Recommended: Tyre Sizes and Pressure values for E39 skid

ChrisJ · 2005-09-13T10:03:59+00:00

Ok, after having a hair raising skid (no damage! thank goodness), andthen experiencing a certain feeling of instability with my E39. I havebeen trawling through this board for some answers and would like a fewrecommendationsI've read that the most common cause of BMW E39 feeling unstable ismismatched tyres or incorrect pressure first. So I need to be sure ofthis before turning my attention to other parts of the car.My E39 523 has225/40/R18 on Front265/35/R18 on RearMy problem seems to be from the rear, which I lost on the skid in wetcondition I might add..A poster recently asked if these weren't 235s on the front. Is there aproblem with 225s?Should I be running with the same size tyres all round? I've readdiffering opinions as to which set should be bigger front/rear.Considering the wet conditions that would be encountered soon, whatwould be best??What tyre profiles does BMW recommend as standard for R18's on E39??And what pressures are best for all round driving. If not whats the dryand wet condition values.Thanks

Sep 13, 2005 21 Replies

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Malt_Hound 20 years ago

You ain't gettin it, Jeff. This is n't somethin that we're making up. It's more like this:

|\/\/\/\/| |/\/\/\/\| |/\/\/\/\/\/\/| |\/\/\/\/| |\/\/\/\/\/\/\| |/\/\/\/\|

get it?

-Fred W

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Alistair J Murray 20 years ago

[...]

...at any given tyre pressure - it's the air that bears the load.

Lowering the pressure lets the tyre flatten more increasing the area of the contact patch, and vice versa.

My B10's 265/35 R18s at 3.0 bar actually have smaller contact patches than the narrower tyres fitted as standard to a 523 running at lower pressures.

The extra grip is down to the tyres generating bigger slip-angles due to the shape of the contact patch (plus stiffer sidewalls, sticky compound (with OE Michelin Pilot Sports or similar), progressive rate springs and twin-tube dampers tuned for the wheel/tyre combo).

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