Newbie Tire pressure/rollover questions. - Ford Mustang Forums : Corral.net Mustang Forum
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post #1 of 19 Old 10-12-2017, 07:53 PM Thread Starter
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Newbie Tire pressure/rollover questions.

The last track day I ran I was at 34psi F, 30psi R hot. These are nt01 255/40/17 and 235/40/17 front. The car seemed to understeer a lot which surprised me because I've heard so much about snap oversteer on foxbodies but I did not experience that. Now I am thinking my fronts were underinflated and undersized because they are worn badly on the outside and my rears look relatively fresh. This is after 3 track days, apx. 60 laps on a 1.5 mile course. What is the optimal point on the sidewall for rollover? I noticed little arrows on the sidewall. Are they for rollover? Or is it the raised ring around the circumference of the sidewall?
I've since put 255's on the front for a square set-up. I had to use a BFH to get it to clear. That is one of the reasons I went with a staggered setup to begin with. The other is I didn't know any better!
Is optimum grip occurring when the tires are squealing? I'm starting to think I may have been just trashing my tires and not going any faster. After analyzing my videos it looked like possibly I may have been faster when I was not squealing around every corner, but it's hard to compare lap to lap because of heavy traffic on the course.
I am running coilovers with -2.5* camber and maximum caster. Toe is set at 0. The rear has coilovers and aftermarket lcas and ucas.
Thanks in advance for advice. I'm running one more track day this Sunday if the weather holds out. 1st pic rear, 2nd front

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post #2 of 19 Old 10-12-2017, 08:51 PM
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Did you take any tire temps when you came off the track?

What springs and sway bars are you running?

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post #3 of 19 Old 10-13-2017, 09:14 AM
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I'm not using the same tire but I find 34-38 hot on both ends work best and a square setup. Don't know what your shock, spring sway bar setup is but there is a good chance that body roll is causing your wear problem.

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post #4 of 19 Old 10-13-2017, 12:24 PM
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That seems really low to me. I start at 32 cold and look to achieve 40 hot.

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post #5 of 19 Old 10-13-2017, 01:01 PM Thread Starter
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No on the tire temps. Stock sway bars. I'll check the springs tonight. I believe they are stamped. D+D lcas. Some adjustable ucas.
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post #6 of 19 Old 10-13-2017, 03:23 PM
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Quote:
Originally Posted by Hammer Down View Post
The last track day I ran I was at 34psi F, 30psi R hot. These are nt01 255/40/17 and 235/40/17 front. The car seemed to understeer a lot which surprised me because I've heard so much about snap oversteer on foxbodies but I did not experience that.
The car will snap oversteer in certain situations, but the primary handling trait is understeer. Running a staggered setup just added to that; I imagine the car will be significantly happier with 255s square.

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Now I am thinking my fronts were underinflated and undersized because they are worn badly on the outside and my rears look relatively fresh. This is after 3 track days, apx. 60 laps on a 1.5 mile course. What is the optimal point on the sidewall for rollover? I noticed little arrows on the sidewall. Are they for rollover? Or is it the raised ring around the circumference of the sidewall?
The real purpose of the little arrows is to indicate where the wear bars cross the tread face; all tires have those little arrows (or something similar), look at your street tires and you'll see them. Folks do use those arrows as a guide to see how much they're rolling over onto the sidewall, but what amount of roll-over is "right" is a judgment call. An R-compound can almost certainly accept more roll-over than a street tire, but I'm not sure I would go as far as that raised ring.

Like Curt C said, I've found NT01s prefer a bit higher hot pressure, up around 40#. That's on my CTS-V (~4000# track weight, 275/35-18 R-comps), and is just based on feel and not based on tire temps (since I've never had a tire temp probe to play with).

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Is optimum grip occurring when the tires are squealing? I'm starting to think I may have been just trashing my tires and not going any faster. After analyzing my videos it looked like possibly I may have been faster when I was not squealing around every corner, but it's hard to compare lap to lap because of heavy traffic on the course.
Depends on how much squealing and the tone of said squealing. In my experience, you start out with a lower pitched howl (as opposed to a squeal), which is good. If you push harder, you get into the higher pitched squeal, which indicates you're at or beyond the optimum slip angle. And if you push it even farther than that, you go back to a lower pitched grinding noise as the tire is just scraping across the pavement. I don't recall hearing anything in your video clip that made me think, "Whoa, he's really over-driving those tires."

Street tires are actually better at "talking" to you than R-comps, which is one reason why most folks say you should really learn to drive on street tires first. They have more gradual break-away characteristics, and they provide more aural feedback as you're approaching the limits. In my experience, NT01s are better with aural feedback than some of the more hard-core R-comps.
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post #7 of 19 Old 10-13-2017, 06:10 PM Thread Starter
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Thanks to all for the great information. I have read several times to run street tires as a beginner but that was after I bought the nt01 which I thought were actually sticky street tires. when I upgrade the suspension and brakes I'll research first! Is there a street tire you recommend for my situation? Keep in mind my car has 550hp at the crank. Although I hardly use it at the track. I'm probably a great example of doing everything assbackwards!!
My Springs are front 12-250 and rear 10-150. The front/rear have an adjustable threaded sleeve. I assume that's for ride heighth. Will tightening that make any difference in handling?
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post #8 of 19 Old 10-13-2017, 10:16 PM
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I agree those tires need 38 to 40 hot.....a street tire with a treadwear rating around 200-300 would be ideal IMO.

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post #9 of 19 Old 10-14-2017, 10:39 PM
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Foxes are front heavy and will always be fighting understeer. Turning up front springs to shift some weight to rear may help a bit but not much. I would start at 34 cold got to 38-40 hot with all season Mastercrafts.

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post #10 of 19 Old 10-16-2017, 11:11 AM
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Gotta address the obvious first. 250 lb/in spring at 12" length is not near enough spring rate for HPDE duty. A relatively small tire like a 235/40 17 (the size when you were at trackday) is going to overload quickly with such a soft spring. Expectations have to be realistic with those parts.

I've run a similar setup, and oversteer came very quickly at speed on an open track. Hooning on the street at slow speeds was the only time I could load up the rear end enough for snap oversteer.

Another thing about tires. I pay attention to rollover as a guide to see how much camber I need. Looking at your pic I'm seeing not enough rollover, personally I'd try 2* or less and see what happens. Ideally tire wear should be even across the tire.

Experiment with tire pressures too. Keep in mind you can induce oversteer with too much rear pressure.


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post #11 of 19 Old 10-16-2017, 02:12 PM
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Quote:
Originally Posted by Curt C View Post
That seems really low to me. I start at 32 cold and look to achieve 40 hot.
Grass Roots Motorsports tested the tire I use and found that 34 hot produced the best result with no change up to 38. I found 36-38 seems to suit my car the best.

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post #12 of 19 Old 10-16-2017, 05:21 PM Thread Starter
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Any recommendations on front spring rate? It seems as though my current setup is more street/drag oriented. I don't think I'll do much to it until I get more track time. Unfortunately I didn't make the last OTD because of poor weather and the track is closed for the season.
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post #13 of 19 Old 10-17-2017, 03:35 PM
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Any recommendations on front spring rate? It seems as though my current setup is more street/drag oriented. I don't think I'll do much to it until I get more track time. Unfortunately I didn't make the last OTD because of poor weather and the track is closed for the season.
Call MM.

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post #14 of 19 Old 10-17-2017, 04:58 PM
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Ok here is my 2 cents, a 235 tyre on a foxbody mustang is useless, (unless class rules)

im on 275 square Nitto NT01 and I really like them, (still tuning the rest of the car/suspension) also my fox is 2774lbs est with me in it, going hoosiers next year, and hopefully zero offset wheels



1. run a square setup and I would say atleast 275s ( I noticed your went square with 255s I guess that would be a decent starting point)

2. try 3 to 3.5 degrees neg camber up front

3. put stock upper rear control arms back in

4. pull weight out of the front end ie battery in trunk, lightweight tubular front bumper, aluminum heads, remove HVAC, emissions whatever you can if this is a trackcar of course. Lighten up the front and that would help tremendously

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post #15 of 19 Old 10-17-2017, 07:57 PM Thread Starter
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1. run a square setup and I would say atleast 275s ( I noticed your went square with 255s I guess that would be a decent starting point)

2. try 3 to 3.5 degrees neg camber up front

3. put stock upper rear control arms back in

4. pull weight out of the front end ie battery in trunk, lightweight tubular front bumper, aluminum heads, remove HVAC, emissions whatever you can if this is a trackcar of course. Lighten up the front and that would help tremendously[/QUOTE]

1) I think a 275 is too much for my 8.5" wheels. Although those will be replaced when I upgrade the brakes this winter. I picked up some sn95 hubs/spindles and am planning on 13" cobra brakes but I've run across this vintage venom 14" gt500 setup and am thinking of that now. Any insight on big brake setups you guys are running is appreciated.
2)I've got my camber plates maxed out now. I got 2.5* left and 3.2* right. Not sure why there is a difference. Will I be able to get more camber with sn95 spindles?
3)easy enough
4)my engine bay is all business, carbed 347, alum heads and intake. Battery is in the trunk. It's still full interior though, I could lose some weight there.

I also believe I may need fender mods to fit a
275 up front. They definitely fit in back though.

I also checked MM website and they recommend spring rate of apx 400 for track duty so I'm way too soft there.

Looks like I need a master plan here and a lotto ticket.
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post #16 of 19 Old 10-18-2017, 07:01 PM
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When considering new spring rates be sure your dampers can handle them. MM's site has a tech reference on Bilsteins, Konis and I believe Tokicos, for both conventional and C/O spring ranges. I ran 300# C/Os on Bilstein HDs on the front of my 86, and H&R Super Race conventional rears when I ran both the PM3L and T/A. Before those mods, I ran "C" rears. This was a huge mismatch in F/R wheel rates but I was aiming at ride quality rather than all-out track performance. Turns out ride quality improved dramatically, along with rear suspension performance, just switching to the PM3L (need a PHB or Watts for this mod).

As for tires, I've run 255/40/17s up front as well as 255/45/17s. The 40s were on an 8" rim; the 45s on a 9". I was running the stock 86 K with sn95 a-arms which are about 1.25" longer per side than the Fox arms (5-lug conversion on sn95 spindles). However, because the 86 K has the pick-ups inboard .5" per side, the net front track increase is about 1.5" (.75" per side) over the later Fox GTs. There was a little rubbing at the peak of the fender opening (that little fastener holding the inner well), but otherwise I didn't need to roll the fenders or use other than stock limiters. I did have to run about -2* camber and hold ride height to 25-3/8" ground to lip, otherwise I got a bunch of rubbing.
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post #17 of 19 Old 10-19-2017, 01:46 PM
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I have to agree that you need different springs, 350 to 450 in front and 100-125 lbs less in the back to start with. and Yes, don't over tax your dampers, springs are cheap find good shocks first.

Brakes, I'm running 04 cobra setup front and rear with a 93 cobra master 1" bore I think, with Hawk HP+ pads. In my full weight car and likely 200 hp less than you they work great. Cooling ducts are a must have.

I'm running a PHB in the rear and longer ball joints in the front, -2.5 camber for what I have it corners very flat. My tokico blues and matching springs are really soft for running at Grattan but it rides like a caddy. Last time out I ran a 1:36 on old 240 TW tires. Considering how heavy and weak my car is I'm real happy with that.
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post #18 of 19 Old 10-19-2017, 04:24 PM Thread Starter
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I have to agree that you need different springs, 350 to 450 in front and 100-125 lbs less in the back to start with. and Yes, don't over tax your dampers, springs are cheap find good shocks first.

Brakes, I'm running 04 cobra setup front and rear with a 93 cobra master 1" bore I think, with Hawk HP+ pads. In my full weight car and likely 200 hp less than you they work great. Cooling ducts are a must have.

I'm running a PHB in the rear and longer ball joints in the front, -2.5 camber for what I have it corners very flat. My tokico blues and matching springs are really soft for running at Grattan but it rides like a caddy. Last time out I ran a 1:36 on old 240 TW tires. Considering how heavy and weak my car is I'm real happy with that.
What springs are you running now? I am actually planning on running Grattan next year. What speed are you hitting there?
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post #19 of 19 Old 10-20-2017, 08:27 AM
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I currently have stock location Tokico 680 front 350 rear that came in a kit with matching shocks. On the shelf waiting or winter I have Koni DA'a and 375 front 275 rear and a torque arm to install.

On a good day I just break 110 on the front straight, best lap time is a 1:36. My lap timer showed 8 consecutive laps with in .5 of each other at 1:39. Grattan is like half roller coaster and half race track, don't expect to get to know the track until you have about 40 laps in. Don't ever expect to feel like you just nailed a perfect lap. I race at Gingerman and Joliet in an 89 notch back, those track are flat and smooth, Grattan is all off camber blind corners, a jump, lots of fun.

Any body want my old setup, springs and shocks, $250.
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