456GT Highline wheels - tire sizes

What size are the rims? This will have a great influence on tyre selection.
Also with a 52mm offset, you are going to need very big spacers to get that "flush" look.

 

You'd need 255/40 fronts. The 235 Section's way to small and will affect your speedo reading. Optimally rear's 295/35 but on a 10" wheel the sidewall's bulge wouldn't look nice. 275s should look taut round the rim and the circumferential difference is negligible.

Just my $0.02

 

Yes, 255/40 front,
The 550 has an 8.5 front and 10.5 rear, standard sizes are 255/40, 295/35.
You can squeeze a 265/35 on the front, but with only a 10" rear, I wouldn't try anything wider than the 295.

 

This is how I normally calculate tyre sizes. ( a Pirelli man gave me the formula during the P-Zero launch in Malaysia years ago...and I've been using it ever since..)

Example : 255/45/17

255 (section width) X 2 X 45 (aspect ratio) / 100 + 17X 25.4mm

229.5mm + 431.8mm

Total Tyre Height = 661.3mm

For any given tyre size, you can extrapolate the figures to come up with the total tyre height and you can see that most of the time the correct upgrade is not spot on because of the availability of tyres in pre-set aspect ratios and width, 45/40/35/ and 235/245/255/265 etc...

PS : the 245/45 fronts would have a higher TTH and basically bigger circumferential than the 295/35 rears. Not Good. Stick with the 255 fronts. Runflats gives a harsher ride than normal tyres too.

Bear in mind that even with the same width and profile the tyres from different manufacturers can differ especially when mounted on the car. Sidewall rigidity and tread depth etc...Eg : a 255 section Yokohama or Bridgestone 'looks' fatter than a Pirelli with the same size.

 

I have 575 19" split-rim wheels on my 456 (mainly to allow for much bigger Brembo brakes from a 612) but also a quantum-leap improvement to looks and handling. My rears are 305/45/ZR19 - from memory - and fronts 265/35/ZR19, with Pirelli P Zero Rossas on, and I can assure you that even this size doesn't get close to 'filling' the wheel-arches as much as I would like. However for two reasons, I am not going to fit spacers to increase the offset. Firstly, plenty of Fcar mechanics and professional drivers I spoke to warned me off this for suspension / handling reasons (several threads on here discussing this to allow you to judge for yourself, one of which called 'lowering a 456' is well worth a read). Secondly in London with silly width-limits down many roads, increasing the risk of kerbing the wheels by widening the track is not really a bonus - but this may well not apply in your case. Have a quick surf on my posts to see pics of the upgraded wheels, and hopefully fuller info, if you wish.
Good luck.
J.

 

Try this thread, and the links from it to other threads with pictures.

http://www.ferrarichat.com/forum/showthread.php?t=14980

Good luck.
J.

 

I am a new proud owner of a magnificent 456 so i am looking for as much advise as is available can anybody please advise me as to where is the best place to buy service parts (kits) Belts ect.

 

Trutlands or Ricambi America are good places to get the parts you need.
BT

 

Tifosi, I absolutely agree w/ our calculation, however, can you elaborate a bit more on your comment regarding 'sidewall's bulge wouldn't look nice?

 

I'll be VERY curious as to how it pans out. I'm also thinking of getting their wheels for my 456GT and the sales were less than helpful. All they have said is that I needed to purchase a set of four 1.5" spacers and I couldn't get them to tell me how they came to that conclusion!

 

Have you noticed some cars have 'flabby' sidewalls ? i.e there's too much excess rubber(width) as compared to the width of the rims. Example, a 10" wide wheel would have 254mm width ( 1" = 25.4mm). Therefore with a 295 section tyre ( 295/35/18) you'd have 295-254 = 41mm excess which when you divide by 2 will be 20.5mm excess rubber on either side of the rim.

Now, if it's a 10.5" wide wheel, the width in mm is 266.7mm. Based on the same section width tyre, you'd get 295-266.7 = 28.3mm/2 =14.15mm either side of the rim.

Generally speaking, you 'need' the extra rubber to protect your rims from kerbing easily and as the above calculations show, the sizes of the tyres against the width of the rims affects it. That said however, too much 'flab' on the sides doesn't augur well for handling because of the sidewall flex that occur as compared to the 'tauter' ones. The ones on the 550 looks just right. But mount the exact tyres on a 'thinner' wheel and you'll wonder what's not right with the picture. Too wide a rim against too thin ( tyre width less than rim width, mm for mm ) a tyre has adverse effects too. Aesthetically it'll look like rollerskates, dynamically, the tyre beads can be offed from the rims in corners...dangerous...

NOTE : Refer to my previous post above on different width of tyres for the given same size. Different sidewall design for the same given size..etc...

Good Luck!

 

Have you gotten it yet? What kind of spacer did you get in the end?

 

Actually with 18" it's a toss between 285/35/18 and 295/35/18. "The" perfect tire would have been 290/35/18! I'm thinking of going w/ 19" which would be 255/35/19 and 295/30/19. If only I can figure out the spacer I need at the rear. Will be looking forward to your conclusion.

 

Thanks Tifossi66 for the clear explanation. I'm thinking of 19 x 10.5 on the rear so with 295/30/19 my excess would be roughly the same. (Currently 285 on 17x10 stock wheels) If only I can figure out this spacer I would need...

 

This site is a really great tool and can help you dial in tire/wheel combos for any car.
http://www.miata.net/garage/tirecalcold.html

 

Actually wouldn't that be too much? at 1.75" spacer that's almost 45mm whereas the difference in offset between the old wheel 10" and 24.6mm offset and the new one: 10" and 52mm is only abt. 27.5mm? It sounds to me that the tire/wheel will be 'extending' by almost 20mm?

 

Any update on the fitments of your highline wheels?

 

I'm afraid you might still have to lower your car a tad to achieve the 'right' look. This has got something to do with optical 'illusions'. Eg : Even if you get the rolling diameter spot on for the 18"s, the 'thinner' rubber as seen from the side elevation, compared to the wheel gap will render the car looking like it's on stilts! Or raised. That wouldn't look nice.
The section/profile of the tyres against the wheel to tyre gap plays an important part in getting the 'right' looks. Rule of thumb : The wheel arch gap has to be Equal or preferably LESSER than the thickness of the rubber(tyres) to the rim. To achieve the said look, you might have to lower it maybe an inch (25.4mm) all round. I think this topic has been covered in the other thread somewhere..19" rims with correspondingly 'thinner' profile will cause the lowering to be more to get the right look.
Bottomline is : You can't get away WITHOUT lowering the car if you upsize the tyres/rims combo and still want it to look right.

I think Christian's Ex-456 with the 575 rims looks great. He lowered it by 1" all round, IIRC.