Tires

[Dave SanF 50]

Chris, I believe you meant "buffing" not "buffering" a tire. It is also called "shaving" the tire here in the States. This is mostly done on a brand new street tire with full thread. The shop shaves almost all the thread off the tire-down to the legal limit for the sanctioning body (typically 3/32") The amount removed depends on if the sanctioning body measures the tire pre or post race as to how much can be removed. Removing the thread makes the tire last longer because tire "squirm" is reduced. Squirm results in heat build up and thread chunking. A shaved tire is also much faster than a new tire.
Guys, did I miss anything?

[chrisw52]

Chris, I believe you meant "buffing" not "buffering" a tire. It is also called "shaving" the tire here in the States. This is mostly done on a brand new street tire with full thread. The shop shaves almost all the thread off the tire-down to the legal limit for the sanctioning body (typically 3/32") The amount removed depends on if the sanctioning body measures the tire pre or post race as to how much can be removed. Removing the thread makes the tire last longer because tire "squirm" is reduced. Squirm results in heat build up and thread chunking. A shaved tire is also much faster than a new tire.
Guys, did I miss anything?

ah... that crazy UK proper english.. I know what tire shaving is, I didn't make the translation between english and english

thanks

[Neil_Roberts]

I'm sure they are viable, but I'm not sure if they have the potential to be faster. I'm going to try it and see, mostly to reduce the setup differences between autox and club racing.

Well, I tried autocrossing the skinny tires. Here is what I learned.

[Dick R.]

Well, I tried autocrossing the skinny tires. Here is what I learned.

Neil,

Thanks for the detailed report! I hope I can come up to speed quickly after "minimal" autocrossing for the last 10 years.

Questions: Still GY tires? If so, which compound? What was the ambient temperature range and how much time between runs? "Some" of your grip issue may have been cold tires, especially with GY's since the last I heard they don't have a compound competitive with the Hoosier 25B for autocross.

FYI for reference I was repeatedly seeing about 1.5 to 1.6 g's in long turns (i.e. not quick transitions which tend to be high if not smoothed) on a sealed asphalt course on brand new 25B's. Data was smoothed over 0.3 seconds. DA was R-T DL1.

Dick
CM 85

[Neil_Roberts]

Questions: Still GY tires?

Yes, the same R430s I ran in the Buttonwillow school. I'll be on used hard tires until I get my act together and get the setup closer. The day was sunny and low 70s. It was about 5 minutes between pairs of runs.

FYI for reference I was repeatedly seeing about 1.5 to 1.6 g's in long turns

Thanks for the data point!

[mwizard]

Glad we got the skinny back tires option put to rest My car is very neutral, most of the time, with 15 lb tire air. I did find that on new tires I needed to stiffen the rear bar a lot to get rid of the push. I have not done any shock changes so have no data.
Mark

[Dick R.]

Neil,

I really don't know how the GY R430's grip at relatively low tire temps compares to Hoosier R25B's in the same conditions. However, with a dirty site and possibly much less grip than 25B's I don't think you've really answered the question regarding wide versus narrow rears. Even traditional wide rears with a "hard" compound or "old' soft compound would probably have been extremely tail happy with autox gearing . . . especially if your gearing kept you at high revs so any throttle was "too much".

Dick

[Dick R.]

Neil,

Regarding steering: My 85 VD originally had about 20 degree max tire angle at full lock which resulted in about a 50 foot turning diameter . . . much too big for many local courses. Did some stuff to get it down to about a 38 foot or so circle which is fine. I don't know the ratio but lock to lock is about 1 1/2 turns of the steering wheel. I can check my notes for inner and outer wheel angles with my 93 inch wheelbase, standard ackerman, and a little front toe out if needed.

Dick

[Neil_Roberts]

I can check my notes for inner and outer wheel angles with my 93 inch wheelbase, standard ackerman, and a little front toe out if needed.

That would be great! PM or email me if you don't want to tell the whole world.

[Dick R.]

That would be great! PM or email me if you don't want to tell the whole world.

Steering angles on my car with zero toe are ABOUT 24 outer and 28 inner at full lock. I simply removed the rack stops and then did filing of various castings to get some more lock.

Dick

[TeamFRD]

. . . much too big for many local courses. Did some stuff to get it down to about a 38 foot or so circle which is fine. Dick

I made some 1/4 inch bushings - 3/4 OD, 5/8 ID - to extend the inner rack so that it slides into the outer rack more. Found some thinner nuts to lock it down. One of my steering arms is now at it minimum adjustment though. I have about 190 degrees each way of turning.