Road course tire issue - Ford Mustang Forums : Corral.net Mustang Forum
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post #1 of 16 Old 02-01-2016, 04:58 PM Thread Starter
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Road course tire issue

This was my first summer doing track days in my 88 LX. Did a few mods on it like new shocks, lowering springs,frame stiffeners and a panhard bar. Was running with some cheap Mastercraft all season tires 225/50/16, all I could afford at the time, it is a daily driver a lot over the summer. After the third track day, ran six all summer, front tires were loosing big chunks of rubber from outside edge. Was running 38 psi typically weather was in the 80's. Was this because of type of tires or what, any ideas? https://youtu.be/ldrDFD59NQU

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post #2 of 16 Old 02-01-2016, 08:42 PM
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Generally not enough negative camber and/or too much body roll eating up what negative camber you have, plus pushing them too hard in the corners.

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post #3 of 16 Old 02-01-2016, 11:06 PM
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Mastercraft all-season tires just aren't designed to take the sort of abuse you can subject them to on track. It won't take much to over-drive them in the corners and tear them up.
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post #4 of 16 Old 02-03-2016, 04:40 PM Thread Starter
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I have some camber in it, can't remember how much, papers in car its covered up for winter, had aligned to specs that came with CC plates. I'm sure the sidewall of performance tires should be a bit stiffer, guess I'll see what happens with them next summer.
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post #5 of 16 Old 02-03-2016, 09:17 PM
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Video of a foxbody in the 90s doing a slalom showed it lost 6* of camber on the outside tires. The fronts of these cars are that poorly designed. I run -3.75* on radials when auto-x'ing (any more, and straight line braking becomes more lock-up prone).
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post #6 of 16 Old 02-04-2016, 09:43 AM Thread Starter
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I guess I'll see what happens with some decent tires and experiment with different cambers, go to some races and see what guys are doing on their cars. My goal is to race the car, gonna work on getting competition license this summer. The racing class I would like to be in limits the mods that can be done on the car.
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post #7 of 16 Old 02-04-2016, 03:50 PM
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All season's overheat and chunk. Take a look into some of the current "street tire" offerings in the 200ish treadwear category. We run on BFG Rivals and can get 30-35 hours of racing out of a set (obviously proper alignment is very key here).
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post #8 of 16 Old 02-04-2016, 08:01 PM
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Many years ago I ran a track day in my then new 1986 GT. It had the GY Gatorback tires and running the car stock I overworked the outside edges of the tires and "chunked" them badly. The tires back then just couldn't handle the abuse. Today there are many street performance tires that can be run on a road course without issues.
More camber when on track is better. With adj. camber plates you should be able to go up to 2-2.5 deg. neg. for track duty. Going higher can lead to uneven front tire lock up and flat spotted tires, ask me how I know this.

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post #9 of 16 Old 02-05-2016, 08:24 AM
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I'm running 2 1/2 degrees and the body roll was eating it up so I went with a larger front bar and it's much better now.

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post #10 of 16 Old 02-27-2016, 08:56 PM
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If you don't need anything larger than a 275/18, look at the Bridgestone Potenza RE-71Rs.

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post #11 of 16 Old 02-29-2016, 01:24 AM
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I autox my 90 and have 2.7 of neg camber (most I can get with plates) and the stiffest front springs I can get that aren't custom made (H&R Super Races, the white ones), and I was still eating the outside of the tires. I slapped on a bigger front bar (34mm) and that reduced roll but also caused too much understeer. So I slapped on the small bar again (23mm from a 4yl) and did something a little unorthodox. I didn't want to go full coilover since I've heard stories of the strut towers not being able to handle the extra weight of the engine and subframe plus the already present damping forces. So I decided to leave the H&R springs in the subframe but add a set of 175 pound springs with a coilover setup on the struts. It reduced roll quite a bit and didn't have the understeer I had with the big front bar. Here's a pic of what I did. The helper springs are needed cuz the red springs are barely preloaded while the car is sitting still, they come into play under breaking and cornering, because of this I added the helper spring so they wouldn't separate completely from the tophat during full droop. My tires are no longer being trashed on the outside.
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post #12 of 16 Old 02-29-2016, 01:27 AM
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Also, the Rivals have more meat on the shoulder and are a very good tire for cars with crappy camber curves that tend to destroy the outside of the tire.
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post #13 of 16 Old 02-29-2016, 10:14 AM
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Quote:
Originally Posted by karloz View Post
I didn't want to go full coilover since I've heard stories of the strut towers not being able to handle the extra weight of the engine and subframe plus the already present damping forces.
This is a somewhat common misconception with no bearing on reality. Ignore any advice from the person who told you this. Tons of cars out there doing HPDE and serious auto-x with coil-overs and I've never heard of any sort of strut tower failure.

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So I decided to leave the H&R springs in the subframe but add a set of 175 pound springs with a coilover setup on the struts.
That's an...interesting solution. Let's see, your wheel rate from the springs alone should be (1000/4)+(175*.9)=407.5. You could get that wheel rate with a 450# coil over. That's quite a bit, I'm not surprised the car is now flatter. For instance, I run 375s, the max recommended for Koni yellows, so my wheel rate is 337.5.

I'm very curious to see what Jack has to say about your setup. My guess is he is going to tell you to ditch the H&Rs and upgrade the 175s to an appropriate rate for your dampener.
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post #14 of 16 Old 02-29-2016, 12:39 PM
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Would the wheel rate actually be the sum of the two components? Using the above rates, the H&Rs by themselves would yield a wheel rate of 250#, whereas the C/Os by themselves would yield 157#. Wouldn't the C/Os just be riding along? I'm having trouble understanding how the C/Os help at all.
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post #15 of 16 Old 03-03-2016, 02:34 AM
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Sorry, even though I'm a little familiar with motion ratios and the like I didn't really do any serious calculations before going this route. It was more of a trial and error plus experimentation journey. The 175 wasn't really chosen mathematically, it was just the 2 softer springs of 4 that I got pretty cheap on ebay, the other 2 are 300 LB.

I've had the car since December and I've done 5 autocrosses and one tarmac rally with it.
1st autox I did with the Konis on 4cyl front springs/unknown rears (springs were on the car when I got it)... horrible. Too sloppy everywhere with ample bodyroll. I was rolling the sidewalls on the front tires until I inflated them to about 45 PSI.
2nd autox I had the Konis plus the H&R springs with a 33mm front bar (or 34mm? whatever the stock LX 5.0 front bar is) and 17mm rear bar. A bit less bodyroll, too much understeer for my taste. Still eating outside of tire.
3rd autox swapped the front bar for a 23mm from a 4banger and grabbed a 24mm rear from an SN95. Loved the balance, no more plowing but still had too much bodyroll and was still eating the outside of the tires. The 24mm bar let me know my LSD was tired, I had a lot of inside wheel spin.
5th autox I went with the 17mm rear bar to help the LSD and it was my first event with the 175 springs on the strut. Car felt nice with a hint of understeer which I can probably dial out once I rebuild the LSD and put the 24mm rear bar back on. Less bodyroll. Less or barely any outside tire wear.

The entire time the front camber was at -2.7, can't get more without installing some camber bolts or going with SN95 LCAs.

The coilover springs are definitely NOT "going along for the ride". Right after slapping them on I had to ramp up the knob on the konis a bit cuz it was rebounding too much after dips. I went from 1 turn to 1.5 turns. max is 2.

Maybe in the future I'll get rid of the H&R springs and grab a stiffer coilover spring. When I first did this though, I was scared to mess the towers up since they dont actually support the weight of the car. The motor sits on the subframe, the springs push up on the subframe from the LCA and the body sits ON the subframe while the towers handle the damping forces. I felt that adding the weight of the car to those existing forces would be too much. Guess not.
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post #16 of 16 Old 03-03-2016, 10:02 AM
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While I have heard of some Mustang owners seeing strut tower damage it was only after very hard use on track or should I say "off track". It can also happen to a street car but again only after doing some "Dukes of Hazard" type stuff first.

I raced my '93R for all of the 11 years I owned it and for most of the time it had coil overs on it. I ran rates as high as 600lbs! But most times it was 400-450 lbs. That's with a weight of 3200 lbs (Driver included). I did shift the engine back so my F/R balance was better then a stock Fox, so that helped as well with front tire wear. I also never ran more then -3 deg. camber and often less as I had RF tire lock up problems under braking.

Sometimes your driving style can make front tire wear worse than it needs to be. On a Fox you should get the car slowed down by corner entry and then get on the power as you aim the car at the corner apex. This shifts the weight of the car onto the rear tires as well as helping to "rotate" the car reducing the load on the front tires and the amount of wear they get.

Look at how you drive the car in the turns and then see if your trying to carry to much speed into the turn and just when you do apply power. It could be that a simple change in your driving style could reduce your front tire wear with no loss of lap times.
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