View Single Post
  #4  
Old October 11th 18, 10:57 PM posted to rec.bicycles.tech
Andre Jute[_2_]
external usenet poster
 
Posts: 10,422
Default MTB 29*2.20 65 PSI

On Wednesday, October 10, 2018 at 11:02:45 PM UTC+1, Emanuel Berg wrote:
Today I had the first flat tire with the
29*2.20 MTB. This presta valve stuff is
obviously alien to me at this point, but
I managed to make it full again.
1) Some people say you don't even need an
adapter, you can just use
a Dunlop interface.


You need a pump either with two holes in the head, one for Dunlop, one for Presta, or with a specially made head that self-adapts to the valve -- I've never had one of the latter that works better than a two-hole type.

2) But of course I do have an adapter, only it
wasn't a pleasant thing fiddling with it
back and forth. I'm getting a quality pump
soon, God willing.


Of the two-hole types, the SKS Rennkompressor is the undisputed champion but it is a garage pump, not a carry-along, it is pricey, and if you wear spectacles the dial is far away and the divisions small; on the other hand, all those racing mechanics who use it can't all be wrong, and the thing is rebuildable only forever.

3) On the tire, it says 65 PSI. This must be
some theoretical possibility in a lab
setting with all brand new stuff, right?
Like when you buy a tent for three persons,
which is barely big enough for yourself to
sleep comfortably in?


It's a joke. Why should you ever wish to pump up a tyre 2.2in in width to 65psi? That kills all the comfort. I run an always laden bike (my painting gear, often shopping) under my 95kg or so on 2.35in wide tyres at 2 bar/28psi and a casual bit but definitely under 30psi and down to 1.6 bar with no ill effects and all the comfort a bike can give

4) Tires are 29*2.20 or 57-622. What is a good
PSI for going on asphalt ~98% of the time?


2 bar, unless your tyres' sidewalls are incompetently designed or manufactured.

5) Is there a difference what PSI one would
like in the front and rear tires?


Depends on the geometry of your bike and how you would like it to react to steering inputs and road irregularities. My own bike was chosen for lazy, relaxed geometry and a long wheelbase, and I inflate the tyres front and rear the same, to preserve that predictable understeering characteristic because downhills over which I often touch 50kph+ too often have road surface surprises, which on a twitchy bike can hurt or kill you even if you still have reflexes as fast as mine. On the other hand, my study and studio are both at home, so I have no need to duck in and out of rush hour traffic, for which one might want a bike with "faster" geometry and slightly harder fat tyres (still not 65psi! -- maybe 33 to 40psi, nothing over 40psi). My everyday bike is fitted with both a Rohloff hub gearbox and a motor/battery combo chosen for high instant torque, and I'm a retired jock and a masher, four factors that all contribute quick reactions in traffic, so there's more than enough power in the rear wheel to drive nippy behavior if I want it, but I'm assuming yours is a derailleur bike and powered only by your legs. You could try a few pounds differential first at the rear and then at the front, and see how the bike behaves, but I think the difference will be subtle. When I was an automobile racer at a time when the sidewall construction of the tyre set the limits of inflation pressure, I discovered in a set of high-speed tests that only a few millimeters in contact width made much more difference than front-rear pressure differentials in the car's handling (handling being what happens when the driver exceeds the car's native capability which is called roadholding...), which is why, especially in midengined cars the rear wheels started wearing much bigger tyres than the front wheels..

Andre Jute
Oh, nostalgia!
Ads
 

Home - Home - Home - Home - Home