Formula Atlantic slicks - experience/opinions?

[MadMaxAtom]

The taller tire is OK for high speed tracks where you can utilize 4th gear longer without having to shift to 5th..but it does make the back end of the car a little more rubbery feeling and also affects brake bias.The 13.75 wides also like a 14"+ wide wheel. I actually have a set mounted for certain tracks that they are a slight advantage over the shorter 23.5" tires...the extra 3/4" of width rubber isn't really noticeable.

[cvjoint]

Does anyone know why Hoosier changed the compound on FA tires to 35a?

[MadMaxAtom]

The FA tires are built for the Formula Atlantic racing series and sometimes they change the compound and sizes.If you are going to run in warmer temps the 35a compound will be fine and actually better than the r25b compound which will overheat on hot (>95 degree) days. We don't have many (as in none..) of those days in the northeast.

[cvjoint]

I was hoping the r25b compound would be available. In ideal conditions it should be quicker!

[cvjoint]

I run them. Have been for years. I have set a couple of track records on them and I think it is THE tire to run on the Atom, IF you want the MAX traction.(hehe..)
Yes,superior to the Hoosier A6 and the new A7s.(yes,I have run them) The Hoosier FA r25b has proven to be the best tire I have found,bar none.(and I have tried many..)
The Hoosier R25b compound is very sticky and likes track temps in the 70-100 degree range,but are useable down to 45 degrees.Less than that you are wasting your time.
I run 9.5x23x15 frt and 12 or 13.50 x23.5x15 rears.
You need to run proper width wheels. I run 10" wide fronts and 13.5" wide rears (I like the Keizer 3 piece wheels and have never bent one,and yes,they are expensive..but they are the best for the money)

Your car needs to be set up to take full advantage of them..you will not get full grip without a proper setup.
They like heavy spring rates..350lb fronts and 550lb rears,and shock valving to match.(not just cranked up settings)
If you run the suspension too soft,the tire patch will not stay in contact with the track due to the Atoms suspension geometry.It just doesn't work. Simple as that.
The negative camber needs to be proper for your ride height or you will cord an edge quickly.This is done mostly by trial and error,but a good starting point is -2.5 for the front and -3 for the rears.
Watch tire wear rather than just tire temps.Yes,I know..temperatures are important but it is not the only factor in determining proper suspension settings.
This I have learned: improperly recorded tire temps (doing them by yourself, or not doing them HOT) will mislead you….but the tire wear pattern NEVER lies..! Some may not agree, but that's fine. My way works for me.
I run my Atom ride height with the control arms set parallel to the ground.This is more important than getting it as low as possible as it puts the suspension in the "sweet" spot of its travel. Trial and error has proven this out for me.
I like about 1/6" toe IN up front and zero toe, in the back. Tires wear well and car is not nervous at speeds over 100mph.

I usually get my FA r25bs as scrub take-offs from a guy in NY who handles race tires. Best part..a set cost me under $300,shipped. Yes, $300 for 4 uber-sticky tires. You can't even buy one new A7 for that money. Occasionally, Hoosier puts NEW ones on sale for $450/set..with free shipping. The R25b's will last a long time on a car set up properly. My first few rears I went through quickly learning how to set the car suspension and correct air pressures.(cold,18 front/25 rear) Once I had the magic formula (pun intended) the tires wear incredibly well. I can get 15-20 events out of a set of rears, and the fronts will heat cycle out before you wear them out.

Important for MAX tire grip and life with R25bs: Don't leave your spare race tires out in the sun! (Cover them or put them in the trailer) Don't subject them to temperatures below 45 degrees. Flip your tires when they start to show any shoulder (edge) wear. ( I usually flip the rears every 4 events,fronts every 6)

Seat time!! You will need to learn to drive the FA R25Bs. They are a soft side walled tire, and the car does move around on them a bit,but they are not sliding. You will need to learn to trust this feeling. They do not like to be shocked. (hard inputs from steering,brakes or throttle) They do not like to be really slid around on purpose, (forced rotations etc) but are quite controllable if sliding, once you really understand what is happening and what they are doing. Slow imputs are rewarded.

Make sure you brake bias is properly set as well. The setup I use is heavily biased to REAR brakes. If you are locking your front tires,you have too much front bias. Period. Take advantage of all that fat sticky rubber back there and adjust your bias to juuust about lock up the rear tires on heavy braking and you will be amazed how nicely the Atom will trail brake or threshold brake. It really is very different than most cars needs. My bias is about 30frt/70 rear. It works.

You will need to anticipate rather than react to what is happening.The tire needs to be fully loaded with finesse, or it will not hold,and it will wear fast!

There is a learning curve..and you either learn it or you will get no benefit from the tire. It's as simple as that.

They will NOT make you Superman (or Wonderwoman..) overnight. Once you feel the grip they offer, you will never want less..

Seat time is your best friend!!

All this information is true,and tested in the real world,by me personally,for many years and laps.

I have official recorded track times (and trophies) to prove it..

I'll bet you're sorry you asked…

Getting exactly this setup alligned now! The tips are gold.

[cvjoint]

FYI for anyone wanting to run FA R25B tires on stock SRA:

The 245/355 combo is just as fast as the 200/245 combo both on R25B. The additional cornering grip is canceled out by extra rolling resistance and drag. MadMaxAtom's recommendations were spot on, I get just slightly hotter inner shoulders. However, the only change I recommend for stock SRA is to use lower starting pressures, I do 16 PSI all around. MadMaxAtom's car has more power and aero so higher PSI likely keeps his tires from overheating, whereas I still try hard to reach optimal temps. I built 50* in the tires on Saturday, from 60* ambient to 110* optimal for R25B. Lap times were identical to 200/245 combo which you can run on stock wheels.

Time to add boost and aero!

[Phoenix Atom]

MMA: In your first post, you mention setting track records at several tracks and I'm curious what tracks and what times. With luck, the tracks will be places I've run and I can then have a benchmark for my times. Thanks for any info.

[cvjoint]

Update on R25B in 245/355 sizes. I finally adjusted my driving to account for the extra grip and it's going well. I'm at least 3 seconds quicker at Laguna Seca and Thunderhill now vs. 200/245 combo, doing 1:39.xx (LS) and 1.59.xx (Thunderhill over the top).

The wear is minimal, looks like the tires will heatcycle before they wear out.

Tire temps are equal front to back. I can get them to 110* in 45* ambient and to 160* in 103* ambient. Optimal tire temp for max grip is 130* to 150*.

I got a puncture at Sonoma, the tire rolled off the rim, and I spun out in the carousel. The tire carcas is extremely thin. That's about the only downside I can find to them. Shame Hoosier doesn't make them anymore as I now prefer them to other tires.

Max G at Laguna Seca is 1.6G. I can hit that in four consecutive turns.

Max G at Thunderhill is 1.7G. I can only hit that in one of the turns.

Odly I can't ever do more than 1.3G in braking. I guess there simply isn't enough weight on the front.

Car understeers at the limit, I'd say moderate understeer. It benefits greatly from trail braking.

[cvjoint]

Long term use update:

The fronts lasted 52 sessions before showing cords. The cords were on the inside on one wheel, which suggests I might have locked them under breaking. With ideal rotations and no wheel lock I think 55 20 minute sessions are to be expected. The performance degraded very slowly with heatcycles, I still did a 1:49 flat at Sonoma raceway at 50 heatcycles, and regularly pulling 1.5G without aero, pretty impressive grip.

The first set of rears had a flat due to road debris. Do not drive these on the road. The debris ripped out a huge chunk, carcass and everything from the middle of the tire. The new set is at 30 heatcycles and still have a lot of meat left on them.