Conference terri::cars_uk

    
    Have you checked the tyre pressures? - We improved the roadholding of
    the Maestro by reducing them _to_ the manufacturers recommended, which
    was a couple of pounds less than what they had been supplied with.
    (And DON'T trust the pressure guage on the garage forcourt - buy your
    own!)
    
    Elaine

    What make of tyre is it on ??  Rather than go for a wider tyre I'd go
    for Grippier rubber.
    
    John

    re -2......
    
    minor rat-hole, but how do you know that the one that you buy is
    accurate?

    
>>    minor rat-hole, but how do you know that the one that you buy is
>>    accurate?
    
      You don't, you have to rely on the QA of the manufacturers, or do
    your own QA excercise! (I'd still rather trust that than garage
    forcourt air-lines, even the ones they charge 10p for, but that's
    another rathole!) 
    
    Elaine

On the subject of tyre pressure, I read somewhere that if its too high or too
low you get over/under steer, but I can't remember which way round it is.  Can
anyone enlighten me?

I'm not sure if there's a separate tyres note, so I'll ask this one here:

What do tyre size measurements actually refer to?  How can you work out which
tyres are going to fit a particular size wheel, as 185x13 are far bigger than
155x13, yet both supposedly fit 13" wheels?

Which measurement of tyre size relates to the wheel width, which to the profile
depth, which to the tread width, which to the overall tyre circumference, and
so on.

Scott.

   195       60         13
   width     profile    diameter

   The width could be in centimetres, diameter (inner) in inches. The 
   profile relates outer diameter, inner diameter and width. The smaller
   the number, the lower the profile...

Mark

So is the profile the distance from one bead, up one side of the tyre, across
the tread, then down the other side to the other bead?
What's it measured in?  If 60 is a realistic figure, probably centimetres?

If width is in cm, a 195 tyre is pretty big: 6 feet across!!??

So is the 195 the circumference in centimetres, or the width in millimetres, or
something else entirely?

Why are some bits in metric and some imperial?

Scott

    I think the 195 is 195 mm. Sorry about that :-)

    The profile is a ratio of tyre diameter, rim diameter and width.
    For a fixed rim size and tyre width, decreasing the profile, reduces
    tyre diameter, making the circumference smaller. Not sure of the equation.

    Why are some bits imperial, some metric ??? Perhaps this goes back to
    the days of cross-ply tryes. Then it was all imperial. The metric type
    width came in with radial-ply tyres I think.

  Mark

    With reference to Tyre Pressure Guages I have a pretty little Digital	
    (meaning non-analogue, not DEC!) tyre pressure guage which is
    supposedly accurate to +-<1 PSI. 
    
    the tyres my Astra came with are Uniroyal Ralleye 340s. I was thinking
    of sticking Pirelli 195s on maybe. I tend to keep the pressures about
    2-3 PSI above the normal recommended figures in the handbook, but it
    also says up the pressure by something like 4PSI for 'sporty' driving,
    so mine are somewhere in between.
    
    Thanks for the interest.... What tyres have you lot fitted then ?
    
    
    Howard.

    
    
    Hi,
    
    
        The profile of the type detemines the side wall height.
    
               195/60 x 13   =       195 mm tread width.
                                    
                                      60 relates to 60% of tread width
                                         = sidewall height. i.e 195 x .60
                                         = 117 mm.
    
                                      13 = rim diameter.
    
     
                          Is of any help?
    
                                       Alan.
    

    In regards to what tire make to choose, I have used, Micheline MXV's
    which lasted a long time and were comfortable but not much grip,
    pirelli p600 which were comfortable had good grip but didn't last
    to long and finally Bridgestone RE71's which were comfortable, lasted
    a long time and had great grip.  My final and future choice for
    tires will now be the RE71's.  FYI they are now on a (86) 323 GT which
    I believe is only available in Canada.  
    Just my $0.02 cdn worth ;-).
    JP 

    
    I'll second the RE71 choice. Will replace the Dunlops for them within a
    month. I have heard good things about the Michelin MXX and the BF
    Goodrich Comp T/A as well though.

Just replaced the RE71's (standard tyres) on the back of the RX with a pair
of P600's, they seem to grip very well, but have yet to see how long they last.
(Only did it 'cos the tyre shop couldn't get hold of RE71's)

Peter

    Dont forget to measure your tyre pressures with cold tyres. Presumeably
    the pressure whilst driving will rise.
    
    As an aside, if anyone can explain why swapping my front wheels/back
    wheels was the cure for a bad drifting to the left on my golf, I
    would be interested.
                                         
    Rich

>Note 1006.15
>    As an aside, if anyone can explain why swapping my front wheels/back
>    wheels was the cure for a bad drifting to the left on my golf, I
>    would be interested.
>                                         
>    Rich

How about badly scrubbed edges. I had this after I had the steering bushes 
changed. The tyres were badly worn but only on the edges. I got them to 
change them and the pulling to one stopped.
Regards

    
    
    Tail out driving around roundabouts again?
    
    Bill.

    Rubbing the wheel arches because the wheels are too big?.
    
    Richard

    
    Assume you mean a circuit, or handling circle - where have you
    tried? Learn much? Feel you're improving?
    
    Bi||.

    re 1006.16
    
    how much did it cost for your replacement steering bushes. (What
    car you got ?)
    
    Rich

    Howard,
    
    	On my old GTE (1.8 new shape) I had Pirelli P6s and these
    	did not have very good grip on this particular car - I
    	used P6s on a Fiat Supermirafiori to great effect, but
    	on the the GTE they were naff.
    
    	I asked lots of people about wot to replace them with
    	and the consensus was Yokohama A008s. They were brill,
    	and as soon as I get a chance on my 16v (yes it's turned
    	up in a sorry state after having bin nicked) I will replace
    	the current wotevertheyares.
    
    	Contray to popular belief width isn't the only consideration (?)
    	when changing tyre sizes. U have to bear in mind the rolling
    	radius size. This will effect speedo accuracy, gearing, economy,
    	top speed and accelaration.
    
    	Increasing the rolling radius will reduce accelaration by
    	increasing the gearing and hence your speedo will be slow.
    	Reducing the rolling radius will have the effect of lowering
    	the gearing so make it a bit quicker on the acceleration
    	but may reduce the top speed and maybe the economy will be
    	worse - your speedo will now be fast ofcourse.
    
    	U have a 185x65 tyre. The 195x60 has about a 1% reduced
    	rolling radius but is probably the closest u will get
    	unless u change your wheel size as well.
    
    	I phoned up Irmscher with this very problem and they
    	recommend a 15" wheel with 195x50 tyres - dont know
    	if they do any speedo calibration as well.
    
    	So to sum up, I'll be going for Yokohamas 195x60 on the
    	existing 14" rims.
    
    Colin.
    x
    
    	

Glad you got your car back... i was beggining to get woried.


If those tyres are gud enuf for you, then they're gud enuf for me !

My front tyres are showing considerable wear already and I've only done 
5k miles. I think I'll swap the fronts for the rears in a while so all 4
are worn then I can swap all five tyres together.


Thanks for the info..... see you soon.

Howard (sideways round the roundabout) Page.

    The handbook in my 16v recommends 30 psi plus an extra 3 or 4 psi for
    "fast" driving.  I used 32 psi, and wore the middle of the tyres out
    due to overinflation.  Micheldever Tyres (who I tend to trust)
    recommended that I run the new ones at 26 psi.
    
    What tyre pressures do other 16v drivers use ?  What type of wear do
    you get ?
    
    
    John

The tyre pressure will depend on the make, and design of tyre (as well as car
loading, type of roads, driving style, etc, etc)... were the tyres you had at
32psi "original equipment" ones?  If not, the handbook data is meaningless...

Scott

    
    Loaded up and on Mways (I mean loaded) I've run 32Front 38Rear,
    cold, which becomes about 36:42 when hot. 
    
    That definitely feels too hard for unloaded driving, but 32:30
    seems ok. Driving with the pressure much lower than that seems 
    to send the suspension to sleep and you 'crash' over everything.
    
    Front tyres look good for about another 3-5k, which will mean
    they've done 22k+ on the set. They're original fit Kleber tyres,
    but I hope when I change them to find some that run a bit quieter.
    
    Richard.
    

A good "rule-of-thumb" is that a correctly inflated car tyre should have the
tread *FLAT* on the ground (i.e. all parts of the outer surface of the tread
touching the ground) and the tyre walls slightly curved outwards. 

Handy Hints #362...

A good way to test whether the tread is "flat" on the ground is to paint a line
across the tyre, then roll the car forward.  The line of paint that appears on
the ground should be even acros the full tread width.

Scott

Derek,

I would have expected the temperature to be higher on the outside edge of the
tyre (ie the left on a clockwise circuit)?

Scott

    Re. .26, a few thoughts:
    
    The pressures in the handbook should be used unless you have a _good_
    reason for not believing them. Vauxhall will have probably specified
    these pressures to be suited to various makes of tyre (manufacturers
    rarely rely on just one brand of anything). This of course assumes you
    haven't fitted non-standard replacements.
    
    I believe the extra for fast driving is intended for _fast_ driving,
    i.e. over 100mph all day on the autobaan (sp.?) - does the handbook say
    anything about this? Therefore this "extra" is not appropriate for
    normal driving.
    
    Finally - is your pressure guage accurate? - they can be out by several
    lbs.