Help with tire sizing for 355 wheels on 348

No spacer up front. 15mm in back. Check with Hill for lug bolt sizes - one is replaced. Tires up to 285 in back and 235 in front. Anything larger looks like you are trying too hard. Plus you will trash the lower rear fenders with road splash. I use 265 in rear but the replacement tires will be wider. Fronts I also use stock 215 but they also wil increase slightly, depending on what's available at the time.

 

i agree Vincenzo

 

sorry to change the subject
did nick that has that black 348 tb do a video of his level 3 capristo on his 348 after selling his tubi

 

i found 225/40 are the widest i can go in the front w/no spacers... any wider and i would hit the outter fender lips because those rims have an outwards offset.

as for the rear, im running 265 w/no spacers. If you want to go wider i would try without spacers first. I have a 1992 so not sure for you.

I found you can fit very wide tires on the car with proper offset rims. The wheel wells have lots of room but the rims have to be offset inwards. For track i have a set of rims measuring 18X12 and 18X9 with 305 rear and 275 tires front. These tires fit inside the wheel wells and dont rub... and my car is lowered about 1.25"

"what are your thoughts on changing out my old rubber bushings for Energy Suspension bushings? Do I need to change them all or just the control arm bushings? Does anyone sell a complete kit for the front and rear? "
I changed my rubber bushings because they were cracking. (the cars are getting old) I bought about $180 worth of Delrin and machined myself all the control arm susp bushings and lower shock mount bushings... installed last year. Big difference in handling. I would do all the bushings since if you do only the front or back it will throw off the handling. For street Energy Susp would work fine except if they get squeeky. You can call ES to see if they have a kit.

this is an old pic before i did the susp work... but was running no spacers and 225/40 front, and 265/30 rear


***just knowticed your talking about 355 rims... sorry***
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i wanted to keep the bushing outer sleeves in the control arm so i torched the rubber out and re-used the inner sleeve for my delrin bushing. It was messy but didn't need to grind and press them out since i left the outer sleeve in place. Not sure if the Poly bushings come with outer sleeves or you re-use the originals which would make it easier.

 

+1 ....... though on the front 225/40 is the ticket !

 

I used 225/40R18 with 10mm spacer at the front and 265/40R18 with 15mm spacer at the rear on my 348 spider. Great looks and great handling!
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Here you go!
Are you looking for any specific pictures?
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I run 225/40 ZR18s front and 275/40 ZR18s rear.

There are two things to watch out for when changing tire sizes. To a large first order make sure that the rolling diameter is very similar (as close as possible) to the rolling diameter of the OEM tires. The calculation proceeds as follows:

xyz/ab-ZR18: {(18*25.4) + (0.ab * xyz * 2)} = rolling diameter

The second thing to note is that the tread front and rear shold have the same ratio on the new set of tires compared to the old set of tires. This leaves the oversteer/understeer relationship close enough to be tuned with air pressure only. The calculation proceeds as follows:

(old-front-xyz/old-rear-xyz) = (new-front-xyz/new-rear-xyz) within 4%-5%

The third thing to note is that you can put almost any rolling diamater on the car and then reset the ride heights to adjust the ground clearance back to standard.

The final thing to note: is that you can adjust oversteer/understeeer by altering the rear ride height: Up allows more oversteer or less understeer: down allows more understeer or less oversteer.

So I believe that the OEM sizes on a 348 are 215/50ZR17 and 255/45ZR17. So, if you decide on a 275 rear, you will be faced with two choices the 275/35ZR18 and the 275/40ZR18.

so
(17*25.4)+(0.45*255*2) = 431.8+229.5 = 661.3
(18*25.4)+(0.35*275*2) = 457.2+192.5 = 649.7 to short by 11.6
(18*25.4)+(0.40*275*2) = 457.2+220.0 = 677.2 to tall by 15.9
So
One requires the rear ride height adjusted upwards, the other requires it to be adjusted downward by rather similar amounts.

To the ratio:
(215/255) = 0.843
(xyz/275) = 0.843 -> xyz = 231.85
So, a 225 front will probably create a little understeer, while a 235 front will likely create a little oversteer, AFTER the ride heights are reset to standard.

A 265/40ZR18 has a rolling diameter of 669.2 and can be considered essentially a perfect fit. The corresponding fron tire is 223.5 so the 225 fronts are near perfect.

A 285/35ZR18 has a rolling radius of 656.7 and might not need any reseting of the ride heights. This rear is perfectly matched to a 240 front So we are left again to pick between wanting oversteer and wanting oversteer. This can be corrected by alter the rear ride height as stated above.

A 295/35 has a rolling radius of 663.7 and can be considered a perfect fit. The corresponding front is a 248.7 so a 245 is about as perfect as one can get. HOWEVER, neighter of these tires fits on the F355 wheels (being too wide): however**2; some tire changers will put these tire on those rims with a little persuasion.

Do not use spacers with tires wider than 275.

 

i put 18'' wheels from a testarossa "355 style" on my 348. the tires are stretched to meet the rim. a wider tire would be much much better and 100% fit. they are currently 285's on the back. i put a 15mm or 20mm spacer on there too. i still have a 1/2 space to the fender. the over all tire is actually smaller then the original tire/wheel combo so i had to lower it quite it bit to make it look right. however it might be a little quicker to 60mph becuase of the smaller tire! looks badass from the back with such a wide tire.

can post a pic or 2 later if interested

Robert

 

Hey Mike, I spent all night going through the threads too! Still can't find my answer though.

Dont mean to hijack Mike, But does anyone know if I need longer bolt's to mount 360 mods on my 348 SS?

Fronts are 215/45/18
Rears are 275/40/18


Hey Mitch, Before I even begin to understand what your saying, I would personally fly you out and put you up in a 5 star hotel plus per diem for you to mount these rims for me


Cheers!

 

348 with 355 wheels.. do they need spacers? or no?

 

Will I need 355 bolts to mount 355 wheels on a 93 348 Speciale?