wheel wells: how big is (just) big enough?

[Richrad]

Building a 5X11 and I want flush sides. How much do I need to allow for wheel wells, beyond range of motion of the tire? No fair saying really-really big! Using 13" by 4.5" wheels, probably 175/80 tires.

[Tigris99]

you need to not rub when suspension is fully compressed. That's how much clearance you need.

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[noseoil]

The "worst case" scenario is what you need to do a layout for. To me it's having one tire in a pot-hole & the other on a curb or large bump. Remember an axle can go up on one end while going down on the other. This will increase the width of the tire beyond its actual size, since they don't always work in unison. I would think that an inch in all directions, over & above the axle movement to the stops, would be good. A blown & shredded tire can cause problems as well, as it bounces & slaps around while stopping....

[working on it]

The "worst case" scenario is what you need to do a layout for. To me it's having one tire in a pot-hole & the other on a curb or large bump. Remember an axle can go up on one end while going down on the other. This will increase the width of the tire beyond its actual size, since they don't always work in unison. I would think that an inch in all directions, over & above the axle movement to the stops, would be good. A blown & shredded tire can cause problems as well, as it bounces & slaps around while stopping....

• What he said...! Also, clearance needed varies with the type of suspension you use: noseoil describe what happens when a leaf-spring axle typically does, while independent trailing arm suspensions like the Timbren have less effect from one side to the other.
• Your choice of smaller 175/80-13 size tires indicates to me that you will not be going offroad, so you'll probably not need extra clearance (2" or more) that the typically larger-tired offroad trailer uses, and thus up & down wheel travel clearance shouldn't be a problem, but as he also said, the tire can still be moved too close to the wall/frame of the trailer, or to the curled-lip of most trailer fenders (often sharp-edged), if the fender is sized too small, or installed with too little clearance. And, if the tire comes apart, the remnants can tear-up fender or trailer wall, if not sturdy enough, too tight a fit, or having the fender mounted directly to a wall (without inner fenders or fender-liners).
• My TTT is leaf-springed, but the axle has limited travel (1.25-1.5"), and has bumpstops to prevent catastrophic over-travel, so my fenders' 2+" clearance (over the tire) should never be tested, even after I added larger/wider all-terrain LT tires. The fenders are welded to my frame, with steel inner fenders to protect the frame & walls from debris, and are of heavy-gauge material, and so solidly-mounted that I don't fear damage to them, in any case. When I discarded my original axle in favor of a stronger axle with added brakes, my axle width became wider, moving my tires away from the inner fender (more clearance there is a plus), and outward towards the fender lip. The tire barely remained under the fender (which prevents spraying water, mud, gravel onto following vehicles (a good thing, often required by law), which I measured for, before I OK'd the axle order, since my welded-on fenders were not to be moved.
• The switch to the LT tires, years later, closed-up clearances on the top and inside of the fenders, and spurred me to add fender flares to cover the exposed tire tread, now sticking out from under the fender. Take that into consideration prior to fender purchase/installation...you might want to put bigger tires/wheels (or axle/brakes) on your trailer in the future. Unless you want a super-streamlined look, or a low-rider trailer, then having excess clearance all-around the tire is preferable (more is better, IMHO).

[Richrad]

Thanks to all for the replies! My suspension will be flexiride half axles, so fully independent each side. Planning on 3” clearance fore and aft. Vertical clearance harder to guess since this type ( I think) has no vertical stop. Hard to estimate the effect of dynamic loads on wheel height. Maybe have friend drive over curbs while I ride in trailer and watch