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.

Don't forget that we also got to keep our identity as the Germans never kicked our ass in war- not once or even twice. But hey, thanks for the waffles with the big squares, they're tasty!

But I have to agree with @projectXTR, the metric system is much easier and much more intuitive!

This thread is making me rethink my desire to get 245/40/17 when I get my summer wheels. Even when it's above 60 degrees here during the day, it's rarely that warm when I leave for work. There's probably only a two-three month period in the year where I'd be able to use these tires if they're no good below 60 degrees.

this thread actually brings up some great points about the reality of wider tires and that they aren't necessarily better for street performance (maybe worse in a lot of cases).

There's a tendency to set up our street cars like they're track cars when a lot of guys dont actually drive on the track very often. It's nice when a little bit of education comes around, but ignorance is king.

^ Yes lots of good points brought up in this thread. I'd like to thank everyone for chiming in and teaching me a thing or two about tire setups.

The first thing I thought when I actually tried out the tires was "did I ruin the balance of the car?". I'll have to wait for warmer temps to see as I'm putting the winters on shortly.

Might have to go back to 215/45/17 if that is the case.

I do plan on getting some RCE yellow's and a rear strut bar next spring so we shall see what happens :)

Yeah. For a street car with ~200HP, 215s or 225s with good compound are probably enough for most folks.

Maybe even 205, as imho eg. MPSS of 205 will still be slightly grippier then stock primacies of 215. Also 205 was stock tire width for 16" options of lower FT86 trims.

Also it is good to look at tire cost, because these summer tires do not last that long, so you are going to replace them more. And 245 are at minimum $30 more a tire, and even 225 tires can be more expensive.

And weight is worth thinking about too. Wider tires and the wheels for them weigh more, and for daily driving that can hurt not just performance but also handling and gas mileage.

Interesting, I have the same exact tire and wheel spec except different brand wheels and mine handles amazing well; much more grip than stock primacys. However I did get coilovers and running camber front and slight in back. Also lowest temps I've driven in were around 65F here in SoCal.
In regards to mileage and wear I can attest that mileage has gone down for me however slight and of course tire wear will occur much quicker.

I haven't had a chance to AutoX or track yet with the new setup.

P. S this is my first true sports car so I'm still learning the ways about tuning/car handling characteristics with the help of this community.

Hope you get your setup to your liking👌🏽


Sent from my iPhone using Tapatalk

I have ultra high performance summer tires and even when the temps are 40-50F here I have tons more grip than the stockers (225 Front/255 Rear). I am stumped by this one.

I watched this over a few days before posting, I run exact same tire as you, they have about 2k on the, and Im just an hour away from you, so we have pretty much the same weather.
I do notice a difference in grip between say early crispy morning at 5C after cold night, vs during the day at 15C, that is pretty much given. But not to the point that I can't take normal turn due to slipping. This morning was about 10C, cold tires, 2nd gear, about 35km/h, mid turn I was able to get some tc action, mostly because I induced it myself (yank the wheel and play with gas). At about 15C or above, I feel MPSS have noticeably more grip than stockers. Below that it does drop down.

FWIW I track and daily my car on two different sets of rims and tires because they're meant for different things.

Street - 255/30-19 +45 square Pirelli PZero Nero GT
Because they look awesome

Track - 225/45-17 +45 square MPSS
Because they drive awesome after a couple laps

You would think that a naturally aspirated car couldn't break those 255s loose, but since I can barely get them up to temperature even here in Phoenix, I can slide them sideways all day long. TC is never turned on in the car.


Tapatalk - because smoke signals would be too easy.

I'm assuming you traded for a set of used tires?

You may have tires that are heat cycled out or otherwise beyond normal/advertised usable grip due to neglect by previous owner.

-alex