Thoughts & Pics From First 4 Autocross Events - Page 3 - Alfa Romeo 4C Forums
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post #21 of 28 (permalink) Old 04-23-2019, 11:37 PM
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What seems to be lacking is any info on what your hot pressures were. For the track I’ve been told by the resident tyre expert at Eastern Creek that you should be looking at around 30-32 psi hot for Hankooks then fiddle around with pressures to get tyre temps across the tread roughly even. That means starting out a little lower than 26/29 psi. More like 24/25 psi F/R for starters. What info does Bridgestone provide for pressures and working temps for your tyres? Get yourself a pyrometer to take out the guesswork regarding which way you should be going with pressures. It helps for me.
If there are markedly more corners in one direct than another you’re going to have to start off with different pressures on the left to those of the right side too.
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Last edited by Alfanut; 04-23-2019 at 11:43 PM.
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post #22 of 28 (permalink) Old 04-24-2019, 09:17 AM Thread Starter
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Originally Posted by DrPyro2k View Post
That is a very good point, Since I have never done autocross, I don't know how big of an issues running in "automatic" shift mode. I run on road tracks, and I have gotten to the point of using manual mode. The reason, as @4Canada has pointed out is that you can control the rpm that the engine is in midcorner (and the boost). The 4C does "okay" in automatic mode, but where it lacks is that in longer corners it will tend to upshift. With the RE71s, you should be struggling for traction on the rears (and power oversteer). I could see where you have understeer on exit only if you got on power too hard midcorner and just push the car out on exit.

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I use race mode typically, so manual. I am going to downshift more into corners to keep the rpm range more in boost for throttle exit. Generally, i have stayed in 2nd, but exit rpm is usually directly below boost range.

Rear traction has been pretty fantastic. Even LC at course start, very little wheel spin.

Getting on power too hard on exit is definitely part of the issue.
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post #23 of 28 (permalink) Old 04-24-2019, 09:28 AM Thread Starter
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Originally Posted by RKBerta View Post
For front tire pressure.....higher pressure increases oversteer so you want to add a couple of pounds in front
OR
For rear tire pressure.....lower pressure increases oversteer so you would want to reduce a couple of pounds in rear

That tells me that you would be better off with tire pressure closer to the same front and rear...maybe a pound difference rather than 3# as stock.

Also.....I am not certain what effect having a wider track will change the balance but try removing spacers.

I attached a chart to determine how various changes effect over/under steer. Excuse the poor quality of the chart....one of these days I will have to redo it ;-)

I run without spacers and at or close to factory 26/29 pressure on +1 Michelin Super Sports for auto cross although with pressures closer to each other as described above. Using trail braking my front end sticks very well and don't have any real issues with understeer. Note that the hard launches out of corner on a mid or rear engine car can tend to lift the front end unloading the tires so the trick is to squeeze on the gas....don't use it as an on/off switch. Same for braking.....if you go too hot into the corner and slam on the brakes the car will start under steering and will be harder to recover, especially if you than hit the gas hard. In short....4Cs like smooth braking and transition to power application especially with its mid engine weight distribution where most of its mass is right behind the driver rather than spread out more towards the front/rear of most cars.

I am going to try consistent cold pressure across the board next event, 29/29, and go from there. I think that combined with altering my driving style will help significantly. The dynamics of this car are just so substantially different than previously autox'd cars that changing the muscle memory is difficult.
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post #24 of 28 (permalink) Old 04-24-2019, 09:32 AM Thread Starter
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Originally Posted by Alfanut View Post
What seems to be lacking is any info on what your hot pressures were. For the track Iíve been told by the resident tyre expert at Eastern Creek that you should be looking at around 30-32 psi hot for Hankooks then fiddle around with pressures to get tyre temps across the tread roughly even. That means starting out a little lower than 26/29 psi. More like 24/25 psi F/R for starters. What info does Bridgestone provide for pressures and working temps for your tyres? Get yourself a pyrometer to take out the guesswork regarding which way you should be going with pressures. It helps for me.
If there are markedly more corners in one direct than another youíre going to have to start off with different pressures on the left to those of the right side too.
That's the thing, heat hasn't been building much. I haven't seen anything more than .5psi increase after a 45sec course. This is something I have and will continue to monitor.
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post #25 of 28 (permalink) Old 04-24-2019, 11:51 AM
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The biggest difference between a Mustang and the 4C is front grip. You have to trail brake far deeper with the 4C to maintain the same levels of front grip.

Good job on the top ten finishes! Good to see people competing with a relatively stock car.
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post #26 of 28 (permalink) Old 04-24-2019, 06:59 PM
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With your previous experience with the Mustang, I think you will quickly find out the trick to getting good times. Sounds like you are already doing very well. Of course the course layout will make a big difference. Being a light and nimble car with great braking (its strong suit) it does very well at complicated courses with tight turns. On a more open course with longer straights it still does well but in its class SS you have cars like various Porsche models, Vipers, and Corvettes that have tons of power. But getting it to the ground is an issue ;-) If there is a tight wet course they might as well just give you the trophy before you run. That is one area the stock P Zero AR or ARR tires have an advantage....they work pretty well in the wet. There was an autocross last year that was run in rain....a dead stock 4C (not my car as I was running timing gear) beat everyone else by a substantial margin. It ended up with the 2nd or 3 fastest time of day and there were some pretty serious experienced competitors as it was a Championship points event. The guy who did so well was just running for fun. I was impressed!

I do run in R mod to eliminate the nannies. I think after trying D mode, R mode for autocross works better. Since I am not in any real danger of loosing it and needing the nannies to save my bacon in auto crossing, the R mode should be faster but that may need further testing.
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post #27 of 28 (permalink) Old 04-25-2019, 08:49 AM Thread Starter
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Originally Posted by RKBerta View Post
With your previous experience with the Mustang, I think you will quickly find out the trick to getting good times. Sounds like you are already doing very well. Of course the course layout will make a big difference. Being a light and nimble car with great braking (its strong suit) it does very well at complicated courses with tight turns. On a more open course with longer straights it still does well but in its class SS you have cars like various Porsche models, Vipers, and Corvettes that have tons of power. But getting it to the ground is an issue ;-) If there is a tight wet course they might as well just give you the trophy before you run. That is one area the stock P Zero AR or ARR tires have an advantage....they work pretty well in the wet. There was an autocross last year that was run in rain....a dead stock 4C (not my car as I was running timing gear) beat everyone else by a substantial margin. It ended up with the 2nd or 3 fastest time of day and there were some pretty serious experienced competitors as it was a Championship points event. The guy who did so well was just running for fun. I was impressed!

I do run in R mod to eliminate the nannies. I think after trying D mode, R mode for autocross works better. Since I am not in any real danger of loosing it and needing the nannies to save my bacon in auto crossing, the R mode should be faster but that may need further testing.
I am definitely hoping so lol. So far the courses have been fairly open. Most of the regions around here do more simple power courses towards the beginning of the year to knock the rust off, which makes sense. We should be getting into slightly tighter courses here in the next few weeks.

I agree about R mode. After thinking about it more, I believe more of my understeer issues have been in D, which makes sense. I plan to use R going forward.
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post #28 of 28 (permalink) Old 04-26-2019, 03:15 PM
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Originally Posted by ColtronH View Post
Finally got some seat time in the 4c. 25 total runs over 4 very different courses in very different conditions. Overall, I am happy with it so far with 2 top 10s in raw and winning my class twice. It is considerably different than what I'm used to.

215/245 RE71r
-1.7* front camber
-2.1* rear camber
0 front toe
0.20" rear toe in
Factory everything
this is not original alignment - how did you reach it?
do you have rear swaybar on your car?
mine didn't and like you i was experiencing understeer in most situations.

anyway - IMO more front camber is must.
also too much rear toe in for my taste. 20" is 4mm, right? even with 1.5 mm total my car didn't feel too oversteary.
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