Rolling resistance question

[MichaelW2]

The variables are tyre width, pressure and construction ( grip pattern, sidewall flexibility).
At constant pressure and same construction wider tyres have lower rolling resistance.
At constant width, higher pressure has lower rolling resistance.
When all three variables are in play it is hard to predict which tyre has lower RR.

For climbing, tyre weight may be equally significant.
Air resistance is less significant at climbing speeds.

 

[ChrisEyles]

On road grip is never an issue (unless you're climbing out the saddle with poor technique and getting rear wheelspin) - so I'd have thought whatever gives lowest rolling resistance on the flat would be best. As mentioned, weight is important to consider when climbing hills.

Off-road climbing is much more complicated, and best tyre choice (and pressure) will depend on surface, rear suspension or not, how much it's been raining, what gear you're in, skill in picking lines etc etc

I've yet to come across an on-road hill I can't get up (however slowly!), but there are plenty of off-road climbs that have me scrabbling for traction or bumping into a big rock and stopping dead.

Crap road surfaces will be in between the two.

I'll bet the difference you'd feel blindfolded between two sets of tyres is less than you'd notice if you had a nice big bowl of porridge for breakfast beforehand

 

[CXRAndy]

Got that bit. Was more wondering about on the hill. An extreme example could be walking up hill in flats compared to spikes. Does, say, the knobbly tyre hold you better on the incline whereas, a smooth would seem to have more capacity to want to slide backwards?

Is this off road or tarmac? If the latter a smooth tyre will always be better

Edit seen its on road.

Tubeless 25-30mm will give best rolling resistance

 

[brucers]

On road grip is never an issue (unless you're climbing out the saddle with poor technique and getting rear wheelspin) - so I'd have thought whatever gives lowest rolling resistance on the flat would be best. As mentioned, weight is important to consider when climbing hills.

Off-road climbing is much more complicated, and best tyre choice (and pressure) will depend on surface, rear suspension or not, how much it's been raining, what gear you're in, skill in picking lines etc etc

I've yet to come across an on-road hill I can't get up (however slowly!), but there are plenty of off-road climbs that have me scrabbling for traction or bumping into a big rock and stopping dead.

Crap road surfaces will be in between the two.

I'll bet the difference you'd feel blindfolded between two sets of tyres is less than you'd notice if you had a nice big bowl of porridge for breakfast beforehand

Cheers for that. Oddly enough it was a noticable difference in a change of tyres that got me pondering.

 

[Globalti]

As ChrisEyles suggests above there will be a bigger difference due to how much you had for breakfast and when you last opened your bowels!

 

[Ajax Bay]

Rolling resistance tends to rise linearly with speed

Care to explain that, Roger? Does that force rise linearly with speed, or does it rise approximately linearly, or does speed have no effect on the rolling resistance force of a tyre (hint)?
I agree that, when climbing rolling resistance of the tyres is of 'minor' importance (cf gravity).

 

[rogerzilla]

A linear relationship. Proportional. Double the speed, double the resistance?

Now resistance and power are not the same thing...

 

[MichaelW2]

Care to explain that, Roger? Does that force rise linearly with speed, or does it rise approximately linearly, or does speed have no effect on the rolling resistance force of a tyre (hint)?
I agree that, when climbing rolling resistance of the tyres is of 'minor' importance (cf gravity).

In contrast to air resistance which is proportional to velocity2.
At slow speeds RR dominates. At high speeds, AR dominates. Somewhere in the middle is your cruising speed.
I would be interesting to find out if there is a formula for cruising speed

 

[confusedcyclist]

On paved roads, I've yet to encounter a hill where my tyres didn't grip the road!

 

[ChrisEyles]

As ChrisEyles suggests above there will be a bigger difference due to how much you had for breakfast and when you last opened your bowels!

Aaah, but would the extra energy and calories from the porridge offset the extra weight of the porridge? These questions matter

 

[matticus]

A linear relationship. Proportional. Double the speed, double the resistance?

Now resistance and power are not the same thing...

power = I^2 * Resistance, doesn't it?

 

[roubaixtuesday]

power = I^2 * Resistance, doesn't it?

Only if you've been struck by lightning

 

[confusedcyclist]

In contrast to air resistance which is proportional to velocity2.
At slow speeds RR dominates. At high speeds, AR dominates. Somewhere in the middle is your cruising speed.
I would be interesting to find out if there is a formula for cruising speed

Actually there's an excellent calculator that was shared on this here forum that calculates rider speed based on output watts, weight of rider and bicycle, gearing, incline and other variables etc. If anyone knows of it, I'd really appreciate the link as I lost it in my bookmarks.

 

[Randomnerd]

Jan Heine did some real world tests and found that wider tyres with supple casings and lower pressures offer significantly less rolling resistance. Loss of watts through hysterisis etc. I think it was a roll down test over 250 metres with lots of tyres, but should still apply uphill. Bumpy surfaces, even rough tarmac, can sap a lot of watts.

 

[faster]

At slow speeds RR dominates. At high speeds, AR dominates. Somewhere in the middle is your cruising speed.
I would be interesting to find out if there is a formula for cruising speed

All true, and obviously the speed at which there is a change over between whether AR or RR dominates relies on many factors, but I think I'm right in saying that in most cases that speed will be pretty close to zero.

AR will almost always dominate.

I have no idea what any of this has to do with cruising speed.