Heat Build-up With Pacenti SL23 and Swiss Stop Flash Pro (Black)
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  1. #1
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    Heat Build-up With Pacenti SL23 and Swiss Stop Flash Pro (Black)

    OK, this one shocked me today. I was riding in 60 degree F weather with my new Pacenti SL23s. I was also using new Swiss Stop Flash Pro (black) pads. After doing a 10% descent with average braking, I ended up having a tube explode on me and throw the tire bead off the rim. I couldn't believe how hot the rim was. I could understand this maybe with carbon clinchers, but I've done this descent several times with different rims/pads and the brake surface rarely gets warm. This time it was HOT!

    I experimented some more on other descents and couldn't believe how hot the brake surface was, even more than I get with carbon clinchers. These seemed very odd to me.

    Any ideas? Is this an issue with Swiss Stop Flash Pros or brand new Pacenti rims? I'm tempted to swap to my old Shimano pads just to see if that makes a difference.

    Thanks!
    -Pete

  2. #2
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    Allenpg, I had noticed quite a lot of brake fade on a very long and fast descent on my Sl23 rims, while using the same brake pads as you. Mind you, I experienced the same thing on the same descent, using the same bike and pads, on a Mavic CXP33 rim the week before. Both days were much hotter than the temps you experienced. Have not had the tube explosion issue, however. What I have noticed is I tend to like braking a bit harder with the Swiss Stop pads than the Durace pads I used to use - not sure why I do this, and I then. It is because I am still testing to see how well they perform, as they seem to have less bite than the DA pads.

  3. #3
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    I suspect a tubed pinched between the rim and tire bead.
    ... 'cuz that's how I roll.

  4. #4
    wheelbuilder
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    The Pacenti rim is still aluminum just like other alloy rims. The same alloy is used by other companies as well. I'm no metallurgist, but I don't think the minor differences in the alloys used in bicycle rims are enough to change the heat dissipation properties much. Brake pads on the other hand vary greatly in compound and I imagine would more likely be the cause. That's just my first impression.

  5. #5
    changingleaf
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    I also suspect that the tube was either faulty or was pinched between the tire and the rim on initial installation. The Pacenti rim is similar alloy to most aluminum rims.

  6. #6
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    This happened to a friend while we were descending a very steep grade about 20%.
    She had Dura Ace wheels and the braking surface was worn down and very thin.
    The force of the tube blowing actually bent the rim.
    Aluminum is a good heat conductor but it needs to be thick enough to conduct the heat. I suspect the thin brake surface had something to do with the tube overheating. Pacenti rims have quite a large surface area which will help to dissipate the heat, but due to the light weight this might be negated by the use of thinner walls, it could be analyzed with the right tools but I don't know how to do it. In any case I would think they are no worse than other aluminum rims as far as heat dissipation goes. I have the same rims and same brake pads, I will see hot they get after a steep descent.

  7. #7
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    Thanks for the insights. I know it wasn't a pinched tube, since I had just installed it the day before and double-checked to make sure the tube wasn't pinched. My hunch is that it's the brake pads.

    My wife was on the same descent as me and braked more than I did. She was using Kinlin rims with Shimano pads and the brake surface was barely warm. While I'm heavier, she rides the brakes more than me...

  8. #8
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    Quote Originally Posted by allenpg View Post
    Thanks for the insights. I know it wasn't a pinched tube, since I had just installed it the day before and double-checked to make sure the tube wasn't pinched. My hunch is that it's the brake pads.

    My wife was on the same descent as me and braked more than I did. She was using Kinlin rims with Shimano pads and the brake surface was barely warm. While I'm heavier, she rides the brakes more than me...
    I kind of doubt it was the pads. Those are their "rim friendly" model. But regardless of that heat comes from friction and I think you are going to apply the same amount of friction regardless of which pad you use. you'll just squeeze harder or softer to adjust for differences in brake pads to slow down the same amount (meaning the same friction was applied). I'm kind of guessing here but that would seem to be the case to me.

  9. #9
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    I've measured the wall thickness of the brake track on the Pacenti rims and they are in line with everyone else. I would change the pads and try it again.

  10. #10
    woz
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    I'd say it was just a bad coincidence and that the heat actually didn't have anything to do with the blowout. Unless the rim was so hot that it physically melted the tube. I have seen warnings against using latex tubes in carbon because of high temperatures causing melting, but never have I seen a warning for butyl tubes. And of course we're talking about alloy rims which dissipate heat better than carbon.

    Two years ago I got to spend some time at the Enve facility in Utah and got to play with the different testing equipment. One of the machines they have applies the brakes and then spins the wheel with the brake applied measuring the heat buildup as well as air pressure changes in the tube. The test ran wheels at a 600 watt continuous brake load for 3 minutes. (they chose that number because it was beyond the point where quite a few carbon rims failed from heat). What I found interesting was that the biggest change they ever recorded in PSI from heat during the test was a gain of 12psi. Without some added circumstance, not enough to explode a tube.

  11. #11
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    A tube failing in a tire won't blow the tire off. It'll just go flat. A tube's job is the same as tape and sealant in a tubeless setup, to prevent the air getting out. The force of the pressure is supported by the tire and rim, not the tube. A tube failing is like the tape or sealant failing in a tubeless tire. It goes flat. However:

    If the tube is trapped between the bead and rim, when it fails at that point it can let the high pressure get between the bead and rim unhooking the bead from the rim which is what causes the bead to blow off the rim.
    Last edited by looigi; 01-14-2014 at 06:55 AM.
    ... 'cuz that's how I roll.

  12. #12
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    Quote Originally Posted by Jay Strongbow View Post
    I kind of doubt it was the pads. Those are their "rim friendly" model. But regardless of that heat comes from friction and I think you are going to apply the same amount of friction regardless of which pad you use. you'll just squeeze harder or softer to adjust for differences in brake pads to slow down the same amount (meaning the same friction was applied). I'm kind of guessing here but that would seem to be the case to me.
    Maybe the OP got a bad patch from the factory? I know it's rare but it happens...

  13. #13
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    What brand tire/size and pressure were you running?
    Last edited by mikerp; 01-15-2014 at 03:49 AM.

  14. #14
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    Quote Originally Posted by looigi View Post
    A tube failing in a tire won't blow the tire off. It'll just go flat. A tube's job is the same as tape and sealant in a tubeless setup, to prevent the air getting out. The force of the pressure is supported by the tire and rim, not the tube. A tube failing is like the tape or sealant failing in a tubeless tire. It goes flat. However:

    If the tube is trapped between the bead and rim, when it fails at that point it can let the high pressure get between the bead and rim unhooking the bead from the rim which is what causes the bead to blow off the rim.
    This.

    These rims are about the hardest rim I have had to get a tire on or off also. The bead isn't going to just slip on these rims. The installation of the tire/tube was wrong. I have pinched a bunch of tubes on these rims before. I now use latex tubes which are pink and easy to see which makes it easy to see exactly where the tube is.
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  15. #15
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    Quote Originally Posted by jmorgan View Post
    This.

    These rims are about the hardest rim I have had to get a tire on or off also. The bead isn't going to just slip on these rims. The installation of the tire/tube was wrong. I have pinched a bunch of tubes on these rims before. I now use latex tubes which are pink and easy to see which makes it easy to see exactly where the tube is.
    I tend to agree. I can see how it would, in what some see as a battle to get the tyre on these rims, a tube might be pinched. There is also a need to make sure the bead snaps in to place, so some care is needed when using a cO2 canister. That said, I have not found the Pacenti rimes to be too difficult - just need to work at it. I have never had to use levers to get a tyre on or off my Pacentis, and the only tyres I have put on it have been brand new. Mind you, those same tyres slip very easily on to my CXP33s and Open Pros...

  16. #16
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    Here's a pretty good blog post about rim differences and how they affect tire mountability. I don't know if this has anything in common with your issue but it's worth looking into.

    Mounting Tires on Rims with Deep Wells | Off The Beaten Path
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  17. #17
    changingleaf
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    The blog post does show some nice images of the differences that rims can have, but when the writer uses the phrase "overly deep wells" "makes mounting tires difficult" he means it makes "seating" tires difficult. Even that is not exactly true because tires can be difficult to seat with shallow wells. If the bead seat is significantly larger than the tire bead like you will find on many "tubeless-ready" rims then it will require higher inflation and/or manipulation of the tire to get the bead to ramp-up into the bead seat. Also, "overly deep wells" can mean overly high sidewalls. So, if the sidewall were reduced then the tire would mount easier. So, given the same outer rim width a rim with a deeper well will allow easier tire mounting.

    There are many other inner rim shapes that were not shown in the blog, including "tubeless ready" designed rims that have a narrow inner well and horizontal bead seats, like Velocity A23, Pacenti SL23, Stan's Alpha 340's.

    Also, the tires out there vary quite a bit in bead diameter and bead strength. Basically the standard of 622mm bead diameter for 700c rims and tires is pretty loose. The tubeless tire and rim standard seems to vary the least, but these rims are designed to (or attempted to be designed to) fit both tubeless and tube-type tires, which doesn't always work that well.

    It would be nice if the tire and rim manufacturers would rewrite the standard for better compatibility and less confusion, but on the other hand it could stifle innovation.

    You can see from the image here that the Pacenti has a shallow center channel which makes tire "mounting" more difficult.
    Attached Images Attached Images
    Last edited by changingleaf; 01-15-2014 at 06:46 AM. Reason: add info

  18. #18
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    Quote Originally Posted by ergott View Post
    The Pacenti rim is still aluminum just like other alloy rims. The same alloy is used by other companies as well.
    True. . . 6061-T6 with thermal conductivity of 167 W/mK. No voodoo in 6061-T6 with Pacenti and most other manufacturers use. . HED does use some Scandium alloy though in the (rear?) C2.

  19. #19
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    Quote Originally Posted by allenpg View Post
    Thanks for the insights. I know it wasn't a pinched tube, since I had just installed it the day before and double-checked to make sure the tube wasn't pinched. My hunch is that it's the brake pads.

    My wife was on the same descent as me and braked more than I did. She was using Kinlin rims with Shimano pads and the brake surface was barely warm. While I'm heavier, she rides the brakes more than me...
    As others have posted it pretty much had to be pinched between the rim and tire. If the the "exploded" that meant it had to have someplace to expand. If the tire stayed on the rim, there would be no "bang". Since your tire was blown off the rim, and we know that heat can only raise tire pressure by a small amount, we can say that heat wasn't the issue.
    You may think the tire wasn't caught between the tire and rim, but the way you flatted says otherwise. The difference in heat (energy) between you and your wife is due to one thing: the weight difference between you. Also the Shimano pads may not hold heat like the SwissStop pads.
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