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Thread: Another tire question

  
  1. #1
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    Another tire question

    So Iím ready to pull the trigger on some autocross tires and just donít know if I should go 235s. Iíve read practically every post on this site about wheels and tires. Some of you say 245s donít rub and some say they do. I figure Iíll be safe with 235/60-16s but not sure. Iím currently running 225/55-16 so 235/60s would be .5 inch taller which will clear the finder just fine. I have plenty of room in back its in front that Iím worried about. When I reach my hand over the top of tire to feel how much room is between the tire and strut I can barely get my index finger between the two. I can see some rubbing on the strut as well. Not goodÖ I also notice that my caster plates (pictured) look like I can adjust them and even adjust in toward the engine bay. Can you adjust stock caster plates? Thoughts?
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  2. #2
    OVER-BOOST!! svono50's Avatar
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    Your strut plates are way outboard, I would almost have to guess you have positive camber or at least zero with the plate turned out all the way like yours. Of course, without knowing the condition of your car and also where the k-member located to the chassis it is hard to tell. To adjust, you simply loosen the (3) plate nuts and you can pivot the (2) nut end of the plate inboard to give yourself some negative camber. Now on my own car with the stock springs I was running one side all the way inboard (i.e.- position #1) and the other side one pin position in from full inboard (i.e.- position #2) to have the same camber on both sides. You may be best suited to go to an alignment shop for your first alignment to see if things are out of whack or not. Talk with the shop before going to see if they will perform a 'custom' alignment to your request, some shops won't others will. You cannot adjust your caster setting with the stock onion head plates, only with aftermarket units.

    As for tires, the stock size is 225/50R16, so your 225/55R16's are already taller and the 235/60R16's will even yet taller. Not sure why you are looking at taller aspect tires, especially if you plan on auto-x use. Let's put some numbers to what I am talking about. My own experience and calculations show that the effective rolling diameter of a tire is 97% of the pure calculated tire height from its width/aspect ratio for some additional explanation. A 225/50R16 = 24.11", 225/55R16 = 24.97" (+3.6%) and a 235/60R16 = 26.29" (+9.0%), so you can see that you are kind of going in the wrong direction from an aspect ratio when considering clearances. The rubbing on the strut body is likely due to the dust boot on the strut mount, which is perfectly normal, as I can't see you rubbing with your 225/55's. At one time I did run 245/50R16's on the back of my SVO (drag racing days) and I can say the rear fender lips would make contact with the tires when the suspension compressed enough and those tires are 24.88" or about the same as your 225/55's. I never ran those tires on the front, but I am currently running 245/45R17's all the way around, but on a different width and offset rim, so take that FWIW.

    With all that said, if you want to go to a slightly wider tire on the stock rim, I would suggest a 235/50R16...if they exist but a quick search on Tirerack shows none. Those are just +1.6% over stock, yet offer ~1/2 wider tread depending on the brand of tire. The stock tire size (225/50R16) shows a good selection of extreme performance summer tires, which will work well for auto-x/street use. Heck, the following tires would be my top (3) in the stock size for your use: BFG Rival, Bridgestone RE-11A & Dunlop ZII Star Spec!

    Hopefully I haven't made your head spin too much.
    Ted
    86 SVO Mustang
    17 Cooper S Clubman ALL4

  3. #3
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    Thanks for the input, I've been researching tire combos for weeks now and its not getting any easier. The reason for the 235/60 is because of availability. You can't test fit tires so instead of buying 245s and have them rub I figured 235s would be safe but the only ones available are 60s. And of course money drives everything so buying wheels and tires is out of the question so only tires this year. I guess I will stay with 225s, The explanation on effective rolling diameter sounds fancy and I'll just take your word for it. Thanks
    So if I adjust my strut plates will it seriously affect my alignment?

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    OVER-BOOST!! gbeaird's Avatar
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    It will affect alignment, not sure if I'd call it 'seriously', though. Our 86 ran the hats about mid-way on the tower. Before autocross events, I'd just loosen them and push them all the way toward the center of the car. That provided much-needed negative camber, and a little toe-out which helped for turn-in. I'd drive on them like this, usually readjusting them when we got home. Toe is easy to measure with a tire crayon, and a measuring tape, but you may also be able to find a shop who may do the alignment to your values.

    I'll check to see what tire we're running now, but I think they're 245-50's. We get no rub, but we're running stock springs.
    Gene Beaird,
    86 2R SVO, G Stock,
    Pearland, Texas

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    OVER-BOOST!! svono50's Avatar
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    The 245/50R16's should effectively fit the same as my 245/45R17's as they are virtually the same diameter (24.88 vs 24.91"). Up front I don't think you would have any clearance issues, but in back you may rub the rear fender lip against the outer tread block if you get a heavy compression on the rear suspension. With the stock springs/setup, that takes a pretty good jounce to get down there. The only times I ever clipped my 245/50R16's in back was over a real rough RR track crossing, a heavy dip in the expressway off ramp with a load in the back of the car or with 3 passengers in the car...so nothing to be overly concerned with IMHO. Up front, the strut to wheel clearance doesn't really change as the strut is fixed in relative position to the spindle. You only need to keep 1/4-1/2" clearance to be 'safe' there.

    Back to tire sizes, a quick check on TireRack shows only (2) choices in the 'summer' tire category for the 245/50R16 size, while the 225/50R16 has (21) in the 'summer' category and (9) in the 'extreme performance' category that you should stick to if you plan on auto-x fun. The latest crop of extreme performance tires out there are pretty darn good, to say the least and relatively affordable for their capabilities.

    Moving the strut plates inward will also effect your toe in/out setting, as Gene mentioned, pushing it generally from slight toe in to slight toe out. For auto-x, toe out is a good thing as the car will tend to react to steering input quicker than toe in setting. Toe out setting will make the car more apt to wandering driving on the street as it will be more sensitive to variations in street crown/ruts. Personally I don't mind driving on the street with slight toe out, just keeps my mind from wandering to keep the car on the straight and narrow. It is all up to personal preference, you may not like it or maybe not notice it. Doesn't hurt to try it.
    Ted
    86 SVO Mustang
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  6. #6
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    I am also running stock springs. The tire choices do seem to be pretty limited when you want to go wider on a 16" rim. It gets better on 17" wheels which it the goal next year, so for this season it may be best to stick with the stock size. TireRack has a good selection at good prices for stock size. I do eventually want to lower the gap between the fender and tires with a spring change that will be another day. I'll mess with the strut plates this weekend as well as educate myself on camber, toe-in, toe-out probably help me around the course too. Great help! thanks

  7. #7
    OVER-BOOST!! svono50's Avatar
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    If you do a search on "Mustang self alignment" you can find a lot of information on how to perform your own alignment. This guy has a decent video showing one method of string alignment, but he states to have the same measurement front/rear on the front tire, which would be 'zero' toe. You really want ~1/8" toe out for auto-x use, while street driving is usually recommended for ~1/8" toe in. Remember to set your strut plates BEFORE adjusting the toe setting, because move the strut plates will effect the toe setting. Good luck.


    String alignment video:
    http://youtu.be/0sguZ-gRF9I

    Great alignment guide on a Fox:
    http://www.hotrod.com/how-to/chassis...ignment-guide/
    Ted
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  8. #8
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    Thanks for the help......til next post. Later

  9. #9
    OVER-BOOST!! gbeaird's Avatar
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    We're running 225-50 Kuhmos on our stock rims. We ran 245-50 Victoracers when we autocrossed the car, and had absolutely zero rubbing, so with stock springs, you'll be fine with 245's.
    Gene Beaird,
    86 2R SVO, G Stock,
    Pearland, Texas

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    Update. I went with the stock size. Just for discussion I wanted to bring up the clearance between the tire and fender. I have owned a few fox body mustangs and been around a lot of fox mustangs and don't remember them sitting up this high. Maybe not "sitting up" high but the gap between the tire and finder is greater than I remember. And the pics on this site and all over the web doesn't seem to look like this. I'm not really worried about it just figured I ask opinions. One of my next upgrades is going to be eibach sportlines, although 1.5 inches or less might not change the look much. Thoughts?

  11. #11
    OVER-BOOST!! svono50's Avatar
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    Interesting, it is usually 86's that sit up that high, not the 84's. With that said, not out of what I would consider normal with stock suspension components. One thing to consider was if the suspension arms were ever worked on/removed. If the person putting them back on tightened them down with them in the full droop positions, then you would end up with a higher ride, as the bushings would 'boost' the springs by being under tension. You shouldn't tighten down the suspension arms in any position other than normal ride height, which means the weight has to be on the tires or suspension. If you have poly bushings then you don't have to worry, as the sleeves are free to rotate in the bushings, while the stock rubber units are bonded.

    If you check my thread on Eibach springs, you will see that the Sportlines won't give you their full advertised drop on our cars. You will see something in the neighborhood of 7/8" front and 5/8" rear drop, that is what a former SVOCA member saw on his 85. I saw that same drop on my 86 with the Pro it, so don't be surprised to not see the full 1.5" drop. It doesn't sound like a lot, but even 1/2" is pretty noticeable on our cars.
    Ted
    86 SVO Mustang
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  12. #12
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    I installed poly bushings a few years back and I'm sure I tightened with wheels off and in the air but you mentioned that didn't matter with poly bushings so I'm good there. Yes I did read your thread on Eibach springs and figured it would not give the full 1.5" I really would like to get a lower appearance for both aesthetics and handling but its looking like a bust. What about shocks? The only other thing I can think of is I bought a bunch of parts from a guy years ago who had an 86 SVO he crashed. I sent the 86 shocks to Koni for a rebuild and installed the 86 shocks on my car. Pretty sure there the same? Thanks.....

  13. #13
    Administrator SVOeric's Avatar
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    there was a slight difference between 84 and 85-86 shocks and struts, but that had to do with valving. Physically they are exactly the same

    Polly usually will move better, especially if it was lubed before install, as far as holding the rear up, but most of us don't recommend polly in all attaching points in the rear. Tends to cause binding and snap oversteer.
    Eric C
    SVOCA Webmaster

  14. #14
    OVER-BOOST!! svono50's Avatar
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    Eric is correct, the later shocks/struts were rumored to be valved 'softer' than the earlier units, but spring rates didn't change so there shouldn't be any effect there on ride height. The front certainly should not be effected, but the rear may sit a bit higher due to some binding on the bushings if you are running poly units in all 8 rear locations. I used to run poly's in all 8 rear locations and can speak pretty well about snap oversteer...not fun when you hit even a small bump mid-corner and end up looking at the traffic behind you.

    I spoke with Koni about whether or not my Pro springs would cause any issues with the stock units and they didn't have any concerns with them handling the higher spring rate. My guess is the Sportline's would be similar. Only thing they noted is that the firmness settings would have to be higher to have the same effect on the higher rate springs. You may want to give their tech line a call to see if they have any issues with those units.
    Ted
    86 SVO Mustang
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    Yes I have researched and found poly on upper arms is bad, so where were you guys 15 years ago when I installed them on my car I am planning on upgrading the rear suspension soon. I did see the spherical bearing for the upper is the best route to go but I didn't see them for a 7.5 rear end. I would like to install a Panhard bar but also read that this not good with poly bushings and you get the best out of the panhard bar with a torque arm which I don't see them made for a 7.5 rear. Therein lies my dilemma.... So the only route is to go back to rubber bushings on the upper arms? I would like to smack the genius at Ford who thought is was a good idea to put the 7.5 rear in these cars. Just doesn't make sense when you use axles shafts out of a 8.8 Anyway thanks for all the input. If your wondering why I want to upgrade the rear suspension, I have been bitten by the race bug. I have put some autocross laps in with the local scca club. And yes I have felt the great mustang oversteer that seems to be so prevalent in our cars. I can even see it with new stangs' sorry this turned into a suspension thread.....

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