Commuting - Fat or Thin

I have put in enough Km's to justify changing my knobbies to slicks to speed up my commute.
There is a choice of slicks available regarding the width.
Can't seem to work out the differences , the only thing I have worked out is that the fatter slicks might be more comfortable.
Is there a down side to fatter slicks

The thinner the tire, generally the higher the tire pressure. The higher the tire pressure the lower the rolling resistance. The higher the tire pressure, the more "harsh" the ride.

It's all a compromise. Are you after speed? Get a 26x1" with 110 max psi, and it'll be harsh and fast. Want more comfort? Get a 1.5 or 1.75 with 80 max psi. Or, for a SMOOTH ride get a 2" tire with a max 60 psi.

L8R

Well almost.
Higher pressure gives lower rolling resistance.
Give the SAME pressure, a fatter tyre will have LOWER rolling resistance.
Fatter tyres usually have a lower max pressure.
Thinner tyres are lighter in weight and have lower aerodynamic drag, so will accelerate, and brake faster, and will be more efficient at very high speeds (aerodynamic drag is proportional to speed squared, double the speed, quadruple the drag).

In practical terms, what most commuters and touring-style road riders use is a 1.5ish" slick at about 80-100PSI. If you want to try your hand at a fast century, a time trial or a triathalon on a roadified MTB, then use a 1-1.25".

A lot will depend on the smoothness of your commute. Good roads can easily offset the need to be overly picky about the soft feel of thicker tyres. If I had my time over again with my mtb I would definitely go thinner than the 1.5s I used.

I use the 1" on my MTB. Tom slicks at 115lbs. No flats in months and are as fat as my 700x28s.

Harsh is relative.

ehenz

I use thick tires - 2.1, But I use expensive brand - Michelin. They are very light, but strong. I would never return to the low-cost tires, as long as I can afford the good ones.

I tried to use thinner tires - 1.75, but returned to 2.1, because my route goes over the roads wth a lot of potholes.

The thick tires negotiate such roads much better and safer.

Increase in resistance is negligible, at least I did not notice any.

But I do notice a lot of difference if I use the heavy tires or high-tech light foldable ones.

I use relatively thick (1.9) tyres myself. I don't know about Brisbane, but down here on the coast, the council has a habit of digging unnecessary holes in roads, so I find it better to be a little bullet proof if I can.

If you buy good tires the rolling resistance will not be an issue, I've tried all types of tires, thin high pressure, fat low pressure and both have advantages. From a commuter stand point, the Conti. top touring 2000 26 X 1.75 is the best I.ve found, they roll well, carry heavy loads well, handle well over rough roads and dirt, flat very, very little and last over 4000 miles. Thin higher pressure tires seem to flat easier, I ride the conti's at 45 psi.
By far the worst tire I have ever used was the panaracer pasela, it rode hard handled the every day road crap poorly and flatted way too often, It's a tire that can really make you late for work. I dumpstered those babies.
I also ride the toop touring on my touring bike 77 - 32C with the same satisfaction, many miles no flats.

But I have used Paselas in 700cx32 for 2 years of commuting, on roads and trails, with plenty of curb-hopping and glass. I wont say its the toughest tyre out there, I managed to slash the sidewall of one after a week of use, but the other has soldiered on for 2 years. It works about as well as a much cheaper Vredenstein commuter tyre.

Another nod here for using 26x1.9 slicks. Gives a good smooth ride Max pressure on mine is 70psi. I ride on fairly smooth roads too.

1.95 semi-slicks (smooth central band) - vredestein spiders, copes with Kent County Council's idea of road maintenance...

700x28 Gatorskin Ultra's at 120PSI on a mix of so-so and awful roads on a 20 mile round trip daily commute and loaded touring. Ride is somewhat harsh, but few flats.

Paul