New Alloys

[Guest dodgers1008]

hi everyone i just got myself a new set of alloys for my zx 15"x6.5" could anyone please advise me on the best size of tyre for these ,thanx,

[Guest Colin Hunter]

Hi There.

 

The standard tyres fitted to most ZXs are 175/65x14. According to my handbook, the only ZX that had 15" wheels as standard was the 2.0i 16V. That was fitted with 195/55x15. The pressures quoted are 32psi front. 33psi rear. Depending on what model your car is, you may need to do a small calculation to get the size right.

 

I'm not sure you know what the numbers mean so I'll go through it with you. Say your car is fitted with 175/65X14 tyres. The 175 is the width of the tread in mm. The 65 is the "Aspect ratio" which means that the tyre height from the bead to the tread is 65% of the width of the tread. the 14 is the diameter of the rim in inches.

 

The calculate the rolling radius of your tyres it's quite simple given these figures. You need to do this so that your new tyre is as near to the same radius as possible to avoid errors on your speedo. If your wheels are much bigger than standard then your speedo will read low, and you'll end up getting lifted when you thought you weren't speeding.

 

So there are 25.4 mm to one inch so we'll go to inches for eveything.

 

175/25.4 = 6.9" x 0.65 = 4.48"

 

Add that to 7 (half of your 14" rim) and you have 11.48" Rolling radius.

 

Multiplying out To get the circumference (2 Pi r) gives

 

11.48 x 2 x 3.14 = 72.15" so each time the wheel rotates it goes forward just over 6 feet, or two yards. Seeing there are 1760 yards in a mile the wheel will rotate 880 time in a mile. Approximately.

 

The exact un rounded figures are.

175/25.4 = 6.889 x 0.65 = 4.478 + 7 = 11.478 x 2 x3.14 = 72.12 = 6.01 feet

or 2.003 yards. = 878.53 rotations per mile.

 

For the 195/55X15 wheel combo the sums are

 

195/25.4 = 7.677 x 0.55 = 4.22 + 7.5 = 11.722 x 2 x 3.14 = 73.65 = 6.137 feet

or 2.046 yards. = 860.23 rotations oper mile.

 

This means that the 195/55 tyre on the 15" rim will rotate approximately 18 times less in a mile. This is approximately 2% so that's the amount of error (LOW) that would be in your speedo. Seeing it's so little it's acceptable, seeing as most speedo's read a little high anyway.

 

I'd go for the 195/65 X 15 tyres on the strength of that. Just make sure the wheel offsets are right so you don't get any fouling on the bodywork and suspension.

 

Hope this wasn't too long winded! Cheers. :lol:

[Guest martin r]

Hi There.

 

The standard tyres fitted to most ZXs are 175/65x14. According to my handbook, the only ZX that had 15" wheels as standard was the 2.0i 16V. That was fitted with 195/55x15. The pressures quoted are 32psi front. 33psi rear. Depending on what model your car is, you may need to do a small calculation to get the size right.

 

I'm not sure you know what the numbers mean so I'll go through it with you. Say your car is fitted with 175/65X14 tyres. The 175 is the width of the tread in mm. The 65 is the "Aspect ratio" which means that the tyre height from the bead to the tread is 65% of the width of the tread. the 14 is the diameter of the rim in inches.

 

The calculate the rolling radius of your tyres it's quite simple given these figures. You need to do this so that your new tyre is as near to the same radius as possible to avoid errors on your speedo. If your wheels are much bigger than standard then your speedo will read low, and you'll end up getting lifted when you thought you weren't speeding.

 

So there are 25.4 mm to one inch so we'll go to inches for eveything.

 

175/25.4 = 6.9" x 0.65 = 4.48"

 

Add that to 7 (half of your 14" rim) and you have 11.48" Rolling radius.

 

Multiplying out To get the circumference (2 Pi r) gives

 

11.48 x 2 x 3.14 = 72.15" so each time the wheel rotates it goes forward just over 6 feet, or two yards. Seeing there are 1760 yards in a mile the wheel will rotate 880 time in a mile. Approximately.

 

The exact un rounded figures are.

175/25.4 = 6.889 x 0.65 = 4.478 + 7 = 11.478 x 2 x3.14 = 72.12 = 6.01 feet

or 2.003 yards. = 878.53 rotations per mile.

 

For the 195/55X15 wheel combo the sums are

 

195/25.4 = 7.677 x 0.55 = 4.22 + 7.5 = 11.722 x 2 x 3.14 = 73.65 = 6.137 feet

or 2.046 yards. = 860.23 rotations oper mile.

 

This means that the 195/55 tyre on the 15" rim will rotate approximately 18 times less in a mile. This is approximately 2% so that's the amount of error (LOW) that would be in your speedo. Seeing it's so little it's acceptable, seeing as most speedo's read a little high anyway.

 

I'd go for the 195/65 X 15 tyres on the strength of that. Just make sure the wheel offsets are right so you don't get any fouling on the bodywork and suspension.

 

Hope this wasn't too long winded! Cheers. :rolleyes:

blimey!