Wheels & Tyres
When choosing wheels and tyres for your 306 there's a lot of technical
data you may feel you need. Some of it can seem daunting the first time
you look at it but it really is pretty straight forward. So to help you
understand things better we thought we'd give you a simple guide.
It is confusing because wheel and tyre manufacturers mix metric and
imperial measurements in almost all cases.
The obvious measure meant you're probably already aware of is the rim
diameter. These are fairly easy to understand, simply it's the inner
diameter of the tyre that fits the wheel. Typically this will be either
14, 15, 16 or 17 inches for the 306. It's almost always given in
Rim Width (J)
The rim width gives a good pointer to how wide a tyre you're going to
need. It also tells you how deep the rim is going to be into your wheel
arch. Too wide and it won't all fit inside the arch. This is usually
specified as a J fitting and it's typical to see it in the for 5J, 6J,
6.5J or 7J where the numeric part is once again in inches. So a 6J rim
width indicates a width of 6 inches, 6.5J is 6.5 inches and so on.
On the 306 once you start hitting 7J the width can become an issue and
rub the inner arches and the outer arch too. You may find you need to
use an arch roller to "flare" your arches outwards a little, or at
least fold the lip in.
If you've ever fitted a wheel you'll notice it isn't the 4 bolts that
actually hold the wheel in place, but a small ridge in the centre of
the hub. This hub needs to be matched by the bore size of the rims you
are fitting. Without ensuring the bore size matches the hub size you
will be putting the load of the car onto the wheel bolts and this is
incorrect. If you have a rim with the wrong bore size you can get an
adapter called a "spigot ring", to fit that will act as a shim between
rim and hub so the weight is correctly held on the centre of the hub.
Unfortunately if you have rims with a smaller bore size than your hub
there is little you can do. However, if you have to use a spacer you
could get a custom made spacer that acts as a very thick spigot ring.
The Peugeot 306 has a
bore size of 65.1mm
The offset is simply the distance between the inner face that mates
with your hub to the centre of the rim width (J). This is probably the
one that confuses most people. The higher the number the further away
in millimeters the face is from the rim width centre. The confusion
tends to happen because in order to maintain the manufacturers centre
line for the rim you need to know the ET of the vehicle. In the case of the Peugeot 306 it
has an offset of ET13-18
. Between 13mm and 18mm. So if
you have a rim that is ET28 you would need a 10mm spacer, to bring the
offset down to ET18 (28 - 10 = 18) in order to align the centre of the
rim with the manufacturers intended centre for the hub. Typically
spacers are available in 5, 10, 15, 20mm thickness, so you should use
the closest match or have a custom thickness made.
The reason this gets difficult is because wider rims can cause problems
with rubbing on the inner arches, even if you have the correct spacer
for your offset. So in order to compensate you may have to ad 5 or 10mm
to your spacer to stop it from rubbing, but your offset will then be
wrong. Although wrong in terms of manufacturers spec, you're not going
to see much of an issue unless you go way too far.
Pitch Centre Diameter (PCD)
Every wheel has to be held onto the hub somehow. The PCD is a guide as
to how many fixings (bolts/studs) it uses and the diameter to the
centre of those fixings. This is given in the format of "PCD 4 x 108".
Where the 4 represents the number of fixings and the the 108 tells us
they are arranged in 108mm diameter circle around the hub centre. So
PCD 5 x 100 means 5 fixings at 100mm diameter. So to make sure the rim
you choose fits the hub on your car, you need to make sure it has the
The Peugeot 306 has a PCD
4 x 108
Now you know how to choose the right size spacer, the next thing you
need to think about is back to the bore size notes. You can't just pad
the rim out by 10mm and not consider the centre bore - remember, it's
the bore that takes the vehicle load, so it's important! This is where
you'll need what are called "Hub centric Spacers". A hub centric spacer
is simply a spacer with a centre lip so it meets the hub centre lip and
then replicates it on the outer edge for the rims to connect to.
With a 5mm spacer there may be enough of the hubs rim
protruding to not need a hub centric spacer. But once you go beyond
you must use a hub centric spacer.
Thicker spacers means you'll need longer wheel bolts. Again once you go
above 5mm, things change. After 5mm the standard bolts don't have
enough turns on them to hold the wheels on safely. So if you put on
10mm spacers, please also use 10mm longer bolts. Similarly 15mm spacer,
15mm longer bolts.
At around 20mm you may then prefer to look at spacers that bolt onto
the hub and then the rim bolts onto the spacer using the existing
standard wheel bolts. I'm always wary of using bolts that are overly
long for your wheels. So bolt on spacers offer a great replacement and
the cost can be offset by not having to buy new bolts.
reason for using bolt on spacers could be to convert the PCD to match
your new rim. Let's say your new rims have a PCD of 4 x 100, these
obviously won't fit your 306 which has a PCD of 4 x 108. Well using a
bolt on spacer you can use the PCD 4 x 108 to bolt onto the hub, but
have the wheel fixings onto the spacer as PCD 4 x 100, or even 5 x 100
to convert the amount of fixings.
As an alternative to solve the longer bolts issue you can
convert from using
bolts by fitting studs into the hub and then using nuts to hold the
wheels onto the studs. The added benefit of this is that you'll also be
able to get your wheels on easier. No messing around trying to hold the
wheel on and aligning the holes to put the bolts through.
- The width of the tyre tread that contacts the road surface in
Profile / Aspect
- The height of the sidewall of the tyre in relation to it's tread
width. So a 55 profile tyre has a sidewall height of 55% of it's tread
width - in this case 55% of 195mm
construction of the tyre is made of radial plys of banding inside the
rubber construction. You may also see a ZR marking here, which simply
indicates a high speed tyre rated beyond 149mph.
- The diameter in inches on the inside fitting of the tyre. This is the
part to match against your rims.
Many tyres you're probably interested in are designed for cars and are
made to carry only a specific weight. You need to make sure that if
you're fitting a tyre to a larger, heavier vehicle, a pickup or MPV,
that the tyre can carry the additional load. You can check this at many tyre sites
in this example a rating of 85 gives us a maximum load rating of 515kgs.
- This indicates the maximum speed for which the tyre is designed for.
In the example a V indicates a maximum speed of 149mph. Again many tyre
sites have tables to cross reference
As a general rule of thumb you should keep the outside diameter of a
tyre exactly the same as the original tyres fitted by the manufacturer
(OEM = Original Equipment Manufacturer). Keeping the diameter the same
ensures your speedo reads correctly and that your gearing remains
constant with the new tyres. But when you fit a bigger rim fitting the
same width tyre with the same profile will result in a bigger overall
Generally speaking you can achieve this with some simple changes. For
each inch of rim diameter you increase by, you should decrease the
profile by 5%. So as standard 195/55R15 tyre becomes a 195/50
R16 on a
16" rim and 194/45
on a 17" rim.
Similarly for tread width. If you fit a tyre with a wider width tread
then for each 10mm added in width you should decrease the profile by 5%
too. So a 195/55R15 becomes a 205/50
R15 on a
tread width of 205mm.
Conversely, if you fit smaller rims or narrower tread increase the
Typically the Peugeot 306 comes
with 195/55R15 tyres on Cyclone alloys.
This means that changing the alloys for wider, bigger gives you the
16" Rims 195/50R16, 205/45R16
17" Rims 195/45R17, 205/40R17
A handy calculator for working out the differences in tyre widths,
profiles and diameters can be found here: http://www.miata.net/garage/tirecalc.html
Further more detailed reference: http://www.carbibles.com/tyre_bible.html