Slicks for commuting 1.35 vs 2.0? Any difference?

Klang180

Hello Everyone

I posted a thread about which brand of slicks to get and i think the consensus was on the Schwalbe Kojaks for the best overall blend of comfort, speed and puncture protection although the Conti Sport Contact were also worth a mention. However i am confused by tyre widths. I currently run Sport Contacts at 1.3 on the front and 1.6 on teh back and sometimes it can be a little rough. However what i don't like above all else is rolling resistance and drag.

So, my question is, does it really make a significant difference between a 1.35 and a 2.0? Would i really feel a difference when running on an MTB on standard 26" rims. I suspect there is more to it than simply the width but i am not an expert. So shall i get the slightly cheaper and more comfortable 2.0 or go for the skinnier 1.35?

The Rookie

Rolling resistance will be little if any different, on rougher surfaces the wider tyre will have a lower rolling resistance than the skinny one, however aero drag will be very different, when comparisons have been done on road bikes, aero resistance exceeds rolling resistance at below 20mph, so even at circa 18mph half your resistance is aero (more if its a headwind!) and narrower tyres means less aero resistance, 28mm road tyres have a lower rolling resistance than 25mm, but road racers use the 25mm for the lower aero drag (and that's only a 3mm difference!). So really it depends on how fast you ride, if you pootle at circa 10mph then it won't make much odds, if you are pushing 15mph or more then I'd be looking for a 1.5" at the fattest (which is what I have).

mpie

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19654848#p19654848]The Rookie[/url] wrote:

... So really it depends on how fast you ride, if you pootle at circa 10mph then it won't make much odds, if you are pushing 15mph or more then I'd be looking for a 1.5" at the fattest (which is what I have).

Back of a fag-packet calculation suggest that going from 1.3" to 2.0" wide tyre on an MTB adds about 2% to your frontal area (most of it is you). If air resistance account for ~50% of your work done, then you are only going to experience ~1% difference in speed/effort. I would suggest that that is insignificant in the grand scheme of things.

The Rookie

Which ignores the fact that a rolling bike wheel has a truly dreadful Cd and so the front area calc isn't relevant as the rest has a much better Cd. It's CdA that matters not just A.

Aero road rims don't change frontal area but have a big effect on drag, disc wheels increase frontal area but reduce drag even more. http://www.sheldonbrown.com/rinard/aero/aerodynamics.htm aero wheel gives a 4.8% reduction in total aero drag for the same frontal area for example.

Very significant in the grand scheme of things if you actually think about it.