''Nervous'' front end with new 17/18 wheels...

[panic]

...I just have fitted my new 17 (front) and 18 (rear) wheels to my Griffith 500, tires are 215/40/17 front and 255/35/18 rear (Bridgestone Potenza asimmentric), I feel the front end too ''nervous'', specially at high speed. Steering needs continuos corrections and does not give me a safe feeling for some reason.



Comments?

Edited by panic on Friday 5th December 22:01

[slideways]

get your geometry checked, i had mine set up and it felt just as you described but it is correct just more positive so i just had to get used to it
Rich

[Podie]

Consider the tyres pressures, and as already posted - get a geo check.

Or, go back to what you had...

[Bluebottle]

Like the others have said above.
Tyre sizes chosen still give you the same overall diameters as before but it is still worth checking to make sure the car is angled down at the front, you want the front to be about 1/2 inch lower than the rear. Also, you now have much less compliance from the tyre walls now so the car will be more prone to tram lining and much more sensitive to minor geo alignment issues.

E.T.A. As these are new wheels, do you have the hub offsets correct? It can make a difference to the handling if its out.
When I spec'd my 17" rims I made sure I had all the offsets correctly ordered but when the fitters put them on, they decided to put spacers on the rear wheels "cos it made them fill up the wheel arches better" was what they told later after discovered what they'd done. Before i found out and removed them the car was lethal to drive, extremely twitchy and prone to oversteer.
When i discovered the spacers i removed them, taking the rear track back to the correct width the handling returned back to normal.

Edited by Bluebottle on Friday 5th December 22:48

[spend]

What are the load characteristics of the Pirellis? I would guess they were spec'ed for a much heavier car?

You can play with pressures, camber & toe to try & get the best out of them. Try checking temps across the tread this may give you some ideas. But basically if the walls are too stiff you may not be able to tame them.

Eta must look what I write

Edited by spend on Friday 5th December 23:04

[Chimjunkie]

You may need to upgrade your suspension to adjustable from standard if you fit lower profile tyres. As said before, less compliance in the tyres will lead to a firmer more skittish ride...

Do check the tyre pressures as already stated. often the numpties at the garage just chuck in 30 psi!!! General consensus is 22-24 front 24-26 rear on 17"/18".

[HRG]

Podie said:

Consider the tyres pressures, and as already posted - get a geo check.

Or, go back to what you had...

Mine nearly spontaneously fell off the road above the ton when I accidentally left 32 PSI in it after a tyre change.

Also check the ride height hasn't altered.

[RichB]

spend said:

What are the load characteristics of the Pirellis?

Eta must look what I write

Don't know but the chaps using Bridgestones

Edited by RichB on Saturday 6th December 00:11

[RichB]

Chimjunkie said:

You may need to upgrade your suspension to adjustable from standard if you fit lower profile tyres.

I'm on 17/18" with exactly the same size tyres but Goodyear Eagle F1 GSD3s but... I also have Nitrons and Racing Green set up the geometry to match and I must say it's perfect at 130-140 mph. (track days of course)

Edited by RichB on Saturday 6th December 00:10

[spend]

RichB said:

spend said:

What are the load characteristics of the Pirellis?

Eta must look what I write

Don't know but the chaps using Bridgestones

Edited by RichB on Saturday 6th December 00:11

Wrote it in between doing other things, and put Bridgestone... posted saw assimetric and then edited after putting 2+2 mentally thinking assimetricos... Really should concentrate more, but I was doing something that interested me

[panic]

spend said:

.....but I was doing something that interested me

[panic]

Thanks for the inputs...

I'll follow these procedures then:

Check tire pressure, as chim said, 22/24 front and 24/26 rear.

Check alignment, i guess this is the biggest iussue of all.

The guys at the tire shop didnt add any spacers..

The new wheels have et 40 rear (to be sure they didnt rub) and stock front.

I guess the car points down front properly with these wheel/tires measures, even if i used to have 225/45/16 front and 245/45/17 rear which i believe made the front car lower then the combo i have now?

Suspensions are upgraded and adjustable (BTW also braking...).

Could also be that tires are new and need some running in?

Thanks again and have a sweet weekend.
Giuseppe

[Pupp]

panic said:

Thanks for the inputs...

I'll follow these procedures then:

Check tire pressure, as chim said, 22/24 front and 24/26 rear.

Check alignment, i guess this is the biggest iussue of all.

The guys at the tire shop didnt add any spacers..

The new wheels have et 40 rear (to be sure they didnt rub) and stock front.

I guess the car points down front properly with these wheel/tires measures, even if i used to have 225/45/16 front and 245/45/17 rear which i believe made the front car lower then the combo i have now?

Suspensions are upgraded and adjustable (BTW also braking...).

Could also be that tires are new and need some running in?

Thanks again and have a sweet weekend.
Giuseppe

Whilst there's no harm in trying different pressures, I'd view 22 or 24 etc as being rather too low for tyres of those profiles. Been down this road with Toyos on 17/18 rims (likely quite different sidewall rigidity admittedly) and settled on significantly higher pressures after seeking advice from their techie guys (there's a thread on it somewhere). That said, the reduced compliance in the wheel/tyre package will require to be compensated for elsewhere in the suspension equation but there's no reason at all why it can't be made to work with some thought and fettling.

[RichB]

Pupp said:

panic said:

Thanks for the inputs...
I'll follow these procedures then:
Check tire pressure, as chim said, 22/24 front and 24/26 rear.
Check alignment, i guess this is the biggest iussue of all.
The guys at the tire shop didnt add any spacers..
The new wheels have et 40 rear (to be sure they didnt rub) and stock front.
Suspensions are upgraded and adjustable (BTW also braking...)

Whilst there's no harm in trying different pressures, I'd view 22 or 24 etc as being rather too low for tyres of those profiles. Been down this road with Toyos on 17/18 rims (likely quite different sidewall rigidity admittedly) and settled on significantly higher pressures after seeking advice from their techie guys (there's a thread on it somewhere). That said, the reduced compliance in the wheel/tyre package will require to be compensated for elsewhere in the suspension equation but there's no reason at all why it can't be made to work with some thought and fettling.

I use 24/25f (prefer the feel slightly harder) and 26/27r on GYF1GSD3. Nitron suspension is mid-firm (not hard) and about 10mm lower than originally. p.s. Have you got the "air defelctor" under the nose? I have heard this can adversly affect hige speed handling if it's missing.

[GreenV8S]

High speed handling is very sensitive to tyre flex, and this changes significantly with new tyres. I suggest you get the new tyres fully cured before you look for more drastic problems, and see if you can get advice on tyre pressures for those specific tyres. Lower profile tyres are more sensitive to camber changes so you might find it suits slightly less camber, but don't start playing with that until you have got the basics sorted out.