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M5 Russ

E35 M5 TYRE SIZE EXPERIMENT

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Before I buy my new 19 inch rims for the M5, I thought I would experiment with tyre sizes so I bought some part worn 285 30 19 Continental 5 in place of the 275 30 19's for the rear and so far not had any rubbing plus they offer more protection for the rims and look a bit better

 

Next up is 255 35 19 on the front - up from 245 35 19. Anyone used this size ?

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Hi Russ,

 

You've got to check the rolling radius of each tyre size to make sure it's as close to the oem rolling radius as possible. If you stray too far out, it can confuse the systems on board and make the car cut power etc. 

 

Whicn 19 inch wheels have you gone for?!

 

The recommended tyre sizes are 245/35/19 front and 275/30.19 rear. You can 'get away' with using 235/35/19 front and 265/30/19 rears. Depending on how low your suspension is, you can also experiement different tyres as they have different sidewall profiles - some are more 'rounded' others more square.

 

Have a look at this website where you plug in your existing wheel and tyre specs, then new ones. You'll see the percentage difference and rolling radius differences. http://www.willtheyfit.com/

 

I've hardly seen any posts where others are using just one size width up from the recommended sizing. Usually, it's either those doing a stretch of varying degrees and using thinner section tyres, or those running much wider wheels and going for really big 295/305 width tyres.

 

Cheers, Dennis!

Edited by DennisCooper

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Hi Dennis.

I will be getting a new set of LM reps the same staggered size as i already have. I am only changing the width so going from 275 to 285 and 245 to 255.

I was just thinking more of the fronts fouling the arch but after the success of the rears i think the fronts will be fine. My car is not ubber lowered really. The tyre guy thinks there will be no problem so will hopefully find out next month.

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Out of interest any pics on the lm reps as interested in a set for mine possibly. Are they the bmautosport ones?

Yes they are -  I would not use any others to be honest. They have lasted 4 years but after numerous kerbings and various, I have decided to renew them rather than refurb them. At £500 a set it just aint worth messing about.

Edited by M5 Russ

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Hi Russ,

 

Keep in mind that the tyre sidewall ratio is a percentage of the width. Many people wrongly assume that the tyre sidewall measurement is 'centimetres'. 

 

This is why a 335/35 tyre has the same 'height' of tyre sidewall as say a 225/50 (for example) 

 

So in this case, if you are going from a 245/35 to 255/35, the wider tyre will have a marginally higher sidewall which is shown when you plug it into that calculator site I linked to!

 

It 'sounds' as though it should be ok, but as ever, it might be enough to 'upset' the car or, it might be enough for you to feel the difference when driving etc. 

 

Cheers, Dennis!

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Have you had any cracking issues with the LM reps? I had 19" reps on a previous e39 and got rid of them as they got several cracks in them

Not any. They are a bit battered especially the fronts but balanced no problem. I had a good look at the wheels whilst they were off the car and saw no signs of cracking. 

 

Edit. thanks for the link Dennis. Thats a great site and it confirms that all changes are well within tolerances. 

Edited by M5 Russ

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Hi Russ,

 

You've got to check the rolling radius of each tyre size to make sure it's as close to the oem rolling radius as possible. If you stray too far out, it can confuse the systems on board and make the car cut power etc. 

 

The only thing it will do is alter the speed accuracty (slightly) and trigger the tyre pressure monitoring system (if fitted), it won't cut the power.

 

I'm currently running the official BMW winter wheel & tyre package for the E39 M5, which are 235/45/17 all round, the standard sizes are 245/40/18 front and 275/35/18 rear, which give a -1.5% and -1.0% error respectively, so different rolling radius error front & rear.

 

All this did was trigger my tyre pressure warning (so I reset the system) and my speedo now shows 1mph different at motorway speeds than it did previously, based on my GPS Road Angel, other than that there has been no affect.

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Dennis i assure you going up 10mm in width affects the overall rolling radius so little it isn't worth bothering about. Put it this way, the difference between a 275 35 18 (Original size) to a 285 30 19 is 4mm difference in the whole diameter, or to put it midly, once you've worn your new 19's tread down 2mm from new, they'll be exactly the same size and read the same.

 

As Rich pointed out the difference in the standard sizes compared to standard winter sizes already show some small discrepancy, which given that profiles rise in stages of 5 percent and width in 10mm increments isn't unusual. You can't get every tyre combo dead on. Anything under 2% is deemed acceptable although you can run outside of this a little with no ill effect.

 

The only time you will trigger a fault is if on wheel or one axle is spinning at far greater a speed than the other. You'd have to be running seriously mismatched tyre sizes for that to happen, this is why cars put on the rolling road have to have fuses pulled so the car does not limit revs, as the front wheels are still whilst the back ones spin.

 

Russ, many lads over on M5board run tyres wder than standard. Perhaps a quick look over there will guide you although i know some users are running 295 rears with standard arches. Just be aware that although tyre manufactureres quotre "285" etc for a width, that the actual width does differ slightly from manufacturer to manufacturer and so whereas some 295's may be tight or foul, others will not

Edited by jamiepeers

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I do browse M5 board as it is almost the e39 M5 bible for our cars. So far so good with the rear tyres.

I will have to reset the tyre pressure monitor but I am not even sure its still works !

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I do browse M5 board as it is almost the e39 M5 bible for our cars. So far so good with the rear tyres.

I will have to reset the tyre pressure monitor but I am not even sure its still works !

 

It works off the ABS wheel speed sensors in the M5, so it will work, I used to think mine was duff too.

 

If you press the button on the dash it comes up with a message about it being inactive, as the button turns it off and the manual is not very helpful, you basically set it once and it will warn you if it detects that a wheel (or wheels) are turnining slower due to the tyre pressure dropping.

 

When I changed to the winter wheels it flashed up the warning with a 'bong' noise and I just reset the system

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how do you reset it - was holding it in for 10 seconds or something ?

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how do you reset it - was holding it in for 10 seconds or something ?

 

Make sure all the tyre pressures are set correctly first, then follow this procedure:

 

- Turn the ignition on but don't start the engine

- Press & hold the tyre pressure monitor button for about 10 secs

- A message saying 'SET TYRE PRESSURE' appears on the high OBC

- You can now start the engine, the system is in learn mode

- Drive the car for at least 10 mins, ideally at varying speeds and faster than 30mph

- You won't get anything to confirm it's done, but it will be set after this

 

If you ever just press the button it disables the system, you get a message telling you it's inactive, it resets again once you turn the ignition off, the manual doesn't tell you this and most new owners push the button, get the message and assume the system is broken.

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Thought I would post a quick update on running with 285 30 19 tyres on the rear. 

 

There was some arch rubbing on hard acceleration and with passengers when driving over less than even ground. On closer inspection there is only a part lip on the leading edge by the sill so I decided to get my son to use his arch roller on it.

We only went in a few mm but it has completely cured the rubbing in all situations. The rolled lip is hardly noticeable to be honest but it is not easy to do as its double skinned. I will take some pics later for you guys.

 

Russ

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