I’m trying to convince my 142-lb, 55-year-old dad not to fill his tires to 120psi because it’s slower and less comfortable.
There was a chart out there, and of course jackmott is constantly reciting it, that there is an optimal psi for every rider weight that is somewhat less than 120psi, above which rolling resistance increases dramatically. But my search skills are failing me, because I can’t find it.
Does anyone know where that is?
there is tom’s field test:
there are manufacturer charts:
http://www.michelinbicycletire.com/michelinbicycle/index.cfm?event=airpressure.view
You can go to Biketechreview and look at the AFM rolling resistance charts, he did some pressure tests, I think Tom Anhalt did a road test.
At 120 PSI at his weight, depending on the tires, and the road surface, your dad isn’t particulary high. 110 front and 115 rear would likely be a bit better, but I doubt your dad has slid to far down the slope. Much above 120 and it can get ugly quick though.
Is there an article that goes along with the chart, or anything that gives an explanation of the phenomenon?
think “tire rebound” off surface imperfections.
too much tire pressure is (in my mind) a lot like ‘heel striking’ while running. every impact is like hitting the brakes.
Pretty much, you want your energy to move you forward, you dont want your energy to move you up and down. Look at a pogo stick. It takes a lot of energy just to bounce, with out moving forward.
Ideally you would repeat Toms work with your tires/tubes on the specific road.
Styrrell
Is there an article that goes along with the chart, or anything that gives an explanation of the phenomenon?
the idea is that at some point more pressure, while decreasing tire deflection, and thus saving energy there, starts to waste more energy shaking your body around and or moving you up and down over each tiny little bump on the road
it should be noted that the guy who runs biketechreview tried to do a similar field test and did not find the same break-point where more pressure was worse
so, probably some unresolved questions in this universe.
So how hard do you run your tires Jack?
110/115 - I’m 175lbs
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110/115 - I’m 175lbs
Holy Crap I am doing something right I guess. 110/115 and I am 172
Is there a description of the surface quality for the"on-road" test? Or does it matter? I don’t think I’ve ever raced where the surface was particularly smooth asphalt on average.
there is tom’s field test:
Hrm according to that chart even at 152 lbs I’m supposed to run 110/115 as well on the evo corsa CXs . Seems high. Last minute IMC tweaking/2nd thoughts. 
keep in mind we have no idea what the manufacturers criteria is for their chart. comfort, safety, speed etc.
but everything is in agreement that 130/150/160 psi is a bad idea =)
Hrm according to that chart even at 152 lbs I’m supposed to run 110/115 as well on the evo corsa CXs . Seems high. Last minute IMC tweaking/2nd thoughts.
At IMC on the crappy free wireless, fretting over trivialities as usual. If my front wheel is carrying more weight than the rear (with me on it) should it not be higher or at least equal PSI to the rear? Weight with no fluid was 96 front wheel, 84 rear.
I was thinking the same thing. I’ve not weighed myself on the bike, but I have a feeling I have more weight on my front wheel since I have a long torso.
110/115 - I’m 175lbs
Holy Crap I am doing something right I guess. 110/115 and I am 172
I’m about 168. For training I prefer to go a bit lower, about ~103/108 on road bike, 105-8 both wheels on tri bike. For me that’s the sweet spot, 110 starts feeling a bit harsh to me, lower than 105 in the rear starts to feel a bit squishy and I’d worry more about pinch flats.
For racing on the tri bike I generally use same pressure front and rear and vary pressure depending on the road surface expected, using same pressure as training if the pavement isn’t great, slightly higher (112-115) if the pavement is decent, very occasionally 120 for very good pavement, never higher.
It also depends on the size of the tire (23 vs 25c) and the construction of the tire. Ex: Michelin PR3s are listed as a 127 tpi tire vs. the Evo CX at 290-320 (depending on year/model). Michelin recommends a much lower pressure (assume due to the less flexible casing) than does Vittoria with the more supple casing.
So really if you have a 20c on the front and a 23c on the back, and more weight on the front - you could run 120/105 and not be a loon?