Back from Track day, and review on Alfaworkshop rear arm... - Alfa Romeo 4C Forums
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post #1 of 37 (permalink) Old 04-03-2017, 06:37 AM Thread Starter
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Back from Track day, and review on Alfaworkshop rear arm...

Guys, I just came back from Mainland China and spent 2 great track days there.

This time, I hired a professional driver to give me some lesson and let him drove my car by himself so i can record his driving and hopefully learn from there (he did 1:54.8). I also had Kansai sway bar , KW v2 and Jamie's bar installed. I know I shouldn't do it all in once, but here in Hong Kong, we don't get to go to track often.

The sway bars was set at the softest setting, the KW at 9 click open at KW stock height, and tire pressure was 23.5 psi cold. I found out the ideal tire (A050R) pressure is a lot lower on the 4c compare with other cars, probably it is due to the light weight. I didn't change the setting during the event beside the tire pressure as the jack simply wont slot under the car...

As I previously posted here, I had a big snap over steer at T3 last time i was there, and this time I was still afraid of turning the car into high speed corner (you can tell by the video)

But luckily I was able to shave 2.6 sec from my previous best record thanks to the driving instruction and Jaime's rear arm.

The car would over steer very easily last time i was on track, especially at mid to corner exit. This time, I could put on the power earlier and I don't remember over steer once at corner exit. The KW was too floaty (not sure about the right word) at the suggested setting and since the sway bar was at its softest setting (109% harder than stock) I am not sure if I can tell the difference.

I also tried trail breaking, and it worked really well for me, the car would steer as I release the brake. The front brake pad DS 2500 chipped and was almost gone by the end of the event, but there is still a lot left at the rear. My friend pointed a laser gun at the front brake disc 2 mins after I went back to the pit, and the reading was 485c, so I think I can use a more high temperature break pad in the future.

One weird thing is that my car would steer to the right hard when I lift off gas from full throttle during the time I was on the track. Now it would steer to the left when I put on full throttle as the turbo kick in on my way back home. Does that mean I have a bent wheel?

Anyway, I had great fun and was really happy about the result.

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post #2 of 37 (permalink) Old 04-03-2017, 06:53 AM
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I know the feeling of changing too much stuff at once but as long as you don't have your own garage and your own race track, what do you do?

The throttle induced steering issue should be in the same direction if it had been caused by a wheel being off so I think you should look for the reason elsewhere. It might also be that you weren't as straightly lined up as you thought when it happened.
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post #3 of 37 (permalink) Old 04-03-2017, 08:31 AM Thread Starter
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Yes, I am going to have the car well inspected starting from changing back to stock wheels and see if the problem still occur.

BTW, here again there is a speed reading differences. The small speed reading on the left is GPS data. the large one from overlay is from OBD reader, and they both don't match with the dash... Hopefully as Mutil ECU Scan release their support on 4C I will be able to do something about it.
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post #4 of 37 (permalink) Old 04-03-2017, 10:04 AM
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Good job on getting an instructor. It's invaluable. I'd love to drive at a track in China. Have some projects starting there . . . maybe?

The pull sounds like there is something loose in the suspension. The times I've experienced something like that it was a stretched/loose camber bolt. Could also be a ball joint or bushing. A good inspection should find it. A bent wheel will cause a vibration, not a pull.
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post #5 of 37 (permalink) Old 04-04-2017, 05:32 AM
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As I have said on a number of occasions on the forum for track use with sticky tyres the rear arm modification is a must, it is more significant than the front geometry change as a circuit is nearly always flat.

Jamie Porter
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post #6 of 37 (permalink) Old 04-07-2017, 03:23 PM
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I can just confirm what Jamie says... I had a very nice feeling of the car with the Arr but with the Trofeo just too much oversteer and unpredictable one... Installed the rear arms and it was so much better... Toyo 888r are quite less grippy than the Trofeo but get into temperature much faster and are more progressive... Next step ohlins...

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post #7 of 37 (permalink) Old 04-07-2017, 04:41 PM
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Quote:
Originally Posted by Alipapa View Post
Yes, I am going to have the car well inspected starting from changing back to stock wheels and see if the problem still occur.

BTW, here again there is a speed reading differences. The small speed reading on the left is GPS data. the large one from overlay is from OBD reader, and they both don't match with the dash... Hopefully as Mutil ECU Scan release their support on 4C I will be able to do something about it.

Great that you bested your previous times and your video is very informative.
What camera do you use to capture action and is it mounted along the back
Window compartment?

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post #8 of 37 (permalink) Old 04-07-2017, 05:24 PM
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If you were being timid about that corner, I sure couldn't tell!

Interesting that the OBDII reader is different from the dashboard (193 vs I think 204). I assume sampling delay since you were accelerating at WOT at that moment. The speedo should be faster sampling than whatever OBDII reader you were using, although you can usually adjust that somewhat with the reader's settings. The difference between GPS and speedo could be sampling error as well, but it is consistent with the 3% to 5% "optimistic" reading that others have found on the speedometer reading.

As for the throttle steering on the straight, is it possible that something on the rear alignment was thrown out with your mods? Did you do an alignment afterward?

Thanks for taking us along for the lap!

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post #9 of 37 (permalink) Old 04-08-2017, 08:39 AM Thread Starter
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Quote:
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If you were being timid about that corner, I sure couldn't tell!
I used to get into T3 at over 160km and T5 at 150+, now I am cold feeted Maybe I will get better next time I visit the track.

The camera I used is the Sony x3000, shooting at 1080p 60fps in MP4 format. I chose MP4 as RaceChrono seems to have problem dealing with the audio file of Sony's own format. and yes, I placed it at the back window using a mid size suction mount with a sturdy adjustable arm.

I am going to change back to stock wheels, brake pads and fluid changed next week and have my mechanic to check on all suspension related bolt. If the pulling still occur on both full throttle acceleration and gas lift off then I will have the alignment guy to double check everything. I had the car corner balanced and alignment done right before trackday and all data are perfectly, like exact match from left to right. Hopefully it is just a lose camber bolt and not like a bent chassis or something serious...
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post #10 of 37 (permalink) Old 04-09-2017, 12:29 PM
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Nice to hear about the rear control arms. Is an interest of mine.

The front pads are overheating, which is why they are chunking and pitting. The stock rear pads are crap and don't share enough of the workload. Change all pads to the same material as a starting point. I'm not certain about what you should use, there's quite a few good choices out there.

If you have a bent wheel, you will feel a lumpity-lump-lump as you drive that will change with the speed of the vehicle.

The throttle steer, deceleration steer could be an alignment issue, or as suggested, something loose.

I'd love to see a track video if you have one.

What was your lap times compared to your previous lap times and compared to the instructor's lap times?

Rac
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