CM FF Tires

[Craig Henry]

Hi all,

I recently retired so I finally have time to work on the RF92 I purchased back in the summer of 2006 to replace the S2 CM car I ran long ago (I ran two different S2's infrequently.) I have some questions. I’ll start with tires as the new Hoosiers bagged in the basement, purchased back in 2007, are likely rock hard by now.

The new Hoosier tires I need are: Looking for confirmation and/or other options.

Fronts: 46163 20.5 X 7.0 – 13 R25B
Rears: 43309 22.5 X 7.2 – 13 R25B

Rains: Looks like radials are the only option?

Fronts: 44421 185/60 R13
Rears: 44426 205/60 R13

More questions to come. Thanks in advance for the help.

Craig

[t walgamuth]

Hi all,

I recently retired so I finally have time to work on the RF92 I purchased back in the summer of 2006 to replace the S2 CM car I ran long ago (I ran two different S2's infrequently.) I have some questions. I’ll start with tires as the new Hoosiers bagged in the basement, purchased back in 2007, are likely rock hard by now.

The new Hoosier tires I need are: Looking for confirmation and/or other options.

Fronts: 46163 20.5 X 7.0 – 13 R25B
Rears: 43309 22.5 X 7.2 – 13 R25B

Rains: Looks like radials are the only option?

Fronts: 44421 185/60 R13
Rears: 44426 205/60 R13

More questions to come. Thanks in advance for the help.

Craig

Welcome to C mod. It is a hoot in a FF.

[OneWayOut]

Looking at the Hoosier website, the FC fronts are now listed as 43164. Mine are certainly 43163. I also see references to 46164 in old threads. Maybe they change the item numbers around from year to year.

But yes, your sizes look good. FF rears, FC fronts, R25B.

[TedV]

They will tweak the construction from time to time. If you look close you probably will see A2000 on the 163 and A2500 on the 164. The compound changes might not result in a line code change. Just look to see if its followed with a letter. Like R25, R25A, R25B.

[Lynn]

Radials are the only wets.

[Craig Henry]

Thanks everyone.

Craig

[Jim Garry]

Radials are the only wets.

Which ones? A7?

[Lynn]

Circuit racing radial wets. Item numbers 44421 and 44426. A7s are not available in the proper size, but R7s are.

[OneWayOut]

...you probably will see A2000 on the 163...

Nope. My 43163 says A2500.

I don't think the "A2500" has anything to do with the item number or the R25B compound. If you look at the Hoosier West catalog, and it says 46163. The main Hoosier catalog says 46164. Both have A2500, both available in the two different compounds.

[CM/FFdriver]

Nope. My 43163 says A2500.

I don't think the "A2500" has anything to do with the item number or the R25B compound. If you look at the Hoosier West catalog, and it says 46163. The main Hoosier catalog says 46164. Both have A2500, both available in the two different compounds.

Thats what I just got.

Ben

[TedV]

Just to clarify.
The “A2500” has been a method over the years to know at a glance there is a slight variation change to the construction of the tire in a line code. “A2000” would be ancient. 46164 has a slight change in construction compared to 46163 and will eventually replace it as they move away from the letter-number suffixes. The 46164 may have a slight spring rate difference compared to 46163 but more than likely you will not notice. They give equal lap times and are close enough they can be used together.

The compound has nothing to do with the line code or the “A2500” except being used as the compound designation in addition to the line code. They have used the compound number with letter suffix over the years to indicate the changes to a compound without panicking drivers. It is always good to verify you have 2 of the same when you pick up your tires. For a time they would swap between say, R33 and R35. Folks would be concerned the lower/higher number meant softer/harder and would be upset because change is bad. By keeping number the same and changing suffix there is no confusion if you have the same soft, medium or hard compound that you intend to use.

It’s always good to look at the yellow chalk mark on a new tire. That is the hot out of the mold rollout distance at a certain test pressure. I prefer same numbers to ¼” max difference per axle. Unless you are running circle track and need the stagger.

Summed up, run whatever 20.5x7.0-13 R25 & 22.5x7.2-13 R25 you can get your hands on and have fun!