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Short answer for the bikes we sell: check the sidewall max first, then start around 18 to 20 PSI for road, 16 to 18 for gravel and 14 to 16 for sand.
Tyre pressure is the most commonly neglected thing on a fat tyre e-bike. It's also the easiest to get right, and it changes how the bike rides, how far it goes on a charge, and how safe it is when the surface changes.
First, ignore most of what you read online
Nearly every fat tyre pressure guide online is written for a 26 x 4 tyre. Those are the American snow bikes, and they hold a lot of air. You'll see 8 PSI, 10 PSI, even 5 PSI recommended.
The bikes we sell run 20 inch wheels. Fatboy Bagus, Scrambler, Harlem and DNA, and both FlightRisk models all sit on 20 x 4 or 20 x 4.8 tyres. Super73 is the same wheel size.
A 20 inch tyre holds noticeably less air than a 26 inch one at the same width. Less volume means you need more pressure to do the same job. Run a 20 inch fat tyre at the pressures those American guides quote and you'll be pinch flatting and steering like a shopping trolley.
Why fat tyre pressure is different at all
A road bike runs 80 to 120 PSI. A mountain bike runs 25 to 35. Seeing 18 recommended for a fat tyre looks like a typo the first time.
It isn't. Fat tyres work on volume, not pressure. The tyre holds so much air it doesn't need much pressure to hold you up, and the big contact patch you get from not over-inflating is the entire point of the shape. First-time fat tyre riders often think their tyres are flat. They aren't.
Where to start
Starting points for a 20 x 4 or 20 x 4.8 tyre with tubes, average adult rider.
| Riding on | Start at |
|---|---|
| Road and bike paths | 18 to 20 PSI |
| Gravel and hardpack | 16 to 18 PSI |
| Loose dirt | 15 to 16 PSI |
| Sand | 14 to 16 PSI |
The sidewall is the authority, and it varies a lot. Some 20 x 4 tyres are rated to 20 PSI max, others to 30 or 35. That's a big spread, and the number on your tyre beats any table online, including this one. If yours says 20 max, 20 is the ceiling, not the target.
Super73 publish theirs, and the handbook says 20 to 25 PSI depending on rider weight and terrain. That's about where you'd expect.
The thumb test doesn't work
This catches nearly everyone.
A four inch tyre feels firm at 18 PSI, and it also feels firm at 10. The casing is thick enough that your thumb can't tell the difference. People squeeze it, decide it's fine, and ride all summer at half the pressure they think they're on.
Buy a gauge, or a floor pump with one built in. Twenty dollars, and it's the difference between guessing and knowing. Check whether your bike runs Schrader or Presta valves before you buy — we stock both.
Adjust for weight
Those ranges assume an average adult. If you're heavier, carrying cargo, running a rear rack, or riding two-up with a passenger seat, you need more air.
Rough rule: add 2 to 3 PSI for every 10kg over average. A 65kg rider and a 95kg rider on the same bike want different numbers. Lighter riders can start at the bottom of the range.
Worth remembering these bikes are heavy before you even get on. A Fatboy Bagus or a FlightRisk FR777 is a long way north of 30kg with the battery in, roughly double a normal bike, and every kilo of it sits on two tyres.
Run the rear higher than the front
Fat tyre e-bikes are rear-biased. The motor is in the rear hub, the battery sits behind or under the seat, and you sit further back than on a road bike. Something like 55 to 60 per cent of the weight is over the back wheel.
Run the same pressure front and rear and one of them is wrong.
Put 3 to 5 PSI more in the rear. Better grip off the front, less squirm out the back, and the bike will feel more settled without you being able to say why. If you carry a passenger or a kid seat, make it more like 5 PSI.
What goes wrong
Too low and you'll pinch flat. E-bike motors deliver a lot of torque off the line, and that'll slam a soft tyre into the rim. Go far enough under and the tyre can unseat entirely in a hard corner. The bike will also feel sluggish and heavy, and the tyre will visibly squash flat when you sit on it.
Low pressure costs range too. More rolling resistance means the motor pulls more current, and you'll lose somewhere around five to ten per cent of your battery. It's not the biggest thing eating your range, assist level and hills are well ahead of it, but it's the easiest one to fix and it costs nothing. More on that in our real-world range guide.
Too high and you lose the reason you bought a fat tyre. Smaller contact patch, less grip, harsher ride, and the bike skips over rough surfaces rather than rolling through them. Over the sidewall max on a hot Melbourne afternoon, you're risking a blowout.
Practical stuff
Check it monthly. Tubes lose one to two PSI a week doing nothing at all. Two months in the shed and you're down 10 to 15 PSI without having touched it. Check after any impact that felt harder than usual, too.
Air down before the sand, not after. Ride onto soft sand at road pressure, bog down, and letting air out then doesn't undo it. Carry a small pump, drop it going in, pump it back up for the ride home. Ninety seconds and it's a different bike.
Watch the heat. Pressure climbs as the tyre warms up. Set it to the max on a cool morning and you can be over the limit by afternoon on dark bitumen.
Grip test. If the rear steps out under hard braking on gravel, you're too high. Drop 2 or 3 PSI and try again.
Frequently asked questions
What PSI should a 20 x 4 fat tyre e-bike run? Around 18 to 20 PSI for road and bike paths, 16 to 18 for gravel, 14 to 16 for sand. Check the sidewall max first, because some 20 inch fat tyres are rated to only 20 PSI.
Why do online guides say 8 or 10 PSI? Because most are written for 26 x 4 snow bikes, which hold far more air. A 20 inch tyre needs more pressure to do the same job.
Can I use my thumb instead of a gauge? No. A fat tyre feels firm across a huge pressure range. Use a gauge.
Should front and rear tyre pressure be the same? No. Run the rear 3 to 5 PSI higher, because most of the weight sits over the back wheel.
How often should I check e-bike tyre pressure? Monthly. Tubes lose one to two PSI a week just sitting there.
Does tyre pressure affect battery range? Yes, by around five to ten per cent. Assist level and hills matter far more, but it's free and takes two minutes.
If you're not sure
Bring it in. We'll set it and show you what it should feel like, so you can do it yourself next time.
We service e-bikes at Richmond. Our general service is $180 and includes tyre inspection and pressure correction along with brakes, gears, drivetrain and a full safety check. Bookings are essential.
We also stock replacement tubes and Vee Huntsman tyres in 20 x 4 and 20 x 4.8, so if yours is past it we can sort that at the same time.
Full maintenance guide | Real-world range | Battery care
435A Bridge Rd, Richmond VIC 3121 | 03 9421 2293
Frequently Asked Questions
Fat tyres run at much lower pressures than standard bike tyres — typically 8 to 25 PSI depending on the tyre, rider weight and terrain. For sealed path commuting, run toward the higher end of the recommended range for less rolling resistance and better battery efficiency. For mixed terrain and gravel, drop to the middle or lower end for more grip and cushioning. Your bike manual gives the recommended range for your specific tyre.
Monthly is the minimum. Fat tyres lose pressure gradually through the tyre and tube material. A tyre that was correct a month ago may be noticeably soft today. Also check after any impact that felt harder than usual — hitting a pothole or kerb at speed can unseat the tyre bead at very low pressures. Five minutes with a pump and pressure gauge once a month is all it takes.
The bike feels sluggish and heavy. Range is noticeably shorter than usual. The tyre visibly squashes flat on the bottom when you sit on it. On rough ground the tyre bottoms out — you feel a sharp impact through the rim. Under-inflated tyres also increase the risk of pinch flats. If your ride feels harder than usual, check tyre pressure first — it is almost certainly the issue.
The ride becomes harsh and jarring. The bike skips and bounces over rough surfaces rather than rolling through them. Traction on gravel or wet surfaces feels reduced. The cushioning benefit that makes fat tyres valuable on varied surfaces disappears. Run too high and you lose the fundamental advantage of a fat tyre electric bike over a standard narrower-tyred bike.
Yes. Heavier riders need slightly more pressure for the same terrain. A 65kg rider and a 95kg rider on the same bike will get the best results at different pressures. If you are 90kg or more, start toward the middle of the recommended range rather than the bottom, and adjust from there based on feel. We will advise on the right starting pressure for your weight when you pick up the bike.
A floor pump with a pressure gauge that reads in PSI and a valve fitting compatible with your bike. Most fat tyre electric bikes use either Schrader valves (same as car tyres — wide, with a pin in the centre) or Presta valves (narrower, threaded tip). Check which valve type your bike uses before buying a pump. We stock pumps compatible with both types in store at 435A Bridge Rd, Richmond VIC 3121.
