Replacing wheel/tyre compatability - upgrading to alloy

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PenguinWithHair

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Hey everone,

Can someone help me get my head around the general rules in changing wheels/tyres on a car?

I've got an old mk4 astra, and the tyres are going to want replacing soon. Seeing alloy wheels with tyres pop up second hand is quite tempting especially when they're about the same price as new tyres.

Even if I don't replace my wheels I'd quite like to know how the numbers work.

Generally speaking, is it worth the upgrade from steel wheels?

Bolt holes, are there millions of different sizes or are they generally compatable if there's the right number?

Tyre width, is this specific to the wheel, or the car?

Tyre profile and hub diameter, what's the general rule here? I get really easily confused by this. Can you get away with bigger wheels, if you have lower profile tyres? For example can I replace my 175/70 R14 with 195/45 R16 and not mess up my gears and speedometer and so on?

Lots of questions here... I guess I'm just looking for some general guidelines. Oh and also has anyone experianced a massive surge in insurance cost after having made such an upgrade to an old car like mine?

Cheers everyone!
 
You do need to tell the insurance company

There is no difference in ride due to alloy wheels, but there is due to profile

Low profile gives a harder ride

Easiest is to find wheels that specifically say they fit your car
Manufacturers vary the stud numbers and size

Ensure that the tyre width is compatible with body shape
 
Tyre sizes briefly explained...
175/70/14 means tread width 175mm, sidewall height 70% of the tread width, wheel diameter 14 inches. Total diameter 23.6 inches.
195/45/16 is 195mm tread width, sidewall height 45% of tread width, wheel diameter 16 inches. Total 22.9 inches diameter.
The 16 inch wheels are overall 3% smaller, thus you'll be travelling 3% slower than your original speedo reading. Bear in mind the difference between a new tyre and a worn one is maybe 5mm of tread (top and bottom) which can easily be 10mm over the diameter of a wheel anyway.
Google tyre size calculator for helpful sites.
There are different stud patterns, centre hole sizes, number of studs, offsets etc. Again, there are helpful websites.
Fitting bigger wheels with less air cushioning between the wheels and the rubber gives a harsher ride.
 
Definitely go for a make that is designed for the car....the offset is crucial, as is clearance around the brake calipers.
John :)
 
The Mark4 Astra (G) came out of the factory with either steel or alloy wheels. IIRC the most popular size was 185/65x15 or 195/60x15, but I seem to recall the bottom of the range 1.4 was on 175/70x14. Are your wheels 4 or 5-stud fixing? I would have thought a set of alloys from the Astra G could be picked up pretty cheap at a dismantlers. (You may need to change the wheel bolts though.) A quick internet search shows tyres in the popular sizes above start at around £40 each.
 
My 2014 Astra came with no spare - just a pot of gunge and a mini compressor- I paid £100 for a good ali (online auction) and £40 for a budget tyre. The gunge will be used in wheelbarrow wheels(y)
 
the wheelnuts or bolts are also different, I'm told that nuts for steel wheels can crack alloys.

I too bought fullsize spare wheels, discarding the manufacturers space-savers.

The can of gunge is even worse, because if you use it, it spoils the tyre so it can't later be repaired.
 
John makes a good point, there are two types of nut: tapered or square. You need the correct nuts for the wheels (and obviously the studs).
 
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