Michelin Pilot Sport 4S in 295/30/21 backordered - what about 315/30/21 ?

[Bull]

I need to replace both rears on my Plaid and the 295/30/21 is backordered and it will be months before it is available. I did find that the 315/30/21 is available now:
Discount Tire | Tires and Wheels for Sale | Online & In-Person
(I have a Discount Tire certificate so the replacements are free.)

Jamie at @SignatureSales confirms that this MO/MB spec tire will fit the rear on my OEM size 21x10.5 wheels (SV104).

I have a ton of questions before I commit to these tires. How does it look and perform? Will the sidewalls look ok? What about performance, handling, road noise, and efficiency? Anything I should be concerned about?

 

[Bull]

They fit! These are 315/30/21 on @SignatureWheel SV104 with OEM offsets. They are 21"x9.5" fronts and 21"x10.5" rears. According to Jamie the MO1 designation is needed (red arrow). At Discount Tire it is the Mercedes branding. Pics are at low setting (no lowering links) and the mud flaps were made by @M4H4X.

For reference here is the link to these tires Discount Tire | Tires and Wheels for Sale | Online & In-Person

They do feel grippier but I have not had time to test 0-60 times with my Dragy. Road noise does not seem different but I run my tires a couple pounds lower that recommended and that already helps road noise a lot. I started out with the m at 40psi and they were noisier than I like. I amd very happy with the noise now that I have them at 38psi.

The clearance is tight but so far the tire has not made contact. I tested over speed bumps at different speeds. I also have a little more curb protection for my rims due to the wider rubber.

Too early to tell any difference in efficiency. I was at 320 Wh/mile with the OEM rears after 11,000 miles. Will update with the new efficiency after I have driven at least a few hundred more miles.

 

[Bull]

A few more side pics by request.

 

[SignatureSales]

A few more side pics by request.

Brushed Black Triple Tinted matches so well with the paint color! Also, love how the slightly taller tire looks. Matches the front tire and fills up the fender gap a bit better.

 

[Bull]

Brushed Black Triple Tinted matches so well with the paint color! Also, love how the slightly taller tire looks. Matches the front tire and fills up the fender gap a bit better.

I agree completely. At this point I’m feeling like it is just about perfect, red calipers will complete the look for me.

 

[Bull]

Important Update / PSA

I started noticing problems with the Michelin PS4S 315/30/21 rears almost as soon as I put them on.

The problems seem to stem from the fact that the 315s are .5" larger diameter. I started seeing problems related to GPS. Instead of the nav showing me precisely where I was on the road, I was offset from my actual location. The amount of offset changed as I drove around. Also, the garage doors that I have programmed to automatically open stopped working. The screen would say "opening in xx feet" where xx would be anywhere from 10 to 50 feet and it varied each time I arrived. FSD was really bad and was constantly trying to change lanes or turn at the wrong location. Apparently Tesla does not rely solely on GPS for location buy also counts tire rotations between GPS checks.

I also had problems with traction control where my tires would spin during drag strip launches. I'm guessing that was related because it went away with the OEM size tires.

At least in my case these tires are absolutely not compatible. They physically fit but really screwed up things. I took them off and put OEM Michelin PS4S 295/30/21 rears on and all of the problems went away.

@SignatureSales

 

[EightYears]

Seems like we really need some additional manufacturers to create tire choices for these cars.

 

[BitsAndWatts]

Does @SignatureWheel still recommend 315/30/21 M01 for the rears?

 

[Bull]

Does @SignatureWheel still recommend 315/30/21 M01 for the rears?

I have not heard from him and he has not posted any responses to my reports here or elsewhere. Jamie is normally very responsive and is definitely on top of which tires work with his wheels. The tires physically fit but it is hard to look at any other cause when the problems went away after changing back to the OEM tires.

I have one last issue to test and that was slow times (9.6 - 9.8 seconds 1/4 mile) on the drag strip due to excessing wheel spin. Testing on the street, the spin is much less. The next time our local drag strip is open is 7/9 so I'll post how it does afterward.

@SignatureSales

 

[SignatureSales]

Hey @Bull, sorry for the delay response. After talked to few owners who has the same 315 rear in the past few days ( including myself who run 325/30/21 rear which are 0.7” taller in diameter) we haven’t found any owner who had the same issue.

It’s hard for us to explain why that’s happening on your car since we never experienced this issue. My suggestion for now is to keep your rear in size 295/30/21 as you did recently.

 

[Bull]

Hey @Bull, sorry for the delay response. After talked to few owners who has the same 315 rear in the past few days ( including myself who run 325/30/21 rear which are 0.7” taller in diameter) we haven’t found any owner who had the same issue.

It’s hard for us to explain why that’s happening on your car since we never experienced this issue. My suggestion for now is to keep your rear in size 295/30/21 as you did recently.

Thanks for getting back to me on this. I have also gotten the same feedback from others running the 315s. It is hard to ignore how fast the problems went away when I changed tires back to the 295/30/21 size though. One other thing that might be relevant, I am on FSD Beta. Perhaps there is something there that was causing the problems.