Quick Check - anyone on 245 up front with 17" OEM `Stars or Turbines ??? - The Unofficial BMW M5 Messageboard (m5board.com)

IvanDias · 21st August 2002, 18:17

Just to check as my fronts are going to need replacing the end of this month.

I have stock MSystem II rims, ie, take Turbine or Throwing Star covers, in 17". The original size is 8.0"J with 235/45/17.

I recall at least one of you has put 245 up front without rubbing. Do you know who it was, or can you confirm is OK???

235/45/17 gives a choice of 245/45/17 or 245/40/17.

The 45 profile will be nearer (just over) the original rolling diameter, the 40 profile a bit under.

I`m tempted to go with 245/40/17 if OK, because this will also give a 7.75mm drop to the front, which may help keep the front down at speed. (70mph on UK motorways !! LOL)

The speedo will be unaffected as this is obviously taken from the rear diff.

Have I missed anything, or are all systems go ??

Ivan.

Mmm-Five · 21st August 2002, 22:43

Ivan,

What are your front/rear wheel/tyre sizes?

I ask as I was wondering if you can put the rears on the front and put 255/40 Z17 on the rear?

245 width do fit on the later 3.8 M-Parallels fine though (245/40 Z18) so I don't think you'd have any problems with either 245/40 or 245/45 in 17s.

Ben · 21st August 2002, 23:08

Been running 245/40s on all four corners for several years. Street and track. No trouble.

- Ben

Captain Kirk · 22nd August 2002, 20:38

The height of 245/45R17 is the issue. It may clear, or not depending on brand of tire and if your struts are bent. Heard one report that they only rub when the car is driven hard.

IvanDias · 22nd August 2002, 22:09

That`s why I`ll go with 245/40 over 245/45 on a 17".

Ta.

StormMaster · 23rd August 2002, 08:26

While we're at it, what about mounting 265/40s on the rear?

My stock setup (w/N'ring package) is 235/45R17 F and 255/40R17 R. Has anyone played with a slightly wider tire on the rear? More to the point, is this likely to enhance -- or adversely affect -- overall handling? I can't say as I've been disappointed with the factory specs, but curiousity occasionally gets the better of me.

Chuck

Bryn · 23rd August 2002, 11:12

Yes I've had 265x40x17 Bridgestone S02 on the 9" rear alloys, and they were fantastic. Grip was phenomenal - it was even hard to break traction under full throttle in the wet

I have also used 265x35x18 AVS Sport on 8.5" BBS alloys, but the Bridgestone's are in a different league.

I haven't run any other width of tyre, so I can't say what the difference is, but I've had no problems with rubbing.

Cheers,
Bryn.

IvanDias · 23rd August 2002, 11:16

StormMaster,

They are normally fine, 265/40/17 on the rear.
275 won`t mount on a 9"J rim safely, and will rub the struts with the BMW factory wheel offset unless used with spacers.

Interesting point.
The diameter of a 255/40/17 is 25.03 inches.
The diameter of a 265/40/17 is 25.35 inches.

The diameter of a front 235/45/17 is 25.33 inches.

So, the 265 tyre actually is a closer match than the specified factory size. LOL.

(Just for reference, a 245/40/17 is 24.72".

IMHO BMW probably didn`t put a 265 on the rear as it would increase the understeer even more, and there is already quite a bit with 9"J rears on 255 compared to the 8"J running 235s.

Ivan.

PS. Yes, when the rears run out, I`ll be either buying a set of E39 M5 wheels and some spacers for 255 front, 275 rear or if money is tight then just some 265s for the standard wheels.

Captain Kirk · 23rd August 2002, 18:02

275's are safe on 9 inch wheels. I have heard 275/35R18's fit with an ET22 offset. I assume 275/40R17 would work as well.

IvanDias:
To fit 255's in front you will need front camber plates for clearance between the tire and fender, the ET13 wheel will let the tire clear the strut, but all the new width is outboard. I am not a fan of E39 wheels on an E34. Wrong offset. I took off 255/40R17 on ET15's (all around) and camber plates. Too much wander.

StormMaster:
Any discussion of improving handling must start with an understanding of slip angles, i.e., what is happening where the rubber meets the road. Wider tires and lower profile tires reduce slip angle for a given cornering load. For the same size tire, the one with more weight on it will have a higher slip angle (double whammy here, more weight means more cornering load).

This is where all this oversteer/understeer stuff comes from. With a 235 up front and 265 in the rear, the front will "slip" more, providing the nice safe understeer that the majority of drivers prefer. Add to that a bigger front bar, a rear camber bias, and the car handles like a pig. A pig on rails, but still a pig.

We equate big rear tires with performance. Why? Muscle cars use big rear tires to improve straight line performance. Porche uses big rear tires because they have more weight over the rear tires.

E34's have near 50/50 weight distribution, therefore handle best with the same size tire front and rear. Period. Well, I'll make an exception for cars making 500+ HP.

Here is what I'm running
245/40R18 S03's on ET20 wheels
Dinan front bar, 20 mm Touring rear bar, M-Technik springs, Koni Sports in the front, LAD in the rear, -0.5 degree factory strut bearing in front and K-MAC trailing arm bushings in the rear set for -1 degree total camber front and rear.

I like this for a street setup. Tire size, camber and weight distribution are essentially equal front and rear, which leads to similar slip angles and that elusive neutral handling. I'm using big sway bars to limit body roll and currently am experimenting with the front bar full hard, so there is some understeer.

IvanDias · 23rd August 2002, 18:39

Quote:

Originally posted by Captain Kirk
275's are safe on 9 inch wheels. I have heard 275/35R18's fit with an ET22 offset. I assume 275/40R17 would work as well.

I wouldn`t say I`m a wheel guru, but 275 on a 17" wheel at 9.0"J generally is not safe. There is too much overhang for the profile.

I don`t recall ever seeing a factory car of any make with 275 on a 9. They all used 9.5", even the E39 M5.

On the M Parallels, I thought 275/35/18 rubbed on the rear, standard offset ET22.

This thread is wandering a bit. The thread title specifically stated the OEM M5 M-Series II wheel, not M-Parallel or any others with different offsets.

Thanks for the info though, I`ll start collating it all and post a definitive page on my website and copy it to the BMWFAQ site stating what you can and can`t do for the E34 M5.

Ivan.