sreten

Hi,

Just thought I'd throw this out for discussion.

My tyres state :
Max 3 bar 43 psi 65Kg load, (47-406, 20x1.75).
(Reality is probably tested to double the numbers).

I don't have bathroom scales but estimate my
75Kg + 15Kg for the bike pans out at about 60Kg
on the rear tyre and about 30Kg on the front tyre.

To me a total maximum load rating of 120Kg to
130Kg for a bike + rider + stuff makes sense.

Seems clear to me though for heavier types
the rear wheel is going to go way over 65Kg.

I'm not worried, regarding the tyre numbers
as being made up by marketing, perhaps
my tyres are intended for kids BMX's.

rgds, sreten.

BassNotBass

When I bought a KHS Mocha a few years ago the stock tires were very low-budget Kendas with a max psi of 35 lbs. I assumed that the actual working pressure would be considerably higher so I overfilled the tires to 45 lbs. After only a couple of weeks the sidewall casing of the rear tire tore open on my way to work (of course at the half-way mark ). So now I don't trust any budget tire that comes with a bike.

badmother

I tend to put BA`s on our small wheeled bikes.

Edit: https://www.chainreactioncycles.com/M...?ModelID=24554 Thank you smallwheeler.

smallwheeler

for any of you who may not know, "BA" is the acronym for Schwalbe Big Apples; the primo modern-day high-tech ballon tire.

sreten

Hi,

You've missed the point of this post, which is generally if
you inflate tyres to the stated maximum, skinny tyres are
usually under inflated and fat tyres are usually over inflated.

I started with 50 psi in my 3 bar 43psi 1.75" tyres, its not right at all,
its horrible. Currently trying 39psi rear, 26 psi front and may drop to
30psi rear 20psi front to see what that is like, possibly lower front.

High pressure gives high rolling resistance as does low pressure.
In the range of reasonable pressures for small wheels IMO your
looking for the.lowest pressure with decent rolling resistance,
so you get good suspension to compensate the wheel size.

rgds, sreten.

BassNotBass

This is the comment in your post I was addressing.

cplager

Hi,

I don't know that I agree with this generalization.

I agree that low pressure does mean higher rolling resistance. And yes, very high pressure tires can also cause higher rolling resistance. But depending on roads, total weight, etc, this is usually pretty high pressure, not usually the regime of most (but not all) 20" tires.

The pressure you're running in your tires seems extremely low. I'm guessing you are significantly lighter than I am. Regardless, I don't disagree that people may want to trade off higher rolling resistance for more comfort.

Cheers,
Charles

Elvis Shumaker

My pattern is 'pump up rock hard, check a couple of weeks later, realise tyres are down to half pressure, pump up rock hard again'

The rear tyre does seem to take a beating on a folder. I always err on the side of higher pressure and don't notice many issues one way or the other.

sreten

Hi,

For want of an any more scientific method I think
I'll just go for 40psi rear and 25psi for the front.

Makes sense from what I've read for 1.75"/ 47mm tyres.
[For 75Kg (me) and 15Kg (the bike) - total 90Kg.]

My experience indicates a hard front tyre is not good
in any respect and dropping its pressure works well.

rgds, sreten.

The above implies a 62%/38% rear/front weight ratio
and I'm pretty sure for a folder it is more than that.
Still sensible ballpark is a lot better than guessing.

Tourist in MSN

For skinny tires, I usually use the 15 percent tire drop as a minimum pressure in my rear tire, usually run higher pressures especially in my front tire.
https://www.bikequarterly.com/images/TireDrop.pdf

Unfortunately, this does not list data for the wider tires like 1.75 or 2.0. But, with that wide of a tire if you were running 15 percent drop, that is a much softer ride than most people would want. So, not sure if that philosophy should be used for that wide of a tire.

For loaded touring on my 700c touring bike, I drew longer lines to the right of the graph to estimate the pressure I needed in my 37mm tires when I had my camping gear on the bike. I need about 85 to 90 psig in my rear tire with that load to have a 15 percent drop.

If you are using really high pressures, the tire is only one component that keeps the pressure in the wheel, the rim also needs to be strong enough. Usually the tire is the weak link, but if you put a good tire on a cheap rim you might have a problem with the rim at really high pressures.

I fail to see how really high pressure causes more rolling resistance. I can see how it can make you bounce off of the pavement and spin the tire in mid air, but that is not the same thing as increased rolling resistance.

cplager

You've basically got it. If the tire is too high pressure, it doesn't roll smoothly and adds resistance. It's obvious how a drive tire that isn't gripping causes loses, but even a front tire will do the same as well.

Note that a wider tire running a high pressure will have less of a problem than a skinny tire running a high pressure (more volume to soak up bumps) and that we're generally talking about pretty high pressure that causes problems.

sreten

Hi,

Solid tyres have more rolling resistance than pneumatic
on everything except the smoothest surfaces, due to
the tyre lifting the whole bike over ripples rather than
the tyres absorbing the ripples.

There is an update of that PDF with "minimum" tyre
pressures for wider tyres for offroad and the like.
The results do extrapolate to wider tyres.

Basically the worse the surface, the worse too high
pressures are, for comfort, grip and loss of speed.

I appreciate its not a hard and fast science for
small wheel bikes. For rolling resistance you
probably want less than 15% as the walls
deflect more on small wheels, but for comfort
you want more than 15% as small wheel react
to bumps and surfaces more than large wheels.

I'm heading towards about 40psi in the rear
and 30psi in the front for 1.75"/47mm tyres.

I tried 50psi front and back at first. The front
was definitely too hard, harsh and bouncy,
which didn't inspire roadholding a grip, or
going fast downhill over any sort of bumps.

rgds, sreten.

smallwheeler

[h=3]from https://www.balloonbikes.com/en/tires.html[/h][h=3]Air pressure[/h]How much to inflate a tire to achieve maximum comfort depends upon the rider’s weight and luggage. Comfort is also a subjective and personal issue, but our recommendation is: 2.0 - 2.5 bar.
Heavier rider or luggage weight will require great inflation pressure.

[TABLE="class: content-table, width: 395"]
[TR]
[TH="width: 10%"] [/TH]
[TH="width: 18%"]ETRTO[/TH]
[TH="width: 20%"]Inch[/TH]
[TH="width: 17%"]Weight[/TH]
[TH="width: 18%"]Preassure[/TH]
[TH="width: 17%"]Load*[/TH]
[/TR]
[TR]
[TD="width: 10%"]12"[/TD]
[TD="width: 18%"]50-203[/TD]
[TD="width: 20%"]12 x 2.00[/TD]
[TD="width: 17%"]320 g[/TD]
[TD="width: 18%"]1,5-4,0[/TD]
[TD="width: 17%"]70 kg[/TD]
[/TR]
[TR]
[TD="class: tab_zoll"]14"[/TD]
[TD="class: tab_txt"]50-254[/TD]
[TD="class: tab_txt"]14 x 2.00[/TD]
[TD="class: tab_txt"]360 g[/TD]
[TD="class: tab_txt"]1,5-4,0[/TD]
[TD="class: tab_txt"]70 kg[/TD]
[/TR]
[TR]
[TD="class: tab_zoll"]16"[/TD]
[TD="class: tab_txt"]50-305[/TD]
[TD="class: tab_txt"]16 x 2.00[/TD]
[TD="class: tab_txt"]370 g[/TD]
[TD="class: tab_txt"]2,0-5,0[/TD]
[TD="class: tab_txt"]70 kg[/TD]
[/TR]
[TR]
[TD="class: tab_zoll"]18"[/TD]
[TD="class: tab_txt"]50-355[/TD]
[TD="class: tab_txt"]18 x 2.00[/TD]
[TD="class: tab_txt"]470 g[/TD]
[TD="class: tab_txt"]2,0-5,0[/TD]
[TD="class: tab_txt"]75 kg[/TD]
[/TR]
[TR]
[TD="class: tab_zoll"]20"[/TD]
[TD="class: tab_txt"]50-406[/TD]
[TD="class: tab_txt"]20 x 2.00[/TD]
[TD="class: tab_txt"]535 g[/TD]
[TD="class: tab_txt"]2,0-5,0[/TD]
[TD="class: tab_txt"]80 kg[/TD]
[/TR]
[TR]
[TD="class: tab_zoll"] [/TD]
[TD="class: tab_txt"]55-406[/TD]
[TD="class: tab_txt"]20 x 2.15[/TD]
[TD="class: tab_txt"]555 g[/TD]
[TD="class: tab_txt"]1,5-4,0[/TD]
[TD="class: tab_txt"]95 kg[/TD]
[/TR]
[TR]
[TD="class: tab_zoll"] [/TD]
[TD="class: tab_txt"]60-406[/TD]
[TD="class: tab_txt"]20 x 2.35[/TD]
[TD="class: tab_txt"]575 g[/TD]
[TD="class: tab_txt"]1,5-4,0[/TD]
[TD="class: tab_txt"]105 kg[/TD]
[/TR]
[TR]
[TD="class: tab_zoll"]24"[/TD]
[TD="class: tab_txt"]50-507[/TD]
[TD="class: tab_txt"]24 x 2.00[/TD]
[TD="class: tab_txt"]650 g[/TD]
[TD="class: tab_txt"]2,0-5,0[/TD]
[TD="class: tab_txt"]100 kg[/TD]
[/TR]
[TR]
[TD="class: tab_zoll"] [/TD]
[TD="class: tab_txt"]60-507[/TD]
[TD="class: tab_txt"]24 x 2.35[/TD]
[TD="class: tab_txt"]750 g[/TD]
[TD="class: tab_txt"]1,5-4,0[/TD]
[TD="class: tab_txt"]130 kg[/TD]
[/TR]
[TR]
[TD="class: tab_zoll"]26"[/TD]
[TD="class: tab_txt"]50-559[/TD]
[TD="class: tab_txt"]26 x 2.00[/TD]
[TD="class: tab_txt"]740 g[/TD]
[TD="class: tab_txt"]2,0-5,0[/TD]
[TD="class: tab_txt"]130 kg[/TD]
[/TR]
[TR]
[TD="class: tab_zoll"] [/TD]
[TD="class: tab_txt"]55-559[/TD]
[TD="class: tab_txt"]26 x 2.15[/TD]
[TD="class: tab_txt"]770 g[/TD]
[TD="class: tab_txt"]1,5-4,0[/TD]
[TD="class: tab_txt"]130 kg[/TD]
[/TR]
[TR]
[TD="class: tab_zoll"] [/TD]
[TD="class: tab_txt"]60-559[/TD]
[TD="class: tab_txt"]26 x 2.35[/TD]
[TD="class: tab_txt"]830 g[/TD]
[TD="class: tab_txt"]1,5-4,0[/TD]
[TD="class: tab_txt"]140 kg[/TD]
[/TR]
[TR]
[TD="class: tab_zoll"]28"[/TD]
[TD="class: tab_txt"]50-622[/TD]
[TD="class: tab_txt"]28 x 2.00[/TD]
[TD="class: tab_txt"]820 g[/TD]
[TD="class: tab_txt"]2,0-5,0[/TD]
[TD="class: tab_txt"]135 kg[/TD]
[/TR]
[TR]
[TD="class: tab_zoll"] [/TD]
[TD="class: tab_txt"]55-622[/TD]
[TD="class: tab_txt"]28 x 2.15[/TD]
[TD="class: tab_txt"]840 g[/TD]
[TD="class: tab_txt"]1,5-4,0[/TD]
[TD="class: tab_txt"]140 kg[/TD]
[/TR]
[TR]
[TD="class: tab_zoll"] [/TD]
[TD="class: tab_txt"]60-622[/TD]
[TD="class: tab_txt"]28 x 2.35[/TD]
[TD="class: tab_txt"]895 g[/TD]
[TD="class: tab_txt"]1,5-4,0[/TD]
[TD="class: tab_txt"]145 kg[/TD]
[/TR]
[/TABLE]
* Maximum Load

sreten

Hi,

Still i'm confused about front to rear ratios and general tyre spec nonsense.

My tyres are rated 65kg max each, and my best assumption is that either
that means a total load of ~ 100Kg for both taking into account weight
distribution, or it means a maximum load of 130Kg divided by half for
two of them, ignoring bike weight distribution.

rgds, sreten.

cplager

For maximum tire load, they mean the maximum load on each tire. So, yes, that means they either expect that you aren't very close to the maximum, or have actually figured out the weight distribution of your bicycle.

rgds??

If you're trying to write "regards", then I'd recommend doing that.

badmother

I would think like this: When producing tyres they know nothing about what you are going to use them for. You could put them on a trailer, on a trike, on a folder or on a recumbent. You could even put it on a monobike. For this reason you must expect 65kg written on each tyre is 65 kg on each tyre. Simple as that.

Not all folders have the typical "folder distribution" on weight. I have seen somebody sit straight up on short wheelbased folder, I am guessing 70% (of approx 125 kg) on the rear wheel. Also with a much more aero ridingstyle and long wheelbase it can be close to what you find on a "normal" bike. Some folders are heavely loaded in front (like ours when on vacation).

I think you must expect to decide for yourself what tyres to use where, using the information from the producer. For this reason some peopel use different tyres front and rear. If you decide to buy low preassure cheap tyres you must expect they could be made mainly for childrens bikes and trailers, they are not automatically suited for your weight, weightdistribution and ridingstyle.

jur

The tyre load figure comes from a very simple idea: If you have it pumped to the max casing value, then

1. It should not rupture
2. At the max load value it should not collapse more than about 30%.

So the tyre max load value has nothing to do with some inherent loading characteristic - it is a direct consequence of the max tyre pressure and max reasonable collapse amount.

sreten

Hi,

The problem is then with my bike and my average weight the rear load
in very near the maximum taking into account weight distribution, and
that means the basic bike is unsuitable for heavier types or for me
with any substantial rear loading.

Whilst you all may be right about the loading being absolute I get
the feeling cheap tyres are rated half the total load of the bike,
(taking into account typical weight distributions), not per wheel,
which would explain relatively low cheap tyre ratings to me.

rgds, sreten.

P.S. My informal English is fine.

sreten

Hi,

Any tyre that collapses 30% at its maximum load and pressure is rubbish.
(I've never seen a tyre specified such that the above makes any sense,
it might for high pressure very skinny tyres, but not 1.75" tyres.)

The real fact is that optimum "tyredrop" is about 15% and the tyre pressures
to do that depends on tyre width and very little to do with the ratings stated
on the tyre - ratings on tyres can be very misleading in a practical sense.

rgds, sreten.

cplager

If the tires you have on your bike aren't rated for the weight you are putting on them, get better tires. Having a tire blow out is something to avoid.

'rgds' is not an English word, nor a recognized abbreviation. It may be considered fine for IM, but if you look around on this board, you won't see anybody else using it. As a non-native English speaker, I would think you would want to make sure you are being understood (but I've been wrong before - maybe that isn't your goal).

smallwheeler

charles.. have some chamomile tea and chill out..

badmother

@sreten:

I have this nasty feeling you do not know your audience. I suggest you take some time where you read more and write less. We are in this forum to share ideas and knowledge- and also opinions. If you feel it is your duty to inform us about the facts of bicycling you are in the wrong place!

Elvis Shumaker

ID rgd tht as prfctly OK rcgnzd UK usg! But maybe that's just me

I wonder how everyone knows their tyre pressures like the back of their hand. Are you running around with nifty digital manometers?
They never seem to stay stable for long, and for many the answer to how much pressure your tyres have must be 'less than you think'.

badmother

Personally I know my tyre pressure from when I pump my tyres. 95% of my pumping is done with pumps w a gauge so I know what the preassure is "down to" before I start pumping. Most of the time I decide I want to know my tire preassure is when the tyres starts deforming more than I think they should.

I think wit tyre preassure like with a lot of other things you learn over time, you can squeeze the tyre and guess quite close to the right preassure.

Elvis Shumaker

Similar here, I use a 6 Euro 'track' pump and check that (not sure if the cheap ones are very accurate though). By the time I get round to refilling pressure is about half. When I squeeze the tyres I can usually only differentiate between 'rock hard' and 'too soft'.