Putting Tire Sealant in Presta Valve Tubes


I got a new bike earlier this summer (a Kona Dew Deluxe) and it’s a sort of cross between a mountain bike and a road bike. It uses the narrow 700 cm road tires and so I’m learning to deal with Presta valves whenever I need to inflate the tires. That requires putting an adapter on the valve stem since my air compressor is set up for much more common Schrader valves.
One of the annoyances of bicycling on the Front Range of Colorado is the abundance of thorns called ‘goat heads‘. They will easily puncture bicycle tires. I learned this many years ago when I purchased my first bike in Colorado only to get two flats tires on the same day I took it for its first spin. When I returned to the bike shop, they asked if I had put TR tubes in it yet. TR tubes? “What are those and why didn’t you let me know about this when I bought the bike?” I was new to Colorado and never heard of TR tubes. “TR” stands for thorn resistant and their outside wall is about 4 times thicker than that of standard tubes and so the goat heads generally cannot penetrate in far into the tube wall enough to puncture it. After installing these tubes, I didn’t have any more problems with flat tires from the goat heads on my mountain bike.

However, with my new bike, despite putting TR tubes in it before leaving the bike shop, I’ve had several flats from goat heads. I guess it’s because the rubber on both the tire and the tube is thinner to begin with than standard 26″ mountain bike tires. So I needed another plan. I see a lot of Slime tube sealant for sale these days in bike shops, and I was wondering if there would be a way to get it into tubes that had these newfangled Presta valves since the cores didn’t appear to be removable. I looked on the Internet and found several websites that talked about a method of using cutters to clip off the last few threads on the part that holds on the nut you need to loosen to put air in Presta valves. This causes the threaded part to fall into the tube which allows enough room to put the Slime in the tire. Then you have to push the threaded part back up into the stem and secure it with the nut, which now has no locking thread to keep you from unscrewing it all the way. I was hoping that I would not have to do that. I found that I was in luck because my tubes had Presta valves that allowed me to remove their cores. If you look at the part of the valve that has the threads to hold the valve cap on and it has flats on it, then that means the core can be unscrewed.


This Presta valve above has flats on the threaded part that holds on the cap which means the core can be unscrewed from the valve stem.



In my case, I already had some Slime but my local bike shop guy, Mark at International Bike in Greeley, is a strong proponent of True Goo. He believes that this product is easier than Slime to put in the tire due to its lower viscosity and that it seals better too.

If you search on the Internet, you’ll see a lot of people telling you these tube sealants don’t work. I think the reason for this is that it’s still possible to get a flat even with tube sealant, especially if the hole is so big that the sealant comes out so fast it can’t solidify. Also, people are much more likely to post a rant about a product that let them down rather than to take the time to post a positive review. In addition, when tire sealant works, you don’t really have hard evidence to let you know that you would have gotten a flat if you didn’t have the sealant in the tube. So it’s hard to measure tube sealant’s effectiveness.

In my case, I had the perfect experiment. My rear tire’s tube was losing nearly all its air every 2 days. It meant that each time I wanted to go for a ride, I needed to put air in the tire. I had debated on whether to patch or replace the tube, but then I realized that it would be a great experiment to see for myself whether tire sealant actually works, especially on slow leaks, which are the kind you generally get from the tiny holes that goat heads put in the tubes.

In order to put the sealant in the tire, my bicycle guy gave me some good advice. The rubber transfer tube that comes with these sealants is sized to be a press-fit on Shrader valves, which is much too large in diameter to seal on Presta valve stems. However, if you gradually cut the top of the cone-shaped nozzle until it is a press-fit for a .22 caliber cartridge, it will also be a press fit on a Presta valve which is about .235″ in diameter. You can also use the .22 bullet as a cap because the red cap that is included with it will no longer fit after you cut that much of the tip off the nozzle. You can use a spent .22 caliber casing or something else that is similar in diameter if you’re worried about using live ammunition to seal the bottle. Here’s a picture of what it looks like:

True Goo tire sealant

True Goo tire sealant

If your Presta valve has a removable core, you can even put the sealant in when the tire is on the bike. Just rotate the valve to the top, insert the nozzle on the valve stem, and rotate it back around to the bottom. Squeeze in about 3 ounces of fluid, rotate back to the top, remove the bottle. Then replace the valve core and fill it with air.

I found that my tire that leaked down every 2 days consistently has now held its pressure for several weeks, which leads me to believe that this stuff actually works as advertised.

12 thoughts on “Putting Tire Sealant in Presta Valve Tubes

  1. Hi Lee
    Thanks for the helpful post . I was able to remove the presta valve core from my tubular road tires in order to install Stan’s no tubes. I have not heard of True Goo until searching your post. My questions are, if you can answer them : Where can I buy True Goo ? Does True Goo seal punctures and cuts in tires with air pressures of 140psi and more ? I tried the Stan’s and it did not seem to seal a small tire cut on the tread with high pressure tubulars. I have some caffe latex to try next and would like to try the True Goo as well if I can find out where to order some.
    Thanks in advance

    • Hi Clyde, I got my True Goo at my local bike shop in Greeley, CO. It’s manufactured in Boulder, CO. The owner of my local store said it’s the best sealant he had ever used, and I’ve had it in the tires for 2 years now and haven’t had a single flat since I started using it. Colorado has a type of thorn called a ‘goat head’ and on road tires, even with thorn resistant tubes, I was getting flats all the time from these thorns. If you can’t find True Goo near where you live, their website is http://truegoo.com/ and they do have an on-line store if you want to purchase it directly. Most questions you may have about it are answered on that website. There’s also a contact form to ask the owner of the business questions if you can’t find the answer on the site. -Lee

  2. Thanks for the tip about cutting off the top of the valve! I wasn’t sure what would happen if I tried that, but it worked great. I haven’t slimed that tube yet (it currently has a small hole in it), but I’m going to patch it with a speed patch and then slime it.

    I already tried stretching/ripping a slightly bigger hole in a pinhole-puncture flatted tube and squirting the slime in that way. I pumped up the tire and after some finesse (rotating the wheels so that the leak was at the bottom where the slime was), it finally sealed. I haven’t ridden on it, but it has held 100 PSI for the past 24 hours. I’ll see how it handles a ride in the heat tomorrow.

    I’ve had slimed tubes on my mountain bikes for the past 18 years, and they were the solution to my “sticker weed” and thorn problems in the desert. Now I just have to see if they’ll handle the glass and steel belting punctures in the city.

    I was going to buy removable core tubes, but I can’t seem to find them at a reasonable cost (about $8 on Amazon including shipping is the best, pre-slimed tubes appear to cost about $12), but I can find regular road tubes for less than $5 on Nashbar and can slime each with about 1 oz. from my gallon jug (about $0.25). Then I’ll just carefully bend the top of the cut value so that the cap can’t come off–it’s not like I’m going to bother sliming a tube more than once! If it’s like my mountain bike tubes, when the tube comes out, it will have at least 20 holes in it!

    So, after flatting out 5 road tubes these past two weeks due to glass, metal staples, etc., perhaps slime will solve my road cycling pains like it magically repairs my mountain bike, repaired 2 sticker-weed flats on my jogging stroller, and other situations.

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