CRSturdivant

So I just got my new red/black 700x23c gp4000 tires in the mail today and I immediately put them on my bike. I looked at the pressure recommendation which said I should run them at 120psi. I am used to my previous pressure of up to 155-160 with my old fortezza se's. I pumped both the front and back up to 140ish psi and started making some lunch. About 20 minutes after inflating the tires I heard a loud bang only to discover that the rear tire blew off the rim ripping my tube to shreds. I changed the tube and lowered the pressure to 115 in both the front and rear and now I am afraid of riding them because I don't want to die coming down a hill pushing 40mph. I noticed when I changed the tube in the rear that there was a slight thread coming off the lowest point of the sidewall where the tire came off the rim. Am I safe to ride on these tires? I have read some reviews and some people said they had some issues with the tire blowing off the rim while riding, does that mean that they were running too high of a tire pressure? Is the pressure rating on these tires very strict? Thanks for the help in advance guys!!!

blacksquid

Hmmm, I've been riding Continentals (GP4000s, Attack/Force) for a while but never at anything over 115psi. Tires have never blown off the rims. Just stay at or below recommended pressure and you should be fine.

The stray thread seems to be normal and doesn't affect the tires any.

ehidle

Chances are that you did not mount the tire properly and that is why it blew off the rim. You also need to observe the maximum pressure rating of the rim in addition to the maximum pressure rating of the tire and make sure you are below the lower of the two.

onRoffR

the lowest part of the sidewall is the bead. if that has any fraying or distortion I would not use the tire. You may be able to get this replaced by Conti, I would not mention the PSI issue. This may have failed due to the amount of over Inflation that occurred. You should never exceed the max Inflation Number. That and the bead not being set under the clincher lip of the rim would both be reasons for a tire blowing off the rim, this is not a normal occurrence. If the tire is installed properly it is unlikely to happen. Your more likely to take something sharp through the tread causing a blowout.

Bob Dopolina 

The lowest point of the tire?

You are talking about the chafer strip. It wraps around the section of the tire where the bead is molded inside of.

These things tend to loose threads on occasion. DON'T PULL it off. Cut it. It's like a loose thread from the sweater grandma made you for Christmas.

At to pressure, Conti tires are fully capable of handling 1.5x their rated pressure. This is a fact, not conjecture.

BTW, what are you doing riding at 150psi? Only tubs on the track function well at those pressures. Try 120-125 psi for the tires you have. They will be faster AND more comfortable.

FIVE ONE SIX

i've ridden 700x23 GP4000's for over 2 years, and i've never ridden them over 110 psi, and right now i'm 204 pounds and have hit 40mph on some downhills and never felt that my tire pressure would be a problem...

i run 100psi in the front, and 110 psi in the rear, and last year when i was 189 pounds i was running the rear at 105psi and never had a problem either...

i've personally gotten more flats from over inflation than from anything on the road...

Skewer

I weigh 150 lbs and believe that I get the best performance out of my 700*25 4000 on the rear at around 100 lbs psi and the best performance out of my 700*23 4000 on the front also at around 100 psi. If I had a 700*23 4000 on the rear, I would run it at about 110 psi. These are my starting pressures for all day long rides. I often knock another four or five psi off for one or two hour rides. When I say performance, I mean a combination of smoothness, cornering/handling, and overall speed. There may be good arguments to go higher psi than than I do on the Conti 4000, up to 120 psi for example, but at 140 psi, I believe your ride quality very likely deteriorates for all three of the categories above---smoothness, cornering/handling and speed. At the really high pressure, 140 psi, I believe you very likely have inefficient contact patches with the ground.

MAK

I'm +/-235 lbs and have been running my 4000s tires at 120 lbs and have had no problems. I may try experimenting with a bit lower pressures to see how the ride changes. My problem is that I went from 25c Armadillos to the 23c Contis so they were bound to feel smoother and more comfortable.

MadeInItaly

Try a 25mm rear GP4000 and a 23mm front. I was introduced to it and love the combo.

Skewer

Here is a general tire pressure table that Psimet shared earlier in his Tip of the Day thread. I generally run a bit higher pressure than the table, but have no evidence that it is any better than running at the pressures in the table. Probably the pressures in the table are better!! It is just hard to overcome the old habit of wanting to fill the tires up.

<<Proper inflation is the easiet way to avoid flats.

Tire Width=20: Pressure(psi) = (0.33 * Rider Weight in lbs) + 63.33
Tire Width=23: Pressure(psi) = (0.33 * Rider Weight in lbs) + 53.33
Tire Width=25: Pressure(psi) = (0.33 * Rider Weight in lbs) + 43.33
Tire Width=28: Pressure(psi) = (0.33 * Rider Weight in lbs) + 33.33

Tire Width=32: Pressure(psi) = (0.17 * Rider Weight in lbs) + 41.67
Tire Width=37: Pressure(psi) = (0.17 * Rider Weight in lbs) + 26.67


Example: You are 150lbs running 28's

Pressure (psi) = (0.33*150) +33.33 = 82.83psi (rear)
Front Pressure = .9*Rear Pressure = .9*82.83psi = 74.55psi front >>

Fox Farm

Unless you are riding on glass smooth roads, why would you pump up your tires to 150psi? All you will get is a pretty harsh ride! I run 110psi or so.

Szczuldo

yeah, sorry to tell you but at 140psi you aren't doing yourself, your tires or your safety anything good. You are more likely to get a blowout and as you found out it can cause the tire to fall off the rim, which would be due to installation error. 120psi is plenty, 110-115 is what i run at.

merlinextraligh

To about a 99% certainty. Take a look at the rim, and make sure there are no irregularities just to be sure.

The events you describe are a classic result of getting just a little bit of innertube sticking out between the rim and the tire.

Molto Lento

I regularly blow tires off of rims but they are other rider's rims! Zoom!

CRSturdivant

Thanks for everyone's help I really appreciate it. The reason I run such a high psi is because I like to feel everything on the road (preference I guess). I checked and rechecked the bead and it doesn't appear to be irregular in any way, but when I went to mount the tire after checking it, one side of the tire slides right onto the rim with no pry tool, and the other side definitely needs one. normal?