Tyre size and speedos

[HAIRIBO]

Tyre Size.

Some cavs come with 14" (185/65/14) wheels so if replace them then you should get (205/40/17) in order to keep the rolling radius correct.

But the cavs that came with 15's (195/60/15) have a bigger rolling radius than those with 14's, so in theory you should put the bigger (205/45/17) tyres on.

Has any one done this or not? Or dose every one run 40's

I have replaced the clocks in my cav and have no idea what car they are out of and what the original tyre size of that car was. Can you tell buy the W=**** number printed on the speedo?

[Cavalier342]

I can't tell you about tyres or rolling radius and all that, but what I do know is that most clocks have W=1742 on them. At least on both my 1800's and the C20NE's. I've been told that as long as you get the same number, you won't read wrong.

[HAIRIBO]

I think W=1742 is for cars with the smaller rolling radius and W=1719 are for cars with the higher one. but i'll have to look into it more.

[Envoy CDX]

The difference is minimul anyhow. If I remember rightly, the haynes manual confirms the 14" and 15" tyre sizes

[Robsey]

The difference is minimul anyhow. If I remember rightly, the haynes manual confirms the 14" and 15" tyre sizes

Agreed - the speedo error will only be about 5%,
This is a similar amount to the general accuracey of Cav speedo's.

The best way to tell how accurate the speedo is, is to go for a drive with a sat nav unit as a comparator.

I did this in my Cavalier to check my Digi Dash.

I found that my speedo reads slightly high at approx 20 mph..
reads spot on between 40 and 50 mph..
and reads slightly low at 65 and above...

above 85 mph, the speedo is just a pretty display item that is way out.
You'll find that normal Cav dashes are similarly afflicted.

there is a mini program on one of the older websites for calculating overall tyre diameter by entering wheel rim sizes and tyre aspect ratios. (width and ratio figure).

probably Mig or Vxon etc...

[HAIRIBO]

205/45/17 match the standard 195/60/15's

and 205/40/17 match the standard 185/70/14

[Mikebmth]

Have a look on this post, I used a tyre size calculator online to check my tyre size..May help may not..

viewtopic.php?f=59&t=10830

[HAIRIBO]

I know what size tyeres on a 17 match the standard 14's and 15's, I was just wondering if any one has every used 205/45/17 on a cavalier.