SC300T

Since I've gone to 17" wheels, the directional stability on my car has gone to s#!T. When it had 15" stock wheels and Michelin MXVs, the car was a pleasure to drive on the freeway, it knew exactly where straight ahead is.

Now that I have the 17s on the car, it follows every rut in the highways, darts left and right, and will only go in a straight line if the highway is perfectly flat (as in brand new pavement). I've had it aligned twice, once to factory specs, and the second time to tweaked settings, but the problem is the same.

I've got 40 offset 17x8 monsoons and 234/45/17 Dunlop SP5000s in front and 275/40/17s in back.

Does anybody have any experience with this? Could tire brand / type cause this? Could the offset cause this? Supras with this size wheel have 49 or 50 offset, as to the GS400...

I don't understand why our GS400 doesn't have this same tendancy as it has the exact same wheel size and tire size.

The thing I don't understand is that I only went up from 215 to 235 in width, not exactly a huge change.

I'm thinking of putting the GS400 wheels on the car to see if its the wheel/tire combo...

Any ideas?
Any help would be greatly appreciated.

FastSC300

hey scott
it might be the off set....I think I have a 45mm offset on my 18's and hold the road great. I have 255/35 in front and 285/35's in the rear. But my SC does drive really smooth with the stock wheels and tires. highway driving is like butta. You should get some used supra TT rims and tires...that would look great!

Scot hail
93 SC300 5 -speed

abdul10000

I have the same problem. My tires are 235 40 17, but my off-set is 35mm on a 8' wheel.

SC300T

Digging into the problem a bit tonight, I put the coupe's 40 offset 17x8 wheels with Dunlop SP5000s on our GS400.... I'm on to something... Now the GS400 adapts much of the same tendancy - darty steering, doesn't know where straight ahead is... So, its either the 40 offset or the SP5000s or a combination of both. I immediately found that the SP5000s are quite a bit quieter than the Michelin Pilot Sports. Unfortunately, that is the only place they are better than the Michelins. The Michelins ride better, stick better, and the steering feels heavier. The Michelins are also round, which is a good tendancy for a tire to have. The SP5000s have an imbalance that could never be cured, whereas the Michelin seems in perfect balance. I've got it narrowed down to either tire or offset... I think ideally the best combo would be Michelin Pilot Sports on 17x8s with earplugs and a 50mm offset. I originally wanted to put the GS wheels on the SC, but with the Supra Calipers, there was absolutely no way... The spokes on the GS rims are just too close to the hub of the rim.

If anyone has a plus size tire configuration that DOESN'T follow ruts in the highways, please share!!! state the wheel diameter/width and offset, the tire size and brand....THANKS!

FastSC300

I have enkei RP01's 18x8.5 45mm off set and 18x9 with 45mm offset...My tires are Nitto 555's in front 255/35 and rear...spo2(?) 285/35's..good luck.
SCOT

mkilty

I am running 245-40/18's front 295-35/18's rear using OZ Opera wheels. Hmmm....I can't remember my offset but I'll try to find the spec's around here somewhere.

Now I am running SO2 Pole Positions and have NO darting problems BUT my previous tires were SP9000 and how BAD tracking with the car following every groove on the road. There were times when I had to fight the wheel to keep it from following grooves.

SP9000 - problem
SP5000 - problem
SO2 pole position - No problem

Pattern maybe?

ChrisK

iTrader: (1)

In December I put the set of new SP5000s on my 95 SC400's stock 16 inch wheels, and the first thing I noticed is the same problem you are describing.
Now, after I drove 2,000 miles, on them, I don't feel it as much, perhaps I got use to it. One thing I still notice is that with a strong side wind the car is more difficult to control that with the stock tires.

Hopefully this helps,

ChrisK
95 SC400

kmn5

I have been wondering about this......
How do the SC's take to having front and rear wheels thats are the same size: 235/45/17's
The factory wheels on my car are the same size, so it should be OK, right?
But I've notice that many of you that upgrade go whith a wider rear set.
Any comments or opions?

Thanks
Ken

SC300T

I think for most, its an appearance thing... The SC has ample room under the rear fenders for substantial rubber. It just looks RIGHT. For me, with the turbo, I need the extra width for traction. Even 275s aren't wide enough to handle the power. There have been comments that the SC oversteers a bit in stock form, so the extra width in back will bring the handling closer to neutral... The Supra TT which shares the same platform, has larger rear tires as well... There is a MAJOR downside, though - you won't be able to rotate the tires front to back...

If you're inclined to stick with all four the same size ---235/45/17, you can't go wrong... Its the proper diameter, has no clearance problems, will look good and is not much of a jump over stock to kill the ride...

I'd make note of this thread, though and get the proper offset - on a 17x8" rim should be 50mm or very close. The tire brand / model is also critical on these plus sizes, as it seems like the dunlops although a quiet tire, are prone to wandering and following ruts on the highway... The Michelin Pilot Sports are excellent in every regard except they are noisy.

abdul10000

Hello

Just a side note. With the 235 all around the car will understeer too much, that’s from my own experience.

SC300T

do you mean oversteer?

why would a narrower tire in back (all 4 the same size) increase understeer? More tire width = better dry lateral grip, right?

abdul10000

Hello Scott,

What you are saying is very true. A car with a narrow tire in the rear will oversteer. When moving up from 215 to 235 the car will show its original nature which is understeering, and if you look at the cars design and weight destitution, you will come with the conclusion that the cars nature is understeer. That's what I personally experienced. Now you may recall when I left a post asking about the off-set, and left a comment about moving up to 275 in the rear, you may ask why would I do that if the car is understeering, knowing that changing to bigger tires in the rear will not change the understeer problem. That is true, but from so many tests I noticed that the car in some turns does oversteer. To sum everything up, The 235 set is great and there is nothing rung with it, but this set will reveal the cars real nature. Any one disagree please tell me what you think, as I am not an expert in cars handling natures.

VeilsideRSPsc

i used to have 235/40/18 all around... and the ride was decent not much worse than stock. having switched to 245/35/19... i've found the ride quality decrese tremendously. i basically feel every bump or crease in the road..sucks. im about to switch to 285/30/19 on the rear and 255/35/19 on the front. hope that helps out the ride.

-brian
'92 veilside rsp soon to be turbo sc300
'01 silver is300

JBrady

Wow, this is interesting. I was just about to buy a set of Dunlop SP5000s for the LS. I bought the car (certified with 52k) and it had/has Dunlop SP4000s and I have never thought the car had a proper on center feel. I never even considered this to be a tire problem. While this is non-conclusive I am going to have to reconsider my tire choices. Bummer because the SP5000s sounded like a great tire at a great price.

abdul10000

Hello Brian,

I don't think you will feel a much difference, if you are going with the same tire, what brand are the 245s. What is the off-set of your new wheels?

Abdulrahman