In short. A low profile tyre is one whose sidewall is short compared with its width: the second number of the size, the aspect ratio, is 50 or less (Kia's handbook uses "lower than 50"). In exchange for a sharper steering response and the look of a larger wheel, you get less rubber and less air between the wheel and the road, so potholes and kerbs are more likely to damage both the tyre and the wheel: one carmaker, Kia, and one tyre maker, Bridgestone, say so in writing. The ride is often firmer, but a university study run with the aftermarket trade found the difference "much less than anticipated" on the vehicle it measured. What matters most when you choose a lower profile is not the look but the load index, which must stay at or above what the car maker specifies, and the overall diameter, which should stay close to the original.
What "low profile" means, in numbers
A tyre size such as 225/40 R18 reads: 225 mm of nominal section width, a sidewall height equal to 40 per cent of that width, a radial structure and an 18-inch rim. The UK MOT inspection manual puts it in one line: "The aspect ratio of a tyre is included in the size marking. For example, a 215/55R15 has an aspect ratio of 55%." There is no legal definition of "low profile". Here is where the sources we read draw the line:
| Source | Where "low" starts, or the reference point |
|---|---|
| UK MOT inspection manual, 5.2.3 | "Standard" car tyres have a nominal aspect ratio of 82 per cent unless marked otherwise |
| Kia owner's manual (2026) | "Low aspect ratio tyres, whose aspect ratio is lower than 50, are provided for sporty looks" |
| Tire and Rim Association (US), quoted by Modern Tire Dealer in 2019 | The lowest aspect ratio it has standardised is 25 |
| Two of the top-ranking guides for the query | 50 or lower |
So a tyre that the MOT manual calls "standard" has a sidewall 82 per cent of its width, and today's low profile sizes run from 50 down to 25. Our guide to reading a tyre size explains the rest of the marking.
The aspect ratio is not a height. Because it is a percentage, the same series gives different sidewalls on different widths. Our arithmetic: a 205/40 has 82 mm of sidewall (205 × 0.40), a 275/40 has 110 mm, and a 255/35, at 89.3 mm, has more sidewall than the 205/40 although its series is lower. A tyre industry executive put it the same way in Modern Tire Dealer: "the wider the section width, the taller the sidewall becomes in actual measurement", and so "the minimum section height is the real limiting factor". When you compare two sizes, compare millimetres, not series.
Sidewall heights from 16 to 21 inches
When people move to a larger wheel, the usual practice is to keep the overall diameter of the tyre close to the original and take the extra wheel diameter out of the sidewall. The table below is our own calculation for two families of sizes, a compact car and a large SUV. These are examples of the arithmetic, not sizes for any particular car: only the car maker's list tells you what fits yours. Diameter is the rim diameter plus two sidewalls; "rubber in the radius" is the sidewall as a share of the wheel's rolling radius; "air envelope" is the outer volume between the rim and the tyre's outside (π × (outer radius² − rim radius²) × width), an upper bound that serves only to compare sizes with each other.
| Size | Sidewall | Overall diameter | Change in diameter | Rubber in the radius | Air envelope | Sidewall vs first row |
|---|---|---|---|---|---|---|
| 205/55 R16 | 112.8 mm | 631.9 mm | reference | 35.7 % | 37.7 l | reference |
| 225/45 R17 | 101.3 mm | 634.3 mm | +2.4 mm (+0.4 %) | 31.9 % | 38.2 l | −10 % |
| 225/40 R18 | 90.0 mm | 637.2 mm | +5.3 mm (+0.8 %) | 28.2 % | 34.8 l | −20 % |
| 225/35 R19 | 78.8 mm | 640.1 mm | +8.2 mm (+1.3 %) | 24.6 % | 31.2 l | −30 % |
| 225/30 R20 | 67.5 mm | 643.0 mm | +11.1 mm (+1.8 %) | 21.0 % | 27.5 l | −40 % |
| 235/65 R17 | 152.8 mm | 737.3 mm | reference | 41.4 % | 65.9 l | reference |
| 235/55 R19 | 129.3 mm | 741.1 mm | +3.8 mm (+0.5 %) | 34.9 % | 58.4 l | −15 % |
| 255/45 R20 | 114.8 mm | 737.5 mm | +0.2 mm (0.0 %) | 31.1 % | 57.2 l | −25 % |
| 265/40 R21 | 106.0 mm | 745.4 mm | +8.1 mm (+1.1 %) | 28.4 % | 56.4 l | −31 % |
From 16 to 20 inches, the compact car loses 40 per cent of its sidewall and, on our envelope measure, about a quarter of its air. Yet the SUV on 21-inch wheels keeps more sidewall (106 mm) than the compact car on 17s (101 mm): a "low profile" label says little on its own. To compare any two sizes yourself, use our tyre size calculator; for the 19-inch sizes in detail, see 19-inch tyre sizes.
What you gain
Steering response and handling. Bridgestone's tyre maintenance and safety manual says that high performance and low aspect ratio tyres "generally" provide "increased vehicle handling capability", with "numerous engineering performance trade-offs". Kia's handbook says its low aspect ratio tyres "are optimized for handling and braking". A Bridgestone product strategy director told Modern Tire Dealer that low profile tyres give less damping and that some drivers prefer "the more direct, responsive feel".
Room for larger wheels and brakes, and the look. A lower profile lets a larger wheel fit the same arch without changing the overall diameter, and a larger wheel leaves more room for the brake. The look is the reason Kia gives first.
What we could not confirm. Several top pages claim better braking, lower rolling resistance or better fuel economy for low profile tyres. None of the pages we read cites a test for these claims, so we do not repeat them. Width and tread depth also change how a tyre deals with standing water: see our guide to hydroplaning.
What you lose
Comfort and noise. Kia: "it may be more uncomfortable to ride in and there is more noise compare with normal tyres". Bridgestone: high performance tyres "may also wear more quickly, ride more firmly, and produce more noise". Bridgestone's sentence is about high performance tyres, often but not always the low profile ones.
How much firmer? The one measured study we found points the other way. The SEMA Wheel & Tire Council and Clemson University's automotive research centre (CU-ICAR) measured plus-sized wheel and tyre combinations on a 2013 Ford F-150 and reported that "in many cases, shorter sidewalls did not translate into a harsher ride", and that the difference in harshness "was less than generally understood and much less than anticipated" (Modern Tire Dealer, 27 April 2015). Read it with its limits: one vehicle at first, run with an aftermarket trade body, and the article publishes no numbers or protocol. Our reading is that ride depends on the whole car, its suspension, the tyre's construction and its pressure, not on the sidewall alone. The weight of a larger wheel also plays a part: see unsprung weight explained.
Load capacity. A Bridgestone director, in the same 2019 article: "when you decrease the height of a sidewall, you are limiting the amount of air the tire can hold". Our table shows it: about a quarter less air from 16 to 20 inches on the compact car. Our reading: less air at the same pressure carries less load, which is why many low profile sizes exist as XL (extra load) tyres, run at higher pressures, to reach the load index of the original size. Our guide to XL tyres explains how load and pressure go together.
Winter. Bridgestone's manual notes that high performance tyres fitted to new cars "may be more optimized for warmer weather use" and that "colder, winter weather traction may be reduced". This is about the tread compound and pattern of summer performance tyres, not the profile: winter tyres are sold in low profile sizes too, though car makers may list a smaller wheel for winter.
Potholes and kerbs: tyre damage and rim damage
This is the trade-off that carmakers and tyre makers write down most plainly.
- Kia, owner's manual: "Because the sidewall of the low aspect ratio tyre is shorter than the normal, the wheel and tyre of the low aspect ratio tyre is easier to be damaged." It asks you to drive slowly over potholes, speed bumps, manholes and kerb stones, to inspect tyre condition and pressure every 3,000 km (2,000 miles), and warns that damage from a pothole, manhole or kerb stone "will not be covered by the warranty".
- Bridgestone, maintenance and safety manual: low aspect ratio tyres "may be more susceptible to damage from potholes, road hazards, and other objects such as curbs. This is true for the wheels as well."
- MINI USA, notice in its 2024 tyre warranties guide: damage to wheels, tyres and suspension "is more likely to occur with low-profile tires that provide less cushioning between the wheel and the road".
The mechanism follows from the table: with less sidewall and less air, there is less distance for the tyre to deflect before the wheel's rim edge meets the pothole edge. The tyre can be pinched between the two (a cut or a bulge in the sidewall), and the rim edge can be bent or cracked.
How often does it happen? No source we read counts pothole damage by tyre profile. The general figures: AAA estimated in February 2016 that 16 million US drivers had suffered pothole damage in five years, costing $15 billion in repairs, with an average reported repair of about $300. In Britain, the RAC's patrols attended 26,048 breakdowns in 2025 for damaged shock absorbers, broken springs or distorted wheels, punctures excluded.
After a hard hit. Look for a bulge or cut in the sidewall, a dent or crack at the rim edge, a vibration in the steering, a car pulling to one side or a tyre losing pressure. Kia warns that tyre damage is not easy to see. If you see any of these, have the wheel and tyre inspected before you go back on the road. A bulge means the tyre's structure has failed: the MOT manual lists "a lump, bulge or tear caused by separation or partial failure of its structure" as a dangerous defect. Our guide to tyre sidewall bulges explains why it cannot be repaired. Keeping the pressure at the car maker's figure is the one thing every source asks: see tyre pressure.
Changing to a lower profile: the rules by country
None of the texts we read bans low profile tyres. What they check is that the tyre carries the load, suits the rim and matches the tyre on the other side of the axle.
| Territory | Text | What it says about a different tyre size |
|---|---|---|
| Great Britain | Road Vehicles (Construction and Use) Regulations 1986, regulation 27 | A vehicle must not be used on a road if "the tyre is unsuitable having regard to the use to which the motor vehicle or trailer is being put or to the types of tyres fitted to its other wheels" |
| Great Britain | MOT inspection manual 5.2.3 (updated 14 October 2026) | Tyres of different sizes on the same axle: major defect. Load and speed rating checks apply to classes 5 and 7 only, not to ordinary cars |
| United States | FMVSS No. 110, 49 CFR 571.110 (a rule for the car maker, on the car as sold) | "The vehicle maximum load on the tire shall not be greater than the applicable maximum load rating as marked on the sidewall of the tire" (S4.2.1.1), and the normal load not above 94 per cent of the rating at the recommended pressure (S4.2.1.2); size and pressure are on the placard on the driver's side B-pillar |
| Australia (Queensland) | Light Vehicle Inspection Manual, effective 7 July 2026 | Rejected if tyre load ratings are less than the minimum specified by the vehicle manufacturer, if the speed rating is insufficient (at least 180 km/h for a car, or its top speed if lower), if the tyre does not suit the rim, or if a car's tyre is more than 1.3 times the width of the manufacturer's widest optional tyre |
| Canada (Ontario) | Passenger / Light-Duty Vehicle Inspection Standard, section 9 | Rejected if the tyre "has a lower load rating / capacity than specified by the vehicle manufacturer", if the wheel size does not match the tyre size, or if the nominal size differs left to right |
In Australia, the Queensland manual sends the fitting of alternative rim and tyre sizes to section LS of the national code of practice (VSB 14), which we could not open on 16 October 2026; your state's registration authority has the current text. In the US and Canada, rules vary by state and province. Everywhere, the handbook and placard list the car maker's sizes, and a size outside that list can matter to your insurer: tell them before you change.
Onyx Forged does not recommend a size or an offset. The sizes, load index and speed rating for your car come from the car maker's documents; our job here is to explain what changes when the sidewall gets shorter.
How to choose, if you are considering a lower profile
| Check | Why | Where to find it |
|---|---|---|
| The size is on the car maker's list | Suspension, brakes, speedometer and driver aids are set for those sizes | Handbook, tyre placard, the size fitted when new |
| Load index at or above the original | FMVSS 110 sets it for the car as sold; Queensland and Ontario inspections reject less | Sidewall; the placard or handbook for the original |
| Overall diameter close to the original | Our table keeps it within 2 per cent; a larger change alters gearing and speed reading | Tyre size calculator |
| Pressure from the car maker, for that size | Less air volume leaves less margin | Placard or handbook; XL sizes have their own figures |
| Your roads | Potholes are the main cost of a short sidewall | Your own experience; the RAC and AAA figures above |
Frequently asked questions
What does low profile mean on a tyre?
A low aspect ratio, the second number in the size: the sidewall height as a percentage of the width. Kia's handbook uses "lower than 50"; the MOT manual treats 82 per cent as standard; the US Tire and Rim Association has standardised series down to 25.
Are low profile tires worse than regular tires?
They trade comfort and impact protection for steering response and the room for a larger wheel. Kia and Bridgestone write that they are more easily damaged by potholes and kerbs, with the wheel. How much firmer the ride is depends on the car: one study on a pickup found it much less than expected.
Do low profile tyres cause rim damage?
They leave less rubber and air between the rim edge and the road, so a pothole that a taller tyre would absorb can bend or crack the rim. Bridgestone's manual says the higher susceptibility "is true for the wheels as well".
Do low profile tires go flat more easily?
No source we read counts punctures by profile. What the sources do say is that impact damage, a sidewall pinched between rim and pothole, is more likely, and Kia asks you to check the pressure every 3,000 km.
Can I fit lower profile tyres to my car?
Only in a size the car maker lists, or after checking load index, diameter, rim width and clearance with a tyre professional. Your insurer should know about any change.
Do I need higher pressure with low profile tyres?
Use the pressure the car maker gives for that size on the placard or in the handbook. XL versions of a size often have their own, higher figures.
Are low profile tyres OK in winter?
The profile is not the issue; the compound is. Many low profile tyres fitted to new cars are summer performance tyres, which Bridgestone says lose traction in the cold. Winter tyres exist in low profile sizes.
For wheels made to order for your car, designed to JWL/VIA standards, see the Onyx Forged catalogue.
Sources
- Car makers: Kia, owner's manual, low aspect ratio tyre; MINI USA, 2024 tire manufacturers' warranties guide, with Bridgestone's Tire Maintenance and Safety Manual.
- Trade press: Modern Tire Dealer, How low can a tire profile go? (27 June 2019); Modern Tire Dealer, The impact of plus-sizing on vehicle performance dynamics (27 April 2015).
- Rules: GOV.UK, MOT inspection manual, sections 5.2.2 and 5.2.3; Road Vehicles (Construction and Use) Regulations 1986, regulation 27; 49 CFR 571.110, FMVSS No. 110; Queensland Light Vehicle Inspection Manual; Ontario, Passenger / Light-Duty Vehicle Inspection Standard.
- Pothole figures: AAA, 18 February 2016; RAC Pothole Index.
Not read: the ETRTO Standards Manual (sold to members), the text of UN Regulation No. 30 (the pages refused access on 16 October 2026) and the Australian VSB 14 section LS (the server did not answer). All other pages were read on 16 October 2026.
The Onyx Forged design office.