At what gradient are TPU tubes faster than latex tubes?

Equipment
1

TPU tubes are lighter than Latex but Latex is faster as numerous tests have shown on Aerocoach and BicycleRollingResistance. I have some good wheels that are not tubeless compatible.

I have been using TPU tubes for a year. They have some advantages in making me feel like my heavy aero road bike is a climbing bike on the hills. In races and hard group rides on hills 6%+ I would always feel fast responding to attacks while I would notice my friends who are stronger than me on lighter bikes and different tyre types take a few seconds to get to speed.

For me the biggest downside is dealing with punctures. TPU tubes do have some puncture protection capabilities but on rough roads they seem to suffer a bit. This comment I found on one the forums resonates with my experience:

There is a clear limit in the TPU tubes that is not widely mentioned: their stiffness increases the impedance losses (how much vibrations are transmitted to the rider, then energy wasted) when the road degrades.

Their “equal” performance to Latex is only valid on very very good roads. Overall Latex remains more efficient.

For puncture resistance, they do resist better to perforation but lets be honest, if you have something in your tire that penetrated the protection bed, the tube is not what will resist. where latex has another benefit if for “snake-bite” types of punctures, they resist more when “pinched”

Patches work sometimes but if it does not then it becomes an expensive headache. Ridenow tubes were cheap but the prices are slowly increasing.

I have considered adding some sealant inside the TPU tubes for training as I hate dealing with punctures in races and hard hard group rides but only a few TPU brands have removable valve cores like Schwalbe. Schwalbe on their website recommend not adding sealant inside their Schwalbe Aerothan tubes while Tubolito recommend using OKO sealant and those spray sealants like Vittoria Pit stop however their road tubes do not have removable valve cores.

Can Tubolitos be used with sealant or repair sprays?

Only with Tubolitos with premounted valve extenders.

We performed tests with different products. Following products seal Tubolitos:

Sealant: Oko Puncture free Bike

Repair Spray: Nigrin Reifendicht; Vittoria Pitstop Super Magnum; Tip Top Pannenspray; GĂĽp Kwiki

Residues of tubeless milk do not harm Tubolito products

I am considering the move to Latex. They cheaper, more repairable and is proven to work with sealant which saves me from stopping to change a puncture. My questions are

  1. At what gradient on a hill would I be better of with TPU tubes? Put differently at what stage does the advantages of the lower rolling resistance of latex tubes fall away to the weight advantages of the lower weight of tpu tubes?

  2. Has anyone tried pre-filling tpu tubes with a bit of sealant to help it self seal without having to stop?

  3. If I do move to Latex I have read that I need to also add two loops of tubeless rim tape to the wheel. With the rim tape and the sealant added is the rolling resistance still faster than TPU tubes?

Some context: I ride a Merida Reacto Aero bike which is quite heavy. I am already close to my racing weight of 67 kg’s at 1.77m tall and cannot lose any more weight. I tend to feel the drop in weight of anything part on my bike quite quickly. I live in a mountainous area and ride 12 - 15 hours a week.

2

Are you really going to feel 100g or less even!?

2 Likes
3

For tyres and tubes I 200% feel any weight changes. I had a puncture recently and put on some lightweight butyl tubes and I was slower at the same power on hills that I usually ride on. I just feel sluggish.

With weight anywhere else on the bike I marginally feel the difference but it’s a “could be in my head feeling”

4

I think it’s just placebo (or nocebo rather). Just try the different weights

1 Like
5

The differences in each case are so minuscule, that this is purely theoretical. For both the rolling resistance differential and the weight differential we’re talking about seconds over an hour of riding.

3 Likes
6

For anyone interested: Someone replied on the weight weenies forum. Basically Latex tubes will always be faster unless doing a massive hill climb with average gradients above 15%.

This isn’t difficult to calculate, if you have the data. Inner tubes don’t affect power production or aerodynamics, they just affect weight and rolling resistance.

Drag due to mass on a slope is: Fgravity = (M + m) x g x sine(A)

Rolling resistance drag is: Frolling = Crr x m x g x cosine(A)

where:

M = entire mass of bike/rider minus mass of inner tubes
m = mass of inner tubes
g = acceleration of gravity
A = angle of slope
Crr = coefficient of rolling resistance.

The angle where the extra rolling resistance of TPU tubes balances out the lower rolling resistance of latex can be found by setting the gravity and rolling resistances of TPU and latex tubes equal:

Fgravity,ltx + Frolling,ltx = Fgravity,tpu + Frolling,tpu

(M + m,ltx) x g x sine(A) + CXrr,ltx x (M + m,ltx) x g x cosine(A) = (M + m,tpu) x g x sine(A) + Crr,tpu x (M+m,tpu) x m x g x cosine(A)

Rearranging to solve for angle A, leaves this formula

A = arctangent( ( (Crr,tpu - Crr,ltx) * M + Crr,tpu * m,tpu - Crr,ltx * m,ltx ) / ( m,ltx - m,tpu ) )

The Aerocoach web page has some data on inner tube mass and rolling resistance (https://www.aero-coach.co.uk/inner-tube … resistance):

Vittoria latex tubes: m,latex = 72 grams, Crr,latex = 0.002612
Tubilito S TPU tubes: m,tpu = 22 grams, Crr,tpu = 0.002931

Assuming a total bike/rider (minue inner tubes) mass of 75 kg (75,000 g), the slope at which the lower weight of TPU tubes overcomes their higher rolling resistance is 25.4 degrees, or a grade of 48%. Which means on a practical basis, latex tubes will always be faster, even on steep slopes.

Hi Mark, this is great, but your specific calculation of 25.4 degrees appears to be for a unicycle. If the rider+cycle mass is shared by two wheels then things look quite a lot better for TPU.

Oops! Good catch! You’re right, I only added the weight of a single tube. When considering the weight of two tubes, than the “critical” slope for the 75 kg bike/rider is 23.6% (13.3 degrees), and for the 50 kg bike/rider the critical slope is 15.7% (8.9 degrees). So there are a few, rare, real world cases where the slope is steep enough for TPU tubes to have a performance advantage, but for most riders most of the time TPU tubes will still be a net performance disadvantage, compared to latex.