STX (Street Touring X) Have a Cooper S and want a modded class where you can run street tires? Join the discussion in the fast growing class!

Tire pressure baseline?

  #1  
Old 02-22-2014, 06:25 AM
grantsfo's Avatar
grantsfo
grantsfo is offline
1st Gear
Thread Starter
Join Date: Feb 2005
Location: Bonny Doon
Posts: 46
Likes: 0
Received 0 Likes on 0 Posts
Tire pressure baseline?

What do you guys run for pressures in Dunlop ZII tires front and rear? Off to my first Autocross Sunday.
 
  #2  
Old 02-22-2014, 10:56 AM
Btwyx
Btwyx is offline
6th Gear
iTrader: (2)
Join Date: May 2007
Location: Mountain View, CA
Posts: 3,531
Likes: 0
Received 0 Likes on 0 Posts
What size ZIIs?

I havn't run them yet (and mine isn't an STX car), but my 225/45-16 seem to like very high pressures up front. I'm up to 50/40.5 and the fronts still aren't showing even temperatures.
 
  #3  
Old 02-22-2014, 09:07 PM
67morris
67morris is online now
4th Gear
iTrader: (3)
Join Date: Jan 2009
Location: Buffalo, NY
Posts: 438
Received 6 Likes on 6 Posts
I ran 40 front and 38 rear last summer.
 
  #4  
Old 02-22-2014, 11:04 PM
hsautocrosser
hsautocrosser is offline
6th Gear
Join Date: Apr 2010
Location: California
Posts: 1,914
Likes: 0
Received 0 Likes on 0 Posts
On my 2010 Hardtop my Dunlop Direzza Star Specs didn't stop rolling over until I had 49 in the front and 44 or 45 in the rear. I haven't had the Roadster out yet but I will chalk the tires and start at 49/44 when I do.
 
  #5  
Old 02-23-2014, 06:25 AM
v10climber
v10climber is offline
6th Gear
iTrader: (1)
Join Date: May 2013
Location: FL
Posts: 1,394
Likes: 0
Received 13 Likes on 12 Posts
Our STX car we usually start at 39 front and around 41 rear then tweak from there depending on course/surface

Sent from my Nexus 10 using NAMotoring
 
  #6  
Old 02-23-2014, 04:39 PM
grantsfo's Avatar
grantsfo
grantsfo is offline
1st Gear
Thread Starter
Join Date: Feb 2005
Location: Bonny Doon
Posts: 46
Likes: 0
Received 0 Likes on 0 Posts
Wow I'm way off you giuys. I went with 35 front and 32 rear. That kept things ok. What's the thought behind running high rear pressures? I was fastest STX car with couple of BRZ etc. Fastest ST class car overall. Beat plenty of dot r clad cars too. I'm thniking with LSD and wider tires and wheels this car may be pretty quick at regional level.
 

Last edited by grantsfo; 02-23-2014 at 04:44 PM.
  #7  
Old 02-24-2014, 06:33 PM
v10climber
v10climber is offline
6th Gear
iTrader: (1)
Join Date: May 2013
Location: FL
Posts: 1,394
Likes: 0
Received 13 Likes on 12 Posts
Originally Posted by grantsfo View Post
Wow I'm way off you giuys. I went with 35 front and 32 rear. That kept things ok. What's the thought behind running high rear pressures? I was fastest STX car with couple of BRZ etc. Fastest ST class car overall. Beat plenty of dot r clad cars too. I'm thniking with LSD and wider tires and wheels this car may be pretty quick at regional level.
Surface temps, grip levels, tires, alignment numbers all contribute to tire pressures. So it's not surprising that you're a few psi off other people.

We run a higher rear pressure to encourage the car to rotate more.
 
  #8  
Old 02-26-2014, 11:06 AM
grantsfo's Avatar
grantsfo
grantsfo is offline
1st Gear
Thread Starter
Join Date: Feb 2005
Location: Bonny Doon
Posts: 46
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by v10climber View Post
Surface temps, grip levels, tires, alignment numbers all contribute to tire pressures. So it's not surprising that you're a few psi off other people.

We run a higher rear pressure to encourage the car to rotate more.
Interesting I have heard of FWD guys doing this but shouldnt rotation be managed by proper suspension setup? To me it seems suboptimal to overinflate rear tires (reducing contact patch) to get rotation? Im a FWD rookie so excuse my ignorance. I have driven mostly FP and XP rear wheel drive cars so this is all new to me but I know a bit about suspension dynamics and setup.

My car seemed to rotate fine. If anything it tended to over rotate but I can live with that!

I have to look at whether I have a little preload in my rear bar as car snap oversteered in couple places.
 
  #9  
Old 02-26-2014, 12:54 PM
v10climber
v10climber is offline
6th Gear
iTrader: (1)
Join Date: May 2013
Location: FL
Posts: 1,394
Likes: 0
Received 13 Likes on 12 Posts
Well in STX you can fix some of the shortcomings of a strut/multilink suspension but you don't have nearly the allowances you have in the prepared classes like you are used to. Tire pressures are a tuning tool just like everything else and they're used to dial in the car to surface conditions just like shock settings. Some people will change springs/alignment/shock settings/tire pressures just to switch from asphalt to concrete. We just use shock settings/tire pressures.

Do you have an aftermarket rear swaybar? If so I'm not surprised to hear your car has snap oversteer. Mismatched roll rates from a large rear swaybar will do that. I know everyone does suspension setup differently but I'm a "more spring less bar" person which means our car rotates just fine with stock swaybars.

But hey if you're happy with what you have than stick with it. Seems like you're doing pretty good at a regional level so unless your local competition is getting faster or you're planning on going to national level events there probably isn't any reason to mess with it. If the car is fun to drive that's all that really matters.
 
  #10  
Old 02-26-2014, 07:49 PM
Btwyx
Btwyx is offline
6th Gear
iTrader: (2)
Join Date: May 2007
Location: Mountain View, CA
Posts: 3,531
Likes: 0
Received 0 Likes on 0 Posts
A friend who races pointed out you shouldn't ignore the tire spring rates. Increasing the tire pressures will increase the overall spring rates at that end, which would shift the grip to the other end.

My tires seemed to like hot pressures of 49.5/46.
 
  #11  
Old 02-27-2014, 04:45 AM
v10climber
v10climber is offline
6th Gear
iTrader: (1)
Join Date: May 2013
Location: FL
Posts: 1,394
Likes: 0
Received 13 Likes on 12 Posts
Also keep in mind you can't get to the top of the shocks in the rear of the mini without removing the suspension so if you need to make changes on site sometimes tire pressures are the only thing you have. Cutting holes to get to the top of the shock is not STX legal.
 
  #12  
Old 02-27-2014, 12:02 PM
grantsfo's Avatar
grantsfo
grantsfo is offline
1st Gear
Thread Starter
Join Date: Feb 2005
Location: Bonny Doon
Posts: 46
Likes: 0
Received 0 Likes on 0 Posts
THanks!
 

Last edited by grantsfo; 03-10-2014 at 11:49 AM.
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
igzekyativ
MINIs & Minis for Sale
31
02-07-2019 05:23 PM
khumpert
MINIs & Minis for Sale
1
11-30-2015 11:48 AM
oldkid6
R56 :: Hatch Talk (2007+)
5
08-30-2015 08:28 AM
TJANK
Countryman Wheels, Tires and Brakes
2
08-24-2015 06:11 PM
nomar116
MINI Parts for Sale
0
08-09-2015 09:42 AM


Thread Tools
Search this Thread
Quick Reply: Tire pressure baseline?


Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: