Tire Upgrade

[dwreed3rd]

Here are several links that may be informational:

Tire code - Wikipedia, the free encyclopedia

Uniform Tire Quality Grading (UTQG)

Treadwear rating - Wikipedia, the free encyclopedia

Before places like PC, I would use the Traction and Temperature(Speed) standard ratings to try to make an intelligent compromise of wear vs traction/handling and speed/performance vs cost. Treadwear rating is relative to all tires tested with a 400 rating falling pretty much in the middle of the pack. Since I learned about these ratings sometime in the '70's, I look for tires with ratings of Traction=A, Temperarure(speed)=A and Treadwear~400 for our primary cars. Currently running Michlein MXV4 Plus' on our 2000 Avalon XLS, 34psi front/32psi rear. Third set(original plus 2) still good tread @ 108K. Averaging right around 40K per set. Keep them rotated. Running B/B ratings on the '87 Ford Club Wagon XLT. It hasn't been over double-nickle in over 8 years, <1000mi last year.
While the rating are informational for new or unfamiliar tires, and good for comparing tires, I would rely heavily on the real life experiences and opinions of PC members.

[Highly ImPriused]

Originally Posted by Highly ImPriused

Here's a bit of early feedback on the Pirelli P4 Four Seasons in 195/60/15. Had them installed on 7/3 and left for a family vacation the next morning with a very full car (wife, 2 kids, and as much stuff as we could fit for 10 days). Traveled over 1200 miles in both dry and very wet (torential downpour) conditions. The tires handled great in all conditions. Just a huge improvement over the Intregrities, where I would have been very antsy and nervous in the downpours at highway speeds; I barely had to slow down with these Pirellis. They just hug the road.

I haven't noticed any significant hit to mileage. It's hard to compare though since we haven't done this exact trip before. But overall we averaged about 46 mpg (cruising in the low 70s mostly). This is with about 800 lbs of passengers and cargo I would estimate. I had seen similar results in the past with the stock tires under similar conditions. The only difference is that I had the Integreties at about 40 PSI at that time and went right up to 50 PSI with these Pirelli's. So perhaps there is a bit of a mpg decrease. I'll know better after a few days of commuting by myself where I can compare apples to apples and will report back later in the week.

OK, after a week of commuting with the new tires I can confidently say that there is a hit of about 2-3 mpg going from worn out OEM GY Integrity tires to brand new Pirelli P4 Four Season tires in the wider 195/60/15 size. Both sets of tires at 50 PSI all around. This week I've been getting right around 56 mpg on my commute in (was around 58) and 63 mpg on the ride home (was around 66).

Not too bat at all and the handling is noticeably better. I bet mileage would be very similar in the OEM size. Now that I have a good basis for comparison, I'm going to try bumping the psi up a bit higher to see if I can get back to my previous mpg range. I haven't noticed any ride discomfort to speak of with them at 50 psi. I'll report back over the winter once I've had a chance to try these new shoes out under more challenging conditions.

[dwreed3rd]

Q for those running at a high psi. My experience, non-prius, has been that if I go too high, still within tire max., that the tire will wear the center of the tread faster than the outter edges, if no compensating weight is on the vehicle to keep the tread flat on the road. It's happened to me when I would increase the psi in my rear tires to compensate for towing the trailer. Then forget to adjust it back down after towing. I would notice some degradation in handling and that they were wearing faster in the center of the tread. Checking the tires for treadwear is how I determine my optimum psi(s) for front and rear as to handling, economy and even treadwear. Feathering will indicate an alignment problem, usually in the camber on front wheels.
Has anyone experience this with the Prius. I cant imagine that at some of the high psi(s) posted on PC that the tire isn't ballooning at least a little without a compensating weight on the wheels.
Thanking everyone in advance for your replies.

[Highly ImPriused]

Try searching on tire psi and you'll find a lot of varying opinion on here. The one thing I haven't seen is any documented proof of uneven center wear at high psi. To the contrary, most people experience edge wear at the manufacturer recommended PSI of 33/35. Also F8L has provided high resolution photos of his OEM Integrity tires, which he runs north of 60 PSI I believe, with completely even wear across the treads. I don't remember which particular thread that was in, but you could probably find it with a search including his username.

The only difference I've noticed with mine at 50 PSI is perhaps a bit of a stiffer ride (not enough that I've ever had any passengers mention it though) and that traction control is a bit more prone to kick in when going over a big enough bump/pothole. I plan to lower them down a bit during the winter for better handling.

[dwreed3rd]

Thanks! That's interesting info. It may just be that the newer tire disigns, sizes, shapes, and materials distribute the psi in a manor, that the psi range, between min & max psi, does not change or distort the tread cross section, so the car's weight is distributed evenly on the tread and thus, to the road, at the full recommended psi range. Sorry for the horrorably long sentence. That would explain it, because psi used to have a significant affect on treadwear. Now that you mention it, I have not noticed it on the MXV4 Plus tires I've been running on the Avalon. I think I'll run them up to Max on the front/less 3psi in the rear, and work down from there to find a happy median between Toyota's recommendation and max psi. Currently running @34/32. 2000 Avalon XLS w/108K. City went from 17-19 to 19-21 due in part to ScangaugeII and in switching to Mobil1 5w30.
Haven't done enough highway yet to note change there. Maybe I can get a couple more mph upping the psi. I won't sacrifice handling though.
Thanks again! I'm an old dog that likes to learn new tricks.
My Dad always told me: "It doesn't matter who you are or what you know. Evrybody knows something that you don't. Even a bum in the gutter". His choice of words, not mine, and he did not mean it in a derogatory manner. I don't remember the term homeless in the '40's - '50's. Anyway, I'm always open to reprogramming the old grey matter.

[apriusfan]

Originally Posted by Highly ImPriused

Both sets of tires at 50 PSI all around.

You might want to reconsider your choice of inflation pressure - Pirelli specs 44 psi as the max inflation pressure. If the tire fails due to over-inflation, you are on your own.

[Highly ImPriused]

Originally Posted by apriusfan

You might want to reconsider your choice of inflation pressure - Pirelli specs 44 psi as the max inflation pressure. If the tire fails due to over-inflation, you are on your own.

If I thought there was a chance of tire failure due to over inflation, I wouldn't be doing it period. Regardless of who may be responsible. Do you know of any documented cases of tire failure at reasonable speeds (say under 70 mph) due to overinflation at up to 50% increase over the sidewall listed max pressure (i.e. up to 66 psi for a 44 psi rated tire)? I searched before deciding to go up this high and didn't find anything. I'd love to hear about it if there's something out there.

[apriusfan]

Originally Posted by Highly ImPriused

If I thought there was a chance of tire failure due to over inflation, I wouldn't be doing it period. Regardless of who may be responsible. Do you know of any documented cases of tire failure at reasonable speeds (say under 70 mph) due to overinflation at up to 50% increase over the sidewall listed max pressure (i.e. up to 66 psi for a 44 psi rated tire)? I searched before deciding to go up this high and didn't find anything. I'd love to hear about it if there's something out there.

You might try posting on PC to see if anyone has done what you are contemplating doing (66 psi for a 44 psi rated tire). I personally wouldn't go more than 44 psi on a 44 psi rated tire. But you may have a higher risk tolerance level than I do.

[mrblaise]

I have to agree. There's a reason the maximum psi is posted on the tires. A lot of testing goes into tire failure before they're placed on the market. When they "do" fail, they result in humongous lawsuits the the Cooper Tire suits.

[Highly ImPriused]

First of all, mine are currently at 54 PSI. I don't plan to go over 60, but many people do. 44 PSI is the industry standard maximum PSI rating for most passenger tires. Tire manufacturers don't reverse engineer back to that number for tire failure. They make tires according to industry standards with slight differences in tread patterns, etc. There is a huge factor of safety involved in the industry-wide maximum rated tire pressure. Typical engineering FoS where loss of life can occur is 3x. That would mean that a 44 PSI rated tire might be expected to fail at over 130 PSI. Am I going to test that? Hell no. There's a reason that big of a safety margin is there, the true number is not exactly predictable. But if there were even a slight chance of failure at 60 PSI, you can bet the tire rating wouldn't be anywhere near 44; it would be more like 20. You can choose to believe me or not. Bottom line is that no one I'm aware of has found any credible evidence of tire failure under normal (i.e. non-racing) conditions due to over inflation.

The Rubber Manufacturers Association warns that underinflation is a tire's number 1 enemy. It results in unnecessary tire stress, irregular wear, loss of control and accidents. http://www.rma.org/tire_safety/tire_...ce_and_safety/


* Highly ImPriused does not recommend that you exceed the maximum rated pressure printed on the sidewall of your tire. Your decision to stay within that limit is the right one. Sleep easy at night my friends.