To tubeless or not to tubeless

[Hot Flatus]

The long posts are post-hoc justifications for Brucey's desperate axe-grinding arguments. It's a shame. He's so much better when he is talking about things he knows about.

[teethgrinder]

After talking to Bikey Mikey, who has weak hands, so unable to change a tube, about tubeless, they seemed like a no brainer for my year record attempt, so I built some wheels and road tested them myself, even though Bikey Mikey had ridden over 30,000 miles and did a very good road test for me.
I used them so I could run faster tyres even in winter. I was using Schwalbe Pro Ones, which are really fast summer tyres but I wasn't riding especially rough lanes. I'd use G One Pros for winter or lots of "Wessex SR" type roads as they're almost as fast as Pro Ones but built for some off road.
I carried tubes, spare tyre, pump and tyre levers. I did have to put a tube in a few times when I got a big cut, usually in the sidewall, but I'd expect that with light tyres anyway. They probably could have been patched, but my job was to keep moving so I did whatever would get me going ASAP. I kept the cut tyres so I can repair them at leisure.
If it wasn't for the year record, I'd still be using tubes as it's a lot of money (for me) to switch but I do think they are much better and I noticed improvements even between my 2 record attempts. The tyres roll better now and the sealant is better. I used Schwalbe Doc Blue (rebranded Stans) but have heard from various good sources that Orange sealant is the best of them all. Trek bike store had a faulty tyre they couldn't keep inflated with any sealant and got some Orange sealant from the rep and their faulty tyre stayed inflated.
If you're switching sealat, be sure to clean the rims etc thoroughly, as some sealants don't mix with others and having sealant cocktails can prevent the sealant from working as well.

Ironically, I'm going back to my tubed tyres for the winter. I have a stash of sturdy tyres that are much slower than my tubeless, so I'll run them down purely to save money, or not waste useful equipment. But when spring comes and I am fitter, it'll be even better to get my tubeless tyres out for the proper rides.
Though I'll probably use tubeless for the Full Fat 500 Audax because that's a proper ride.

[teethgrinder]

I also carried some sealant. I did have a few incidents of topping up the sealant on the road. Seen sealant spraying out of a wheel and having to stop once or twice to top up the air. At worst had to put the hole at 6 o clock so that the sealant puddles around the hole and plugs it and that would be a bigger hole than usual. But perhaps with Orange sealant and G One tyres...?
How many tubes I didn't have to replace with tubed tyres with equal performance is unknowable but I do know that it has saved me the need to change tubes at the roadside, having plucked thorny branches from my front tyre a few times and hearing a hiss, followed by silence as the sealant did it's work. One of my concerns riding tubeless was that when I go back to tubes, will I rmember not to ride over thorny branches or even wheel my bike over brambles with impunity if I stop for a pee...

[faster]

One of the key reasons for moving cars from tubes to tubeless was safety iirc. Tubeless significantly reduces the risk of blowouts.

You can run sealants in car and lorry tyres if you wish too of course. Also, tyres are sealed to the rim when they are mounted, with beads that require mechanical assistance to remount. actually this is incorrect, they just use tyre soap to mount like we do with tubeless sometimes

Re the safety thing; tubeless tyres and radial tyres almost went hand in hand on cars. These tyres/rims  have lips that  retain the tyre; it is this (rather than the presence or not of the tube) which is where the major improvement in safety arises. What folk choose to call "a blowout" is often where the tyre comes off the rim, and this is far less likely to happen with such lips.  Also the way a radial tyre runs when it is soft or flat is somewhat more benign than a cross-ply, so you have more chance of controlling the vehicle if a tyre is soft or even flat.  The main danger when running tubes inside tubeless car tyres is that tyre overheats more easily when run at the extremes of its operating envelope.  You may or may not be aware of this but the maximum load/speed rating of car tyres only applies when they are also inflated to their maximum pressure rating; they got too hot (through internal friction from flexing) otherwise. Adding a second layer of rubber inside the tyre just makes this happen earlier. Provided you are well within  the load/speed rating of the tyre, running a tubeless car tyre with a tube in it is pretty much no problem.

Overheating is not so much of a concern with bicycle tyres. However there have been calls for tyres that don't come off the rim so easily, the argument being that you cannot stop quickly enough at speed if you get a puncture such that you can always avoid having a prang because the tyre comes off the rim. This is of most concern to those that regularly travel at 40mph plus, hence there is a whole article about this in the IHPVA archives (from memory  issue 52 ?) . It would be interesting to see this updated so that the effects of tubeless tyres are assessed and compared.

Breaking the bead on car tyres requires quite a lot of effort.  'Road tubeless' on bicycles aims to replicate that in miniature, only it is a long floppy/stretchy thing wrapped round another long and less floppy thing, so the chances of getting a consistent fit are somewhat reduced.  Having said that, so far (which is not many sets admittedly) UST seem more a more consistent fit than many others. There is presumably a benefit in bicycle tyre retention if tubeless tyres are a tight fit on tubeless rims, but this is only likely to be of any value in the event of a sudden deflation at speed. This (fortunately) isn't a very common event on standard road bikes.

IIRC all car tyre manufacturers do not recommend that you use sealant inside their tyres (unless you already have a problem, hence Dunlop's 'denovo' system).  The reason for this is that leaks are sometimes  nature's way of letting you know your tyres are falling apart. The tyre manufacturers are concerned that the tyre could be in a state such that it will fall apart at speed with no 'warning' (i.e. the air coming out) first.  A similar concern applies to bicycle tyre tubeless; I have seen tyres that are so badly cut up that the carcasses have gone wonky such that I wouldn't ride them any more; the rider had no idea that the tyre was in that state because they hadn't checked. Like self-adjusting hydraulic disc brakes (where you have to check the pads have not worn out yet, else your first clue will be a ghastly scraping sound and wrecked discs) a convenience also turns into an increased proactive maintenance obligation.

Sealant in car tyres also has the capacity to throw the wheel out of balance. The same thing can happen with bicycle tyres, especially if the sealant starts to congeal.  You probably won't notice this unless it is very bad or you are in the habit of riding like a lunatic down hills but when riding in the Alps it is worth making sure your wheels are not too far out of balance and/or that your sealant hasn't turned lumpy. However checking wheels for good balance (without a balancing machine that runs at speed) is pretty much impossible if there is anything loose inside the tyre. I have even had car tyres go out of balance because they used too much tyre soap when fitting the tyre; the soap dries out, turns into 'crumbs' which then roll around the inside of the tyre. Because they don't distribute themselves evenly the wheel can go out of balance.

QG's 'blowout' on a Brompton was (IMHO, if as reported) almost certainly the tyre coming off the rim first, then the tube failing, not the other way round. The reason is that if the tube fails inside a securely mounted tyre, it makes a 'plip- pfffft' sound, not a 'loud bang'. The 'loud bang' happens when the tube swells through a large gap of some kind and then bursts. After the fact it isn't easy to see that the tyre came of the rim first, but this is what happens if you hear a loud bang.  It is made vary much more likely with new tyres; they are covered in mould release compound and this is an effective lubricant. Old Brompton rims didn't have pronounced hook beads and were a fairly loose fit with some tyres, so the tyres can blow off if they are not seated carefully and there is still release compound present.  I have been lucky (or unlucky) enough to see a new tyre creeping off a hookless rim; I'd ridden the bike thirty miles with the new tyre fitted but sat in the sunshine the mould release compound turned fully liquid and the tyre started to come off the rim. I happened to be looking in that direction and I actually saw the tyre move. Ten seconds later I would have had a 'blowout'. Nothing to do with the tube, everything to do with the fit of the tyre and the shape of the rim. A lot of 'blowouts' are to do with a tyre being mounted without being cleaned first; everything to do with fit, nothing to do with tubes.

Car tyres are retained by having a very heavy, stiff bead and no 'clincher' style hook bead. UST bicycle tyres work in a similar way (and are therefore heavier twice over; extra rubber in the sidewalls and extra strength in the bead); there is only a small hook bead on a UST rim and anyway this can play only a small role in retaining the tyre. The reason is that the position of the seal cannot be guaranteed. If the seal is at the tyre lip the tyre is forced into a hook bead lip and the tyre is better retained (as per all tubed tyres on such rims). However if the seal is at the rim lip, a hook bead cannot do any good; there is nothing forcing the tyre bead into the hook; there is air pressure all around the tyre bead and it is not being pushed in one direction. Since there is nothing to dictate that the seal is made at any one position (and anyway the sealant would probably render deliberate leak paths between the tyre lip and the rim lip moot) hook beads are of little value if you want consistent tubeless tyre retention.

This explains some of the observations and comments here https://janheine.wordpress.com/2017/05/29/the-trouble-with-road-tubeless/ although I don't think the author fully understood this when he wrote the piece originally. It is clear that if you don't go about it in the right way, there is not so much a safety benefit in running road tubeless so much as the other thing.

FWIW you can run normal tyres on UST rims but the safe pressures are lower than normal in good part because the rim lips are very small. For example IIRC the maximum pressure rating on the new open pro is just 87psi, regardless of tyre width or type. I suspect this is in part because other tyres will be in danger of coming off the rim (regardless of type) for various reasons.

Non tubeless rims may lack any real benefit in tyre retention in the event of deflation, and may or may not retain (non UST type) tyres in the event of a rim lip seal condition. 'Compromise' rim designs (eg the kinlin ones) are likely to behave in a similar way but may retain tyres (with stiff beads eg UST) better if they are a tight fit to start with. Tubeless only rims have little or no hook; the reason being that if there is a hook and  the seal location changes as you ride, a tyre that appeared to be OK when you started can just blow off the rim.

Doubtless I will be accused of 'mansplaining' things again. What a daft thing to say; only someone who cannot recognise informed comment (as distinct from "it worked for me so far therefore it ought to work for everyone all the time") when they see it would say such a thing.

Really interesting post which has raised a few questions for me about the rims and tyres on one of my bikes.

I never realised that the maximum pressure warnings were there to prevent tyres blowing off the rim - I'd always assumed it was something to do with the strength of the rim, which might fail under high pressure, like they do when the brake tracks become very worn.

I have a set of 23mm Conti GP4k tyres on a set of wheels which have what I believe to be the 'compromise' rims (ie tubeless ready Kinlins) mentioned above. The max pressure written on the rims is 80psi, but I've had good results so far running them at 100psi. I actually thought that whilst the rims were relatively new and unworn, I'd be fine!

There is also the other angle mentioned in one of the other posts about narrow tyres on wide rims - in my case 23mm tyres on 24mm wide rims.

How much of a risk am I taking here? They have been absolutely fine for the last 1,000 miles or so - comfortable and quick, so I'd like to keep running them the way they are if it is safe.

[Zed43]

Ironically, I'm going back to my tubed tyres for the winter.

Me too. Expensive Compass tyres (tubeless) for spring/summer when the long brevets are organised and GP 4Seasons (32mm, with tubes) in autumn and winter.

[sojournermike]

One of the key reasons for moving cars from tubes to tubeless was safety iirc. Tubeless significantly reduces the risk of blowouts.

You can run sealants in car and lorry tyres if you wish too of course. Also, tyres are sealed to the rim when they are mounted, with beads that require mechanical assistance to remount. actually this is incorrect, they just use tyre soap to mount like we do with tubeless sometimes

Re the safety thing; tubeless tyres and radial tyres almost went hand in hand on cars. These tyres/rims  have lips that  retain the tyre; it is this (rather than the presence or not of the tube) which is where the major improvement in safety arises. What folk choose to call "a blowout" is often where the tyre comes off the rim, and this is far less likely to happen with such lips.  Also the way a radial tyre runs when it is soft or flat is somewhat more benign than a cross-ply, so you have more chance of controlling the vehicle if a tyre is soft or even flat.  The main danger when running tubes inside tubeless car tyres is that tyre overheats more easily when run at the extremes of its operating envelope.  You may or may not be aware of this but the maximum load/speed rating of car tyres only applies when they are also inflated to their maximum pressure rating; they got too hot (through internal friction from flexing) otherwise. Adding a second layer of rubber inside the tyre just makes this happen earlier. Provided you are well within  the load/speed rating of the tyre, running a tubeless car tyre with a tube in it is pretty much no problem.

Overheating is not so much of a concern with bicycle tyres. However there have been calls for tyres that don't come off the rim so easily, the argument being that you cannot stop quickly enough at speed if you get a puncture such that you can always avoid having a prang because the tyre comes off the rim. This is of most concern to those that regularly travel at 40mph plus, hence there is a whole article about this in the IHPVA archives (from memory  issue 52 ?) . It would be interesting to see this updated so that the effects of tubeless tyres are assessed and compared.

Breaking the bead on car tyres requires quite a lot of effort.  'Road tubeless' on bicycles aims to replicate that in miniature, only it is a long floppy/stretchy thing wrapped round another long and less floppy thing, so the chances of getting a consistent fit are somewhat reduced.  Having said that, so far (which is not many sets admittedly) UST seem more a more consistent fit than many others. There is presumably a benefit in bicycle tyre retention if tubeless tyres are a tight fit on tubeless rims, but this is only likely to be of any value in the event of a sudden deflation at speed. This (fortunately) isn't a very common event on standard road bikes.

IIRC all car tyre manufacturers do not recommend that you use sealant inside their tyres (unless you already have a problem, hence Dunlop's 'denovo' system).  The reason for this is that leaks are sometimes  nature's way of letting you know your tyres are falling apart. The tyre manufacturers are concerned that the tyre could be in a state such that it will fall apart at speed with no 'warning' (i.e. the air coming out) first.  A similar concern applies to bicycle tyre tubeless; I have seen tyres that are so badly cut up that the carcasses have gone wonky such that I wouldn't ride them any more; the rider had no idea that the tyre was in that state because they hadn't checked. Like self-adjusting hydraulic disc brakes (where you have to check the pads have not worn out yet, else your first clue will be a ghastly scraping sound and wrecked discs) a convenience also turns into an increased proactive maintenance obligation.

Sealant in car tyres also has the capacity to throw the wheel out of balance. The same thing can happen with bicycle tyres, especially if the sealant starts to congeal.  You probably won't notice this unless it is very bad or you are in the habit of riding like a lunatic down hills but when riding in the Alps it is worth making sure your wheels are not too far out of balance and/or that your sealant hasn't turned lumpy. However checking wheels for good balance (without a balancing machine that runs at speed) is pretty much impossible if there is anything loose inside the tyre. I have even had car tyres go out of balance because they used too much tyre soap when fitting the tyre; the soap dries out, turns into 'crumbs' which then roll around the inside of the tyre. Because they don't distribute themselves evenly the wheel can go out of balance.

QG's 'blowout' on a Brompton was (IMHO, if as reported) almost certainly the tyre coming off the rim first, then the tube failing, not the other way round. The reason is that if the tube fails inside a securely mounted tyre, it makes a 'plip- pfffft' sound, not a 'loud bang'. The 'loud bang' happens when the tube swells through a large gap of some kind and then bursts. After the fact it isn't easy to see that the tyre came of the rim first, but this is what happens if you hear a loud bang.  It is made vary much more likely with new tyres; they are covered in mould release compound and this is an effective lubricant. Old Brompton rims didn't have pronounced hook beads and were a fairly loose fit with some tyres, so the tyres can blow off if they are not seated carefully and there is still release compound present.  I have been lucky (or unlucky) enough to see a new tyre creeping off a hookless rim; I'd ridden the bike thirty miles with the new tyre fitted but sat in the sunshine the mould release compound turned fully liquid and the tyre started to come off the rim. I happened to be looking in that direction and I actually saw the tyre move. Ten seconds later I would have had a 'blowout'. Nothing to do with the tube, everything to do with the fit of the tyre and the shape of the rim. A lot of 'blowouts' are to do with a tyre being mounted without being cleaned first; everything to do with fit, nothing to do with tubes.

Car tyres are retained by having a very heavy, stiff bead and no 'clincher' style hook bead. UST bicycle tyres work in a similar way (and are therefore heavier twice over; extra rubber in the sidewalls and extra strength in the bead); there is only a small hook bead on a UST rim and anyway this can play only a small role in retaining the tyre. The reason is that the position of the seal cannot be guaranteed. If the seal is at the tyre lip the tyre is forced into a hook bead lip and the tyre is better retained (as per all tubed tyres on such rims). However if the seal is at the rim lip, a hook bead cannot do any good; there is nothing forcing the tyre bead into the hook; there is air pressure all around the tyre bead and it is not being pushed in one direction. Since there is nothing to dictate that the seal is made at any one position (and anyway the sealant would probably render deliberate leak paths between the tyre lip and the rim lip moot) hook beads are of little value if you want consistent tubeless tyre retention.

This explains some of the observations and comments here https://janheine.wordpress.com/2017/05/29/the-trouble-with-road-tubeless/ although I don't think the author fully understood this when he wrote the piece originally. It is clear that if you don't go about it in the right way, there is not so much a safety benefit in running road tubeless so much as the other thing.

FWIW you can run normal tyres on UST rims but the safe pressures are lower than normal in good part because the rim lips are very small. For example IIRC the maximum pressure rating on the new open pro is just 87psi, regardless of tyre width or type. I suspect this is in part because other tyres will be in danger of coming off the rim (regardless of type) for various reasons.

Non tubeless rims may lack any real benefit in tyre retention in the event of deflation, and may or may not retain (non UST type) tyres in the event of a rim lip seal condition. 'Compromise' rim designs (eg the kinlin ones) are likely to behave in a similar way but may retain tyres (with stiff beads eg UST) better if they are a tight fit to start with. Tubeless only rims have little or no hook; the reason being that if there is a hook and  the seal location changes as you ride, a tyre that appeared to be OK when you started can just blow off the rim.

Doubtless I will be accused of 'mansplaining' things again. What a daft thing to say; only someone who cannot recognise informed comment (as distinct from "it worked for me so far therefore it ought to work for everyone all the time") when they see it would say such a thing.

Really interesting post which has raised a few questions for me about the rims and tyres on one of my bikes.

I never realised that the maximum pressure warnings were there to prevent tyres blowing off the rim - I'd always assumed it was something to do with the strength of the rim, which might fail under high pressure, like they do when the brake tracks become very worn.

I have a set of 23mm Conti GP4k tyres on a set of wheels which have what I believe to be the 'compromise' rims (ie tubeless ready Kinlins) mentioned above. The max pressure written on the rims is 80psi, but I've had good results so far running them at 100psi. I actually thought that whilst the rims were relatively new and unworn, I'd be fine!

There is also the other angle mentioned in one of the other posts about narrow tyres on wide rims - in my case 23mm tyres on 24mm wide rims.

How much of a risk am I taking here? They have been absolutely fine for the last 1,000 miles or so - comfortable and quick, so I'd like to keep running them the way they are if it is safe.

If you look at the Mavic link there is a chart produced by ETRTO giving safe pressure for tubeless tyres by rim internal and tyre width. Tubes are allowed 15% or 15psi more iirc. It isn’t clear whether this is a tubeless ready or UST chart. However, the pressures I run are all well within their suggested limits.


For tubes, I’ve just mounted a set of Challenge Paris Roubaix on some DT Swiss RR511. They are some 30mm wide on these rims,  but only 26mm high. I’ll see if they can be squeezed under the guards in the morning. Been a while since I rode tubes, but I still like open tubulars.

Mike

[sojournermike]

The link is here

http://engineerstalk.mavic.com/en/the-right-tyre-width-on-the-right-rim-width/

Unfortunately, you have to pay chf138 to buy the full spec from etrto

[Brucey]

I never realised that the maximum pressure warnings were there to prevent tyres blowing off the rim - I'd always assumed it was something to do with the strength of the rim, which might fail under high pressure, like they do when the brake tracks become very worn.

in fairness both things can be true.

Regarding the (tyre pressure) stresses in worn rims, I recently did some (not very hard) sums and calculated the effect on stresses in the rim as the rim wears. If you assume that the rim is definitely OK (at the rated tyre pressure) if the braking surfaces are 1.0mm thickness, the stresses double (vs 1.0mm thickness)  once the rim is worn to 0.8mm and triple (vs. 1.0mm thickness) once the rim is worn to 0.7mm.  So things can go bad very quickly. Obviously it only takes one thin area on the rim to allow a failure to occur.

I don't know the answer re your tyres and your kinlin rims for sure. I'd hope that the hooks (which are bigger than on many tubeless rims) are able to retain most tyres well provided they are fitted with tubes. Regarding the rim stresses arising from tyre pressure, this varies with both tyre pressure and tyre section. Thus (to a first approximation) the load on the rim goes with the product of tyre section width and tyre pressure. So a 25mm tyre @ 100psi is likely to load the rim similarly to a 50mm tyre at 50psi.

Tyres can just blow off the rim at very high pressure, but (excepting that the tyre structure itself can fail too)  mostly they come off the rim because the loadings between the tyre and the rim change in some way. The changes can arise variously, eg.

1) the tyre is unstable w.r.t. perturbations. In other words should the bead start to crawl up the rim in one place, that'll be where it moves again; the loads become even higher in that area once the tyre moves. This is how tyres can blow off hookless rims (tubed or not). This imposes high loads in the tyre bead; some beads are stretchy enough to let the tyre escape, in other cases the tyre is badly fitting/fitted, and part of the tyre bead is in the rim well; this allows enough easy movement to allow enough slack for the tyre to crawl off the rim more easily.

2) changes in friction.  The tyre is at least partly held in place (or at least prevented from moving around) by friction. As I mentioned upthread, mould release compound is an effective lubricant and some types just melt when the rim get hot. I have also seen tyres move around when they shouldn't if they are  contaminated with chain lube, talc, you name it. It is possible that liquid sealant can act as a lubricant (between the tyre bead and the rim edge) in some cases. If the 'lubricant' (whatever it is) is able to move around the tyre may be secure one minute and then blow off the next.

3) changes in loading. Tubes push the tyre bead into rim hooks and this helps to retain the tyre. [If you are interested, read up on 'Clincher' brand tyres; these had no reinforced bead at all, just a rubber lip moulded into the edge of the tyre; pressure from the tube forced these lips into a deep 'clincher' rim lip and this retained the tyre. These tyres were used on bicycles, motor cycles and cars. The tyre was only well retained when the pressure was high. For example a 2.5" motorbike tyre might only be secure at 60psi or more; deflation to (say) 45psi could allow the tyre to come off the rim without warning. There has been at least one death of a vintage motorcycle enthusiast in recent years because of this exact thing.]  With most tubed HP tyres the retaining force goes pro-rate with the pressure and this is fine; the tyre is usually flopping around hopelessly before it is in danger of coming off the rim because it is no longer well retained.  However tubeless tyres can seal at the tyre bead lip (in which case the hook bead works in your favour as normal) or at the rim lip (in which case it doesn't; there is no force pushing the tyre bead into the hook any more). If the seal location changes (all it takes is a slight difference in the leak rate at the two locations) then a tyre that appeared to be secure on the rim may suddenly turn into one that isn't at all secure. I believe that this explains many of the occurrences reported in the OTBP link I posted upthread.

Apologies for the length of some of my posts. Unfortunately rims and tyres are not such simple things as folk would hope/suppose. You have a choice; you want to stay uninformed? Don't bother reading/inwardly digesting then. Quite a few people obviously haven't bothered to and confine themselves to making fatuous and inaccurate comments about things they have not read and/or don't understand. Great. Very useful.

[Hot Flatus]

Chris N, the person who initially made the comments about your post length ("pages of dogma")  is an engineer. Not saying he is a good one...he might be shit...but I suspect he has no trouble understanding your posts

Anyway, back to the real world, and away from the hysterical drama-queenery about things that just don't seem to happen to people who use this stuff and actually know what they are doing (ie. almost everyone who has posted on this thread, including 100k+ p.a. riders)...

Tubeless is great 

[De Sisti]

I was on a bike maintenance course a few years ago and the the bike mechanic running it said
that the max recommended tyre pressures on tyre sidewalls are quite conservative figures stated
by the manufacuturers; who are fearful of litigation in case the actual max figures were used
by cyclists, who then suffered from tyres separating from the rim.

[Hot Flatus]

The recommended pressure range can be pretty narrow, maybe 20psi in some cases. 

This is inversely proportionate to the range for the incompetent to get it wrong.

[Chris N]

I suspect he has no trouble understanding your posts

It starts well but I have a tendency to nod off about halfway through.

Tubeless is great 

Indeed it is.

[Ben T]

Regarding the (tyre pressure) stresses in worn rims, I recently did some (not very hard) sums and calculated the effect on stresses in the rim as the rim wears. If you assume that the rim is definitely OK (at the rated tyre pressure) if the braking surfaces are 1.0mm thickness, the stresses double (vs 1.0mm thickness)  once the rim is worn to 0.8mm and triple (vs. 1.0mm thickness) once the rim is worn to 0.7mm.  So things can go bad very quickly. Obviously it only takes one thin area on the rim to allow a failure to occur.

Rim wear? 
There's obviously a simple solution to this phenomenon...

[quixoticgeek]

QG's 'blowout' on a Brompton was (IMHO, if as reported) almost certainly the tyre coming off the rim first, then the tube failing, not the other way round. The reason is that if the tube fails inside a securely mounted tyre, it makes a 'plip- pfffft' sound, not a 'loud bang'. The 'loud bang' happens when the tube swells through a large gap of some kind and then bursts. After the fact it isn't easy to see that the tyre came of the rim first, but this is what happens if you hear a loud bang.  It is made vary much more likely with new tyres; they are covered in mould release compound and this is an effective lubricant. Old Brompton rims didn't have pronounced hook beads and were a fairly loose fit with some tyres, so the tyres can blow off if they are not seated carefully and there is still release compound present.  I have been lucky (or unlucky) enough to see a new tyre creeping off a hookless rim; I'd ridden the bike thirty miles with the new tyre fitted but sat in the sunshine the mould release compound turned fully liquid and the tyre started to come off the rim. I happened to be looking in that direction and I actually saw the tyre move. Ten seconds later I would have had a 'blowout'. Nothing to do with the tube, everything to do with the fit of the tyre and the shape of the rim. A lot of 'blowouts' are to do with a tyre being mounted without being cleaned first; everything to do with fit, nothing to do with tubes.

Except the tyre didn't leave the rim. There was a loud bang, the tyre went flat, i took the wheel off, took the tyre off, found the tube has a split along its seem. The shop I got it from replaced the tube without question. The tyre was a Schwalbe Marathon Plus, give that fitting one of those is like wrestling with a rubber monster, and requires a bead jack to fit, it's hardly a surprise that it didn't come off.

It was a faulty tube.

J

[andrew_s]

If there was a loud bang, the tube exploded outside the tyre. End of.

If the tube is trapped between rim and tyre bead, it can be trapped over a fair length (15 cm). Pressure will stop air leaking into the trapped section for quite a while, but once leakage starts there's a runaway, and the tube explodes over the full length of the trapped section, giving what looks like a split along the length of the tube. The tyre then just pops back into place so it looks normal.

The seam in a tube is transverse anyway - any longitudinal marks are mould marks

[Brucey]

[Andrew was quicker to say it than me but I'd typed this anyway...]   ....nonetheless you wouldn't (couldn't) get 'a loud bang' if the tube was entirely confined within the tyre when it failed.

    Another possible explanation is that the tube was pinched and then blew out between the tyre and the rim. That makes a loud bang and almost invariably splits the tube lengthwise. The inside of the tube is covered in talc and if the tyre bead has trapped the tube, the tyre bead can slide (up and off the rim) more easily and there is a good size force pushing it too. The explosion of the tube is normally so violent that the whole tyre moves on the rim and it may not be clear how the tyre was seated beforehand.

BTW a tyre that was tight to fit can still blow off the rim; Marathons are difficult to fit because the carcass is stiff, regardless of bead length.  All it takes is a section of bead to be too low or the tube to be pinched and the tyre is likely to become unstable; it is then only friction that is preventing parts of the tyre from crawling up the rim, and there isn't enough friction in many cases, new tyres being case in point.

I repeat; tubes that fail within tyres do not, indeed cannot, make 'a loud bang'; that only ever happens if part of the tube escapes somehow.

In an LBS near me there is a chap who is often stressed and in a hurry; this is sometimes one step forward, two steps back. At least once a week he inflates a tyre that is not correctly seated and there is a loud bang. On several occasions I have seen him pump to 50psi before he checks the seating of the tyre and realises there is a problem;  the usual thing is to hear him holler a warning, then see him desperately trying to hold the tyre on the rim with one hand whilst trying to work the valve with the other. He doesn't always see the problem and/or isn't always quick enough to let the air out. It is easily done; the tyre can be barely off the bead seat one second and blown off the next .

  The LBS pays two-thirds of stuff all for inner tubes (you might be surprised how little sometimes). They really don't care about the cost of a tube so a customer's tube can be 'faulty' and replaced whether there was or wasn't a problem with it.

cheers

[rafletcher]

[Andrew was quicker to say it than me but I'd typed this anyway...]   ....nonetheless you wouldn't (couldn't) get 'a loud bang' if the tube was entirely confined within the tyre when it failed.

I beg to differ. I stupidly forgot rim tape once, and when pumping the tyre up the tube burst with a very loud bang. It failed where it had been deformed into one of the spoke holes which of course were unprotected.

[Brucey]

if you had heard both you would know the difference.   

FWIW if in your case the rim was double-walled, you could get a louder bang than normal; the reason is that the tube wasn't confined fully and could blow into the space between the rim walls.

cheers

[Hot Flatus]

Never happens with tubeless.

Just saying 

[Zed43]

If there was a loud bang, the tube exploded outside the tyre. End of.

Well... I once had a (very) loud bang when the rear tyre had formed a bulged that (increasingly) rubbed against the chain stay and the resulting heat melted a hole in the tube (the tyre was not rubbed through).

[rafletcher]

Never happens with tubeless.

Just saying 

True. I sold the wheels  .

[Brucey]

when the tyre comes off the rim without a tube....

[zigzag]

^^ that looks like an incompatible rim/tyre combination (or the guy didn't install it properly). if you are trying to make something work that is not designed to, the risk of it going wrong always goes up.

[Hot Flatus]

Quite.

A photo with no context.

Anyone here ever had that happen?

Anyone?

[Kim]

Anyone here ever had that happen?

Anyone?

My brief foray into the world of slime-filled inner tubes ended in broadly similar circumstances.