Rubber tire selection for “GT” cars is a huge and drawn out topic, I’ll do my best to be brief so nobody’s eyes bleed.
First off, on the tracks that I’ve been fortunate to race “GT” on rubber slicks are king, threaded tires don’t have the same amount of contact patch area to develop the same amount of available traction; its simple physics that can’t be intelligently disputed.
Shore ratings & tire inserts are a lot like tire compounds and air pressure on real race car tires. In real car racing, teams adjust tire air pressure and rubber compounds to give the driver the best possible combinations.
A great “Crew Chief” considers the tire’s wear or loss of traction due to driver’s actual style of driving, ambient temperature, track surface, surface temperature of the track, track layout and race length or interval between tire changes. It’s a balancing act to make an educated guess to find that “sweet spot” in tire performance.
Some times a pit crew will vary air pressure by as little as half a pound in order to see the gains needed to have a shot at the win.
In our world of R/C racing, we can choose to emulate what the real race car teams do with shore ratings, but it really is a “thinking man’s” game.
Let’s say you go to a race and the track is very technical in design and only has a small back straight. The surface is pretty nice and it’s 75 degrees at 9am in the morning. The weather man says that the high for the day will be about 83 degrees. OK
First off, we all know that traction drops as the track surface heats up right? So off the bat, you know that a rubber shore tire that works great at 75 degrees will be a sloppy mess at 85 degrees, hence its ridicules to think the “one shore fits all’ theory hold any merit at all.
If that wasn’t enough, there are all the other variables stated earlier in this post that should be considered in tire shore selection.
Some racers “wing-it” with what they have or “chase their set-up” to find traction with the wrong shore, this practice usually results in hi-tire wear and/or never realizing the full potential of their chassis.
Other racers see what the “fast guys” are running and do the same. This can get you close, but a gifted driver can find a way to be fast with the wrong shore tire anyway.
Last weekend at “The Fort”, I ran my first qualifier with 40 shore tires. I figured that it was early in the day and the groove on the track wasn’t “up” yet. At the start of that race it only took about 1 lap for the rubber to heat up. (Remember “The Fort” is in Florida)
As the 5 minute race went on tire traction increased right up around the end of the of the qualifier, at that point I could feel traction starting to get a little loose. Right then and there, I knew I had chosen a little too soft a shore.
On my second qualifier I went with the 50 shore tires. It took them a little longer to “come in”, but they increased in traction all the way until the end of the race and never got loose.
On the third qualifier, I dropped shore to the 45s just to see if my times would improve with a better balance between the two previous runs. It was not the right move because the track’s surface temps had gone up and made my car feel like it was driving on ice.
So when Sunday rolled around, I knew the best tires to use for the track with my car and driving style was the 50 shore Ipanema, but what about the Main?
I decided to “scuff-in” a set of 55 shore tires in practice and use them in the final qualifier before the 30 minute Main. The 55 shore tires turned out to be the correct tire because they gave great traction, didn’t over-heat and allowed me to run well for the duration of the race.
If the race length would have been 60 minutes or if the track temps were higher, I would have relied on 60 shore tires instead.
If the race was in a colder environment, I would have started track testing with lower shore ratings.
Hope that all helped no more secrets for you guys today.