Tyre pressures

[allen-uk]

Trying to find a nice 'stable' setting for my new bike, the internet wisdom seems to be that heavyweight riders should have loads of pressure in the rear tyre, much less in the front. Makes sense, so...

My Marathon Plus are rated at 45 to 115 psi, so I put 50 in the front, and was going for 100 in the rear, got to 80 on my (quite good) track pump, and could scarcely get another push into it. So I stopped on the basis that an exploding rear tyre was not a good idea.

Any ideas? Is my pump not up to it, is the gauge dodgy, and I getting even older and weaker than I thought?

Something, like the importance of spokes, that I hadn't thought about in decades of bike ownership.

A.

 

[flecc]

It is very difficult to get above 80 lbs into a largish tyre with most pumps. I never took a Marathon Plus above 80 lbs anyway, they are quite stiff types and easily get uncomfortable when too hard.

Being near the lighter end of the spectrum I usually had 55/65 in my MPs.
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[anotherkiwi]

I went to check what the hell PSI was (NZ went metric in '72...) and found that I am running without much pressure - 3.5 BAR front and rear and my Michelin City tyres are very comfortable at that pressure with no sign of sagging under my 78 Kgs. We shall see when I add another 7Kgs of motor and battery...

Tony

 

[flecc]

We also have metric and BAR measurement but most prefer to stick with the more precise pounds per square inch (lubs per squinch ).

conversion is 14.5 lbs/sq" to the BAR

 

[Alan Quay]

We also have metric and BAR measurement but most prefer to stick with the more precise pounds per square inch (lerbs per squinch ).

conversion is 14.5 lbs/sq" to the BAR

Why do you say that PSI is more precise? Surely you can't have been taken in by the old 'it uses a bigger number' argument?

 

[flecc]

I meant in the sense of not needing to resort to a decimal point or fraction. In this case the bigger number measure is superior since it spans in whole numbers the whole of the need with tyre pressures.

The metric system is an arbitrary one which has many very inconvenient measures, unlike our old imperial one that grew to mans needs over time.
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[Deleted member 4366]

Just pump them up until they're hard, which is normally when your arm starts to get tired from pumping. My tyres have never seen a pressure gauge, and I've never had a problem apart ftom that damaged Marathon Plus that kept blowing off the rim at relatively low pressure. Did pressure gauges exist when we were kids? It's a bit like those chain gauges that tell you your chain is knackered after 200 miles. Before we had them, the chain used to last for thousands of miles.

 

[JohnCade]

The walls of Marathon Plus tyres are quite stiff and can lead the inexperienced to believe they are at a good pressure when they’re not if relying on the finger and thumb test. I’m a bit surprised the OPs says that they can take up to 115 psi. Mine have up to 85 psi on the sidewall. 115psi is a good bit more than I used to put in narrow road bike tyres.

 

[allen-uk]

John: I did look on my sidewalls, but fading light (fading eyesight) made it difficult, so I took my figures from various sources on the interweb. Your 85 sounds more realistic, as when my track-pump gauge reads 80 the tyre is rock hard.

Yes, point taken d8veh about not having gauges till the last few years, and I quite agree that most things are over-measured these days - but the notion that tyres should be softer in the front than the rear struck me as a probably useful idea.

A

 

[mfj197]

... but the notion that tyres should be softer in the front than the rear struck me as a probably useful idea.

That is because the front wheel carries less weight than the rear. Therefore for both tyres to be compressing an equal amount requires the front to be inflated to a lower pressure than the rear.

Michael

 

[flecc]

That is because the front wheel carries less weight than the rear.

Never more true than with the Hillman Imp of yesteryear. After changing it from the intended twin-cylinder engine to a larger four, it was very back heavy and tended to lift the front over bumps.

So the standard tyre pressures were 15 lbs front, 30 lbs rear, to keep the front wheels in contact with the ground so it could steer!
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[Alan Quay]

I meant in the sense of not needing to resort to a decimal point or fraction. In this case the bigger number measure is superior since it spans in whole numbers the whole of the need with tyre pressures.

The metric system is an arbitrary one which has many very inconvenient measures, unlike our old imperial one that grew to mans needs over time.
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No, the arbitrary system is the imperial one. The metric system relates units to each other in a consistent way.

I'm pretty sure the awkward numbers thing is because you have grown accustomed to a certain set of numbers (who could blame you).

 

[flecc]

Not so Mike, and you're confusing consistency with arbitrary, the latter having a quite different meaning. I've used metric in engineering from my mid teens onwards and freely use both all the time, depending on which is most suitable at a given moment. I also convert on the fly when necessary, so familiarity isn't a consideration in my preferences.

And I repeat, it's the metric system that is arbitrary since it was locked to a randomly chosen arbitrary start measurement that had no logic. As a result it's measures are often inconvenient in day to day life for many.

The Imperial system is in no way arbitrary since it developed through experience to match each common requirement on a human scale.
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[allen-uk]

Having taught English, perhaps I can arbitrate.

The imperial system, based largely on body parts (how big's yours?), can be well described as arbitrary.

The metric system, which tried to impose a scientific basis for measurement, is certainly more consistent - at least it's based on tens.

Me? Like most old people, I use both, as it suits me.

A

 

[flecc]

Once again I have to disagree, the metric system was based, not on tens, but on an arbitrary factor, the circumference of the earth. Then the construction of a very logical system from that basis makes every measure arbitrary, regardless of it's undoubted consistency.

At no time in the creation of the metric system was there any consideration of human needs, and it cannot evolve for that purpose.

The imperial system was not tied in such a fixed manner, it evolved and developed over time to suit the human needs. The exact measures and which we used took time to settle and that process continues. We no longer use rods, poles or perches, and the fathom's use is now very restricted, changes showing just why the imperial system is anything but arbitrary. Certainly it's not consistent, logical or mathematically convenient, but those are different matters, humans aren't any of those things either.
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[Alan Quay]

Once again I have to disagree, the metric system was based, not on tens, but on an arbitrary factor, the circumference of the earth. Then the construction of a very logical system from that basis makes every measure arbitrary, regardless of it's undoubted consistency.

At no time in the creation of the metric system was there any consideration of human needs, and it cannot evolve for that purpose.

The imperial system was not tied in such a fixed manner, it evolved and developed over time to suit the human needs. The exact measures and which we used took time to settle and that process continues. We no longer use rods, poles or perches, and the fathom's use is now very restricted, changes showing just why the imperial system is anything but arbitrary. Certainly it's not consistent, logical or mathematically convenient, but those are different matters, humans aren't any of those things either.
.

With all due respect, It's a bit misleading to say that the metric system is based on the circumference of the earth. Only the measurement of distance is.

Mass is based on volume (admittedly cubic distance) of water. Energy on heat rise in water, pressure on distance below water. So you could argue it's based on water.

Other measurements rely on the acceleration on earth caused by gravity. Distance and time squared. So you could argue it's based on time. Or gravity.

Ultimately it's the simplicity with which the units are related that is the brilliant bit.

 

[flecc]

Ultimately it's the simplicity with which the units are related that is the brilliant bit.

I agree and would never have disagreed with that premise Mike. My contention only had regard to the human scale and needs. The USA have probably made the best choice, metric for science, engineering and finance, and a form of imperial for much of everyday life.
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[Alan Quay]

I agree and would never have disagreed with that premise Mike. My contention only had regard to the human scale and needs. The USA have probably made the best choice, metric for science, engineering and finance, and a form of imperial for much of everyday life.
.

Ah, perhaps the imperial system is good for measuring body parts.

I spend more time using a measurement system to describe physical quantities of stuff on good old planet earth.

 

[flecc]

Not only body parts, but what we use. As I remarked earlier, using BAR for tyre pressures is daft, it's scale not relevant to the need. Likewise but opposite, the gram is far to small in daily use, too often having to be expressed in hundreds and rarely useful singly or in tens. And how many would want to order a litre at a bar?

I won't go on, the list of ways in which metric doesn't measure up to the day to day life of most is endless.
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[Alan Quay]

Not only body parts, but what we use. As I remarked earlier, using BAR for tyre pressures is daft, it's scale not relevant to the need. Likewise but opposite, the gram is far to small in daily use, too often having to be expressed in hundreds and rarely useful singly or in tens. And how many would want to order a litre at a bar?

I won't go on, the list of ways in which metric doesn't measure up to the day to day life of most is endless.
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...but the metric system is anything but arbitrary, and that's the problem.

A system where the physical measure has been adjusted to 1 unit (pint) in order to make life easier for the inebriated may well be described as arbitrary.

And then, imperial spirit measures are far more complex. 1/4 gill? Can anyone honestly say they they have used Gill to measure anything other than spirits in a pub?

Even in places where the Gill may be of use it is shunned for the Cup.

Likewise the Cup for the Mug, then the Jug, Bucket, Gallon....Don't get me started on the friggin Gallon!