Kumho kr21 = LRR?? vs sumitomo htr T4...

[96vtec]

So my current tires have been long overdue and I've been in search of some new tires for my civic HX. I just can't get any confirmation for the kr21's being low rolling resistance. I decided to choose them in the size of 185/70/14 since most have agreed that wider tires offer better lrr. From my understanding,
longer treadlife = harder rubber = less traction = lower rolling resistance
however, these Kumho KR21s seem to do fine as far as traction goes.

185/70/14
Kumho KR21 = $51 per tire (640)
Sumitomo HTR T4 = $49 per tire (560)

The KR21 provides a treadlife of 640 with a traction rating of mid eights disregarding snow traction. (I live in SF where it's usually foggy)

The HTR T4 on the other hand provides a treadlife of 560 while giving the advantage of providing a max psi of 51 (from what I hear at least). These tires seem to not grip the road as easily since it's received low sevens as an overall traction rating.

I find myself torn between these two tire models... Anyone with first hand experience of these two models?

[theholycow]

Originally Posted by 96vtec

From my understanding,
longer treadlife = harder rubber = less traction = lower rolling resistance

I don't think that's quite how it works. It seems about right until the last '='. Less traction =/= LRR. Things that reduce RR may also reduce traction, but plenty of other things reduce traction without reducing RR. I don't think harder rubber reduces RR.

The KR21 provides a treadlife of 640{...}
The HTR T4 on the other hand provides a treadlife of 560

That's well within the margin of error between brands. UTQG, the "Uniform Tire Quality Grade", isn't uniform at all; it's an acronym without a standard to back it up. Manufacturers mostly seem to cooperate/behave with it, using similar specifications, but it's possible that the tires would have equal life. OTOH, it's possible that the KR21 could wear twice as long....I'd definitely read lots of reviews very critically trying to compare.

while giving the advantage of providing a max psi of 51 (from what I hear at least).

Confirmed:
http://www.kumhousa.com/Tire.aspx?id...7942a2d&cat=22
http://www.sumitomotire.com/cars/pro...HTR/htrt4.aspx
KR21 max: 44psi
HTR T4 max: 51psi

Do you run 51psi now? If not, do you think it would be too stiff for you?

For me on my car with my driving, if after reading reviews I thought the the KR21 had a big treadwear advantage I'd choose it, else I'd choose the higher pressure HTR T4.

[trollbait]

Like HC stated, there is no standard. Two manufacturers may be using the same test method, or not. It's likely better than 'testing' standard used for the contrast of monitors and tvs, but it still leaves treadware numbers only actually useful between models of the same manufacturer. The published milage life is probably a better comparison. Use the warranty to judge how much faith the manufacturer puts into it.

[96vtec]

Well, the sidewalls on my "Big O Tires" (installed from previous owner) have sidewall cracks but I still keep them at 40psi while the limit is 44. Would running 51psi on alloy rims do any damage if I were to run with the sumitomos?

I've always loved running tires near max psi even before discovering this site since it always made my car feel more efficient but I kept getting warnings from friends and family of the consequences. Also had a friend crash because his tires were running near max psi but then again, he was probably racing.

Well, I've compared the warranties and...

Sumitomo HTR T4:

Treadlife Warranty 5 Years / 75,000 Miles
(Excludes staggered fitments)

Uniformity Warranty First 2/32" of wear

Workmanship & Materials Warranty 5 Years / Free replacement first 50% of tread then prorated to final 2/32".

Manufacturer's Road Hazard Warranty None

Manufacturer Special Warranty None

Overall Tire Warranty Rating* 4 / 5


Kumho KR21:

Treadlife Warranty 4 Years / 85,000 Miles
Uniformity Warranty First 2/32" of wear

Workmanship & Materials Warranty 6 Years / Free replacement first 2/32" of tread, then prorated to final 2/32" of tread.

Manufacturer's Road Hazard Warranty First 25% of usable tread.

Manufacturer Special Warranty 24-hr Roadside Assist 1st 2 years
Overall Tire Warranty Rating* 4.5 / 5


I'm leaning towards Kumho for safety/comfort but the Sumitomo's seem like they would yield better mpg gains while staying under it's psi limit. If only there was a chart on this site comparing tire pressure to mpg.

[theholycow]

Your friend who crashed may have been racing, and I doubt the pressure was really to blame anyway...but if it was, then he must have ignored some awful handling before the crash. If you increase your tire pressure and your car handles noticeably worse then you definitely need to back it off.

I've found that the limit is ~72 on my pickup's rear tires when the truck isn't heavily loaded, even though the tires are rated for up to 80. If I run them at 80, I can start to notice a little squirrelyness on rough roads and inclement weather.

Rolling resistance of tires is current an art, not a science, due to the huge quantity of variables involved, lack of concrete data, and lack of ability to get concrete data. I think one of the tire threads linked in my sig has links to some RR measurements but probably nothing that would help with this decision.

I'd say get the Kumhos. They have a longer mileage warranty and include roadside assistance.