest or deserts, though I did encounter another type of thorn in the desert. (According to another bicycle tourist I talked to, goatheads are also common in heavily grazed ranching areas of New Mexico, even though these areas are far from civilization. Heavy grazing evidently has similar effects as mowing weeds in populated areas, in that it disturbs the native vegetation and allows opportunistic species like goatheads to move in.) Over time I've learned to recognize the sort of areas where goathead thorns might be a problem, and I make a point of staying away from these areas. Or else I dismount and push the bike through these areas, carefully checking the tires as I go to see if any thorns have been picked up. Avoiding thorns is the first and simplest line of defense.


Good modern tires include a builtin Kelvar (aka aramid) puncture protection liner, which greatly reduces flats due to goathead thorns as well as glass and other sharp objects, compared to tires with no such liner. Currently, I run Schwalbe Marathon Mondial 55-559 size folding tires (865g each), which is what Andy Blance of Thorn Cycles recommends for expedition touring, with a Schwalbe Marathon Extreme 50-559 size folding tire (600g each) as my spare. (The Extreme was replaced by the Mondial and is no longer in production.) Both these tires have builtin Kelvar protection liners. I compared pushing a needle by hand through these Schwalbe tires versus a cheap Kenda tire. It is clearly much easier to push through the Kenda than the Extreme or Mondial.

Rivendell Bicycle Works says folding tires (Kelvar rather than wire beads) tend to roll off instead of staying in place during mounting. My experience with Schwalbe folding tires is that they do indeed tend to roll off during mounting, but this presents no real difficulty in getting the tire mounted. Rivendell also warns that folding tires will flop off if the tire goes flat and you have to walk the bike home. My experience is that this is not a problem with Schwalbe Extremes. After getting a flat about a half mile from home, I decided to walk the bike home rather than fixing it on the side of the road. No problem with the tire rolling off.

Schwalbe also offers a Marathon Tour tire, which Schwalbe rates as having the best puncture protection of any of its tires. However, this tire has many disadvantages: (a) very heavy (1100g for 50-559 version); (b) only comes with a wire bead and so a folded tire can't be carried as a spare; (c) maximum width is 50-559, which is insufficient for desert sand; (d) there are are reports (confirmed by Schwalbe) that this tire is extremely hard to mount, to the point where special mounting fluid and tools might be required to get it on the rim. So I ruled out this tire for my use. On the other hand, this tire is probably the best solution to the goathead thorn problem for cyclists using road tires inflated to high pressures, since high pressures are incompatible with sealants. [Update 2015: Or such was the traditional view, maybe modern sealants do work with high pressures.] Such cyclists will simply have to bring along the special mounting fluid and tools as part of their repair kit.

The Nomad page has a discussion of my experiences with Schwalbe Marathon Mondial tires, including photos of the eventual failure modes.


Ordinary tubes offer essentially zero resistance to puncture protection. However, there is such a thing as a "thorn tube", which has very thick walls on the outer side. The idea is that the thorn or tacks may penetrate the tire and tube, but won't reach all the way to the inside of the tube, due to the thick rubber, and so the tube will stay inflated. The problem is that these tubes are very heavy (I measured 580g, versus 195g for the regular tubes I use), which causes the bike to feel very sluggish. The thorn tube I tested was filled with 190g of Slime sealant and thus weighed 770g initially, which would have really ruined performance. (To determine the tube weight without sealant, I removed the valve core, washed the sealant out with water, then allowed the tube to dry.)

And even worse idea is the solid rubber "inner tube", though "inner torus" would probably be a more accurate term, since tube implies hollow. Solid rubber is heavy, gives a harsh ride, and will eventually destroy rims or spokes due to lack of cushioning. The only reason such junk sells is that people are desperate for a solution to the problem of goathead flats.

Though ordinary tubes offer no puncture protection, it is still better to use quality rather than cheap tubes: (a) tube stays inflated much longer due to better quality rubber; (b) less likelihood of valve stem tearing off; (c) better quality control and so less likely to discover in the field that your spare tube is defective. I use the av13 tubes by Schwalbe (195g each). When running these tubes at 36 PSI (2.5 bar), I only have to top up pressure once a month, whereas I would have to top up pressure weekly with cheap tubes.

I prefer Schrader valves for two reasons: (a) valve less likely to be clogged with sealants, if sealants used; (b) Presta tubes with removable valve cores not widely available whereas all Schrader tubes have removable valve cores, which are required to use sealants; (c) more difficult to install sealant, because Presta valves narrower than Schrader, unless using a special filling tube that screws onto the valve, but that is one more thing to carry; (d) Presta valve stem more easily damaged; (e) Schrader pumps more widely available in remote areas. Andy Blance recommends Presta valves, on the grounds that the seal is better between pump and tube. Evidently, he had some bad experiences with cheap hand pumps, especially those without a flexible tube, not being able to inflate a Schrader tube properly. With my Lezyne Pressure Drive hand pump, the flexible tube screws on to the valve, rather than using a flimsy locking gizmo, and this guarantees a good seal. (The flexible tube on the Lezyne pump is also reversible, with one end for Presta and one for Schrader, so the pump works for both valve types—ingenious design.) So if you drill your rims for Schrader, as I recommend for those in goathead territory, be sure to get a good hand pump. I've never had problems getting a good seal using even the cheapest floor pumps with Schrader valves, at least for pressures up to 45psi (3.1 bar), which is the most I would ever use.

A more valid reason to prefer Presta valves is that they require a smaller rim hole, and smaller holes are less likely to weaken rims than larger holes. Somewhere on the internet, I read a report by a bike tourist who had no problems with his original rims, drilled for Presta valves, but then later, after he had the rims redrilled for the larger Schrader valves (because Schader valve tubes are more widely available in that part of the world), the rims started to crack near the valve hole. This particular problem may be due to improper drilling technique, since he had other complaints about the bike shop that did the redrilling. Most rim failures occur at the spoke holes (overtensioning) or braking surface (wear from rim brakes) rather than from flattening or splitting near the valve hole, especially when using sturdy rims like the Ryde Andra 30 on my Nomad.

Both tubes and tires degrade over time due to oxidation. To reduce oxidation, keep spares wrapped in plastic. An opsak (odor-protection sack, by the aloksak corporation) is best for the spare tire if you plan to store it in a pannier with food, water or clothing, since tires often have an intense rubber smell which can contaminate these other items. Degradation of mounted tires will be obvious, but that of mounted tubes will be hidden. It is thus a good idea to inspect tube occasionally. Or just replace tubes whenever tires are replaced.

Sealants in inner tubes

The idea is that the sealant plugs the puncture while escaping under pressure. Sometimes it is necessary to reinflate the tire, because pressure is lost during the sealing process, but it won't be necessary to dismount the tire and apply a patch to the tube. Sealants fail under two cases: (a) head of the thorn breaks off, leaving the thorn itself attached to the inside of the tire, so that it constantly rips open the puncture in the tube, causing all the sealant to leak away; (b) very large punctures, such as from nail, and blowouts.

There are a number of brands of sealant on the market. Slime is sold everywhere but failed to work in my test, which consisted of installing sealant, turning bike upside down, spinning wheel, puncturing tire 10 times with a sewing machine needle gripped in a pair of pliers, continuing to spin wheel for another two minutes to push sealant to outer surface of tire via centrifugal force, reinflating tire (in case some pressure was lost during sealing process), waiting several hours to see if tire remained inflated. Stans sealant passed this same test several times, and so that is what I use. Slime is also heavier than Stans, at 190g per tube versus 60g. During field experiments, Stans also worked well. (I have heard good things about TrueGoo, but have not tested it myself.)

[Update as of May 2014: the Slime corporation has recently introduced a new product called Slime Pro, which appears to be a knock-off of Stans. Like Stans, Slime Pro has natural latex rubber as the primary ingredient, and weight of Slime Pro is about 60g per tube, same as Stans. I have not yet tested Slime Pro myself.]

To install sealants, you will need removable valve cores and a valve core removal tool (which Stans sells). All Schrader tubes have removable valve cores, but only some Presta tubes. There are complaints on the internet that sealants clog valves and ruin tire pumps, but these problems appear to be confined to Presta valves. I read no reports of clogging problems with Schrader valves nor have I had any problems myself using sealants with Scrader valves. The valve should be placed at the 10 o'clock position when inflating/deflating, so that sealant will flow away from the valve, reducing likelihood of clogging.

Another complaint is that sealants make a mess inside the tire and on the surface of the tube, so that patches will no longer stick (assuming the sealant doesn't work so a patch is required). My experience is that Stans sealant can be rinsed away with a squirt of water or wiped off with a paper towel, at least until it dries out, and after that a patch can be applied and will adhere in the normal way. Even if the sealant did dry out, it could still be easily removed using the sandpaper included in most patch kits.

A more serious issue with sealants may be that some natural latex-based sealants (such as Stans) use ammonia as a solvent, which supposedly can damage aluminium rims. I am not sure if Slime uses ammonia or other harmful solvents. CaffeLatex sealant supposedly uses synthetic rather than natural latex, and so does not require ammonia as a solvent, and hence is safe for rims. Schwalbe warns that some sealants may damage tires, though they don't say whether it is the ammonia or something else that causes the damages, and recommends their own DocBlue sealant (much more expensive and less readily available than Stans sealant). There should be no problems with sealants damaging tires and rims for someone who puts the sealant in an inner tube, rather than directly in the tire (as is done with tubeless systems). Perhaps sealants also damage tubes, but then tubes are much easier and less expensive to replace than tires and rims. I haven't noticed any damage to my tubes from using Stans sealant in the course of several years and 10,000 miles of touring.

Sealants will not work with high pressure tires. This is not an issue for me, since at most I would use 45 PSI (3.1 bar).

[Update 2015: Schwalbe has recently introduced tubeless road racing tires (Schwalbe One line), whose minimum pressure is 5 bar (70 psi) for the 23-622 version. In the discussion of this tire on their website, Schwalbe states that these tires are intended to be filled with sealant, which seals punctures in a fraction of a second, and they also state that their own DocBlue sealant is actually made by Stans. I am not sure how to reconcile these statements with the traditional consensus that sealants such as Stans only work with low-pressure tires.]

CO2 inflation may cause problems with tires/tubes containing sealant, since the cold CO2 gas may cause the latex to solidify. (The CO2 will be cold because gases drop in temperature as they expand, which is how refrigerators and air conditioners work. This is less of a factor with air compressors, since compression heats the air, so that partial expansion merely cools it back to near the original temperature, assuming not much time elapses between compression and expansion and the heat is not otherwise lost.)

Adding sealant to spare tubes in advance might seem convenient, so as to reduce time to install the spare tube. However, this risks sealant drying up over time. Better to wait until time to install tube on wheel. Likewise, better to buy Stans in individual 60ml bottles, even though slightly more expensive than larger sized bottle, because small bottles have factory seal and thus are less likely to dry out.

Stans sealant will eventually dry up, leaving a lump of latex in the tube. I sliced open a tube after several months of use to inspect. The lump shown below was about 3cm long and weighed about 4 grams. A lump this size should not cause wheel unbalancing, so I don't think lumps like this will be a problem. Note that only some of the sealant had solidified into a lump, and there was still plenty of liquid sealant remaining. For someone who rides year-round, always uses sealant, and replaces the sealant every 4 months, there might be 3 lumps in the tube at the end of a year. At that point, it might be worthwhile to replace the tube with a fresh one. My experience is that if I install Stans sealant in inner tubes in July and don't add any more sealant after that, there will still be liquid sealant in the tubes 7 months later in January, after 4000 or more miles of touring in the hot and dry conditions most likely to cause sealant to dry up. Compare with tubeless systems, where new sealant typically needs to be added monthly. So adding sealant every 4 months is probably overkill.

latex lump

For those of you having problems overcoming an aversion to sealant, it might help to compare tubes without sealant to hemophilia. Untreated hemophilia has the advantage that it eliminates internal blood clots which can cause ischemic strokes. But that minor advantage is offset by the more serious disadvantage that a minor cut can cause a hemophiliac to bleed to death. Analogously, a tube without sealant has the minor advantage of saving a bit of weight, but with the offsetting disadvantage than even a pinhole puncture causes the tube to go flat. Adding sealant to tubes is analogous to giving hemophiliacs artificial clotting factor. Slime would be analagous to low-quality clotting factor, which doesn't work properly and has serious side-effects (190g of added weight per tube), whereas Stans would be like modern high-quality clotting factor, which works well and has minimal side-effects (60g of added weight) and also costs a bit more ($3/tube vs $2/tube for Slime).

Tubeless system

It is also possible to run tires with no inner tube, using a special rim strip with incorporated valve plus sealant to seal between tire and rim. Visit the Stans Notubes site for details. Advantages: (a) reduced weight, since no inner tube; (b) possible to run tires at very low pressure, for better traction in deep sand, without danger of pinch flats; (c) better performance during aggressive riding, since no friction between tire and tube; (d) thorns that break off and remain attached to the inside of the tire will not cause problems, because there is no inner tube to tear open. Disadvantages: (a) hassle to install initially; (b) if seal breaks in the field ("burps"), probably necessary to switch back to the normal system with inner tube, including removing that special rim strip with incorporated valve, because difficult to get a good seal under field conditions. The Stans kit for converting ordinary rims to tubeless requires drilling out the inner rim to a diameter somewhat larger than the standard Schrader hole, in order to get the special rim strip to seat properly. I'm not sure what effect that would have if it were necessary to revert back to ordinary rim strips with inner tubes. I have no experience running tubeless myself, but the system is intriguing, provided the seal is long-lasting (at least 3 months). I have no plans to experiment with tubeless myself at this time.

Tire liners

Supplementary tire liners (that is, inserted between tire and inner tube, as opposed to incorporated into the tire itself) have numerous problems: (a) nuisance to install because of how they flop around while putting the tire onto the rim; (b) weigh at least as much as sealant, if not more; (c) less effective than sealant at stopping flats from goathead thorns; (d) convert easy-to-detect flats into slow leaks that can only be detected by putting the inner tube under water; (e) cause flats by slicing into inner tubes. A bad idea all around.

I experimented with the StopFlats2 liner for 26 x 2.25"-2.50" tires (sage model) by California Bike Gear, which weighs 155g. Compare with 60g for Stans sealant. This liner is supposedly double thickness and I was running inside Schwalbe Marathon Mondial tires, which have a builtin Kelvar liner, so there was effectively triple thickness of liners. I ran over a nest of goatheads (vacant lot just south of the town park in Bullhead City, Arizona, where I had to get off the sidewalk to make way for a pedestrian) and picked up at least 30 thorns per tire. I pulled these thorns out as soon as I noticed them. The triple thickness tire liners stopped all but 2 of the thorns, or 97%. However, the two thorns that did get through caused very slow leaks, so that I had to put the inner tubes under water to find these leaks, which is a nuisance while touring. Granted, 2 patches is better than 60+ patches, but with sealant I probably wouldn't have had to apply any patches, nor would I have had to remove the wheel and tire, though I might have had to reinflate the tire somewhat. Later, after about 1200 miles (1930 km) of touring, the liner caused one tire to go flat because of how it had sliced into the inner tube as the liner and tube shifted against one another. See the photo below, where the slicing is the semicircle to the right of the number 13 (the black line down the middle of the tube is shadow). I threw away both liners at this point and reverted to my old system of Stans sealant inside inner tubes. Note that this StopFlats2 liner, in addition to being double thickness, had softer edges than both the Slime liner (a strip of urethane plastic weighing 65g) and Mr Tuffy's liner (I didn't have a chance to weigh this). So these other liners will probably perform worse than the StopFlats2 liner: allow more flats due to goatheads, cause more flats due to slicing into inner tube.

inner tube damaged by tire liner

Incidentally, though this has nothing to do with goathead thorns, I had a similar problem with a maladjusted nylon rim strip slicing into the inner tube. I replaced with velox cotton rim tape. I discussed this with Andy Blance of Thorn Cycles and he pointed out that the glue on Velox rim tape can melt and allow slipping in hot weather. And indeed, one of my Velox rim tapes did shift, as shown below. I'll be going back to nylon rim strips in the future, but will be more careful about making sure the rim strip is not maladjusted when I install tires. I'll also throw a spare nylon rim strip into my repair kit, in case the rim strip on the wheel somehow gets permanently wrinkled and won't stay in place properly.

slipping velox rim strip

[Update Jan 2016: nylon rim strips appear to become stiff with age, so I'm going to replace periodically in the future, such as every 13000 KM or so, which is roughly my replacement schedule for tires and tubes.]


As of Jan 2019, I have completed 16 long bicycle tours in the American West (15 tours with the Nomad, 1 with the Novara), plus a small amount of riding in the city, for a total of about 22600 miles (36363 km). Most of that riding was with Stans sealant (65g) inside Schwalbe av13 inner tubes (195g) inside Schwalbe Marathon Mondial 55-559 tires (865g), for a total weight per wheel of 1120g. I encountered numerous goathead thorns and also many other sharp objects when running with this system, but only had to dismount the tire and apply patches three times due to punctures: (a) twice when a particularly large thorn (not a goathead) got embedded on the inside of the tire and kept ripping the tube open; (b) once when I rolled over a piece of scrap lumber with a large nail sticking out of it, which made a huge hole in the tube that the sealant couldn't seal. (There was also the flat due to a maladjusted rim strip cutting into the inner tube, and the flat caused by tire liners, as discussed above, but those two flats are unrelated to goathead thorns or other sharp objects puncturing the tube from outside the tire.) Perhaps 10 times I had to stop and reinflate the tire, due to partial pressure loss when a thorn was removed, but without having to dismount the tire and install a patch.

On one tour, as discussed above, I experimented with tire liners, and found these to be an inferior solution compared with Stans sealant in the inner tube. On another tour, I experimented with running without sealant, but soon got flats in both tires (from goatheads), and so installed sealant and thereafter had no further problems on that tour. Since that tour, I have gotten much better at recognizing and avoiding goatheads, so am now more confident about running without sealant. Therefore, I may not install sealant the next time I replace inner tubes as part of periodic maintenance. However, I will still carry sealant in the repair kit, so I can install sealant during the tour, if necessary.

Whenever dismounting tires, either to patch inner tube or replace tire/tube, I inspected and often noticed a large number of thorn fragments attached to inside wall of tire, and yet tire had remained inflated. So it is only sometimes that these thorn fragments on inside wall of tire cause problems. Whenever you dismount a tire, be sure to run your finger around inside wall to check for thorn fragments.

My repair kit includes: (a) 1 x Schwalbe Marathon Extreme 50-559 folding tire, weighing 615g including opsak wrapper to slow down oxidation; (b) 2 x Schwalbe av13 tubes, 200g each including opsak wrapper; (c) 2 x 60ml bottles of Stans sealant, 75g each; (d) 2 x puncture repair kits (total of 2 tubes of rubber cement, 16 patches). Spare sealant is either for use in spare tubes, or for cases where sealant leaks out but I am still able to patch tube, and then have to add new sealant. Bottles of spare sealant can leak, so I keep them inside a plastic bag and put that bag inside saddle bag, which is only used to hold tools and other items that would not be damaged by leaking sealant. Avoid putting bottles of sealant at bottom of pannier, where they might be crushed and then leak all over everything, causing a big mess—I'm speaking from experience here.


Schwalbe tires and tubes can be ordered from Schwalbe North America. Some Schwalbe tires and tubes available from resellers, such as Cyclo Camping or SJS Cycles.

Stans sealant and a very nice Schrader valve core removal tool can be ordered from Stans Notubes. Stans sealant is also widely available at local bicycle shops throughout the western United States.