Bigger Tires - Page 3 - Saturn Sky Forums: Saturn Sky Forum
Autocross and Racing Discussion (SKY/Kappa) Tips, tricks, vehicle prep and setup, etc.

User Tag List

 1Likes
Reply
 
LinkBack Thread Tools Display Modes
post #31 of 45 (permalink) Old 04-29-2011, 04:05 PM
Senior Member
 
Nova-Exarch's Avatar
 
Join Date: Sep 2007
Location: Puget Sound Area
Posts: 1,279
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 81 Post(s)
Quote:
Originally Posted by kudelt07 View Post
What you said there is correct, though, the equation for braking force is BF=BT/DRR. As for your question about reducing mass but increasing rolling radius, you can figure it out using the following equations:

Let's assume that the wheel and tire make a thick walled cylinder (not really the case, but it'll work for what we're doing here). In this case, I=0.5*m*(r1^2 + r2^2), where I=rotational inertia, m=mass of the wheel and tire, r1=ID of wheel, and r2=OD of tire. Plug in the appropriate numbers to see how your inertia changes. A decrease in inertia will results in better braking/acceleration. Once again, this won't be a huge difference when you look at all the other mass the brakes have to slow down, but it is there.
So, assuming there was a modification that could change ER... would a larger ER (moving the point where the calipers grab the rotor further out) increase BF?

Not that I plan to do any of this (except maybe better pads/rotors sometime in the future), lol... I am just curious, and it's somewhat worth thinking about when considering wheel/tire choices.
Nova-Exarch is offline  
post #32 of 45 (permalink) Old 05-02-2011, 07:57 AM Thread Starter
Senior Member
 
Join Date: Mar 2008
Posts: 184
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Yes, increasing your effective radius will increase the braking force at the road. That being said, I really don't think these cars need it, especially if you're not running race tires. You have to remember, you're tires can only handle so much force in a given direction before they start to slip. I haven't installed the new front brakes yet (still waiting on rotors), but my guess is that the new pads will offer more than enouigh braking torque with the current dimensions.

I did install a set of rear pads and rotors this weekend (European OE friction material) and was surprised how much of a difference it made in pedal feel. The difference with new fronts should be huge.
kudelt07 is offline  
post #33 of 45 (permalink) Old 05-09-2011, 11:25 AM Thread Starter
Senior Member
 
Join Date: Mar 2008
Posts: 184
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
I've got a couple hundred miles on the new front and rear brakes now, and they feel great! There is WAY more grip, especially when they've warmed up, pedal feel is much more confident, and the initial bite is quite a bit better. So far no noise, but we'll see what happens after they've burnished for a little longer. I haven't had them long enough to evaluate how dusty they are.
kudelt07 is offline  
post #34 of 45 (permalink) Old 05-09-2011, 12:33 PM
First 2000 Sr. Member
 
MCW Sky's Avatar
 
Join Date: Mar 2006
Location: Ohio
Posts: 1,640
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2 Post(s)
more bite

Quote:
Originally Posted by kudelt07 View Post
Yes, increasing your effective radius will increase the braking force at the road. That being said, I really don't think these cars need it, especially if you're not running race tires. You have to remember, you're tires can only handle so much force in a given direction before they start to slip. I haven't installed the new front brakes yet (still waiting on rotors), but my guess is that the new pads will offer more than enouigh braking torque with the current dimensions.

I did install a set of rear pads and rotors this weekend (European OE friction material) and was surprised how much of a difference it made in pedal feel. The difference with new fronts should be huge.
Not that I have ever really had any issue with the brakes - but they do feel different than other cars I have driven and there have been a few times where I needed a tad extra braking force near the end of a stop and the pedal felt very hard - which in other cars has always felt like sorry, that's all I got - whereas in this car a little extra effort and despite the pedal feel - the extra braking force is there.

I wouldn't mind something with a different profile (of feel and effort to effect) whereby I got a more responsive feeling system that was more consistent across the range of effort applied. even if that means I end up with a system that has more total braking force than I will ever need for normal daily use.

On the other hand I don't have $4000 to spend right now on a full upgrade to something like a TCE Plus 1 for front and back - but someday.

I agree though - that upping your brakes to the point where you can more easily lock the wheels if the traction in not sufficient to transfer that force to the ground is not a good idea. And I don't think I have ever had the ABS system kick in on this car - and only maybe once in normal driving on any car - and maybe once or twice in a parking lot to get an idea of what would happen - also tried cranking on the handbrake in a snow covered parking lot - found out quickly that may help in a straight line - but don't try it under any other conditions - even on a front wheel drive with ABS - it got squirrely in a hurry - but fun when your passenger is not expecting it. And yes dear I meant to do that - because getting familiar with how your car behaves when you are not in an emergency situation helps you handle it better if and when you do get into an emergency situation.

'09 RL Ruby Red Manual
3rd brake pulser-seq'l tail lights
Retracting motorized front license
HID low beam & fogs
3" Magnaflow
DDM Works - Charge Tubes,Cross Bay Brace,Tunnel Brace,Center Console,Fender Trim,Sway bars,Drilled Rotors,Hawk pads
MCW Sky is offline  
post #35 of 45 (permalink) Old 03-22-2017, 11:37 AM
Member
 
Join Date: Jan 2016
Posts: 21
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 6 Post(s)
Wheel/Tire Fitment Question

Hi! I was hoping to piggy back off of this thread, which I know is several years old. I just have a fitment question, sort of related to this thread.

I've got a Redline and want to get a set of TIS 536 wheels for it, 20x8.5". The recommended tires for it are 245-35-20, but I've got an opportunity to get a fantastic deal on a set of 255-55-20. I've done a size comparison and know that these should be about .4" wider, and about .3" larger in diameter than total sizes of stock rims and wheels. (The recommended 245-35-20 size on the 20" is very very close to that of the stock, so there is almost no change there).

I just want to see if anyone can tell me whether I will have any fitment issues with the larger tires, regarding rubbing or hitting of the sidewall? Or any reason that I should stay away from this larger size?

Any help is appreciated.
kloos1502 is offline  
post #36 of 45 (permalink) Old 03-22-2017, 06:05 PM
Member
 
Join Date: Jan 2012
Posts: 26
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 5 Post(s)
Offset is VERY important... I have OZ 20x8.5 +55 255/35 tires, with the car lowered and extra camber I had some minor rubbing inside the plastic wheel wheels.

Last edited by tallcraig; 03-22-2017 at 06:10 PM.
tallcraig is offline  
post #37 of 45 (permalink) Old 03-22-2017, 06:13 PM
Super Moderator
 
Robotech's Avatar
 
Join Date: May 2006
Location: Temecula, CA
Posts: 10,613
Mentioned: 64 Post(s)
Tagged: 3 Thread(s)
Quoted: 1671 Post(s)
Garage
Damn tallcraig, even with a 55 offset!? Was it on the inner part of the liner or the outer? I could see that offset being to far in and causing a rub on the inside of the wheel well but it sounds like it was closer to the outside since you mention your camber played a role in it.


V.A.L. (#1108)
2007 2.4 Base
MagnaFlow dual outlet, quad tip exhaust test car
**Sold**

Max (#1547)
2007 TURBO 2.4
Too much to list here. See my Garage for details.
Robotech is online now  
post #38 of 45 (permalink) Old 03-23-2017, 12:10 AM
Member
 
Join Date: Jan 2012
Posts: 26
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 5 Post(s)
Light rubbing on the inside rear. I have a fairly aggressive autox alignment. Going with 18x10 +45 this season. I made them fit... Sorry kloos1502 for stepping on your thread.
(I would love to talk some Kappa Autox)
tallcraig is offline  
post #39 of 45 (permalink) Old 03-23-2017, 05:49 AM
Super Moderator
 
Robotech's Avatar
 
Join Date: May 2006
Location: Temecula, CA
Posts: 10,613
Mentioned: 64 Post(s)
Tagged: 3 Thread(s)
Quoted: 1671 Post(s)
Garage
Quote:
Originally Posted by tallcraig View Post
Light rubbing on the inside rear. I have a fairly aggressive autox alignment. Going with 18x10 +45 this season. I made them fit... Sorry kloos1502 for stepping on your thread.
(I would love to talk some Kappa Autox)
Where you running autocross? I'm using 245/45/18 on RE-71Rs. Beat an ACR Viper with them on. What are you running on your AutoX Setup with those tires? I have 1.5 all four corners. Ran 2.5 up front but had bad tire wear since I daily drive it too (and didn't want to constantly change back and forth) so I went to 1.5. Have 5K springs in front, 7K out back but the front feels a bit soft. Have to turn up the front BCs to full stiff and set the rears to full soft to get the car to feel neutral. Front sway is the FE2 bar and the rear is the Redline Z0K. I think if I went with 6K front springs I could set the shocks to a setting that is closer front to back.

I wouldn't mind going with some wider rubber but I know SCCA limits tire size based on stock tire size. Hence why I wondered where you were AutoXing at...


V.A.L. (#1108)
2007 2.4 Base
MagnaFlow dual outlet, quad tip exhaust test car
**Sold**

Max (#1547)
2007 TURBO 2.4
Too much to list here. See my Garage for details.
Robotech is online now  
post #40 of 45 (permalink) Old 03-23-2017, 02:57 PM
Member
 
Join Date: Jan 2012
Posts: 26
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 5 Post(s)
I'm with the Thunder Bay Autosport Club. We run only three class A/B/C using SCCA street category guide lines and are lumped into a class from there. A base Solstice (BS) would end up in the A class from the get go. We also fill out classing work sheets. My car started out as a base model loaded and within a year and a half it had a SC, full DDMWorks brace bundle, GXP ZOK bars, BC coilovers, VDI doors, OZ rims...all stuff for car shows.
Last season I wanted to play with it more so I autocrossed for the first time. Thinking my car was "all that and a bottle of pop" I was humbled. Bad setup, old, hard, crap tires and a TOTAL lack of ability....but it was fun! We get maybe 25 cars in smallish parking lots around the city. It's a good group of people (excluding the Subie kids LOL)
Being in the top class I can do anything I like. I have two sets of 18x10 rims with 275/35 G-Force R1 S on one and 275/35 RE-71S on the other. I'm going to try a GXP FE3 front bar, Hawk HPS front and HP+ rear.
Alignment is Front -2 camber/ 8 caster/ 0 toe Rear -1.75 camber/ -4 caster /0 toe if recall correctly.
I'm hoping the FE3 helps with the oversteer. HATE the push. Braking sooner would also help. I should have the 5k springs in the front... I do have time...
I just yanked off the VDI door hinges. Trying to decide if I want to sell them or not. Hoping to get a new alignment and the car corner balanced. Still playing with ride height. Any suggestions would be appreciated Robotech and thank you for all you do for the Kappa community !
I came in 2nd in points last year on events attended not ability. LOL
tallcraig is offline  
post #41 of 45 (permalink) Old 03-23-2017, 04:20 PM
Super Moderator
 
Robotech's Avatar
 
Join Date: May 2006
Location: Temecula, CA
Posts: 10,613
Mentioned: 64 Post(s)
Tagged: 3 Thread(s)
Quoted: 1671 Post(s)
Garage
Are you running the stock BC 7ks all around? If so, drop to the 6ks up front first and put your stock swaybar on up front. Gives a LOT of bite. The RE-71Rs helped a ton too. I think with the 6ks my setup would be spot on for me.

Looking at your setup I think you made the same mistake I did. The 7k Springs with Z0K (GXP) bars and that much camber doesn't work. Soften the front spring and bar and I think you'll get enough roll up front to use all that camber. Right now I bet if you turned the camber down to 1.5 or so you'd get more front bite. With the 7k springs and Z0K bar up there, you're just not going to be rolling over enough to get the most out of those front tires. the softer springs will also let you shift more weight up front under braking and thus helping with your late braking technique. LOL

Depending on where in the turn you have push says a lot too. Curing it on corner entry can be a lot different than mid corner or corner exit.

I don't know where you're at ride height wise but I want to say the GM recommended height for their racing Solstices was 4.5" or 5"...somewhere around there measured from ground to frame rail.

One thing I learned with braking (took like a novice course offered by our San Diego SCCA groups) is all I needed was a quick, hard stab of the brakes while driving straight and that would be enough to bleed off most speed. It surprised me that you didn't need a long braking period, just a short, quick, but firm braking period.

But yea, they put me in the top class too. I run against all the sports cars. ACR Vipers, Z06 Z07 Vettes, supercharged 350Zs...but the fastest guy in the group is a supercharged FR-S who works for Hotchkis Suspension (who is the title sponsor of the event) as a Suspension engineer. LOL Go figure he's the fast guy.

Me on course:
Attached Thumbnails
Click image for larger version

Name:	14462898_10154563959379777_7466819264276044322_n.jpg
Views:	146
Size:	49.8 KB
ID:	89874  


V.A.L. (#1108)
2007 2.4 Base
MagnaFlow dual outlet, quad tip exhaust test car
**Sold**

Max (#1547)
2007 TURBO 2.4
Too much to list here. See my Garage for details.

Last edited by Robotech; 03-23-2017 at 04:27 PM.
Robotech is online now  
post #42 of 45 (permalink) Old 03-24-2017, 11:57 AM
Member
 
Join Date: Jan 2012
Posts: 26
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 5 Post(s)
Thanks Robotech, My FE2 bar is at the scrap yard LOL. They are cheap and available. With 6k front/7k rear springs and a FE3 bar front, where would you set your dampening to start? Full soft front and full hard rear? The same goes for a FE2 up front. If I drove within the limits of last years setup and "curbed my enthusiasm" the push would have been less of a factor. The biggest problem with my car is the driver! I'm working to improve both.
I think your right about the camber on my setup. I've read as you go wider and stickier there is a point of depreciating returns with camber. I will try try to brake a bit earlier, a sharp stab on the brakes on a straight line. Do you want the front to recover before you start your turn? I think DDM Dave's custom street alignment had a bit more rear stance (higher) than than the book states for the racing setup.
Where do you start your tire pressures front and rear with the RE-71 R's?
I do appreciate your interest in the sport and sharing with the group what has worked for you.
Craig

Last edited by tallcraig; 03-24-2017 at 12:00 PM.
tallcraig is offline  
post #43 of 45 (permalink) Old 03-24-2017, 01:54 PM
Super Moderator
 
Robotech's Avatar
 
Join Date: May 2006
Location: Temecula, CA
Posts: 10,613
Mentioned: 64 Post(s)
Tagged: 3 Thread(s)
Quoted: 1671 Post(s)
Garage
I am warning everyone up front, this is going to be a LONG one.

With a FE2 or FE3 front bar and the 6K front 7K rear with a rear ZOk bar I would start the BCs at the mid point both front and rear and then tweak from there. I only say that because I have never had that setup on my car and I know with just the 5Ks up front and the FE2 bar I need to have it full soft in front and full hard in rear. So, based on that, I'd start at a mid point and speculate I'd be going a bit softer in front and a bit harder in rear but knowing it is going to come down to how the car feels with that setup first.

For braking, you need to understand what you are doing when you brake. Most people feel it is to slow down but with autocross, that's not really the point. Yes, you're going to bleed off SOME speed but the main reason for the quick stab on the brakes is for weight transfer and the reason you do it in a straight line has to do with how much traction you have available in your front tires.

Think of your available traction of your front tires as a circle and, when the car is cruising at a constant speed, the dot representing how much traction you're using is at the center of that circle. We call it the traction circle. As you accelerate, this dot moves to the bottom of the circle. As you brake, it moves to the top. If you turn right, the dot moves to right side of the circle and if you turn left, it moves to the left. The maximum traction the tire can provide is defined by the outside edge of the circle. if the dot stays in the circle, you have traction...if it moves outside the circle, the tire has lost traction and is slipping instead of gripping. Slipping = push generally.

So...the other thing to note is the more weight you put on a tire, the more traction the tire can generate. The less weight on a tire, the less traction it can generate. So more weight equates a bigger traction circle and less weight means a smaller traction circle.

Now then, if you brake super hard but don't lock up the tires, your "dot" will rest on the upper edge of the circle. If you're turning really hard to the left, the dot will be on the left edge of the circle. If you do both at the same time, the dot will be completely off the circle to the top left...and you're pushing. Again, that's bad.

So remember I said we don't brake to slow down in autocross? What we're doing by braking hard is shifting the weight of the car onto the front tires. When you brake, and you feel the nose of the car drop, that's putting weight on the front tires and thus increasing their amount of available traction.

Your question was do you want to quickly stab the brakes and then let the front recover before turning and the answer, as you have probably already figured out, is NO! You do all your braking in a straight line because, when it comes time to turn, you wan to use as much of your traction circle for turning. If you're doing any braking, you are reducing how much turning you can do. So the technique should be just before you hit the spot where you want to turn into the corner, you stab your brakes quick and firm to shift that weight onto the front tires and get that traction circle really big. Then you let off your brake as you start initiating the turn in with your steering wheel.

With your foot off the brake you are no longer asking the front tires to use any of their grip to slow you down. Yet, by doing that just before starting your turn in, you have weighted the front tires thus increasing how much traction they have to make the turn.

Ride height is doing much of the same thing. You mention DDMs settings and while I have my car set to about 0.2" lower in front than rear, I can't comment on what is "correct". What I can say is that when you're moving a couch, always pick up your side before the other guy does. LOL The reason being is that whichever side of an object is lower, that side is carrying a higher percentage of the object's weight. So if your front end is slightly lower than the back, your front end is carrying slightly more weight (and thus the front tires have a slightly larger traction circle) than the back. Doing this reduces the car's tendency to squat (and push) under acceleration.

For my RE-71Rs, they like about 33 psi of pressure. If you're not using RE-71Rs, that info won't help you as each tire will have a different "sweet spot" for pressure.

When it comes to camber, remember the goal is to use as much of the tire tread as possible when cornering and have even usage. to check your camber, go out and do a session (2-3 laps) and then immediately take a temp gun and shoot the inside portion of the tread, the middle of the tread, and the outside portion of the tread across a straight line parallel to the ground. These temperatures should be within a degree of each other. If not, the tire is telling you something is wrong.

If you get a reading like this (from inside to outside): 120 115 110, the tire has too much negative camber as the inside edge of the tire is hotter than the middle, which is hotter than the outside edge.

If you get something like: 110 115 120 then you have too much positive camber as the tire is colder on the inside edge than the middle, which again is colder than the outside.

Now, you could get something like this too: 110 115 110. This is an overinflated tire where the center is higher than the edges. Underinflated is just the opposite: 115 110 115.

Where it gets tricky is if you have an overinflated tire with too much camber. Then it can look like: 115 115 110

Or too little camber: 110 115 115

Or underinflated with too much camber: 125 115 120

Or with too little camber: 115 110 125

I'd pick up a temp gun and just see where you're at with tire temps and see if that helps give you an idea of how close you are on your camber and pressure setups.


V.A.L. (#1108)
2007 2.4 Base
MagnaFlow dual outlet, quad tip exhaust test car
**Sold**

Max (#1547)
2007 TURBO 2.4
Too much to list here. See my Garage for details.
Robotech is online now  
post #44 of 45 (permalink) Old 03-25-2017, 12:42 PM
Member
 
Join Date: Jan 2012
Posts: 26
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 5 Post(s)
Thanks for providing ALL that information. You made it very easy to understand. It looks like I'll be ordering more suspension parts for my car. You just can't have enough anti-sway bars LOL. To correct most of the push ( I grew up with tail happy cars ) and have it more neutral would be a big plus. When it oversteers I stop looking well ahead and become like a deer in the headlights. After last years debacle using 8 year old Hankook V12's, too stiff of a suspension and (most importantly) my lack of ability, I now have the tools to improve my times.
I thought it was going to be point and shoot but soon found out it's walking the course, looking for the correct line and in the end... having a great time with my Pontiac and fellow drivers.
Thanks again !
Craig
tallcraig is offline  
post #45 of 45 (permalink) Old 03-25-2017, 01:01 PM
Super Moderator
 
Robotech's Avatar
 
Join Date: May 2006
Location: Temecula, CA
Posts: 10,613
Mentioned: 64 Post(s)
Tagged: 3 Thread(s)
Quoted: 1671 Post(s)
Garage
Glad to help Craig. New tires are going to be a big help.

Cornering is all about weight transfer and weight management. So keep in mind where each suspension component is going to affect the transfer of weight.

Springs and shocks are working all the time to manage your weight. When braking and accelerating in a straight line, softer springs will allow more weight transfer and firmer will allow less. Shock settings are going to affect this too. Firmer will allow less transfer and for it to happen slower while softer will allow more and for it to happen faster.

Sway bars will only affect weight transfer in corners and how much the car rolls onto the outside tires. In a straight line, sways do nothing.

Can't wait to hear how you do next time out.
tallcraig likes this.


V.A.L. (#1108)
2007 2.4 Base
MagnaFlow dual outlet, quad tip exhaust test car
**Sold**

Max (#1547)
2007 TURBO 2.4
Too much to list here. See my Garage for details.
Robotech is online now  
Reply

  Saturn Sky Forums: Saturn Sky Forum > Saturn Sky Discussion > Autocross and Racing Discussion (SKY/Kappa)

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Saturn Sky Forums: Saturn Sky Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome