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034 RSB, tire pressure, and traction control settings - looking for advice

Waltari

Go Kart Newbie
Location
Portland, OR
Car(s)
MK7 GTI
I have a 2015 MK7 GTI non-PP diff, an 034 RSB, stock suspension, and OZ Ultraleggera 18" rims with 225/40r18 RE71R tires (less than 1000 miles and 1 track day). On my last track day (78 degrees, no rain), I did air down tire pressure after my first session and was running with traction control off. The 034 RSB is set to the softer of the two settings. I noticed that I was occasionally getting wheel spin on the inside under hard acceleration out of turns. Any recommendations on how to best correct? Should I just continue to play with tire pressures? Change the RSB to the stiffest setting? Turn traction control back on? Next track day is in May so I'm trying to plan ahead. Appreciate everyone's input.
 

jay745

What Would Glenn Danzig Do
Location
Slightly Outside Chicago
Car(s)
Mk6 racecar, Tacoma
You could try changing your sway bar to the stuff setting to get a little more rotation. An lsd and some camber plates are really the best way to combat what you're describing. What tire pressures are you running? I'd start around 30 psi cold and pay attention to the wear indicators from there. Re71r heat up fast and lose grip quickly. A few hot laps is about all you're going to get before those start to get greasy.
 

Waltari

Go Kart Newbie
Location
Portland, OR
Car(s)
MK7 GTI
You could try changing your sway bar to the stuff setting to get a little more rotation. An lsd and some camber plates are really the best way to combat what you're describing. What tire pressures are you running? I'd start around 30 psi cold and pay attention to the wear indicators from there. Re71r heat up fast and lose grip quickly. A few hot laps is about all you're going to get before those start to get greasy.
I was running 32psi, but could probably pay better attention to the wear indicators and possibly run different psi front to back left to right.
 

FlyingNugget

Go Kart Newbie
Location
Toronto, Canada
Inside wheel spin while accelerating out of a corner is inevitable with an open diff -- this is essentially the nature of the beast.

You either need to use XSD(so the brakes grab the inside wheel after it starts slipping), or get an LSD.

My advice is to either run it in ESC Sport, or play around with the different XDS settings in ODB11.

It also depends on the track: tracks with tight hairpin type turns are where you're really going to struggle with that inside wheel.
 

Waltari

Go Kart Newbie
Location
Portland, OR
Car(s)
MK7 GTI
Inside wheel spin while accelerating out of a corner is inevitable with an open diff -- this is essentially the nature of the beast.

You either need to use XSD(so the brakes grab the inside wheel after it starts slipping), or get an LSD.

My advice is to either run it in ESC Sport, or play around with the different XDS settings in ODB11.

It also depends on the track: tracks with tight hairpin type turns are where you're really going to struggle with that inside wheel.
Thanks, sounds like in addition to the stiffer RSB setting and tire pressure, it's worth keeping the OBD11 plugged in and trying different settings between sessions. As reference, I'm running PIR in Portland Oregon and am mainly experiencing a little inner wheel spin through turn 2, a bit going into 6 , and occasionally coming through 12 back onto the front straight.
1920px-Portland_international_raceway.svg.png
 

xXDavidCXx

Autocross Champion
Location
AZ
Car(s)
2017 GTI SE DSG

Waltari

Go Kart Newbie
Location
Portland, OR
Car(s)
MK7 GTI
As a side note, I would run much higher tire pressures when using RE71Rs, like 40 psi. There is 2000lbs of car over both tires not including any weight transfer from braking and turning.
Really that high? At 37psi I was still probably a full 1/4"-3/8" above the wear marks.
 

xXDavidCXx

Autocross Champion
Location
AZ
Car(s)
2017 GTI SE DSG
The wear marks are not a good reference to grip. A tire needs to be supported with air, 30 psi is deflated.

Besides you are camber limited and beating up the outside tread already.

My experience says that the grip curve is decreasing as you go below 35 psi, and increases as you go towards 40 psi, then drops off at some point.

This won’t help you with your power-downthough.

And RE71Rs hate heat and you get more heat with less tire pressure.
 

Waltari

Go Kart Newbie
Location
Portland, OR
Car(s)
MK7 GTI
The wear marks are not a good reference to grip. A tire needs to be supported with air, 30 psi is deflated.

Besides you are camber limited and beating up the outside tread already.

My experience says that the grip curve is decreasing as you go below 35 psi, and increases as you go towards 40 psi, then drops off at some point.

This won’t help you with your power-downthough.

And RE71Rs hate heat and you get more heat with less tire pressure.
Got it, appreciate the input!
 

Will_

Autocross Champion
Location
SF Bay Area
Car(s)
2017 GTI S DSG
The wear marks are not a good reference to grip. A tire needs to be supported with air, 30 psi is deflated.

Besides you are camber limited and beating up the outside tread already.

My experience says that the grip curve is decreasing as you go below 35 psi, and increases as you go towards 40 psi, then drops off at some point.

This won’t help you with your power-downthough.

And RE71Rs hate heat and you get more heat with less tire pressure.

Are you referencing cold or hot PSI? I find 34 psi cold the sweet spot when tracking, this has been true of both my old Yokohama Advans (the 280tw type) and my current Nexen 200tws.

I have a document saved somewhere from Michelin. They recommended 35-40 PSI hot on their road tires for track days.
 

Waltari

Go Kart Newbie
Location
Portland, OR
Car(s)
MK7 GTI
Are you referencing cold or hot PSI? I find 34 psi cold the sweet spot when tracking, this has been true of both my old Yokohama Advans (the 280tw type) and my current Nexen 200tws.

I have a document saved somewhere from Michelin. They recommended 35-40 PSI hot on their road tires for track days.
Hot...I had dropped to 37psi hot initially, but since I was referencing the wear marks and they were still that far off, it was leading me to believe I should drop more.
 

Will_

Autocross Champion
Location
SF Bay Area
Car(s)
2017 GTI S DSG
Hot...I had dropped to 37psi hot initially, but since I was referencing the wear marks and they were still that far off, it was leading me to believe I should drop more.
Sorry, I was referencing David’s post in my comment. However on the topic of determining best PSI. I use the old school way of checking psi by just examine wear on my tires.

In the first photo (taken right after a track session) you can tell I’m a bit overinflated as there is no wear on the outer edge of the tire.
182E0807-90E9-42F2-BCCD-CC98E97A4211.jpeg


Second photo tire is at a better PSI. Much closer to limit without rolling into sidewall.
5122B64F-7263-425D-843C-CC150876BBCC.jpeg


My rule of thumb is start at 34psi for 1st session and bleed down if need be. On summer days at Thunderhill I may be at 32psi cold because the tire is gaining so much heat/pressure during a session. Sonoma I can stay at 33.5/34 all day as it’s fairly low grip and the tires don’t get as much heat in them. I don’t think there’s any “best” PSI you can apply each time out, just need to evaluate each time and go from there. I check after each session how the wear looks.
 

Will_

Autocross Champion
Location
SF Bay Area
Car(s)
2017 GTI S DSG
Also (kinda rambling now) but sometimes you can get wear that is misleading. I was at 33psi cold at Laguna Seca this weekend and noticed some wear on the shoulder of the tire, indicating too low of pressure. I was confused as it was about 75F out and I was driving quite hard so if anything 33psi should be on the high side of ideal. But check out the deflection of the tire in this photo. Huge compression zones like at the bottom of the corkscrew can inflict some unusual wear on a tire that is otherwise the correct psi. Reiterating my last point, I think you just have to go on a case by case basis.

2D776322-659D-48B1-B23D-F8E41DB06726.jpeg
 

xXDavidCXx

Autocross Champion
Location
AZ
Car(s)
2017 GTI SE DSG
Always hot pressures.

Again, the wear bar is just an indicator of wear, not an indicator of grip.

I think these photos by @Will_ are just fine, if you want to go by wear.

There is no reason to lower pressure to "make sure the wear goes down to the wear bar".

Think of the wear bar as a limit, not a goal.
 
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