General Tyre size explained.

[RuSZ]

so dave, if mine is 20 mm higher, would you suggest getting 16" instead of the standard 15", without going for the lower profile tyres? or is this not allowed because is changes the overall wheel diameter?

Dont worry about the suspension height.

you need to match the rolling radius of the wheel. once thats done you can lower it.

The gap between you tyre and wheel arch will be identical to what you have now.

 

[Rpayne]

kk cool, ill just do that, want to avoid lowering for now so hopefully they will look alright like that, lowered every car so far, and just cba with the problems that come with it atm... cheers for youre help pal

 

[colinf1]

Both me and Colin have different Specification's of Punto's i believe. Yet we have identical ride heights.

mines a standard 1.2 8v, currently undergoing engine replacement, just another 1.2 8v...

only difference imo is mk2 and mk2b and 5 year difference in car ages

so dave, if mine is 20 mm higher, would you suggest getting 16" instead of the standard 15", without going for the lower profile tyres? or is this not allowed because is changes the overall wheel diameter?

you can have larger profile tyres if you want, it only means that your speedo will be out, so say when your doin 30, ud really be doin 35mph
the way around this is to use a sat nav which will give the true speed, then ull know exactly how much the speedo is out

 

[bredsticz]

Biger rolling radius means slower accelreration but a slight higher top speed aswell.
Slight more strain on the gearbox is there?

 

[chaos]

No such thing as a silly question, only stupid answers (which happens alot around here)

Whilst your's (and colinf1's) explanation of offset isn't a stupid answer, they're both got bits wrong.

Negative offset will push the wheel centre line further out of the wheelarch (i.e. the wheel will be pushed out of the arch). A more positive offset will move the wheel further into the wheelarch. Spacers are used with alloys with too much positive offset to push the wheel centre line outwards.

Using mk2 Puntos as an example

A JTD has 6" wide wheels with an offset of 35mm (i.e. ET35).
A Sporting also has 6" wide wheels but an offset of 33mm (ET33).
A HGT has 6" wide wheels but are ET37.

If you fitted the ET33 wheels onto a JTD, the wheel centre line will move out of the wheelarch by 2mm.

If you fitted the ET37 wheels onto a JTD, the wheel centre line will move into the wheelarch by 2mm.

If you had ET37 wheels fitted but wanted the centre line to be the same as if the ET35 wheels were fitted, you would need 2mm spacers. If you wanted the same ET37 wheels to have the same centre line as the ET33 wheels, you would need a 4mm spacer.

Another example is fitting Punto GT alloys onto a Cento Sporting.

Both wheels are 5.5" wide.
A PGT alloy has an offset of 40.5mm.
A Cento alloy has an offset of 30.5mm. However, a Cento Sporting also has a 3mm spacer fitted as standard on the front, so the overall offset on the front only is 27.5mm.

If you want the PGT alloy to sit in the same place in a Cento wheelarch as standard then you would need 13mm spacers (40.5mm-13mm=27.5mm) and do away with the standard fit 3mm spacer.

On the rear, where there's no factory fit spacer, there's a 10mm difference in offset. If you fit a 10mm spacer onto the rear with a PGT alloy, then the wheel will be in the same place as standard on a Cento Sporting.

Make sure you use good quality spacers and that different length wheel bolts may be needed. Also make sure the centre bore of the alloys is correct too.

I would be very surprised if a ET45 alloy fitted straight on a mk2 Punto with no spacers.