With all mid-engined cars the front is lighter than the rear and doesn't require the same tyres all round. The rear requires tyres that will cope with the weight and power, whilst the fronts can be smaller as the weight is less and they only have to cope with the normal suspension and steering. All Bagheera generally had 5.5J x 13" steel or alloy wheels with 155HR x 13 tyres front and 185HR x 13 tyres rear; since there was little difference in weight or power between the two engine options. (1300 or 1442) The spare was a 155 front tyre. Note: these tyres have no low profile designation in their specification as was common at that time, but they are in fact 82% profile, and the new 80% low profile tyres are effectively the same and can be mixed on the same axle. Neither the original tyres nor the new 80% profile tyres are generally available in that 185 size (although you may be able to get front tyres in that size - 155/80HR x 13). You can still get them through vintage tyre suppliers and in XVS tread pattern too, although that means they will be a little expensive, but if you want original...
The original rear tyre was the widest size you should fit to a 5.5J rim and if you tried to fit a later 70% profile, you would need to go much wider to give the same rolling radius and therefore the correct ride height and gearing; but you cannot go wider on 5.5" wheels. So if you used a 185 with a 70% profile instead, you would lower the rear of the car, and with the front of the car higher the aerodynamics would be wrong and cause the car to lift at speed. You could of course fit 70% profile tyres at the front too, at least keeping the car level, but you would find the gearing a lot lower. Better for acceleration but lowering the usable cruising speed! With only a four speed gearbox the original large high profile tyres gave the car a reasonable gearing. With 70% profile tyres the car will be under-geared. So you are stuck with vintage tyre supplies of the correct size at least at the rear, if you retain the original wheels and wish to keep the original gearing.
Bagheera tyre pressures
1.4 bar front, 2.0 bar rear (13" Michelin 82% profile tyres)
Wheel bolt torque given in the manual is 8 daNm, or 60 lb ft.
The Murena had different wheels as well as tyres on the 1.6 and 2.2 models, since compared to the Bagheera there was a substantial difference in the weight and power of the two models. The steel wheels and lesser tyres of the 1.6 were partly to keep the cost down, but also since the different weights and distribution created different requirements. A standard 1.6 had a 48%/52% front to rear figure, whereas a standard 2.2 model had a 41%/59% front to rear figure. The standard wheels and tyres were:
1.6 models: 5.5J x 13" steel wheels with 175/70HR x 13 tyres front and 195/70HR x 13 tyres rear.
2.2 models: 6J x 14" alloy wheels with 185/60HR x 14 tyres front and 195/60HR x 14 tyres rear. These rear tyre widths were again right on the limit for the rim widths.
N.B. There are two versions of the Murena alloy wheel. The standard one and the version for Germany/Austria, because their laws require a certain minimum specification for any alloy wheel, so Matra had to produce a second version. To distinguish the two which are designed to look the same, there is a small difference where the radial fins meet the rims.
Also note: if a 1.6 was ordered with alloys, the spare remained a steel 13" wheel and front tyre, whilst the 2.2 always had an alloy spare with a 185/60 tyre, so in the event of a puncture the spare is a straight swap for a front wheel and tyre but is slightly smaller than a rear tyre. However it is at least a full size wheel and tyre not a speed and distance limited 'space saver', and is perfectly adequate as an emergency replacement. I have since found that a more ideal front tyre for the Murena 2.2 is a 185/55HR x 14 which was a size not available when the car was new. The slightly smaller profile brings the relative ride heights back to correct and improves the handling; and since it drops the car a small amount, lowers the centre of gravity and the fractionally lower front improves the aerodynamics too, without really affecting the speedo accuracy. In fact the 55 profile front brings the Murena on alloys and 14" tyres back in line with the original design on steel wheels and 13" tyres as far as car attitude is concerned.
Explanation
The 1.6 front ride height on 13" steel wheels with 175/70HR x 13 was 1mm lower than if you had the 14" alloy wheels with 185/60HR x 14 tyres. However, the rear ride height on steel wheels with the 195/70HR x 13 tyres was 7mm higher than if you had the alloys with 195/60HR x 14 tyres. So a 2.2, or 1.6 on alloys, had an incorrect slightly 'nose high stance'. On my recommended 185/55HR x 14 front tyres, the 2.2 front ride height drops to 8mm less than the car on 13" steel wheels and tyres, so with an 8mm drop at the front and a 7mm drop at the rear the 2.2 or a 1.6 on alloys, has virtually the same horizontal attitude as the original 1.6 on steel wheels. Note the 1.6 rear tyres (195/70HR x 13) are now getting hard to find, and the only real source may be vintage tyres suppliers just as with the 185HRx13 rear tyres on the Bagheera.
These cars use a 4 bolt fixing (12mm x 1.5mm pitch) with 98mm P.C.D. (pitch circle diameter) 29mm offset, and a hub spigot diameter of 58mm. This is where the wheel locates for concentricity. This is the point where wheels can stick after they have been on for a while so people often put grease here. Please do not use copper grease - copper and aluminium react because of their positions on the Galvanic scale. You should use Alumslip made by Molyslip who also make Copaslip. Alumslip is the correct grease for this purpose but a small amount of LM grease is better if you don't have any Alumslip. The wheel specifications are similar to the Simca/Fiat/Lancia/Alfa wheels, but the Italian cars' wheels generally have a 38mm offset. If you use the wrong offset, you alter the cars track width, and the load through the wheel bearing becomes offset which will cause it to fail earlier as it now has to cope with a side torque. The 38mm offset will give a narrower track as each wheel is 9mm further in and closer to the suspension. So if you wish to use different wheels and buy ones designed for an Italian car, you will need wheel spacers and longer wheel bolts. I strongly suggest you don't use bolt extenders! Murena wheel arches were made large enough to take much larger wheel and tyre combinations without modifications, since I speculate, it was planned to put more powerful and probably larger engines in it, if it had continued in production. I have seen 15" and 16" rears with 215 and 225 widths at 50% profiles and they appear to fit comfortably. However, always check suspension clearances with any wider wheel and tyre combinations and expect movement under hard cornering reducing the clearance a little from the static figure. From experience the widest wheel that can be used using the correct offset is 7.0" and therefore I suggest a 225 tyre width.
Finally, tyre sizes and pressures are always important but especially so with a mid-engined car, and the pressure disparity between front and rear are often much greater than a normal car. Equally the front and rear sizes should be different. The size that is correct for the rear is too big for the front, and the front size is inadequate at the rear. Those who have fitted the same size tyres front and rear will testify to how dangerous the car can become, so don't do it. Always make sure the tyre pressures are correct too if you wish to drive safely! The pressures are in the handbook and the cars also had a sticker on the drivers door near the lock mechanism, as an easy reminder. Early handbooks had a mistake and often had one of the door stickers over the original settings. If you're not sure if yours are correct or have lost the handbook/door sticker, these are the correct original figures:
Murena tyre pressures
1.6 models steel wheels - 1.8 bar front 2.1 bar rear, any brand tyre (13" originally Michelin 70% profile tyres)
1.6 models alloy wheels - 1.8 bar front 2.4 bar rear, any brand tyre (14" originally Pirelli 60% profile tyres)
2.2 models alloy wheels - 1.8 bar front 2.5 bar rear, any brand tyre (14" originally Pirelli 60% profile tyres)
[2016 Update] Note: Although it is now impossible to get 185HR x 13 rear tyres for a Bagheera or the 195/70HR x 13 rear tyres for a Murena 1.6 on steel wheels without using someone like Vintage Tyre Supplies, this may be about to change. I was contacted by someone at the Restoration Show that is involved in re-making tyres for the popular sixties and seventies classics so they have some 13" and 14" already and more are coming, and at reasonable prices. So you may have to use Vintage Tyre Supplies at present but watch the classic press for further announcements. Also note that tyres change so quickly that what is available one moment may not be the next!
I strongly recommended 55 profile tyres on the front of the Murena on alloys i.e. 185/55 R x 14 front with the normal 195/60 R x 14 at the rear. (see my technical article on tyres) Presently (January 2019) Vredestein do an all-season Quatrac 5 in these sizes. Also having now used winter tyres for the past few years I can recommend these because they are softer and have terrific grip at low temperatures and yet they don't wear out quickly on dry roads or a U.K. summer. They might not have the ultimate braking in the dry of a proper summer tyre so you need to consider your particular usage. Since the Murena is light at the front, a set of winter tyres used all year round would probably still last 40,000 kms or more! If you want an 'H' rated winter tyre in 185/55x14 there is a Nankang (SV-3) with this rating and whilst this brand may not be that well know I have used Nankang on my Espace the last 3 years plus, and they are really good. If you prefer to stick with well known brands there are Continental, Falken, Uniroyal, or Kleber in 'T' ratings, and Vredestein do an asymmetrical summer Sportrac 5 in both recommended sizes although the 195/60 rear may now becoming difficult to find. Tyres change so rapidly it is always difficult to keep up, so you have to check at the time you need them. One final point, I don't recommend low energy 'eco' tyres or low rolling resistance tyres as they simply don't have the grip of the normal tyres and it is grip that is the important criteria.
Also think about the spare wheel and particularly the tyre. Since the front and rear tyres are different, and the spare needs to be available for use either end and either side, it would be best to stick to a non-directional tyre, and one of the original size so that it can be used in any position. I keep a used normal 185/60 HR 14 on my spare, which is in between the front and rear sizes (slightly larger than a 55 profile front and smaller than the rear, so is suitable for either in an emergency). Why carry around a brand new tyre that is only going to be used occasionally on the rare occasions you might get a puncture? If you have a half worn tyre that is fine (and better than a skinny space saver IMHO).
Murena wheel bolt torque
Workshop manual states 6.3 daNm, (48 lb ft) or up to 7.5 daNm
However, I would say even the same as the Bagheera: 8 daNm (60 lb ft) is fine.
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