I’ve looked around, but don’t understand what they’re telling me. I’m feeling a bit dense today I suppose.
I’m considering a set of Wranglers for my truck, and there’s a speed rating of 98S on them. What does that mean?
Also, will P225/70R14s fit on my truck? I currently riding on P215/75R14s.
There was no one around to ask when I popped in quickly, that’s why I ask here.
Thanks
Here is an excellent article on speed ratings
Here is another one
As far as the fit goes, the 225/70 should have the same outer diameter as the 215/75, but they will be wider. Not know what your wheelwells look like, I cannot answer your fit question. A good tire shop should be able to.
I’ve heard tell that the higher the speed rating, the stiffer the sidewall, and as a result the handling traits of a vehicle will change as the speed rating changes, even when you are NOT exceeding the speed ratings of either new or old tire.
I’m uncertain as to whether this was wholly accurate, as neither of the (admittedly fine) cites that Rick gave seem to mention it.
The speed rating is the speed you can drive up to, without exceding the tires design. They’re rated for the speed the manufacturer feels they won’t seperate or blowout at. Don’t buy a tire with a speed rating of 55 if you plan on using the car on the interstate. I don’t know why the government allows the sale of tires under the maximum speed limit. The other numbers are as has been stated by others, width, and radius of the tire. The R means radial tire. Tires can be put on rims for witch they are not manufactured, but then your changing the shape and safety of the tire. Find out the tires traction rating before you buy. I would not go with a rating less than B, and suggest you chose A. That gives you the best ability to keep the car under control in adverse conditions.
Speed rating is essentially the speed at which the tire’s rated for sustained use, i.e. highway cruising. S= 112 mph, IIRC.
225/70 R14 will definitely fit a 14" rim- your speedometer may be slightly off due to very minor differences in diameter, but it’s probably not worth worrying about.
Since it hasn’t been mentioned yet, the 98 in 98S is the load index, not the speed rating. It tells how much weight can be put on the tire. I can’t remember the conversion.
Also, the most important thing for tire sizes is the wheel diameter (14 in your case). The width also has to be in the same neighborhood or the tire won’t seal. Going from 215 to 225 should be fine, but 215 to 255 might give you problems. I wouldn’t stray by more than 10% without a wider wheel. Also, a wide tire may rub against suspension components, but you usually have more than a centimeter to work with. (Tire width is measured in millimeters.) The profile of the tire (listed in percentage of height divided by width) has nothing to do with the tire fitting on the wheel, but you will want to keep the outside diameter roughly the same if you want your speedometer to be useful. You can find the outer diameter by:
tire diameter = wheel diameter + 2 * (width / (profile / 100))
There are online calculators for this, but it’s not very hard on a regular calculator. Do remember to either convert the wheel diameter to millimeters or the tire width to inches as you can’t mix units.
From my first link
Two things here. First off it is obvious that speed ratings are alphabetic not numeric. Secondly the lowest rating is M which is above the speed limit in the US with the exception of Montana IIRC. Off the top of my head I don’t recall ever seeing a rating below S.
The truck’s quick, but it probably couldn’t get to 112 MPH even if it was dropped out of a plane. 
Since traction and temperature ratings came up, I thought I’d throw in a brief bit of information - available lots of places, but handy from the following NHTSA Report :
Note that the traction rating is for wet pavement, so a tire can test well but still not be considered a performance tire for dry-weather handling.