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[AlBinVA]

I have done searches on the replacement of runflats with non RF tires and in most cases I read that the non RF (because of a softer sidewall) are often described as mushy on "turn in". Does this mean that this sensation will be realized in every day daily driver situations or only when driving agressively such as taking a cloverleaf on/off ramp at speed? or both.

thanks

[doublevanosrc]

Originally Posted by AlBinVA

I have done searches on the replacement of runflats with non RF tires and in most cases I read that the non RF (because of a softer sidewall) are often described as mushy on "turn in". Does this mean that this sensation will be realized in every day daily driver situations or only when driving agressively such as taking a cloverleaf on/off ramp at speed? or both.

thanks

From what I understand turn in is how the car behaves as soon as you turn the wheel. How much of the car moves in reference to how much the wheel is turned and how the suspension reacts. I just replaced my RFTs this weekend with Michelin PSSs and I already set up an exchange for OE RFTs again. The car's turn in is slower than before, for example with RFTs on in order to avoid something on the road doing 70mph all I had to do was barely nudge the wheel towards the left or the right. Without RFTs it requires the wheel to be turn about a quarter of the way or about twice as much. I can't stand it the car seems to react slower like its lazy or something, definitely very unBMW like. I never knew RFTs would have such an impact on the steering but i guess everything is tuned for RFTs. Aisde from the turn in the PSSs are great, quiet, comfy and with loads of grip but I cannot stand the lazy turn in.

[GaryS]

Originally Posted by AlBinVA

I have done searches on the replacement of runflats with non RF tires and in most cases I read that the non RF (because of a softer sidewall) are often described as mushy on "turn in". Does this mean that this sensation will be realized in every day daily driver situations or only when driving agressively such as taking a cloverleaf on/off ramp at speed? or both.

thanks

You will feel the difference on pretty much every turn. But putting it in perspective, Michelin PS2 and now PSS are intended to be the best all-round street tires in the world. No one complains about lack of sharpness or steering response with these tires unless they were used to runflats or extreme performance track tires. Actually, most reviewers make a big deal about how good the steering response is with PS2 or PSS.

If sharpness like the runflats have is very important to you, I think a better alternative would be extreme performance track-oriented tires like Yokohama AD08 or Dunlop Star Specs. I use AD08 on my track wheels and PS2 on my street wheels. AD08 are harder and noisier like the runflats, and they have awesome sharpness and steering response and tremendous grip. Still, I personally prefer the comfort and quiet of PS2 or PSS for street.

[VMRWheels]

I'm sure you've driven cars with non-run flats. It's a pretty dramatic difference between run-flats and non especially if you daily your car. Honestly, the ordinary driver probably won't notice a difference unless you pointed it out to them and had a side by side comparison. Just as everyone stated, a soild non run flat would be the PSS's

[doublevanosrc]

Originally Posted by AlBinVA

Does this mean that this sensation will be realized in every day daily driver situations or only when driving aggressively such as taking a cloverleaf on/off ramp at speed? or both.

The mushy feel is there ALL the time from your driveway to the highway. It's amazing to me that it's such a huge difference IMHO. My E46 330 with PS2s wasn't like this and it didn't have runflats.

[GaryS]

One more thing about this. My impression is that most people on this forum replace the stock 215/245 tires with 225/255. That by itself causes a noticeable increase in ride comfort and decrease in steering and handling sharpness.

[AlBinVA]

Thanks all, have a better understanding now.

[icabod7]

Originally Posted by GaryS

One more thing about this. My impression is that most people on this forum replace the stock 215/245 tires with 225/255. That by itself causes a noticeable increase in ride comfort and decrease in steering and handling sharpness.

Gary, can you explain why a wider tire up front would cause a decrease in steering and handling sharpness? My impression was that wider tires up front (especially when very close or identical to the width of the back tires) decreased understeer at a minimum and in some instances produced neutral handling or even oversteer. I would expect the car to not "push" as much in corners with wider tires at the front. Of course in this case the same width proportion to the stock setup are maintained -- but I still don't see how that would cause worse steering and handling sharpness. I'd expect better traction in the back due to the increased contact patch, but not necessarily worse handling.

[GaryS]

Originally Posted by icabod7

Gary, can you explain why a wider tire up front would cause a decrease in steering and handling sharpness? My impression was that wider tires up front (especially when very close or identical to the width of the back tires) decreased understeer at a minimum and in some instances produced neutral handling or even oversteer. I would expect the car to not "push" as much in corners with wider tires at the front. Of course in this case the same width proportion to the stock setup are maintained -- but I still don't see how that would cause worse steering and handling sharpness. I'd expect better traction in the back due to the increased contact patch, but not necessarily worse handling.

Between 215 and 225 street tires on the stock front wheels, I don't know which ones give better traction for less understeer. I expect that varies from tire to tire. I'm just talking about sharpness and precision.

With a 215 tire on the 7.5" wheel, the sidewalls are straight and taut. With a 225 tire on the same wheel, the sidewalls bulge, which allows them to flex over bumps and absorb more road shock for a softer ride. But it also allows the sidewall to flex on turn-in, which causes a mushy feeling and delay in response.

[Dackelone]

Going with the 225/255 tire setup - the tires are slightly taller and wider than the 215/245 OE tires. By slightly I mean like a few mm's. (~10mm).

I think the 225's up front work really well. I noticed with my car the high speed bump steer(over 120 mph) was much less with the 225's vs the 215's. Apparently BMW AG must think so too... bc on all the F20's and F30's they come with 225's/245's (front/rear).


The thing to remember when replacing your tires is to choose the best possible, highest performance tire you can afford. No question, the Michelin PSS (or in Europe the PS3's) are THE best tires you can buy.

When I was looking at non RFT tires... I discovered that there are XL rated sidewall tires and standard tires. I wanted to go with the XL rated sidewall loads, bc the sidewalls would be stiffer - than the same tire without the XL rating.

I also run fairly high pressures in my PS3's. 2.3 Bar (33.3 psi) up front and 2.8 Bar (40.6 psi) out in back. I feel this makes for a decent ride while giving the car decent turn in response/handling.

As far as how I can describe "turn in response" to you... the best way would be to say drive at highway speeds and moving your steering wheel just a bit left or right. See how little motion you can input before the car starts to track in THAT direction. With run flats I'd say the amount you need to turn the steering wheel is 1/4 inch. With non RFT tires... you need to turn the steering wheel just a tad bit more. I'd say maybe 1/2 or 3/4 of an inch. It is just a ever so slight difference... and I think everyone gets use to the tire response or slip angles or what ever you want to call it. Its just with non RFT you need to turn the steering wheel just a TAD more to get the same response as before with RFT's. THIS is the only downside to regular tires.

And I would be that IF you were to install all the front M3 control arms and links... the turn in would be far better than with RFT's on an OE suspension.


I really LOVE my PS3's. I would not go back to RFT tires. I do have RFT for my winter tires... and when I switch over from one set of wheels to the other... this "turn in" issue is most noticeable. But after a weeks worth of driving - you adapt and forget about it totally. Non RFT will OUT PERFORM RFT's in every other performance category! You car will still handle great and be responsive. Trust us 1addicts... you won't be unhappy.


Run Flat tires vs Normal tires - dealer cut away carcus...
http://www.1addicts.com/forums/showthread.php?t=412903



My new Michelin PS3’s 225’s & 255’s…
http://www.1addicts.com/forums/showt...chelin+PS3%27s

[icabod7]

Originally Posted by GaryS

Between 215 and 225 street tires on the stock front wheels, I don't know which ones give better traction for less understeer. I expect that varies from tire to tire. I'm just talking about sharpness and precision.

With a 215 tire on the 7.5" wheel, the sidewalls are straight and taut. With a 225 tire on the same wheel, the sidewalls bulge, which allows them to flex over bumps and absorb more road shock for a softer ride. But it also allows the sidewall to flex on turn-in, which causes a mushy feeling and delay in response.

Gotcha -- makes sense.

[doublevanosrc]

Got some OEM RFTs back on the 1er, glad to have the sharp steering back.

[bmw1racer]

^ Can't see the image.

[ZIPNBYE]

Firstly...BMW doesn't install run-flats on M cars.

Secondly...while run-flats have stiffer sidewalls, the overall impact of them on every aspect of handling is worse. Increasing unsprung weight (half the weight of the suspension arms and full weight of the brake assembly, wheel, and tire) causes slower steering response, slower acceleration, slower braking, and harsher compliance with bumps. (Thus why BMW doesn't put run-flats on M cars!)

Thirdly...if you ever take your car to a track, you'll hate the run-flats.

Fourthly...given the added price (sticker shock many times), the liklihood that you'll have to replace the tire if you drive on it while flat, and all the other negatives, the "butt dyno" of what you percieve the turn-in to be with the run-flats vs. regular tires comes down to zip, nada, nix, nothing, etc...

[EuroTunerz5]

So far I have been happy with my new set up.... Difference is not noticeable. Running a 19x8.5 et45 with 225/35/19 Khumo Ecsta SPT. Nice and firm just the way I like it with tons of grib and response

[bmw1racer]

Originally Posted by ZIPNBYE

(Thus why BMW doesn't put run-flats on M cars!)

Does this mean the M-cars have a spare tire or similar?

[Tom K.]

Originally Posted by bmw1racer

Does this mean the M-cars have a spare tire or similar?

No, like Porsche and some others, they are provided with a "mobility kit" generally consisting of a 12v compressor or CO2 cartriges, and either a sealant or plug kit.

And for those who object to the non RFT's "mushy turn in", it only affects feel - not grip - and may be ameliorated by increasing the tire pressures a few psi over stock.

Tom

[ZIPNBYE]

Originally Posted by bmw1racer

Does this mean the M-cars have a spare tire or similar?

Nope. They receive the BMW mobility kit, which you can buy too. What kills me is that they don't even supply the cars (with oem RFTs) with a jack anymore.

[bmw1racer]

^ The mobility kit looks like a really good deal, considering all the money you save when switching from RFTs to non-RFTs... I'll definitely get one when I replace my RFTs with non-RFTs in the future.

EDIT: Hmm, my car has TPMS. The sealant used in the mobility kit might be a problem...

[Dackelone]

Originally Posted by bmw1racer

EDIT: Hmm, my car has TPMS. The sealant used in the mobility kit might be a problem...

That is why this is always in my trunk...

[alvitdk]

Originally Posted by bmw1racer

^ The mobility kit looks like a really good deal, considering all the money you save when switching from RFTs to non-RFTs... I'll definitely get one when I replace my RFTs with non-RFTs in the future.

EDIT: Hmm, my car has TPMS. The sealant used in the mobility kit might be a problem...

Well, I always carry the green slime thing with me and used it twice, it is TPMS save!

[BrokenVert]

Hey dack, whered you get a doughnut that actually fits over the front brakes?