DaveLeeNC

I was out on a normal ride today and had a flat. I weigh 160 lbs and am riding Conti GP 5000 (23mm) clincher tires that measure 25mm. I am pushing limits on tire pressure and riding at 80 pounds in the rear.

I had ridden about 10 miles and the last 1.5 miles was on the absolutely smoothest asphalt in the tri-county area (just put down about a month ago). I suddenly noticed some vibration from the rear (20 mph maybe) and looked down at the pavement to see if it was suddenly a bit rough and it was not. So I pulled off and I had a flat. I changed that out and just rode home (don't like riding without a spare and didn't feel like finding/patching a tube on the road).

When I got home I found a 'kind of snake bite pattern' in the Bontrager tube that is only a few months old. Here is the picture.



The first slash in the tire is clear. The second one didn't come out of the picture so I drew it in as the small red line. The two slashes are 5mm apart and roughly in the area where the tube would meet the bead of the wheel (and about 180 degrees from the tube stem).

I had not hit anything remotely rough on this ride and the previous 5 or so minutes had been on the smoothest pavement around here. I have checked the rim insides in that area and I guess that I need to take the tire completely off and give the inside a good scrubbing/inspection. But thoughts on what this is. I have never had a snake bit flat, but this is not exactly what I thought that one would look like. It clearly was not made by each side of the rim bead smashing against the tube.

Thanks.

dave

redlude97

Yea probabaly. You dont always get snakebites on both sides if you dont hit a object squarely. Say you hit a rock on one sidewall only it can compress and deflect that side alone. More likely to happen when the tire is deflecting when the bike is leaned over

DaveLeeNC

Thanks for the response. That makes sense but (to me) is inconsistent with both the angles of the slashes and the fact that there are two of them 5 mm apart. Then again - it isn't like I have an answer that is better.

dave

ThermionicScott 

Looks like it. The temptation on BF is always to scold people for not pumping their tires high enough, but in many cases, it's likely they had a slow leak that made it easier for a snakebite to happen.

Another thought: did you use any tire levers to finish installing the tire? You mentioned that it happened about 180 degrees from the valve.

DaveLeeNC

There have been times that I have had to use tire levers to install a tire. I don't think that this is the case with the particular tire/tube, but I cannot be certain of that. I am pretty cautious when forced to do that. My 70 year old, somewhat arthritic hands simply cannot (sometimes) manage otherwise. But I just don't see how that particular pattern would come from impact with the rim. And given my aggressive choice of tire pressures, I air up/check my tires before every ride.

dave

redlude97

More common with MTBs but still possible with road tires if there is enough rollover which is more likely with low pressures

seypat

Did you see a snake in the area? I also see only 1 fang mark.

DaveLeeNC

The 2nd cut did not show up in the pic. I drew it in as the small red line. Dave

DaveLeeNC

Well, I found the problem. First I watched the TdF that we had recorded. Fortunately for me my wife has become something of a pro cycling fan - she has more opinions about this than the typical BF poster . I took the tire off, carefully cleaned out the insides (nothing there) then carefully inspected the outside. At or just below where the sidewall starts, were two relatively sharp gashes that exactly match the gashes in the tire. Obviously I hit something pretty sharp, didn't notice (or didn't remember) it, and it forced the tire against the inside of the rim wall. And the rest is history. I doubt that another 10 psi would have mattered. And another tire bites the dust.

Thanks for all the comments/help.

dave

OldTryGuy

Bet +20psi might have prevented it.

berner

I am surprised your tire bottomed out at 80 PSI. I am about the same weight and pump up my tires, 28mm, to 60 PSI or slightly over and don't get snake bites. There is the possibility that your air pressure was low to begin with. Before going to 28mm tires I used 25mm pumped up to 70 PSI.

DaveLeeNC

If you believe that 'standard' recommended psi vs. wheel load chart generated long ago, (e.g., https://i.stack.imgur.com/9RFfR.png ) and you assume that my spec'ed 23 mm tires are about 2 mm less wide than your (spec'ed) 25 mm tires, 70 psi at 25 mm is probably a tad 'safer' than is 80 psi at 23 mm.

dave

GreenAnvil

At 160# 80psi seems to be plenty, but it depends on what you hit and at what speed, and if you had your full weight on the saddle at the moment of impact. Stuff happens.