H vs. T Speed Ratings

NYSpeed Automotive
1

Can someone help fill me in on speed ratings for tires and how much it matters for a daily driver.

I need to buy new tires for my car, Cadillac CTS, the factory recommends H rated tires. Do I need to go with H rated tires or can I go with T rated ones? Dunn Tire says they will do it, but don’t necessarily advise doing it, but couldn’t give me a reason other than, “because it’s what the factory recommends and your ride won’t be as nice.”

I’m not concerned about the cost of the 2 different tires I’m looking at, as it’s only about $40. My concern is that the video reviews on the T rated tire (Continental TrueContact) were excellent in snow and wet surfaces and was rated top in the group among both H and T rated tires they were compared against. The H rated tire (Continental PureContact) was still good, but they didn’t fair as well in their respective group.

What am I going to lose by going down a level in rating?

Videos if you care:
PureContact: http://www.tirerack.com/tires/tires.jsp?tireMake=Continental&tireModel=PureContact+with+EcoPlus+Technology&partnum=355HR7PUREC&vehicleSearch=false&fromCompare1=yes#testResults

TrueContact: http://www.tirerack.com/tires/tests/videoDisplay.jsp?ttid=189&videoID=303

2

It’s just a speed rating, so you’ll lose some safe max speed. It’ll still be safe to 100mph though.

3

Top speed is part of it, but there is also sidewall stiffness and a few other specs that go into the rating.

4

Yeah on paper he might lose some cornering ability but at the H & T level of speed rating I’m not sure he’ll notice it. Especially on a daily driver.

5

It is a speed rating, not a sidewall stiffness or cornering ability rating:

http://www.nhtsa.gov/cars/rules/rulings/UpgradeTire/Econ/TireUpgradeII.html

6

Yeah you’re right, I guess I was thinking load rating?

They were all concerned about putting on tires less than the recommended speed rating, but the load rating is actually 1 more (99 vs 98) on the new tires vs stock.

7

Load rating is not an indication of sidewall stiffness or cornering ability.

For example a Dunlop Direzza ZII is load rated 91, has great dry cornering ability and subjectively speaking has a stiff sidewall.
I would assume the Dunlop Winter Maxx with a higher 94 load rating does not have the same cornering abilities.

http://www.tirerack.com/tires/TireSearchResults.jsp?width=225%2F&ratio=45&diameter=17&rearWidth=255%2F&rearRatio=40&rearDiameter=17&zip-code=

Here are 3 Dunlops (Z102, ZII, SP Sport Signature) that are all load rated 92, but I am sure they have different sidewall stiffness and cornering abilities:

http://www.tirerack.com/tires/TireSearchResults.jsp?width=225%2F&ratio=50&diameter=16&rearWidth=255%2F&rearRatio=40&rearDiameter=17&zip-code=

Those aren’t direct links, you’ll have to filter by brand.

8

Usually manufactures will set their top speed governor based on the speed rating of the tire, which is the reason they’ll list a minimum speed rating for the replacement tires. If you’re not planning on exceeding 118mph for extended periods of time the T rated replacement will be fine.

If GM put T rated tires on it from the factory they would have to set the governor at 118 or under though, and when people reading car review see “governor limited 118” on a luxury car they would assume it’s garbage compared to the other vehicles in it’s class that were limited to 130 or 150.

9

That makes sense. Wish the dummies at the tire shop could explain it like this.

10

I’m sure they’re not allowed to. If they let you put T rated tires on your H rated car then you go blow a tire at 125mph your family will sue the tire place, and sadly they’ll likely win.

11

I remember going through this with BMW. The car is limited to 160 but the tires from the OEM factory are Z rated and they wouldn’t downgrade them since the OEM safety requires them even if the tires are rated faster than the car goes.