I have a Trek DS 1 hybrid with disc brakes with 700x38 tires...rims Bontrager Connection alloy, 32h
What are the widest tires that I can swap out on these with the least amount of problems or issues

no fenders

I have a DS 8.4, and I'm not sure the frames are the same. It came with the 700 x 38s and I just put 29x2.0 Schwalbe on it and they fit fine. They're 50mm at the widest with 48psi of air....

Wow....50mm fit? I'll look around. Wont be able to get to my local bike shop until the weekend...ill look into it. I assume you had to get different rubes?

I assume you mean tubes.

You can often go with slightly larger tires than the size range indicated on a tube's packaging. The exception is with puncture-resistant tubes -- they are often so thick and firm that they just won't stretch enough.

Pros to going slightly undersized in the tubes:

• Lighter weight, all other things being equal.
• You may already have them on hand.
• Often easier to install (not as much tube to cram into the gap before inflating).

Cons to going slightly undersized in the tubes:

• Undersized tubes may be more puncture prone.
• Undersized tubes may be asked to stretch too far, in which case they'll fail.
• Undersized tubes aren't as happy with a patch applied; the patch doesn't stretch much (or at all), so this puts additional stress on the tube.

I've used 23-25mm tubes with my 28mm tires. They worked out fine except for that last point; my patches didn't last very long with them.

If the tube's advertised is range is 700x35-38 you can probably safely go up to a 40mm tire. I'm pretty sure you wouldn't like the reliability of those same tubes if you went up to a 50mm tire, though. On the other hand, tubes are pretty cheap, and it's a good idea to replace them when tires are replaced anyway. So that being the case, go with a tube where the tire is within (or just slightly above) the tube's rated range.

Yes I got tubes to fit, 29 x 1.9-2.1. The way it rolls I doubt I will go back to the original 38s again....Oh and there is plenty of clearance even on the back.. Just a hair under a quarter inch.

which model? my 29x2 marathon winters are only 47mm at about the same pressure

Schwalbe Hurricanes ....on the bontrager 17mm rims

interesting tread pattern. looks like they give you some bite for turns in the rough stuff. thanks for the rim size info. amazing how big tires fit on rims that aren't necessarily wide, huh? my Trek FX 1.0 Alpha has wider rims than my GT Timberline 29r mtb. of course the GT mtb fits wider tires than the FX hybrid. that's why I initially thought to suggest 40mm for the OP from my phone. funny how some bikes are called "hybrids" when they have front suspension forks & can fit beefy tires. is that correct? your bike is not considered/referred to as, a mountain bike?

Yea it's considered a hybrid, it's a nice ride, for me. Got a ride in yesterday on the Hurricanes eight miles of asphalt and three miles on a sandy gravel road. Loved the way it handled on both...