the psi rating on sidewalls?

[Ks45672]

I have a cheap mtb for recreation and I checked the sidewall for psi and it said 40-65psi

 

I put 50 in the front and it seemed fine, but the rear exploded off the rim in a gas station between 40 and 50psi and scared the shit out of everyone, especially me

 

I tested the air pump itself and its accurate with a digital tyre pressure gauge so it's not the pump that was displaying  inaccurate pressure 

 

I'd like to put 65psi in both for  road use but I don't want another explosion so I'm currently  rolling at 30psi until I can pinpoint the issue 

 

I checked the rim tape and it seems fine with no protruding spokes and replacement tube from bike City seems fine, wheel is still true and didn't seem to suffer from the blowout

 

Tyres are budget Chinese  "csi jack rabbit " and they're  26" x 1.95" wide with generic tubes 

 

Should I invest in better tubes/tyres to run 65psi or was it probably just a dodgy tube that blew the first time? 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[el jefe]

You probably didn't have the tube seated in the tire properly if it blew at less than 50 psi and the same thing did not happen with another tube.

[StreetCowboy]

Is the tyre damaged?  If the tyre is not damaged, then I don't think the problem is the tyre.  And the tubes should not care about the pressure, so long as they are inside the tyre.

 

Possibly you had the tube nicked underneath the rim of the tyre; that happened to me, and the tyre burst 1 km from home.  At least it wasn't too long a walk back (that was before the arthritis really got me down...).

 

I always put a little bit of air into the tube before I put it into the tyre, just to stop it getting twisted.  Then I put a few psi in to seat the tube properly in the tyre before seating the tyre beads in the rim, checking that I can pinch the tyre beads together underneath the tube all the way round, before pumping up to target pressure.

 

I don't know what is the limiting aspect of the tyre with respect to pressure.  Maybe the pressure at which the beads will start to stretch and there is a risk of the tyre rolling off the wheel on sharp curves? Or maybe the side walls will start to stretch and the threading start to fail?  Neither of these woudl cause the tube to burst, but would make the tyre unsafe.  So based on that speculation, I think the problem with over-pressuring your tyres will not be that the tubes will burst, but the risk of an accident while out on the road.

 

SC

 

[n210mp]

You may find this video helpful

 

if you wish to get to the relevant bit it starts at 5 minutes:

 

 

 

[bobfish]

Above ideas probably valid, but 65psi in a 26x1.95 is waaay too much. As you say, a cheap quality tyre/rim combo, so your experience is not really surprising. 

Depending on your weight, I'd run around 40psi max for general use. Basically as low as possible without pinch flatting or rolling off on corners. You'll be comfy with more grip.

[observer90210]

When it comes to vehicles/bikes whatever runs on a road, no matter what their use is, surely all of you deserve parts of best quality and safest (and unfortunately most costly) ?

[StreetCowboy]

1 hour ago, bobfish said:

Above ideas probably valid, but 65psi in a 26x1.95 is waaay too much. As you say, a cheap quality tyre/rim combo, so your experience is not really surprising. 

Depending on your weight, I'd run around 40psi max for general use. Basically as low as possible without pinch flatting or rolling off on corners. You'll be comfy with more grip.

What are the potential problems with too much pressure in the tyre?

[vogie]

6 minutes ago, StreetCowboy said:

What are the potential problems with too much pressure in the tyre?

The tyre will wear in the middle of the tread.

[StreetCowboy]

50 minutes ago, vogie said:

The tyre will wear in the middle of the tread.

Not the way I weave, coming home from the pub

[bobfish]

3 hours ago, StreetCowboy said:

What are the potential problems with too much pressure in the tyre?

Well in general less comfort and less grip, so slower and not efficient for the intended purpose. At the extreme scale, more chance of blowout, blowing off the rim or carcass failure..... even exploding [a bit unlikely in the OP's case.]

[Ks45672]

6 hours ago, bobfish said:

Above ideas probably valid, but 65psi in a 26x1.95 is waaay too much. As you say, a cheap quality tyre/rim combo, so your experience is not really surprising. 

Depending on your weight, I'd run around 40psi max for general use. Basically as low as possible without pinch flatting or rolling off on corners. You'll be comfy with more grip.

I had not  heard of Cst before but Google search shows they sell a wide range of tyres on amazon in USA and UK and reviews are ok

 

Usually tyres are made with a tolerance for error  (Thai "mechanics" always put 50-60psi in scooters when it says 30-36psi on the sidewall every time I get an oil change at the dealer and when I go out I have to let out half the air) 

 

It is not unusual to use a mtb tyre at 60-70 while only riding on the dry roads, used to do it myself too

 

40 is  usually more for grass and mud where you need maximum bite for traction

[Ks45672]

17 hours ago, n210mp said:

You may find this video helpful

 

if you wish to get to the relevant bit it starts at 5 minutes:

 

 

 

I usually inflate to  just 10 psi and check the beads are in place before going up any higher 

 

Also go up in increments of 10psi and stop to make sure the tyre is inflating evenly before going up to 30-40-50-60 etc 

[Ks45672]

21 hours ago, el jefe said:

You probably didn't have the tube seated in the tire properly if it blew at less than 50 psi and the same thing did not happen with another tube.

The bike was delivered to me in a flat pack box and the factory were the ones who put the tube and tyre on the rim originally

 

I probably should have taken it off again and put it back on carefully but I didn't think of that at the time and assumed that it would be OK to just inflate

[Ks45672]

18 hours ago, StreetCowboy said:

Is the tyre damaged?  If the tyre is not damaged, then I don't think the problem is the tyre.  And the tubes should not care about the pressure, so long as they are inside the tyre.

 

Possibly you had the tube nicked underneath the rim of the tyre; that happened to me, and the tyre burst 1 km from home.  At least it wasn't too long a walk back (that was before the arthritis really got me down...).

 

I always put a little bit of air into the tube before I put it into the tyre, just to stop it getting twisted.  Then I put a few psi in to seat the tube properly in the tyre before seating the tyre beads in the rim, checking that I can pinch the tyre beads together underneath the tube all the way round, before pumping up to target pressure.

 

I don't know what is the limiting aspect of the tyre with respect to pressure.  Maybe the pressure at which the beads will start to stretch and there is a risk of the tyre rolling off the wheel on sharp curves? Or maybe the side walls will start to stretch and the threading start to fail?  Neither of these woudl cause the tube to burst, but would make the tyre unsafe.  So based on that speculation, I think the problem with over-pressuring your tyres will not be that the tubes will burst, but the risk of an accident while out on the road.

 

SC

 

It is possible that the tube was  wedged under the rim ,or kinked or twisted from it left the factory and didn't blow until the pressure was raised 

(I should have checked instead of trusting the factory to send it out assembled properly) 

 

Live and learn I guess

 

Usually on mtb forums I read you can go to the recommended max and some people even regularly go a bit higher for road use without any issues 

 

 

 

[el jefe]

2 hours ago, Ks45672 said:

The bike was delivered to me in a flat pack box and the factory were the ones who put the tube and tyre on the rim originally

 

I probably should have taken it off again and put it back on carefully but I didn't think of that at the time and assumed that it would be OK to just inflate

When I wrote "You probably didn't have the tube seated in the tire properly if it blew ...", that meant  whoever installed the tire. No one has come up with any other explanation. I've always done the same as you and pumped up the tires on a brand new bike without checking that the tube was seated properly in the tire. I've now learned the lesson that I should check that before I use the pump. Thanks.

 

As for your other question, the maximum pressure stated on the tire is one at which the manufacturer thinks will never cause a blowout. Lots of people pump it up to the maximum. Manufacturers don't need the liability of tires blowing off at that pressure. Lower pressure will give you a softer, smoother ride off road and on rough paved roads. When I've ridden an MTB on smooth paved roads, I've always pumped the tires to near the max.

[n210mp]

I'm amazed that people have not mentioned the effects that things like  "weight",  surface matter and condtion, ie rippled concrete or smooth tarmac  must plainly have on  tyres and tubes in  a hot Country.

 

 long downhill braking down some of the big hills  around here must also  increase the temperature of the rim on wheels with rim brakes and ergo increase the tyre pressure significantly! 

 

The only times I have had a blowout other than a conventional puncture   on my Giant escape bike is with pressure of 85 psi in a 700x32 hybrid type tyre   when I was not  gradually seating the tube properly on inflation and the tube got caught between the rim and the tyre (A good lesson to learn)

 

 

[Ks45672]

3 hours ago, n210mp said:

I'm amazed that people have not mentioned the effects that things like  "weight",  surface matter and condtion, ie rippled concrete or smooth tarmac  must plainly have on  tyres and tubes in  a hot Country.

 

 long downhill braking down some of the big hills  around here must also  increase the temperature of the rim on wheels with rim brakes and ergo increase the tyre pressure significantly! 

 

The only times I have had a blowout other than a conventional puncture   on my Giant escape bike is with pressure of 85 psi in a 700x32 hybrid type tyre   when I was not  gradually seating the tube properly on inflation and the tube got caught between the rim and the tyre (A good lesson to learn)

 

 

Weight had nothing to do with it

The tyre exploded with nobody on the bike

[bobfish]

4 hours ago, n210mp said:

I'm amazed that people have not mentioned the effects that things like  "weight",  surface matter and condtion, ie rippled concrete or smooth tarmac  must plainly have on  tyres and tubes in  a hot Country.

 

 long downhill braking down some of the big hills  around here must also  increase the temperature of the rim on wheels with rim brakes and ergo increase the tyre pressure significantly! 

 

The only times I have had a blowout other than a conventional puncture   on my Giant escape bike is with pressure of 85 psi in a 700x32 hybrid type tyre   when I was not  gradually seating the tube properly on inflation and the tube got caught between the rim and the tyre (A good lesson to learn)

 

 

I guess that's why I said 'depending on your weight' and 'intended use'. ?

Seems like the OP has done his research on the topic anyway, so nothing to add.

 

[bobfish]

Well okay... In the interests of learning something, I just pumped 27.5x 2.1 Schwalbe Rocket Ron Evo [with tube] up to 50psi on my hardtail XC. Pretty much rock hard. Handling a bit skittish. I could get by on unblemished supersmooth tarmac I guess, but I don't know where that exists in the real world. I weigh around 80kg, and can't ever foresee increasing the pressure to 65psi! 

[Ks45672]

53 minutes ago, bobfish said:

Well okay... In the interests of learning something, I just pumped 27.5x 2.1 Schwalbe Rocket Ron Evo [with tube] up to 50psi on my hardtail XC. Pretty much rock hard. Handling a bit skittish. I could get by on unblemished supersmooth tarmac I guess, but I don't know where that exists in the real world. I weigh around 80kg, and can't ever foresee increasing the pressure to 65psi! 

When you say "nothing to add" , you should just quit your rant..... ?

[StreetCowboy]

6 hours ago, n210mp said:

I'm amazed that people have not mentioned the effects that things like  "weight",  surface matter and condtion, ie rippled concrete or smooth tarmac  must plainly have on  tyres and tubes in  a hot Country.

 

 long downhill braking down some of the big hills  around here must also  increase the temperature of the rim on wheels with rim brakes and ergo increase the tyre pressure significantly! 

 

The only times I have had a blowout other than a conventional puncture   on my Giant escape bike is with pressure of 85 psi in a 700x32 hybrid type tyre   when I was not  gradually seating the tube properly on inflation and the tube got caught between the rim and the tyre (A good lesson to learn)

 

 

Same.

1 km from home and the tube blew with an almighty bang.  I can't imagine a bike tyre bursting, but I suppose if it was under too much pressure it might split, which would pretty quickly get nasty.  I have scrapped tyres because of cracking, particularly side-wall cracking after taking too long to stop following a puncture.

My path from less than 500 km between punctures to more than 2,500 km:

1. Increased tyre pressure
On my mountain bike I had a hand pump only, and no pressure gauge.  I reckon I was running about 30 - 40 psi, and I got a puncture every few hundred km.  Pinch flats, and the soft tyre sweeps so much more of the road surface and can pick stuff up so much more easily.  I bought a floor pump and started running my tyres at 80 psi; number of punctures reduced greatly

2. New tyre brand
On my 2nd (cyclocross) bike that I do most of my kilometres on I run Schwalbe Marathon 38s at 85 psi.  Not had a puncture yet, and the tyres last longer than the chain (maybe...). 

 

[bobfish]

2 hours ago, Ks45672 said:

When you say "nothing to add" , you should just quit your rant..... ?

Apologies if my response came across as a rant. Not spoiling for a keyboard war - no offence intended.

Well, I did have nothing more to add, but then did my quicky experiment, and thought it worth sharing. Hence, my tongue in cheek 'well okay': Guilty as charged! ??

As I mentioned, it looks like you've done your research. But, if like me you're interested, there is a good article on bike radar https://www.bikeradar.com/mtb/gear/article/trail-tech-mountain-bike-tyre-pressure-all-you-need-to-know-36626/

Sorry for adding even more!:

I'd probably put your exploding tyre down to a bad sample. I've inflated a brand new Conti GP4000II - a high end road tyre - only to notice a huge sidewall bulge. Thankfully no bang, and the dealer replaced it.

Cheers 

Edited June 2, 2018 by bobfish

[n210mp]

10 hours ago, Ks45672 said:

Weight had nothing to do with it

The tyre exploded with nobody on the bike

I didn't say it did, did ?

 

I was talking generally and specifically it was the "weight" of the internal pressure that caused it to explode (For one reason or another )

 

Just as a matter of bad coincidence my front wheel for no reason blew out its total valve stem  earlier tonight  ( But I have had iit in use for the past 16/17 months at 85 Lbs ) silly me, should have changed it 6 months ago! 

 

Oh and another one for those  people who think they know all the answers , tyre or tube  age cannot be determined so easily and many blowouts are just the result of "old age and rubber granular degeneration" 

 

And just as a final comment on this thread, it seems that some of the so called sports cyclist that are posting  are just as "bloody surly" as they are when you have the bad luck to meet up with them on the open road, God almighty, what happened to politeness and courtesy and the friendly greeting for heaven sake.
 

Reminds me of the gym when you meet those "Steroid ingested bruisers" who only "grunt" an answer to a friendly  greeting whilst carrying two rolls of carpets under each arm!

 

Think about it and you might get lucky and understand the point I am making!

Edited June 2, 2018 by n210mp

[StreetCowboy]

The pressure in the tyre doesn’t go up when you sit on it.

[n210mp]

19 hours ago, StreetCowboy said:

The pressure in the tyre doesn’t go up when you sit on it.

If we are going to be pedantic but  specific; 

 

The pressure does go up as defined by the plagiarized  hereunder;

 

"

An alternative way to calculate the solution:

The pressure in the tyre is 100psi. Pressure equals force divided by area. The surface area inside the inner tube (for a 700x23c tyre) is (very) roughly 7.2cm x 210cm = 1512cm square [or in square inches = 234insq]. The total forces involved on an unladen wheel are therefore 100 ‘pounds per square inch’ x 234 square inches = 23400 ‘pounds’. By sitting on the bike, one adds another 100 pounds to the wheel and thus to the forces, ie 23500 ‘pounds’. Assuming the inner tube does not change surface area ie the wall in contact with the ground is deformed in shape but overall not stretched or shortened, then the final pressure will be 23500 ’pounds’ divided by 234insq = 100.4 psi. Overall an increase in pressure by 0.4%.

I have used different assumptions/ approximations to previous posts:

1. The dimensions for my inner tube are actually external dimensions rather than internal.

2. The tyre (and therefore the inner tube) is assumed not to measurably stretch when at an appropriate pressure. Similarly the deformation of the tyre wall from curved to flat is assumed not to change the surface area much.

3. Overall designed to be relatively quick maths (and for the benefit of reading I simplified to fewer significant figures along the way) so still prone to a largish margin of error."

It did come as a surprise that the effect of "weight" would be so minimal but what about "heat" does that also have a minimal "effect"  and what about a combination of  increased weight and higher temperatures?

[StreetCowboy]

The only way you can increase the pressure in the tube is either by putting in more air (does not happen when you sit on the bike), heating it up (doesn't happen when you sit on the bike) or reducing the volume (maybe that happens when you sit on the bike, but I don't think it is significant - but might be about 0.4% as calculated above).

 

The reduction in volume is by compressing the round tyre into a flattened tube at the contact patch, which has an area of about less than 2 square inches (depending on how heavy is the rider, what proportion of weight is carried by each wheel etc.

 

Unfortunately I don't have my slide rule with me just now to do the sums...