10-22-2014, 02:10 AM | #1 |
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GSR Autosport Global Time Attack M4
Featured on BIMMERPOST.com We thought we would spring this one on everyone prior to SEMA since a lot of people saw us testing at the Global Time Attack event last weekend. The GSR Autosport Global Time Attack project car is being developed to run in the 2015 GTA Pro Am Series in Street Class. The overall concept is sort of a Jekyll & Hyde thing where certain parts will be able to be swapped back and forth - between track duty and street duty - parts such as the front splitter, rear decklid/wing, roll bar, seats, wheels/tires, etc. We started this project with some baseline testing at Buttonwillow Racepark with basically a stock car – Toyo R888s, Pagid Yellow pads and GS610 brake fluid. As many you have discovered the stock setup has a lot of understeer so lap times were less than stellar – 2:00.5. Our test just this last weekend, at Willow Springs, was supposed to be with KW Clubsport 2-way coilovers but they didn’t get to the shop in time so we had to settle for the H&R 435 lowering springs a lot of people are using on stock dampers. This setup wasn’t actually that great on the track. The dampers would load up and settle on the bump stomps so the suspension got really harsh with a sustained lateral load like in Turn 8 at Willow Springs – the car would basically bounce through the bumps which was a little unnerving at 130mph. We did switch tire/wheel to a 285/35-18 (Hankook RS-3) square setup on Apex 18x10 wheels and added a rear wing but we weren’t really testing aero because we were unable to finish the front splitter prior to the weekend – so we ran the rear wing virtually flat. Although much improved over stock the car still had considerable understeer, especially in long sustained turns like Turn 2 and Turn 9. We were hoping to break 1:30 but with the understeer, particularly in Turn 2 our best effort resulted in a 1:31.4. We’re now getting most of the intended upgrades on the car prior to SEMA. Come check out the car if you happen to be at SEMA – it will be in the Achilles Tires booth. We have a full photo shoot scheduled so we’ll update this post just after SEMA (Nov 4-7). The next test day for the car will be the Global Time Attack Super Lap Battle at Buttonwillow Racepark (Nov. 14) |
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10-22-2014, 04:38 AM | #2 |
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Good comments on the second video... A little disappointing that the ABS system in the M4 isn't very efficient and it's best to avoid it.
Would be interesting to do a 60-0 test with full ABS activation and then with manual brake modulation to see the difference in stopping distances.
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10-22-2014, 10:14 AM | #3 |
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10-22-2014, 10:42 AM | #4 | |
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Good to have some testing done, thank you for the notes. What are the tire sizes you were using?
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10-22-2014, 10:45 AM | #5 |
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Beast. Those are good lap times.
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10-22-2014, 10:56 AM | #6 | |
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And the second test day at Willow Springs we were running Hankook RS-3 - Square 285/35-18. We have a max tire size in the GTA Street Class of 285. |
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10-22-2014, 11:04 AM | #7 |
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The reason I asked about the tire sizes is because the rear to front RPMs may be contributing to potential ABS softness. The electronics may not take into account a large difference between front and rear RPMs.
Thank you for your response. |
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10-22-2014, 11:26 AM | #8 |
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It's a good question. We have a big issue with that on the newer 911s we run/support at the track. If the ECU sees too big a difference it goes into ice mode which is no bueno on the track.
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10-22-2014, 12:20 PM | #10 |
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So the springs are not the way to go for the track days?
Why there is so big difference 30 seconds between 2 runs?
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10-22-2014, 01:25 PM | #12 |
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this should read "because lowering springs with stock dampers are terrible for performance"
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10-22-2014, 02:57 PM | #14 |
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@Jackkk - Are you comparing times between the 2 videos? They are at different tracks, the first is Buttonwillow Raceway and the 2nd is the Big Track at Willow Springs Raceway.
@KennyPowers - True, but in some ways they were an improvement from stock. Lots of people are running these springs so we wanted to give an impression of how they compared on the track to the stock suspension, and the KW Clubsports that we are ultimately putting on. @jballs16 - Nope, it is the standard Yas Marina Blue. It is a difficult color to replicate in photographs, which often come out much darker than it appears in person. I think that's because of the high amount of pearl/metallic in the paint. |
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10-22-2014, 03:29 PM | #15 |
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Having more seat time now in the M4 I think the answer is somewhat yes and no. If you really want to put down some good times you really need to move to a performance oriented damper.
We tried the lowering springs mainly because we were looking to get more front negative camber (we were able to get -1.8), which is not ideal but something... again trying to deal with the understeer issues. With a lower CG the weight transfer of the car was a bit better but because of the reduced operating range of the damper and the fact that the H&R 435 springs we were using were not heavy enough to support the compression weight under load, high speed cornering composure was less than ideal. Willow Springs was not a good track for the lowering springs because it is a fast, flowing track with bumps in critical braking areas (Turn 1) and corners (Turn 8). There aren't too many technical sections where you need to aggressively transition the car. I would expect the stock spring setup might be better at this track. Now Buttonwillow is a much more technical track so transitioning the weight of the car is much more critical. It's also very smooth as it was just recently paved. I think the lowering springs could actually help at this type of track. If you are just doing a track days for fun, every once in awhile I think the lowering springs are fine just note there limitations and be cognizant of the potential behavior changes in the car when you load up the suspension. -Nick |
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10-22-2014, 03:49 PM | #16 | |
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Stock brake bias is towards the front I'd bet, might hold off ABS longer with a higher friction compound in the rear...Pagid black if or when they make it for our cars.
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10-22-2014, 04:53 PM | #18 |
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When we ran Spec Boxsters a lot back in the day we spent a lot of time playing with the front/rear compounds trying to get the bias right. For me I settled on Pagid orange front and black rear. I don't really have a feel for the M4 yet. We are slowly getting all our data hooked up on the car so hopefully we'll be able to look at some objective data on what the car is doing rather than the 100% seat of the pants method. ;-)
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10-22-2014, 05:13 PM | #19 | |
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Most street cars can use more rear pad as manufacturers don't want us spinning off tail first under any circumstance, common logic is to just incorrectly put more and more friction in front.
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10-22-2014, 08:02 PM | #20 |
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I saw the car the other day, looked and sounded awesome out there.
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10-22-2014, 08:14 PM | #21 | |
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There are a lot of terrible drivers out on the road who can afford performance cars who love to jerk the wheel into a corner while still standing hard on the brakes, or unintentional trail-braking through incompetence which could lead to disasterous results on the street if cars were delievered with more neutral brake bias. Big front brake bias, and understeer-biased setups are right for 98% of the driving population IMHO. If someone has the driver training, experience and skills to intentionally alter the brake bias (and suspension characteristics) to suit their driving style, then excellent! ... But I'm happy with manufacturers setting up cars to cater for the lowest common denominator, so some idiot next to me doesn't spin the car across 4 lanes and take out a bunch of cars while doing so.
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