So the bike I'm currently prepping came with 40mm Schwalbe Marathon. They feel decent, definitely plush, just wondering if there is a drawback to going big. Most of my bikes have/have had 32-35mm tires, which I enjoy, but these things look monstrous and too far in the fat direction.

Besides weight, is there any practicable drawback to a bigger tire? I've also got a new set of Conti Top Contacts in a 37 (which come out far closer to my 35 Clement USH than these 40 Marathons) I'm considering tossing on, but if there is no drawback I'll probably just run these into thr ground

Acceleration when unloaded. Weight--Eh difference is maybe a pound, on a 30# bike with a 170-200# rider schlepping 50# or more of gear?...suddenly that extra bit of seems very inconsequential.

Whether it is "too big" depends on what you're riding on, how much gear you're schlepping...and how high a PSI you can/are-willing to run.

The first time I rode with some Little Big Ben tires on my LHT (38mm wide) I thought I had made a mistake. I usually rode 32 and 35mm. They felt slow and heavy, but my ride times were still the same. What you feel, probably isn't real.

Yeah normally I'm solidly in the "weight dont matter" category, but it is a rotating mass. I cant say I see a lot of difference going from mid 20s to mid 30s but then again, these things are massive and Marathon aren't known for being speedy tires to begin with.

What inner width do you have on your rims. Some rim manufacturers make wild claims like one of their rims will work fantastic on any tire from 23 to 57mm wide. But I think the chart on teh bottom of this page is the best chart out there.
Tire Sizing Systems

I unfortunately have a set of rims that the manufacturer claimed would be good for up to 57 mm. And the dealer said they were the best rims you could buy for an expedition bike so I bought them thinking that the dealer had a clue. Unfortunately, the dealer had no clue, the rims are 19 mm wide (inner width) and the bike handles terribly if I try to run the 57 mm tires at low pressure because the rim is too narrow. The chart for 19 mm width says my tire should be no more than 44 mm wide.

So, yes, you can have tires too wide. Besides the rim, frame and fork clearance are also concerns but you already knew that.

Regarding your 40mm wide Schwalbe Marathons, I have 40 mm wide Marathons on my folding bike and on one of my dérailleur touring bikes, very happy with the tires on both bikes. If they look too fat to you, ride more gravel and you will start to like them. I usually use 50 mm or wider on gravel, 37 or 40 mm on pavement for loaded touring. I used my 40 mm Marathons on my Glacier Waterton loop trip and Florida Everglades & Keys trip, both of those trips were fully loaded. On the rough chip seal in the Everglades, I was pretty happy with the 40 mm Marathons. In Texas near Big Bend, the chip seal pavement was so rough that I was running between 40 and 45 psi pressure in the front on my folding bike (not loaded for touring, I was day tripping) and the 40 mm tires were wide enough that there was no danger of pinch flats.

It is rotating, but it only really "matters" in acceleration and deceleration....or if you're trying to "outrace" your buddies on 700x23 road racing rigs.

I run 700x42 on my gravel/touring rig. Currently they're Specialized Sawtooth and have a thicker center-tread for better flat resistance, IIRC they're 600gr each. Sure they're slower to accelerate. OTOH once accelerated they hold momentum more. I've had puncture issues with lighter larger tires (Say Vittoria Terrene Dry 700x38 at 400gr), on my commute in particular. Being a big tire, they're just not that thick to resist random bits of glass. Very comfy on the worst roads. When the road becomes MMR or dirt or gravel...I keep riding with confidence, and they're comfy. Because they're a moto-inspired sawtooth, they don't work that well in pea gravel of course.

Per Tourist_in_MSN...you can run into handling issues with narrow rims...OTOH generally you run into frame clearance issues, in 700C anyway, before that happens (generally).

I'd have to look at rims to see if they have a width, but should say they don't look too big for the Bontrager Fairlanes. It is just that they look massive compared to other 35-37mm tires I have in the garage.

Good to hear that other than rims there isn't much of a concern. Probably will just give them a go, they still have manufacturing nubs on the outer edges, cant be that old. Really wish bike tires had manufacturer date codes like car tires so I had more actionable data when buying used

I agree. Too wide for the rim and if feels squirrely when cornering.

I'm running 42mm tires on 19mm (inner) rims, and that's a little squirrely - I can live with it (and enjoy the cushioning) but in the future I don't think I'll be getting any more 42mm tires for those rims. 35-38mm seems to be the sweet spot for 19mm rims, for me.

Let's see; Climbing, accelerating, decelerating, carving, gliding ...and overall weight. What's left?...oh yeah "roiling resistance" on web bloggers test bed .

I'm disqualified from answering, I've gone back to 23s on my fronts 25s otherwise,

But other than that...

I agree. I'm running over 2.0 on my MTB and MTB tourer. Of course, you could argue big tires make any ride a long ride.

Seriously, I ride in two different groups 15+ riders. In both, the big tire riders bring up the rear, and we wait for them regroup after every grade. Nothing wrong with that, I respect their choice, but if these tires so "fast" why are the bikes they're on so uniformly slow?

I ride on Almotion 2.1"

​​​​​1. This is at the limit of what my v-brakes can handle when removing the wheel. (Not an issue with disks)

2. The fatter the tire, the lower the pressure. Means that they keep enough pressure to ride an entire season between top ups. Easier to bring to the desired pressure. Possible to ride at very low pressures which is useful on some surfaces.

I ride 1.75", if my bike could handle it, I would go 2". When it comes to touring, for me comfort is more important than speed

I can't keep up with other people.
But I tour alone so it doesn't matter.

Aero. Obviously nobody makes any high-performance aero road racing rims that are designed for them, but wider tires tend to increase CdA in general. Whether it's actually significant is a matter of perspective, since even a 2" tire is a pretty tiny object compared with, say, a cyclist's torso.

The particular tire used tends to be a lot more significant than the size. Riding on the flats in calm conditions, I don't really notice a difference between my gravel bike with its 53mm Rat Trap Pass ELs and my skinny-tired road bikes; but when I had ThickSlicks on the same bike, it was averaging a pretty considerable ~5% slower in the same circumstances.

For touring? Any benefits/drawbacks are going to be a lot more subjective than if you're obsessing over just going fast I'd think. I usually run 35s on the bikes that I take on extended trips. They're a little more comfortable on long days than say, my road bike with 23s, but other than that I think the differences are pretty minor for the most part.

It depends a lot on how you're touring. Hours/Miles per day? Days?

I put some Michelin Protek Max (32mm) tires on my Hybrid conversion. They're OK tires. A couple of thousand miles, and I don't think I've had a flat yet.

But, the added rolling resistance really beat me up with my last Eugene to Portland (and back) trip. 130 to 150 miles each way. My next trip will have to be on 23 or 25mm tires.

I'm working on my next "touring" bike build... hopefully. I have Surly ExtraTerrestrial 29 x 2.5" (63mm?) tires planned for it. It will take me a while to get it going, but hopefully it will be ready sometime this year. But, the bike will have a very specific purpose, of rough gravel touring.

Definitely a personal preference thing. I pack really light and have been touring on 25mm tires lately. That said I did a mixed dirt/pavement tour on fat mtb tires with lots of low knobs and was surprised how well they worked out even on the pavement. I plan to continue to use skinny tires on the pavement.

I will add that the tire construction probably has as much effect on ride quality as width if not more. So the width of 2.1" Kenda Slant Sixes that I used on my pavement/dirt tour was actually less of a detriment than the stiff sidewalls of Marathon Pluses in 32mm width. The MPs are the worst riding tire I have ever tried. I took them off and sold them after a couple hundred miles. Additionally the 700 x 32mm MPs (810 grams) were heavier than a 29 x 2.0" Kenda Slant Six (730 grams).

My touring bike is a Surly Troll (26") with 2.35" Extra Terrestrials, 45lb up front, 50lb rear. Toured last summer with a friend riding 700x32mm. I didn't slow him down. Our average was 95 miles, 125 was our long day. The ETs are comfortable, ride well on pavement, gravel and trails. Wider tires are just fine.

There's also that pesky gyroscopic precession factor that I can barely remember from engineering physics.

I'm also sticking with 25s, with my lightly loaded style.

I sure wouldn't have toured magnificent, empty, unpaved roads in Utah, British Columbia, or Alaska with skinny tires.

Thanks! Beyond the rim size issue sounds like not much to worry about if I am not concerned with fast-paced performance, which I am most assuredly not. Forgot to look at the rim size last night, but I found references to the spec'd rim tape being 19mm, so I'm guessing it is wider than that. I did ride them for 20-25 miles before ripping the bike apart, they didn't really feel to be any oversize compared to rim issues.

Perfect. It'll slow me down and let the wife keep up

After trying almost all sizes between 32 & 42mm, I've settled on 38mm Schwalbe Marathons on my Trek 520 and 40mm on my Haro 'Niner. I use the 520 for centuries and touring & the 'Niner more as an around town utility/commuter/winter bike. I found 33 and 35 too narrow on the 520 as I had too many snakebite flats with them on the poor road surfaces we have here in Upstate NY. The 38mm & up seem sufficiently robust as I haven't had any such flats since using them. Perhaps if you're riding on better quality roads than I, the narrower tires would be OK. At one point I had 42mm Conti Top Contacts on my 520 and then switched to the 35mm Schwalbe Marathons. I saw a huge decrease in rolling resistance which took about 7% off my average times. Of course some of that might also be due to inherent differences between the Schwalbes and the Contis regardless of size. I then switched up to the Marathons in a 38mm because of the aforementioned snakebite flats. The difference in rolling resistance between the 35 & 38 mm Schwalbes seemed to be negligible and I've had no snakebite flats since. Just my $0.02, YMMV.

Smaller ones are easier to carry a spare tire/tube.

Inner tubes for fat bikes, as an example, are rather substantial,
But the tires themselves fold.