Ideal Tyre size for 17" wheels on Mondial 3.2

Like many owners in the past I am replacing my Mondial 3.2 TRX wheels with 348 17” wheels partly because of costs of replacing TRX tyres (£1268 plus delivery, fitting etc) and partly because I don’t want the worry of sourcing TRX tyres if urgent replacements are needed on a long journey.

Many Mondial owners have fitted the standard 348 tyres (215/50 R17 front and 255/45 R17 rear). However, some feel that this increases the steering load and reduces comfort. Looking at tyre specifications (diameter, aspect ratio and tread width) of possible tyres for J7.5x17 and J9 R17 wheels it appears that an option might be 205/55 R17 front and 235/50 R17 rear.

Has anybody experience with fitting these tyres to 17” wheels on a Mondial?

 

Front 225/45 Rear 245/45

Rides like a dream!

 

True, it is !!

Cheers,

Hank

 

Neither the 348 nor the 3.2 were deliverred with the same aspect ratio front to rear. Further, the 348 may have more rear weight which would account for its propotionately greater width difference front to back.

I belive the 'technically' correct adjustment to accomodate one inch larger wheel would be plus 10 mm front and rear width, and minus five from the aspect ratio from each. I believe this formula is intended to provide the same tire circumfrence for each wheel diameter. I could be mistaken.

However, ride quality has more to do with sidewall compliance. For instance, I wore out a set of Pirelli P Zero Nero all season tires in 6,000 miles. Those tires had very stiff sidewalls. So much so they wore out the INSIDE front edges due to the high caster we have in our Mondials. This provides crisper and tighter extreme G force cornering (and in my case little or no understeer) but has a definite harsher ride.

I switched to stock sized Continental ExtremeContact Summer DW tires and there is a world of difference. These are very capable GT tires, they are wearing evenly, have introduced a bit of understeer, but have added greatly to ride quality and straight line and curve tracking stability. (They have three more or less solid rubber circumfrence tred rings.)

However, I do not see them available in appropriate 17 inch sizes.
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Are there any geometry implications (alignment, either front or back) when one mounts these 17" wheels but maintaining the same tire height as the original 16" tires? I ask this because I have read in a thread here that the toe-in/out needs tweaking? I do not understand this comment unless this would be associated with tire set-up for tracking??

 

plug and play!

 

I couldn’t resist doing some math. I calculated the overall diameter of the suggested tire combos, and to me it appears the 225/45 front & 245/45 rears are the correct size. Because you will be switching to 17” wheels I put the measurements in inches.

Tire OD
220/55-390 24.88 in
240/55-390 25.75 in
215/50-17 25.46 in
255/45-17 26.04 in
205/55-17 25.88 in
235/50-17 26.25 in
225/45-17 24.97 in
245/45-17 25.68 in

As you can see the last option is the closest in overall diameter to the original TRXs, with a difference that works out to only about 1mm difference in radius, and it’s also the closest in tire width without going smaller, so I would think it would be the best option. Sorry for the formatting, I couldn't seem to get it to look better, I even tried doing it on Word and pasting it, but this is the best I could do.

 

Discount Tire and Tire Rack have the Conti Extreme Contact DW, in both the 225/45/17 & 245/45/17 sizes. I would hope they're also available in the UK

Cheers,

Hank

 

I believe Longstone's quoted diameter for TRX 220/55-390 is 642mm (25.28"). I think Robogeeks quoted the diameter of the optional Imperial 16" tyre 205/55 WR16.

I measured the tread width of the TRX tyres as approximately 190mm (front) and 205mm (rear). This means that the closest Imperial tyre in terms of diameter and tread width to the TRX front is 215/50 R17 although a 205/50 R17 or 205/55 R17 tyre would perhaps give reduced steering effort.

While 245/45 -R17 is very close to the diameter of the rear TRX the tread width is significantly higher by 15mm. So for speedometer consistency a 245/45 R17 tyre would be best but perhaps taking diameter and tread width into account a 235/45 R17 or 235/50 R17 tyre might be considered overall a closer compromise.

But at the end of the day real experience with actual tyres are the best test which is why FChat is such a valuable resource.

 

why not go up to 18" rims? The car looks good with 18's.

 

Hi Jeff,

Why not? - - because he wants to go up to 17" rims. He thinks the car looks good with 17s'. Funny, neh - how beauty is always in the eye of the beholder.

Cheers mate,

Hank

 

Another reason Jeff is that I am wary about straying too far from the standard specification. I fear the jump from 390mm (15.3") to 18" would be a step too far in terms of overall tyre diameter, tread width, aspect ratio etc.
But I must admit I've never driven a Mondial with 18" wheels so what do I know!

 

I had 18" Speedline 3 piece rims on my Mondial and they looked great, the trouble was the ride was harsh and they did nothing for handling. I went back to the standard 16" rims with Toyo R888's, much better ride and handling how Ferrari intended.

 

My car has the standard TRX tyres. They are newish with tons of tread on them. I've never driven a car with 17 or 18's on so I've no idea how the car drives.

What I do know is that I've seen pics of Mondies on 18's and think the car looks good. I figure changing the wheels does nothing to lower the value of a car if you have the original wheels it's just to swap back or offer them when the car is sold.

So if you're looking at 17" it can be good to know that there is an 18" option too. Not that I know the tyre sizes but there are calculators for that.

Just my 10p's worth

Jeff

 

Would you have a pic of the car Neil? Do you remember the tyre sizes?

Cheerz

 

The fronts were 40's the rears 35's.
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225 on the front 245 on the rear.. Parking takes a little effort but once moving it is very easy to steer and handle.
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When I saw this post I went back and recalculated the OD several times, and I still get the same numbers. Perhaps I am miscalculating the OD. As far as I know the second number in a tire size is the height of the sidewall as a percentage of the width, thus on a 220/55 the sidewall is 55% of the width, so 220 mm x 0.55 = 121 mm, times two because there are two sidewalls in the diameter, so 242 mm, to that I then add the diameter of the wheel, 390 mm + 242 mm = 632 mm. Using the standard conversion factor for mm to inches, 25.4 mm/inch, 632 mm / 25.4 = 24.88 inches. Using the same calculation for the rear tire, 240 mm x 0.55 = 132 mm, x 2 = 264 mm, + 390 = 654 mm, / 25.4 = 25.75 inches. Perhaps the calculations are different for metric wheels and tires like the TRXs, so I could be wrong, but if I am using the correct formula, I stand by my numbers.

As far as width, the actual physical tread width will always be a little less than the section width, on any tire, so if you are increasing section width by only 5 mm I doubt you would be increasing tread width by 15 mm, unless the TRXs had an unusually high difference between section width and tread width; however, the smaller the sidewall, the closer the two measurements are, so the actual tread width difference would probably be larger than the 5 mm difference in section width, but not by much, probably less than 10 mm.

I like the look of wide tires on a car, so I would never go smaller, I would always go wider, within reason of course, you don’t want to go so wide that it looks ridiculous, and negatively affects handling and braking. Since the OD is the closest with the 225s & 245s, that’s what I would use. In fact, my tires are due to be changed soon, and I am going to put 225/50-16s and 245/50-16s, just like with the 17” tires these give me the closest OD to the originals for speedometer and odometer readings, and they will give me the closest overall combination of wheel and tire size to the TRXs the car was originally designed for.

 

Hey robogeeks,

You are correct in that your choice of new 50 aspect ratio tires, are almost identical in diameters to the original OEM 55 aspect ratio tires. But, I would only caution you as regards having the total (increased) tire tread measurement (a function of lower aspect ratio numbers) appearing wider than the rim itself. When that visual line is crossed, well - - IMHO, it looks quite obtuse. It reminds me of the old days - when true muscle cars had engine muscle, while many pretenders without muscle, had those super wide tread "Radial T/As mounted on polished Mags". But hey, if you like it, bless ya, mate. When it comes to visual appreciation, no rules exist.

Cheers,

Hank

 

Robogeeks has hit on a curious anomaly which I’ve not seen reported in FChat before. His calculations (which I cannot fault) suggest the diameter of the front Mondial tyre (TRX 220/55 VR390) 632m and the rear (TRX 240/55 VR390) tyre is 654mm.

In my earlier message on this thread I took the Michelin Classic website (TRX | Michelin Classic) figures of 642mm and 654mm respectively and these are also quoted by the current manufacture of TRX tyres (Ferrari Mondial | Longstone Tyres) and by many other sources.

So why does the calculated diameter agree with Michelin’s quote for the rear (240/55 VR390) tyre but is 10mm less for the front (220/55 VR390) tyre? Could it be 30 years ago Michelin misquoted the true diameter and this has not been challenged since? Does anybody have an alternative suggestion?

A further consideration is that when Mondials switched to 16” Imperial wheels they used 205/55 WR16 front tyres and 225/50 WR16 rear. These have theoretical diameters of 632mm and 631.4mm respectively and these figures are used in many comparison websites (e.g.: Tyre overall rolling diameter). Was the gearing changed to reflect the significant reduction in rear wheel diameter?

As others have pointed out comparisons of tread width between TRX and Imperial tyres is not straight forward. As Coker Tire states TRX tyres and rims were designed to complement one another and work as a single unit. The rim had a flatter, lower flange allowing a gradual curvature of the tyre casing, without the "S" shaped flexing inherent in traditional designs. The result is that TRX tyres have significantly less tread width compared with an equivalent sized Imperial tyre and for this reason the figures I used in my earlier note were measured not calculated tread widths.

 

Hi caterus,

Correction mate The tire sizes on Mondials with Imperial 16" wheels are as follows:

Front - 205/55/ZR16
Rear - 225/55/ZR16 (larger diameter by about 3/4")

The 225/50/ZR rubber was mounted on the rear of 308 and 328. The difference here is that the rears, though very similar in diameter to the fronts, were wider. The fronts were like Mondials in that they were 205/55/ZR16.

Cheers,

Hank

 

Hank,
You are absolutely right that Ferrari recommended for Mondial 3.2 with 16" wheels (8Jx16") rear tyres Goodyear Eagle 225/55 VR16 whose diameter is identical to TRX 240/55 VR390.

However I was taking the Superformance currently recommended Mondial (8, QV,3.2) rear tyres for 8Jx16" wheels which is CONTINENTAL 225/50WR16
(see: Wheels & Tyres for Ferrari Mondial - Superformance) the diameter of which is about 20mm less than that of TRX 240/55 VR390 which would effect gearing and performance.

Don't ask me why Superformance recommends this tyre over the Ferrari recommendation but I guess many would take it without asking too many questions.

I should have made this clear and sorry for the confusion.

 

Hi Tim,

Taking this to a different level, that being the visual, the use of the smaller diameter 225/50/16 tire on the rear of the Mondial, reduces the car's aggressive stance and opens up even further, the gap between tire and wheel arch. IMHO, this weakens what should be a visual strength.

I would simply say: Ferrari had it right.

Cheers,

Hank