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Sat Dec 24, 2005 12:54 am

I’m going to try a different set of new tires on my 87’ Wolf. I’m removing the Michelin XGTZ4 P225/60ZR16’s I got a few weeks ago and mounting them on one of my other cars.
On Tuesday I’m installing a new set of Michelin MXV4+ 225/60R16/RF’s. I think these are premium upgrades for Eurovan. They’re ‘reinforced’ and have a VW O/E class code.
In larger diameters these are O/E on BMW X5 and S-class Benz.
I’ll report the differences observed between these two tires on the new GoWesty 16x7.5” wheels, but in the mean time here are published specs:

What the car originally had on the 6X14” VW alloys:

P-O-S Brand X 205/70R14 no real wear, car stored for years, tires hard as wagon wheels
Service rating: 93 – 1433@35psi (sweet)
For rims: 5-7”
Section width: 8.2 on 6” rim
Diameter: 25.1”
Revolutions per mile: 828

Then came:

XGTZ4 P225/60ZR16 on 16X7.5 wheels
Service rating: 97W – 1609lb.@51psi, 168mph
For rims: 6-7.5”
Section width: 9.2” on 6.5 rim
Diameter: 26.3”
Revolutions per mile: 789

And the next incarnation:

MXV4+ 225/60R16/RF
Service rating: 102H - 1874lb@50psi, 130mph (hella-bitchen)
For rims: 6-8”
Section width: 9.3 on 7.5” rim
Diameter: 26.8”
Revolutions per mile: 785

I’m looking forward to seeing if these are noticeably any more quiet and cushy than the XGT4’s. I’ve had both tires before but different sizes on different cars. How often do we get a chance to test two different premium tires back to back, brand new, and on the same car? Let the chimp science begin! :D

Tue Dec 27, 2005 10:14 pm

A remarkable discovery!

The Michelin MXV4+ 225/60/16RF mentioned above has turned out to really surprise me. I was planning that there would be more similarities between it and the XGTZ4 than differences, but I was totally wrong.

Both tires have pretty tough service ratings, but the tire pressure needed to make the perfect footprint is a 10-12psi difference between the two.

The XGTZ4 is the expected 'squareish' shape of all the Pilot series performance tires I've used and caries it's greatest section width very close to the tread shoulder. The MXV4+ on the other hand, is a more 'rounded' shape carrying it's greatest section width almost 1 1/2" lower than the other tire. At the same time, it is slightly taller and wider than the XGTZ4, but actually fits the car better.

The XGTZ4 is a fairly quiet tire, but once aired correctly the MXV4+ is nearly silent.

On dry pavement there is no appreciable difference in handling between these tires on the Vanagon. Both tires can resist greater g-forces than the vehicle can generate and still stay upright, so the car is effectively over-tired.

Diameters of both tires are greater than stock, so there is an effective reduction of maybe 250 rpm at 85mph for the XGTZ4, and 300 rpm for the MXV4+. I’m guesstamating since speedo’s now going to read a few ticks less at the same speed. There isn’t a great enough reduction in acceleration to really notice, but at the higher speeds I’m no longer zinging the engine.

Now about the remarkable discovery -

I began testing both tires at 40psi cold, and aired down to the point at which they made their perfect footprint.
In order to read the footprint and measure the tread section I used the talc and wax paper method. I then confirmed the print by rolling the laden vehicle (front driver & passenger weight in car) over an inspection window at a friend's alignment shop. I chose yellow #77 as the goo of choice because it's bright yellow and within arm's reach. When the 'goo-line' is displaced evenly across the tread, I knew I had a good print. It is important to note here that this is actually a good indicator of pressure ideal for dry pavement use. Always add about 5psi over the 'dry' number for rain driving at speed and you'll discover most tires are much less likely to hydroplane.
I just couldn't believe what I was seeing, the new MXV4+ made it's perfect print at 24psi!
Road tests were also made at each pressure setting.
The MXV4+ at it's ideal, and weirdly low pressure was amazingly smooth and quiet, but at the same time the vans handling became more linier and predictable. At 80-85mph on the freeway the steering response was solid and velvety, and the van runs totally straight and true with hands off the wheel regardless of the rain grooves and other imperfections in the concrete. The feel at the steering wheel is also mildly heavier while under way, but there is really no difference in effort while maneuvering in a parking lot. In fact there was little difference in this part of the test between these two bigger tires/wheels and the OEM rolling stock, regardless of pressure.
The more stable feel, and slightly heavier steering feedback was a very welcome improvement.
The next test was to see if this wonderfully stable feel translated to real stability. I initiated a series of progressively dramatic jogs across both two and three lanes of the freeway at speeds of 65 and 75mph. This confirmed the tires ability to outperform the vans capabilities.

In summary, while both tires are capable of speeds and lateral acceleration greater than the Van can dish out, the MXV4+ RF comes out a clear winner for this application since it requires so little pressure to return desirable handling and feedback characteristics, that as a benefit it delivers a really quiet and creamy ride. I suspect this is not only due to it being specially reinforced, but because of it's design (shape and construction).

Lastly, wet traction, snow traction, and wear are other issues for another time. But wear is never much of a concern for me. I have never got more than about 18-20,000 miles out of a set of tires - any brand on any car, and 12- 14,000 is more the rule. Tires also get old, and like brake fluid, most people keep them way longer than they should. I figure you might as well use the sh@%t out of ‘em over a two year period then ditch the suckers.

Here's a few quick shots of the wheels and tires. Tires at 30psi - look ma, no bulge! :D

http://home.comcast.net/~polycon/TOASTER/index.html

Tue Dec 27, 2005 10:21 pm

Nice write-up!

Wed Dec 28, 2005 12:51 am

Phil G wrote: perfect footprint.

How do you know what the perfect footprint is?
If the tire were at operating temp. would it not be more pliable and change it's footprint?