Tyre [tire] Pressure

[bobfish]

There's been a bit of chat lately about recommended tyre pressure.

 

Generally, I use the lowest pressure I can get away with depending on the ride and conditions. Sometimes around 100psi on a road bike down to 23psi on a MTB. Aside from personal preference, and in the search for some objective guidance, I stumbled upon the Silca calculator: https://silca.cc/pages/sppc-form?submissionGuid=da5896df-5304-4cf4-bd99-051b2808d277

 

You need to sign up for the pro version - obviously Silca then want to send you product info, but you can opt out later. Of all the tyre pressure calulators this one seems to have been derived from the largest database. And it is predicated on having an accurate pressure gauge [$ilca?].

 

Probably the best starting point I've found, though I think there's still room for personal preference on the day: Particularly for less mainstream antics like big hit jumping etc.

Anyone anything better? 

Edited May 13, 2020 by bobfish
Trying to get rid of the line -- sorry

[damascase]

I don’t use - or need - a calculator for tyre pressure. Usually I aim for a value close to the maximum pressure that a particular tyre can bear, as that results in the lowest rolling resistance. On my MTB, on-road, the limits given on the tyre walls is 65 psi. I usually ride with 60 in the rear tyre and 55 in the front one. However, I do understand that that would be far too much for any serious offroad riding.

Edited May 13, 2020 by damascase
Typo

[bobfish]

 I wouldn't go near the max limit unless I was looking at big jumps onto a smooth touchdown surface...????. And I'm getting much too old for that!! Normally I just want to avoid pinch flats/rim damage or unwanted deformation/burping during cornering loads. For road, as high [low!] as is 'comfortably fast' ie speed, smoothness and grip.

I hear you though with highest pressure giving lowest rolling resistance: smallest contact patch etc. But that's only true for a billiard-smooth surface. For a given tyre, load and [less than perfectly smooth] surface, there is a point where an increase in pressure increases rolling resistance due to the kinetic energy conversion: Lack of tyre deflection exerts vertical forces to lift both bike and rider rather than being absorbed. Certainly feels fast though!

Definitely not telling anyone how to live their life, so the correct answer is "whatever you like" I guess. More important to just ride. ????‍♂️ ????????????

Edited May 14, 2020 by bobfish
Added last paragraph: saw what Damascase did to the last guy!

[StreetCowboy]

44 minutes ago, bobfish said:

 I wouldn't go near the max limit unless I was looking at big jumps onto a smooth touchdown surface...????. And I'm getting much too old for that!! Normally I just want to avoid pinch flats/rim damage or unwanted deformation/burping during cornering loads. For road, as high [low!] as is 'comfortably fast' ie speed, smoothness and grip.

I hear you though with highest pressure giving lowest rolling resistance: smallest contact patch etc. But that's only true for a billiard-smooth surface. For a given tyre, load and [less than perfectly smooth] surface, there is a point where an increase in pressure increases rolling resistance due to the kinetic energy conversion: Lack of tyre deflection exerts vertical forces to lift both bike and rider rather than being absorbed. Certainly feels fast though!

Definitely not telling anyone how to live their life, so the correct answer is "whatever you like" I guess. More important to just ride. ????‍♂️ ????????????

When I switched tyres from 38s to 28s I moved from 85 psi to 110 psi, and noticed the difference. 

 

I think the pressure has more to do with rolling resistance than tyre width, as for a given pressure, less of a large tyre will deflect and the contact patch will be shorter (and thus the extent of deflection less).

 

I've not considered changing back, but I might if I knew I was doing some serious off-roading again

 

[WaveHunter]

Nothing makes more of a positive difference on a ride than proper tire pressure ????  It pays to invest in a good foot pump with an accurate gauge.  They are cheap enough on AliExpress

[StreetCowboy]

1 hour ago, WaveHunter said:

Nothing makes more of a positive difference on a ride than proper tire pressure ????  It pays to invest in a good foot pump with an accurate gauge.  They are cheap enough on AliExpress

Good route planning makes a big difference.
It doesn't matter what tyre pressure, if the ride does not finish at the pub, it's not a good ride.

 

[Chomper Higgot]

I ride 23mm Continental 4000 at 110 dry weather and 85 wet weather.

[StreetCowboy]

8 minutes ago, Chomper Higgot said:

I ride 23mm Continental 4000 at 110 dry weather and 85 wet weather.

For a man of my girth (96 kg) I would think 85 psi for 23 mm would be risking pinch flats.
If it's a long ride, I'll pump my 28 mm up to 110 psi on the back, and not push it too hard on the corners if it's wet.  If it's a short ride, I'll pump up to 110 if its dry, and not bother if its wet.

 

[bobfish]

With a sixpack, that's 0.1 tonne! ????????. Good idea!

[StreetCowboy]

I’m frightened to go below 95 kg or that will put me in a different Strava weight class.

[StreetCowboy]

The last off-road rampage left a nick in my rear tyre,

and the tread is fading. It’s done between 5,000 and 6,000 km, so a replacement would not be premature.

At the same time, the rear tyre on the shopping bike developed a bulge, and then a split and a puncture, so I took a 28 mm off the mountain bike for the shopping bike, as the mudguards stop me using the spare 38s I have lying round.  The mountain bike can suffer the weight and comfort of the 38s.  Then I found a staple in my road bike front tyre, soft as yesterday’s popadoms.  
You have to laugh or else you’d cry.

So I postponed my plan to cycle to the office and get a tyre on the way home, till I’d fixed that puncture.  I noticed the front is a 38, and considered whether I should change that to 28, or go back to 38 on the back. I decided to stick with 28-38 for a bit less vibration on my arms, but high pressure for speed at the back.

Anyway, on Thursday I cycled into office, planning on stopping by the bike shop to get the rear tyre swapped, after the bike shop boss had assured me on Sunday that he had Schwalbe Marathons in stock. I should’ve called his bluff there and then.

My buddy had called the day before, to ask if I wanted some new pedals, as I doubt they will last much longer after the infuriating squeak they have developed; some emergency maintenance with a discarded roadside can of oil outside a motorbike shop had restored peace on Sunday, and I thought they were good for another 500 km, but why push it?  Since I’d planned to stop for dinner in a pub near his place, and not far from the bike shop, everything fell neatly into place.  When we got to the pub, Big G was there, so truly a serendipitous evening, other than the bike shop not having the tyres in stock, but that was the last thing on my mind as I set off homeward at closing time.

But to backtrack a bit, I’d realised that the bike was in no fit state to go into the shop, still with farm mud on it from two Sundays previous, so I’d put it into the car wash at the office, and the paintwork was gleaming polished, and as I rode through the traffic to the bike shop it was smooth as a dream and I was chortling away in happy contentment as I zipped through the traffic and down through the suburbs.  I stopped in the DIY shop for a new set of Allan Keys, a moment of disappointment at the bike shop, a quick skinful with the lads, and home.

Anyway, I still wanted a new tyre, so I went to another shop - another branch of the shop where I’d bought the same tyres previously. It was busy, and there was only one guy working, so I didn’t ask him to fit the tyre.

They’re not easy things to cycle with, bike tyres.  I didn’t want to change it there and then at the shop, as I want to keep the old one as an emergency “get to the shop” tyre, so I twisted it into an 8 and folded it, and held it looped over the bars in my left hand.

I swapped the tyres over; it was harder work than I expected getting the new tyre seated on the wheel, and in retrospect if I’d known it was going to get harder each time I’d have left the tyre with the tread facing backwards the first time. But I didn’t. Turned the tyre around, battled it back on, and must have nicked the inner tube. At first, I thought my floor pump was faulty, so I tried my hand pump.  25,000 km on the bike with no TLC has rendered it scrap, and I’m glad I found out at home. Checked the floor pump on the mountain bike, and pulled the tyre off for a third time to put a new tube in.

 

Anyway, to cut a long story short, I’ve had enough of tyres.

[StreetCowboy]

And I must've nicked the tube under the bead again, because 20 km into the ride, as we stopped at a petrol station for water, it burst and blew the bead off the rim.  So another quick tube change, and now I needed to stock up on tubes, as well as buy a new hand pump...
 

[bobfish]

You need some of these. Kill two birds.....

 

[StreetCowboy]

On 7/25/2020 at 4:09 PM, bobfish said:

You need some of these. Kill two birds.....

 

I've not tried it in my tyres, but I've been to the pub and bought the shirt

[StreetCowboy]

If you want to, you can skip the digressive waffle of the next three or four paragraphs and skip straight to the end...

 

I'd wasted two tubes trying to horse my leftover Schwalbe Marathon 35mm on to the front of the mountain bike without success, and had really had enough of it.  My buddy had commented on the importance of talc in the tyre to keep it dry and loose, and I'd thought maybe I needed to replace the spoke tape, so procrastinative shopping let me put off resumption of battle for a couple of weeks.  I wasted another tube; its worth pointing out that I tried to patch the tubes, but the tubes were a bit small, and the holes quite large, so that the patches were large compared to the diameter of the tube. 

 

From earlier in the thread, you'll know the Schwalbe Marathons take a bit of work to fit, and if I'd remembered that the mountain bike front wheel was so hard to fit, I'd have borrowed the tyre off the back instead.  And its not even the mountain bike front wheel anyway.  Its the replacement front wheel for the road / cyclocross bike, after I'd wasted that front wheel putting the bike down losing grip at the front four years ago.   The rim had got buckled and twisted, and the shops could not straighten it, so I'd borrowed the front wheel off the mountain bike, and had a new wheel built for the mountain bike.  But the hubs were 20(? or something else odd) spoke, and no-one had 20 spoke rims, so I had to get a new hub as well; when the guy in the shop asked if I wanted a road rim or a mountain bike rim, I asked for the mountain bike rim.  

 

Anyway, enough of the digression.  At first I'd swapped the wheels again to put the new wheel on the road bike, but it was a bit tricky replacing tyres on that rim, so I put it onto the mountain bike, which gets less usage, and the original mountain bike wheel on the road / cyclocross bike.  I figure it sees more rough roads and potholes than does the mountain bike in any case.  But they both have mountain bike front wheels in any case.

 

It had taken weeks to get round to trying again.  A bit of calmness, stoic fortitude, patience, and studious diligence saw me finally wrestling the bead over the rim.  I pumped it up, and the tube held air.  When was fitting the wheel to the bike I noticed that the tyre was on backwards, and when I thought about trying to fit it again ... "I'll pretend I never saw that".  Anyway, I also noticed that the tyre was pressed "for crotched tyres only".  I had no idea what that meant.  The rims are "tubeless ready", and I think they have a shallow depth so I assumed that the crotch was the depth of the rim, but apparently not - apparently it relates to a hooked lip on the top of the rim.  I don't recall what the rim lip is like, and I'm not going to take the tyre off to have a look, even if the tyre is on backwards.

[Hanuman2547]

I usually ride on 25mm tires on two of my road bikes and 23mm on the other.  I generally ride high pressure as in 110psi.  Hopefully my 92kg will flatten out the rear tire a bit to give me more forward momentum from the watts I'm producing.  Not that I track my wattage output.  

[StreetCowboy]

I’ve just had a spate of punctures on my friend’s bike; I’d fitted a new tube, talced the inside of the tyre, careful not to nip the tube, and ridden a couple of km to check it felt smooth. It had sat in the apartment a week at pressure quite happily, but a kilometre down the road she came out of the butcher’s and the tyre was flat as a politician’s humour.  So I scrupulously searched the tyre for foreign objects, patched the tube - and it burst again as I got it up to pressure.  My second patch may have missed the target, as I had to apply a third; and she was off again- with exactly the same result.  The holes were all in the same area, on the inside (rim side) of the tube, so I was confident it was not something in the tyre.  I had a suspicion it might be a flake of foil from the painting of the rim, which has been chipped by the steel tyre levers, or something in the rim tape.  So I studiously swept the rim and changed the tape, and put in a new tube, even though the latest leak was a new hole and none of the three patches were leaking.

As I was checking everything, I noticed that my tubes are not specced for that tyre size (23-28mm tubes in a 38 mm tyre) so another failure will tell me that is probably the problem, and I hope you can share that Painful lesson without sharing the pain

Edited October 17, 2020 by StreetCowboy