135i - Switching to different tire type/brand in rear only - Bad Idea?

An unscrupulous nail jumped into the left rear tire of my 135i. Obviously, it needs a new tire.

I'm still on the OEM run-flat Bridgestone Potenza tires. I've been thinking of switching to the Michelin PSS. However, the front tires still have plenty of tread life left.

If I just switched out the two rear tires to the non run-flat PSS, would that be advisable? Obviously, I'd like to replace all four tires, but that seems like a waste of money with so much life left on the front tires. What's the going opinion/best practice? Thanks!!

So, it would be run-flats in the front and non-run flats in the rear? I wouldn't; if for no other reason than because tires are so crucial to suspension and good handling...I think you would adversely affect your car's balance by having stiffer sidewalls up front and more flexible sidewalls at the rear. Either replace the one OEM rear with another run-flat, or replace all 4 tires with whatever you want...if you're looking to save a few bucks, TOYO makes a quite decent performance tire.

I definitely want to eventually switch to all PSS tires, I just hate replacing the front tires with so much life left on them. I am admittedly frugal. :-) It sounds like I'd do better with getting another OEM tire, waiting for the rest of the tires to wear out, then replacing all at once with the PSS. Is that the safer/better performing way to go?

Originally Posted by chronoton7

I definitely want to eventually switch to all PSS tires, I just hate replacing the front tires with so much life left on them. I am admittedly frugal. :-) It sounds like I'd do better with getting another OEM tire, waiting for the rest of the tires to wear out, then replacing all at once with the PSS. Is that the safer/better performing way to go?

Yes. My 135i convertible came with PZeros and after replacing both front tires within the span of about a month...at a cost of $380/tire...I was prepared to switch to the TOYOs this fall...$900 for the complete set. However, that problem was solved when I sold the car in July. Don't be penny wise and pound foolish...running mismatch tires could create another series of problems. Replace the OEM rear tire and have a plan of action to replace all 4 when you've worn down the tread.

Originally Posted by chronoton7

I definitely want to eventually switch to all PSS tires, I just hate replacing the front tires with so much life left on them. I am admittedly frugal. :-) It sounds like I'd do better with getting another OEM tire, waiting for the rest of the tires to wear out, then replacing all at once with the PSS. Is that the safer/better performing way to go?

I went through something kind of similar, somewhat recently. I replaced all 4 with PSS. No nail, but rears were getting a bit low, while the fronts had plenty left. Have you measured your tread? I think my fronts had about 6/32" left. I decided to keep them just in case, wrapped them up in the garage. While a few may say you can go down to as low as 2/32" (maybe only in the dry I suppose?), most might say 3/32", but I'm pretty sure BMW's spec is even greater than that (metric, of course) being closer to 4/32"? Well, I'll just use the 3/32" figure to show how my thinking went, to help justify the purchase :

I used about 57% of the life of the fronts (or maybe 66% in BMW's eyes?), or I could say I'm "throwing away" 43%.

Then, I then figured out what 43% of my most desired tire would be (and not the OEMs, because that's not what I'm buying; twisted logic? yeah maybe sure whatever), would be $181 today.

THEN, I tried to put $181 (or whatever it really was at the time) in perspective. Yes, it's nothing to sneeze at. But- it is arguably paltry compared to the figures that many people easily drop; $1,000 on an exhaust, $1,000 on a bumper, $1,000 on a tune, or what have you.

THEN*, I thought about how if there was *one* single place where your dollar went the very, very, very furthest for performance vs value, yep, it would be the tires. If there was JUST ONE place where you could feel alright about splurging, yep, it would be the tires.

So for discussion's sake, let's say your old fronts are identical to my old fronts. $181 is the difference between questionable(?), compromised(?) driving, and having the best possible summer tires available in the world for your wheels, on all 4 corners, fresh, brand new, full 10/32" ready to go for the winter. IMO, the biggest, hugest difference to me was in the wet. I realize the tread depth plays an enormous role, but I still stand by that.

THEN**, there was a promo going on at the time, some free cash card, was it $70?

If you replace rears, mismatched, I imagine you will increase your oversteer, not just with fresh rubber, but because they just grip way more than the OEMs. FWIW, I am not 100% convinced that mismatching front vs rear is necessarily a bad thing, maybe like 75% convinced. I had a friend who had done so, put on some Hankooks on the rear of his leased Z4 35is, I haven't heard any complaints.