Topeak pump accuracy

[sayek1]

I have a new Topeak track pump which when I push down on, the gauge shows 120psi (for example), but as soon as I stop pumping it slowly drops down and sits at about 100 psi about 2 seconds later.

Which is the accurate reading - I don't want to over-inflate my tyres, but at the same time don't want to be under-inflating by 20 psi each time.

Is this the same for other track-pumps - the Topeak was one of the more expensive!!!!

So far I've had a couple of nightmares - I changed my tyres (for Marathaon+'s) and after inflating the tubes went out for a test spin - 20meteres into it a huge explosion as the back innertube exploded - probably a pinch. Then I inflated a tube out of the tyre and after about four pumps it exploded - probably me putting too much air in. However, both incidents have made me wary of the pump and thinking about its accuracy!

Thanks
Kevin

 

[jimboalee]

We all worry about whether we've put the correct pressure in the tyres.

The 'acid test' is when you put your weight on the saddle and see how much the tyrewalls spread.

A road bike rear tyre will spread about 1mm each side when you do a 'belly over' the saddle.

Most minipumps don't have gauges, so this is the way to judge after a roadside repair.

BTW, the way to test by 'finger pinch' is across the walls, not on the apex of the tread.
This is less accurate due to different people's hand strength.

On the walk between the sheds and the road, I do a short scoot on one pedal and glance at the tyre spread.
After a while, you will get a 'knack' of whether the tyre is inflated enough.

 

[HJ]

There are quite a few minipumps which do have gauges, but there is no guarantee as to their accuracy...

You could try using one of these...

 

[sayek1]

Thanks guys.

Any ideas on the correct reading of the track pump - as I end the down stroke or 3-4 seconds later?

 

[GrasB]

When it's settled usually, the problem is that a pressure gauge removes some air from the tyre to start with so it reads lower than the pressure before you started.