Tyre Size Calculator

Calculate Tyre Dimensions for Plus Sizing/Up-Stepping

Tyre size markings can be found on the tyre's sidewall and usually look similar to this:

Tyre Size Designation Example: 195/65 R15 91 T

Let's see what each symbol means.

195 mm: Section Width. Nominal section width of the tyre in millimeters.
65: Aspect Ratio. The sidewall height as a percentage of the section width. For example, sidewall height of this tyre will be 195 x 0.65 = 126.75 mm
R: Construction Code. Denotes radial construction which is dominant for passanger tyres.
15: Rim Size. Wheel diameter in inches to which the tyre fits.
91: Load Index. Load capacity of the tyre which is the maximum weight the tyre can carry. You may lookup the value in the load index table.
T: Speed Index or Speed Rating. Maximum speed at full load. You may lookup the value in the speed index table.

Tyre dimension may be prefixed by a letter which denotes tyre's intended usage. Here is what each means:

There are more markings on each tyre, but these are the most important.

Index	km/h	mph	Index	km/h	mph
N	140	87	U	200	124
P	150	94	H	210	130
Q	160	100	V	240	149
R	170	106	ZR	over 240	over 149
S	180	112	W	270	168
T	190	118	Y	300	186

The table gives indices together with theoretical load in kg each tyre can carry.

Index	Capacity [kg]	Capacity [pounds]	Index	Capacity [kg]	Capacity [pounds]
71	345	761	91	615	1356
72	355	783	92	630	1389
73	365	805	93	650	1433
74	375	827	94	670	1477
75	387	853	95	690	1521
76	400	882	96	710	1565
77	412	908	97	730	1609
78	425	937	98	750	1653
79	437	963	99	775	1709
80	450	992	100	800	1764
81	462	1019	101	825	1819
82	475	1047	102	850	1874
83	487	1074	103	875	1929
84	500	1102	104	900	1984
85	515	1132	105	925	2039
86	530	1168	106	950	2094
87	545	1205	107	975	2149
88	560	1231	108	1000	2205
89	580	1279	109	1030	2271
90	600	1323	110	1060	2337