Catastrophic Blow-out

[Sparky731]

Catastrophic blow-out. Those were the first words my Trek Tech said as he eyed my rear tire when I carried my bike into the Trek shop where I bought my Allant 7s.

No injuries or damage, other than the tire. I was on clear asphalt path going <10 mph next to my wife when we thought we heard a shotgun blast.

The tubeless tire spewed sealant all over the back of the bike.

I carry a flat repair kit, but nothing I had would fix that tire, or get it back on the rim.

Long story short, the Tech explained that my fav. tyres — PanaRacer GravelKings, are not an ebike rated tyre and susceptible to such blowout on an ebike due to increased twisting torque on the sidewalls vs. acoustic pedaling.

The theory is the less-rigid sidewall can unnaturally bend and pop over the rim — which appears to be what happened to a visibly stretched/buldged couple of linear inches of abnormal shape of the sidewall and bead. We could detect no particular failure or rupture in the tire or sidewall, but we did not dissect the rubber casing.

The blow-out tire had ~600 miles but I have ridden 6K miles on 2 sets (3K each) of GravelKings without so much as a flat tire. I always loved them until it blew.

Now convinced by the Tech that it would be much more catastrophic for me if the front tire blew, he sold me 2 new Schwable Super Moto X tires and tubes since the new tires are not tubeless. 27.5 x 2.40 . 650B.

I rode the new tyres home and they feel good.

Trek’s charge for 2 tyres, 2 tubes, and to swap/mount all, clean, inflate and flight inspect my ride, was less than my Local Bike Shop charged me for one Gravelking and mounting last Fall.

Ride long, ride strong.

 

[mschwett]

Catastrophic blow-out. Those were the first words my Trek Tech said as he eyed my rear tire when I carried my bike into the Trek shop where I bought my Allant 7s.

No injuries or damage, other than the tire. I was on clear asphalt path going <10 mph next to my wife when we thought we heard a shotgun blast.

The tubeless tire spewed sealant all over the back of the bike.

I carry a flat repair kit, but nothing I had would fix that tire, or get it back on the rim.

Long story short, the Tech explained that my fav. tyres — PanaRacer GravelKings, are not an ebike rated tyre and susceptible to such blowout on an ebike due to increased twisting torque on the sidewalls vs. acoustic pedaling.

The theory is the less-rigid sidewall can unnaturally bend and pop over the rim — which appears to be what happened to a visibly stretched/buldged couple of linear inches of abnormal shape of the sidewall and bead. We could detect no particular failure or rupture in the tire or sidewall, but we did not dissect the rubber casing.

The blow-out tire had ~600 miles but I have ridden 6K miles on 2 sets (3K each) of GravelKings without so much as a flat tire. I always loved them until it blew.

Now convinced by the Tech that it would be much more catastrophic for me if the front tire blew, he sold me 2 new Schwable Super Moto X tires and tubes since the new tires are not tubeless. 27.5 x 2.40 . 650B.

I rode the new tyres home and they feel good.

Trek’s charge for 2 tyres, 2 tubes, and to swap/mount all, clean, inflate and flight inspect my ride, was less than my Local Bike Shop charged me for one Gravelking and mounting last Fall.

Ride long, ride strong.

interesting explanation, seems very unlikely. those tires are used off road by very strong riders, who surely put them under MUCH more rotational stress than you were exerting at 10mph on pavement on a stock Allant. with one of those e-motorcycle bafang motors, maybe!

 

[fooferdoggie]

Had the front blowout on our tandem. I bought what I thought was the tubeless version of the Schwable tire and it was fine on a fatter rim. put it on a more normal size rim and it blew off 100 feet from our house. For the most part besides weight, e-bikes are not going to put that much stress on a tire unless you're going crazy.

 

[Sparky731]

Had the front blowout on our tandem. I bought what I thought was the tubeless version of the Schwable tire and it was fine on a fatter rim. put it on a more normal size rim and it blew off 100 feet from our house. For the most part besides weight, e-bikes are not going to put that much stress on a tire unless you're going crazy.

I stress the tires to the max daily. I am a sprinter and start and ride as fast as my bike will start and go. My Trek Techs tell me I ride my bike too hard but the Bosch Sport motor has not failed me in 9K+ miles. I replace mechanical drive train parts frequently as needed.

 

[Stefan Mikes]

interesting explanation, seems very unlikely. those tires are used off road by very strong riders, who surely put them under MUCH more rotational stress than you were exerting at 10mph on pavement on a stock Allant. with one of those e-motorcycle bafang motors, maybe!

The riders you mention are lightweight people riding lightweight bikes

 

[indianajo]

I bought a panaracer firexpro when modernbike.com was out of 26x2.1" knobby kendas. I agree the sidewall is floppy. The first time I installed it the bead slipped off the rim and the tube blew out in 10 miles. The advantage of this tire, it will fold flat and I can carry a spare in the pannier. After 3 years in the bag I installed it last winter because the rubber was getting old. I have about 1000 miles on it.
The roll-up Schwinn tires were absolute garbage. I could never get any of those to stay on the rim. I donated several tubes to that failed experiment. The diamondback rim I was riding may have been undersized. I had trouble with kenda tires slipping off that rim too.

 

[mschwett]

The riders you mention are lightweight people riding lightweight bikes

the trek shop claim was "increased twisting torque on the sidewalls" which is affected by acceleration, not weight!

 

[Stefan Mikes]

Does acceleration depend on mass?
Or, is it irrelevant here?

 

[PCeBiker]

Does acceleration depend on mass?
Or, is it irrelevant here?

It's the power or torque at the wheel that counts.
As far as I know a human can put about 250 Watts into the drivetrain.
A motor can easily put out 4 times that power added to what the rider is putting out.

I remember dirtbikes that had so much power/torque that the tires would spin on the rims and had to be clamped to the rim.

 

[PCeBiker]

Does acceleration depend on mass?

Yes.
A three hundred pound rider will not accelerate as fast as a hundred pound rider, but the torque or power to the ground will be the same for each rider.

 

[PCeBiker]

,.. he sold me 2 new Schwable Super Moto X tires and tubes since the new tires are not tubeless. 27.5 x 2.40 . 650B.

I have a set of 27.5 x 2.8 Schwable Super Moto X tires on my e-bike and I got a flat yesterday.

As the tire was going flat I could see the stretched/buldged couple of linear inches of abnormal shape of the sidewall as the tire rolled around almost flat. (I stopped 4 times to fill the tire to make it home without riding on the rim.)

I was surprised at how thin the sidewalls are, and that's on a "Moped" rated tire.

 

[Sparky731]

I have a set of 27.5 x 2.8 Schwable Super Moto X tires on my e-bike and I got a flat yesterday.

As the tire was going flat I could see the stretched/buldged couple of linear inches of abnormal shape of the sidewall as the tire rolled around almost flat. (I stopped 4 times to fill the tire to make it home without riding on the rim.)

I was surprised at how thin the sidewalls are, and that's on a "Moped" rated tire.

Now you are causing me concern re: my new Moto-Tires.
everything I read indicated e-bike rated per the rigid sidewalls.

My peeve is more tubed vs. tubeless. You may well have made it home with tubeless and sealant.

 

[PCeBiker]

Now you are causing me concern re: my new Moto-Tires.
everything I read indicated e-bike rated per the rigid sidewalls.

My peeve is more tubed vs. tubeless. You may well have made it home with tubeless and sealant.

As it turned out, my rim tape had slipped and the edge of the spoke hole cut the tube.

So it wasn't a tube or tire failure.
I'm going to glue the rim tape in place or use Gorilla Tape to replace it.

I had flat-out with me when I got the flat, so I put about 10 ounces in the tube and couldn't figure out why it wasn't working and why I couldn't see the flat-out leaking out.

There wasn't a drop of flat-out anywhere. It all stayed in the tube.
It couldn't find it's way to that part of the tube.

 

[mschwett]

It's the power or torque at the wheel that counts.
As far as I know a human can put about 250 Watts into the drivetrain.
A motor can easily put out 4 times that power added to what the rider is putting out.

I remember dirtbikes that had so much power/torque that the tires would spin on the rims and had to be clamped to the rim.

a strong-ish human can easily put out 1,000 watts for a brief instant and several hundred for a couple minutes. a 200lb person standing with one foot on a pedal produces over 100 lb-ft of torque. while the motor can put out much higher sustained power for a few hours, even a tire designed for use by acoustic bikes still needs to resist similar short-term loads. braking forces, of course, can be absolutely enormous compared to accelerating forces. a 250lb rider+bike combo decelerating from 45mph on a steep downhill is putting way more strain on the tire than any kind of acceleration every could, to the point that you can easily break traction between the rubber and the road. can even the most powerful rider or ebike do that accelerating on paved ground?

the explanation does not hold water to me given the relatively modest usage of the e-bike in question, especially compared to the beating some very strong riders give similar tires for thousands of miles. there are other failure modes where the weight of the bicycle (which is what flexes the sidewall rather than twisting it) is a completely believable explanation for an e-bike, especially a heavily loaded one, killing a tire. but not the one described above, IMO.

 

[mschwett]

Does acceleration depend on mass?
Or, is it irrelevant here?

f=ma

the more massive object accelerates slower with the same force, or requires more force to accelerate at the same speed. either way the force is the force, and of course the tire doesn't care whether it comes from a human, a motor, or gravity (braking force downhill, which is more than any of the other forces!)

 

[PCeBiker]

interesting explanation, seems very unlikely. those tires are used off road by very strong riders, who surely put them under MUCH more rotational stress than you were exerting at 10mph on pavement on a stock Allant. with one of those e-motorcycle bafang motors, maybe!

What do you suppose would be a good explanation?
Maybe just a bad tire?

The blow-out tire had ~600 miles but I have ridden 6K miles on 2 sets (3K each) of GravelKings without so much as a flat tire. I always loved them until it blew.

 

[mschwett]

What do you suppose would be a good explanation?
Maybe just a bad tire?

just a bad tire, or perhaps a bit of a wrinkle or twist or kink in the mounting that weakened it temporarily or permanently in one spot? perhaps a bad batch or subtle design flaw, check out this recent review from the panaracer site - not an ebike rider -

Had a custom titanium gravel bike built in 2023. The bike was built with Enve SES wheels with Panaracer gravel king tires (32). After approximately 1000 miles the sidewall of the rear tire seemed to have given out causing a bulge to develop preventing the tire from turning properly. Unknown what caused the sidewall to give out.

what size gravelkings and what pressure were you riding?

 

[BlackHand]

the explanation does not hold water to me given the relatively modest usage of the e-bike in question, especially compared to the beating some very strong riders give similar tires for thousands of miles. there are other failure modes where the weight of the bicycle (which is what flexes the sidewall rather than twisting it) is a completely believable explanation for an e-bike, especially a heavily loaded one, killing a tire. but not the one described above, IMO.

Agreed. But if an ebike rider comes in with such a failure and the tech knows this rider has a class 3 bike and rides in Turbo mode basically all the time, then the tech would pretty much be negligent not to recommend a tire that the mfgr rates for such usage. Definitely more of a justification for switching to the heavier duty tire than an explanation though.

Or maybe the tech had vague memories of reading about the controversy from the tire that blew off a rim in the UAE Tour this past spring.

Pretty good, albeit tangential to Sparky731's situation, info in this piece.

UAE Tour and Tubeless: What is Safe?

If you are following bike racing and/or tech, you will have heard of Thomas De Gendt's mysterious crash during Stage 5 of the UAE Tour in Abu Dhabi. Video footage shows the front wheel of the Belgian breakaway specialist jerking to the right before he falls.…

www.renehersecycles.com

 

[indianajo]

What do you suppose would be a good explanation?
Maybe just a bad tire?

The Panaracer fold flat tires do not seat deep in the rim automatically. I have just changed rims because the hub motor wore out. I have seated the panaracer tire twice and it still has a patch of inner wall sticking out of the rim. WIll let out air and try again this afternoon. I think the rim tape is interfering with it. I tried to push the tire down inside the rim last time and it would not go.
The advantage of fold flat tire, I can carry one at all times. Last time I ripped a tire sidewall I had to push bike & 40 lb groceries 7 miles to summer camp where I had a spare tire. Push up 25 hills and it was 96 F that day.

 

[Stefan Mikes]

f=ma

the more massive object accelerates slower with the same force, or requires more force to accelerate at the same speed. either way the force is the force, and of course the tire doesn't care whether it comes from a human, a motor, or gravity (braking force downhill, which is more than any of the other forces!)

It might help to know Sparky always rides his e-bike in Turbo mode Yes, he has a high acceleration!

Once, I was thinking perhaps I would try my luck and go tubeless with my full power Vado. Then I decided keeping the powerful e-bike with the tubed setup would be reasonable. I'm interested how long would my Pathfinder Pro 47-622 hold (these are basically made for the tubeless setup).