Question about Tires

[kellerdp]

Hey all,

Apologize if this has been asked before.

I'm pretty much a newbie with bikes, so this may be a no-brainer answer.

I've got a Specialized Langster, and when I sit on my bike, the rear tire squishes down a bit. The front tire looks fine. I weigh ~215-220 lbs, so I'm not sure if it's because of my weight or if it's not inflated properly.

I've got this pump and when I'm pumping until I can't pump anymore, the psi readout is only 50 psi when the sidewall says between 120-125 psi.

Any suggestions would be much appreciated.

Oh yeah, any books or anything y'all would recommend on Bike Maintenance?

[xerxes]

I'm not sure which book to recommend, but getting tyres up to 120psi is going to take a bit of effort and a track pump, like the one you have, is the best thing for the job.

Do you have Presta or Schrader valves?

See here: http://www.sheldonbrown.com/brandt/presta-schrader.html

If you have Presta valves, make sure you open them before you attach the pump.

[kellerdp]

(06-08-2010, 06:03 PM)xerxes Wrote:  I'm not sure which book to recommend, but getting tyres up to 120psi is going to take a bit of effort and a track pump, like the one you have, is the best thing for the job.

Do you have Presta or Schrader valves?

See here: http://www.sheldonbrown.com/brandt/presta-schrader.html

If you have Presta valves, make sure you open them before you attach the pump.

Thanks for the reply!

Presta valves. I fully deflated both tires and pumped up the tires and they still hit 50 psi. I'll double check tonight when I get home, but I'm beginning to think the gauge is messed up.

What's a 'standard' pressure I should be looking for for road bike tires.

Thanks again!

[GeorgeET]

Do not trust the gauges that come with pumps . I have not seen any that are accurate, especially after a few bangs.

Go to an automotive store and buy a pencil gauge that goes up to high pressure, usually a truck gauge. If you can get a Syracuse or Camel made they are good. In many tests the pencil gauges rated tops and were not damaged after being dropped.

Not sure how well they work on presta.

[kellerdp]

George Wrote:Do not trust the gauges that come with pumps . I have not seen any that are accurate, especially after a few bangs.

Go to an automotive store and buy a pencil gauge that goes up to high pressure, usually a truck gauge. If you can get a Syracuse or Camel made they are good. In many tests the pencil gauges rated tops and were not damaged after being dropped.

Not sure how well they work on presta.

Thanks for the suggestion. I'm thinking I'll get a Valve adapter and try that with a tire gauge tomorrow.

[Bill]

Ok see if I can help out a little. For a while I was thinking there were two different PSI measurements. There is not. However, Mountain Bikes "usually" only require 40-60 PSI which most pumps and gauges are commonly made for and they widely use Schrader valves. Hybrids again "usually" require 80-??? PSI and they can use both Presta or Schrader valves. Road bikes use 100-12x PSI and come in both Presta and Schrader valves. As far as your pump you got well what you paid for . The sad misconception of companies that make pumps, is that they put a high pressure gauge on a lower end pump to make them believe it is gonna put its max capacity in the object they are inflating. There is a 50.00 air compressor I bought sometime back that the gauge said 100+ PSI but it always turned off at 80! Pi$$d me off something bad, took it back and the reason I gave is that it did not do what it was marketed for. I have a digital tire gauge that seems to be more accurate then most of the ones I have ever owned. For a decent tire gauge you may have to end up paying around 10.00usd or more like this one, http://www.amazon.com/Accutire-MS-4020GB-Standard-Digital-Gauge/dp/B00005AXI5 . The only down thing about it is that the Lithium Battery is permanent, but it has a 5yr warranty. Always check your tire pressure each week. Believe it or not tires on average loose about 10 PSI a week.

Hope this helps,
Bill

[trevgbb]

Are you sure you are not reading the pressure in 'bar' rather than 'psi', a lot of gauges have both units on the dial, and 5 bar is roughly 80 psi.

[kellerdp]

Trevgbb-I double checked before I left for work today and the gauge has both bar and psi. It's still reading about 50 psi.

I bought a presta valve adapter, but it doesn't work with my pressure gauge that I've got for my car. I'm going to take the pump back tomorrow and pick up one from the bike shop by my work. I'll let y'all know how the tires 'feel' when inflated with a better pump. Then I'm going for a long, long ride tomorrow afternoon to make up for the lack of riding this week.

[trevgbb]

For thin tyres I have always used a frame fit pump like this;
http://www.raleigh.co.uk/p_details.aspx?id=3530
as you can see, it doesn't have a gauge but will reach 115 psi.

[kellerdp]

I'll have to look into that pump.

I took my bike to the shop and had them check the psi. It was at 50 psi. I'm returning my pump to good 'ol Walmart and I'm going to pick up a good track pump. I'll get a better frame pump in a few weeks after my extra hours at work pick up.