Should you put tubeless sealant inside tubular tyres? Pro teams think so

by Dave Rome


One of the key benefits to tubeless tyres is the use of liquid tyre sealant that provides self-sealing properties. However the use of such sealant isn’t limited to just tubeless tyres, and it seems the recent interest in tubeless technology has lead to others finding ways to reduce the incidence of flats in tubular technology.

A Israel Start-Up Nation case study

According to Jost Zevnik, team operations manager at Israel Start-Up Nation (ISN), the WorldTour outfit is now racing every event with tyre sealant inside its tubulars as a flat-prevention measure. According to Zevnik, “there is no reason to not use it,” and suggests they’re not the only team doing so. I can guarantee they’re not the first.

The idea of putting liquid tyre sealant inside tubes and tubulars isn’t new. Vittoria has sold its PitStop emergency sealant-based tubular repair canister for well over a decade. Slime has offered self-sealing tubes for far longer than that. Those who pay for their own tubulars have long fixed pinhole flats with tubeless sealant. And heck, I even used to inject Stan’s original sealant into the inner tubes of my commuter some 13 years ago.

Israel Start-Up Nation, though, has been using Orange Seal’s original “Regular” formula for about four years. And that timeline suggests the use of sealant has little to do with the team’s recent use of prototype Maxxis tubulars.

At best punctures are a significant waste of energy to get back to the pack. At worst they’ll cost a chance at a win. Add in that whole bike changes have become more common with the advent of disc brakes, and it’s no wonder teams are looking to keep their riders rolling.

According to the team, testing the effectiveness of the sealant isn’t difficult to do and they’re confident in the results. No doubt the sealant works, but it’s not a guarantee as evidenced by the team having had four-wheel changes and three bike changes during the entire 2020 Tour de France. Still, that’s a pretty low failure rate across three weeks of racing.

So Zevnik suggests there’s no reason not to use it, and I’m sure the likes of Orange Seal concur. But what are the issues here and why doesn’t this ambitious WorldTour team see a downside to sealant? Before we dive into that, it’s worth discussing tyres.

Not all tubulars are equal

Maxxis and Israel Start-Up nation have a technical partnership in place, and together they’ve been developing a new range of tubulars intended for the consumer market. Unfortunately, both parties are being tight-lipped about any details of these new tyres.

All the team did share was that they have access to many sizes, most with a 170 tpi casing and that they’re tested for efficiency independently. “For normal road races and time trials in 25 and 26 mm,” Zevnik said of the tyres tested. “For classics in the last two years, we tested from 27, 28 and also 30 mm for Roubaix.”

ISN has been racing on a mixture of tyre types, but most of the time they’ve been seen racing on prototype tubulars.

The secretiveness suggests the construction of these Maxxis tyres is a little different to the normal latex tube, cotton casing and rubber tread construction that many teams race on. And the suspicion is that these tyres likely feature a “tubeless tubular” construction, albeit with a fresh approach that creates more supple and faster rolling air-tight casing than what the likes of Tufo offer.

And that different construction is an important element. Latex inner tubes and latex-based tubulars both share issues in relation to using sealant. Vittoria themselves warn of a deflated latex-based tubular becoming stuck to itself, and then tearing upon re-inflation. The tyre manufacturer also warns of chemical reactions and material degradation caused by some sealants. Orange Seal says this doesn’t apply to its formula.

Meanwhile, Tom Anhalt, an engineer and respected expert on the topic of tyre rolling resistance efficiency, speculates that the liquid sealant helps to lubricate punctures when used in latex tubes, resulting in a puncture that’s worse than it would have otherwise been. “I’ve never really been a fan of sealant in latex tubes,” he said. “I don’t think it really helps.”

Ok, so let’s assume the Maxxis tubulars don’t use a latex tube for holding the air and that the sealant can work like it would in a tubeless tyre.

Rolling resistance woes?

Increased rolling resistance is commonly cited as a reason not to use liquid tyre sealant, but surprisingly it seems the losses aren’t nearly what one would assume them to be. According to Zevnik, the team commissions independent efficiency tests for the tyres and sealant it races with. “The last test was with 40 ml of sealant in the tubulars,” he said. “I can not give you numbers but I can say that you would not lose a bike race because sealant will make the tires slow.”

There are a small number of facilities offering independant rolling resistance testing. Additionally a number of brands have internal facilities, such as the pictured setup from Vittoria.

Anhalt confirmed that the measured differences he’s seen are extremely minimal and in line with what Jarno Bierman at Bicycling Rolling Resistance has published on the topic. However, it wasn’t long for Anhalt to follow up with an “A ha” discovery, one which suggests that liquid sealant impacts rolling resistance even less than first thought. Below is Anhalt’s explanation he provided to CyclingTips:

We know from many tests that the addition of a latex tube inside a tubeless tire adds basically no measurable Crr [rolling resistance coefficient] drag to the same tire when run with either no sealant, or a minimal amount (just enough to seal). This tells us that solid latex has extremely low hysteresis losses.

However, both Jarno’s testing and my own show that above a certain volume of latex sealant, there’s a measured additional loss when tested on a roller testing machine. Now, we know that solid latex has minimal losses when flexed, but does it make sense that a liquid latex solution has more? That seems backwards to me, especially considering the relative low viscosity of sealant liquid.

Here’s why: temperature has a fairly high effect on tire Crr. The warmer the tire material, the more flexible the casing is, and the lower the losses. This temperature dependence is high enough that in my own roller testing I monitor the ambient air temperature and apply a temperature compensation to the results (which I developed through my own observations). Additionally, I follow a set protocol for “warming up” the tires prior to testing, and then only take the data from the last half of the four-minute test run for my power and speed averages.

All of that is to make sure the tires have basically come to an equilibrium temperature and then can be compared “apples to apples” with the results all converted to what would be expected at 20ºC ambient. I know Jarno does something similar with the warmups, and instead of applying a temperature compensation, he has the luxury of his test rig being located in a temperature-controlled environment.

Why all the talk about temperature sensitivity? Well, and this is purely speculation at this point, but I think what we may be observing in the increasing Crr measurements with additional sealant volume might be more related to the additional heat capacity of the liquid, rather than any intrinsic flexing losses. In other words, that additional liquid mass and heat capacity is resulting in it taking longer for the tires to come to an equilibrium temperature, and thus are cooler during the test session than they would be with a longer warmup.

In any case, what does this mean for Crr in “real life”? Well, it would mean that after riding for a few minutes, the sealant wouldn’t be adding any additional Crr at all, and these increases we’ve seen may just be artifacts of the testing procedure.

Clearly, there is more testing to be done here, but regardless of the findings, we’re talking about loss numbers that likely sit in the realm of “meh” for a professional rider.

Weight and longevity

Ok, so if rolling resistance is effectively unchanged, what about weight?

A sealant like Orange Seal weighs 56 grams per 50 ml. Assuming ISN is using 40 ml per a tyre, that’s approximately 90 g added to the bike.

The topic of tubeless sealant weight is something we’ve discussed before in an episode of the Nerd Alert podcast, and it’s known that professional mountain bike racers seek to have the bare minimum sealant in order to reduce rotating weight. And from that same podcast, we know just how little 90 g effects power output for the same climbing speed.

However, over time that sealant will dry out and need topping up. For Orange Seal, it’s original formula is claimed to last just 30-45 days. Given teams have racks and racks of wheels in rotation, I worried that the sealant would require constant topping up, but again, Israel Start-Up isn’t too concerned.

“Well, we do top up our sealant in some cases,” explained Zevnik. “However we have our wheels in constant movement as well, so that helps. Must say that usually if we have to take the tire off the rim, the sealant is not completely dry, so I do not see it as a huge problem.”

Still, on the assumption that the team doesn’t just wastefully throw away its tubulars once the sealant dries inside, there will be further weight additions over time. “You should see a 65-75% reduction in weight as the main carriers evaporate,” said Orange Seal’s owner, John Vargus, when asked about the weight of dried sealant. Over time the weight gain of sealant will surely add up, and there’s no way to remove it from the inside of a tubular tyre.

Israel Start-Up Nation is sponsored by Orange Seal. The team’s only ever used the company’s “Regular” sealant, which offers better puncture-sealing versus the longer-lasting “Endurance” sealant.

Currently, ISN doesn’t seem too concerned about the weight gain. However, I can’t help but wonder whether running sealant will lead to a higher disposal rate of tubulars. Perhaps they’re wearing through tyres faster than the sealant is drying. Or perhaps the fact that the sealant is forever plugging pin holes helps to reduce regular tyre waste? It’s a tough one to answer.

Playing at home

On the assumption that you don’t mind the increased weight, having to top-up dried sealant, or deal with the potential of clogged valves, then there’s little stopping you from adding sealant into your inner-tubes or tubulars. Such a modification may help with getting more life out of a tubular with a slow leak or preventing glass- or thorn-based flats from ruining a ride.

In both cases, you’ll need valves with removable valve cores to inject the sealant through. From there you’ll want to use a tyre sealant that’s good for higher pressures – such as Orange Seal Regular or Stan’s Race Day. And if you have latex tubes, then be careful not to let them sit deflated – that’ll be the end of them.

Editors Picks