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Discussion Starter #1
Hi everyone,

This is my second post on this forum, but I wanted to summarize my first track experience with the gla. I went to Palmer Motorsports Park run by the scda and had a blast! Overall the car did well, but I wanted to share my thoughts and a few issues I also had. As background, this is my 4th track day (three prior with a 2013 Ford Taurus SHO performance pack) and I consider myself a fairly capable driver for my limited experience.

Car:
2018 GLA45 AMG stock with AMG ride control
Tires: Atturo AZ850 235/40r20

Track conditions:
Clockwise configuration, 90 degrees (very hot), and dry

Observations:
-The engine was very strong all day. I was in a group with a newer WRX Sti and Chevrolet SS and had no issues pulling just as hard or harder on straights when I didn't have traction issues (more on that later).

-I really liked the balance of the car and suspension. The Atturo tires do not have quite the level of grip of the stock Continentals but howl and slide nicely at the limit. If you eased off the throttle mid-corner you could nicely rotate the rear around and while on-throttle pulling out of the corners there was mild to moderate understeer.

-The transmission was flawless. I put the car in race mode with the transmission in manual and didn't have one hiccup all day. The car fired off upshifts and downshifts very well.

-The brakes were also excellent but quircky. We were running in a tight pack and the Mercedes brake assist kept engaging as I was approaching the next car towards a turn. I later found out this is pretty easy to disable in the menu options but didn't have a chance to try it off. The brakes had zero fade but did deposit a decent amount of material onto the rotors which caused a temporary humming noise when I left the track. After using them and scuffing off the deposits this went away. For reference I was running pagid pads (OE friction formulation) with new brembo rotors (stock geometry) and new Mercedes brake fluid.

-Now for the bad. In the last session we were pushing quite hard. Out of the corners I was getting wheel spin while on throttle and could feel the 4matic transferring torque to the rear. After about two hard laps the diff started overheating and the message 4matic currently unavailable kept coming on. After that my traction was significantly reduced since I was pulling out of the corners with front wheel drive only and spinning quite a bit.

For those of you who have gone to the track does the rear differential typically overheat? It's a bit disappointing since this is an AMG and should be able to handle going around a track without overheating. For reference my old Ford had extra coolers as part of the performance pack for the transmission, ptu, and engine oil, had a similar haldex based awd system and had zero overheating issues. I have a theory that the tires I used contributed to the issue. Because they had less grip than the stock Continentals I was getting more wheel spin out if the corners. I believe this was causing the rear diff to transfer power more frequently to the rear axle. Since it's a clutch based system I'm assuming the friction heated up the fluid and contributed to the overheating issues.

So in a nut shell that was my experience. Any thoughts on the rear differential? Feel free to ask any other questions.

Thanks,

-Brett
 

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You make good points on the tires putting more strain on the rear diff.

When was the last time you changed the diff oil? Any possibility it is low?
 

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Discussion Starter #3
Hi Wayne,

Yes between the tire traction and 90 degree weather it makes sense. As far as the fluid I have only had the car a few months and put about 2000 miles on it during that time. The car only has 25k on the clock so I have not changed the fluid yet. The car had maintenance records but it is possible it was not changed per Mercedes recommendation at 10k. I'm planning to do the fluid soon and will report back once I do. The fact that the Mercedes manual directly acknowledges that the diff can overheat and cause the warning I was getting says that the engineers are aware of this potential design issue. I am actually a mechanical engineer myself and can tell based on the aluminum bracketing around the differential that they designed everything as a heat sink for dissipation into the air likely to combat excessive heat. From what I have seen, this differential design combines the clutch pack and rear differential into one casting with shared fluid ( someone correct me if I'm wrong). This will make the issue worse since you have added heat from the gears in the rear differential contributing to the issue. I believe Porsche and VW have separate fluid reservoirs for similar designs.
 

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I can vouch that Porsche does have two chambers. I've never had a problem with my 997.2.

The 45 is a single chamber.
 

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the same message happened to me when i tried launch control on slippery road. sounded like you pushed the car pretty hard so i'm glad this was the only issue :)
 

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Discussion Starter #6
Thanks to everyone who replied so far. I would be curious to hear from other members who have taken their car on the track. Has anyone experienced similar issues on a road course?
 

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Discussion Starter #7
Anyone? Or is there anyone who is on this forum that takes their car to the track often who I can contact?
 

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Great info. Thanks for posting Brett. When are you planning to track the car again? It might be interesting to see how the rear differential reacts to a stickier tire.
 

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Stickier tire was my thought. But I've tracked zero times. It was on my list of activities for this year before the coronavirus problems hit. Probably delayed to next year now.
 

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I haven't tracked a GLA but a number of others and putting the power down is most always promoted by stickier tires. The differential is also more efficient and less stressed when it's thus more easily able to transfer the torque without/with less wheel spin. Automotive TV shows love sensationalized burning rubber (and brake pads) but on the track it's the last thing you want.

btw: As you know, for the track a low profile tire has its advantages, but for auto crossing and its constant relatively low speed cornering you need a bit more sidewall height-flex. Stickier tires still applies to the latter tho'. I run Potenza RE 71R | Tires Engineered for Cornering & Braking on my Audi TTS 19" OEM rims (rather than the optional 20").

Palmer is an excellent facility. I'm overdue for a return myself. Enjoy!
 

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Hey Brett, thanks for the track day write up! I've got a few hours of track time under my belt for sure, but none really in the GLA45 yet as it's pretty new to me. How much track time experience do you have? Just for a reference point. It sounds like you've done more than a few hot laps for sure.

Do you have the "Performance" Recaro seats, or the plain standard ones? That's a big issue for me. I roll around like a pop can in the seat.

I fully intend to have mine on the track for sure, but not until I can get proper wheels and tires on it. The stock 20" Conti's are not that great at all. Pretty disappointing so far on the street taking my usual fun and fast routes. Sometimes downright sketchy. It feels like my E350 Wagon can nearly match it in the corners with stock tires. The RE17R where my favorite tire for a daily driver, but still totally ready for the track. Just limited sizes that match final circumference properly. I've got a 19" setup selected, but the fit in the wheel wells needs to be fully reviewed before I pull the trigger as the offset and width is quite different. Plus, with nothing happening around me, so the push to do it is pretty light.

When I get on track, I will certainly be reporting in like you did. You really gave some great info for sure.

And no offense, but you gotta get rid of those Atturo tires...;)
 

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Thanks for the response RichZilla. This was my 4th track day but I have also done some karting and did formula SAE when I was in college. I hear the RE71's are great tires but they are definitely expensive. Based on a recommendation, I am looking at a 19 inch wheel setup with federal 595rs-pro tires. Much more reasonable price wise and should have very good grip. Federal also makes r compounds but they are only available in 18's. And no offense taken on the Atturos lol they were an experiment. For $120 installed per tire I will say that they make excellent daily drivers though and when I get my track tire setup I will probably bring both sets of tires to the track and keep the Atturos handy if it rains.. They actually handled the abuse pretty well at the track considering. I have already paid up for two more track days this season and might even try to squeeze in a 4th if possible with everything going on. I'll report back when I am able to get to the track again (with better tires). As far as the seats I have the stock seats. The biggest thing I have found that helps is to set up your seating position properly. You should be fairly upright, low, with about a 90 degree bend in your arms. This position also allows you to better push your body into the seat so you can hug the bolsters. There are some decent videos on YouTube that talk about proper seating position for racing.

-Brett
 

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That's pretty awesome you can get that many track days! Still not too much happening in Minnesota, but the racing is opening up a little more. I prefer track days for this car though. Not ready to leave it in the dumpster if things go wrong.

My issue with the seats is that I don't touch either side of the bolsters, so I have to move left or right in the seat before I touch something. Kind of annoying when you're used to a racing seat that wraps several inches up the sides, and holds you tight on both sides. So far the only used AMG performance seats I've found are $4500 plus shipping. Ouch.
 

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...I hear the RE71's are great tires but they are definitely expensive. Based on a recommendation, I am looking at a 19 inch wheel setup with federal 595rs-pro tires. Much more reasonable price wise and should have very good grip...
Have you looked at the Firestone Firehawk Indy 500? They make a 245/45R-19.
 
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