In short. The Highway Code gives typical stopping distances of 12 metres at 20 mph, 23 m at 30 mph, 36 m at 40 mph, 53 m at 50 mph, 73 m at 60 mph and 96 m at 70 mph (40 to 315 feet), on a dry road for an attentive driver. In the wet, rule 227 says stopping distances "will be at least double", so about 192 m at 70 mph; on ice, rule 230 says up to ten times. Worn tyres add to that: in a published wet test from 50 mph (80 km/h), the same car needed 36.6 m on new tyres and 45.5 m on tyres at the UK legal limit of 1.6 mm.
The Highway Code table, and what it means
This is the chart linked from rule 126 of the Highway Code (GOV.UK, page updated 22 October 2025). Thinking distance is covered before you press the brake; braking distance is covered after. The car lengths assume an "average car length = 4 metres (13 feet)".
| Speed | Thinking distance | Braking distance | Overall stopping distance | Car lengths |
|---|---|---|---|---|
| 20 mph (32 km/h) | 6 m | 6 m | 12 m (40 ft) | 3 |
| 30 mph (48 km/h) | 9 m | 14 m | 23 m (75 ft) | 6 |
| 40 mph (64 km/h) | 12 m | 24 m | 36 m (118 ft) | 9 |
| 50 mph (80 km/h) | 15 m | 38 m | 53 m (175 ft) | 13 |
| 60 mph (96 km/h) | 18 m | 55 m | 73 m (240 ft) | 18 |
| 70 mph (112 km/h) | 21 m | 75 m | 96 m (315 ft) | 24 |
The chart carries its own warning: "The distances shown are a general guide. The distance will depend on your attention (thinking distance), the road surface, the weather conditions and the condition of your vehicle at the time."
For the theory test, these are the figures to learn. For the road, it helps to know what they assume.
What the chart assumes: our calculation
Work backwards from the chart and two numbers fall out.
- Thinking time. 21 m at 70 mph (31.3 m/s) is 0.67 seconds. The same 0.67 s comes out at every speed in the chart. That is a quick, alert driver. Queensland's road safety page, by contrast, says "in an emergency the average driver takes approximately 1.5 seconds to react", and its own table uses 1.5 s.
- Grip. Braking from 70 mph in 75 m means an average deceleration of 0.665 g (6.5 m/s²). Across the chart, the figure stays between 0.655 and 0.679 g. Queensland's dry table works out at 0.70 g, and it says a modern car with good brakes and tyres can stop at "approximately 7 m/s²".
So the Highway Code chart describes a fast reaction and a good dry road with decent tyres. Neither is guaranteed. With a 1.5-second reaction instead of 0.67 s, add 26 m at 70 mph and 11 m at 30 mph before the brakes even start working (our calculation).
For reference, the US federal brake standard for new cars, FMVSS No. 135, requires a stop from 100 km/h (62.1 mph) within 70 m (230 ft) on a test surface with a peak friction coefficient of 1.02, with the pedal pressed at no more than 500 N. Taking out the 10 m of the formula's first term (S ≤ 0.10V + 0.0060V²), which we read as the time allowed to apply the brakes, that is a minimum of about 0.66 g: almost exactly the grip the Highway Code chart implies. The chart is close to what a legal new car must achieve on a dry test track.
The stopping distance formula
Stopping distance = thinking distance + braking distance:
d = v × t + v² / (2 × µ × g)
- v is speed in metres per second (mph × 0.447, or km/h ÷ 3.6);
- t is reaction time in seconds;
- µ is the average deceleration as a fraction of g (the grip between tyre and road);
- g is 9.81 m/s².
Worked example at 70 mph with the Highway Code's assumptions: v = 31.3 m/s; thinking = 31.3 × 0.67 = 21 m; braking = 31.3² ÷ (2 × 0.665 × 9.81) = 75 m; total 96 m.
Two things follow. Thinking distance grows with speed; braking distance grows with the square of speed. Double the speed from 30 to 60 mph and thinking distance doubles (9 to 18 m) while braking distance roughly quadruples (14 to 55 m). And braking distance is divided by grip: halve µ and you double the braking distance.
The formula assumes constant deceleration. On the Continental test described below, it reproduces the measured distances to within 0.1 m, which is a fair check for a car with ABS.
The quick trick for the theory test
A common memory aid multiplies the speed in mph by a factor that rises by 0.5 for every 10 mph: 20 × 2 = 40 ft, 30 × 2.5 = 75 ft, 40 × 3 = 120 ft, up to 70 × 4.5 = 315 ft. It reproduces the chart in feet (40 mph gives 120 ft against 118). It is a memory aid, not a formula: it has no term for grip or reaction, so it cannot tell you anything about rain or tyres.
Stopping distance in the rain
What the rules say
- United Kingdom. Rule 227 of the Highway Code: "In wet weather, stopping distances will be at least double those required for stopping on dry roads". Rule 126 adds that the two-second gap "should be at least doubled on wet roads and up to ten times greater on icy roads". Rule 230, for ice and snow: "stopping distances can be ten times greater than on dry roads".
- United States. There is no national stopping distance chart. The California Driver Handbook tells drivers to "use the three-second rule" and, on wet roads, to "reduce your speed by 5 to 10 mph".
- Australia. Queensland publishes a wet table: from 100 km/h, 122 m in the wet against 98 m in the dry, of which 42 m is reaction in both cases.
- Canada. Ontario's official driver's handbook says the two-second rule "applies only to ideal driving conditions" and that you need extra space in bad weather; it gives no wet multiplier.
Why "double" and the measurements differ
Doubling the overall stopping distance at 70 mph (192 m) while thinking distance stays at 21 m implies braking at only 0.29 g, less than half the dry figure. Queensland's wet table implies 0.48 to 0.49 g. Continental's wet track test with new tyres measured 0.689 g, as good as the Highway Code's dry figure.
These numbers are not in conflict; they describe different roads. A test track is smooth, clean asphalt under a controlled film of water (0.66 mm in Continental's test). A real road in the rain has polished patches, standing water, diesel, leaves and road paint. The Highway Code's "at least double" is a margin for those roads, and for drivers who react later in poor visibility. Our reading: treat the track figures as the best case and the doubled chart as the figure to drive by.
Worn tyres: what published tests measure
Continental: new, 3 mm and 1.6 mm
Continental publishes the report of a test run on 29 June 2021 at its Contidrom track: a Mercedes A-Class (W177) on EcoContact 6 tyres in 225/45 R18, braked with ABS from 80 to 0 km/h on wet asphalt (0.66 mm of water, 21.4 °C), with the tyres new, worn to 3 mm and worn to 1.6 mm.
| Tread depth | Braking 80-0 km/h (50-0 mph) | Mean deceleration | Longer than new | Speed still left when the new-tyre car has stopped (our calculation) |
|---|---|---|---|---|
| New | 36.6 m | 0.689 g | 0 | |
| 3 mm | 40.9 m | 0.615 g | +4.3 m (+11.7%) | 26 km/h (16 mph) |
| 1.6 mm (UK legal minimum) | 45.5 m | 0.554 g | +8.9 m (+24.3%) | 35 km/h (22 mph) |
The last column matters more than the metres. Where the car on new tyres has stopped, the one on legal-limit tyres is still moving at 22 mph.
ADAC: tread and aquaplaning
Germany's motoring club ADAC compared winter tyres in 185/60 R14, new (about 8 mm) and worn to 4 mm (article of 19 May 2026). From 80 km/h on a wet road, the worn tyre took about 7 per cent longer to stop, and it began to aquaplane at 63 km/h instead of 87 km/h. On a dry road, the worn winter tyres stopped slightly shorter, because shallower tread blocks flex less. The ADAC advises replacing summer tyres at 3 mm and winter or all-season tyres at 4 mm. For the speeds and conditions at which a tyre starts to float, see hydroplaning and aquaplaning.
Michelin: the tyre model counts as much as wear
Michelin published a wet braking test on a 2017 Toyota Camry (215/55 R17) with two unnamed brands, new and buffed to the wear indicator (2/32 in). Brand A stopped in 87 ft (26.5 m) new and 107 ft (32.6 m) worn; brand B in 118 ft (36.0 m) new and 165 ft (50.3 m) worn. The page does not state the test speed for this comparison. One worn tyre stopped shorter than the other brand new.
The legal minimum
In Great Britain, regulation 27 of the Road Vehicles (Construction and Use) Regulations 1986 requires the tread grooves of a car tyre to be "of a depth of at least 1.6 mm throughout a continuous band comprising the central three-quarters of the breadth of tread and round the entire outer circumference of the tyre". The tests above show that 1.6 mm is a legal floor, not a performance threshold: wet braking gets longer progressively from new. US, Australian and Canadian limits are set differently, often state by state or province by province: see legal tread depth in the UK, US, Australia and Canada. Tread is not the only clock, either: rubber ages too, as explained in how long tyres last.
Our table: stopping distance by grip
Our calculation with the Highway Code's 0.67-second reaction. Each cell is the overall stopping distance.
| Speed | Wet, new tyres (0.689 g) | Wet, 3 mm (0.615 g) | Wet, 1.6 mm (0.554 g) | Wet, Queensland figure (0.49 g) | Highway Code dry × 2 (rule 227) | Add for a 1.5 s reaction |
|---|---|---|---|---|---|---|
| 20 mph | 12 m (39 ft) | 13 m (41 ft) | 13 m (44 ft) | 14 m (47 ft) | 24 m | +7 m |
| 30 mph | 22 m (73 ft) | 24 m (78 ft) | 26 m (84 ft) | 28 m (91 ft) | 46 m | +11 m |
| 40 mph | 36 m (117 ft) | 38 m (126 ft) | 41 m (136 ft) | 45 m (148 ft) | 72 m | +15 m |
| 50 mph | 52 m (170 ft) | 56 m (185 ft) | 61 m (200 ft) | 67 m (220 ft) | 106 m | +19 m |
| 60 mph | 71 m (234 ft) | 78 m (255 ft) | 84 m (276 ft) | 93 m (304 ft) | 146 m | +22 m |
| 70 mph | 93 m (306 ft) | 102 m (335 ft) | 111 m (364 ft) | 123 m (403 ft) | 192 m | +26 m |
0.689, 0.615 and 0.554 g: decelerations measured by Continental on a wet track at 80 km/h; 0.49 g: implied by Queensland's wet table.
Three limits of this table:
- Above 50 mph, the Continental columns are an extrapolation. The test was run from 50 mph. At higher speed the tyre has less time to clear water, so wet grip usually falls; our reading is that these columns are optimistic at 60 and 70 mph.
- A track is not a road. Read the first three columns as the best a given tyre can do, and the doubled column as the Highway Code's margin for real conditions.
- Load, brakes and ABS calibration also count. We have not modelled them; nothing in the sources we read quantifies them for a road car.
The tyre label: wet grip classes
Every new car tyre sold in the EU carries a label with a wet grip class from A to E (Regulation (EU) 2020/740, Annex I, Part B; the same text appears on legislation.gov.uk as derived on 31 December 2020). The class comes from a wet grip index G measured under UN Regulation No. 117, with G = G(T) − 0.03. For car tyres (C1):
| Wet grip class | Wet grip index G (C1 tyres) |
|---|---|
| A | 1.55 ≤ G |
| B | 1.40 ≤ G ≤ 1.54 |
| C | 1.25 ≤ G ≤ 1.39 |
| D | 1.10 ≤ G ≤ 1.24 |
| E | G ≤ 1.09 |
The European Commission says "the difference between a class and another can mean an extra 3-6 metres on the stopping distance", and that "wet grip decreases when the tread is worn". The label describes the tyre when new. Other countries use other markings, which we have not compared here. To read the rest of the markings, see how to read a tyre size, load and speed index.
Following distance: two seconds, three seconds, and the law
Rule 126 of the Highway Code opens with the principle: "Drive at a speed that will allow you to stop well within the distance you can see to be clear." It then says "the safe rule is never to get closer than the overall stopping distance" and asks for "at least a two-second gap between you and the vehicle in front on high-speed roads and in tunnels where visibility is reduced".
| Country | Rule | Source |
|---|---|---|
| UK | At least two seconds; at least doubled in the wet, up to ten times on ice | Highway Code, rule 126 |
| US (California) | Three-second rule | California Driver Handbook |
| Australia (Queensland) | "A sufficient distance behind" to "stop safely to avoid a collision"; no number in the law | Road Rules Regulation 2009, s. 126 |
| Canada (Ontario) | At least two seconds, a minimum for ideal conditions | Official MTO Driver's Handbook |
Two seconds at 70 mph is 63 m, less than the 96 m it takes to stop (our calculation). That is not a contradiction: the car in front is braking too, so your gap only needs to cover your reaction plus any difference in braking. If you brake worse than the car ahead, because your tyres are more worn or your reaction is slower, the margin shrinks. Three seconds at 70 mph is 94 m.
What does not shorten your stopping distance
- ABS. Ontario's handbook says that with anti-lock brakes "you should not expect the stopping distance for your vehicle to be shortened". ABS keeps the wheels turning so you can steer.
- Bigger brakes, once the tyre is at its limit. On a car whose brakes can already lock or trigger ABS, the tyre sets the deceleration: the Continental test changed only the tyres and moved the distance by 8.9 m. This is our reading; none of the sources we read gives a figure for brake upgrades on a road car.
- A guessed tyre pressure. The correct figure is the car maker's, on the door pillar or in the handbook; see what tyre pressure should be.
- The wrong season. Winter tyres in summer and summer tyres in the cold both move away from the grip the tyre was built for; see winter tyres in the UK.
If the tread is near the wear bars, a tyre is cut or bulging, or the car pulls to one side under braking, have it checked before you drive on.
Frequently asked questions
What is the stopping distance at 70 mph?
96 metres (315 feet) on a dry road in the Highway Code: 21 m thinking and 75 m braking, or 24 car lengths. In the wet, rule 227 says at least double, about 192 m.
What is the stopping distance at 30 mph?
23 metres (75 feet): 9 m thinking and 14 m braking, six car lengths. At least 46 m in the wet.
How do you calculate stopping distance?
Convert speed to metres per second, multiply by your reaction time, then add v² ÷ (2 × µ × 9.81), where µ is the grip (about 0.67 in the Highway Code chart). At 50 mph: 22.4 × 0.67 + 22.4² ÷ 13.1 ≈ 15 + 38 = 53 m.
How much longer is stopping distance in the rain?
The Highway Code says at least double. Measured on a wet track with new tyres, the loss can be small; on real roads and worn tyres it is much larger. Use the doubled figure.
Does tread depth really change stopping distance?
Yes, in the wet. In Continental's test from 50 mph, 3 mm added 11.7 per cent and 1.6 mm added 24.3 per cent compared with new tyres. On a dry road, the difference is small and can even reverse.
What reaction time does the Highway Code use?
About 0.67 seconds, worked out from its thinking distances. Queensland uses 1.5 seconds for an average driver in an emergency. Tiredness, alcohol and a phone make it longer.
Is the two-second rule enough to stop?
It covers your reaction while the car ahead brakes too, not a full stop from speed. It is a minimum in good conditions: the Highway Code doubles it in the wet, and California's handbook asks for three seconds.
Do wider tyres or bigger wheels stop shorter?
Not by themselves. Stopping distance depends on the tyre's compound, tread depth and pressure, and on the road. Compare sizes with the tyre size calculator and see what changes on 19-inch wheels; fit only sizes listed for your car by its maker.
Made-to-measure wheels and the car maker's tyre sizes
Onyx Forged wheels are designed to JWL/VIA standards and drawn around the tyre sizes the car maker lists. Onyx Forged does not recommend a size or an offset: stopping distance is decided by the tyre and the road, not by the wheel design, and the car maker's documents remain the reference. To start a set, see customise your wheels.
Sources
- GOV.UK, The Highway Code, rules 103 to 158, rule 126, and Typical stopping distances (PDF), updated 22 October 2025.
- GOV.UK, The Highway Code, rules 226 to 237, rules 227 and 230, updated 22 October 2025.
- The Road Vehicles (Construction and Use) Regulations 1986, regulation 27.
- Queensland Government, Stopping distances on wet and dry roads, updated 14 November 2016; Road Rules Regulation 2009, section 126.
- Government of Ontario, Official MTO Driver's Handbook, Driving along, updated 31 March 2026, and the section on driving at night and in bad weather.
- California DMV, California Driver Handbook, Safe driving.
- 49 CFR 571.135, FMVSS No. 135, S7.5 cold effectiveness.
- Continental, test report, stopping distance with ABS on wet asphalt, new, 3 mm and 1.6 mm, Contidrom, 29 June 2021.
- ADAC, Mindestprofiltiefe Reifen: Wann es gefährlich wird, 19 May 2026 (in German; our translation).
- Michelin, The Truth About Worn Tires (feet converted to metres by us).
- Regulation (EU) 2020/740, Annex I, Part B, wet grip classes.
- European Commission, Energy Efficient Products: Tyres.
All pages were read on 16 October 2026.
The Onyx Forged design office.