Technical > Wheels, Tyres and Brakes
Rene Herse tire pressure calculator
JohnR:
--- Quote from: UKTony on March 26, 2022, 11:17:18 am ---30psi for 2” tyres seems low to me unless it’s for particular surface conditions.
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I should add that's for my normal lightly-loaded condition with me, the bike and a small bag being no more than 85kg. Some sections of my local roads include some badly patched potholes.
Andre Jute:
--- Quote from: UKTony on March 26, 2022, 11:17:18 am ---http://www.sjscycles.com/thornpdf/thorn_mega_brochure.pdf
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Thanks for the link. Tony. It turns out I already had an up-to-date copy in my Bike Bible. But I spent a most enjoyable hour reading here and there.
--- Quote from: UKTony on March 26, 2022, 11:17:18 am ---30psi for 2” tyres seems low to me unless it’s for particular surface conditions.
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Two bar, which is about 29psi if I remember correctly, seems good to me on 622x60mm Big Apples. I've been lower but not recently since I'm heavier and the roads are worse, so I'm adapting, as you did.
I would add though, about your scary moment, that in the longer term it is worth considering going to wider bead-to-bead rims if available. Tyres seat more securely in rims wider across the beads than 40 percent of nominal tyre width, and under 40 percent bead width definitely calls for higher inflation to keep the tyres attached and working.
Andre Jute:
--- Quote from: martinf on March 26, 2022, 06:37:20 am ---I run the front tyre with a lower pressure than the rear, it has worked for 40+ plus years so I will carry on doing this.
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I've been cycling only 80 percent as long you, Martin. But I reckon that is long enough to conclude that unnecessary experiments with the dynamic friction joint between the tyre and the road could itself easily be the cause of an unwanted incident.
PH:
Thanks for the link Dan, that made interesting reading, though my thoughts and methods remain as per the previous thread you've referenced - That is I start with the 15% drop and experiment till I find what I like, which doesn't seem to stray far from it. I also have a preference for a narrower tyre on the front, I'm not recommending or justifying, it's something I've done for years and works for me. It also has the advantage that it evens the pressure so I only have one number (Per bike) to remember and also wear goes some way to matching the wear.
As the first paragraph in that article says, there's so many factors and preferences - IMO so many it's impossible to separate them. A quick comparison to the calculator shows that all mine are roughly within the range, though it's noticeable that the narrower the tyre the firmer I like it - which brings me back to previous point, because it's also the fact that the narrower the tyre the more likely I am to be using it on better surfaces.
Then there's the difference between optimal and acceptable, both how far from the optimal you can wander and how much difference it makes. None of my roadside pumps have a gauge, I've ridden countless miles with sub optimal pressures and it's been fine. sometimes noticeable, sometimes not, never enough to bother doing anything about it till I'm home.
When I rode an E2E, averaging 100 miles a day for 11 days, I took a Schwalbe gauge and checked the pressures each morning, my companion checked his the week before we set off and not again - Who was right? Who cares ;)
I'm not sure about this:
--- Quote ---Front v. Rear Pressure
Most bikes carry more weight on the rear wheel than the front. However, when you brake hard, almost the entire weight shifts to the front wheel. For that reason, it’s not advisable to run a lower pressure in the front tire.
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Assuming you're braking in a straight line and the pressure is enough to keep the rim away from the road, what's the problem with the front tyre compressing under braking? I'd have thought the extra contact patch would be an advantage.
mickeg:
--- Quote from: UKTony on March 26, 2022, 11:17:18 am ---... Not long after I bought my Mk 2 Nomad I had a very scary experience on 26”x2” Schwalbe Duremes at speed on a narrow lane round a sharp bend at the bottom of a hill when the front tyre started to wobble. I rang Thorns and spoke to Andy Blance as a result of which I started using his recommended tyre pressures on page 40 of the Mega Brochure, for the Duremes and subsequently for the Marathon Supremes which I’ve been using all year round now for a few years, here
http://www.sjscycles.com/thornpdf/thorn_mega_brochure.pdf
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Thanks for posting. I had forgotten that Thorn published recommended pressures. I knew they had max pressures based on rim strength but I had forgotten that they had recommendations.
I almost always run 57mm tires on my Nomad Mk II, Andra 30 rims. I had some screwy handling on a curve at speed several years ago from too little pressure in a on a too narrow rim for that tire width. Since then I have quit trying lower pressures that I wanted for better grip on that too narrow rim. But on several previous threads I ranted about my disagreement with Thorn on tire and rim widths so I won't elaborate here.
Since then for around home use on an unladen bike I run 35 psi Front and 45 psi Rear. For that tire width, they recommend 35 Front and 40 Rear which is same as I have been using for the front, I have been 5 psi higher in the rear. I will keep using the pressures I have been using for unladen riding.
Touring with a heavy load, I do not have a firm list of numbers that I follow, but I think that I probably used about 45 Front and 55 Rear on that bike with 57mm.
Touring on that bike I have been using Marathon Extremes (discontinued) at 57mm and folding bead. For around home use have been using a Hutchinson Cobra 57mm mountain bike tread. Both tires have a pretty supple sidewall and roll surprisingly well on pavement.
I have a piece of paper taped to my floor pump that lists the pressures for unladen riding around home for my bikes. I am not going out to the garage to get the pump to cite them, but it lists my common tire sizes and the F and R pressures:
28mm
32mm
35/37mm
I do not recall if I listed 40mm, that bike is in storage.
50mm
57mm
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