Foss 36 tube question

Why cant the Foss 36 tube be used in a drilled 36 rim?
and if it is true that it can not be used can you use a 29er tube in a drilled 36 rim.

I have a Foss (no relation) tube in a drilled 36" rim. It’s the loaner wheel Bronson gave me while I await something from Schlumpf. The stuff bulging in the holes looks like tube color, but I imagine he’s got a layer of something in between. It doesn’t bulge as far as the inner surface of the rim. I’d ask Bronson for details (

BTW, the combination of that tube with the drilled rim is a noticeable difference in rotating mass when riding. I’ll be sorry to go back to what came with my uni…if that ever happens.

I think the Foss tubes have more plastic deformation than conventional tubes and may get a bit lumpy after extended use in a drilled rim with a bulging rim strip. I can’t see it being an issue if you use a non-stretch rim strip (fibre tape works great)

I have one in my 36er but my rim is drilled only on the outer surface.

I had a Foss tube in a drilled rim with the stock green rim tape and multiple tubes failed around there edge of a hole. I think the combination of pressure against the relatively sharp edge of the hole and the thinner tube is what produces the failure. I did use a 29er tube in the same rim, but it also failed in the same manner, however it lasted a while longer than the Foss tubes did (never more than 2 rides). I think that Eric’s idea of using fibre tape could work well but could also add a bit of weight. The expensive solution is to get the Stealth2 rim because it is both stronger and lighter than the Impulse drilled rim, however it does not have the holes, so it works great with the Foss tube.

Also, unlike Bronson’s wheel that John is using, the Foss tube in my rim bulged past the second wall of the rim.

What do you guys mean by a ‘drilled’ 36" rim? Is that a Stealth rim you’ve custom drilled, or is there a special drilled rim I don’t know about?

I have a Stealth Pro rim, but will probably upgrade to a Stealth II rim because tyres are just about impossible to remove from the original stealth rims.

The nimbus impulse rim.

Impulse is not a rim name but related to disc brake model, all Nimbus 36" rims are stealth

original one, named Stealth, and very difficult to remove the tyre as said by Gizmoduck, 38mm, …

they were some Stealth rims drilled but I cannot find pictures anymore ! according to my memory they were just drilled on the outside

current rim is Stealth2, 40mm, new profile to make easier the tyre fiting

Roger may explain in details

The only Stealth 2 rim with holes is mine. :slight_smile:

It was an experiment to see the effect of putting holes in the rim. It gave only a marginal saving in weight, weakend the rim, doubled the cost and caused more potential problems with the inner tube.


In the US, sold the drilled rim from the Impulse unicycle separately and listed it as the Nimbus Impulse rim (though it still said Nimbus Stealth on the rim itself). This was before the Stealth2 rim was announced. I considered buying one of the Impulse rims when building up my 36" last year and I know mountainuni1 did buy one and is riding it currently.

Exactly. I own all three model. Stealth, impulse (drilled stealth), and Stealth2. I am considering drilling the stealth2 (just on the inside, by expanding the spoke holes). Roger, what do you think? Would it make the rim too weak for 36er muni? (For a 60kg rider…) It’s not worth the weight savings if I can’t use the Foss tube in the drilled version however…

I don’t think it is worth it. The rim is amazingly strong so it can take it.


If drill the rim, be sure to use a full bottle of green slime to protect against flats.



What is this mysterious green slime? And do I put it inside the tube to fill leaks, or around the drilled holes to lube them up and make them less sharp?

I find stans tubeless sealant works better than slime; plus you need less stans, so less weight. If I have a finicky tube that gets flats often I put a few ounces of stans in and the flats stop.

Before UDC added the “Not recommended for rims with cutouts/holes” note on their website, I had purchased a FOSS 36" clear tube with the intention of putting it on my first run (with the drilled Stealth1 rim) Impulse. The original “commuter” (heavy) tube was bulging out of a couple of the holes pretty bad. The tube ended up being a defect (UDC refunded in full, of course) that was fused together in spots so my LBS put the heavier tube back in and replaced the Green Rim Strip tape with duct tape. I’ve put over 1k miles on it since then and it seems to be holding up fine (no bulges). It does not leak air like the FOSS tube in King’s Stealth2 which seems to like to revert back to 40psi whereas the heavy tube in my Impulse is holding tight at right around 60psi. I’m probably taking a hit on rotational weight (the most important kind) with the heavy tube and duct tape on the Impulse. But, if it ain’t broke…

I was thinking about picking up a $6 Green Rim Strip (see picture below) on my next UDC order just to get the color theme back. I guess I will abandon the FOSS tube (based on your recommendation) for that wheel. I’m not going to build up another wheel (funny how the un-drilled Stealth2 rim is lighter than my drilled Stealth1) for my back-up/loaner to be just a “little” lighter.

My Stealth rim with holes (actually it’s Bronson’s) is the same as the one pictured above. Bronson said you need “several layers of rim tape” for it to work, which it does on that wheel with no leakage. Bulging is similar to the photo above, if not less.

So I guess the question is whether too much rim tape negates the value of having the holes? I also like the way the holes look, and am planning to get one of those rims for when I rebuild my wheel with my new hub.

I just wonder why people drill holes right through the inner rim in the first place.

Wouldn’t’ it make sense to drill bigger/more holes on the outer rim so you keep the inner one tubeproof? Or if you have to drill holes on the inner rim- to drill lots of really really small holes so that the tube doesn’t have a big hole to poke out of?

A problem I encountered when riding off road with a drilled rim/tubeless, water from puddles would fill up the rim making it heavier. Kind of defeats the purpose of the weight savings.

I got the drilled Stealth (Impulse) last year from UDC USA. It was the only one in stock. I got it about a year ago. It was in the order of parts I got for building a geared 36er.
My Schlumpf just returned after a 9 month stay at the SSHS(Swiss Schlumpf Health Spa). Since puting everything back together, I have had a rough time with tubes. I have destroyed the original 36er tube and three 29er tubes. I am only using the green rim tape that I got from UDC. The tubes do fine up to about 40 psi. After words it only takes a few hours from a fully inflated tire to a popped one. Every time I have a tube failure I take the tire off of the rim and do a thorough inspection. I never find anything.
I have a non drilled Stealth I rim on my Nightrider Pro with a 29er tube and it has 65 psi on it. It has been that way for 8 months now with no problems.

It looks like I might have to put more rim tape on it or go tubeless.

I can’t decide what’s funniest - Corbin’s joke or people taking his comment seriously. The slime will weigh a whole lot more than the shavings savings. :smiley: