tyre pressure and weight speed diiferential

FATTRIATHLETE said:

I have been riding 23mm tubs ( vittoria ) at 7-8 bar (100 - 115 PSI )
Current average speed on flat 10 mile TT is 22mph.

I weigh 224 pounds

Am considering using 19mm 12 bar ( 170 PSI ) for 10 mile TT ( much further would be pretty uncomfortable on that thin and that pressure for me at present I believe )

Is it possible to work out what speed increase I could achieve by swapping to a 19mm 12 bar ( 170 PSI ) Tub

Thanks.

That's a good physics question... are you thinking about switching from a 224 pound frame to a less than 200 pounder as well? That would be cheaper and probably get you more speed.

I recently dropped 12 pounds on my frame and it's done wonders. I'm already using the 19mm tires but only at 120psi.
😄

FATTRIATHLETE said:

Is it possible to work out what speed increase I could achieve by swapping to a 19mm 12 bar ( 170 PSI ) Tub

There's an interesting article about tire size, pressure and rolling resistance here: http://www.cyclingnews.com/tech.php?id=tech/2005/features/conti_tech

Switching to 19mm will give you better aerodynamics and worse rolling resistance. The one variable that they missed in the article is handling. Narrow, high pressure tires seem to bounce around quite a bit on rough pavement, so that's something to think about.

Seems this discussion has been batted around in the past. Rolling resistance is a subjective measure, highly dependent upon the smoothness of the road surface, air pressure in the tire, and the weight of the rider. Fat tires really shine when the road surface gets rough, while narrow tires take off on smooth roads. It's the ability to deform around road imperfections, rather than having to bound over them, that gives the fatter tire much of its lower resistance. But that only applies if there are enough road imperfections to deform around. On very smooth roads, the advantage is to the thin tire.

Weight of the load matters, too. Heavier riders benefit from wider tires that don't deform as much to handle the load. Remember that the 19mm tires were made with skinny 150 pound riders in mind. 224 pounds might not go over so well.

Note that there are 28mm tubulars made for rough surface racing, such as cyclocross or Paris-Roubaix.

Simplest answer is to try the narrower tires and see how they feel. You can also crank up the pressure in your current tires if they will handle it - I ride my 22mm cotton Dugast tires at around 140psi. And changing to a sub 200 pound rider is going to make a huge difference in all aspects of cycling.

You can work it out but it won't be an increase. You weigh far too much for 19mm tyres. You are more likely to go better on 25mm despite the increase in drag unless your roads are as smooth as glass.

There are a lot of threads about this on here already.

Jay