A tyre that needs topping up every few days is telling you something. Understanding why tyres lose pressure can help you catch a small issue before it becomes a roadside flat, a damaged tyre or a missed journey. Sometimes the cause is as simple as a cold snap. Other times, a nail, leaking valve or damaged wheel needs professional attention.
Why tyres lose pressure: the main causes
Tyres are not completely airtight forever. A small, gradual reduction in pressure over many months can be normal, but frequent or noticeable pressure loss is not something to ignore. If one tyre is consistently lower than the others, there is usually a fault to find.
A puncture from a nail, screw or sharp object
This is one of the most common reasons for a tyre losing air. Nails, screws, fragments of metal and sharp stones can work their way into the tread without causing an instant blowout. You may only notice the issue when the tyre pressure warning light comes on or the vehicle starts to feel less stable.
Do not pull a nail or screw out yourself. It may be slowing the leak, and removing it can leave the tyre flat very quickly. A technician needs to inspect the tyre properly to establish whether the puncture is in a repairable area of the tread, or whether a replacement is the safer option.
Punctures near the sidewall, large holes, damage caused by driving while flat, or tyres with exposed internal cords will normally require replacement. A quick plug from a roadside kit is not the same as a full professional repair and should never be treated as a long-term answer.
A leaking tyre valve
The valve is the small fitting behind the cap where air is added. Valve cores can wear, seals can perish and valves can be damaged during inflation or tyre fitting. Even a tiny leak here can gradually lower the pressure over days or weeks.
A missing valve cap does not usually cause a major air leak by itself, but it allows dirt and moisture to reach the valve. That can lead to corrosion and a poor seal over time. Keep valve caps fitted and replace damaged ones when needed.
A poor seal between the tyre and wheel rim
The tyre bead is the edge of the tyre that seals against the wheel rim. Corrosion, dirt, old sealant or physical damage around the rim can prevent that seal from holding properly. This is particularly common with older alloy wheels, where corrosion can build up beneath the tyre bead.
You may find that the tyre loses pressure slowly despite having no visible puncture. The wheel may need cleaning, treating and resealing before the tyre is refitted. If the rim is bent or cracked after hitting a deep pothole or kerb, it may also need repair or replacement.
Pothole and kerb damage
Surrey and West Sussex roads can be unforgiving, especially after heavy rain and colder weather. A sharp pothole impact can damage the tyre, bend a wheel or knock the bead seal loose. Kerbing can also harm the tyre sidewall, even if the mark looks cosmetic at first glance.
Look for cuts, bulges, deep scuffs or a raised section on the sidewall. A sidewall bulge can mean the tyre’s internal structure has been damaged. It is not safe to keep driving on it, even if the tyre is still holding air.
Temperature changes
Tyre pressure naturally drops as the temperature falls. A cold morning can make a previously acceptable tyre read lower, while warmer weather can increase the reading. As a rough guide, a tyre can lose around 1 PSI for every 5 to 6°C drop in temperature.
This does not mean you should dismiss a warning light every winter. Temperature affects all tyres, so one tyre falling much lower than the others still points to a likely leak or fault. Check pressures when the tyres are cold and use the vehicle manufacturer’s recommended setting, usually shown on a sticker inside the driver’s door frame or in the handbook.
Slow air loss through the tyre over time
Tyres can slowly lose a small amount of air through the rubber itself. This is known as permeation and is more noticeable over long periods, rather than from one day to the next. Regular checks are still necessary, particularly before a long journey, a family trip or a busy week of van work.
If you are adding air monthly, monitor it closely. If you are adding air weekly, or the pressure warning light returns soon after inflation, arrange an inspection.
How to tell whether the pressure loss is serious
The speed of the pressure loss matters. A tyre that drops a few PSI over several months needs monitoring and a routine check. A tyre that goes down overnight, loses pressure while driving, or cannot be inflated at all needs urgent attention.
Signs that you should stop and have the tyre checked include a tyre pressure monitoring system warning, a visibly low tyre, pulling to one side, increased steering heaviness, vibration, a thumping sound or a sudden change in how the vehicle handles. Do not assume the problem will disappear after adding air.
Driving on an underinflated tyre generates excess heat and puts more strain on the sidewalls. It can reduce grip, affect braking and cause uneven wear. If the tyre becomes very low, the wheel can damage the tyre internally even over a short distance. That can turn a repairable puncture into a replacement job.
What to do when a tyre keeps going down
First, park somewhere safe and inspect the tyre without putting yourself at risk. Check for obvious objects in the tread, cuts, sidewall bulges and damage to the wheel. If you are on a motorway, a fast road or an unsafe location, do not attempt an inspection beside moving traffic. Move to a safe place if you can do so without driving on a flat tyre, or call for assistance.
If the tyre is only slightly low and you can safely reach an air pump, inflate it to the manufacturer’s cold pressure. Make a note of the reading and check it again later. Do not overinflate the tyre to compensate for a suspected leak.
Avoid driving on a tyre that is visibly flat or repeatedly losing pressure. Vehicles with run-flat tyres may be able to travel a limited distance after pressure loss, but the exact allowance depends on the tyre and vehicle. Check the handbook and do not exceed the stated speed or distance limit. Run-flat tyres still need a professional inspection after a loss of pressure.
Tyre sealant can be useful in a genuine emergency where the vehicle manufacturer permits it, but it is not suitable for every puncture. It may not work on sidewall damage, larger holes or a damaged rim, and it can make later inspection more difficult. Tell the technician if sealant has been used.
Can a tyre that loses pressure be repaired?
It depends on where the damage is, how large it is and whether the tyre has been driven while underinflated. A simple puncture in the central tread area may be repairable after the tyre has been removed and inspected from the inside. Damage in the shoulder or sidewall is usually not repairable safely.
The condition of the tyre also matters. If the tread is worn close to the legal limit, the rubber is badly aged, or there is internal damage, replacement is often the sensible route. Fitting a new tyre may feel like the more expensive choice on the day, but it is cheaper than risking another failure, wheel damage or a loss of control.
For vans and small business fleets, it is especially worth acting early. A slow puncture can easily become lost jobs, delayed deliveries and an unplanned recovery bill. Keeping tyre pressures checked as part of a weekly vehicle walk-round helps spot trouble before the vehicle leaves for the day.
Preventing repeat pressure problems
Check all four tyres and the spare, if fitted, at least once a month and before long journeys. Use a reliable pressure gauge rather than judging a tyre by sight. Modern tyres can be significantly underinflated before they look obviously flat.
Check pressures when tyres are cold, replace missing valve caps and inspect the tread for embedded objects after driving through building sites, country lanes or areas with roadworks. If you regularly hit potholes or notice a new vibration after an impact, have the tyre and wheel inspected.
When a flat tyre or persistent slow leak disrupts your day, Prime Mobile Tyre Fitting brings the tyre shop to you across Surrey and West Sussex. A technician can assess the damage at your home, workplace or roadside location, explain whether repair or replacement is appropriate, and help get you back on the road.
A pressure warning is rarely convenient, but acting on it early gives you more options. Check it, protect the tyre from further damage and get professional help before a slow leak becomes the reason you are stranded.