New tires, replacement wheel

Bought a wheel on ebay to replace the wheel I hit with a curb. I also ordered
some new Dunlop Direzza Sport Z1 tires yesterday. The current wheel looks bad
but is still functional, so I intend to keep it, with the tire on it, as a
spare. hopefully I can get a large wheel bag to put it in and keep it in the
utility room, out of the heat, so it won’t get dry-rotted.

Hopefully the wheel will arrive before the tires!

New wheels and tires

bought an extra set of wheels with factory bridgestone potenza RE040s. can’t
decide if I just got some tires for cheap for the street, want to put race
tires on the extra wheels, or if I should re-sell them and just get some nice
tires to use for both street and autocross.

I ended up selling the wheels and tires individually on ebay for a tidy profit,
and using the proceeds to buy some Dunlop Direzza Sport Z1 tires. These tires
rock, they are by far the best tires I have ever had on any car I have ever
owned. I bought them from Carrol Shelby, who is a sponsor of my local SCCA
club.

New Tires

I put 32,111 miles on the tires which shipped with the car from the factory. They were Bridgestone Potenza A030s, the size was P225/45ZR18. These tires seemed to be too small for the wheels.

The new tires are Kumho Ecsta SPTs, in size 245/40ZR18. These seem to fit much nicer, and look much better, plus I get an extra 20mm or so of tread width!

The old tires had a treadwear rating of 140, the new ones have a treadwear rating of 320! somehow I doubt I’ll get 71,339 miles out of them, but hopefully I’ll get more than 30,000.

The old tires had gotten VERY loud when driving at highway speeds. the first drive in the new tires was startling, there seemed to be no road noise whatsoever. All I could hear was the engine, and a very slight whisper of some wind. much nicer. And I haven’t even driven on any rubberized sections of highway yet!

In the little bit of performance testing I’ve been able to do, the sidewalls on the new tires seem to be less stiff than the old tires, but they feel grippier than the old tires. whereas before a snap of the wheel resulted in a razor sharp response, now it’s more of a quick lunge (if that makes any sense).

The only bad part of all this is that Discount Tire, where I bought the tires and had them installed, managed to break the tire pressure sensor in the driver’s side front tire. They have ordered a replacement from Mazda, and are supposed to install it today.

Fit on the wheel:

too small
Stock tire: sidewall 4.0 in tall; diameter 26.0 in; circumference 81.6 in.
just right
New tire: sidewall 3.9 in tall; diameter 25.7 in; circumference is 80.8 in.

 

 

 

 

 

 

 

 

 

The small difference in size adds up to about a 1% difference to the speedometer. If the speedometer was dead accurate before, now it would be off by about .6mph at 60 mph (if the speedo said 60, I would actually be going 59.4 mph. I had already noticed an error of between 2 and 2.5 mph around 75 mph, so now it will be a little bit more. I’ll have to check it with my gps.

old
old
new
new
old
old tread close up
new tread, close up
new tread close up
P225/45ZR18
old tire, labelled with the tire size
245/40ZR18
new tire, labelled with the tire size
old tire, sidewall at the bottom
old tire
new tire
new tire

 

 

new tires
new tires