maurici Posted June 16, 2021 Posted June 16, 2021 Well. As some of you know for my posts here, I did buy a 2016 BMW M340I touring about two years ago. Is my tow/family/gofast to places car. The car came, from the bmw dealer with the well known runOncrap tyres BMW tends to fit in all cars since the early 2000s... in that case, a set of 2018 (brand new when i got the car) goodyear efficientgrip in 225/45/18 and 255/40/18. The ride was harsh, noisy, the steering vague, tramlining on the road was terrible, and it was quite understeery. I would seem to crash over bumps instead or round over them... the lateral grip was poor... I allways thought... "well... msport pack, msport shocks, so... fxxx yourself" Lucky me, i did hit a front tyre and developed a bulge in one of the side walls, so was time to change them (the tread was still new). I have assembled now NON runflats eagle f1 assymetric 5 from goodyear. In 225 45 -245 45 reducing the width in the back, coz i know better than BMW engineers. The car feels like a completely different car. -No more road noise. -Rounds the bumps and holes much better, no more crash. -The lateral grip and the braking are A MA ZING in comparison. -The steering is now comunicative. And the precision is great. -Is now neutral when the toys kick in rather than continuosly busting the front end. -the change is THAT BIG that i just cant beleave it. How on the earth BMW vehicle dynamics team gets away signing off that pile of **** with the runoncraps, having the possibility to release a car that behaves as mines does now? Is simply incredible. Has someone else done this trancision? What have been your feelings about it? Im astonished, really. Allways knew that runoncraps where a bit... well... crap. But this difference is so abysmal that i fail to see the point of the runoncrap at all... 1 Quote
Ian Kinder (Bagpuss) - Joint Peak District AO Posted June 16, 2021 Posted June 16, 2021 We've run the same set of non run flat winter tyres on my wife's 320i and then a 115i. Yes the ride is less harsh, hard to compare the grip levels. I think the 115i's handling is sharper with the run flats. Though the tyre sizes aren't identical. the run flats are lower profile and wider. The rolling circumference is the same. Some tyre experts suggest the stiffer sidewalls of the run flats are parts of the suspension effectively. Hence in theory you should possibly change the springs and shocks if running on non-run flats. I'm sure @DamperMan will have some good input to this topic. Given you're driving and ability to feel how a car is handling @maurici, I take your knowledge and judgment on such topics as valued. Many BMW's drivers (I've had two), are more interested in the badge and not so much about the dynamics of how the car rides and handles. 3 Quote
Steve (sdh2903) Posted June 16, 2021 Posted June 16, 2021 Yep. Run flats are the work of the devil. I'm currently running an old 6 series and the transformation just from ditching the run flats was amazing. Reduced tramlining, noise, ride quality improved and the car actually wants to turn in now. I also had read all the stories of people saying the same online but refused to believe how changing a serviceable set of tyres for another could be so transformative. I do now. 1 Quote
TAFKARM Posted June 16, 2021 Posted June 16, 2021 When we had a BMW Mini it was so much nicer even on Winters than the summer RFT. In the end I swapped all of the RFT, it was much more compliant and quieter 1 Quote
Rhett Turner - Black Country AO Posted June 16, 2021 Posted June 16, 2021 36 minutes ago, Ian Kinder (Bagpuss) - Joint Peak District AO said: Some tyre experts suggest the stiffer sidewalls of the run flats are parts of the suspension effectively. Hence in theory you should possibly change the springs and shocks if running on non-run flats I’m not sure that is true, on some cars run flats are an option and on others different wheel options also change the tyre type. We changed from run flats on Wife’s previous mini and it was more supple, then this mini, running the same tyre wheel combo came with standard tyres, there is a mini compressor and tyre weld kit in boot so suspect it come from factory with out run flats. I really can’t see them having different spring damper set ups, but I could be wrong 1 Quote
Kit Car Electronics Posted June 16, 2021 Posted June 16, 2021 7 hours ago, maurici said: Well. As some of you know for my posts here, I did buy a 2016 BMW M340I touring about two years ago. Is my tow/family/gofast to places car. The car came, from the bmw dealer with the well known runOncrap tyres BMW tends to fit in all cars since the early 2000s... in that case, a set of 2018 (brand new when i got the car) goodyear efficientgrip in 225/45/18 and 255/40/18. The ride was harsh, noisy, the steering vague, tramlining on the road was terrible, and it was quite understeery. I would seem to crash over bumps instead or round over them... the lateral grip was poor... I allways thought... "well... msport pack, msport shocks, so... fxxx yourself" Lucky me, i did hit a front tyre and developed a bulge in one of the side walls, so was time to change them (the tread was still new). I have assembled now NON runflats eagle f1 assymetric 5 from goodyear. In 225 45 -245 45 reducing the width in the back, coz i know better than BMW engineers. The car feels like a completely different car. -No more road noise. -Rounds the bumps and holes much better, no more crash. -The lateral grip and the braking are A MA ZING in comparison. -The steering is now comunicative. And the precision is great. -Is now neutral when the toys kick in rather than continuosly busting the front end. -the change is THAT BIG that i just cant beleave it. How on the earth BMW vehicle dynamics team gets away signing off that pile of **** with the runoncraps, having the possibility to release a car that behaves as mines does now? Is simply incredible. Has someone else done this trancision? What have been your feelings about it? Im astonished, really. Allways knew that runoncraps where a bit... well... crap. But this difference is so abysmal that i fail to see the point of the runoncrap at all... It really wouldn't surprise me if the chassis were developed with conventional tyres, then released with a known degradation for run-flats, particularly since Germans are well used to owning multiple sets of wheels for their cars, with winter and summer tyres? Quote
DamperMan Posted June 16, 2021 Posted June 16, 2021 Hate run flats especially on the earlier cars which clearly where not designed for them. My 2014 320d for instance is suprisingly good.. but still better with my winter tyres fitted. They are basically the work of the devil. Tyres have traditionally been the primary suspension, and smooth out a lot of the road. Leaving the secondary suspension at the damper and springs to do more of the bigger ride stuff and handling… These things are at odds with each other.. so you want decent low speed damping to control the rate of roll, pitching etc… and then relatively softer damping to allow the wheels to travel over rougher ground. But with run flats the damper will be processing high frequency, short amplitude stuff all the time which alters the mean low speed movement and also the higher speed movement . The solution BMW uses appears to be softer suspension mounts allowing the dampers not to be dealing with some much of the high frequency stuff.. but this then adds to the next challenge that updated dampers and springs need to work in harmony with the soft top mounts or they get out of phase with each other.. so you can get a whole manner of strange happenings. Noise, wheels pattering on the ground…. All the devils work! 3 1 Quote
maurici Posted June 16, 2021 Author Posted June 16, 2021 1 hour ago, Ian Kinder (Bagpuss) - Joint Peak District AO said: Some tyre experts suggest the stiffer sidewalls of the run flats are parts of the suspension effectively. Hence in theory you should possibly change the springs and shocks if running on non-run flats. I'm sure @DamperMan will have some good input to this topic. Well. Indeed the tyre is part of the suspension. Not only in RTF cars but in all... And It would make sense if they were managing to achieve the same complilance you would have with normal tyres but with RTFs... the thing is... it doens't happens. Changing the tyre wall stiffness you are effectively softening the car on fast and small movements where the tyre should deform and the RTFs don't. I'm also pretty sure the whole wheel resonance frequency gets altered as soon as you put normal tyres. Is that a bad thing? well, In my particular car seemed to work well leaving the shocks to deal with slow long-travel movements and the tyres do what they are designed to do that is smoothen the ride. 1 hour ago, Ian Kinder (Bagpuss) - Joint Peak District AO said: Given you're driving and ability to feel how a car is handling @maurici, I take your knowledge and judgment on such topics as valued. Many BMW's drivers (I've had two), are more interested in the badge and not so much about the dynamics of how the car rides and handles. Glad not everyone sees me as the crazy driving spanish... 😛 1 hour ago, Steve (sdh2903) said: I also had read all the stories of people saying the same online but refused to believe how changing a serviceable set of tyres for another could be so transformative. I do now. I tend to take with a pinch of salt what the forums says... specially in a mainstream "twatt attracting" brand like BMWs and its forums... so i could not beleave It would do such a difference... but... it did. As automotive engineer for a major OEM myself, I hesitate to follow the forum trends of "we know better than the engineers" but in this case, it seems to be the way to go. 1 hour ago, Rhett - Joint Black Country AO said: I’m not sure that is true Well. It is true that the tyre is part of the suspension, so, if they have been developed toguether, definitely they are meant to work with each other, but nobody said they were meant to work well... XD. 25 minutes ago, Kit Car Electronics said: It really wouldn't surprise me if the chassis were developed with conventional tyres, then released with a known degradation for run-flats I doubt that... for certification purposes, rolling resistance, fuel economy, power to the wheel homologation and so on, you are meant to develop the car with series representative stuff... including tyres... Edit... I see I've crossed posts with @DamperMan. I'm glad I've not said anything stupid as he seems to make the same points as me (ish), but correctly explained. 😛 1 Quote
DamperMan Posted June 16, 2021 Posted June 16, 2021 12 minutes ago, maurici said: Edit... I see I've crossed posts with @DamperMan. I'm glad I've not said anything stupid as he seems to make the same points as me (ish), but correctly explained. 😛 That’s a first for me to correctly explain anything… another point I forgot is undamped mass is bad…. So if you allow the wheel to stay still and the tyre to do the work that’s good, there’s only a bit of rubber moving. Where as it appears on my BMW For instance on the front to smooth the ride the top mount is soft as soft so now every road imperfection moves the massive heavy tyre and wheel, wishbones, brakes, strut, whole spring, and the whole lot adds up to the mass of the moon freely moving about independent of damping! 3 Quote
Steve (sdh2903) Posted June 16, 2021 Posted June 16, 2021 Another point aswell, most of the bmw models fitted with rfts have issues with alloy wheel cracking particularly in the larger diameters or heavier cars. I guess as a consequence of the lack of sidewall damping? 1 Quote
cast iron Posted June 16, 2021 Posted June 16, 2021 check your insurance is still valid, if it was supplied as a run flat car they would expect it to have run flats in an accident 1 Quote
Steve (sdh2903) Posted June 16, 2021 Posted June 16, 2021 I think that's a myth that was going the rounds one winter. Afaik you don't have to declare putting winters on. As long as the tyres are legal and on oem rims then the insurance cannot dispute. If that was the case it would open up a whole can of worms where a car is supplied with premium tyres and the tight A*** owner fits a set of linglongs or other ditchfinders. Which is much more pertinent for wet grip or stopping performance than swapping rft's Off topic I know but the lad is currently hot hatch shopping and the amount of cars we've seen with odd mismatched ditchfinders is staggering. Why pay for the expense of a top of the range hot hatch and then compromise it using **** tyres? Quote
maurici Posted June 16, 2021 Author Posted June 16, 2021 48 minutes ago, cast iron said: check your insurance is still valid, if it was supplied as a run flat car they would expect it to have run flats in an accident It is indeed a mith. you can't legally have one of each type, but you don't have to declare consumables as long as they are homologated and roadworthy. (called the insurer years ago when changing to winters and undersized wheels). Quote
DamperMan Posted June 16, 2021 Posted June 16, 2021 Most vehicles have a list of sizes, ratings and and tyre pressures as a sticker on the car.. all approved by the manufacture. Quote
maurici Posted June 16, 2021 Author Posted June 16, 2021 16 minutes ago, DamperMan said: Most vehicles have a list of sizes, ratings and and tyre pressures as a sticker on the car.. all approved by the manufacture. And according to general European traffic rules, a variation of under 3% in any of the sizes, is considered equivalent.... I have not checked in uk, but i guess this is still the same? Quote
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