I had a small problem in handling develop several months ago. The most recent change I had made just before was this.

I was running 245/40 and 335/30 R888. I had removed my front driveshaft to get on a 2wd dyno. Left it off for a couple months and blew through my rear tires.

So in an effort to help tire last longer, I put my drive shaft back in and replaced just the rears with 315/30

Its hard to describe the feeling...its a darty, floaty, side to side sway (but ever so slightly) feeling. The faster I drive the more I feel it. It feels similar to if you've ever driven a too wide front tire car that tracks the pavement like crazy. (I know my tires are wide, but this is a new feeling so something is up)

In an effort to resolve possible issues, I stopped running spacers, tried different air pressures, got an alignment. I checked for loose bushings,bolts etc.

Did I just get a bad pair of tires when I switched to the 315?

 

How much tread difference is there between the pair you already have on the car and the new ones? If there is a difference by more than a few 32nds it will be apparent.

Are the fronts heat cycled? If so they are going to be harder than the more fresh rears.

It's not very warm this time of year, even in TX. Was the test drive done in lower temps (below 50)? R888's don't like to be cold.

Did swapping the drive shaft affect alignment? At all? You may want to have it checked just in case.

 

The fronts had about 4000 miles on them when the rears were put on. They weren't strategically heat cycled, but they were used though the summer. The fronts looked almost new when the rears were put on.

It has been cold even here. Maybe as it warms up they'll start to be similar to the fronts.

When I pulled the driveshaft, it was only the shaft that was pulled, no front or rear differences. And when I had it aligned, they said it was a little off, but not much. The original 335's I had on wore almost perfectly even, so I don't think there was a major change there.

The more I think about it, the more it seems like tires are the culprit.

 

I just had R888's with heat cycling put on in January but just got out today for my 1st drive in 8 weeks for over 100 miles.

I am RWD with GT2 alignment so will post an update on how my tires wear.... I did notice that I filled them cold at 30/33 PSI and got some flightiness as mentioned by the OP (like a sideways pull or shudder) and after only 10 miles on a 40F day the measured PSIs were 33/36.5 PSI...

I dropped them again and it all handles better at hot 30/33

In summer I may run them 28/31.

What PSi were you running stilov ?

 

Stillov, what rear wheel size and offset did you use in the 335? Also, stock suspension?

 

For the 335 I had 18x12 forgelines 52mm offset with a 12mm spacer so I ran 40 total.

I rolled the fenders, heated and molded the liners, even ziptied them back tight.

I was on PSS9 a little lower than stock but not slammed.

 

Wolfhedge.

I have been asking some folks what they run as pressure...I tried 34 front and 36 rear. Now I am running 36 front 40 rear,

No real difference. I didn't think about going lower since it would see that would soften it up...thoughts?

If it has to do with new v old and heat cycles, does anyone think it will get better as I drive. I guess these rears haven't ever really been heated up.

 

I've had a similar, or maybe the same problem on my Turbo. Mine was bad enough I hardly dared to run it over 80 MPH for fear the car would dart out of control and possibly crash. I was running PS2 tires and replaced the rears only with Sumitomo HTR-Z ll. The front PS2 were still at about 80% so I left them on. Actually I did measure the circumference and compared to the new Sumi which looked to be close enough of a match with the AWD to work well.

Early on I did notice some ill handling as I always have when fitting Sumis. It's a matter of scrubbing in for a few days then goes away and handling becomes on par or better then the PS2s for city and canyon sprints. In this case, I was slow to find the issue. I checked and rechecked inflation, even contacted my alignment guy to see if he could align to make the car quit hunting and track straight.

I sat back and studied the issue and realized the problem was the Sumi rears were ever so slightly, different in height from the worn out PS2s even though close to the fronts. I ordered new Sumi fronts, installed them and my car instantly handled better than ever. I was amazed, and I do this type of stuff for a living. Who wooda thunk?

These cars are very sensitive to rake and correct front to rear ride height relationship and also when AWD the relationship between F to R tire diameters. Hope this helps.

 

I have the R888 on the rear (315/30/18) and run 36 PSI. I've found that these ride very well and do not follow the grooves in the road nearly as bad as the Falken RT615 (same size) I had before. I'll keep using the R888 unless I run into disintegration issues closer to the end of their life. A lot of people complain about the tires falling apart rapidly near the end of life.

 

mixing tire brands and tread depths however seemingly insignificant while running awd is a recipe for instability, weird handling and even the dreaded abs/psm cels.

i bet it didn't happen with the cardan removed? when awd, all those rolling diameter issues that get messed with by mixing tread patters/depths crop up when messed with no matter how seemingly within "spec". the system is pretty darn sensitive.

 

Well I guess that's the million dollar question... I put the new rears (315/30) on at the same time I put the cardan shaft back in.

When I ran 335/30 and 245/40 I ran AWD and RWD and never had an issue. I read some threads that said you'd get better front diff action with a slightly taller tire. Well I figured the 245/40 (which is slightly taller to begin with) that had some wear would match the shorter 315/30 being brand new.

Or as Damon had mentioned...does it have to do with heat cycles and tire age? One thing to bear in mind here is that I've never raced the car...so the only "heat" the fronts have had that the rears have not, is summer street driving. Would that even matter?

 

You are way to high i just dealt with the samething as you. I know the feeling LOL......

I check mine in the garage for cold do not run any higher then 35psi in the rear. Start out with 32F 35R

 

Same thing as in the floaty issue?

 

The floaty issue for me happened when my tires got hot i found them over 46psi way to high. I started at that time at 40psi.

I learned alot from 32Krazy.


I finally went out on the street and made the best run without spinning everywhere lol. Start at 32F 35R no higher.

 

There is a good chance that it's the tire height issue. I have seen this first hand with a new set of rears and 1/2 worn fronts...new fronts cured it instantly. But what I had was psm cutting in on mild corners causing very strange handling.