Arete One

My Trek 7700 came with 700x38 tires, but I've long wanted to go down in size, both in the hope of reducing rolling resistance so I can get more speed out of the same effort, but also because the max size for the fenders I have but never put on is 35mm.

The vast majority of my riding is/will be bike paths w/ mud and debris from what's left from high river levels, urban streets in typical disrepair, and some crushed, hard-packed dirt/gravel between trail pavements. There may be occasionally some dirt trail riding in state parks, etc., but minimal.

My thought is to go down to a 32mm, which would give me a bit of wiggle room on the fenders as well. While poking around the Continental website, I found the graph that shows a 28mm at its high pressure end actually has less rolling resistance than a 22. Interesting. So, I may not get any speed increase.

I had a friend strongly recommend Gatorskins for our streets here, but I also don't know what kind of bike he has. When I plug in my info on the Continental site for what I'm looking for, and identify my need as Urban/Tour (rather than Road), with high puncture protection, the results don't show Gatorskins, as that's considered a Road tire. Of what comes up, the best option seems to be the Contact Urban, with its PureGrip compound. A review reports that it's particularly good in wet conditions, which I like because my current tires like to slide a bit on wet asphalt.

Any thoughts on this decision would be most welcome.

hokiefyd 

There is definitely some interesting research lately (scientific, non-scientific, etc.) about the relationship between tire size and rolling resistance. Contrary to convention wisdom, which suggested that narrower tires inflated more were almost always faster, I think the most accurate generalization one can make today is "it depends". There are certainly advocates in the camp of "wider doesn't necessarily mean slower" and Jan Heine is certainly one of them. Here's an article that may provoke some thought:

Why wider tires are NOT slower – Rene Herse Cycles

Trav1s

I'm running SKS Blumel fenders on my Cannondale Quick one with Schwalbe Marathon tires in 700cx35 size and I'm happy with the tire choice. The bike came with Schwalbe Spicer K-Guard 700x30s and was a bit faster but not as forgiving. I considered the 32s but selection was low at the time of the upgrade.

TakingMyTime

Find some good 32mm tires and slap them on. They're still wide enough to handle a small amount of "dirt" while giving you a huge boost on the road compared to the 33mm that you're running. You will definitely feel the difference. Gatorskins have a reputation of being durable and puncture resistant, but don't get the best reviews on mounting and rolling resistance. I have a set of Continental Grand Prix 4 seasons (32mm) on my Trek FX and couldn't be happier. Don't overthink it too much. Pick a brand that you're comfortable with and get one of their long lasting puncture resistant tires and then go ride.

Arete One

Good advice. Don't over-analyze it. Make the change, see how it works out, and go from there. And that means riding, which is always a good thing.

raqball

My Trek FX Sport 6 came with 700x40's Bontrager GR1 tires. I mainly ride on tarmac and I wanted a smoother rolling tire that would still be able to handle some light gravel every now and then.

I settled on a pair of Specialized Pathfinder Pro tires in size 700x32. I also use TPU tubes so I think that also helps but I've noticed a difference in perceived rolling resistance / speed. Nothing scientific as I am 57 and speed is no longer the name of my game but in my head, they roll smoother..

Now this does come at a slight cost to comfort as I do notice bumps in the road a bit more but it's nothing that's extreme...