Tyre Pressure - Berto's 15%

[MikeDee]

Here's an article on tire pressure by Jan Heine, who owns Compass Tires https://janheine.wordpress.com/2016/08/ ... -pressure/ Note the table with recommended tire pressures. These seem in line with Berto's recommendations, and are under the recommended minimums I've seen on tires I own, providing further proof that manufacturers' low pressure recommendations are conservative, a WAG, and bogus.

[RickH]

Here's an article on tire pressure by Jan Heine, who owns Compass Tires https://janheine.wordpress.com/2016/08/ ... -pressure/ Note the table with recommended tire pressures. These seem in line with Berto's recommendations, and are under the recommended minimums I've seen on tires I own, providing further proof that manufacturers' low pressure recommendations are conservative, a WAG, and bogus.

Jan has tempered his 15% view a bit, mainly with regard to the front due to the higher additional loading under braking - see this June 2018 bolg "Myth 11: Rear tires should run at (significantly) higher pressure"

[531colin]

I have been running 32mm tyres 45psi front 55psi rear for a couple of years. Marathon Supremes and Conti. top contact Winter, although the Contis. are labelled 37, and they are nothing like! One pinch flat, quite recently.....I didn't see anything, or even feel it when I hit it, so I imagine I just clipped something with the edge of the tyre. Just that rumbly feeling as it went down!
Other than that, no surprises, no drama, just a less edgy/rumbly ride and a less-sharply defined wear patch in the centre of the tyres. No tyres worn out or "retired" yet. Running 2 pairs Supremes and one Contis. the oldest pair of Supremes were pretty worn when I dropped the pressures (from 60 and 70 Psi)
My weight goes between ten and a half and eleven stone.

[Brucey]

..... These..... are under the recommended minimums I've seen on tires I own, providing further proof that manufacturers' low pressure recommendations are conservative, a WAG, and bogus.

what on earth makes you think that one manufacturer's tyres ought to be run at the same pressures as another's?

cheers

[reohn2]

..... These..... are under the recommended minimums I've seen on tires I own, providing further proof that manufacturers' low pressure recommendations are conservative, a WAG, and bogus.

what on earth makes you think that one manufacturer's tyres ought to be run at the same pressures as another's?

cheers

I think the point Mike's making is that very supple,some would say fragile tyres such as Compass can be run at low pressures,tyres with a stiffer carcass can be run at even lower pressures.

[Brucey]

'tis the other way about; supple carcasses will flex better than stiff-walled ones. The latter will tear themselves apart if they are flexed to the same extent. The loads that can be borne by each tyre are of course likely to be completely different, as indeed are the recommended ranges of pressures that the tyre can be safely run at.

Advising folk that there is a 'one size fits all' pressure based on tyre width and load, irrespective of what it says on the tyre sidewall is sheer folly.

My advice is to run the tyre pressures that suit you provided it does not conflict with the manufacturer's recommendations. If you do go outside the manufacturer's recommendations, on your own head be it. Expect a shorter tyre life, problems in extreme situations and -at the very least- to have to inspect the tyres more often than normal.

cheers

[reohn2]

'tis the other way about; supple carcasses will flex better than stiff-walled ones5. The latter will tear themselves apart if they are flexed to the same extent. The loads that can be borne by each tyre are of course likely to be completely different, as indeed are the recommended ranges of pressures that the tyre can be safely run at.

I think we're in agreement ie; supple tyres need more air in them than supple tyres.

Advising folk that there is a 'one size fits all' pressure based on tyre width and load, irrespective of what it says on the tyre sidewall is sheer folly

.
But no one is saying that!

My advice is to run the tyre pressures that suit you provided it does not conflict with the manufacturer's recommendations. If you do go outside the manufacturer's recommendations, on your own head be it.

We're big lads we'll manage

Expect a shorter tyre life, problems in extreme situations and -at the very least- to have to inspect the tyres more often than normal.

cheers

But that's being disproved in my case at least,my tyres aren't cosseted by any stretch,riding rough gravel,stoney tracks and crapmac and are giving good service especially the Hypers

[Brucey]

I think we're in agreement ie; supple tyres need more air in them than supple tyres.

eh...?

you don't say you get pinch flats or moan about lateral instability either; I don't think your use represents that of everyone else by any means.

Also note that if you have (unacceptably) increased your risk of tyre failure tenfold, from (say) one in a thousand to one in a hundred, you would still have to be fairly unlucky to suffer the consequences; one positive proves little about reliability if you are looking for good reliability.

cheers

[reohn2]

I think we're in agreement ie; supple tyres need more air in them than supple tyres.

eh...?

you don't say you get pinch flats or moan about lateral instability either; I don't think your use represents that of everyone else by any means.

Also note that if you have (unacceptably) increased your risk of tyre failure tenfold, from (say) one in a thousand to one in a hundred, you would still have to be fairly unlucky to suffer the consequences; one positive proves little about reliability if you are looking for good reliability.

cheers

Brucey
Im going to leave it at that.
I've posted what I've posted I ride big supple rubber at low pressures they handle and ride well on all surfaces.I don't get snakebites,I get very few punctures and in the seven or eight years and ten's of thousands of miles of riding them I've never had a carcass failure yet,make of that what you will,but I stick with what I've tried and tested to my own satisfaction and am happy with

[Cugel]

I think we're in agreement ie; supple tyres need more air in them than supple tyres.

eh...?

you don't say you get pinch flats or moan about lateral instability either; I don't think your use represents that of everyone else by any means.

Also note that if you have (unacceptably) increased your risk of tyre failure tenfold, from (say) one in a thousand to one in a hundred, you would still have to be fairly unlucky to suffer the consequences; one positive proves little about reliability if you are looking for good reliability.

cheers

Brucey
Im going to leave it at that.
I've posted what I've posted I ride big supple rubber at low pressures they handle and ride well on all surfaces.I don't get snakebites,I get very few punctures and in the seven or eight years and ten's of thousands of miles of riding them I've never had a carcass failure yet,make of that what you will,but I stick with what I've tried and tested to my own satisfaction and am happy with

There is theory and there is practice. There is what ought or should happen and there what actually happens.

Sometimes they all agree. Sometimes there are discrepancies.

In the final analysis, one may use experience but perhaps in a way limited by one's theoretical understanding.... Why pretend you can fly off a cliff when all the theory says NO!?

Or, if we don't entirely limit ourselves with theory, we might indulge ourselves in experiences that test the theoretical limits by just a little bit. This is known as "pushing the envelope". Perhaps we should call it "underinflating the tyre"? In all events, taking small risks sometimes shows you how to reduce them.

Taking large ones might too - or kill you. Did anyone watch the recent tele programme about "Captain Jack" - a short history of how the demands of WW1 for an aircraft carrier required vast human sacrifice in learning how to land a primitive biplane on a bodged-up platform clagged on to a ship after they removed one of it's gun turrets? It cost a lot of lives to learn what could and couldn't be done; and how to change that.

Cugel

[MikeDee]

Vittorias answer to how they arrive at minimum tire pressure https://www.velonews.com/2015/05/bikes- ... ore_369794

"According to ETRTO, bicycle tires are allowed to deflect 30% of its height at maximum load only. We respect the ETRTO, but we do not limit the body weight of our customers. 115PSI minimum air pressure is the consequence for our high-end 25mm tire with its very flexible casing; the minimum air pressure is related to the worst case: heavy load, rear wheel, aged tire.
We will address this matter more precisely on our MY16 new models.
— Christian Lademann – Product Manager
Vittoria S.p.A."

All I can say is they must have considered some pretty portly customers to get a tire deflection of 30% with the minimum pressures they specify. What do they mean by "maximum load?" (Under what conditions?) How credible does this seem? (Can you spell b-o-g-u-s?)

Hey, when you blokes specify "stones," I don't know W-T-F that means and you have me reaching for my furlongs per fortnight calculator. Can't we all use pounds as a unit of weight?

[NickJP]

I also weigh 65kg, and run the 650b 47mm tyres on my touring bike at 25psi front and 35psi rear. That's with the bike itself plus a Carradice saddlebag with a few kg in it.

Update:
I've been mostly riding my "new" winter bike with 26" hub brake wheels. Tyres are 47 x 599 Continental Contact pumpped up to 3bar/45psi. I've been very happy with the grip, comfort and downhill speed. All was well until last week when I came off on a corner. It was not raining. The surface was not icy, no gravel, no wet leaves, no potholes. I was not going fast nor, according to the motorist behind me who kindly stopped to inquire if I needed help, leaning very much. The surface was good but just a bit wet. The instant I started the turn, my front wheel skidded in the other direction and I went down. I got away with some cuts and bruises but nothing broken but am now wondering are my tyre pressures too high? I'm about 65kg, the bike is maybe another 15kg. Is 45psi too high. Would lowering to 25-30 give more grip?

I'm a trendy consumer. Just look at my Pixel 2 using hovercraft full of eels.

[mjr]

Hey, when you blokes specify "stones," I don't know W-T-F that means and you have me reaching for my furlongs per fortnight calculator. Can't we all use pounds as a unit of weight?

Please don't. After being here 40ish years, I know 10 stone is roughly 63.5kg, but when people start giving weights in massive numbers of pounds, it all goes a bit sideways because I've not memorised my 0.454 times table.

[531colin]

Vittorias answer to how they arrive at minimum tire pressure https://www.velonews.com/2015/05/bikes- ... ore_369794

"According to ETRTO, bicycle tires are allowed to deflect 30% of its height at maximum load only. We respect the ETRTO, but we do not limit the body weight of our customers. 115PSI minimum air pressure is the consequence for our high-end 25mm tire with its very flexible casing; the minimum air pressure is related to the worst case: heavy load, rear wheel, aged tire.
We will address this matter more precisely on our MY16 new models.
— Christian Lademann – Product Manager
Vittoria S.p.A."

All I can say is they must have considered some pretty portly customers to get a tire deflection of 30% with the minimum pressures they specify. What do they mean by "maximum load?" (Under what conditions?) How credible does this seem? (Can you spell b-o-g-u-s?)

..................

So they are embossing on the tyre wall a MINIMUM pressure which reflects a "perfect storm" of adverse conditions.....heavy rider, rear wheel old tyre......and they expect 30% drop at that pressure.
So why shouldn't I inflate my tyres to give (say) 15% drop?