Tyre burping issues - ?hunt rim a factor

fontm0ss

So rode on some g ones in cx round previously and the front burped on warm up lap so set it up with higher pressure for the race. Recently put some specialized terra on for something more cx specific. They were a pain to set up - ended up using co2 as my track pump with compressor didn’t work. The soap I used to set them up still seems to bubble through the sidewalls?!

Rode them for the first time on cx course today and again burped. Had to pit twice to pump the tyres up! I can’t work out if it’s bad luck, running way too low (don’t think I was), tyre issue or possibly the rim? Pretty sure hunt don’t have a hook on inside of the rim and wondered if that made it more prone to unseating/burping?

robertpb

I doubt it's the soap that is bubbling through the sidewalls it will be the sealant, unless you used too much.

Pump the tyres up to full pressure and leave them for 24 hours to let them stretch, then drop them down to your normal pressures and see how they go.

fontm0ss

That’s a good point re sealant. Ta I’ll try that

cycleclinic

the bead hook does not stop burping, it is there to stop the tyrre popping of the rim at high pressure. hookless rims can retain the tyre just fine. burpring happens when the tyre move away from the side wall. you can avpid burping by not turning (difficult in CX) or using a rim with a bump next to the central well now I thought the Hunt rims had that. perhaps this one does not.

fontm0ss

Cheers for that!

Mccrear

fontm0ss wrote:

So rode on some g ones in cx round previously and the front burped on warm up lap so set it up with higher pressure for the race. Recently put some specialized terra on for something more cx specific. They were a pain to set up - ended up using co2 as my track pump with compressor didn’t work. The soap I used to set them up still seems to bubble through the sidewalls?!

Rode them for the first time on cx course today and again burped. Had to pit twice to pump the tyres up! I can’t work out if it’s bad luck, running way too low (don’t think I was), tyre issue or possibly the rim? Pretty sure hunt don’t have a hook on inside of the rim and wondered if that made it more prone to unseating/burping?

try losing some weight, tubby!

psterdeacon

I've burped waaaaay to many tyres racing CX using tubeless. its a tricky balance of burp versus useful (low) operating pressure...
Truth is if you're really racing and cornering fast-sooner or later the conditions will make them burp -unless you're running so much pressure that it's almost pointless to be running them tubeless anyway. Gravel racing and road tubeless i think are okay because you don't have the cornering force VS low pressure issue to roll them.
I suffered various small burps during the season but shrugged them off- but a big-crash inducing one has put the final nail in the coffin. This years National CX- my front PDX tubeless burped running at 25psi and riding hardpack fast..it went immediately flat- causing much lost skin and a DNF. SO never again. Tubulars or latex tubes for CX racing.

joey54321

OP; what pressure are you using?

arturo_belano

psterdeacon wrote:

I've burped waaaaay to many tyres racing CX using tubeless. its a tricky balance of burp versus useful (low) operating pressure...
Truth is if you're really racing and cornering fast-sooner or later the conditions will make them burp -unless you're running so much pressure that it's almost pointless to be running them tubeless anyway. Gravel racing and road tubeless i think are okay because you don't have the cornering force VS low pressure issue to roll them.
I suffered various small burps during the season but shrugged them off- but a big-crash inducing one has put the final nail in the coffin. This years National CX- my front PDX tubeless burped running at 25psi and riding hardpack fast..it went immediately flat- causing much lost skin and a DNF. SO never again. Tubulars or latex tubes for CX racing.

Sry to hear about the crash psterdeacon - awful place for tubeless to fail.

I switched one bike to tubeless last season and it was a revelation - stans grail and vittoria tyres (cross xl and then a terreno wet). Knew it would be boss for just riding around but was sceptical for racing (I'm not light, either) - had a superb run of about 10 races, wasn't even burping them as far as I could see so just though that was CX wheels sorted forever. However, heavy race at Bradford in Dec, swapped onto it mid race and burped it near flat on the first off-camber climb.

Think the cause of this was a dinged rim - the grail had gotten beaten up racing at cross pressures, and afterwards the tyre wouldn't seal at one particular dinged spot. So I don't know if I've just had a v lucky run with tubeless racing or if it is indeed the answer. I've replaced the grail with a DT swiss rim so we'll see how that does.

Mccrear

I think if you have multiple wheel sets and tyre combos then tubeless can be great... but it only takes one bad experience to sour it imo. Last year I DNF 3 races due to puncture/rim issues and mostly cos I was running as low as I could with tubeless - but once confidence in it goes then as well going back to tubes. Worst was on an off camber where lost pressure and tyre started to come off rim! Thankfully I’m fat and slow so no real harm done. I’ll prob give it another try next season (new baby wrote off this season) but now got a second wheel set that I’ll be keeping tubed. I honestly think that other than the wettest, heaviest going, courses then not worth the faff and crash risk unless super confident in it. Would even say that tubulars done well is less of a faff than tubeless.

cycleclinic

Rims that can't retain the tyre without pressure ( you know when setting up) are liable to burp. 25 psi is too low for a CX tyre. I use up to that in 50mm tyres. At 25psi a CX tyre would be squirming.

Run 35psi for CX widths.

cycleclinic

Are these the tubeless g ones that burped. The tubed version run tubeless will burp more easily.

joey54321

thecycleclinic wrote:

Rims that can't retain the tyre without pressure ( you know when setting up) are liable to burp. 25 psi is too low for a CX tyre. I use up to that in 50mm tyres. At 25psi a CX tyre would be squirming.

Run 35psi for CX widths.

Except I ran 20psi in my tubeless set up on Sunday and it was brilliant(in the mornings I weight ~76.5kg, so not super light).

I don't think I've raced with 35psi in my tyres since my first race where I mistakenly put 50 in.

Mccrear

my usual is to start at 35 and lower throughout practice laps until I get the level. I *know* tubeless would prob give me 5/10 psi less and im certain I could go <25psi tubeless (69kg) buuuuttt need to be totally confident that no leakage and 25 will stay in. go under 20 and defo burp. who knew 5 psi would be so important!! such a reality check coming from road where going from 100+ to 80 was a revelation and "felt" slow!

joey54321

Mccrear wrote:

my usual is to start at 35 and lower throughout practice laps until I get the level. I *know* tubeless would prob give me 5/10 psi less and im certain I could go <25psi tubeless (69kg) buuuuttt need to be totally confident that no leakage and 25 will stay in. go under 20 and defo burp. who knew 5 psi would be so important!! such a reality check coming from road where going from 100+ to 80 was a revelation and "felt" slow!

I was a little unsure at 20, but I tried a practice lap at 25 and it was unrideable for me, lots of steep uphill sections (4 per lap) and with the heavy rain overnight they were super slippy. At 20 I could ride up each one during the race, though I did have to be a little careful with the roots during other parts of the course. It was pushing it and I 100% wouldn't have gone lower, but also no burping.

Has made me wonder if its time to invest in tubular wheels/tyres

Mccrear

tubs defo seem best re; PSI and even if you get it wrong its not gonna be terminal to your race/cause a crash. I would be tempted but the faff factor puts me off massively. not a chance id be able to do it the house without some SERIOUS grovelling given the smell of glue, and ive heard tape is good butnot sure if, like tubeless, do it wrong and it defeats the purpose as it wont work.

plenty to ponder! already looking forward to next season*!




*until first race of season when I remember im dreadful and the tyres, wheels, bike, shoes, gloves, skinsuit, helmet, glasses and brakes cant replace the fact im dreadful.

cycleclinic

Well I can run a 2.0" tyre at 20psi below that without an insert it squirms. So to avoid burping you need higher pressures. It that simple. The lower pressures may give more traction but it comes at a price. This is why cross is a horrid sport.

cycleclinic

Even tubs require more than 20 psi. I use 2.0" dugast MTB tubs and some geax MTB tubs and have pinch flatted both running low pressures.

Simply put all cross racers, to get up the impossible climbs, have to use pressure so low it brings complications. There is no magic bullet in this sport. Its a case of pick your compromise.

Its mostly the rim tyre interface though that causes burping. In know IRC tyres are a tighter fitting and that mean more secure. Even then I'd be reluctant to use them below 30psi. I hate sqirm.

joey54321

thecycleclinic wrote:

Well I can run a 2.0" tyre at 20psi below that without an insert it squirms. So to avoid burping you need higher pressures. It that simple. The lower pressures may give more traction but it comes at a price. This is why cross is a horrid sport.

wooooo! I have magic tyres!

thecycleclinic wrote:

Even tubs require more than 20 psi. I use 2.0" dugast MTB tubs and some geax MTB tubs and have pinch flatted both running low pressures.

Simply put all cross racers, to get up the impossible climbs, have to use pressure so low it brings complications. There is no magic bullet in this sport. Its a case of pick your compromise.

Its mostly the rim tyre interface though that causes burping. In know IRC tyres are a tighter fitting and that mean more secure. Even then I'd be reluctant to use them below 30psi. I hate sqirm.

Sounds like they are less secure if they can't be run under 30psi.

Mccrear

which makes some of the pro PSI figures all the more impressive. I suppose their technical skills, and knowledge of grip vs squirm, and relationship with sponsors makes it much more of a science than an art, but even so.

ill just leave this here... (11.5psi!!)
https://www.cxmagazine.com/bike-profile ... -nationals
"Limus mud treads run at 11.5psi mounted to her Knight Composite 35 Disc Tubular wheels with DT Swiss 240s hubs"

arturo_belano

Mccrear wrote:

which makes some of the pro PSI figures all the more impressive. I suppose their technical skills, and knowledge of grip vs squirm, and relationship with sponsors makes it much more of a science than an art, but even so.

ill just leave this here... (11.5psi!!)
https://www.cxmagazine.com/bike-profile ... -nationals
"Limus mud treads run at 11.5psi mounted to her Knight Composite 35 Disc Tubular wheels with DT Swiss 240s hubs"

You can easy run 20psi tubeless at your weight Mccrear, no problem. I race them 20 - 25 psi at 100 kg and they are fine - one issue I posted upthread caused by a dinged rim.

My tub wheelset is a bit battered so just weighing up whether to replace it for next season or go tubeless on both bikes (there's a heavily discounted giepemme set on planetx at the mo, as it goes). Think I will stick with the tubs as they ride a bit better in the heavy conditions. There's a short learning curve with glueing them properly (I've rolled a couple in my time) but once you know what a proper glue job looks like you're set.

Mccrear

but once you know what a proper glue job looks like you're set.

badum tish!

cycleclinic

It's not how secure they are. That actually depends on the rim the tyre are fitted too Mccear, I just hate squirm. If I feel it I also feel the bike moving about under me. I know one race on stans rims that used these tyres at 27 psi but stans rims lack any tyre retaining features (you would have though stans would know better however they dont) so burping is still possible.

Even with a tight tyre fit unless the rim can reatin the tyre without sealant and zero pressure and it requires real force to push it off the rim then burping can and will happen. Most "tubeless rims" on the market lack the feature in the rim necessary a few do. There is description of this on my website. It is to with the whats next to the channel in the rim. If that shelf is flat and horizontal do not use that rim with tubeless tyres for cross. they will burp.

arturo_belano

thecycleclinic wrote:

It's not how secure they are. That actually depends on the rim the tyre are fitted too Mccear, I just hate squirm. If I feel it I also feel the bike moving about under me. I know one race on stans rims that used these tyres at 27 psi but stans rims lack any tyre retaining features (you would have though stans would know better however they dont) so burping is still possible.

Even with a tight tyre fit unless the rim can reatin the tyre without sealant and zero pressure and it requires real force to push it off the rim then burping can and will happen. Most "tubeless rims" on the market lack the feature in the rim necessary a few do. There is description of this on my website. It is to with the whats next to the channel in the rim. If that shelf is flat and horizontal do not use that rim with tubeless tyres for cross. they will burp.

Tubeless will squirm less than tubulars, though thecycleclinic - the stiffer carcass (usually 150 tpi) stands up more in the corners. I don't like excessive squirm either, particularly the feeling of a tubular starting to fold in the corners - v noticeable on a chicaney descent, say, and actually prefer tubeless here. Need to be a bit careful with the pressure though - too much in the front on a heavy course and you're on your backside.