how much will tires affect suspension feel?

[tommyturbo]

Ok, maybe a dumb question. I've got a very clean 1990 I got last year, as well as two 95's.

I've never had a SHO with the 215-65-15 tires, which is the original oe size on the 90. They are a fuzion hri, and I don't know much about that brand.

My 95s have the oe 215-60-16, and even over the years I ave noticed that brand and type of tires change how they feel as well. My 95 ATX has bridgestone potenza grid which feel like they are super low profile and as responsive in cornering as a BMW, really sticky, very tight, no slop. Same car with some all season pirelli's felt really loose and soft.

So back to the 90. It feels soft and sometimes kinda loose. Like there is a disconnect, like driving my grandma's old cadillac. The car has new sensatracs all the way around (done before I bought it) new subframe bushings (I just had them done). All the tension rod strut bushings are in very good shape, and the cups don't look like they have come loose. Tie rods all look good (look like they have been replaced at some point not too long ago) and when yanking on the wheel at 9 & 3 I don't hear any clunking or clicking, it just moves the wheel and the wheel on the other side as well. from 12 & 6 it's tight, no movement. The car was aligned recently after doing subframe bushings.

The car doesn't seem to pull on a level asphalt road, but will follow the crown slightly depending on which way it goes. If the road slants right, car will go slightly right, and if road slants left car goes slightly left, seems normal. If road is level car will track straight with the steering wheel dead on. Which is good. But it seems like some textured concrete freeway road surfaces seem to make it wander some. On big fast sweeping corners it seems to hold path ok with out having to do re-adjustments to the steering. Sometimes it seems like under moderate accel it may need some course correction, but under light or heavy it doesn't.

So would the really tall tires cause some of this feel? Or are these just a crappy tire? I'm no great mechanic, so am I missing something? need to replace the motor mounts, which I have ordered, but doubt they would cause the feelings. I just hear a light clunk sometimes from a dead stop and have the polished spot on the front intake.

 

[rubydist]

the 90 should feel stiffer than the atx because the mtx cars have stiffer springs.

the taller tires will make a difference on the "feel" of the car, and as you noted the brand/style of tires will make a difference as well.

another factor is that various tires need differing amounts of air pressure to "feel right" on the car, so I would start by increasing the tire pressure in the 90's tires to see if that makes a difference.

I also am not particularly a fan of the sensatracs, since to me they feel way too soft under small suspension travel. On large bumps they stiffen up, but for relatively smooth roads they feel "floaty" to me.

 

[zblackbeast]

^^I agree with everything you just said aside from the sensa trac part.. I had a 92 with moog/sensa trac and I felt it handled and rode well..

I would decide what you want and buy a tire and pressurize it to take advantage of the tires capabilities.

I liked my potenza g019 grids. They sucked in the winter but spring/summer/fall they were great. Responded well, rode well and werent too loud.

 

[tommyturbo]

yah, it's not a firmness like ride, but like a rubbery disconnect in the way the car responds. And sometimes just seems like it needs alot of minor course corrections. My 95 ATX has the potenz g019 grids. I have the bigger sway bars 24/26, but kept the softer springs, and it has sensatracs as well. That car feels very good.

I've bumped up the tire pressure some on the 90, might try going higher and see, but I'm at 38 PSI now. Door sticker is something absurd like 30 PSI. I wouldn't mind some different tires, but it's not an easy size to find now, and I'm a purist about keeping things stock and not a big modder (obvious visual mods). Could never put different rims on in place of the black basketweaves the 90 has.

 

[rubydist]

lots of minor course corrections can be due to the toe-in being off. while the factory spec allows for some toe-out, in practice this makes the car hard to drive. also, too much toe-in is hard to drive. you might get that checked.

 

[tommyturbo]

I just had alignment done, should I take it back? It doesn't need the corrections all the time, sometimes it's really good (seems happier on asphalt pavment) and seems to have the slight wander more on textured concrete on the fwy.

If I recall from the sheet, both left and right were set to (.05 in) for a total of (.10 toe in). The print out is not clear what unit of measure this is, but I am guessing tenths of a degree.

 

[kevinspann]

Those should be in degrees....should be Toe Out, not toe in...

 

[RonPorter]

I would suspect alignment, then play with tire pressures.

I had 215/65/15 on my '89, then went to 215/50/17 on 7.5" wheels. Obviously, those felt sharper, but not THAT much.

Yeah, different tires can have a far different feel, as each tire brand can have different sidewall stiffness.

FWIW, I run 36 psi COLD, and always have in all the SHOs I've had.

 

[tommyturbo]

I will look at the print out again when I get home.

 

[rubydist]

Those should be in degrees....should be Toe Out, not toe in...

NO see my post above - toe out makes these cars hard to keep straight on the road.

I have had the best experience with toe-in between 0 and 1/8"

 

[tommyturbo]

ok, pulled out the sheet from shop.
both of the front have -0.10 on each side and a total of -0.20 degrees.
caster is 4.6 left and 4.7 right
camber is -1.6 left and -1.4 right.

as for tire pressure, right now its at 38 cold, should I try higher or lower? I would think lower would just make it softer feeling. the 30 on the door sticker makes the tires look flat.

 

[kevinspann]

Are there stock springs on this car? The negative camber seems a little high if that's the case. Have the plates on the strut tower been drilled?

 

[tommyturbo]

Yes, stock springs. No welds have not been drilled. My 95 ATX with the original stock springs runs -1.8 on each side and it's welds have not been drilled either. I don't mind the negative camber, and I have not had any horrible inside tire wear. I'm guessing over 20+ years the springs just sag. The rears run about the same -1.5.

 

[someguy35]

Tire pressures will be the biggest difference in feel.

 

[tommyturbo]

Ok, I will try messing around with pressure.

 

[rubydist]

ok, pulled out the sheet from shop.
both of the front have -0.10 on each side and a total of -0.20 degrees.
caster is 4.6 left and 4.7 right
camber is -1.6 left and -1.4 right.

as for tire pressure, right now its at 38 cold, should I try higher or lower? I would think lower would just make it softer feeling. the 30 on the door sticker makes the tires look flat.

typically, a toe of -0.20* means toe-out. (btw, .20* is about 0.10") my experience is that much toe-out will make the car squirrelly as heck especially at highway speeds.

you need about that much toe-in.

since the camber is a little negative, you need a little extra toe-in to compensate for that to avoid wearing the tires on the inside edge.

I would call the alignment place and verify if -0.10 per side is toe-in or toe-out and go from there.

 

[platoribs]

I noticed a huge difference in my 95 MTX when the 24/26 swaybar set went in, however a G3 subframe, ZF rack, Ingalls adjustable rear arms all went in at the same time.

The car feels much more flat in a corner, inspiring more throttle with the tires ultimately being the limiting factor, after the driver... I attribute a lot of this feeling to the swaybars.

 

[tommyturbo]

typically, a toe of -0.20* means toe-out. (btw, .20* is about 0.10") my experience is that much toe-out will make the car squirrelly as heck especially at highway speeds.

you need about that much toe-in.

since the camber is a little negative, you need a little extra toe-in to compensate for that to avoid wearing the tires on the inside edge.

I would call the alignment place and verify if -0.10 per side is toe-in or toe-out and go from there.

I've looked at the sheet, and pretty sure after reading here, that it is toed out. So your saying, that even though ford recommends slight toe out, I should set toe in just slightly? Reason I ask is my 95 is set exactly the same, from the same shop (have the sheet from it too) and it doesn't seem to wander.

 

[rubydist]

yes, that is what I am telling you.


edit
btw, Ford does not recommend toe-out - the nominal setting is 0.10" toe-in. it is allowed to go from 0.225" toe-in to 0.15" toe-out in the spec, but the recommended setting is .10" toe-in.

 

[tommyturbo]

May I ask where you get the range? I don't have a factory service book specs, and the range I am seeing from the alignment print out (not sure where they get specs, but would guess ford) is a range of -0.20 to 0.00 each side and -0.45 to 0.05 total. Sorry I am not trying to be a dick. I looked at the sticky on here at the top of the page, and the numbers are not clear as to range and desired setting.