Ariel Atom Autocross Development

[RyanD]

Thanks for sharing those settings. Most of us used to use slight toe out on the front and toe in on the rear. Does anyone know the reason for the change to toe in on the front? Increased stability?

It's also interesting that they decrease the camber on the rear and increase the camber on the front with the stiffer springs on the SRA. If I remember correctly, mine is 2 or 2.5 in the front and 1.5 in the rear with the Brammo "race" springs.

Have you considered adjusting corner weights with yourself (or an equivalent weight) in the driver seat? I found that my right front tire always locked up first due to the uneven weight.

[762]

My guess on the front toe-in on the stock setup would be to add stability for novice drivers. This is consistent with the very soft and conservative settings all over the car.

RyanD I did corner balance the car with my driver weight, that was just the stock setup on the scales as a baseline.

Atom Specs from 02/21/15 (note measurement unit changes):
Toe F: 0 degrees in total R: .26 degrees in total
Ride/Height: F: 115mm R: 110
Camber: F: -2 R: -2

Initial impressions of car with no tender springs on the JRIs is that every aspect of the car's performance is improved. Car still drives all over the bump stops, but the bump stops were tested to be an additional 100 lbs of spring. Shocks are still terrible in slaloms and transitional elements. No low speed compression based on shock dyno and driving impression.

Video from 1st event on no tender springs:<span style="color: rgb(51, 51, 51); font-family: arial; background-color: rgb(250, 250, 250);">

Tires still to come in March and April. I will be replacing the R888s with Bridgestone RE71r's (205/50/15 & 245/40/17) or Toyo R1Rs (195/50/15 & 235/45/17 or 235/40/17) and then getting a spare set of wheels for Hoosiers A7s

[762]

Swapped out the terrible R888s for amazing new Bridgestone RE71Rs for my street tires. Car is significantly faster by about 1.8s to previous benchmarks. Lack of low speed compression in the shocks and soft spring rates keep the car very slow in transitions/slaloms.

Much much closer to many of the national champion level DP, DM, and XP cars located here in Arizona, and this is with the car still on street tires.

Did some initial tire testing and landed at 13psi in the front and 21psi in the rear as the fastest on the stop watch.

Base Shock Settings (measured as clicks to soft from full stiff): Front= 7; Right Rear= 40; Left Rear= 32

Rear shock differences were identified based on shock dynos

Here are a few videos:

[Atommatt]

Holy sh*t ,that's pretty good driving

[RyanD]

Well done! I miss autocross, but too many people attend the ones here. Not worth a full day for 3 minutes driving.

If you haven't already, zip tie your dip stick. I blew mine out at an autocross by running near the rev limiter for a long time.

[timcking]

Update. Just replaced the Hankooks with A7 Hoosiers - 225 fronts/245 rears. I did this because the Hoosiers are 1/2 in. wider tread width front and rear. After one event with the same suspension settings and tire pressures, I can't say I noticed any significant improvement in ultimate grip. But, the transitional stability under braking (such as entering a slalom) is significantly better. I've been told the tire grip will improve with one or two more events.

The added stability is striking. Whereas before I had to concentrate on being very smooth under braking, the Hoosiers almost make the Atom feel like a normal car. When I get a chance, I'll measure the tire temps.

Tim

[MadMaxAtom]

^ Hoosier recommends more camber on the A7/R7s to take full advantage of the new tire. I just swapped over to them on my other track car (not an Atom) and had to add 2 degrees of camber to my old settings to get max grip from them, with nice even temps. Hoosier recommends a minimum of 3 negative and I am actually just over 4. Sticker tires give the best grip..don't let anyone tell you otherwise. Just scrub off the shiny mold release layer and you are good to rip.

[Richard Buckingham]

^ Hoosier recommends more camber on the A7/R7s to take full advantage of the new tire. I just swapped over to them on my other track car (not an Atom) and had to add 2 degrees of camber to my old settings to get max grip from them, with nice even temps. Hoosier recommends a minimum of 3 positive and I am actually just over 4. Sticker tires give the best grip..don't let anyone tell you otherwise. Just scrub off the shiny mold release layer and you are good to rip.

Interesting, I didn't know Hoosier said anything but from what I've seen so far on my last two sets of R7s they got corded at the outer edges in no time at all, I did not have that problem with the R6 all other things being equal. I've since added more camber to the rear but I also just moved to a 11" wheel and 275/35/15 so that may well have much to do with that as the tire sits far better on the wide wheel.

However... I get uneven temperature across the tires now (with higher temps on the inside) so I'm wondering what the best thing to do is? It seems if I run less camber I risk cording the outer edge but I was getting good traction and even temps, now with more camber whilst I seem to get better tire wear so far I see uneven temps and I question if the traction is actually better. I have not been able to test relative performance though so it may just be my mind playing tricks on me and real data might prove me wrong.

Any killer tips on the balance of pressure, camber, temps and wear? I'm willing to keep more camber on and potentially have a little less traction if it means even tire wear because I ate through the last set of tires unreasonably quickly but I've always been told that even temps is what you should look for too.

MMax - you run similar wide tires too I believe and you say to run more camber all around, how much are we talking about on your set-up and do you see even temps across the tire?

[Richard Buckingham]

well I did some googling and this says it all:

"Chassis Setup Recommendations
For optimum performance the Hoosier P-Metric radial tires require about 3 degrees of negative camber. There will be a trade off in maximum performance to maximize wear. Generally, 1/2 degrees less than optimum will result in the best compromise for wear and speed. Less than 2.5 degrees negative can result in excessive wear on the outer shoulder junction. Higher pressures are needed when the vehicle has limited negative camber. The Hoosier tires typically offer better performance with spring/shock rates higher than previous brands you may have run."

Link: https://www.hoosiertire.com/pdfs/TCTR7_A7.pdf

[MadMaxAtom]

I run the Hoosier FA tires on the Atom with about 2.2 negative in front and 3 negative in the rear with excellent traction and wear. If your outer shoulders are getting beat up,and you are already in the mid 30s for tire pressures,you need to add more negative camber.If you run lower pressures,you will have good grip,but tire wear will be intense. A happy medium is what I strive for.. Tire temps are very difficult to do,especially all by yourself and you must do it immediately from coming off speed. Almost impossible. I have found reading the tires visually for wear scuffing to be the best and most accurate way to judge how things are going on at that all important contact surface. Unlike high speed road racing, tire temps alone won't tell the whole story. I am also running the 275/35/15" R7s and A7s (on the non Atom car) and have found 3-4 negative to be ideal.