Tyre pressures

[Ningishzidda]

Robert Forstermann was 14 st 13 lb when he made the ‘Man vs Toaster’ video.

That’s 95 kg. 10% of that is 136 psi, which is over the Conti Gatorskin Maximum pressure recommendation.
The 22 stone bloke was a ‘newbie’ and can shed a bit. Robert Forstermann is far from a newbie, and might gain a bit.

 

[T42]

Obviously there are nominal limits and safety margins.  I have heard that Ulrich used to ride on 10 bars, but then one hears a lot of things.

[LittleWheelsandBig]

Typically bicycle tyres are labelled at half their blow off pressure, to allow for construction tolerances, temperature effects and so on.

[T42]

There's hope yet for our club prez.

[Ningishzidda]

Obviously there are nominal limits and safety margins.  I have heard that Ulrich used to ride on 10 bars, but then one hears a lot of things.

I ride on 10bars.

Conti Supersonic 20mm. 145 psi. Spesh SWorks and Spesh Shiv.

[Otto]

I whack em up to 100 psi whatever they are…. must be a legacy of riding rock hard 18mm tyres in my youth

[phantasmagoriana]

I whack em up to 100 psi whatever they are…. must be a legacy of riding rock hard 18mm tyres in my youth

I run them all (various flavours of 25mm - currently riding GP 4 Seasons the most) at 120 psi, through some weird fear of pinch flats.

[jsabine]

I whack em up to 100 psi whatever they are…. must be a legacy of riding rock hard 18mm tyres in my youth

I run them all (various flavours of 25mm - currently riding GP 4 Seasons the most) at 120 psi, through some weird fear of pinch flats.

Most of the indications I've seen are that 120psi on a 25mm tyre is appropriate for a rider of approximately 120-130kg - 19 stone or thereabouts.

[Ningishzidda]

Study the chart on the BikeQuarterly article.

[Jakob]

Obviously there are nominal limits and safety margins.  I have heard that Ulrich used to ride on 10 bars, but then one hears a lot of things.

My tubulars are rated up to 170psi/~12bar.

[sojournermike]

Obviously there are nominal limits and safety margins.  I have heard that Ulrich used to ride on 10 bars, but then one hears a lot of things.

My tubulars are rated up to 170psi/~12bar.

Indeed, but that's maximum, not recommended - unless you're heavy and they're skinny of corsa

[Deano]

I whack em up to 100 psi whatever they are…. must be a legacy of riding rock hard 18mm tyres in my youth

I run them all (various flavours of 25mm - currently riding GP 4 Seasons the most) at 120 psi, through some weird fear of pinch flats.

Most of the indications I've seen are that 120psi on a 25mm tyre is appropriate for a rider of approximately 120-130kg - 19 stone or thereabouts.

Mrcharly had a similar conversation with phanta on Girsby Bridge during a night ride (two phantas wouldn't equal 19 stone) when he was re-inflating her tyre after a puncture and asked what pressure she wanted in her tyres.

[drossall]

The alternative theory, espoused by Jobst Brandt and many racers, is that you need a much higher front pressure than suggested by its typical load, since under hard braking almost all your weight is borne by the front wheel and fast cornering is safer with less tyre flop.

That's an interesting point, although you shouldn't be cornering and braking hard at the same time. However, for straight-line braking I'd still want to consider it.

[jsabine]

I whack em up to 100 psi whatever they are…. must be a legacy of riding rock hard 18mm tyres in my youth

I run them all (various flavours of 25mm - currently riding GP 4 Seasons the most) at 120 psi, through some weird fear of pinch flats.

Most of the indications I've seen are that 120psi on a 25mm tyre is appropriate for a rider of approximately 120-130kg - 19 stone or thereabouts.

Mrcharly had a similar conversation with phanta on Girsby Bridge during a night ride (two phantas wouldn't equal 19 stone) when he was re-inflating her tyre after a puncture and asked what pressure she wanted in her tyres.

I felt it would be impolite to even hint at asking a lady to reveal her weight ...

[Highlander]

The alternative theory, espoused by Jobst Brandt and many racers, is that you need a much higher front pressure than suggested by its typical load, since under hard braking almost all your weight is borne by the front wheel and fast cornering is safer with less tyre flop.

That's an interesting point, although you shouldn't be cornering and braking hard at the same time. However, for straight-line braking I'd still want to consider it.

I agree it's an interesting thought, and I'd be very interested if anyone can cite examples of racing cyclists who employ this approach.

But as a general principle I just can't see a good reason for having more traction on the rear.  It's the same reason why you should not have a wider tyre on the back wheel.  You at least have a chance of controlling a back wheel slide, a front wheel slide is potentially much more dangerous.

 



     



 

   

[sojournermike]

I think that maintaining comfort and cornering poise whilst moving is more important than minimising rolling resistance under hard braking. Therefore, I subscribe to the softer front approach and use the Bicycle Quarterly/Berto app as a starting point for pressure. In practice, tubeless seems to let me go a bit lower - although the front pressures can seem worryingly low at times.

The suggested pressures for my pass hunter are 60r 40f on 35c tyres cushions.

Mike

[Highlander]

I think that maintaining comfort and cornering poise whilst moving is more important than minimising rolling resistance under hard braking...............

Mike

Exactly my point - surely when braking you want to maximise rolling resistance..?   

I feel remarkably stupid that for years I ran my tyres at the same pressure, and think back to a spectacular crash I had in a time trial caused by a front wheel slide.  The problem is it goes against the grain with most "performance" cyclists to run at anything below maximum pressure, front or rear.   That's another reason I'm extremely sceptical about the lower pressure in the back tyre school of thought and I'd like to see the source of the information attributed to Jobst Brandt it really doesn't strike me as something he would have advised but happy to be proved wrong.   

[Kim]

I whack em up to 100 psi whatever they are…. must be a legacy of riding rock hard 18mm tyres in my youth

I run them all (various flavours of 25mm - currently riding GP 4 Seasons the most) at 120 psi, through some weird fear of pinch flats.

I used to do that, until I realised that the gauge on the pump I was using was chronically under-reading and what I thought was 100PSI was more like 75-80.  100 actual PSI turned out to be pointlessly skiddy on the Streetmachine (40mm Marathons), but somewhat better rolling on the Dawes (28mm Marathons, gets used for hauling a lot of stuff).  I didn't have the Brompton at that point, but 80PSI on the back would noticeably up the treacle factor.

So I invested in a reliable gauge, did a bit of trial and error, and arrived at pressures that seem to work well for each bike.

I've only had a pinch flat when a regular puncture has sneakily robbed the tube of pressure before I've noticed...  Even on the mountain bike at 30PSI (though I've yet to do much in the way of rocky stuff on it).  Barakta managed a spectacular one on the trike once, by landing the rear wheel squarely onto a nasty pothole at 30mph - in that instance we were mostly pleased that the rear mech was undamaged.

[mrcharly-YHT]

I think that maintaining comfort and cornering poise whilst moving is more important than minimising rolling resistance under hard braking...............

Mike

Exactly my point - surely when braking you want to maximise rolling resistance..?   

No, you want to maximise grip. Not the same thing at all.

[Biggsy]

Mike's reference of minimising rolling resistance under hard braking was to the side effect of Jobst Brandt's advice of having the front tyre as hard as the rear - which I too remember.  It'll be in the rec.bicycles.tech newsgroup archive if not in one of his web articles.  It may be difficult to find due to the vast number of posts he made - which included barking mad ideas as well as wise words, IMO, and it was often hard to tell which was which!

Personally, I don't care about my front tyre taking all my weight under hard braking as long as it's still hard enough to resist flatting.  It will still steer all right as well, if I do want to risk simultaneous hard braking and cornering.  It'd have to be ridiculously soft to steer badly, and no-one is suggesting having it *that* soft.

[andrew_s]

The alternative theory, espoused by Jobst Brandt and many racers, is that you need a much higher front pressure than suggested by its typical load,

I agree it's an interesting thought, and I'd be very interested if anyone can cite examples of racing cyclists who employ this approach.

The only figures I've come across are those for Paris-Roubaix, where the pressures are conventionally higher rear than front, but on the other hand can be surprisingly low (by conventional wisdom at least).
http://velonews.competitor.com/2013/04/news/under-pressure-tire-tech-from-paris-roubaix-2013_281135

Perhaps I'm not too far out, pumping 28mm tyres to 80/85 psi, and not particularly worrying until it drops to 50-ish.
I've never had any real problem with pinch punctures - when it happens (rarely) it's either obviously hitting a sizeable rock at speed, or there's already another slow puncture (thorn).

(90kg, before you ask)

[andrew_s]

Mike's reference of minimising rolling resistance under hard braking

Is this not a rather daft thing to want to do?
If you are braking hard, extra rolling resistance is surely an advantage?

[LEE]

Did anyone else spend the last 40 years simply pumping up their tyres until you couldn't dent them with a hard push from a thumb?

[Biggsy]

Mike's reference of minimising rolling resistance under hard braking

Is this not a rather daft thing to want to do?

I don't think anyone particularly does want to do it.

[Biggsy]

Did anyone else spend the last 40 years simply pumping up their tyres until you couldn't dent them with a hard push from a thumb?

It was only 25 years for me.  But it is still a good method!  An experienced cyclist's thumbs are accurate to 10 psi!  The track pump gauge I use now just saves the bother.

Nit pick: actually, you should be able to dent the fully inflated tyres with a really hard push of two thumbs together (depending on hand strength).  The amount of dent indicates the pressure.