Wrong size tyres?

[RedRummy]

Oops..

Just changed my rear tyres.... used to have 245/45 17 but thought I\'d go for something wider and put on 255/40 17..  (was Contintental Sport Contact 2, are now Eagle F1\'s)

Now the back end feels really unstable at speed... feels pretty unsafe.

Feels like the tyres are moving about on the rims.... if you know what I mean.. (doubt they are, but it feels weird)

Not sure of the offset/width of these rims, but it should be able to handle a jump from 245/45 to 255/40 no?

Not sure if it has only affected the tracking and that needs sorting out or what. ... :reallymad

[AshRX]

might need balancing mate thats all

[SmbFD3S]

What size width are the wheels, 8.5 or 9.5??

[logicalChimp]

Don\'t forget that the profile of the car will have changed as well...

The back of the car will now be ~8mm lower - this may be affecting airflow etc, causing the rear to become unstable...

[RedRummy]

ok, thanks..  not sure on the width of the wheels... and I paid for balancing etc when I got them done.... grrrrr

need to get the tracking all sorted too - had a new set of Tein SS put on a week ago...  

Don\'t think I drive fast enough for the aerodynamics to have changed hthat much  

[Prof]

If the tyre is too wide for the rim then it will allow \'wobble\' from side to side as they will be like balloons on the rear.
 
According to the tyre bible:
 
http://www.carbibles.com/tyre_bible_pg2.html
 
...your ideal rim for that size tyre will be between 8.5" and 10" (9 is ideal)

[Matt_K]

F1\'s come with a silicone release agent \'coating\' on the tyre from new, whenever i\'ve fitted F1\'s they\'ve felt really unstable for a while until it\'s scrubbed off.

Big burnout required

[shaunwil]

255/40/17 is the right size of tyre for the car. As said just may be too narrow a wheel !

Shaun

[RedRummy]

not sure of the width... how can I check - is it printed on the inner rim?

or can I measure from rim edge to rim edge?

I knew about the greasy coating... first thing I did was do a small burnout

[mpk490p]

good website Dave :chat
the width should be stamped on the inside of the wheel

Mark

[RedRummy]

ok, thanks all.

Back to the tyres centre then... cos I know the tyre should fit fine.

bloody muppets... got them all-inclusive through blackcircles.com as well.

[Nik da Greek]

They\'ve got to be better than those "racing slicks" with the staple stuck in one that you had on before, chap, surely!

Different makes obviously have different characteristics, maybe the Eagles just have a softer sidewall than the Continentals or something? If it\'s a balancing issue, the easiest way to check is go really fast, the faster you go, the worse it\'ll feel, and really bad balancing will sart up a pronounced feeling of vibration that gets more obvious as the speed increases. Obviously, you may not want to try this if it feels really dangerous already, but you\'ll know before you hit warp speed if its this! Try fiddling with the tyre pressures a bit, may help too

[RedRummy]

Those continentals were great... even as almost slicks...  

The rear end wobble definitely gets worse with speed... going in a straight line is ok, but its very hard to keep it straight cos it makes the steering very twitchy and when it twiches the back end wobbles.

really dodgy!

[Nik da Greek]

Definitely sounds like sh!te balancing to me, dude. Eagle F1s are very good tyres, should be very stable at speed.

[Ricco_04]

Just to add another one is that maybe they got them mixed up and the rotation is facing the wrong way? (maybe 1 maybe both?)

Only a possable but least its easy to check