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Discussion Starter #1
Used the M5 for towing for the second time this weekend, and had a nasty surprise............

The rear passenger (UK) side tyre developed a big rip in the sidewall........

Now, initially I thought this was possibly caused by a slow puncture and the subsequent overheating caused the blowout.

But now, I'm thinking it might be due to the tyre catching on the inner bodywork. The car sits a good deal lower at the back once the trailer's hitched up......

Haven't had chance to investigate further (off work with flu!), and the marks on the tyre are inconclusive, but I wondered if anyone else had had similar problems...........?
 

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What size rear tyres are you running - the SLS should adjust for the extra weight automatically.
 

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Discussion Starter #3
Hi Tony,

Well then, my SLS isn't working at all, cos it dips down at least an inch..........but bear in mind with the trailer and race car, plus the tools etc., there's probably around a tonne sat on the back of it.........

Tyres are 245/40x18.

Just another thought - my spare is a narrower rim, but with the same width tyre. Having used the spare, it will be interesting to see if there's any signs of rubbing against the bodywork on it.

The extra width is on the outside yes?
 

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I might be in left field, but how much tongue weight are you asking the M5 to bear, what kind of overall trailer weight? If it goes down only an inch, this seems like a reasonable amount at rest. The problem might be that you have too great an overall load and the high compliance of the M5 suspension is having a hard time dealing with it. As you were towing and would go over bumps, did the load feel a little unstable? Kind of like the back of your car was a bucking bronco?

Me personally, could not allow myself to tow another car with my touring. Without knowing what the M5 is rated at, it seems like a nice trailer limit would be no more than 1000lbs. or a 150lb. tongue weight, assuming a properly loaded trailer.

Bad part about the M is it has enough power to tow 5000lbs.+, so this might give you a false sense of security as to its towing potential(low).

Good luck, Greg.
 

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Discussion Starter #5
Cheers Greg - Reckon I've got about 1 tonne (2200lbs) on there. VERY stable - correctly loaded. I'll be p1ssed off if I can't use it for towing..........VERY p1ssed off...........

BreakerBacker said:
I might be in left field, but how much tongue weight are you asking the M5 to bear, what kind of overall trailer weight? If it goes down only an inch, this seems like a reasonable amount at rest. The problem might be that you have too great an overall load and the high compliance of the M5 suspension is having a hard time dealing with it. As you were towing and would go over bumps, did the load feel a little unstable? Kind of like the back of your car was a bucking bronco?

Me personally, could not allow myself to tow another car with my touring. Without knowing what the M5 is rated at, it seems like a nice trailer limit would be no more than 1000lbs. or a 150lb. tongue weight, assuming a properly loaded trailer.

Bad part about the M is it has enough power to tow 5000lbs.+, so this might give you a false sense of security as to its towing potential(low).

Good luck, Greg.
 

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Rob Plummer said:
Cheers Greg - Reckon I've got about 1 tonne (2200lbs) on there. VERY stable - correctly loaded. I'll be p1ssed off if I can't use it for towing..........VERY p1ssed off...........
Hi!!
I`ve used my car ocasionally for towing (-93 touring with original EDC. The last time I surely had about that amount of weight on the trailer ~1000-1200kg (2200-2500lbs) with a tongue weight of ~70-75kg(160lbs?) (the recommended max weight) The back end didn`t drop at all. Interestingly enough, I also had a puncture that time(nail) and was forced to change rear wheel(s) -The back end sagged completely after jacking the car up on both sides+putting the trailer back on before starting the car, but when I started the car the back end raised it self to original position-if I Had only seen the back end of the car, I couldn`t have told that there was a trailed connected to the car.
Maybe that your SLS/EDC isn`t working properly (is it 3,6 or 3,8 M5?). Anyway, if your tires are of somewhat correct dimension there should not be any rubbing even if the back end sagged a bit

:M5launch: (with trailer)
Sakke
 

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Not sure if this helps............I have the original brochure for the 6-speed 3.8, and as your car looks exactly like mine.......assume its the same...........

it says ;

Permitted axle load -
front 1030 kg or 2271 Ib
rear 1250 kg or 2756 Ib

Permitted trailer load -
Unbraked 700 kg or 1543 Ib
Braked - up to max 12% gradiant 1400 kg or 3086 Ibs

I don't know about the techy physics of it, but thats what BMW state.

All the best
Mark
:cheers:
 

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Discussion Starter #8 (Edited)
Thanks guys.

Mark - you're spot on with your data - I've checked the handbook as well!

My race car/trailer combined can't possibly weigh over a tonne - so we're OK there then...........

Ball weight or nose weight (or whatever you wanna call it) is specified as 75kg. My mate's got a gauge for his caravan, so we're gonna try that.

What I don't understand is that I drove all the way to Elvington and back, and NEARLY to Oulton Park before it let go - that must be somewhere in the region of 160 miles..............

For interest, the spare I put on is showing NO signs of rubbing on the inner bodywork. It is a front wheel/tyre, but the extra width's on the outside isn't it?
 

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Discussion Starter #9
Sakke - how quickly did the suspension raise itself up after you turned on the engine??

I've always been looking at mine with the engine switched off............. hmmm
 

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Rob Plummer said:
Sakke - how quickly did the suspension raise itself up after you turned on the engine??

I've always been looking at mine with the engine switched off............. hmmm
Hi!!
Well, I had the time to start the car and step out to look. It took maybe 5-10sec to start raising and it took no more than 5 sec for the suspension to be in right position.
looked quite cool actually....

Sakke
 

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Rob,

The SLS has a low height warning switch so if its too low the OBC 'bongs' with something like 'SLS - failure' (can't remember the exact words!).

The SLS is purely hydraulic with a directional valve linked to the anti-roll bar. It can only raise the car with the power steering pump running but I suppose it could lower the car by draining oil back to the reservoir without the pump - for instance when you unhitch a trailer (it would be undesirable for the car to raise itself).

The same happens when you jack the rear end up - the oil drains and your left with only the gas in the spheres - not sufficient to support a trailer!.

I've never seen mine working but believe it does however I don't think its that sensitive. I can catch the exhaust exiting my drive with just two kids in the back seat! Take the kids out and it clears no problem - contrast the SLS air system on my Discovery which is good for +/-2mm.

SLS is perfect for a towing vehicle because it corrects the ride height (obviously!) but it also increases the spring rate.
 

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Rob,

I think this is a slow puncture - happened to me a while back with serious damage to a rear inner sidewall. Any signs of damage or foreign objects in the tread?

Kurt
 

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Discussion Starter #13 (Edited)
Thanks chaps.

Bit more info:

There is a definite scoring all the way around the sidewall on the inside of the knackered tyre. It's definitely rubbed against something on the car.

Not checked properly for foreign objects in the tread......

Having had a bit of a rummage around underneath, I'm bvggered if I can see what it could touch???!!! :grrrrr:

Also, I've now checked the other side - and there are no marks on the tyre whatsoever. The spare which I put on is also completely unmarked.

Getting a pair of rear tyres tomorrow (Michelin Pilot Sport £165 each - good price?), and towing the car again on Sat, so will find out then..................
 

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Rob Plummer said:
(Michelin Pilot Sport £165 each - good price?), and towing the car again on Sat, so will find out then..................
That's at the top end of what I'd expect to pay for 245/40-18s.

Regarding the tyre damage, it MUST have rubbed on something!! Could this damage have been there before you bought the M5?

Also, you should've been able to hear/feel it rubbing - you do sound like you have mechanical understanding/sympathy!

Have you managed to check the SLS ride height with the trailer on and with the engine running?

:noSMG:
 

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Discussion Starter #15
AndyE said:
That's at the top end of what I'd expect to pay for 245/40-18s.

Regarding the tyre damage, it MUST have rubbed on something!! Could this damage have been there before you bought the M5?

Have you managed to check the SLS ride height with the caravan with the engine running?

:noSMG:
Cheers Andy - cheapest price I could find for Michelins.

Tyre DID definitely rub on something, but was it done, as Kurt suggested, because of a puncture?

Not checked the ride height with the TRAILER (NOT CARAVAN!!) attached................
 

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Yeah, sorry - I don't know why I wrote caravan. I corrected it immediately, but you'd already replied!! Super Fast! I also added some more stuff to my post though. It could well be that the sidewall damage was caused if the tyre was still rolling with hardly any pressure. Those walls are so short that if it was low, it could easily fold in half without even being completely flat! :crying:

Regarding tyres, I presume those are Pilot Sport 2s. Otherwise;

www.johnsonstyres.com

245/40ZR18 MICH SPORT PS2 - £148.52
245/40ZR18 MICH SPORT PS1 - £133.19

Obviously this has them delivered to your door, but my local tyre man fits them for £15 a pair, so I only paid £248 for my last pair of rear S03s.

If you're paying £330 for a pair (of PS1s), it could be said that the £50 difference is not worth the hassle. But then, I'm really tight :hihi: ;)
 

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Discussion Starter #17
That's cheap!

Think you're doing well to get them fitted for £15 a pair. Most places HATE fitting tyres if you've bought them elsewhere.

I've gone for the Michelins for 2 reasons: already got a full set on the car! And I THINK they offer a good compromise between grip and longevity........... Might try summat different next time.

I'm hoping it's looking like a puncture and then collapse of sidewall - cos I can't see where it was rubbing........

It happened quickly too. Was absolutely fine, but after stopping at some lights, I heard that horrible flat tyre noise - only drove 20-30yds max.............

Plan now is to get new tyres, then I'll use the nose weight gauge to ensure race car is loaded on trailer spot on, then I'll give it a try..............will keep you posted!
 

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Discussion Starter #20
ste said:
And if you keep having trouble I'll buy the towbar back. :D

No need Steve! All sussed now!!

Just had new tyres fitted, and while the wheels were off, I looked for signs of rubbing on the damper/bodywork/anything! No signs whatsoever........

Also, found a staple type thing in the offending tyre. Looks like it was a puncture which because I then ran on it for a short (VERY short!) distance, caused the sidewall to disintigrate............

Hopeful of a successful towing mission on Saturday now. Panic over................................hopefully...........

Thanks for all the input.

Rob :byee55amg
 
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