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Ask five gravel riders what pressure to run and you’ll get six answers. That’s not because they’re all wrong. Tire pressure depends on how much load is on the tire, how much air volume you have, and what you’re rolling over. Rider weight and tire width are the two biggest inputs, so that’s where to start.

This post gives you starting numbers, shows where the popular calculators disagree, and covers the two things that trip people up: rim width and hookless limits.

Start with system weight, not body weight

Every serious calculator wants total system weight, meaning you plus the bike plus whatever you’re carrying. A 75 kg rider on a 10 kg bike with bottles and a bag is closer to 85 to 90 kg on the tires. Weigh yourself in kit, weigh the bike loaded the way you ride it, and add them up.

The second input is tire width, and here’s a catch. Silca’s calculator asks for the measured inflated width on your actual rim, not the number on the sidewall. Silca’s input guidance, as explained by BikePSI, notes that tires often inflate wider than labeled on modern rims. Other write-ups put the gap at roughly 1 to 3 mm. Put a caliper on your tire once it’s mounted and aired up, and use that number if the calculator asks for it.

A starting chart by rider weight and tire width

Here’s a single-number starting point from one published chart, organized by rider weight and tire width. Treat it as the middle of the road for tubeless on mixed gravel, and add your bike and gear weight when you’re on the heavier side of a row.

Rider weight 35mm 40mm 45mm 50mm
130 lb (59 kg) 35 psi 30 psi 26 psi 22 psi
150 lb (68 kg) 38 psi 33 psi 29 psi 25 psi
165 lb (75 kg) 42 psi 36 psi 31 psi 27 psi
180 lb (82 kg) 45 psi 39 psi 34 psi 29 psi
200 lb (91 kg) 48 psi 42 psi 37 psi 32 psi
220 lb (100 kg) 52 psi 45 psi 40 psi 35 psi

The pattern matters more than any one cell. Each step up in width takes about 3 to 6 psi off, and each 15 to 20 lb of rider weight puts a few psi back on. That chart is from RunBikeCalc, which also says the rear should run roughly 5 to 10 percent higher than the front.

Why the calculators don’t agree

I compared outputs for a 75 kg rider on 40mm tubeless tires, mixed gravel. They don’t match.

One calculator gives 40 psi front and 44 rear on a 21 mm internal rim. Another lands at 41 front and 45 rear with a 10 kg bike. A third pegs it at 35 front and 37 rear. A SRAM-method implementation says 38 front and 41 rear for a 175 lb rider plus an 18 lb bike on a 25 mm rim.

That’s a six-psi spread at the front, from the same rider and tire. Most of these are third-party tools that copy the SRAM or Silca models, so even the “official” methods can drift in the copies.

The disagreement gets bigger for heavier riders on wider tires. In one cross-check, a 100 kg rider on 45mm tubeless got 29.5 front and 30.5 rear from Silca, while Rene Herse’s range for the same setup ran from 35 to 43. Rene Herse says most calculators work best for average riders on 38 to 42 mm tires and get shakier at the edges. If you’re very light, very heavy, or on 50mm-plus tires, expect to do more of your own testing.

None of this means calculators are useless. It means they’re a first guess, and the best use is to run two of them and see where they overlap.

Rim width and hookless limits

A wider rim lets the same tire sit wider and hold more air, so it wants less pressure. One calculator’s example for that 75 kg rider on 40mm tires shows 38 front and 42 rear on a 25 mm rim versus 40 and 44 on a 21 mm rim. That’s about 2 psi, so it’s real but modest.

Hookless is a different question, because it sets a ceiling. ETRTO’s recommended maximums on hookless rims are 5 bar (72.5 psi) for 25 to 29 mm tires, 4.5 bar for 30 to 34 mm, and 4 bar for 35 to 39 mm. They’re recommendations rather than law, and a lower rim or tire maximum overrides them.

The ceiling drops further as tires get wider. Schwalbe’s published limits for its tubeless tires on hookless rims fall to about 44 psi (3 bar) for 45 to 54 mm tires. A 220 lb rider on 45mm tires is roughly at 40 psi in the chart above, so there’s not much headroom. Check your rim’s stated limit and your tire maker’s hookless guidance before you pick a number. If you’re shopping for tires, my best gravel tires roundup is a decent place to see what’s out there, and the tire clearance post will help you figure out how wide your frame can go.

Front, rear, and terrain

Gravel bikes carry about 47 percent of system weight on the front and 53 percent on the rear in Silca’s weight-distribution model. So the rear gets a bit more air. A couple of psi is usually enough. Some calculators go to 3 to 5 psi, and I’d treat that as the upper end.

Terrain moves the number more than most people expect. For a 40mm tubeless tire at 75 kg system weight, Silca’s calculator returns about 29.5 to 42 psi from its smoothest gravel category to its roughest. That’s a 12 psi swing with no change in rider or tire. Loose, rough stuff lets you run lower, while hardpack and pavement-heavy rides want you toward the top of your range.

Rene Herse’s advice for gravel is to pick the soft value from its calculator. It also points out that smoother pedalers can go lower and that sprinting needs firmer tires. Terrain matters here too: rough ground may need more air to stop bottoming out on big hits.

Dial it in on the road

You won’t find your number on a chart. Pick a starting point from the table, drop 2 to 3 psi, and ride a loop you know. Go lower if the bike feels skittish or harsh, and go higher if the tire squirms in corners or you feel the rim on hits.

A couple of signs help. On wider tires, if the bike runs wide in sharp corners, the pressure is probably too low. Rene Herse also suggests checking tread wear on its smooth tires. If only the center lines are worn, you’re likely too high. If wear reaches the shoulders, you’re probably too low.

You’ll want a gauge you trust. Floor pump gauges can be off by several psi at low pressures, which is exactly where gravel lives. A digital tire pressure gauge is cheap and lets you repeat settings. Also keep your sealant fresh. Rene Herse suggests 100 ml per wheel for 35 to 44 mm tires and 120 ml for 45 to 55 mm, topped up at least monthly. Tubeless sealant dries out, and low pressure with dried-out sealant is how you end up on the side of the road.

Going much wider has its own tradeoffs, which I covered in my post on putting 2.35" MTB tires on a drop-bar gravel bike. The lower pressures there come with more weight and a different feel.

Bottom line

For a typical 75 kg rider on 40mm tubeless tires, mixed gravel, expect somewhere in the mid-30s to low-40s psi, depending on which calculator you ask. Go a few psi lower for each size up in tire width and a few psi higher for every 15 to 20 lb of rider weight. Keep an eye on your hookless ceiling, run the rear a little firmer, and then go ride until the numbers stop mattering.

Sources