RFT Query:Please Participtate :-)

[Zeefour]

With much of recent discussion revolving around tires, I wondered how many here are still running on RFT's? And if so, what are your feelings about them and will you change?
I still run on RFT's and love the harsh, tight ride. I have driven/ridden in plenty of sports cars w/ and w/out them and can appreciate the smoother ride. Still, there's something about the RFT's that puts a smile on my face . Am I the only one?

Does your Z4 have sport suspension?

When i was test driven Z4s i drove one without the sport suspension with RFTs and the ride was decent but still noticed the tramlining. But with the sports susp tramlining is more pronounced and the car felt skidish over chopping pavement especially in corners and even choppy at highway speeds on farily smooth roads. I drove 1 year with the RFTs, and then ditched them. Now no more tramlining being skidish or my head moving like a "bobble doll" over bumps and ripples in the road. I rate it in the top 2 for improving the car...

 

[scottyD]

No, I opted against the sport package and sport suspension, in favor of having a more practical setup with wheels and tires, and being able to rotate all 4 around the car. Even with the standard suspension, I feel the ride is pretty rough, but I guess I just expected that a sports car is supposed to have a stiff suspension, and in my opinion, it would be silly to buy a sports car for a nice smooth and comfortable ride. I guess I would have to try the non-runflats to make a fair statement there though....

I imagine the ride is stiffer with the sports suspension, but I haven't been able to drive one with that setup, so I would have to try that both ways (with and without runflats) also to make a fair statement.....

anyone feel like lending me their cars to do some comparison testing???? :wink:

just my humble opinion... doesn't really matter, just as long as the car is thoroughly enjoyed by the driver

 

[ovrkll]

I will add my two cents here, since I have used both in performance areas. The RFT's do not handle corners as well as non-RFt's,,,,,the RFT's have a much stiffer sidewall and do not flex, hence the propensity to wheel hop when taking a sharp corner at speed. The non-RFT's with a softer sidewall will flex and allow better adhesion in performance applications. That is my main noticeable (besides the tramlining) experience in a nutshell.

Cheers!

 

[AlanL]

Ovrkll has hit on one of the fundamental problems with the current generation of the RFTs - the sidewalls are far too stiff for what should be expected behaviors from a high performance tire.

Great choice for a touring sedan but not ready for prime time on a performance car. I loved non RFT Bridgestone RE050's on my Honda S2000 enough to drive them for 27 track events with a great big grin on my face and wanted to like them as an RFT on my Z4. I tossed the RFTs after 2000 miles and would never even consider trying them again until some major breakthroughs happen for performance RFT tires.

Yes I carry a portable compressor, tire repair kit, a can of fix-a-flat and an AAA Plus card these days.

 

[20ducks]

I've run RFT's and my GSD3's during high performance road course runs: GSD3's are my choice.

 

[Gauss]

When I first drove the ///M that had no runflat tires I couldn't really tell much of a difference from when I had my roadster with runflats. Of course there was like a 3 month gap in between ownership so maybe I had just forgotten what it was like.

And when I switched to Michelin Pilot sports I couldn't really tell much of a difference between them and the Conti's except for the fact that there was more grip when accelerating and less understeer on corners.

 

[cj10jeeper]

I will add my two cents here, since I have used both in performance areas. The RFT's do not handle corners as well as non-RFt's,,,,,the RFT's have a much stiffer sidewall and do not flex, hence the propensity to wheel hop when taking a sharp corner at speed. The non-RFT's with a softer sidewall will flex and allow better adhesion in performance applications. That is my main noticeable (besides the tramlining) experience in a nutshell.

Cheers!

ovrkll - I'm not in any way challenging the comment but seeking a deeper understanding.

If you comment that the stiffer sidewall prevents flex, why do the majority of performance cars, track, etc go to lower profile tyre. I thought the reason was to reduce sidewall flex and thus keep the tread planted squarely on the road across the full tyre width. Is it the different internal construction to support driving without inflation that creates the issue on the RFT's?

Clearly if RFT's performed as well in the limits of performance we would see all serious track motor sport at the highest level using them and of course they don't.

Just curious

 

[Aebous]

<---too lazy atm to read other replys.
I have the runflats....want to change them immediatly for better gripping tires

 

[zee42]

Ditched my rft's for some Dunlop Sportmax,took a posted 15mph downhill right hand west virginia mountian road at 60mph,little roll over on the left front,but no loss of traction or a hint of squeal.....I'm sold

 

[ovrkll]

cj10jeeper, It may be a give and take issue, if their is no flexibility, then the wheel hop issue, too much and then the tires will lose adhesion. I think a big reason to move to low profile type tires is to prevent the tire from rolling over and breaking the bead at the rim. I am far from a professional driver/mechanic, just seems logical to me and I had not seen any other posts regarding the performance diff's.

 

[AlanL]

I'll take a stab at explaining the problem of an overstiff sidewall from a performance perspective but will preface this with the caveat that most books on high performance driving and racing devote entire chapters (or more) to the topic of traction so anything I describe here is going to have to skip over a lot of details.

For starters you need to be aware that the suspension setups of most racing vehicles is almost totally undrivable on the streets so things that work for racing don't always translate nicely to our daily drivers.

The basics of traction are pretty simple - everything hinges on the 4 patches of rubber you present to the pavement at all times. Anything you do to diminish the size of those contact patches at any time while you are driving will detract from your ability to control the car. Acceleration, braking, and turning are the primary driver inputs that the patch shape and size. The first 2 are not a big point of concern here - acceleration unweights the front patches (reducing their effective traction) and braking unweights the rear end.

In a turn we are concerned with the lateral forces that move the center of gravity to the outside of the car while in the turn. The more the lateral force, the farther over we move the center of gravity. If you look at pictures of cars in mid turn carefully you will see that the wheels on the outside of the car are no longer perpendicular to the ground. This leaves the tire patch on the outside of the wheel in a state where it no longer is as effective in delivering traction where we need it the most.

Racers get around this by tilting the wheels in at the top (negative camber) so they can apply more lateral force in a turn and still present a flat tire patch to the ground. With a bunch of negative camber dialed in you can now run with a far more stiff sidewall or lower profile tire and get good results. This adjustment comes with a price and that is less of a tire patch for driving in straight line. Not a big issue for the track but definitely not a nice option for freeway driving.

Back to the street car - since we don't have the negative camber the racing car does there is less of a benefit to the super narrow tire profile (other than the bling factor) or super stiff sidewall because it robs the tire of the ability to flex enough to keep our tire patch flatter to the ground. Lots of folks head out to the track thinking they need very high tire pressures when in fact they will get better performance out of their tires when they make sure that the pressure allows the sidewalls to flex at least a little. When the lateral forces in the turn increase to the point where the top of the rim is starting to tilt outward and the wheel is no longer perpendicular to the ground the sidewall flex will allow the tire patch to stay flat to the ground for a little bit longer and provide more traction than if the sidewall was completely rigid.

The RFT tosses all of this out the window by making the sidewall stiff enough to hold the weight of the car when the air is gone. This probably works quite nicely for a higher profile tire on passenger cars, but once you start getting down to the lower profiles we are using on our sports cars this can be quite dysfunctional. The effect might not be so bad with the 225/45R17s as it is with the 18" tire sizes on cars with the Sport option but I found the result to be intolerable with the 18s on my car. Installing the Pilot Sport PS2s was a stunning difference and I knew it before I even got the car out of the parking lot at the tire place that did the swap.

I thought about RFTs for my 17" winter tires (225/45R17) but decided against it and got non RFTs instead. It is possible that the 17" RFT winter tires might not have been as bad an idea as they seem to be with an 18" performance tire.

Sorry for the War and Peace post but the topic is actually a complicated one and you could spend a lot more time going through the details beyond what I just scribbled here....

 

[fire-n-ice]

Still though Alan, great post and thank you for taking the time to explain the details you did

 

[cj10jeeper]

Alan,

I really appreciate the detail of the reply you have put together. It all makes a lot of sense.

My core expertise to date on tyres has been a lot more to do with gaining traction from small rims, high profile tyres and balancing low pressure for traction with likelihood of puntures and rolling off rims - somewhat different to the compromises between street and track.

 

[ovrkll]

Good post Alan,,,pretty much summed up the major differences.

 

[Wondermike]

AlanL, that's a really great post. I had the 18s on mine, and the ride was back-breaking, especially if the tyres had lost a bit of pressure, but I did like the fact with the RFTs that if you had a puncture you would be able to drive on.

The RFTs are expensive too I paid £253 for a rear :roll:

 

[sp3ctre]

Nice post AlanL, thanks :bow: