tire weight vs rolling resistance

Try to figure out what is more important...a light tire (say 200 grams) that is good to 110 psi or a 240 gram tire good to 145 psi. Is there a method to calculate the tradeoff?

 

NO...

Your question is laden with incorrect assumptions...rolling resistance is not determined soley by tire pressure, as a matter of fact neglecting low pressures, rolling resistance is determined by the tire construction more than anything.

 

The thing that really matters is fitness. The nano-percentage difference from one tire to the next is meaningless.

 

Yep, fitness will do more for your riding than a few psi or a few grammes off the tyre weight.

However, you would notice a difference between a 240g tyre at 100psi and a beautiful Veloflex record (130g) with a latex tube at the same pressure.

Fitter people would still pass you though (take it from who knows)...!!

 

Yeah you will but this hair splitting 21mm vs 23mm tire crap. It's pretty meaningless.

 

could not agree with you more Iron Donut but psychologically, if it feels faster some people enjoy it more and if that gets more people out on bikes, that's got to be a good thing in my book

 

You'll get lots of enjoyment from pumping your tires up to 145 and have them blow of the rims at high speed.
Are your rims rated for 145?

 

The fastest tire would depend what kind of terrain you're racing on, as well as your weight, speeds, and road surface conditions. Best pressure would also depend on these criteria: it's not the max rated pressure on the sidewall, unless you're running on a track or ultra-smooth paved surface.

As a recreational rider I look for a tire with good puncture resistance, decent tread life and a smooth ride. Saving 40 grams a tire doesn't appeal to me if I have to compromise on either of these. Today I carried 1200 grams of water and sport drink on my ride, so saving 80 grams isn't that big a deal.

 

But dhk, this is rotational weight!

 

The lightest will roll fastest, thinner, more flexible tire walls runs faster.
Higher PSI gives higher roller restance on normal roads, approx 110 it the ideal (fastest). Very high PSI is only fastest on real smooth surfaces = wooden velodromes.

 

For roads, the optimal tyre pressure is dependent on the weight of the rider, all other things being equal. The front tyre shouldn't be taken to as high a pressure as the rear, as it bears less weight. I've seen a formula that recommends front 90psi and rear 120psi for me at 88kg (don't ask me where to find such formulae - try google).

 

A pre-ride dump is going to matter far more than 20 grams on a tire. I can have great rides on my (relatively) heavy beater bike and crappy ones on my 17 pound race bike. Leave the weight weenie issues to guys like Lance.

 

Sounds like the next fad:
"pre-ride power bars, now with laxative for your best performance"

 

Dang, I gotta go patent that idea before PowerBar hops on it!

 

I'd also throw in handling at the top of the list. It doesn't matter how low your weight or rolling resistance is if you're face down in a ditch.

 

By handling, not sure if you're talking about grip, or steering response. Certainly grip is important for cornering and braking. I didn't mention it because I haven't noticed any big difference in grip on the tires I've used. I'm sure there would be measureable differences on a skid pad, but it's not something I care to investigate on the road!

Actually, I recall clearly the last time I experimented with limit braking. Was setting up for a downhill left-hander, thinking I could make it fine at 35 mph when the rider two in front of me hit the brakes as I was looking ahead into the turn and not at him. Resulted in what David Hobbs (the F1 announcer) sometimes refers to as a "lurid moment".

 

Not necessarily true. Rolling resistance depends also on tire width. A wider tire (up to a point) with equal PSI will generally roll easier than a narrower but identical tire, because there is less sidewall deflection, and hence less friction - not because of "more flexible tire walls".

Also, it depends on the design of the tire casing. 110 is not a "magic number" for PSI. Many tires such as those made by Vittoria and Vredestein perform better with slightly higher PSI's because of their more compliant casings, with Vred's usually rolling better at 125-130 PSI, "all else being equal".

Overall rider/bike weight also comes into play.

Try it sometime. I can guarantee you that my Vred's roll much easier at 125 than at 110, with no loss of traction or shock absorption compared to others at similar PSI's, such as Mich's or Conti's.

As to the OP's question, an extra .5 to 1.5 oz. of weight will make very little if any difference in speed/efficiency as compared to a faster rolling tire. If you can't push a 240 gm. tire as well as a 200 gm. one, then you need more miles on the bike.

 

My experience has been that narrow tires with stiff casings just bounce all over the place if anything gets underneath them. I'm not sure if the more suple tires have a better coefficient of friction, but it doesn't matter how sticky the rubber is if it's not touching the road.

 

Dumb question .
What the heck difference is 40 grams going to make when you´ve got 60 or 70 KILOS sitting on top of the tyres .

tyre pressure will be a factor of total weight related to the tyre design , but you could try running 1/2 a bar less than the max rec pressure - too bouncy ?lower the pressure , wet / cold weather ? lower the pressure . but remember that mavic recommend a minimum pressure for their rims / wheels of about 7 bar (100 psi )

 

Agree lower pressures can help with grip and roadholding on rough roads. I've ridden with a guy who had to slow on a 45 mph descent when the surface got a bit rough. Sure enough, he was running max pressure in his tires, and weighs 160 lbs.

Also, since we have so many high-speed descents around here, I've taken a little time to balance my wheels. I was surprised to find my new Velomax wheels were considerably out of balance when I spun up the rear wheel in a big gear. (They are heavy opposite the valve stem, where the rim splice is located.) If the saddle is jumping up and down a couple of cm's at 35 mph, that can't help roadholding....