Pressure and p******* proofing

[Ajax Bay]

I stay around the 66-68kg mark so with the 2" wide tyres 55psi seems alright?

The loads are per wheel (overall load split 60 rear / 40 front) so that implies a loaded bike of 35kg (say) and rider weight of 130kg (say) would mean 55psi for the front tyre (on your interpolation of the graph).

 

[Ajax Bay]

if you have a half decent tyre, and maintain the pressure at a level sufficient to avoid pinch flats

And that pressure is what, Si? How do you decide what pressure to set which will "avoid pinch flats"?

 

[ColinJ]

And that pressure is what, Si? How do you decide what pressure to set which will "avoid pinch flats"?

These days*** I find that 'near enough' is near enough!

I mean that if I inflate a tyre to what feels like a reasonable firmness (firm but not hard) and then measure the pressure, it tends to be within +/- ~8 psi of what I would have opted for anyway. I don't get many punctures, my tyres roll okay, and they are fairly comfortable so I am happy not to worry too much about it.

If anybody is actually interested in what pressures I use ...

• 23C: About 85-95 psi front, 95-105 psi rear.
• 25C: About 80-85 psi front, 90-95 psi rear

*** I admit that I got it wrong when I was first cycling. I rode with pressures that gave super comfort but little protection against snake bites/pinch flats and so suffered quite a few of them. Then I overreacted and pumped my tyres up so hard that my bikes were horribly uncomfortable. I now use the pressures listed. They are lower than a lot of people use but I value comfort on the rough road surfaces round here.

 

[Ajax Bay]

@ColinJ - worth adding / editing in the total load (ie you plus bike).
For me - total weight 86kg, split 38kg/48kg and 75/90psi front/rear.

 

[si_c]

And that pressure is what, Si? How do you decide what pressure to set which will "avoid pinch flats"?

Bitter experience. I find that when the rear drops below 75, i start to get more flats. I keep it around it to 95 on 28c, but then I'm larger than average.

 

[Thorn Sherpa]

The loads are per wheel (overall load split 60 rear / 40 front) so that implies a loaded bike of 35kg (say) and rider weight of 130kg (say) would mean 55psi for the front tyre (on your interpolation of the graph).

I didn't realise it was per wheel by the graph sounds like I'm running the pressures too high. I wouldn't say it's an uncomfortable ride but maybe I've just become use to running with the tires that hard?

 

[mjr]

I didn't realise it was per wheel by the graph sounds like I'm running the pressures too high. I wouldn't say it's an uncomfortable ride but maybe I've just become use to running with the tires that hard?

Yep, you've bashed your undercarriage smooth like Acton Man, so it doesn't matter any more.

 

[ColinJ]

@ColinJ - worth adding / editing in the total load (ie you plus bike).
For me - total weight 86kg, split 38kg/48kg and 75/90psi front/rear.

Sounds about right - total load for me + bike is currently about 95 kg. I always put 10-15 psi more in the rear.

 

[Thorn Sherpa]

Yep, you've bashed your undercarriage smooth like Acton Man, so it doesn't matter any more.

years of undercarriage abuse

 

[PaulSB]

I run 8 bar (115psi) in summer and 7 (100psi) in winter on 25mm Gatorskins. I’ve had one puncture in 2017.

 

[gbs]

Yes, I agree with Banjo The only puncture that I have had with Duranos on my winter/wet weather bike, about 3000k this year, was because of rimtape failure . I have not had any punctures on the summer bike with Vittoria Rubino Graphene tyres - about 4500k this year. I am fairly well convinced that you have to payup for quality and then not try to run the tyres until the last k of usable life.

Turning to my original qn: from the above comments, I conclude that p******* vulnerability does not significantly increase with lower pressures and that I may as well enjoy the increased comfort.

I have also learnt about tyre drop, a concept totally unknown to me until I read Ajax Bay's post, and the notion of differential pressures between FW and RW. The fgures sugggested by the chart for my 80kg weight say 95k all up load on 28mm tyres on the winter bike are 5.0 bar on the FW and 6.2 bar RW - these seem v low. So, lower I will go but step by step .

Thanks everyone - very instructive.

 

[Ajax Bay]

on 28mm tyres on the winter bike

Just check the 28-622 tyres measure up as 28mm wide (at 80psi say) as the Continental GP 4 Season I have on the front is 28-622 but measures 26.5 (average) so that affects the read off from the chart. Oddly the ContinentaL 4000S II, also in 28 which I hoped to run (but can't with reduced clearance from mudguards), measures 30+mm (same rim). Go figure.