245/45R17 Tyre Size: Dimensions, Alternatives & Speedometer Effect
245/45R17 is a wide low-profile tyre size for a 17-inch rim, and the first thing to know about it is the overall diameter: 652.3 mm (25.68 inches). That single figure drives almost everything else on this page — the speedometer reading, the gearing, the ground clearance and which sizes can replace it without changing how the car behaves. The sidewall stands 110.2 mm tall, the tyre rolls 2049.3 mm around its circumference, and it turns 785.3 times for every mile travelled. If you are here because 245/45R17 is the size on your door-jamb placard, or because it is printed on the sidewall of the tyres on your car now, those four numbers are the ones to carry into any comparison.
That puts 245/45R17 in the wide, low-profile bracket: the 245 mm tread is paired with a sidewall 45% as tall as the tread is wide, on a 17-inch rim. Drivers usually meet this size when they are checking a replacement, comparing a plus-size option, or trying to work out why the speedometer reads slightly differently after a change — and every one of those questions comes back to the same four numbers in the table below.
This is a calculation, not a safety approval. Always check your vehicle's door-jamb placard, load index and speed rating, and confirm fitment with a tyre professional before fitting a different tyre size.
245/45R17 dimensions
| Measurement | Value |
|---|---|
| Overall diameter | 652.3 mm (25.68 in) |
| Sidewall height | 110.2 mm |
| Circumference | 2049.3 mm (80.68 in) |
| Revolutions per mile | 785.3 |
| Revolutions per kilometre | 488.0 |
| Rim diameter | 17 in (431.8 mm) |
These are nominal new-tyre figures, worked out from the size code itself: the diameter is the rim diameter plus twice the sidewall height, the circumference is pi times the diameter, and the revolutions per mile follow from the circumference. Real tyres vary slightly by brand, model, wear and inflation pressure, so two tyres marked 245/45R17 can differ by a millimetre or two in practice — the table gives the standard computed values, which are the right ones to use for comparisons. For scale, 245/45R17 is 3.23% larger in diameter than the widely used 205/55R16 reference size (631.9 mm), so a car moving from that reference size to 245/45R17 would see its speedometer, gearing and ride height shift by that proportion. The ±3% guideline around 245/45R17 runs from 632.7 mm to 671.9 mm: replacements inside that band keep the speedometer error small, and replacements outside it deserve a closer look before fitting.
Decoding 245/45R17: width, aspect ratio and rim
The code 245/45R17 breaks into three parts, and each part is a measurement. The first number, 245, is the section width in millimetres — the width of the tyre from one sidewall to the other at its widest point, measured on its approved rim width. The second number, 45, is the aspect ratio: the sidewall height expressed as a percentage of the width, so 45% of 245 mm gives the 110.2 mm sidewall in the table. The letter R means radial construction, which is the standard for modern road tyres, and the final number, 17, is the rim diameter in inches — the wheel this tyre mounts on. Put together, the diameter is 431.8 mm of rim plus two sidewalls of 110.2 mm, which is 431.8 + 220.4 = 652.3 mm, matching the table. That arithmetic is worth doing once by hand, because it shows why two sizes that look similar can measure differently: raising the aspect ratio by 5 points on a 245 mm width adds 12.2 mm to each sidewall and 24.5 mm to the diameter, while widening the section by 10 mm at the same aspect ratio adds 4.5 mm per sidewall. The size code tells you nothing about load index or speed rating — those are separate markings on the sidewall, and the placard specifies the minimum for both.
Closest alternatives to 245/45R17
The three sizes in the chart closest to 245/45R17 by overall diameter are listed below. Each one is a real size from the same chart, with its diameter difference worked out against 652.3 mm, so the comparison is exact rather than approximate.
| Alternative size | Diameter (mm) | Difference (mm) | Difference (%) | Actual speed at 60 mph indicated | Rim |
|---|---|---|---|---|---|
| 205/60R16 | 652.4 | 0.1 | 0.02% | 60.0 mph | 16 in |
| 275/40R17 | 651.8 | -0.5 | -0.08% | 60.0 mph | 17 in |
| 245/50R16 | 651.4 | -0.9 | -0.14% | 59.9 mph | 16 in |
205/60R16 measures 652.4 mm across, 0.1 mm taller than 245/45R17, a difference of 0.02%. Fitted in place of 245/45R17 it would lift or lower the car by about 0.1 mm — half the diameter change — and at an indicated 60 mph the car would actually be travelling at 60.0 mph. Its sidewall is 123.0 mm on a 16-inch rim, it turns 785.2 times per mile, and its circumference is 2049.6 mm. That puts it inside the ±3% guideline around 245/45R17, so it is a change the speedometer would barely notice.
275/40R17 measures 651.8 mm across, 0.5 mm shorter than 245/45R17, a difference of 0.08%. Fitted in place of 245/45R17 it would lift or lower the car by about 0.2 mm — half the diameter change — and at an indicated 60 mph the car would actually be travelling at 60.0 mph. Its sidewall is 110.0 mm on a 17-inch rim, it turns 785.9 times per mile, and its circumference is 2047.7 mm. That puts it inside the ±3% guideline around 245/45R17, so it is a change the speedometer would barely notice.
245/50R16 measures 651.4 mm across, 0.9 mm shorter than 245/45R17, a difference of 0.14%. Fitted in place of 245/45R17 it would lift or lower the car by about 0.4 mm — half the diameter change — and at an indicated 60 mph the car would actually be travelling at 59.9 mph. Its sidewall is 122.5 mm on a 16-inch rim, it turns 786.4 times per mile, and its circumference is 2046.4 mm. That puts it inside the ±3% guideline around 245/45R17, so it is a change the speedometer would barely notice.
For 245/45R17, a useful way to use this table is to start from the diameter difference column, comparing each alternative with 205/60R16 first. Anything inside ±3% keeps the speedometer, the gearing and the ride height close to the original, and most drivers would not notice the change in daily driving. Anything outside that band changes the car's behaviour in ways that are easy to measure — the speedometer error grows, the gearing lengthens or shortens, and the ride height moves — so it needs the placard check and a professional's confirmation before fitting. Rim size matters here too: the alternatives above use 16-, 17- and 16-inch rims, and a size on a different rim diameter needs different wheels, not just different tyres.
What 245/45R17 does to speedometer readings
The speedometer is calibrated for the original diameter, so any change in diameter changes what the dial shows. The formula is straightforward: error % = (new diameter − old diameter) ÷ old diameter × 100, and actual speed = indicated speed × (new diameter ÷ old diameter). For the closest alternative, 205/60R16 (652.4 mm against 652.3 mm, a 0.02% change), the numbers work out as follows:
| Indicated speed | Actual speed on 205/60R16 | Actual at +3% diameter | Actual at −3% diameter |
|---|---|---|---|
| 30 mph | 30.0 mph | 30.9 mph | 29.1 mph |
| 50 mph | 50.0 mph | 51.5 mph | 48.5 mph |
| 70 mph | 70.0 mph | 72.1 mph | 67.9 mph |
For 245/45R17, a 0.02% diameter change sounds small, and at 30 mph it is — the difference is under a mile per hour either way. At 70 mph the same percentage is worth a little more, which is why motorway driving is where a size change shows up first. The +3% and −3% columns show the edges of the usual guideline: at the +3% edge the car is travelling about 2 mph faster than the dial at 70 mph, and at the −3% edge about 2 mph slower. That is the reason the guideline is ±3% rather than a wider band — beyond it, the error at motorway speed starts to matter for speed limits and for the odometer, which records distance from the same wheel-speed signal and so drifts by the same percentage. A tyre change also affects the odometer reading, the gearing and, on some cars, the calibration of driver-assistance systems that use wheel speed.
Going wider or taller than 245/45R17
Width, height and diameter each pull in a different direction. More width than the 245 mm of 245/45R17 generally means more grip and more rolling resistance, plus a wider tyre that needs more room at the wheel arch and at steering lock. More overall diameter than 652.3 mm lifts the vehicle, lengthens the gearing and slows the speedometer; less diameter drops the car, shortens the gearing and makes the speedometer read fast. A taller sidewall than the 110.2 mm here absorbs bumps better and protects the rim, while a shorter sidewall sharpens steering response at the cost of a firmer ride. Staying within ±3% of the original diameter keeps all of these changes small enough that the vehicle behaves much as it did before.
Ride quality follows the sidewall. The 110.2 mm sidewall on 245/45R17 is 45.0% of the section width, and it is the cushion between the rim and the road: a taller sidewall absorbs small bumps and protects the rim from pothole damage, while a shorter sidewall gives sharper steering response and less flex in corners. That is the trade behind the low-profile label — 245/45R17 is neither the softest nor the sharpest option in its rim size, and moving to a much lower aspect ratio on the same rim would firm the ride noticeably, while moving to a much taller one would soften it. Fuel use moves with rolling resistance, which tends to rise with width and fall slightly with a taller, more flexible sidewall, but the differences between sizes inside the ±3% band are small compared with the differences that pressure, tread pattern and driving style make. Keep the pressures at the placard figure for the size fitted, checked cold, and the tyre will perform as its size suggests it should.
How to check whether 245/45R17 suits your vehicle
The checks for 245/45R17 start from the same place every time: the 652.3 mm diameter on the placard, and the load and speed ratings that go with it. Do the checks in order. First, the door-jamb placard: it is the manufacturer's statement of which size, pressures, load index and speed rating the vehicle was built around. Second, the owner's manual, which confirms the placard and covers the spare. Third, the sidewall of the tyre on the car now — if it reads something other than the placard size, treat that as a question to answer, not as the specification. Fourth, the load index and speed rating on the replacement: both must meet or exceed what the placard requires, because a tyre that is the right size but the wrong load index is still the wrong tyre. Fifth, rim width: a 245 mm section mounts correctly only on a rim within its approved width range. Sixth, the pressure monitoring system, which may need a reset after any change in rolling circumference. Winter tyres deserve the same checks, not fewer — the size rules do not relax in cold weather.
One more check belongs on the list for 245/45R17: the spare. If the car carries a full-size spare, it should match the 652.3 mm size and the load index of the road tyres; if it carries a space-saver, its size and its speed limit are different by design and it is for getting to a repair, not for normal driving. And when the new tyres are fitted, check the pressures again after a short drive and a cool-down, because a tyre that was fitted warm can read differently once it is cold. The placard pressure is a cold pressure, and it is the figure to use for 245/45R17, not a figure carried over from a different size.
Mistakes people make with 245/45R17
Most of the trouble with 245/45R17 comes from treating its 652.3 mm diameter as interchangeable with any size that looks similar on paper. Five mistakes account for most of the trouble with a size like 245/45R17. Matching only the 245 mm width while the 45% aspect ratio differs, which changes the diameter. Copying the size moulded on the current tyres instead of the door-jamb placard, which repeats whatever the last owner fitted. Buying the right size with the wrong load index or speed rating. Changing size on one axle only, so the front and rear roll at different circumferences and the stability and traction systems see a mismatch. And fitting the new tyres at the old pressures instead of the placard pressure for the new size, checked when cold. Each of these is easy to avoid by working from the placard and the four numbers in the table above, in that order.
The last mistake is a quiet one: assuming the size code is the whole specification. 245/45R17 fixes the width, the aspect ratio and the rim, but it does not fix the load index, the speed rating, the tread pattern or the compound, and two tyres marked 245/45R17 can still be very different tyres. Read the full sidewall, match the load index and speed rating to the placard, and choose the tread and compound for the driving the car actually does. The size gets you to the right shelf; the rest of the sidewall gets you to the right tyre.
245/45r17 tyre size: Related sizes and tools
If 245/45R17 is your starting point, the closest sizes to compare are 205/60R16 tyre size, 275/40R17 tyre size, 245/50R16 tyre size. The tyre size calculator page explains how to decode any size code and work out its dimensions, and the tyre size calculator tool does the arithmetic for any size in the chart. The tyre sizes hub lists every size covered on this site, and the tyre size chart shows the full computed table side by side.
Frequently asked questions
What is the overall diameter of 245/45R17?
The overall diameter of 245/45R17 is 652.3 mm, which is 25.68 inches. That is the rim diameter of 17 inches (431.8 mm) plus two sidewalls of 110.2 mm each. It is a nominal new-tyre figure; real tyres vary slightly by brand, model, wear and inflation pressure.
What is the sidewall height of 245/45R17?
The sidewall height of 245/45R17 is 110.2 mm. It comes from the aspect ratio: 45% of the 245 mm section width is 245 × 45 ÷ 100 = 110.2 mm. That low-profile sidewall is the cushion between the 17-inch rim and the road, and it is what gives 245/45R17 its ride and steering character.
How many revolutions per mile does 245/45R17 do?
245/45R17 turns 785.3 times per mile, or about 488.0 times per kilometre. The figure follows from the circumference of 2049.3 mm: one mile is 63,360 inches, and each revolution covers one circumference. A replacement tyre with a different circumference turns a different number of times per mile, which is why the speedometer and odometer readings move when the diameter changes.
What is the closest alternative size to 245/45R17?
The closest size in the chart to 245/45R17 is 205/60R16, at 652.4 mm — 0.02% larger in diameter than 245/45R17. At an indicated 60 mph the car would actually be travelling at 60.0 mph on 205/60R16. The next closest are 275/40R17 (-0.08%) and 245/50R16 (-0.14%), and all three are listed with their full figures in the alternatives table above.
Does 245/45R17 affect the speedometer?
Yes — fitting 245/45R17 in place of a different original size changes the reading, because the speedometer is calibrated for the diameter the car was built with, so fitting 245/45R17 in place of a size with a different diameter changes the reading by the diameter difference as a percentage. A replacement within ±3% of the original diameter — between 632.7 mm and 671.9 mm for 245/45R17 — keeps the error small; outside that band the error at motorway speed becomes noticeable, and the odometer drifts by the same percentage.
Can I fit 245/45R17 instead of my current size?
For 245/45R17, only if the diameter stays within about ±3% of the size on your door-jamb placard, the load index and speed rating meet what the placard specifies, the rim width suits a 245 mm section, and there is clearance at the arch, the suspension and full steering lock. This page gives the measurements so you can make that comparison; it does not approve a fitment. Check the placard and confirm with a tyre professional before fitting a different size.