tire pressure

Reply

  #1  
Old 12-26-11, 10:22 AM
Forum Topic Moderator
Thread Starter
Join Date: Mar 2005
Location: USA
Posts: 43,045
tire pressure

I'm curious as to how much air should be in the tires of a 24" 21 speed mountain bike. The tire states 50 psi.

We bought our grandson a bike from Walmart. Since the tires had less than 10 lbs in them I went to air them up before giving him the bike. I aired the tires to 45 psi. Just as I finished the 2nd tire, the front tire exploded. While Walmart did replace the tube, they claimed I over filled them. They said the tires should never be aired past 32 psi. even though the tire states 50 psi. The owners manual states the tire pressure should be checked before every use and should be pumped up to the psi level stated on the tire sidewall.
 
Sponsored Links
  #2  
Old 12-26-11, 10:32 AM
Group Moderator
Join Date: Oct 2004
Location: WI/MN
Posts: 18,497
Based on the information provided, I would have set them at 50 psi as well. To me, that number seems like it might even be on the low side - I don't have a bike any more but I thought my last one, which was a mountain bike, called for 60 psi.
 
  #3  
Old 12-26-11, 12:22 PM
Group Moderator
Join Date: Mar 2003
Location: NC, USA
Posts: 16,905
Bike tires are pretty small so it's easy to over inflate them if using an air compressor. I tend to run a different air pressure depending on how it will be ridden. Higher pressure makes a rougher ride but easier peddling and it helps protect the rims if he's jumping or hitting rocks.

---
I have a company that makes specialized hand trucks so we use a lot of little wheels. Almost every year a tire gets blown up and it will scare the begeezas out of you. Everyone is used to how long it takes to air a car tire but little hand truck tires (and bike tires) can go up 20 psi or more with a one second shot from a air hose. I tell people to just quickly shove the hose on and then pull it off and check the pressure, and never longer than a 1 second squirt of air without checking the pressure. Still, a newbie always blows up a tire at least once.
 
  #4  
Old 12-26-11, 12:35 PM
Forum Topic Moderator
Thread Starter
Join Date: Mar 2005
Location: USA
Posts: 43,045
While I did use a big air compressor I'm certain I didn't over fill the tire as I checked it several times as I went and didn't need to bleed off any excess psi. It did make a big bang! Got my attention but it sure scared the goat who had come to fence to see what I was doing
 
  #5  
Old 12-26-11, 12:43 PM
Gunguy45's Avatar
Super Moderator
Join Date: Dec 2007
Location: USA
Posts: 20,801
Well...WM bikes are just about the worst of the worst. They get hung up, messed with, rolled around, sat on, beat up, etc, etc. Not to mention they are cheaply made...no matter what name is on them. Not that it really matters for a kid who will abuse it most likely anyway.

You could have had a tube that was old, pinched, or otherwise faulty.

My wife hasn't ridden her fancy Trek in a while (she runs now instead) but just from moving it around and such I noticed a few weeks back that her tires looked low and started to fill them...but the stems are a bit crooked. Didn't air them, figured I'd mess with it when it warms up or take it down to the shop we bought it from and have them do a $40 full service in the spring.

Oh....my manual says the same about inflating to pressure on the tire for general use. Unfortunately the tire says 40-65lbs...lol. I think it depends on usage and the rider.
 
  #6  
Old 12-26-11, 12:52 PM
the_tow_guy's Avatar
Group Moderator
Join Date: Feb 2001
Location: SW Fla USA
Posts: 11,519
Second all the other remarks and I would add I wouldn't take any advice from someone who would make the statement that tires should never be inflated above 32 psi; that's ludicrous.
 
  #7  
Old 01-07-12, 10:47 PM
Member
Join Date: Oct 2008
Location: New England
Posts: 9,808
LOL, I think that 32 psi statement was meant for an suv.
Sorry to have missed the initial post, technical difficulties.
Here are the tips for inflating bicycle tires.
1. Yes, stay within the range listed on the tire.
2. Caution if you use a gas station type air source. Those compressors that go ding, ding, deliver a fixed volume of air per surge intended for car tires. One two many surges can result in the bang.
3. Always measure the tire pressure rather than trusting the gauge on the pressure source.

This is probably what happened in this case.
4. Tires need to be seated perfectly around the rim. If the tire doesn't snap out to the proper position in one place, that means another place will have the ability to slip over the rim. This can occur when a tire is first installed or from setting flat. Many times I have found tires that were never seated right from their initial assembly. A quick spin usually reveals the problem by watching the bead of the tire right next to the rim. There is usually a little bump of rubber that should ride right next to the metal rim.
5. In conjunction with the above, always watch this bead on the tire while inflating to be sure one area isn't slipping too high above the rim. The crocked tire stem is one example of when this can occur.
6. That crooked stem you encountered is a warning sign. A tire that is low on pressure, walks around the rim when ridden and if very low, moves even when walking the bike with no one on it. As the tire walks, or slides around the rim, the tube cannot because of the valve. Since the valve is poked through a hole in the rim, the movement of the tire stretches the tube on one side of the valve and doubles it up on the other side. Besides eventually damaging the tube, this doubling up can create a bulge that can cause the tire to blow off the rim. For a slightly crooked stem when you know it just happened and is barely crooked, you can sometimes cheat and let out most of the air followed by walking the bike backwards. I have done it, but the cheating can still leave the tire poorly positioned and even bunched up, so the proper way is to remove the tire and tube and reinstall them.

Inflate those tires a little at a time, checking the pressure as you go and also spinning the wheel to see if the tire is expanding uniformly around the rim. A bump or a dip means something isn't right and the cause needs to be determined.

Thanks for filling in, I will try to watch more closely.

Bud
 
  #8  
Old 01-08-12, 05:16 AM
Forum Topic Moderator
Thread Starter
Join Date: Mar 2005
Location: USA
Posts: 43,045
My wife thought I over filled the tire also since her car tires inflate to 35 psi and [in her mind] are bigger and need more air than a bicycle

I knew it had to be either a defective tube or bad install since the bike had never been ridden. That's why I refused to buy a new tube. I didn't care to replace the tube myself but as much as the bike cost I wasn't about to pay for the tube. I had to plead my case to 3 different employees but when they realized I wouldn't take no for an answer - they fixed it free of charge.
 
  #9  
Old 01-08-12, 05:47 AM
the_tow_guy's Avatar
Group Moderator
Join Date: Feb 2001
Location: SW Fla USA
Posts: 11,519
Let your wife know that her donut spare is rated at 60 psi.
 
  #10  
Old 01-08-12, 05:50 AM
Member
Join Date: Oct 2008
Location: New England
Posts: 9,808
A defective tube will leak and go flat without the dramatics of a hand grenade. Since the bike had never been ridden, it sounds like the tire had never been seated properly right from the factory. I've seen the box store assembly approach and the little details are usually not on their list. You were correct to stand your ground and the employees missed an opportunity to inspect and explain the above, if they could.

Bud
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
'