Yet Another Cycling Forum
General Category => The Knowledge => Topic started by: quixoticgeek on 23 January, 2022, 01:08:38 pm
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I pump my tyres up in the nice warm of my flat, but when I get outside and start riding, they are always a bit squishier than I'd like.
Is there an easy way to calculate the pressure they will be outside at 5°C, if pumped up at 20°C ?
I aim for 5bar at 20°C.
J
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A a first approximation, I'd use the Combined Gas Law:
P1V1/T1 = P2V2/T2
Assuming a constant volume, we can ignore the V terms and just say:
P1/T1 = P2/V2
(Temperatures are Absolute)
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A a first approximation, I'd use the Combined Gas Law:
P1V1/T1 = P2V2/T2
Assuming a constant volume, we can ignore the V terms and just say:
P1/T1 = P2/V2
(Temperatures are Absolute)
By absolute, do you mean in Kelvin?
If so, that would be
(5/293)*278 = 4.74. If it's 5°C out.
So not a massive drop. Certainly not enough to be noticeable when riding.
Thanks!
J
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By absolute, do you mean in Kelvin?
In SI units, P is in pascals, V is cubic meters and T in Kelvin.
We can ignore V in this case.
Since pressure in PSI is a straight linear multiplication from pascals, I'd reckon you can work with PSI on both sides of the equation. It's just the constant value of PV/T will be different.
If so, that would be
(5/293)*278 = 4.74. If it's 5°C out.
So not a massive drop. Certainly not enough to be noticeable when riding.
I'm not going to mark your homework, but indeed in terms of absolute temperature the difference between 20c and 5C is pretty small so the corresponding pressure drop will be small.
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And presumably the tyre compound becomes less flexible as the temperature drops, which will to some extent cancel out the effect of the drop in pressure...
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You need pressure in absolute as well, I.e. 5 bar guage is 6 bar abs
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You need pressure in absolute as well, I.e. 5 bar guage is 6 bar abs
So using pascals, and kelvin, and absolute, rather than gauge, I get:
(600000/298)*273 (using zero Celsius here)
= 549664.4295
which ignoring unnecessary precision from my irc bot.
Is a drop of 50.3 Kilo pascal or half a bar.
J
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The air put in the tyre will be significantly warmer than ambient temperature whilst pumping up, amount depends on the pump used and the effort put in to some extent - unless using a CO2 inflater, that tends to be cooler.
The effect is more significant with a total inflation than a top up. The temperature of the pump should give a clue as to how much by, larger/heavier pumps are affected less.
CO2 is also slightly soluble in butyl, so that component of the air in the tyre will reduce over time as the CO2 migrates to the lower pressure.
Also water content of air is prone to a massive volume change when it transitions from warm vapour to cooler liquid.
The science is complex - most demonstrations/experiments go to great lengths to minimise/eliminate one or more of the variables.
In the real world you need to guess how much extra (or less) to put in the tyres to compensate for the method of inflation and the expected changes of environment.
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Going the other way, the heat of constant braking will certainly cause sufficient pressure rise to pop off a tyre that's near its maximum to start with (experimentally, some Schwalbes rated for 105psi will blow off at 115psi).
The rim can easily reach 50 deg C (i.e. hand hot, when you can't keep your finger on it) which is about a 10% rise in pressure, should it have time to soak through to the air in the tube.
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Going the other way, the heat of constant braking will certainly cause sufficient pressure rise to pop off a tyre that's near its maximum to start with (experimentally, some Schwalbes rated for 105psi will blow off at 115psi).
The rim can easily reach 50 deg C (i.e. hand hot, when you can't keep your finger on it) which is about a 10% rise in pressure, should it have time to soak through to the air in the tube.
[/quote
One Etape du tour was going to be a hot one, we had advice from Greg LeMond telling everyone to drop a few psi from the tyres. Glad he was next to us in one of the starting pens, would have been interesting if a tyre blew braking hard before going into a bend.
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Is this as much of an issue if using disk brakes?
J
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Is this as much of an issue if using disk brakes?
J
No.
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Is this as much of an issue if using disk brakes?
J
No.
Not a big issue with disk brakes but you are still putting stress into the tyre contact with the tarmac. Just need to look at all the car/lorry tyres that are destroyed lying at roadsides. More likely to scuff the tread off now we have powerful brakes that work in all weathers.
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The other factor is that outside you're sat on the bike and progressing, and those loads will affect the "feel" of the tyres compared to inside. And volume can be significant if using, say 35mm tyres compared to 23mm tyres.
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As much fun as the number crunching is, if 5 bar inside is a bit too squishy outside, why not just pump up to just over 5 bar inside and everything should be good, right?!
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As much fun as the number crunching is, if 5 bar inside is a bit too squishy outside, why not just pump up to just over 5 bar inside and everything should be good, right?!
Yes, except by applying the Maths™ I was trying to work out what pressure I should pump to inside, to be within bounds outside.
J
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As much fun as the number crunching is, if 5 bar inside is a bit too squishy outside, why not just pump up to just over 5 bar inside and everything should be good, right?!
Exactly.
Or pump the tyres outside, and also get warmed slightly.
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Exactly.
Or pump the tyres outside, and also get warmed slightly.
Take bike and pump outside, pump up tire, bring bike and pump back inside, up 7 floors, put pump away, take bike back out, go for a ride.
Sod that.
J
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I use the pump I carry, either on the bike or in my bag.
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I use the pump I carry, either on the bike or in my bag.
That's a lot of faff compared to about 5 or so puffs from my track pump. Feels a lot more complex than knowing "if it's about 5°C outside, pump tyres up an extra 0.5 bar"
J
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I find using my frame pump is less faff than using a track pump but that's just me.
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I find using my frame pump is less faff than using a track pump but that's just me.
I have never ever found a frame pump pleasant to use. Even the pump I carry on my bike is a mini track pump (topeak turbo morph g).
J
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I use the pump I carry, either on the bike or in my bag.
That's a lot of faff compared to about 5 or so puffs from my track pump. Feels a lot more complex than knowing "if it's about 5°C outside, pump tyres up an extra 0.5 bar"
J
Do major fills then leave for "a while" for pressure/temp to stabilise before a gentle top up to an estimated target pressure based on the simple maths/science. The bigger or more vigorous the top up the greater the variables become.
Avoid putting high humidity air into the tyres if possible - don't do a total fill in the utility room with the fresh washing passing on it's moisture.
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Exactly.
Or pump the tyres outside, and also get warmed slightly.
Take bike and pump outside, pump up tire, bring bike and pump back inside, up 7 floors, put pump away, take bike back out, go for a ride.
Sod that.
J
Aha! Another variable!
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;D
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I’m clearly far too casual with my pumping, just doing it every few weeks when it feels like it needs doing.
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I’m clearly far too casual with my pumping, just doing it every few weeks when it feels like it needs doing.
Is my usual approach, with the exception of the Red Baron, which is very sensitive to front wheel pressure (there's a fine line between vagueness in cornering and ratting the front end so hard you get sore ankles and the chain sometimes ends up where it shouldn't), and the trike when shod with Kojaks (which have a definite sweet spot for rolling resistance on crap tarmac).
The chunky Marathons on the other bikes are mostly fine at anything from about 45-70PSI, and I tend to only top them up when I've got the pump out for something else.
So yeah, I think it's one of those your bike may vary things.
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Exactly.
Or pump the tyres outside, and also get warmed slightly.
Take bike and pump outside, pump up tire, bring bike and pump back inside, up 7 floors, put pump away, take bike back out, go for a ride.
Sod that.
J
Aha! Another variable!
Bearing in mind QG's location, she must spend some time cycling below sea level. We therefore have to take into account the densities of salt and fresh water, not to mention the difficulty of using a pump while wearing a snorkel.
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I don't know about her, but I definitely go faster on the flat bits below sea level.
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As much fun as the number crunching is, if 5 bar inside is a bit too squishy outside, why not just pump up to just over 5 bar inside and everything should be good, right?!
This would be my approach, but I’m clearly not of a scientific enough disposition.
What surprises me is that the difference is enough to be noticeable.
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personally I don't find that I notice it, but then my bikes live in the shed, so essentially not far from ambient. I run 28mm GP4 Seasons at about 7 bar and generally don't notice a massive difference until they're down to about 5 bar. As the other variable, I'm a smidge under 70kg, and I've got brown eyes and a grey beard :P
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Going the other way, the heat of constant braking will certainly cause sufficient pressure rise to pop off a tyre that's near its maximum to start with (experimentally, some Schwalbes rated for 105psi will blow off at 115psi).
The rim can easily reach 50 deg C (i.e. hand hot, when you can't keep your finger on it) which is about a 10% rise in pressure, should it have time to soak through to the air in the tube.
Yes, I've seen the aftermath of such off-popping on the descent of the Col de la Croix de Fer during the Marmotte sportif. Some of the (many) riders in front of me had inflated their tyres in the cool previous evening and suffered brown bibshorts moments during the very hot next day.
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Going the other way, the heat of constant braking will certainly cause sufficient pressure rise to pop off a tyre that's near its maximum to start with (experimentally, some Schwalbes rated for 105psi will blow off at 115psi).
The rim can easily reach 50 deg C (i.e. hand hot, when you can't keep your finger on it) which is about a 10% rise in pressure, should it have time to soak through to the air in the tube.
Yes, I've seen the aftermath of such off-popping on the descent of the Col de la Croix de Fer during the Marmotte sportif. Some of the (many) riders in front of me had inflated their tyres in the cool previous evening and suffered brown bibshorts moments during the very hot next day.
Rim wear (IME) can add to this. I descended Ditchling Beacon once on the Pino (tandem, front wheel is a 406). Braking heating was Quite A Lot given the mass of two well nourished riders and not much mass to absorb the heat generated in the front wheel. Made it to the bottom, wondered how hot the rim was, burnt finger tip then watched as the tyre unmounted itself and burst the tube. Couldn't get the tyre to stay back on after that, as the rim kept distorting once the tyre ws inflated.
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Going the other way, the heat of constant braking will certainly cause sufficient pressure rise to pop off a tyre that's near its maximum to start with (experimentally, some Schwalbes rated for 105psi will blow off at 115psi).
The rim can easily reach 50 deg C (i.e. hand hot, when you can't keep your finger on it) which is about a 10% rise in pressure, should it have time to soak through to the air in the tube.
Yes, I've seen the aftermath of such off-popping on the descent of the Col de la Croix de Fer during the Marmotte sportif. Some of the (many) riders in front of me had inflated their tyres in the cool previous evening and suffered brown bibshorts moments during the very hot next day.
Rim wear (IME) can add to this. I descended Ditchling Beacon once on the Pino (tandem, front wheel is a 406). Braking heating was Quite A Lot given the mass of two well nourished riders and not much mass to absorb the heat generated in the front wheel. Made it to the bottom, wondered how hot the rim was, burnt finger tip then watched as the tyre unmounted itself and burst the tube. Couldn't get the tyre to stay back on after that, as the rim kept distorting once the tyre ws inflated.
That's quite... scary!
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The air put in the tyre will be significantly warmer than ambient temperature whilst pumping up, amount depends on the pump used and the effort put in to some extent - unless using a CO2 inflater, that tends to be cooler.
The effect is more significant with a total inflation than a top up. The temperature of the pump should give a clue as to how much by, larger/heavier pumps are affected less.
CO2 is also slightly soluble in butyl, so that component of the air in the tyre will reduce over time as the CO2 migrates to the lower pressure.
Also water content of air is prone to a massive volume change when it transitions from warm vapour to cooler liquid.
The science is complex - most demonstrations/experiments go to great lengths to minimise/eliminate one or more of the variables.
In the real world you need to guess how much extra (or less) to put in the tyres to compensate for the method of inflation and the expected changes of environment.
Also consider the much greater rate of diffusion out of the tyre of oxygen as against nitrogen. The air in a tyre that has been inflated for a while will be oxygen depleted.
Sent from my motorola edge 20 using Tapatalk
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Going the other way, the heat of constant braking will certainly cause sufficient pressure rise to pop off a tyre that's near its maximum to start with (experimentally, some Schwalbes rated for 105psi will blow off at 115psi).
The rim can easily reach 50 deg C (i.e. hand hot, when you can't keep your finger on it) which is about a 10% rise in pressure, should it have time to soak through to the air in the tube.
Yes, I've seen the aftermath of such off-popping on the descent of the Col de la Croix de Fer during the Marmotte sportif. Some of the (many) riders in front of me had inflated their tyres in the cool previous evening and suffered brown bibshorts moments during the very hot next day.
Presumably reduced air pressure at altitude also a factor.
About 10% reduction per 1000 metres so tyres set up at sea level would already be significantly over inflated at the top of the mountain. .
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Rim wear (IME) can add to this. I descended Ditchling Beacon once on the Pino (tandem, front wheel is a 406). Braking heating was Quite A Lot given the mass of two well nourished riders and not much mass to absorb the heat generated in the front wheel. Made it to the bottom, wondered how hot the rim was, burnt finger tip then watched as the tyre unmounted itself and burst the tube. Couldn't get the tyre to stay back on after that, as the rim kept distorting once the tyre ws inflated.
Definitely more of an issue on small wheels. You may have been there: a Fridays tour in Normandy and I remember similar happening to Charlie's Brompton tyre at the bottom of a descent while the large wheel bikes were fine.
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Going the other way, the heat of constant braking will certainly cause sufficient pressure rise to pop off a tyre that's near its maximum to start with (experimentally, some Schwalbes rated for 105psi will blow off at 115psi).
The rim can easily reach 50 deg C (i.e. hand hot, when you can't keep your finger on it) which is about a 10% rise in pressure, should it have time to soak through to the air in the tube.
Yes, I've seen the aftermath of such off-popping on the descent of the Col de la Croix de Fer during the Marmotte sportif. Some of the (many) riders in front of me had inflated their tyres in the cool previous evening and suffered brown bibshorts moments during the very hot next day.
Presumably reduced air pressure at altitude also a factor.
About 10% reduction per 1000 metres so tyres set up at sea level would already be significantly over inflated at the top of the mountain. .
External pressure drop won't affect the absolute pressure in the tyre and will increase the guage pressure by the drop in external pressure, so 0.1 bar (1.4psi) per 1000m.
Not much compared with the other factors.
Sent from my motorola edge 20 using Tapatalk
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personally I don't find that I notice it, but then my bikes live in the shed, so essentially not far from ambient. I run 28mm GP4 Seasons at about 7 bar and generally don't notice a massive difference until they're down to about 5 bar. As the other variable, I'm a smidge under 70kg, and I've got brown eyes and a grey beard :P
Yeah I’ve noticed the pressure can drop over a range before you notice with a sweet spot range in between. I’ll usually inflate to top of the sweet spot then leave it till, like you, I notice it doesn’t feel as good.
I think the revelation for me is when I stopped inflating both tyres to the same pressure.
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Going the other way, the heat of constant braking will certainly cause sufficient pressure rise to pop off a tyre that's near its maximum to start with (experimentally, some Schwalbes rated for 105psi will blow off at 115psi).
The rim can easily reach 50 deg C (i.e. hand hot, when you can't keep your finger on it) which is about a 10% rise in pressure, should it have time to soak through to the air in the tube.
Yes, I've seen the aftermath of such off-popping on the descent of the Col de la Croix de Fer during the Marmotte sportif. Some of the (many) riders in front of me had inflated their tyres in the cool previous evening and suffered brown bibshorts moments during the very hot next day.
Presumably reduced air pressure at altitude also a factor.
About 10% reduction per 1000 metres so tyres set up at sea level would already be significantly over inflated at the top of the mountain. .
External pressure drop won't affect the absolute pressure in the tyre and will increase the guage pressure by the drop in external pressure, so 0.1 bar (1.4psi) per 1000m.
Not much compared with the other factors.
Sent from my motorola edge 20 using Tapatalk
If the external pressure is c.10% lower the tyre will expand more so is more likely to get blown off the rim! Think of a balloon in a vacuum.
It's the argument that the baggage handlers use to get us to deflate tyres on a plane!
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Atmospheric pressure is around 14.7psi at sea level.
Whatever pressure you inflate a tyre to at sea level can only increase by a maximum of 14.7psi if you were to take the wheel into deep space vacuum.
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Given that 5 seems to be the wrong number with your current tyres / pump / indoor temperature / flat altitude / ground conditions / self when riding, I’m wondering what has changed since you determined that 5 was the right number?
Would something like topping up tubeless gunk affect the volume or tyre feel enough to change the sweet spot?
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The air put in the tyre will be significantly warmer than ambient temperature whilst pumping up, amount depends on the pump used and the effort put in to some extent - unless using a CO2 inflater, that tends to be cooler.
The effect is more significant with a total inflation than a top up. The temperature of the pump should give a clue as to how much by, larger/heavier pumps are affected less.
CO2 is also slightly soluble in butyl, so that component of the air in the tyre will reduce over time as the CO2 migrates to the lower pressure.
Also water content of air is prone to a massive volume change when it transitions from warm vapour to cooler liquid.
The science is complex - most demonstrations/experiments go to great lengths to minimise/eliminate one or more of the variables.
In the real world you need to guess how much extra (or less) to put in the tyres to compensate for the method of inflation and the expected changes of environment.
Also consider the much greater rate of diffusion out of the tyre of oxygen as against nitrogen. The air in a tyre that has been inflated for a while will be oxygen depleted.
Sent from my motorola edge 20 using Tapatalk
So it's best to top your tyres up twice a day if you anticipate inhaling from the tube.
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The air put in the tyre will be significantly warmer than ambient temperature whilst pumping up, amount depends on the pump used and the effort put in to some extent - unless using a CO2 inflater, that tends to be cooler.
The effect is more significant with a total inflation than a top up. The temperature of the pump should give a clue as to how much by, larger/heavier pumps are affected less.
CO2 is also slightly soluble in butyl, so that component of the air in the tyre will reduce over time as the CO2 migrates to the lower pressure.
Also water content of air is prone to a massive volume change when it transitions from warm vapour to cooler liquid.
The science is complex - most demonstrations/experiments go to great lengths to minimise/eliminate one or more of the variables.
In the real world you need to guess how much extra (or less) to put in the tyres to compensate for the method of inflation and the expected changes of environment.
Also consider the much greater rate of diffusion out of the tyre of oxygen as against nitrogen. The air in a tyre that has been inflated for a while will be oxygen depleted.
Sent from my motorola edge 20 using Tapatalk
So it's best to top your tyres up twice a day if you anticipate inhaling from the tube.
No empty and refill.
Sent from my motorola edge 20 using Tapatalk
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Going the other way, the heat of constant braking will certainly cause sufficient pressure rise to pop off a tyre that's near its maximum to start with (experimentally, some Schwalbes rated for 105psi will blow off at 115psi).
The rim can easily reach 50 deg C (i.e. hand hot, when you can't keep your finger on it) which is about a 10% rise in pressure, should it have time to soak through to the air in the tube.
Yes, I've seen the aftermath of such off-popping on the descent of the Col de la Croix de Fer during the Marmotte sportif. Some of the (many) riders in front of me had inflated their tyres in the cool previous evening and suffered brown bibshorts moments during the very hot next day.
Presumably reduced air pressure at altitude also a factor.
About 10% reduction per 1000 metres so tyres set up at sea level would already be significantly over inflated at the top of the mountain. .
External pressure drop won't affect the absolute pressure in the tyre and will increase the guage pressure by the drop in external pressure, so 0.1 bar (1.4psi) per 1000m.
Not much compared with the other factors.
Sent from my motorola edge 20 using Tapatalk
If the external pressure is c.10% lower the tyre will expand more so is more likely to get blown off the rim! Think of a balloon in a vacuum.
It's the argument that the baggage handlers use to get us to deflate tyres on a plane!
A balloon in a vacuum will explode because the balloon is weak and cannot stand a 1 bar increase in pressure differential.
A bike tyre that is pumped to say 5 bar is unlikely to explode when the outside pressure is reduced by say 0.3 bar when flying.
However, if the airline carry enough bikes, one will explode. The outside pressure reduction of 0.3 bar is probably not all that important. Bikes tyres could be old, badly fitted, newly inflated etc, so just looking after enough bikes for long enough will have the occasional tyre burst if the tyres are inflated.
IMHO a bike tyre bursting mid-flight is highly unlikely to do any real damage, but it would also probably be loud enough to be heard by someone, and it's exactly the sort of thing that airlines don't want to have happen.
Having the tyres deflated is an easy rule to understand and enforce. A flat tyre can be understood by anyone, and it completely removes the very slight risk.
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Aircraft holds are pressurised exactly the same as the cabin. The pressure drop at cruising altitude is around 25% - the cabin altitude will be around 6-7000ft. The temperature in the hold will be 12-20C, depending on the cargo carried. Bicycle tyres at normal inflation pressures are very unlikely to suffer unwanted carcass failures, though it is slightly more likely than when at sea level. Most of the instructions to deflate tyres prior to flights come from agents and contractors, and credible airlines won't make any such demand. It's worth remembering that the aircraft tyres are at greater pressure even than 20mm TT tyres of years ago, and they remain in unpressurised compartments even when retracted. Exploding aircraft tyres is not a common occurrence.
On both Virgin and in my time in the RAF, we used to carry quite a lot of vehicles in the hold. We were never required to reduce their tyre pressures.
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A bike tyre's most likely to go bang because of poor maintenance: Bead not seated properly, sidewall worn through by badly-adjusted brakes, that sort of thing. Factor in a bit of baggage-handler abuse, and the inherent bathtub curve issues of a bike that's being transported by plane in the first place (it's likely either on the way to or from a cycling holiday, which means it's likely to have either just had some - potentially incompetent - maintenance, or be somewhat the worse for wear at the end of a tour), and you don't even need a change in pressure/temperature to cause a problem. I agree with Diver300 that it's probably happened somewhere at some point, and that's all you need to cause silly rules to be imposed.
Obvious parallels with lithium-ion batteries, which already have strict rules for being carried on aircraft, and are in the process of being banned from trains[1] because someone's e-scooter caught fire on the Underground once.
[1] I expect there will be arbitrary rules in order to permit the CEO's laptop but make things awkward for young or disabled people with electric mobility devices.
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Lithium-ion laptop batteries have had a significant number of spontaneous combustion events on aircraft, and there were quite a few models that are not permitted in any form when I was still flying - including, IIRC, my early-2015 MBP.
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Battery management's moved on a fair bit since then of course *gestures vaguely at the EV thread*, but lithium-ion battery fires aren't the sort of thing you want to be fighting in an aircraft, or anywhere else where chuck-it-out-the-window-and-wait-for-it-to-burn-out isn't an option.
When I bought a large LiFePO4 battery (the non-explodey kind of lithium-ion) for barakta's trike from the manufacturer in China, it was split in half and shipped in two separate packages for this reason. I believe the CAA have a 100 Watt-hour limit for batteries on passenger aircraft these days, which makes most e-bikes a non-starter.
While it might be reasonable to prohibit such batteries on the deep Tube lines (ie. the ones you're already banned from taking bikes on for evacuation reasons) it seems a bit much to ban them from national rail, especially when you consider the impact on wheelchair users.
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While it might be reasonable to prohibit such batteries on the deep Tube lines (ie. the ones you're already banned from taking bikes on for evacuation reasons) it seems a bit much to ban them from national rail, especially when you consider the impact on wheelchair users.
And quite honestly unenforceable in practical terms without inspecting every single bag or piece of luggage going onto a train, can't really see that happening at rush hour
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While it might be reasonable to prohibit such batteries on the deep Tube lines (ie. the ones you're already banned from taking bikes on for evacuation reasons) it seems a bit much to ban them from national rail, especially when you consider the impact on wheelchair users.
And quite honestly unenforceable in practical terms without inspecting every single bag or piece of luggage going onto a train, can't really see that happening at rush hour
Well they won't actually ban the batteries, they'll just ban e-bikes and scooters.
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Spare batteries for devices X, Y, and Z?
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Well they won't actually ban the batteries, they'll just ban e-bikes and scooters.
I wasn't aware that this was an issue. Nuts.
Since I've recently bought an e-bike for the bits of my commute either side of the train, it would be extremely annoying if it were to be enforced on my route.
Luckily, I have no intention of ever taking my e-bike on the tube.
Will they ban phones and laptops on trains too? Imagine the outcry!
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Will they ban phones and laptops on trains too? Imagine the outcry!
Imagine the peace and quiet
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Will they ban phones and laptops on trains too? Imagine the outcry!
I'm sure TEH RULEZ will be carefully worded to allow anything the CEO is likely to travel with.
I note that the Royal Orthopaedic Hospital bans USB battery packs after one caught fire on a patient's bed. I have similarly mixed feelings about that.
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The problem of self-immolating laptops was an issue 5 or 6 years ago; I would suggest that a reaction now would go well beyond waiting till the nag has left the building.
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Battery management's moved on a fair bit since then of course *gestures vaguely at the EV thread*, but lithium-ion battery fires aren't the sort of thing you want to be fighting in an aircraft, or anywhere else where chuck-it-out-the-window-and-wait-for-it-to-burn-out isn't an option.
When I bought a large LiFePO4 battery (the non-explodey kind of lithium-ion) for barakta's trike from the manufacturer in China, it was split in half and shipped in two separate packages for this reason. I believe the CAA have a 100 Watt-hour limit for batteries on passenger aircraft these days, which makes most e-bikes a non-starter.
While it might be reasonable to prohibit such batteries on the deep Tube lines (ie. the ones you're already banned from taking bikes on for evacuation reasons) it seems a bit much to ban them from national rail, especially when you consider the impact on wheelchair users.
It depends on the quality of the battery - I can carry 20 100WH batteries for work on a flight, provided they're properly tested and have a UN sticker on them.
But they're much more expensive than an ebike battery, and have to pass overcharging, shorting and drop tests to be certified.