Tire speed ratings

Does anybody pay attention to the speed rating on tires or just the load rating? I’m getting ready to need new tires and had been looking at 255/75/17. A couple that I was interested in were 106mph max, OE is 112 or 115. Is it sidewall construction that determines speed rating or something else.

 

I don't pay attention to the speed rating on the tires for my 4Runner. Wanna know why? Because it's slow as molasses in winter. It's not built for speed. I get excited if I can hit highway speeds in under 10 minutes.

But I digress. Here's a link about everything you want to know about tire speed ratings: https://www.discounttire.com/learn/speed-rating

https://www.youtube.com/watch?v=2UqVg1cvYK8&t=1s

 

Your speed limiter will become active somewhere between 112-115 IIRC.
So a tire rated at that will be fine.

EDIT: My Toyos are 118, mine won’t get there.

 

My MT's are only rated for 99 mph, so I don't go any faster than that.

 

I’m not really worried about ever getting close to 100mph. I was mainly wondering if the sidewalls would be better constructed or stiffer on a higher speed rating.

 

I figured the video in post #2 might have answered the question.

I do pay attention to speed ratings. But, I don't know what goes into the rating. My Toyos also have a Q speed rating (99), and they feel solid at 90 MPH.

 

If anyone wondering 100mph on 5000lbs 4runner with sliders + every damn skid + 285/70R17 tires no big deal.
If I'm not mistaken per dashcam gps speed at 113 or115mph running 265/70R17 tires the speed governor kicks in.

Lets say I'm not the driver

 

I actually went "ZR" with my 5th gen Limited rims. I think they are 35 series, but what a smooth ride. And the sidewall is stronger.
It also changes the gearing for the better and lowers the center of gravity a few inches.

 

Are you thinking highway tread tires? The speed rating is a measure of whole tire strength. Think of the centrifugal forces trying to tear apart a spinning tire.
I look at tread and sidewall design to make a subjective traction decision. Then the SL, XL, or LT designations. 3 peak snow rating yes or no, then Temperature and treadwear codes are last things I connsider.

 

Regarding actual highway driving I learned Southern Utah has 85 mph for all vehicles including big rigs. These big trucks slow uphill then make up time downhill. 90 mph plus is common. Survival requires keeping up with the flow-first time I ever drove that fast for hours.
I keep my Scanguage2 set on all 4 tire pressures so I can get off highway if I notice a pressure drop.

 

So the Discount tire video does explain the concept of the speed rating but doesn’t say why a particular tire would have a lower rating. I was looking at lt265/70/17 C in an all terrain but noticed there were more options in the a C load in 255/75/17. The Bridgestone ascent AT I was looking at are Standard load T speed in a 265 but LTC at R speed in 255. I just wondering what in the construction of the LT tire lowers the speed rating. If it’s not sidewall it has to be the tread.

 

^The speed rating is tested at the tire's max weight rating, so the LT tire would have had a lot more weight on it during the test, which means more heat buildup.

My load range E Goodyear Duratrac RTs are Q-rated (100 mph). Hasn't been a practical limitation as getting caught at 100 mph on highways in my region results in a street racing charge - license suspension on the spot and vehicle impounded, along with $7k fine. I don't know if the two racetracks outside my city have long enough straights for a stock 4Runner to reach 100 mph.