ALT-1 Tips for Buying Low Profile Tires
When it comes to buying a low-profile tire, where safety is concerned, I can't emphasize this one enough: Load capacity.
When "upgrading" to a lower profile tire than what originally came on the vehicle one has to keep in mind that low-profile tires have lower load carrying capacities - they can not carry as much weight. In some circumstances if done wrong this can be dangerous.
Let's take a common low-profile plus upgrade as an example. Many Hondas in the 90s were fitted from the factory with P185/65R14 85S sized tires at 30 psi front and 29 psi rear inflation pressures, which translate into load carrying capacities of 1,040 lbs front, 1,025 lbs rear.
As teenage males began to snap up these cars and modify them it became popular to fit them with 17-inch diameter wheels and low-profile tires. The logical +3 tire for this application was a 205/40R17 80H and many Honda's were so fitted. Problem is, at the factory recommended inflation pressures of 30/29 this tire size has a load carrying capacity of only 900 lbs. front and 885 lbs. rear. Even at 36 psi - the pressure where this size has its maximum load capacity - the load is only 992 lbs, or short of what Honda recommend. A tire of that size and service description should not be used at all for this application.
The proper tire size for this application is an "Extra-Load" which reads like this: 205/40R17XL 84H.
A tire that size when inflated to 40 psi in the front and 39 psi in the rear can match (actually slightly exceed) the load carrying capacity of the stock 14-inch tires. After a few years even the tire manufacturers caught on to what was happening and the "standard-load" 205/40R17 80 tire size has now almost completely been replaced by XL versions with a service rating of 84, but you still have to mind the proper pressures.
The other boring stuff like maintaining the correct overall diameter to avoid errors in speedometer and odometer readings, choosing a speed rating equal or greater to OE and selecting wheels of the correct offset for the application come next.
