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308 Wheel Upgrade Question

10800 Views 6 Replies 4 Participants Last post by  rivee
I am new to the forum and I have to say this is a great site with large amounts of information. I'm glad to have found it. MY question is: I have a 1985 308 QV and I would like to upgrade my wheels to 18 in or maybe bigger(if possible). What is the bolt pattern for a 308? and what is the biggest rims one can fit on a 308.....I'm not looking to go bigger than 19 in though. Thanks much to anyone who can help.
Jason Fitzpatrick
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Welcome Jason. Had your car long? There are many here who will be pleased to help out, but you have to post pix of your car first (only joking!) :green:

Are you looking for after-market wheels or Ferrari ones? Wheels are spec'd by bolt PCD (pitch circle diameter, measuring across the width of an imaginary circle passing through tne centre of all 5 bolts), and offset (distance from the inner flat mounting face to the wheel centreline). Get this by laying rim upside down on ground and measure overall rim width edge to edge through spoke opening. Divide this by 2 (= A, distance to centreline). Then measure distance from edge of inside rim down to the mounting face (= B) . Subtract B from centreline distance A and you have the rim offset, which will be negative if the mounting flange is closer to the outside of the wheel, or positive otherwise.

With this rim PCD and offset you can go shopping for alternative wheels of same or different overall diameter, bearing in mind:

1. As diam gets larger (15 - 16 - 17 etc), you need to reduce the tyre sidewall height the same amount (ie use lower-profile tyres) otherwsie the overall gearing ratio of the car will change. This will reduce acceleration, drop cruise revs, possibly increase top speed a little but make speedo read too slow.

2. If increase overall tyre diameter (ie not follow step 1) then the tyre will eventually start fouling either the bodywork when turned or maybe some suspension bits, unless ...

3. Reduce rim offset, maybe while increasing width a little. This means making the rim extend INTO the car more than it sticks OUT, and can keep the tyre off the outside bodywork provided that it can clear suspension parts. Careful measuring underneath will show if you have some excess clearance inside the wheel/tyre that can be used. Note: Reducing offset significantly (by say 1" or more) will make the hub bearings work harder and change the steering feel (lighten it), so be a bit careful here. Increasing offset will also wear the bearings faster plus make steering heavier & jump around more.

Sorry for the ramble - you probably know all this already. :nuts:
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jjason981 said:
... there is a slight possibilty of 20in but I think that may be too big....
You might want to keep an eye on the overall wheel+tyre weight compared to the std setup when getting this big, as the unsprung weight can blow-out badly leaving you with crappy ride and bump-characteristics unworthy of a thoroughbred sports car. Make it a consideration when comparing different wheel designs. Good luck - we are waiting to see how it all comes together! 8)
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