Loam
The problem is not getting dirty
Mountain bikes are supposed to get dirty. Mud on the frame is not the issue.
The problem starts when the trail surface is soft enough that a tire changes its shape. Instead of rolling over the tread, it presses into it. A rut forms. Water can then follow that rut the next time it rains, carrying more soil with it.
A simple test
If your tire leaves a visible groove in the tread, the trail is probably not ready for traffic. Turn around before one pass becomes ten.
Why one tire mark becomes a trail problem
Trail damage does not always look dramatic at first. You might see a narrow rut or a soft patch and think it will disappear when the trail dries.
Sometimes it does. But a rut also gives the next rain a place to run. Repeated traffic can deepen it, widen it, and push riders toward the edge of the trail in search of firmer ground. That is how one soft section can turn into a wider maintenance problem.
Not every wet trail is equally fragile
Soil makes a difference
Some soils hold water near the surface and become soft quickly. Rockier or better-drained surfaces can recover sooner. The same storm can therefore produce different conditions on two nearby trails.
Drainage matters
A well-shaped trail gives water somewhere to go. Flat sections, depressions, and poorly draining turns can stay soft after the rest of a network looks good.
Shade changes recovery
Wet ground under heavy canopy may get less sun and wind than an exposed trail. A cool, shaded section can remain soft after an open section has firmed up.
Traffic adds up
One rider may leave a small mark. A busy day can turn that same soft section into a rut system. Waiting protects the tread before the damage compounds.
The frustrating part is that the damage can outlast the weather
A trail can be perfectly rideable again a few days later while still carrying the scars from being ridden too early. The weather moves on. The rut does not necessarily go with it.
That is why trail closures and condition estimates exist in the first place. They are not about keeping bikes away from trails for the sake of it. They are about keeping a short period of bad conditions from becoming a much longer maintenance job.
What to do when the trail is borderline
Check the official status
If the land manager has closed the trail, stay off it. That decision comes first.
Check the current condition
Use the network condition to understand how recent weather is affecting the ground.
Look at the tread
Soft dirt, deep tire marks, and mud sticking to your tires are good reasons to leave.
Come back later
The trail will still be there. A little patience is much easier to repair than a damaged tread.
The science behind the estimate
Loam starts with a simple physical fact: a trail does not dry just because the rain stops. Water has to enter the ground, move through or across the soil, and leave the trail environment. How quickly that happens depends on the soil, terrain, vegetation, recent weather, and how wet the ground already was.
Soil controls infiltration
Soils do not accept water at the same rate. USDA hydrologic soil groups range from high-infiltration soils such as deep sands and gravels to very slow-infiltration soils associated with clay, high water tables, or restrictive layers. Typical infiltration-rate ranges used in the hydrologic-group framework run from more than 0.30 in/hr for Group A to less than 0.05 in/hr for Group D when thoroughly wet.
Previous rain still matters
A storm does not start with an empty soil profile. USGS notes that soil already saturated from previous rainfall cannot absorb much more, so a larger share of the next storm becomes runoff. Recent weather therefore matters even when the latest storm was not especially large.
Terrain changes the water path
Slope changes how quickly water can move away from a surface. Low spots, drainage features, and trail geometry can change where water collects or leaves the tread. Soil classification and slope are separate pieces of the landscape, which is why both matter to a trail-condition model.
Drying is a water budget
After rainfall, water can remain in the soil, move downward or sideways, run off, or return to the atmosphere through evaporation and plant transpiration. Soil-water-balance models use these processes to estimate changing soil moisture and net infiltration over time.
Why Loam is not a rain timer
There is no useful rule that says every trail becomes rideable after the same number of dry hours. Starting moisture, infiltration behavior, terrain, canopy, and weather after the storm all change the answer.
That is the problem Loam is designed to estimate. The model combines public soil and terrain information with recent weather and network characteristics to estimate how conditions are changing. It is a model of likely trail conditions, not a sensor embedded in the dirt, and it never overrides an official closure.
What the research says
USDA and USGS hydrology work treats infiltration, soil moisture, runoff, canopy, land cover, slope, and evapotranspiration as interacting parts of the water cycle. Recent trail research adds an important piece: rainfall intensity and accumulated rainfall can strongly affect runoff and sediment generation on recreational trails, while wet conditions make trail surfaces more vulnerable to degradation.
USDA NRCS: Hydrologic Soil Groups
Soils are classified by infiltration and runoff behavior when thoroughly wet. The framework distinguishes four main groups and dual drained/undrained classes.
NRCS National Engineering Handbook →USGS: Infiltration and the Water Cycle
Explains how soil characteristics, saturation, land cover, slope, and evapotranspiration affect where precipitation goes.
USGS Water Science School →USGS: Soil-Water-Balance
A published water-budget model that estimates soil moisture, net infiltration, evapotranspiration, and canopy interception from gridded environmental data.
USGS SWB Version 2.0 →NRCS: RUSLE2
A USDA model for estimating soil loss caused by rainfall and associated overland flow, connecting rainfall and runoff to erosion risk.
USDA NRCS RUSLE2 →Fang & Ng, Journal of Environmental Management, 2026
A year-long field study found cumulative rainfall and maximum daily rainfall predicted runoff and sediment yield on recreational trails, with maximum daily rainfall the stronger predictor in that study.
Read the research →These sources describe the physical processes and research Loam draws from. They do not describe Loam's proprietary model or disclose its weights and thresholds.