If you’ve read our other articles about tubeless tyres for CX, you’ll know that we have firm views on tubeless' failings for CX racing. However, throughout 2020/21 we have invested a significant amount of time (and sealant) looking at products and methods to make it work better.
We are very impressed with the Getaway, Challenge's higher volume HTLR gravel tyre, and have managed to get acceptable reliability from their Vulcanised Tubeless (VTLR) tyres too.
A lot of people are hoping that handmade open tubulars will offer a real alternative to tubulars by adding some much needed suppleness and grip, which works at low pressure for a broad variety of riders on a broad variety of rims.
If the same feel as open tubular clinchers with a latex tube could be achieved from a reliable tubeless system, it would be a huge development. And if they could get near to tubular’s grip and feel it could be a gamechanger!
Promising hookless rim compatibility, UCI 33 mm compliance on up to 23 mm internal width rims, and the same materials as their PRO tubulars, Challenge's HTLR tyres have been eagerly awaited.
This is the second time we have tested handmade tubeless CX tyres this year. The first resulted in the product being shelved, so this time we have been pretty cautious in our approach.
We are testing the Grifo version, this and the Chicane are available at the moment with Limus and Baby Limus following later, according to the UK distributor, in 2022.
Challenge claim the 33 mm HTLR tyres will pass the UCI’s 33 mm rule on up to 23 mm internal width rims. Measuring the flat carcass width confirms that they have reduced its width compared to their 33 mm clincher open tubular and VTLR, from 94 mm to 90-91 mm.
The HTLR looks very similar to their clincher open tubular cousins. Although sharing the same tread and sidewall material, the sidewalls feel a bit stiffer. The bead is formed in a fold of sidewall material which extends internally inline with the tread.
Clincher open tubular's fold stops 3-5 mm short of the tread so has an area with a single layer, explaining the HTLR's stiffer feel.
The HTLR sidewalls are 1.3-1.45 mm thick. By comparison a VTLR sidewall is 0.8-0.93 mm.
They have a consistent weight. The four we checked were 394g, 384g, 386g and 392g.
There are more "handmade variations" with these than you might be used to with vulcanised tyres, but far fewer than you would see with Dugast or FMB.
For testing we used the LOWMASS AC20-390 and DT SWISS XR391. Both are modern aluminium hooked tubeless compatible rims with a 20 mm internal rim width.
Fitting Challenge open tubulars normally gives your fingers and thumbs (and vocabulary) a good workout. HTLR are no different. As always, getting the bead down into the rim’s centre channel is vital.
We got the pair on without tools or levers.
The first was on a clean dry rim which was a wrestling match. The second was on a rim that had just had a Challenge VTLR removed so was wet with sealant remnants. This was much more tricky, more like a wet slippery wrestling match.
A last minute car park tyre change, with cold hands, just before a race would be interesting...
We were not able to get them to inflate with a track pump, but inflated and seated easily with a compressor.
With vulcanised tyres, a predictor for a reliable tubeless setup is whether the tyre holds air without sealant? By this measure the HTLR failed and lost all of their pressure in a couple of minutes.
Another predictor is to press the tyre at the bead. A reliable vulcanised tyre will hold air with a firm press at the bead? Again the HTLR failed and air escaped.
We repeated set up with 2 additional layers of tubeless tape. This method has helped to get decent tubeless performance from Challenge’s VTLR tyres. But in this case it made little to no difference.
We used Challenge’s Smart Sealant having found it to be the solution to sealing Challenge’s leaky VTLR sidewalls, and it is only fair to use the recommended product.
With 60 ml they didn’t want to seal, but with 120 ml they sealed up easily and there was no sidewall leakage at all. Some sealant seeped from the edge of the rims but they held pressure at 35 psi.
A spin of the wheel showed a nice straight tyre with central tread.
On our 20 mm internal width rims at 26 psi they measured between 32.77 and 33.23 mm.
Worryingly though, now with a press on the tyre bead, a little air and sealant escaped each time.
So - first impressions were a combination of here we go again, these are not going to work and how can it be possible they are UCI compliant on a 23 mm internal width rim.
The next morning the HTLR had held their air overnight, which was encouraging.
Challenge have set a tyre pressure range of 26-35 psi, so we set them to the recommended minimum 26 psi and took them for a smash around Southampton’s Wessex CX race course.
Firstly, they stayed on the rim - which is more than can be said for the other hand made tubeless CX tyres we tested earlier in the year – a good start.
At 26 psi and as a (heavier than I should be) 81 kg rider, they felt like… nothing special.
I’ve ridden 1000’s of miles on clincher open tubulars with latex tubes and at a racing weight of 74ish kg would run them at 22 psi. To put it simply, at 26 psi the HTLR felt too hard.
At the end of the session, they had not burped but there were several areas along the rim edge where some sealant had seeped out. A check with the pressure gauge revealed they hadn’t lost any pressure though.
My mood was changing from this isn’t going to work, to mildly pleased and this might be OK.
Their next outing was at the new Newbury Velo Wessex race course at Hungerford. It was a great testing ground and although not in race conditions, rode them at 24 and then 22 psi.
As the pressures lowered they felt progressively better, and although the slight sealant seepage at the rim edge continued, they did not burp or lose any air. They lost their too hard feeling and began to feel like a hand made tyre should.
Next test was at our local cornering and off-camber practice area to try some really tight cornering, and figure of eights at an even lower pressure.
At 20 psi, they came alive and their grip multiplied.
It was easy to hit the rim with body weight movements only, so probably they were too soft for the speed and dry ground, but with no risk of pinching they felt more like a tubular.
As confidence led to more aggressive riding, it became clear that 20 psi in the rear was a step too far. Hard turning off-camber under power and landing mid turn after being lifted by lumpy ground caused burps. The seepage at the rim went to almost 360 degrees around the rim.
In truth though, this was a "can they be burped?" test. If you turned as aggressively corner after corner as this in a race, you would probably crash or cause a crash. This was fairly extreme, but burps happen in those moments when you hit something unexpectedly hard or have to make evasive manoeuvres.
Pushing the pressures back up to 24 psi on the rear and repeating the test eliminated the burps, but the sealant seepage remained. The rear also lost its tubular like feeling and became more open tubular and latex like again.
Afterwards, and now having been ridden and/or fitted for 48hrs, they pass the press the bead press test. Even with a very firm press no air or sealant escapes.
If you have kept reading to this point, you’ll probably be thinking that Challenge’s HTLR are an interesting option, here are my thoughts so far –
More testing is needed, but Challenge have definitely moved CX tubeless forward with their HTLR CX tyres.
I’m pleased to see a tubeless option where the tread will last. Vulcanised tyre tread life is really disappointing.
At their recommended minimum 26 psi, with Challenge’s Smart Sealant, and now they pass the bead press test I would say they offer reliable tubeless performance. But at that pressure do not deliver the hoped-for like tubular performance.
They are not the same as regular tubeless tyres. They are not fit and forget. Will take some dialling in to gain their advantages and find your own personal lower psi limit.
I am curious to see if or for how long the seepage at the rim edge continues.
Compared to a moulded vulcanised tyre's sharp bead, the HTLR bead looks like a simpler fold of fabric. I suspect that once fitted, under pressure and ridden, it is taking the shape of the rim making a better fit and resisting my bead push test.
I’m yet to fit them to a 23 mm internal width rim, but for now can not see how they will pass a UCI 33 mm test on such a wide rim.
I’ve yet to fit them to a hookless rim. There are so few CX tyres for hookless rims that up to now we have not specified a narrow (enough for CX) hookless LOWMASS rim. We do have a really light option up our sleeve if these HTLR tyres prove to be good enough…
Even with the sealant seepage, I am impressed with how they performed - up to the point where the psi was too low and aggression was too high.
I’m curious to see how these perform with a liner. Earlier in the year we tested the Tubolight CX liners. I am sure they will hold the bead on at lower psi and may help to fix the burps and seepage. But, fitting and removing these HTLR with a liner is likely to make gluing tubulars look like an easy job.
Just like with all tubeless; some rim and rim tape combinations will work better with the HTLR than others. If your wheels are early tubeless models, I would wait until you have a modern design which has the modern ETRTO sizing and bead lock features.
The instruction leaflet needs an update. It makes no mention of tubeless at all. Our tyres came with the same leaflet as comes with clincher open tubulars.
I do not yet think these are anywhere near a competitive or reliable option for serious or pro riders looking for every gain from their tyre's grip.
Right now I would describe Challenge’s HTLR as adding to the game, rather than changing it. I am confident that a goldilocks tyre pressure can be found, but do not think that HTLR will affect tubular’s domination at the performance end of the sport - I'm planning on selling my tubular wheels before an HTLR driven price crash.
(But I haven’t tried them with a Tubolight liner yet… watch this space)
We'll add 4th, 5th etc impressions as we continue testing and dialing in tyre pressure.
We've ridden these several more times and they have definitely settled down / bedded in. At 26psi in the rear and 24psi in the front there is the odd bit of sealant seepage, but they definitely hold air.
We have refitted with Tubolite CX specific liners, at 22psi in the rear and 19.5psi in the front there has been no burping but the sealant seeping has increased and the front is no longer passing the press test.
I suspect the bead will need to re-settle / bed in again - watch this space...
Take a look at our other articles - https://cyclocrossracer.co.uk/blogs/cyclo-cross-racer-ideas-reviews-and-advice