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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Wheels and Tires Forum Sponsored by The Tire Rack > Runflats improve performance?



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      02-14-2013, 01:52 PM   #1
Antartic
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Runflats improve performance?

I went to the dealer to see what it would take to swap my runflats for non-run flats.

The dealer said that runflats are better for performance for my 335i because the whole handling dynamics of the car was designed based on runflats. He added that the stiffer sidewalls of runflats help maintain their shape during hard cornering.

He agreed that non-runflats are quieter and provide a comfortable ride, but if it is performance that I am looking for (I am) then runflats are my best choice.

Do you guys think he is BSing me, or does he have a point?
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      02-14-2013, 01:58 PM   #2
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Do a search there are so many threads on this.

Do a search there are so many threads on this.
I can tell you my friends that race will not have run flats
on there cars.
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      02-14-2013, 02:01 PM   #3
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1. Your dealer will only sell you RFTs so they have a financial interest here. Check out tirerack.com for more info.
2. Which RFTs and which non RFTs are you considering? There is a big variation among each so make sure you are comparing apples to apples.
3. In general, I prefer the ride and price of non RFTs. Handling is largely dependent on tread design and other factors - so some RFTs will outhandle some go-flats and vice-versa.
4. You'll probably get better responses in the Wheel/Tire forum:

http://www.e90post.com/forums/forumdisplay.php?f=12

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      02-14-2013, 02:07 PM   #4
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Is he BS-ing you ? No, and yes.

No BS - the car is deigned with particular tire dynamics in mind, so if by optimal "performance" he means handling exactly as designed by the factory - then the stock RFs are it and anything else will be a little off.

But I call BS because your perception of "performance" is likely different than the factory's. As you've noted RFs tend to be noisy, and many think they are a bit "harsh" due to the stiff sidewalls. This hashness means more energy from bumps is transmitted through the sidewall to the wheel and into the suspension. Consequently many have reported that switching to non RF's makes for a more enjoyable ride. And any detrimental effect on handling (due to the slightly softer suspension system that you have with non-RFs in the mix) is so slight as to be negligible. Finally the actual performance available on non RFs in the after-market can exceed the stock RFs in grip, cornering, wet and dry traction, etc.

Bottom line is it's impossible to say whether changing will improve or worsen handling - you need to let us know specifically which model of tire you're looking at. One thing I wouild recommend is since your car originally came with summer tires (I believe), don't comprimise with all-seasons, but rather stick with summer tires in summer and winter tires in winter.
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      02-14-2013, 02:07 PM   #5
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it is true that the car's suspension was designed around being able to use runflats, however it will not make it perform any better by using them.

Runflats have their own flaws, that the suspension was designed to make up for.

Not having the flawed tires = better performance.
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      02-14-2013, 02:16 PM   #6
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If the run flat tyre was a better performing tyre then the BMW M division would use them on the M3. They chose non run flat tyres. Enough said.

There is a number of reasons for run flats the main being weight saving of a spare, jack etc which helps co2 and emissions and safety in the event of a blow out
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      02-14-2013, 02:28 PM   #7
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The run flats are great for high speed cornering ability and stability on the road when you are trying to avoid an obstacle but then you sacrifice ride quality since you have a less smooth ride (judder and bumps on the road are more easily felt with run flat). Personally, I feel that run flats are great for more aggressive driving style and are more safe if you have a sudden puncture during motor way driving. You are likely to have better control over your car in such a scenario. My summer tyres are run flat (faster speed on the road) and the winter tyres are non run flat (slower speed on ice and snow). So not every thing is bad with run flats.
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      02-14-2013, 02:39 PM   #8
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I don't like them because because places wont patch them..
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      02-14-2013, 03:03 PM   #9
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thanks for the replies guys. the current run flat tires that I have are performance summer Michelin Pilot Sport PS2ZP.

I was planning to get Pirelli P Zero Rosso.

I am not worried about the harshness of the ride or how easy it is to patch it- I want to make sure the car retains (or improves) the driving dynamics that it current has with RFT tires.

Most of the threads I searched for tires talk about the harshness and noise. Very few had any good discussions of performance (as far as I saw).
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      02-14-2013, 03:21 PM   #10
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Ask the dealer if the factory puts RFT on the M3.
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      02-14-2013, 03:27 PM   #11
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Quote:
Originally Posted by Antartic View Post
The dealer said
theres the start of the problem right there
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      02-14-2013, 03:34 PM   #12
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Quote:
Originally Posted by Antartic View Post
The dealer said that runflats are better for performance for my 335i because the whole handling dynamics of the car was
designed based on runflats.
That is true, but it is not really an "advantage". Because RFT are so bad, the shocks have to overwork.

Quote:
He added that the stiffer sidewalls of runflats help maintain their shape during hard cornering.
If that was the case, non-RFT super summer performance xtreme add your superlative Michelin Pilot tires would be as stiff as RFT. They are not.

All I know, is that I preferred the handling of the non-RFT tires by several parsec. It does feel a bit soft on the stock shocks, but it has very predictable limits, RFT tend to loose it more abruptly, I don't like that.
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      02-14-2013, 04:10 PM   #13
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Quote:
Originally Posted by Antartic View Post
I went to the dealer to see what it would take to swap my runflats for non-run flats.

The dealer said that runflats are better for performance for my 335i because the whole handling dynamics of the car was designed based on runflats. He added that the stiffer sidewalls of runflats help maintain their shape during hard cornering.

He agreed that non-runflats are quieter and provide a comfortable ride, but if it is performance that I am looking for (I am) then runflats are my best choice.

Do you guys think he is BSing me, or does he have a point?
WRONG. Salesman is full of it. Sidewalls being this stiff HURT handling. At city speeds they feel more responsive but at speed they are not. Try going through a corner and hitting a bump......car jumps sideways as sidewall is so stiff. We need Captainaudio to explain slip angles again. Sidewalls need to flex more that rft to maintain grip.
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      02-14-2013, 04:49 PM   #14
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Your dealer handed you a line of bullshit. They are expensive and OEM for any dealer. I swapped my RFTs years ago and sold them. Never looked back.
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      02-14-2013, 04:57 PM   #15
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Quote:
Originally Posted by 335BBS View Post
WRONG. Salesman is full of it. Sidewalls being this stiff HURT handling. At city speeds they feel more responsive but at speed they are not. Try going through a corner and hitting a bump......car jumps sideways as sidewall is so stiff. We need Captainaudio to explain slip angles again. Sidewalls need to flex more that rft to maintain grip.
Agreed. Keep in mind that the sidewalls of an RFT are designed to be stiff for run-flat purposes, not specifically for performance. There is no reason that a max performance non-RFT could not be designed with the same level of sidewall stiffness if it was an advantage.
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      02-14-2013, 04:59 PM   #16
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I want to switch but I only have stock 16" tires so its not worth it IMO.

Until I figure out what rims to get to replace current ones. I don't know how big I can go? Would 18" RIMs be the largest I should go with?
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      02-14-2013, 05:37 PM   #17
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Quote:
Originally Posted by Antartic View Post
I went to the dealer to see what it would take to swap my runflats for non-run flats.

The dealer said that runflats are better for performance for my 335i because the whole handling dynamics of the car was designed based on runflats. He added that the stiffer sidewalls of runflats help maintain their shape during hard cornering.

He agreed that non-runflats are quieter and provide a comfortable ride, but if it is performance that I am looking for (I am) then runflats are my best choice.

Do you guys think he is BSing me, or does he have a point?
This may be the default dealer SA response, since the dealer near me said almost the same words ("whole package was designed as a system and the DSC and everything else is all engineered to work together"). Looking at it from the dealer's point of view (forget about the financial aspects for a minute), they may be weary of customers making their own changes outside of the BMW party line, and then running to the dealer when something is not right, and it relates to something the customer did outside of BMW's comfort zone. There is always some consequence for each of our choices. Nothing wrong with that.

I just listen to all sides, read a lot on the forums and other places, make my choices in as informed a way as I can, and accept the results and consequences, or trip up and try something else. On the tire issue, I ended up just putting RFT Blizzak LM-25 on for the cold season, and I will probably put non-RFT on when the warm weather comes back, even though I have a lot of tread left on the OEM RFT all-seasons. The logistics influenced me, because I want to leave the winter tires on the OEM wheels, and the OEM RFT all-seasons won't fit on the new wheels I want, so I decided to bite the bullet. Now the only decision is whether to buy a fifth wheel and tire, or get one of those aftermarket spares.
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      02-14-2013, 06:16 PM   #18
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      02-14-2013, 07:27 PM   #19
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Best move I ever made was switching to Michelin Pilot Super Sport non run-flats. Only problem is I go through tires at a horrendous rate. I get about 25,000 on the fronts, and at best maybe 12-13K on the rears.
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      02-14-2013, 07:42 PM   #20
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The PS2 RFTs aren't bad, but I just switched to Pilot Super Sports and they definitely have more grip.
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      02-14-2013, 10:35 PM   #21
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Quote:
Originally Posted by BEAR-AvHistory View Post
Ask the dealer if the factory puts RFT on the M3.
+1000! That's the story, right there...

I hated the OEM Bridgestone bricks on my 2008 335i -- got rid of them just as fast as I could. I particularly disliked the way they hop on bumpy corners, the car literally went sideways when the tires got air in the corner.

Since driving around the SF Bay area is a study in lousy road surfaces, I am MUCH happier since I sold them to a guy looking for lease return tires and got some **real** tires on the car.

Not to mention, the non-runflats are cheaper and last half again as long in addition.
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      02-15-2013, 12:10 AM   #22
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This statement from the OP is true: "the whole handling dynamics of the car was designed based on runflats".

It's also true that the M3 doesn't use RFT's.

So how would our sport suspensions be different if BMW designed them for non RFT's? Does anyone know? I've read BMW used softer bushings to make up for the stiff sidewalls.

After running original OEM Bridgestone RFT's then PS2's then DW's, I can tell you they all feel quite different. I can also tell you that DW's are 30 pounds lighter (as a set) than RFT's.

Captain Audio posted good stuff on slip angles that explains why RFT's don't handle better even though they have better steering response.
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