Runflats vs Non-Runflats

[Bigtop]

I have read all the threads here, but non of them give specific evidence that BMW designed the X5 E70 to run on only runflat tires and that if you put non runflat tires on it will be detrimental to the suspension and handling characteristics of the car.

Has anyone got any evidence of this and I mean from high up in BMW, not just the salesperson of the month or the local mechanic?

[motordavid]

No xpert, but I cannot believe that running non-RFTs would affect any
of your concerns...many users of all brands of cars, with RFTs oem,
have made the switch to non-RFTs with no problems.
YMMV...
GL,mD

[RxGuy]

Yeah, I switched from my run flats to non-RFT, and my ride is actually better. (went from 18 to 20 in).

[Wagner]

RF have a much stiffer and harder sidewall. Switching to non RF's would result in a softer and sometimes quieter ride. I would make sure you have a spare tire prior to leaving the RF environment.

[x5mad]

Originally Posted by Bigtop

I have read all the threads here, but non of them give specific evidence that BMW designed the X5 E70 to run on only runflat tires and that if you put non runflat tires on it will be detrimental to the suspension and handling characteristics of the car.

Has anyone got any evidence of this and I mean from high up in BMW, not just the salesperson of the month or the local mechanic?

Don't have the evidence your looking for but I switched from 18'' run flats to 20'' non runflats and I can without a doubt say that the non runflats give a much improved ride in terms of comfort and less road noise.

[Fredo]

I will change to non RFT's when my tyres need changing. I did this on my previous E60 535d, it transformed the ride.

Just FYI someone posted on a UK forum recently that a dealer would not accept his 335i in part exchange with regular tyres on...he had to get them change back to RFT's.

I read recently that the X5 M and X6 M will come with RFT's which is a first for an M/// car previously they have all had regular even if the rest of the range have had RFT's. It will be interesting to see if this is because there is an improved generation of RFT's coming or they have lost the battle with the marketing department.

[Roadster]

I too have swapped my RFT to non RFT on my E60. What an improvement that was! I plan to do the same on the X5 if my lease company allows it that is...

[Kasyd]

I'm also interested in hearing more on this topic,, I'm getting close to replacing the rubber on my X and don't now which way to go.
I currently have the bridgestone 20" Dueler HP's and they used to handle great but always gave a back breaking and real noisy ride.. Getting worse as they wear.

[hhhm3]

Originally Posted by Bigtop

I have read all the threads here, but non of them give specific evidence that BMW designed the X5 E70 to run on only runflat tires and that if you put non runflat tires on it will be detrimental to the suspension and handling characteristics of the car.

No evidence is given because there are non.
once the tire are inflated to the proper level there are not difference to the suspension. The only difference is that the RFTs are stiffer sidewalls which would generally give harsher ride.

This statement unclear and is interpretable in terms of what they mean by detrimental. It could mean when you get a flat tire, the non-RFT could damage the wheel or maybe the suspension (depend on condition of road and speed) but where as the RFT will somewhat maintain its sidewall structure the handling.

[JCL]

Originally Posted by Bigtop

I have read all the threads here, but non of them give specific evidence that BMW designed the X5 E70 to run on only runflat tires and that if you put non runflat tires on it will be detrimental to the suspension and handling characteristics of the car.

Has anyone got any evidence of this and I mean from high up in BMW, not just the salesperson of the month or the local mechanic?

We are getting into very small differences, but here is my take:

I believe that the E70 is designed for a run-flat tires. That does not mean you can not change to non-run flats, go right ahead. Take out the word "only" in your quote, above. What it means is that the suspension has been tuned to accomodate the additional harshness of the stiffer sidewall. Noise/Vibration/Harshness (NVH) tuning is all about resonant frequencies, and what the vehicle operator feels in the seat. Early adopters of RFT (like my 2004 Z4) had a very harsh ride. Switching to non-RFT on that model made a huge difference. By 2008, BMW had tuned the suspensions to reduce the apparent harshness. There is a significant difference (in the same model series) over several years of refinement. You will still likely get a more compliant ride with non-RFT, but there is far less reason to get upset about RFTs now than there was in 2004. If you want to switch, you just need to consider the cost of new tires (on the same rims), the need for a spare, and possible refusal of service by BMW assist for towing you free of charge with a flat tire.

My source is engineering articles read over the past five years, not a sales rep.