What’s the physics behind TPU tubes?

[Juliansou]

I’m a recent TPU (ride now) convert. Up until the change I’ve ran slime inner tubes due to my slight paranoia about punctures (I’m a bit more zen about them now!). The difference has been dramatic! I’m very conscious of positive bias here, but over the past two weeks my average speed is up about .75mph (I’m a bit of a data nerd). Not only that, the bike seems to accelerate better and overall feels a lot nimbler. Whilst I appreciate theres a weight saving of maybe 300g over both wheels, this alone doesn’t seems to account for the impact. I’m guessing rotational mass play a part along with rolling resistance? Can anyone put a bit of science behind what I’m feeling? If it’s significant, I’m riding a fairly relaxed Cannondale Synapse on my daily commute (26 mile round trip), pretty much all road but sometimes not in the best condition on a pair of Pirelli Cinturauto sport 32mm which I run quite high at 70psi. Overall system weight in the region of 77kg.
Cheers all.

 

[midlandsgrimpeur]

Yes, you are correct, it is largely the lower rolling resistance and lighter rotational mass of the lighter weight material. I believe there is also something around lower tube deformation as TPU loses air at a slower rate than latex, which I believe also contributes further to lower rolling resistance but I am not 100% sure on this

 

[Sharky]

I suspect that the tubes them selves are not entirely the reason you are going faster. Warmer weather, knowing the road/route better, and perhaps the 26 miles a day is helping.
You are getting fitter!

 

[Dogtrousers]

That is quite a drastic change, from slime to TPU. One extreme to another, so if you wanted to ensure you got a noticeable difference you went about it the right way!

 

[N0bodyOfTheGoat]

Being 77Kg, you will feel more benefit from small weight changes than I will these days at ~96Kg!

Let's say your wheels weigh ~1.8Kg; tyres ~0.6Kg; slime tubes ~1Kg; rotors ~0.3Kg; cassette ~0.3Kg (so ~4Kg total).

You've then switched the slime tubes for TPU, saving ~0.8Kg.

That a big % weight saving and the rolling resistance of TPU tubes is very close to latex tubes, which is close to tubeless, so your tyres will roll better and accelerate quicker.

I could easily see you gaining close to 1mph extra speed.

 

[PaulSB]

Do you have a TPU patch kit?

 

[Webbo2]

Do you have a TPU patch kit?

What a roll of insulation tape.

 

[PaulSB]

What a roll of insulation tape.

I'll suggest that to my buddy who used two tpu tubes on a recent ride. I gave him a butyl tube for his third puncture!

 

[Webbo2]

I'll suggest that to my buddy who used two tpu tubes on a recent ride. I gave him a butyl tube for his third puncture!

It does work. But I’m not sure how robust a repair it is.

 

[Juliansou]

Being 77Kg, you will feel more benefit from small weight changes than I will these days at ~96Kg!

Let's say your wheels weigh ~1.8Kg; tyres ~0.6Kg; slime tubes ~1Kg; rotors ~0.3Kg; cassette ~0.3Kg (so ~4Kg total).

You've then switched the slime tubes for TPU, saving ~0.8Kg.

That a big % weight saving and the rolling resistance of TPU tubes is very close to latex tubes, which is close to tubeless, so your tyres will roll better and accelerate quicker.

I could easily see you gaining close to 1mph extra speed.

I like the sound of that! I’m about 68kg & the bike 9kg so there’s a little extra gain there too!

 

[Juliansou]

Do you have a TPU patch kit?

Yep - it came with a couple of patches but no idea how good they are. If I do puncture, I’ll probably just replace the tube and have a go at repairing when I get home.

 

[Milzy]

I bought the latest Ride now with their fancy metal valves. After a few days flat, not even been out. We all know TPU lose air somehow. I’ve noticed when the garage temperatures are very low the air escapes even faster.
What could the science be for TPU’s staying up for longer in the summer but on cold winters days they quickly lose air?

 

[Pblakeney]

It does work. But I’m not sure how robust a repair it is.

It'll get you home if you have run out of spares but they don't last long term. From personal experience I have not found a repair which holds long term so I will now bin once home. That said, I got 6 tubes 3 years ago and have binned 5. Two of which were from my Angliru experience.

PS - I ride on 25mm tyres at 90-100 PSI.

 

[glasgowcyclist]

I’ve noticed when the garage temperatures are very low the air escapes even faster.

Rather than the tube actually losing air, isn't this just the normal reduction of air pressure as the temperature drops?

 

[Milzy]

Rather than the tube actually losing air, isn't this just the normal reduction of air pressure as the temperature drops?

It must have something to do with it. I have some Stans sealant, I will try injecting some inside the tube. Maybe the TPU is porous like latex tubes.