Tire size question
 

I'm doing a trail bike build on a Trek 700 frameset. While I'm not interested in competitive cyclocross, I want the bike to have cyclocross type capabilities as far as being able to to from paved surfaces to gravel and dirt roads, turf and even some loose trail. I've decided on the Schwalbe Smart Sam tires but want some input on what size would give me the best all around performance. The fork won't take anything over the 40mm so the 45mm is not an option. I've asked around the LBS and a few area cyclocrossers and have had answers ranging from "bigger is better" to "anything over 28 with some tread is fine".

I have the Smart Sam for use on my Monster-cross bike, but it's overkill 99% of the time. The best use of the Smart Sam is soggy and loose earth. The Smart Sam is a good option for 75% singletrack, 25% road.

I would look at these tires as alternatives;

http://clementcycling.com/400/xplor-mso

http://www.kendausa.com/en/home/bicy...py-medium.aspx

http://www.kendausa.com/en/home/bicy...ock-eight.aspx

http://www.schwalbetires.com/bike_ti...s/%252Fcx_comp

I have the 700x45 size Smart Sam. I also have a 700x40 Schwalbe Marathon Dureme, a 700x38 Schwalbe Marathon Cross and a variety of 700x32 tires.

A 700x40 tire can be run at low pressures and provides more suspension than a smaller tire. However, leave enough room for mud accumulation and for rims or tires that are not perfectly round.

A Trek 700 might not accept a tire larger than 700x40, but a 700x35 will fit without issues. If you buy a 700x40, puchase on the condition that the tires can be returned if they are too large.

The Schwalbe Marathon Dureme is an ideal 25% singletrack, 75% road tire. The tread is not knobby, but it works very well on rain soaked gravel or dry singletrack and earth. The tire is very smooth and fast on pavement. The Schwalbe Marathon Dureme is sold in both a 700x40 and 700x35 size.

My opinion, not knowing the condition of your "gravel" roads is, you won't need anything over 35mm. Choose whatever tread pattern you like in that size and play with pressures.

Thanks for the input

That is exactly why I'm building this bike, I never know what the condition will be and want to be able to ride over a wide variety of surfaces. Gravel roads in the area can be packed like concrete but a couple days of rain and some traffic can turn them to oatmeal. Trails can be pea rock, crushed granite, sand, packed clay, worn turf or all of the above. There is a riding area near here called "The Sand Hills" which is a series of trails through sandy loam prairie. Some of the ground is fairly loose but not soft like a sand dune. The rails to trails are usually a mixture of the old granite railroad ballast and crushed rock, pea rock, or gravel.

I have an old pretty much worn out Michelin 42mm semi-knobby tire that I tried in the fork and there was about 1/4" of clearance on each side and just a little more over the midline of the tread, so I ordered the 40mm Schwalbe Smart Sams after checking that I could do a one-time exchange for size if they are unridden.