Traction loss with 245/40/17 MPSS
 

Hey guys,

I just traded for some RPF1's in 17x9 +35 offset wrapped in 245/40/17 Michelin Pilot super sports. I Previously had stock wheels and tires. When I had the stock wheel/tire setup the car handled well and had lots of grip on corners (crazy I know).

I took the car to many twisty roads with the stock setup never losing traction or going sideways. I take the same route to work and back every day and there's this one corner I would take with speed to get that "on rails" feeling. After I swapped to the RPF1 with the Michelin PSS I drove around for a bit not really thinking much about the traction. Yesterday I was driving around town and there's this roundabout, got into the corner in 2nd gear and gave it some gas to see how the tires performed. As I was exiting the corner the car got sideways, good thing I had the TC and stability control on! I was surprised and blamed it on the cold temps (dash read 4 degrees celsius).

Today on the way home on my regular route i take the same corner as always just barely giving it any gas and I feel as if the rear end is "floating". It just doesn't feel like it's gripping anymore. My dash read 17 degrees celsius today too btw so this is where I started to question what's wrong with my setup.

Now I've thought about what could be causing this and I've narrowed it down to 3 possible things.

1. My alignment needs to be checked and possibly fixed now that I have much wider tires.

2. It is just the cold temps and I shouldn't be thinking too much of it.

3. The tires are far too worn out.


The car is a 2015 Subaru BRZ with stock suspension. Nothing else on the car has been changed that would affect the handling other the the rims/tires. I am running around 32-34 psi on the tires according to the gauge at the gas station so i don't think it's my tire pressures.


Has anyone else had this type of thing happen to them when switching to a wider wheel setup?

Pics of setup for reference.

http://i128.photobucket.com/albums/p...016_154521.jpg

http://i128.photobucket.com/albums/p...nTypeR/1_1.jpg

http://i128.photobucket.com/albums/p...101047%201.jpg

Have you checked the tire pressures?

Yes I have they're all within the recommended specs.

Were you on all seasons before? Summer tires become ice skates in cold temperatures.
Are the MPSS new or used? Tread depth?
For reference, I am running essentially the identical setup (slightly different offset) and gained a TON of grip.

The tires were used and I edited the first post with a pic of them before I mounted them. I was on the stock michelin primacy hp tires that they come with from the factory.

From the tire pics they look OK wear wise.

4C is definitely too cold for those tires but 17C should be fine. One other possibility is that they have been heat cycled too many times and lost their grip. If that were the case they would probably show more wear though.

Just a note that the alignment doesn't change when you swap tires/wheels.

EDIT: Just to confirm, what exactly were the tire pressures. Remember, the max on the sidewall is NOT in the recommended range. It's what it can handle without exploding. You should be running around 34 or 35 psi.

245s also take longer to get up to temperature.

hmmm okay, so it's probably just the cold temps?

Found it weird that it slid out on me... I guess I'm not used to it since this is my first set of summer tires. When I drove it in the rain when I first put em on I had plenty of traction so maybe you are right about the cold temps.


When I last checked it was sitting around 32-35psi. Couldn't get an accurate reading since it was a gas station gauge.

Outside temp is not the same as tire temp. Summer tires need to be warm before they grip and are very slippery until warm. For reference, you have to run 1-2 laps at 7/10 on a track before really getting on it or you WILL spin. Yes, personal experience talking.

google tells me 17c is like 63 freedom degrees, which can still be pretty chilly for summer tires.

If they are used tires, heat cycles can have an effect as people have mentioned.

Did you check also what year the tires were manufactured?
http://www.discounttire.com/dtcs/infoSidewall.do

Good point, I shouldn't be too worried then.


Will check in the morning. Thanks everyone for the quick replies!:thumbup:

Sorry, couldn't resist :)
http://pre04.deviantart.net/7b14/th/...07-d5p0ou5.png

Yea summer tires that wide probably are nor going to be able to get warm enough to handle really well even in 60 degree weather. There are people who race on the 245's and say sometimes they cannot warm tires that size up.

because the rest of the world always uses the arbitrary metric system, oh wait, no they don't. Brits use a gallon that is a different size than our gallon. Oh wait, they use stone for weight. I could go on. The US system was based on actual use and what was done for centuries, the metric system was randomly created and made up.

I have the answer for you as I currently do have MPSS on my car currently and I also have had experience with wider wheels/tires with lower offsets on others cars (s2000/rsx-s).

First of all the MPSS are ultra high performance tires, so they do need to get some heat into them. I had an incident similar to yours where I took a corner pretty hard when the tires were cold and the rear lost traction instantly in 50-60 degree weather (traction control helped me in this situation or I would have spun). This was on stock 215 sized MPSS tires. However, when temps are higher and you have gotten the MPSS tires warmed up, they grip very very well. In your case, you have 245 width tires, which will take longer to heat up plus you were in cold weather, which contributed to your lack of grip. The stock tires that come in our cars do not need much heat in them to grip.

As for the wheels, you are using wider and lower offset wheels compared to stock. The lower offset will effectively make your car feel softer and more floaty especially on stock suspension. Only way to fix this is to either get a wheel with an offset that is closer to stock (+48 offset), or get stiffer springs/sway bars. The reason for a softer feel is that a lower offset means you're effectively increasing the lever arm, which alters how your suspension responds to the road. That also changes ideal spring/dampening rates.

So there you have it, the statements above is why your car is handling this way.In my honest opinion, the car handles great from the factory and the 215 tires give it enough grip. When you alter wheel width and offset without modifying other aspects of the suspension, you may actually be making it worse.