[luckyu]

I installed new tires a few days ago, and all the vibrations and rattles are gone. All the harshness at low speed is gone too. In terms of harshness, the ride is perfect now.

I still have a bouncy rear though. The rear suspension resonates up and down about 3 times per second over certain roads with certain bump combinations, at 30-40 mph. I can elicit the rear end bounce at really low speed, so I'm going to try to track it down.

The tires I got are ExtremeContact DW. So far I have only 200 miles on them, and they are extraordinarily squirrely. They are worse than squishy, they are unsafe, because they allow the rear end to start fishtailing after minor direction changes at 65 mph! Simply unbelievable. Well I tried to keep my mouth shut until 500 miles, but there you go. I'll edit this if they change.

[cvc 22349a]

^They're supposed to be good tires. Give 'em at least 500 miles and experiment w/pressures.

[DaanBMW]

Originally Posted by luckyu

The tires I got are ExtremeContact DW. So far I have only 200 miles on them, and they are extraordinarily squirrely. They are worse than squishy, they are unsafe, because they allow the rear end to start fishtailing after minor direction changes at 65 mph! Simply unbelievable. Well I tried to keep my mouth shut until 500 miles, but there you go. I'll edit this if they change.

Are these still on 16" wheels ? If so then your sidewall is so large that the non-RFT tires will be flexing a lot more. I recently put RFT all-season 17" on (for winter) and they feel similarly stiff as my non-RFT 18".

Like cvc said, the only tool you have now is tire pressure. The DW's are a highly-rated tire.

[luckyu]

Originally Posted by DaanBMW

Are these still on 16" wheels ? If so then your sidewall is so large that the non-RFT tires will be flexing a lot more. I recently put RFT all-season 17" on (for winter) and they feel similarly stiff as my non-RFT 18".

Like cvc said, the only tool you have now is tire pressure. The DW's are a highly-rated tire.

I knew somebody was going to bring up sidewall height. The sidewalls on 205 / 55 R 16's are only 113 mm, and I've been running on 123 mm sidewalls for years on 15" wheels. This has nothing to do with sidewall height, and everything to do with tire construction.

[mike-y]

The conti ExtremeContact DWs are known to be a very soft tire. I tested these back to back vs the Michelin pilot Super Sports at an event earlier this year (on an E92 328i), and the difference was significant. That experience was a determining factor when I picked out new tires a few months later, and crossed the DW's off my list.

I know it doesn't help you now, but since you are stuck with them, I'd put a few more PSI in them, to help stiffen them up. What tire pressures are you running right now?

[luckyu]

By the way, when I said fishtailing, I mean the sidewalls actually oscillate in the rear. If I make a medium-fast "lane change" maneuver, the rear squishes one way, then the other way, then returns to center. I hate to complain, but... that's not "max performance"...

I agree on the mileage and the pressures. I've tried 37 and 40 so far, I'm going to try 39 for a while.

[luckyu]

Originally Posted by mike-y

The conti ExtremeContact DWs are known to be a very soft tire. I tested these back to back vs the Michelin pilot Super Sports at an event earlier this year (on an E92 328i), and the difference was significant. That experience was a determining factor when I picked out new tires a few months later, and crossed the DW's off my list.

I know it doesn't help you now, but since you are stuck with them, I'd put a few more PSI in them, to help stiffen them up. What tire pressures are you running right now?

I was running 40. The tires stiffened up after only a few hours, but after 200 miles they are still unacceptable. Gotta wait it out and see what happens after more mileage.

I might have gotten the PSS if they were available in my size; but after this experience I'm much more likely to stick with Michelin.

[mike-y]

Originally Posted by luckyu

I was running 40. The tires stiffened up after only a few hours, but after 200 miles they are still unacceptable. Gotta wait it out and see what happens after more mileage.

I might have gotten the PSS if they were available in my size; but after this experience I'm much more likely to stick with Michelin.

I went from the stock 16" wheels w/ RFT's to 18" breytons (20 lbs) with non-rft bridgestone potenza RE760s. While I loved the PSS, they were just too much money/performance for what I needed on a street car (I have another car for track days that I buy higher performance tires for). For me, the re760s seemed to offer the best balance between handling, noise, and treadwear - without being too soft.

But even with the larger wheel size, and much shorter sidewall (along with increased tire pressure), the ride is still better than what it was with the RFTs. Part of that may be the loss of unsprung weight with the lighter wheel/tire combo.

I believe I'm at about 36/38 psi, front/rear with 225/40/18s all around (I like the balanced handling of a square setup).

[DaanBMW]

Originally Posted by luckyu

I knew somebody was going to bring up sidewall height. The sidewalls on 205 / 55 R 16's are only 113 mm, and I've been running on 123 mm sidewalls for years on 15" wheels. This has nothing to do with sidewall height, and everything to do with tire construction.

Unless you run back-to-back it's really hard to compare. Also a stiffer suspension setup, which is what you have now, will make the weakest link seem even weaker. In F1 the tires are what dampens the ride, the rest is so stiff. Having said that, it sounds like the DW have a softer sidewall so a higher sidewall will make this more pronounced... that is useful info.

On my 18" the rec. pressures for over 100mph are 35/42, for under I _think_ are 32/35. Pressure makes a huge difference, play around with it, but it won't cure a weak sidewall.

[luckyu]

Originally Posted by mike-y

I went from the stock 16" wheels w/ RFT's to 18" breytons (20 lbs) with non-rft bridgestone potenza RE760s. While I loved the PSS, they were just too much money/performance for what I needed on a street car (I have another car for track days that I buy higher performance tires for). For me, the re760s seemed to offer the best balance between handling, noise, and treadwear - without being too soft.

But even with the larger wheel size, and much shorter sidewall (along with increased tire pressure), the ride is still better than what it was with the RFTs. Part of that may be the loss of unsprung weight with the lighter wheel/tire combo.

I believe I'm at about 36/38 psi, front/rear with 225/40/18s all around (I like the balanced handling of a square setup).

OK, I probably would have been much happier with the RE760s. You mention the weight difference. This is the second time I've moved from runflat to goflat, and the ride quality improves in many ways. The 16" runflats I was on did not feel bad -- but, they do generate a lot of extra vibration. It's just not apparent until we remove the isolation in the suspension.

But the new tires (19 lbs each) make the whole car feel lighter. It's very strange but the vehicle as a whole behaves like a better, lighter vehicle. When I moved from 17" wheels to 16", I could feel a smoother ride. But this is different.

At high speed, I actually like the way the runflats rode better. The new tires are not perfect over every impact. But at low speed there's no comparison.

[luckyu]

Originally Posted by DaanBMW

Unless you run back-to-back it's really hard to compare. Also a stiffer suspension setup, which is what you have now, will make the weakest link seem even weaker. In F1 the tires are what dampens the ride, the rest is so stiff. Having said that, it sounds like the DW have a softer sidewall so a higher sidewall will make this more pronounced... that is useful info.

On my 18" the rec. pressures for over 100mph are 35/42, for under I _think_ are 32/35. Pressure makes a huge difference, play around with it, but it won't cure a weak sidewall.

I hear you, but I am comparing back to back. I think you are right about the weakest link. Fix one thing and then there's something else...

A higher sidewall doesn't help matters, but Conti can construct the tire any way they want to to get a result. If they are going to make a "max performance" tire, there are certain expectations that come with that, regardless of sidewall height.