Bike tires go flat from punctures, low pressure pinches, valve or rim faults, or wear; quick checks of pressure, tread, and tape reveal the cause.
Flats feel random, yet they follow patterns. This guide shows the usual reasons your tire loses air and the steps that fix each one. You’ll learn fast checks for tubes and tubeless, pressure habits that work, and when to swap parts.
Why Are My Bike Tires Going Flat? Common Causes By Type
Use the table below to match a symptom to a likely cause and a fast fix.
| Symptom | Likely Cause | Quick Fix |
|---|---|---|
| Two tiny holes side-by-side in tube | Pinch flat (“snake bite”) from low pressure or a hard rim strike | Patch/replace tube, raise pressure, choose wider tire or ride lighter over bumps |
| Single small hole; glass/thorn in tread | Road debris puncture | Remove object, boot if needed, patch/replace tube; try a tougher tire |
| Cut in sidewall; tube bulges | Sidewall slice or worn casing | Install tire boot, ride gently, replace tire soon |
| Hole on tube opposite valve | Rim tape out of place or too narrow | Redo rim tape; use proper width and high-temp tape |
| Hiss when wiggling valve | Loose core or damaged valve | Tighten core, replace valve, or change tube |
| Slow loss over days | Tiny shard, porous casing, aging tube, dry tubeless sealant | Inspect inside, refresh sealant, replace worn tube/tire |
| Air gone after curb hit | Bead burp (tubeless) or pinch (tubes) | Re-seat bead, top up sealant and pressure; avoid square hits |
| Hiss at spoke holes (tubeless) | Rim tape leak or tear | Retape rim; clean with alcohol, overlap ends, press firmly |
| Flat right after a tire swap | Pinched tube or debris left inside | Open tire, remove debris, reinstall carefully |
| Sidewall scuffed by brake | Misaligned pad contacting tire | Adjust pads to the braking surface; check casing |
Fast Pressure Habits That Prevent Flats
Riding under-inflated invites pinch flats and rim strikes. Over-inflating can push a bead off a narrow rim. Aim for a pressure that holds your weight and terrain while staying within the range printed on the sidewall. Check with a gauge.
Road riders often run higher pressure on smooth tarmac. Gravel and trails benefit from lower settings for grip while still high enough to resist rim hits. Heavier riders and loaded bikes need more air than light riders.
Tube Setups
Pinch flats leave two slits where the rim crushed the tube. To stop them, keep pressure high enough for your tire width and stay light over square edges.
Tubeless Setups
Tubeless reduces small punctures, but dry sealant, a nicked rim strip, or a loose valve can bleed air. Refresh sealant on a schedule and snug the valve core. Seat the bead with a firm blast until it “pops.”
Road Debris Punctures
Tiny steel wires, glass, thorns, or sharp gravel can lodge in the tread and keep stabbing the tube with every rotation. Pull the tire and inspect both the outside and inside. Run a cloth along the inside; a snag means a shard. Mark the tube hole, line it up with the tire, and you’ll find the entry spot fast. Install a small boot under a cut to limp home. Replace a tire with deep cuts, exposed threads, or bulges.
Rim Tape And Spoke Holes
Recurring flats that line up with spoke holes point to rim tape. Tape that’s too narrow, old, or misaligned lets the tube push into cavities, where it abrades and pops. Use tape that matches the inner rim width and stands up to heat. For tubeless, the tape must seal airtight; clean the rim, lay the tape with firm tension, and overlap the end.
Valve Problems
A loose removable core hisses when you wiggle it. A cracked base leaks where the valve meets the tube. Dirt can clog a Presta valve and cause slow loss. Tighten with a small core tool, replace damaged parts, and cap the valve to keep grit out.
Installation Errors
Pinching a tube under the bead during install is common. Inflate the tube just enough to hold its shape, tuck it fully into the tire, and massage the bead into the rim before final inflation. Check that the tire’s mold line sits evenly around the rim.
Diagnose The Flat: A Quick Workflow
Pump to the lower end of the sidewall range and listen. Look for glass and cuts. If you ride tubes, inflate the tube and read the hole: two lines means a pinch; a round pin hole means debris; a ragged tear hints at a big rim strike. Map the tube to the tire to find the culprit, then inspect rim tape and the valve base. Reassemble carefully and check the bead all around during inflation.
Pressure Ranges That Keep You Rolling
Every tire has a printed range. Use that as the hard limit. The table below offers starting points by tire type. Adjust for your weight, rim width, and terrain. If you bounce off rocks or feel rims ping through, add a little air. If the ride chatters on broken pavement, drop a little—still inside the printed range.
| Tire Type | Typical Range* | Notes |
|---|---|---|
| Road 25–28 mm (tubes) | 70–100 psi | Higher end for heavier riders and smooth roads |
| Road 28–32 mm (tubes) | 60–85 psi | Balance of speed and comfort |
| Road 28–32 mm (tubeless) | 50–75 psi | Lower to aid grip; watch for rim strikes |
| Gravel 35–45 mm | 30–55 psi | Start mid-range; drop for rough, add for smooth |
| XC MTB 2.1–2.4″ | 20–30 psi | Rider weight and insert use change the sweet spot |
| Commuter 32–42 mm | 45–70 psi | Top up weekly; curb hits need protection |
| Kid’s 1.75–2.125″ | 25–40 psi | Keep within the sidewall range; check monthly |
*Always stay within the pressure printed on your tire sidewall.
Break The Cycle
Repeat flats trace back to one of three roots: low pressure, a sharp edge inside the rim, or an object still lodged in the tire. Tackle those in that order. Top up air on a schedule. Fix the rim tape once, the right way. After any puncture, find both the entry and the exit wound before you install a fresh tube.
Quick Upgrades
- Puncture-resistant tires for glass-strewn routes.
- Quality rim tape matched to inner rim width.
- Fresh sealant and, for rocky trails, foam inserts.
Set Up Checklist
- Confirm pressure with a gauge; recheck after cold snaps.
- Spin wheels; pads should sit on the brake track, not the tire.
- Scan tread and pluck out glass before it works deeper.
- Carry a tube or plug kit, levers, and a pump or CO₂.
Trusted References
For step-by-step removal and install technique, see the Park Tool tire and tube guide. For why pressure matters and how low pressure raises puncture risk, see Schwalbe’s tire pressure notes. Both pages back up the habits in this article. If you’re still asking why are my bike tires going flat, start with rim tape and a new tube.
Reasons Bike Tires Go Flat On The Road: Quick Checks
Here’s a tight recap you can save on your phone. It mirrors the logic pro mechanics use after a roadside puncture.
- Find the hole shape or the wet spot; remove the object.
- Check rim tape under that location and re-seat the bead.
- Test the valve base and core for bubbles.
- Set pressure for your tire size and route.
Stop The Repeat Flats
The pattern is simple: air loss comes from sharp objects, impact hits, or leaky interfaces. The fix is a routine: right pressure, clean casing, sound rim tape, tight valves. Do those well and flats become rare. Skip them and you’ll keep asking, “why are my bike tires going flat?” after every ride.