key finding.. 19" RFT specifically are the issue not RFT in general

[nicknaz]

I recently took the 19" style 296 wheels with RE050A RFT tires off my car to put on 18" style 325 wheels with RE050A I RFT tires and was amazed by the improvement in wheel control from such a seemingly small change of ~3lb of unsprung weight per corner and slightly larger sidewall

It is like I have a completely different suspension set up now. The wheels (especially the rear) don't "crash" when I hit road imperfections, the rear of the car doesn't hop sideways from mid corner bumps, and the turn in feels a tiny bit quicker.

I suspected when I first got the car that the 19" slight increase in unsprung weight and ultra stiff sidewall forced by the 30 series profile and RFT construction were negatives but I did not detect this during the test drive because the roads near the dealer were very smooth.

Now that I have spent substantial time with the 18s on a variety of surfaces including the roads I have been driving daily for a year on the 19s I want to let others who might be on the fence about their vehicle order to avoid the 19 wheel option unless they are planning to go non RFT

As I read more about the new tires, I came across some marketing literature that claims the RE050A I RFT are customized for the sport package E89 (but they are not available in the 19" size, so generic RE050A RFT are used instead)

http://www.tirerack.com/tires/tires....VR7RE050ARFTV2

The Potenza RE050A I RFT (Run-Flat Tire) is Bridgestone’s Max Performance Summer run-flat tire developed exclusively for selected BMW Z4 vehicles, as well as 3 Series cabriolets, coupes and sedans equipped with BMW’s sport packag

It is an interesting claim, since the sidewall does contribute to the "wheel rates".

Whatever the case, I am really glad I got rid of the 19" RE050A RFT (thanks Cedar!)

[Asbjorn]

Thanks for sharing this! It adds to our understanding when reading reviews of especially the Z4 35is.

I however still think the 18" RFTs are way too noisy for this car, and I don't understand why they don't use the lastest gen RFTs.

[HerrK]

Originally Posted by Asbjorn

I don't understand why they don't use the lastest gen RFTs.

Because they (BMW) probably have a contract in place with Bridgestone to supply the RE050A.

It's not about the Ultimate Driving Machine and customer satisfaction. It's about making money for the company!

[Asbjorn]

Originally Posted by HerrK

Because they (BMW) probably have a contract in place with Bridgestone to supply the RE050A.

It's not about the Ultimate Driving Machine and customer satisfaction. It's about making money for the company!

But they already use newer RFTs on other cars like the M135i
The LCI would have been a good chance to upgrade imo.

[Moo]

Yes I've been wondering how the usual complaints about the steering feel and other driving inadequacies (in magazine/online reviews) are attributed to the RFTs. Would love to see an in-depth benchmark between 18 vs. 19 with RFTs and proper tyres...

[nicknaz]

Cedar shared interesting thoughts on 18 rft to 19 non rft via Email. Maybe he will post here also.

I think forum consensus is 19 non rft is more comfortable than 19 rft.

I don't really know of anyone on these boards with 18 non rft.

In 10k miles or so when I wear these out I might get 18" non rft and will let you guys know.

[DslDwg]

There are many good points in the OP but most don't hold true just for RFT's. There will almost always be a point where increasing wheel diameters start giving diminished returns. Usually as you go up braking and handling get better, but acceleration, ride comfort and noise get worse.

I agree with most that a 19" wheel fills out the Z4 well nicely but I'm not sold on it doing anything else better. This is exactly why I didn't get them on mine. Though like many I'm not sold on RFT's on performance cars so will most likely switch to non-RFT's at some point but will stick with the 18" wheels.

My wifes X3 has 18" RFT's on it and I have no problem at all with it. The ride is smooth and I like the idea that she can limp to the tire store and not be on the side of the rode changing tires. But of course they have huge sidewalls making all the difference in the world.

I'm not sure it's some sort of conspericy or money grab by BMW. Clearly they have certain tire vendors they work with like any other manufacturer. What I don't understand is why the M cars don't have RFT's and something like the Z4 35is does?

Whenever I think about this discussion I harken back to my '93 RX-7 which came stock with a set of 17" wheels with matched tires. That car out of the box was capable of 1.0+g on a skid pad. So clearly big wheels with unmatched tires is not the key to going fast or handling well.

[jparnes1]

Originally Posted by nicknaz

Cedar shared interesting thoughts on 18 rft to 19 non rft via Email. Maybe he will post here also.

I think forum consensus is 19 non rft is more comfortable than 19 rft.

I don't really know of anyone on these boards with 18 non rft.

In 10k miles or so when I wear these out I might get 18" non rft and will let you guys know.

In my 2011 Z4 I ran 18" RFT for 11K miles and hated it. After they wore out I went to Potenza Pole Position S-04's non RFT and was blown away by the difference in drivability. In my current Z4 I swapped out my 18" RFT at delivery for 18" PSS non RFT because I wasn't going to go thru that again! I stayed away from 19" because of concern about rim damage.

Nick I think you drive your car harder than I do, but if my experience is of any value, I think you'll agree that they're a major improvement.

[DslDwg]

Originally Posted by nicknaz

Cedar shared interesting thoughts on 18 rft to 19 non rft via Email. Maybe he will post here also.

I think forum consensus is 19 non rft is more comfortable than 19 rft.

I don't really know of anyone on these boards with 18 non rft.

In 10k miles or so when I wear these out I might get 18" non rft and will let you guys know.

I haven't even got my car back from Europe yet but not long after it returns to the states the RFT's will be coming off.

Even if I decide to change wheels I will keep them 18" so I will keep all up to date.

[nicknaz]

I am concerned that if I go with the wrong non RFT I will get less grip and mushy turn in, and I have also been burned in the past with getting stranded in sketchy and remote areas so 3 objections I need to weigh vs. possibility of more grip (I am fine with the 18" RFT ride quality)

[DslDwg]

I certainly understand your concerns but everyone raves about Michelins Pilot Super Sports. If I'm not mistaken they are OEM on most of the "M" cars.

From everything I read you will get better grip, better turn in, less noise, better ride, longer life, cheaper replacement costs.

The difference in the cost of one back tire is enough to buy the tire mobility kit.

I'll be the first to admit the Bridestone RFT's on my Z4 seem less harsh than the Michelin RFT's on my 335i but I just can't ignore all of the benefits of the Non-RFT tires.

[jparnes1]

Yeah, getting a flat would suck, but I have the mobility kit so I wouldn't be stranded. But really, how often do you get a flat tire? And how often would that happen in a remote area at that?

[nicknaz]

Originally Posted by jparnes1

Yeah, getting a flat would suck, but I have the mobility kit so I wouldn't be stranded. But really, how often do you get a flat tire? And how often would that happen in a remote area at that?

Don't jinx me.

Pss seems like magic. More grip,more comfort, longer wear, cheaper than rft!!!

I guess tire tech has just moved on that quickly that all those things are no longer trade offs like they were in the past?

[CedarZ4]

Funny you created this thread, Nick, as the other night I was thinking how we should be having our conversation on the forum so others can share their opinion and experiences.

There are two things that are notable for me. First of all, for those that don't know I went from OEM 18s to aftermarket 19s, so the comparison may or may not hold for OEM 19s as well. While changing out my wheels, I decided to change out the RFTs as well. I thought that my upsizing would counteract the effects of removing the RFTs, as I have read from other threads that ride quality is the same going from 18 RFT to 19 non-RFTs. It is very comparable, but two things that I noticed was that 1) it seems to ride a little softer (floaty), and the turn is not as crisp. I know Nick pointed out switching from 19 to 18 increased his turn-in speed, but since I went from 18 to 19s AND went to normal tires, I wouldn't be surprised if the decrease in performance is even greater with a mushier sidewall. It is not anything extreme by any means, but noticeable if you are really looking for it. The biggest thing that I noticed was what Nick pointed out about his OEM 19s. Every time I would go over uneven pavements or a speed bump, the rear tires would feel very heavy and "crash" down. I originally attributed this to the aftermarket wheels being a lot heavier (and I went to 275 tires), but it is very interesting that this is experienced for OEMs as well as I originally thought it would just be my aftermarket wheels (since I never weighed them and assumed it was a lot heavier). It would seem that even a few lbs (4 lbs) is "too heavy."

This brings me to the second point, which is it makes me wonder what size wheels did BMW optimize the Z4 for and what it was really intended to be used with. My guess is the suspension and everything was tuned perfectly to work with their OEM 17s with RFT, and if you option to get bigger wheels (even OEM) they just chug bigger wheels on without any consideration for the suspension. As a daily commuter, I think 19s work very well for me, but I would have to agree it is a more of a show and no go option. It does fill the wheel well very well, but it does feel heavy and you do lose a bit of handling. 18s seem to be a very good compromise of aesthetics and performance, and I have yet to try 17s but I wouldn't be surprised if performance is the best with those. It's not surprising though, because if you go around to other forums a lot of people vouch for 17s or even 16s as the best size for performance.

For those thinking about going 18s RFT to 19s non-RFT or vice versa, here is how I would describe the feeling of both. On 18 OEM RFTs I had, the ride was indeed very harsh and you could feel every imperfection. However, your car would go along with the wheels. If there was a pothole, your whole car would drop into the hole with the wheel, and the whole motion of the car is very "smooth" and fluid albeit harsh. On 19s and non-RFT, you do gain some more buffer from the tires, even when you upsize. However, with the "crashing" feeling you experience, the overall comfort being "better" is an arguable fact. Whenever you go over uneven pavement, you feel disconnected from the car as well because it just seems like the rear wheels is dropping continuously, but the car itself isn't dropping along with it. It's a weird feeling that I can't describe, and it feels like the car has a very cheap and poorly designed Active Body Control Suspension (where they try to keep the car leveled at all times even through uneven roads), which is what seems to be what I am experience with just the wheels moving along with the road and not the car. Maybe those who are using or had use 19s that have also experienced this came chime in.

In regards to flats on non-RFTs... I haven't really thought about what I would do. As jparnes mentioned, the possibility of a flat is very low, especially if you're careful. However, my daily commute is through a very very bad neighborhood, and it would suck to be stranded on the streets at 9pm in the Z. I've also heard that the mobility kit sometimes doesn't work, and even if it does it screws with the TPMS and you have to buy a new one. Have to figure out how I will solve this problem...

[Crazykoh]

New tpms and a tire patch is still less than a new rft.

[CedarZ4]

True, but under the same argument TPMS + tire patch is still more than just a RFT Tire patch. We all know the "recommended" procedure for a RFT flat (replacement) but normal tire patch-up are technically supposed to be <permanent> temporary fix as well.

[jparnes1]

Originally Posted by CedarZ4

True, but under the same argument TPMS + tire patch is still more than just a RFT Tire patch. We all know the "recommended" procedure for a RFT flat (replacement) but normal tire patch-up are technically supposed to be <permanent> temporary fix as well.

Patch it only if you don't have to drive on a flat RFT. Once you do, you damage the sidewall and repairing it is ill-advised.

[CedarZ4]

True, but I'd imagine the only time you would really be driving on a flat RFT is on a blowout. That, or you really don't check your tire pressures and wait for it to say "Low" then you continue to drive it anyway. In either cause, a non-RFT in the same scenario probably can't be or shouldn't be repaired anyway.

From personal experience, the only time you can really patch up a deflated tire successfully are ones with small leaks from like a nail, and that would work for a RFT as well.

My point being, RFT seems to only be really useful when your tires become completely obliterated, then you can still drive it to a local garage. In normal day-to-day flats or low pressure due to small leaks, patching should work with both tires. Though, I have never experienced a RFT leak or have had too many tire leaks in general, so speaking from limited experience.

[nicknaz]

Cedar, I have had a nail in the tire that caused the air to all leak out in 1 mile and then similar size nail cause a slow leak that would take a day for a noticeable difference.

It is all luck and I would say in the case of then nail causing a fast leak the Rft will still save you.

Are you talking about Newark nj? I would not want to get out at 9pm even to activate the slime goop repair kit

EDIT: for the e89 are 18s automatically included when you buy the sport or m sport package? My suspicion is the dampers were tuned to the standard tire size they are bundled with, which I think is 18? (Ie I thought 35i got 17s only without sport package and 35is only came with 18 or 19s)

Funny enough cedar I was going to get oem 17 but it would have been a hassle because I would have to retrofit newer tpms. I couldn't find any forged light 17s. Seems like vendors know the e89 as a "show" community. Hehe.

[Asbjorn]

Originally Posted by nicknaz

I am concerned that if I go with the wrong non RFT I will get less grip and mushy turn in, and I have also been burned in the past with getting stranded in sketchy and remote areas so 3 objections I need to weigh vs. possibility of more grip (I am fine with the 18" RFT ride quality)

I went from 18 rft oem tires to 18 non-rft non-performance tires. I decided on non-performance summer tires to get tires that were easier to spin and go sideways with (but they weren't). I also wanted tires that were cheaper to replace because 4 oem tires cost 2500 usd here at bmw china.
I then decided on non-rfts mainly because I wanted less tire-road noise for those longer road trips as well as a bit more comfort while driving on certain Chinese roads.

I think the reduced tire noise is reason enough to never put rfts on a Z4. I love listening to music while cruising at say 60-80 mph, and it is just so much easier to enjoy without all of the tire noise coming from the rfts.

However, even with non-performance tires, the grip has improved as well. Therefore the car reacts with less under-steer on sharp turn-in or sudden steering inputs. But the steering itself feels more soft. Actually I could feel this immediately after changing the tires just by turning the steering wheel with the car still parked. The softer sidewalls simply allow the rims to turn more before the tire follows. If you are afraid you won't like this I recommend trying performance tires or maybe 19" instead.

It is a pity that the car was optimized for rfts, as it seems the grip and comfort is just better with any non-rfts.

[CedarZ4]

Originally Posted by nicknaz

Cedar, I have had a nail in the tire that caused the air to all leak out in 1 mile....

+

Are you talking about Newark nj? I would not want to get out at 9pm even to activate the slime goop repair kit...

Had a nice chuckle when you said Newark. Yes, and the above combination you mentioned is a bit concerning. Might just play my luck, and if all else fails, lock my doors, put on some soothing music, call BMW Roadside and hope they want to make a trip down to Newark.

In regards to the Sports Package + M-Sports Package. Yeah, they have 18's standard, so you may be right about 18's being the optimal size for the E89. If this were true, that means the base models don't perform to their potential until they are fitted with the Sports Package, which is a $2k+ option, which doesn't sound right, but I think you are on the right track, since the 35is which is supposed to be the highest performing model, comes with 18's standard. Interesting to see a comparison for someone that had 17s and upgraded, or vice versa.

Asbjorn - I'm no tire expert, but is the grip for RFT really inferior to non-RFTs? To my understanding, I thought RFT worked through additional support within the tire, not the rubber compound itself. If this is true, then RFT should have nothing to do with grip, rather the quality of the specific RFT tire brand/model itself. As an example, I went from the Max Performance OEM RFT to non-RFT Ultra High Performance All-Season, and I can easily let the tire loose through a sharp(er) turn. I know not a fair comparison, but just as an example where it's more-so the rubber compound itself being used, and not so much the type of tire (RFT vs. Non). In regards to the comfort, you are right about the stiff ride. However, aside from the additional unwanted weight, RFT aren't actually that bad in terms of performance. The stiff sidewalls are not a bad thing, and even if you get a Max Performance summer tire, you will be sacrificing comfort level for handling. I think it may just be one of those things where you have to choose your side. But I agree with you that I think non-RFT is a no-brainer, mostly because of the insane cost for them.

[HerrK]

Let's just assume the compounds for all RFT's & NRFT's are equal. It's all about the contact patch in a corner. I would bet my bottom dollar that the NRFT provides a signifigantly larger contact patch, hence the perceived better grip and no understeer. This is due to their inherent flexability. The stiff RFT's understeer because they do not comply or conform and this results in a smaller contact patch. This is why it is safe to drive them around at 50 mph with no air because they are almost as stiff as stones as behave as such.