Autocross- SCCA EV-X Class vs. SS

[dsgerbc]

Anybody has a good source for what's model 3's center of gravity height? I get some random internet links for estimates of 18.5", but those are largely coming from some earlier Model S claims.

 

[Lindenwood]

Anybody has a good source for what's model 3's center of gravity height? I get some random internet links for estimates of 18.5", but those are largely coming from some earlier Model S claims.

I previously calculated its CG height as 18.2”, based on its Google-derived Static Stability Factor of 1.71 (incredibly high) and its track width of 62.2.

 

[Rodney!]

So, two events ago i swapped from 265/35-19 RT660 to 275/35-19 RE71RS, on my SS legal 19x9's.

The RT660 had wore a funky groove in the outside half of the tire. The RE71RS developed this same groove, but much more quickly...

Conversely, a friend has the sister to my car, essentially the identical m3p on 19x9, but he has the 255/35-19 RE71rs. His tires did the same thing after two events...

Is the only fix more negative camber?

After the NJ pro solo, I plan on testing both 255 and 275 back to back on the same car on the same day. Grom the outside, it seems that the 255 has better steering feel and the 275 has slightly more mechanical grip, but feels more vague with the additional pinch on the 9" wheel.

Does this emulate what everyone else is seeing?

 

[SK360]

So, two events ago i swapped from 265/35-19 RT660 to 275/35-19 RE71RS, on my SS legal 19x9's.

The RT660 had wore a funky groove in the outside half of the tire. The RE71RS developed this same groove, but much more quickly...
View attachment 940009View attachment 940010

Conversely, a friend has the sister to my car, essentially the identical m3p on 19x9, but he has the 255/35-19 RE71rs. His tires did the same thing after two events...
View attachment 940011View attachment 940012

Is the only fix more negative camber?

After the NJ pro solo, I plan on testing both 255 and 275 back to back on the same car on the same day. Grom the outside, it seems that the 255 has better steering feel and the 275 has slightly more mechanical grip, but feels more vague with the additional pinch on the 9" wheel.

Does this emulate what everyone else is seeing?

Was quite normal on the old RE71R

 

[SK360]

Yesterday was our last Spring event and my first since the new poly compliance arm bushings and alignment.

I have to say getting some toe in in the rear has helped the car feel way more planted and less twitchy. I used to only run -3 stability because I felt like the car was constantly on edge, yesterday I was down to -8 and probably should have gone to -10. I set regen to 40% to try and stop using it as a crutch, I think I'll just go right to 0% next time.. I'm trying to decide if I should bin these 660's and jump to 71RS as it's their second season... or if I should just learn to drive

Here's a video of my best run plus a run where my buddy asked me to take his 80 year old uncle for a ride along.

 

[superflyrolla]

That's where my RE71RS are wearing the most too. Seems normal.

 

[gearchruncher]

I was down to -8 and probably should have gone to -10

There's data out there that - 10 disables the E-LSD from people playing around in the snow. Because of this I run - 9 and I never feel it intervene, even in the wet.

 

[The Other Dan]

There's data out there that - 10 disables the E-LSD from people playing around in the snow. Because of this I run - 9 and I never feel it intervene, even in the wet.

Interesting. I usually run -10 and don't get much oversteer. This last autox I put it in - 8 and got way more OS than than experienced before. I figured it was from running PS4S in mid 90* temps. Now I guess I know the real reason.
If I have to run Packwood in 2 weeks still on my PS4S, I'll play with the settings and try to confirm.
Fingers crossed the new wheels and tires will be here in time and I can get them installed without much issue. 295/35/18 RE-71RS on 18x11 +40 Hypergrams. And some spacers thrown in the mix.

 

[gearchruncher]

FYI, here's the thread with the person that found the E-LSD change between -9 and -10:

Optimizing track mode for snow driving

Hello everyone, I've just returned from Winter Driving School, now that my MYP has track mode. I thought I would share the settings I came up to optimize track mode for high performance driving on snow (high performance here refers fine control, not outright speed). Here's a video - see below...

teslamotorsclub.com

 

[gearchruncher]

I sometimes get a fair amount of oversteer with my PS4S's too- What always calms this down for me is running 1PSI less in the rear than front.

 

[Clover]

Hmm... I don't love seeing that tire above. I had that but worse on a prior generation Bridgestone after about 3K miles and a handful of autoXs and swore them off at the time. I had chunks rip off. Now everyone seems to rave about them and I was thinking of going that way for my next set, but probably not now. I remember checking with others around the local community and I think I remember them calling it Camber Sheer. I have not herd the term or seen in since until the above photo.

Based off the location, I wonder if you may want to back the tire pressures down a bit. Not sure it would help at all. but if your tires are getting hot enough in your runs it could be causing the center of your tire to to round out putting extra load on that tread line. This is just coming from the basic view of too much wear on the center means overinflated. When I had the problem on another car with earlier Bridgestones, it was my outside edge which were taking too much abuse as the car leaned over in turns an put the suspension in a positive camber. Obviously not your problem, but the location makes me wonder if your tire is a bit round where you really want it flat for the best grip. Sorry about your tires, if it was me, I flog them like a rented mule for another couple days to make sure I got what enjoyment I could out of them before replacing them.

 

[The Other Dan]

I sometimes get a fair amount of oversteer with my PS4S's too- What always calms this down for me is running 1PSI less in the rear than front.

I was spraying between each run and pretty much went slower and slower as the temps got hotter and hotter. Temps were 90*+.
On my last run of 6, I ended up going 60/40 front bias. Went 0.5sec quicker without really driving any different.

 

[Kmann75]

Here are my set of RE-71rs 245/34/19s when new compared to after a handful of autox events. has a very similar center tread wear. Running ~45psi on highways to events, maintain 35-36psi during events. Also compared to worn Falken 235s and brand new P-zero 245 on my 20s.

 

[Lindenwood]

I ended up running down to 30 PSI on my last event and reducing my times by around 3% compared to 36 PSI. Unfortunately, I forgot my temp gun to check across the tread, but I didn’t notice anything unusual.

I would concur with considering lower tire pressures, monitoring outer shoulder acrubbing and, as able, wear across the tread.

 

[GAGT]

So, two events ago i swapped from 265/35-19 RT660 to 275/35-19 RE71RS, on my SS legal 19x9's.

The RT660 had wore a funky groove in the outside half of the tire. The RE71RS developed this same groove, but much more quickly...
View attachment 940009

Conversely, a friend has the sister to my car, essentially the identical m3p on 19x9, but he has the 255/35-19 RE71rs. His tires did the same thing after two events...


Is the only fix more negative camber?

After the NJ pro solo, I plan on testing both 255 and 275 back to back on the same car on the same day. Grom the outside, it seems that the 255 has better steering feel and the 275 has slightly more mechanical grip, but feels more vague with the additional pinch on the 9" wheel.

Does this emulate what everyone else is seeing?

Tire pressure? I'm thinking you are running 35+?

On BFG and Nexan's I was down to around 32 and the outside edge was perfect to the indicator IIRC. If you are running 35+ it is going to be a combination of slight over inflation(our weight makes it more drastic) and the lack of camber we get. But mostly the lack of camber. Once those strips edge is worn then it moves towards the center then the following edge. Ultimately both my BFGs and Nexans ended up wearing very evenly to nothing.

 

[dsgerbc]

Here are my RTs after 50ish runs at ~3.0 degrees of camber. Outside is on the left.
Trying 4.0 degrees of front camber this weekend (before likely moving to 3.5ish while increasing caster).

 

[SK360]

A fellow Tesla autocrosser twisted my arm enough to get me to forego my SCCA boycott and attend the local regions event yesterday. (He needed a codrive so technically it was his money )

Anyways it’s a much bigger site than what I’m used to, had a great time and ended up 8/120 in raw and 9th in pax. Of the Top 10 in raw only 2 of us were on 200tw tires and Jake won the AS national championship last year and that Miata is nationally competitive in STR so I’m not too upset about that. Top 10 in PAX is littered with national level drivers and jacket holders.

It was hot AF yesterday, we were spraying the 660’s between runs and keeping them at 36F/34R. Car felt absolutely fantastic.

I used my GoPro on vacation last week and forgot to disable hypersmoothing so the video of my 2nd quickest run looks weird… also me and my codriver mixed up communication on operating the camera so my last and fastest run ended up being a photo not a video so I pulled the Tesla dashcam video for it instead. I also think I discovered an issue with the 2023.7.10 update as the TrackMode data has gotten VERY choppy. You can see it not only in my overlays but also in the G meter on screen.

 

[dsgerbc]

It was hot AF yesterday, we were spraying the 660’s between runs and keeping them at 36F/34R.

Are those 275-wide ones?
I generally run much lower pressures on 305-wide ones.

 

[SK360]

Are those 275-wide ones?
I generally run much lower pressures on 305-wide ones.

265/35/19

 

[Lindenwood]

Are those 275-wide ones?
I generally run much lower pressures on 305-wide ones.

Indeed, on my 275s I saw about a 3% reduction in my AutoX times between 36 PSI and 30 PSI!