What's wrong with my tires?

[phiebert]

What\'s wrong with my tires?

I just had a new set of Michelin Pilots put on the rear today. My fronts were still good. All of the tires were balanced properly but when I took the car up to about 80 mph it is almost impossible to keep in control on the road. It's like the tires are doing an exaggerated following in ruts. I'm constantly correcting the steering to maintain control. It feels like if I go any faster I will fishtail out of control. It's frustrating because my previous tires were great for control at any speed and didn't do this. It's worth noting that the road I was testing on is newly paved and not rutted.

What is going on? Is it the tires that **** or is it out of line or is it a pressure issue?

 

[-RUNNR]

Re: What\'s wrong with my tires?

Might be a stupid question.....

did they put them on in the right direction? Pilots are directional, so.....

(If stupid, disregard previous mensa testing, and ignore me)

 

[Wing King]

Re: What\'s wrong with my tires?

Patrick, you say "your fronts were ok", but what fronts? Are they old style XGT's, or Pilot MXX3's, or Pilot Sports? If the tires you put on the rear are not the same model and tread pattern as your old fronts, that's exactly why you're having "directional problems". It's recommended that you never "mis-match" the style or tread pattern. Let us know.

 

[jcaspar1]

Re: What\'s wrong with my tires?

Pressure is probably too high. Check that if you haven't already.

 

[phiebert]

Re: What\'s wrong with my tires?

Thanks for the thoughts, I'm having a hard time believing that the tires are different enough to cause that kind of wander, but maybe that's it. The pressure is proper on all tires so I can test it at different pressures but I think that likely is not the problem.

The fronts are the one's on there from when I got the car a couple years ago, probably the original tires the car came with in 94. I guess that makes them the XGTs, I'm too lazy to go out to the garage right now but I'll check in the morning. I would have thought that the tread pattern would be close enough on any of the Michelin high performance tires to keep it from being so bad.

Wing King, are the tires different enough to cause the extreme wander I have?

Steelgts, I'd love to hear more about your problem. Are your fronts the originals too. What do you have on the rear and what on the front? Did you change the fronts and did it fix the problem...if not, wnat to go first?

I'll change the fronts if that is the problem but I'd hate to waste the money on it if it doesn't make any difference.

 

[tradin1]

Re: What\'s wrong with my tires?

Mine does the same thing. I feels like your gonna drive off the side of the road, just all of a sudden, for no reason. Very uncomfortable feeling.

 

[Bill Pemberton Woodhouse]

Re: What\'s wrong with my tires?

Gentleman,

WingKing is on the button, and two things come into play here. The tires DO make a big difference and to put it simply it is do to different tread designs as well as compounding and sidewall strengths. I would imagine that the wandering concern is on rutted roads and it has primarily to do with the enormous size our tires come in. I would strongly suggest a new set of Sports, plus and alignment after they are all mounted. My 2000 , that I got about a month ago, only has 2400 miles on it, but it is horribly misaligned, and this alone will improve some of my problem, but as much as it sounds like a way to sell more tires, the old XGT's are probably worn somewhat unevenly after all these years and they are probably hard as a rock. When replacing make sure you get 285's as this will improve steering response, especially on the track, and spend the extra funds even though none of us want to. I can honestly tell you that the driving characteristics between each model change ( XGT's , MXX3's, and finally Sports ) are an evolution just like any product, but our cars will always wander a little due to the width. Sorry to be so windy, and I respect Jon's view, but testing tires for BFG, Yokohama, and Hoosier over the years, has made me a believer in not mis-matching rubber.

 

[phiebert]

Re: What\'s wrong with my tires?

I'm kind of with McGuire on this, I'm a skeptic when it comes to the mismatched tire theory but I have to admit my car went from riding like it was on rails to acting like a boat without a rudder just by changing the rear tires. I'm going to bite the bullet and get the front tires that match the back and I'll let you all know what happens. By the way, I tested it on the same road I ride every day. It isn't a deep rut issue, and I understand the fact that wide tires will always have some wandering to them.

Bill, which 285's do you recommend. I don't want to compound the problem by getting new front tires that are still 'mismatched'. Thanks.

 

[Chuck 98 RT/10]

Re: What\'s wrong with my tires?

I've heard the XGTs on Gen I were horrible. Several guys I know wouldn't drive in the rain because of them. It might be a good idea to replace them anyway since they might be 8 years old? I agree with JimJon McGuire. The **** has more experience than most and would notice the differences on the street better than the average hacker.

As always, the track is a different story.

 

[Chuck 98 RT/10]

Re: What\'s wrong with my tires?

Jorge, if it's that bad then replace the other two and let us know the results. I have MXX3s on the back and Pilots on the fronts with no complaints.

 

[GTS Dean]

Re: What\'s wrong with my tires?

Tires possess a physical characteristic called Self-Aligning Torque. Tread compound, tread design and casing construction all have an influence on SAT. Throw in additional variable like caster, camber, toe and scrub radius with mismatched tires and you have a recipe for - how shall I put this - an interesting ride.

A few good drivers can think and feel their way through the problems without much trouble, and possibly use it to their advantage. Overall I would consider it a handicap.


BTW, I run XGT-Zs in warm, dry weather and MXX3s in the cooler, wetter months. They perform waaay differently, but the XGTs are better hot track tires.

 

[Tom F&L GoR]

Re: What\'s wrong with my tires?

This is pretty interesting.

One would think all tire models of the same size have about the same amount of actual rubber material contact on the road surface, so it's hard to see that rear tire tread design or compound would cause a big scary difference when traveling straight (excluding rear wheel slippage demonstrations.)

I can understand that sidewall flex or belt stiffness affects how much of the tread contacts an uneven road surface, and hence the rut-roh problem. But this would show up more with front tires rather than rear, perhaps? Rear tires always point in the same direction and it's harder to imagine that slight traction differences at 80 MPH dry road steady speed conditions would "steer" the vehicle. There's no self-aligning torque issue on the rear wheels, is there? And since both rears are the same, we're talking about the rears trying to overtake the fronts?

Alignment makes sense - I yank and replace sport shims and re-do the toe in and toe out, and after a few times occasionally the steering seems light, doesn't feel as if it would "center" when you let go, and hunts ruts... it's fixed by less than a quarter turn towards toe-in on each side. Only need a 15/16 and 7/8 open end wrench and something to lay on. Mark the tie rod and steering rack so you can put it back if you want to. Loosen the clip on the rubber ***** so the threaded rod can turn without twisting the *****. Obviously changing rear tires shouldn't affect front toe in, but maybe the tire carcass on the rear is so different it affects dynamic rear toe? I've fiddling with this, too, but suspect the rear toe would have to change a lot from stock. I would increase the rear tire pressure (make it stiffer) by 10 psi and run around the block to see if that makes a difference. Then try 10 in the front, too.

I'm no expert, but I'm cheap and have run lots of mismatched tires (XGTZs, MXX, MXX3, PZero) in lots of autocross events (yes, not at 80 mph) without anything feeling scary. The tires were always in pairs, I should point out. And as I mentioned, a little toe in or more tire pressure has *always* made the problem go away.

Good thread. And I take used tires...

 

[JonB]

Re: What\'s wrong with my tires?

The tires PERFORM DIFFERENTLY. In fact, place full-treaded SPORTS in the rear, with worn-down SPORTS in front, and the whole handling dynamic changes. And Visa-versa. And that is the SAME tire.

Run a 50% L-rear and a 100% R-rear and LOOK OUT. Same Style!

Those of you who mis-match tire tread designs are making a mistake. Been-there, done that. It was me who posted the Michelin engineer anecdote, 100% truth. [Shame to suggest otherwise.] I receieved 3 identical opinions from 3 Michelin engineers. I wont post their names, so they may be "X" to you, but they talked to me at Laguna, PIR, and Gateway....

--TO RUNNR: Pilot MXX-3s are NON-DIRECTIONAL. XGT-Z and SPORTS are directional.

--My tires were FREE for 6 years (Michelin-sponsored, thanks) not trying to sell me.....and Michelin would NOT let me mix-match for safety reasons. Period. Especially directionals w/ nons.

Patrick proved it.......
Dean and Chuck seconded it....
Bill P ditto.......

I even told one guy that I would REFUSE to sell him tires if he bought em as a result of my safety tirade. Sheeesh.

Mis-match tires, and you could be betting your life on it. And the lawyer who sues you on behalf of whomever you hit (or rent to) will own your house. The plaintiff will win.

Be Safe Out There

 

[Bill Pemberton Woodhouse]

Re: What\'s wrong with my tires?

Guys we are getting too wacko. Everyone go back into the house and put their favorite running shoe on their left foot. Now I want you to to put your best loafer on your right foot. Okay walk around at varying speeds with your little old independent suspension. Don't dat feel good? Now go 120mph .... what you can't do that? Sole food for the mind and the rubber meets da road. Jonknee B and me jest want you to be safe and have fun out there Snakesters.

PS - Go with the 285 Pilot Sport for better steering response, and hope we have all helped out a little.

 

[phiebert]

Re: What\'s wrong with my tires?

Talked to the place where I bought the tires and they too were surprised at my complaint but said that I should try more pressure first before buying new tires for the front. Apparently they put 40 lbs in the new rears to give it a 'softer' ride but the tires can apparently take up to 51 lbs. Even 40 seems high to me because I'm used to around 20 lbs for drag racing but tomorrow I'm going to pump up all around to the maximum pressure for each tire and try again. If that doesn't solve it, I'm going back to get new fronts to match the rears. I just hope that helps because otherwise I'll have wasted perfectly good fronts. I only have 14,000 miles on the fronts even though they are getting old in years.

By the way, one other piece to add to the puzzle. The original tires I replaced on the rears were BF Goodrich G-force. They are very hard and didn't give me the launch traction I hope to get with the Pilot Sports (which I definitely do get now) but they never wandered like the Sports. So the mis-matched theory seems to take a hit with that evidence. That is, the G-force rears and the Michelin fronts were extremely different tires but worked very well together. I had the car up over 170 mph and it handled like a dream. I wouldn't take it over 90 mph the way it is driving today with the new tires.

I'll have more info tomorrow but I would like to figure out the problem with your folks help. Maybe we can have a hard proven case for mis-matched tires at the end of this.

 

[Chuck 98 RT/10]

Re: What\'s wrong with my tires?

40lbs on the rears??? It says 29lbs on the tire doesn't it? Use the recommended pressure first. I would think going up in pressure would make it worse.

 

[pauls]

Re: What\'s wrong with my tires?

***** tire dealer is reading MAX Load (51)vs Mfg recommended inflation (29). That's scary. The quick lub tries to do that all the time on my other cars. They read the tire sidewall vs mfg recommendations!!

 

[Chuck 98 RT/10]

Re: What\'s wrong with my tires?

Even on the tire sidewall it has the recommended pressure 29lbs. I run 40lbs on the fronts ONLY at the dragstrip. I'd drop it back down to 29 for the trip home.

 

[phiebert]

Re: What\'s wrong with my tires?

OK, I finally had a chance to try a few things and I think I have corrected the problem.

First of all, my new back tires are Michelin Pilot Sports and the fronts are the old Michelin XGTZ. The tread pattern is very similar and the fronts are still in pretty good shape.

When I picked up the car from the tire shop the guys there must have been sleeping because the front tires were at 20 pounds and the back tires were at 45 pounds! I didn't test them until today because that's not what they told me they put in them. So this morning I set them all to 36 pounds and the problem has all but gone away. There is still a little rut finding going on but probably normal now for the width of tires. I had the car up to about 130 mph and it felt safe and secure again.

So I'm not saying that mismatching is not a problem, but in my case it seems to be a tire pressure issue. I think the fronts are slightly more worn on the inside of the tire than the outside and that is likely causing the little wander that is remaining.

SteelGTS, I'd try setting all around pressure to 36 pounds or a little less and checking for your front tire wear across the tire. You likely have a similar problem to mine.

 

[SNAKOIL VA]

Re: What\'s wrong with my tires?

Check your toe in and toe out. Too much one way or the other can make the car "twitchy" or have a tendency to wander.

Mine has a tendency to track on asphalt that has linear patching (i.e. the city installs new sewer lines in the drive lane) or on grooved pavement.

Otherwise, it's fine. I have four MXX3's on my 93.

 

[GTS Dean]

Re: What\'s wrong with my tires?

Gen1s on XGT-Zs had recommended inflation pressures of 36 psi. The GTS and Gen2 RT/10s that came with MXX3s have a recommended pressure of 29psi. I don't know what pressures are recommended for the Pilot Sports.

The recommended inflation pressure has *everything* to do with the particular model of OEM tire/rim package installed by the car manufacturer.

 

[Tom F&L GoR]

Re: What\'s wrong with my tires?

My Canadian '94 says 35 front, 35 rear. (Really, it says 240 kPa)

Put a dab of white shoe polish on the shoulder of the tread. Drive around for a while, and some will be worn off by contact with the road. The more "fun" you have around turns, the more shoe polish you'll rub off. Then add pressure if the tire rolls over onto the sidewall, let some out if it doesn't. You're just right when you use all the tread, but no sidewall. After this exercise, you might have different front and rear pressures, but basically you have tuned your tires for your car and for the way you drive it. Done by autocrossers all the time, who often use different sizes, compounds, treads, brands etc from front to back. Well, OK, the cheap guys like me do.