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Old 06-13-08, 09:37 AM   #1
BenRidin
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Rider Down on Mt. D

I'm approaching Juniper while descending down from the summit during the late Thursday afternoon. An ascending rider is waving his arms to warn me about something..."There's accident ahead...you need to go slow..."

Sure enough, as I approach the sweeping turn into Juniper, there is a rider down. He is on the side of the road, and he is with three other riders - one slowing descending traffic, another slowing ascending traffic and one by his side. He is in good hands. The ranger is on his way with lights and sirens.

I continue on towards the Junction where I u-turn to do another climb to the Summit. By now there is a helicopter circling and is landing. As I climb further up, San Ramon Fire and Rescue passes me on the steep little pitch.

I arrive to the scene as the helicopter flies with their new patient. I stop and talk w/ the ranger. He said the rider probably has a broken Clavicle. I remind him not to forget the riders bike. He goes and retrieves it. Upon inspection of the bike, we see that the front tire had a Sidewall Blowout. A rather large one too. This we summarize (using our best CSI TV education) is what did the rider in causing him to lose control and hit the road hard. Further inspection showed the wear and tear of the tires. I mean they looked old.

The lesson learned here is to inspect your tires. Which I did once I got to the summit. Mine were were fine, except for some string like strips coming off the sidewall in the rear. It might be nothing, but it didn't sit well in the back of my mind as I descended back down Northgate. Note to self: Get new tires today.

Eeepa! Do your inspections. Have a great w/e.

br
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Old 06-13-08, 09:52 AM   #2
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Originally Posted by BenRidin View Post
I'm approaching Juniper while descending down from the summit during the late Thursday afternoon. An ascending rider is waving his arms to warn me about something..."There's accident ahead...you need to go slow..."

Sure enough, as I approach the sweeping turn into Juniper, there is a rider down. He is on the side of the road, and he is with three other riders - one slowing descending traffic, another slowing ascending traffic and one by his side. He is in good hands. The ranger is on his way with lights and sirens.

I continue on towards the Junction where I u-turn to do another climb to the Summit. By now there is a helicopter circling and is landing. As I climb further up, San Ramon Fire and Rescue passes me on the steep little pitch.

I arrive to the scene as the helicopter flies with their new patient. I stop and talk w/ the ranger. He said the rider probably has a broken Clavicle. I remind him not to forget the riders bike. He goes and retrieves it. Upon inspection of the bike, we see that the front tire had a Sidewall Blowout. A rather large one too. This we summarize (using our best CSI TV education) is what did the rider in causing him to lose control and hit the road hard. Further inspection showed the wear and tear of the tires. I mean they looked old.

The lesson learned here is to inspect your tires. Which I did once I got to the summit. Mine were were fine, except for some string like strips coming off the sidewall in the rear. It might be nothing, but it didn't sit well in the back of my mind as I descended back down Northgate. Note to self: Get new tires today.

Eeepa! Do your inspections. Have a great w/e.

br
Good post -- hope the rider's OK. I've noticed very small strips had come off the sidewalls of my tires after only 2-300miles. It's easy to miss, but I don't think it's anything to worry about.
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Old 06-13-08, 10:12 AM   #3
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Front tire blowout - definitely a scary scenario. I'm glad you and the ranger did the investigation... otherwise it would probably have been written up as excessive speed and there would be a call for ticketing more cyclists (they never catch the really dangerous ones).

Those threads that come off the casing overlap are nothing to worry about. Rotten fibers in the side wall are a real warning sign.

I always caution people about heating up their rims on the descent, doesn't sound like this was the case here.

And a bike shop owner told me wholesale cost on new tires has gone way up (like 30%) so stock up now!
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Old 06-13-08, 10:22 AM   #4
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I always caution people about heating up their rims on the descent, doesn't sound like this was the case here.
Is this still a problem? I asked a friend about it when I got back into cycling and he said it's not an issue, and don't worry about it... ?

+1 to checking your tires. Before any long descent I check both my tires to make sure the pressure is where I expect it to be. Not a failsafe, but better than nothing.
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Old 06-13-08, 10:27 AM   #5
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Eeepa! Do your inspections. Have a great w/e.

br
As I SIT here, let's also be careful this w/e. Even the newest, true-ist and best tire can only handle so much cornering before it loses grip...
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Old 06-13-08, 10:54 AM   #6
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Is this still a problem?
Heck ya! If you drag your brakes instead of feathering them, the rims can get hotter than boiling temp for water - for heavier riders, and especially tandems, this effect is magnified. For sew-ups you can have glue melting problems, for clinchers you can have blow-off problems. It's happened to me ONCE and I learned my lesson... sounded like a gunshot and left a welt on my leg (back tire).

What really happens physically to make the tire blow off is an issue of some disagreement - there is some pressure increase due to the heat, there are some minor changes in material properties (tires, tubes, and rims) due to the heat, there is some expansion of metal... none of these really seem to be enough of a factor to cause the blowout... yet the blowoffs happen. The bead comes out of the rim and the tube explodes. Some conjecture that the problem is improper tire/tube seating in the first place and the blowoff would have happened anyway but the rim heat was the kicker.

The good news is the rims cool down pretty quickly too once you let off the brakes because there's not much mass to them and the wind takes the heat away. So use both brakes on the steep bits when you really need to, but control your speed the rest of the time by alternating front and back brakes so that they have a chance to cool down.

Last edited by DiabloScott; 06-13-08 at 10:57 AM.
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Old 06-13-08, 11:07 AM   #7
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And a bike shop owner told me wholesale cost on new tires has gone way up (like 30%) so stock up now!
Glad I just got a couple of pairs of new tires although they're not supposed to last for very many miles.
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Old 06-13-08, 11:29 AM   #8
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Bummer about the rider.

But now I have the excuse to go out and replace the tire that got cutup on Weds. (not sure what I hit, but the blowout happened with a bang - had to boot the tire).

JB
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Old 06-13-08, 11:38 AM   #9
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Is this still a problem?
Yep it is, especially for heavy riders or tandems. Since I have a tandem now, I researched about this a ton.

Basically all a brake does is convert your KE (.5mv^2) into heat energy via friction. The rims (or rotors for disc brakes) act as heat sinks to dissipate that heat (using the air/wind), so that they can convert more energy. When the rims get too hot, the braking efficiency suffers since the hot object isn't as effective at absorbing the heat. That's when you get brake fade. If the rims get even hotter, then your air pressure can rise enough to blow the tire beads off the rim. (PV = nRT when Temp goes up, so does Pressure).

Now, the new clincher tires/rims have very good beads/hooks to have a very secure tire to rims connection, so the frequency of brake related blowouts is more rare. Also, tall, thick, machined braking surfaces are better heat sinks, so both the heat carrying capacity and ability to dissipate heat are higher.

I have specially designed rims for my tandem that have a better bead hook, and a thicker braking surface.

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Old 06-13-08, 12:53 PM   #10
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Yikes! Timely reminder. I'm going to change out some older tires on my beater bike right now....
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Old 06-13-08, 01:07 PM   #11
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Yeah, my longtime rider buddy looked utterly confused when I asked about heat-related blowouts..

Initially I was more tentative on descents so I rode the brakes a bit much. My goal was to switch to shorter bursts of heavier breaking to control my speeds, primarily for handling reasons (to avoid braking in corners) but also out of lingering heat concerns. I also have a tendency to alternate front/rear just because it always seemed like a good idea to spread out my braking a bit when it's safe to do so.

Plus I carry more speed thru the corners now anyway, so less need for braking
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Old 06-13-08, 08:38 PM   #12
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Yep it is, especially for heavy riders or tandems. Since I have a tandem now, I researched about this a ton.

Basically all a brake does is convert your KE (.5mv^2) into heat energy via friction. The rims (or rotors for disc brakes) act as heat sinks to dissipate that heat (using the air/wind), so that they can convert more energy. When the rims get too hot, the braking efficiency suffers since the hot object isn't as effective at absorbing the heat. That's when you get brake fade. If the rims get even hotter, then your air pressure can rise enough to blow the tire beads off the rim. (PV = nRT when Temp goes up, so does Pressure).

Now, the new clincher tires/rims have very good beads/hooks to have a very secure tire to rims connection, so the frequency of brake related blowouts is more rare. Also, tall, thick, machined braking surfaces are better heat sinks, so both the heat carrying capacity and ability to dissipate heat are higher.

I have specially designed rims for my tandem that have a better bead hook, and a thicker braking surface.
Have you thought about getting a drum brake for the rear wheel? Takes load off the rims.
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Old 06-13-08, 10:05 PM   #13
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I was riding down Diablo last weekend, and I am a heavier rider, but thankfully I read up on proper descent technique and wasn't riding my brake. Seems like brakes are a double edged sword in many situations.
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Old 06-13-08, 10:21 PM   #14
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I was riding down Diablo last weekend, and I am a heavier rider, but thankfully I read up on proper descent technique and wasn't riding my brake. Seems like brakes are a double edged sword in many situations.
no, just long descents. There are about 3 in the area. More in Colorado.
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Old 06-13-08, 10:55 PM   #15
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Kind of OT:

This thread just got me thinking.. I notice the sidewall of my tires today and the little re-enforcement fibers are starting to fray and come off. I've never had a sidewall blowout, but I certainly wouldn't like to end up like the guy on diablo. How many miles do you guys generally put on your tires before you change them? I'm not looking for total specifics because there are too many variables, but on the average lets say?
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Old 06-13-08, 11:09 PM   #16
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How many miles do you guys generally put on your tires before you change them? I'm not looking for total specifics because there are too many variables, but on the average lets say?
Good Q, I was gonna ask the same but was afraid it was too vague a question. I'm used to how easy it is to figure out when to change MTB tires

Just a "normal" tire like you'd get on, say, a 2008 Trek... But you know, nothing like a super distance touring tire, nor an ultralight race tire.

I just hit 1k miles. Clearly that seems too early (and they're in great shape), but it got me wondering if 5k might be "getting up there".
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Old 06-14-08, 12:41 AM   #17
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Have you thought about getting a drum brake for the rear wheel? Takes load off the rims.
Our team is relatively lightweight, We have bombed down some longer descents. I don't use the brakes that much so that helps

I had the rear wheel fitted with a drum compatible hub, and the frame accepts the drum too, so our ride is ready for me to install one if we ever do loaded touring, etc, but for now I don't need a drum.
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Old 06-14-08, 06:48 AM   #18
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I wonder how modern aero rims with more metal figure in to this. Do my American classic wheels absorb more heat? Do they also, due to surface area, lose it faster?

Mr. Wizzard?
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Old 06-14-08, 09:55 AM   #19
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Our team is relatively lightweight, We have bombed down some longer descents. I don't use the brakes that much so that helps

I had the rear wheel fitted with a drum compatible hub, and the frame accepts the drum too, so our ride is ready for me to install one if we ever do loaded touring, etc, but for now I don't need a drum.
it is a vague question. I usually end up with so many cuts in the tread by the time I change then that the sidewall isn't an issue.

Front lasts longer than the back. Some tires are obviously more durable, but 1500 on the back and 2500 on the front is a "ballpark figure" that you can vary by 90% in either direction.
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Old 06-14-08, 06:19 PM   #20
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I wonder how modern aero rims with more metal figure in to this. Do my American classic wheels absorb more heat? Do they also, due to surface area, lose it faster?

Mr. Wizzard?
How much heat goes into your rims is a function of your stopping energy (weight, slope, speed); deep section rims won't get as hot (under the same conditions) and will disipate the heat faster.



Be careful anyway... k?

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Old 06-14-08, 10:18 PM   #21
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Wow. Thanks for the warning. I hope he's going to be okay. *goes checks tires on older bikes*
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Old 06-14-08, 10:27 PM   #22
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it is a vague question. I usually end up with so many cuts in the tread by the time I change then that the sidewall isn't an issue.

Front lasts longer than the back. Some tires are obviously more durable, but 1500 on the back and 2500 on the front is a "ballpark figure" that you can vary by 90% in either direction.
Tire brand does matter too - when I used Michelin Krylion Carbons, I'd get 4,000 out of the front tire easily, but might get 2,000 out of the back. With Conti GP4000's, I'm down to 2,000 up front, and feel lucky to get 1,000 miles out of the back. However, the Contis feel so much better that I'm willing to put up with it.

JB
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Old 06-15-08, 01:17 AM   #23
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How much heat goes into your rims is a function of your stopping energy (weight, slope, speed); deep section rims won't get as hot (under the same conditions) and will disipate the heat faster.



Be careful anyway... k?
Brakes generate a huge amount of heat, on any type of rolling vehicle. You should never "drag" the brakes on your car, motorcycle, or bicycle. Not only does it heat up the rim on bikes, but on all vehicles it can greatly reduce the effectiveness of your brakes. Nobody wants to be heading into a corner and find out too late that there's not quite enough braking power anymore.
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Old 06-15-08, 12:16 PM   #24
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Tire brand does matter too - when I used Michelin Krylion Carbons, I'd get 4,000 out of the front tire easily, but might get 2,000 out of the back. With Conti GP4000's, I'm down to 2,000 up front, and feel lucky to get 1,000 miles out of the back. However, the Contis feel so much better that I'm willing to put up with it.

JB
Wow - really? I get 2,000+ out of my rear GP 4000. The last one was still showing the tread wear dimples when I had to replace it due to a gash.

I get pretty good mileage out of the Pro Race 2's, as well. Similar to you, I will put up with low mileage tires if they ride well.
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Old 06-19-08, 05:20 PM   #25
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WHOA! I just found out I know the downed rider. He used to be the business unit manager for my office but he changed companies about a month ago.

Here's his story:

I was going down Diablo last Thursday evening just above the Juniper parking lot. Started to make a turn, hit a rock, front tire blew out, I went down. Broken collar bone, helmet broken in three places, and nice road rash up and down the left side. Free helicopter ride off the mountain and some great pain medication. A few sutures in the leg and new titanium plate put in on Tuesday to put the collar bone back together ( I now have titanium in both my foot and my shoulder which makes me pretty much an extension of my titanium bike).
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