Alfa Romeo Forum banner

1 - 20 of 20 Posts

·
Registered
Joined
·
214 Posts
Discussion Starter #1
I've recently changed from 17" to 18" tyres. I was previously running on Michelin PS2 at 35psi (F) and 32psi (R) for everyday use on the standard 17" GTA teledials with great results. I am now running on Bridgestone Adrenalines (which, IMO, are so far no match for the PS2 in dry or wet) on 18" OZ Ultraleggeras. At higher pressure, 34psi (F), the steering feels light and there is a vibration at 100kmh onwards. At lower pressure, 26psi (F), the tyres howl quite loudly when driven enthusiastically, but no higher speed vibration. I had all wheels balanced and aligned. Suspension is AD adjustable coilovers. What is the recommended sweetspot for tyre pressures on 18"? Thanks!
 

·
Registered
Joined
·
30,171 Posts
26PSI is dangerously low.

stick to:
Front 36PSI (2.5Bar)
Rear 33PSI (2.3Bar)

Those are cold unladen pressures for a 147 18" and the only figures I have.
NEVER run lower than those.
 
  • Like
Reactions: OperationAlfa

·
Registered
Joined
·
30,171 Posts
The absolute minimum unladen pressure on 225/45R17 is 2.2Bar 32PSI, so should be taken as the minimum to never run below.
Still can't find any official 18" figures though, but they will not be lower.
 

·
Registered
Joined
·
214 Posts
Discussion Starter #5
Thanks Portti and David C! Problem is, running at 36psi front, the steering feels eerily light above 100kmh, combined with a considerable vibration in the steering. Any ideas on what may be causing this? Lower & upper arms and links all been replaced within the last year (15,000km) or so.
 

·
Registered
Joined
·
30,171 Posts
What are your toe settings set to?
 

·
Registered
Joined
·
214 Posts
Discussion Starter #7
What are your toe settings set to?
Thanks for your help David C.

Looking at the report for "Nominal Values" which I assume is the desired setting, for:

Front Axle
Total Toe Dg -0.45 -0.30 -0.15
Partial Toe Dg -0.22 -0.15 -0.08

Rear Axle
Total Toe Dg +0.32 +0.47 +0.62
Partial Toe Dg +0.16 +0.23 +0.31

Is that approx. a 1/2" toe-out in front, and 3/4" toe-in in back?
 

·
Registered
Joined
·
30,171 Posts
I hope it is not 1/2" toe-in front & 3/4" toe-in rear...!

Original GTA settings were 2mm (0deg 18') toe-out front & 2.5mm toe-in (0deg 23') rear.
 

·
Registered
Joined
·
214 Posts
Discussion Starter #9
Hmmm... I think it could be in millimeters rather than inches.
Turns out the right side front tyre was over-inflated to almost 45psi (I did the left side while the gas staton guy did the right with a separate pump.... just goes to show you have to do things yourself), which was causing the imbalance and vibration. No wonder it felt like driving on balloons. Anyway, all fixed now at 36/34psi. Thanks for all your help.
 

·
Registered
Joined
·
214 Posts
Discussion Starter #11
156GTASW: Yes, it is running well at 36/34, good to know you are pleased with essentially the same setup as mine!

David C: I recall a thread about running neutral toe in the rear, probaby from Peter K and TB, but they were likely talking about track use. Is this suitable for street driving? Or will it make the back too lively? I have an AD LSD, so traction up front is very good.
 

·
Registered
Joined
·
30,171 Posts
Having toe-in at the rear is good for stability.
Having zero toe at the rear will be less stable, but just about usable on road.
Toe-out on the rear will make it very unstable. Track use only.
 

·
Registered
Joined
·
214 Posts
Discussion Starter #13
On the vibration issue, turns out the garage didn't install the hub-centric rings for the Ultraleggeras.... they are on order now and hopefully will solve the problem. I do not recall the GTA rims needing these rings...
 

·
Registered
Joined
·
30,171 Posts
On the vibration issue, turns out the garage didn't install the hub-centric rings for the Ultraleggeras.... they are on order now and hopefully will solve the problem. I do not recall the GTA rims needing these rings...
They are only needed for aftermarket rims with the wrong size centre-bore.
If your new rims also use wobbly-bolts then the wheels will have been nowhere near central.
 

·
Registered
Joined
·
214 Posts
Discussion Starter #15
The OZ Racing box said for Alfa Romeo, PCD 5/98. They came with light-weight OZ lug nuts (not sure wobbly or not), but didn't notice the rings. Garage gave the rims to the tyre shop to mount the Bridgestone Adrenalines and bolt on to the car. Garage said they should be installed with the rings... really confused now. Was hoping that was the source of all evil.
 

·
Registered
Joined
·
30,171 Posts
The lack of centring rings will not be helping...!
 

·
Registered
Joined
·
214 Posts
Discussion Starter #17
The lack of centring rings will not be helping...!
By the sounds of it, there's a difference between centering rings and hub-centric rings? And I need at least one type to keep the rims centred? This is all new to me...
 

·
Registered
Joined
·
30,171 Posts
Im about to get some 225 40 18 Pirelli PzeroNeros on my GTV V6

Should I also use 36/34 PSI ?
Wow, 2-years ago....

as for your GTV v6. Use the normal GTV v6 17" pressures.
 
1 - 20 of 20 Posts
Top