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Discussion Starter · #1 ·
What’s the widest you guys have fitted on the sport or Ti?

I’m thinking on getting 255/40/18 all around




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Have you checked to make sure the height of these are the same as what you have on the car. I thought they were 225 45 18s. The quick rule of thumb i usually use is for each width increase you need to make one aspect ration reduction. Eg 235 40s. So with 255 you would need something like 30s or 35s. Best to compare the height. Also for driving dynamics of a rear drive car, You might not want to increase the relative stickiness of the front of the car so much. Just my non expert thoughts.
 

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2018 Q4 with Fiamenghi Ti exhaust, Race Mod, and Tecnico wheels.
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Racer Z has 255 35R19s on all 4 corners, mounted on the OEM 19x9 wheels. You need 8.5" width rims as a minimum to fit 255 wide tires. I believe that 9.5" wide rims are the "ideal width" for handling for that width tire.

One issue with 18" and 17" wheels on Giulia is availability of anything wider than 8".

Note that 255 35R19 fits a RWD Giulia on the condition that it is not lowered. Fitment is doubtful in the front if the car is lowered.
 

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Have you checked to make sure the height of these are the same as what you have on the car. I thought they were 225 45 18s. The quick rule of thumb i usually use is for each width increase you need to make one aspect ration reduction. Eg 235 40s. So with 255 you would need something like 30s or 35s. Best to compare the height. Also for driving dynamics of a rear drive car, You might not want to increase the relative stickiness of the front of the car so much. Just my non expert thoughts.
Your math is skewed, 255/40 has only 4.7mm different rolling distance from 225/45, it woul be perfect choice if it of course fits on an 8 inch width rim properly....some tires would some wouldnt
 

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A couple users of this forum fit QV tires on regular giulia. That means 245 front / 285 rear.
I am also going this route, if my Tecnico wheels ever get released from Memphis customs.
 

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Have you checked to make sure the height of these are the same as what you have on the car. I thought they were 225 45 18s. The quick rule of thumb i usually use is for each width increase you need to make one aspect ration reduction. Eg 235 40s. So with 255 you would need something like 30s or 35s. Best to compare the height. Also for driving dynamics of a rear drive car, You might not want to increase the relative stickiness of the front of the car so much. Just my non expert thoughts.
The sidewall height of an A BRC size tire is A*B/100. Keep that constant (or nearly so) and you will maintain the same tire diameter. There is some slight variability from tire model to tire model, so if you want precision reference the manufacturers specification.

In this case 225*45/100 = 101.25mm

To find the width tire that matches 40 profile, solve the equation to get

101.25*100/40 = 253mm width

The OPs 255 40R18 is thus the closest to OEM diameter tire that is wider.

The match for 19s looks similar

225*40/100 = 90mm

90*100/35 = 257mm width

It is not so neat for 17s:

225*50/100 = 112.5mm
112.5*100/45 = 250mm (midway between the available 245 and 255 widths, and twice the error of either the wider 18s or 19s)
 

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Good, but then you need to check clearance at full lock both ways. This is what will eat your fender lips on driveway aprons and dips. Also check inside the tubs, especially the secondary inter-coolers and suspensions parts. I have a fender roller if you want to borrow/purchase it. Rolled my 360 fenders in the sweet spot last summer. Wider OZs and tires up front helped eliminate under steer.
 

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Discussion Starter · #8 ·
Excellent responses and read thank you everyone...

I should clarify that I’m stock sport height not going to lower it and only going to use these tires on the track.

I have an extra cheap set of wheels from tire rack that I would be mounting these on.
I know 8.5” would be the minimum but I just might stretch them a little bit

Thoughts??

Also, stuck on that size since I am getting them for 1/2 the price form a fiend and they are brand new








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Good, but then you need to check clearance at full lock both ways. This is what will eat your fender lips on driveway aprons and dips. Also check inside the tubs, especially the secondary inter-coolers and suspensions parts. I have a fender roller if you want to borrow/purchase it. Rolled my 360 fenders in the sweet spot last summer. Wider OZs and tires up front helped eliminate under steer.
Racer Z already checked that 255 35r19 will fit and not rub. This is a pretty good indication that 255 40r18 will fit and not rub. I believe all RWD 2.0Ts are the same height (what Racer Z has) and have the same clearance around the wheels. The Q4 sits higher and the QV sits lower. Racer Z used the OEM 19x9 wheels, which IIRC have a 44.5mm offset. Change the offset and things might not fit.

The Michelin PS A/S 3+ tires in 255 35R19 that I have been eyeing have a tread width of 9.1", so to get some stretch a 9.5" wide rim seems "right". I have no idea if 19x9.5 makes a noticeable difference versus 19x9 for on-road use. A little stretch reportedly does make a measurable difference on the track.
 

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Here's the site I use for wheel/tire size comparisons. I like it because you get some visual representation of how things are changing.

https://www.rimsntires.com/specspro.jsp

Also, the Falken RT-615K is an awesome track tire. They're not quite as fast as the Star Specs and Rivals, but they more than make up for it in longevity and consistency. It is the tire that I would choose, hands down, for street-tire based endurance racing series, or HPDE. I've had awesome experience with them in American Endurance Racing, including an overall win.
 
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Good, but then you need to check clearance at full lock both ways. This is what will eat your fender lips on driveway aprons and dips. Also check inside the tubs, especially the secondary inter-coolers and suspensions parts. I have a fender roller if you want to borrow/purchase it. Rolled my 360 fenders in the sweet spot last summer. Wider OZs and tires up front helped eliminate under steer.
The top of the front fenders come rolled straight from AR.
 

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my impression is wider tyre would affect accelerations, no?
Yes, but it is not as obvious how so as one would think. Wider tires and wheels weigh more and more weight adversely affects both acceleration and handling.

However, a wide tire can make better ground contact than a narrow tire, particularly under high acceleration (lateral or longitudinal) when the contact patch distorts. Acceleration of a stock RWD Giulia is traction limited with the stock tires up to 15-30MPH. I do not know if a stock Q4 can hit the traction limit in acceleration but it probably can in first gear (15MPH max?)

It is possible to go wider without gaining weight by throwing money at the problem. The relatively inexpensive tires and wheels that come stock on 2 liter Giulias can be substantially improved upon weight wise with a large cash infusion.

For my Q4:

Stock Pirelli Centurati RFT all seasons on 19x8 5 holes in 225 40R19 about 50 pounds each.

Best upgrade for width and weight: Carbon Revolution with 255 35r19 on 19x9.5 wheels with Michelin Pilot Cup 2 tires (not what works for me but a good light weight tire), 39-40 pounds each. Plus with about $15,000 less in your pocket, your wallet will weigh less too.
 

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Great thread! Looking to possibly get wider tires as well!
 

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Yes, but it is not as obvious how so as one would think. Wider tires and wheels weigh more and more weight adversely affects both acceleration and handling.

However, a wide tire can make better ground contact than a narrow tire, particularly under high acceleration (lateral or longitudinal) when the contact patch distorts. Acceleration of a stock RWD Giulia is traction limited with the stock tires up to 15-30MPH. I do not know if a stock Q4 can hit the traction limit in acceleration but it probably can in first gear (15MPH max?)

It is possible to go wider without gaining weight by throwing money at the problem. The relatively inexpensive tires and wheels that come stock on 2 liter Giulias can be substantially improved upon weight wise with a large cash infusion.

For my Q4:

Stock Pirelli Centurati RFT all seasons on 19x8 5 holes in 225 40R19 about 50 pounds each.

Best upgrade for width and weight: Carbon Revolution with 255 35r19 on 19x9.5 wheels with Michelin Pilot Cup 2 tires (not what works for me but a good light weight tire), 39-40 pounds each. Plus with about $15,000 less in your pocket, your wallet will weigh less too.
thanks for the detailed explanation.
what do you mean by traction limited @ 15-30mph?
 

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thanks for the detailed explanation.
what do you mean by traction limited @ 15-30mph?
Full torque will spin the wheels in 1st (RWD and Q4) and 2nd (RWD). Traction control will try to stop the wheel spin, messing with your ability to do a burn out or get best acceleration.

In first at full torque Giulia 2.0T will try to accelerate at about 1.1 gs while the Q4 tires have only about 0.8 gs worth of traction. Maybe if you have RWD with staggered summer tires the RWD can get sufficient traction at full throttle in second gear on a warm day.

IIRC:
Stock Q4 Pirelli Centurato tires: about 0.8 gs max.
"ultra high performance" all season tires (Michelin A/S 3+): about 0.95 gs max.
"ultra high performance" summer tires: about 0.98 gs
"streetable track" tires (Pirelli Corsa?): over 1.0 gs (1.1 gs according to some posted on track measurements/videos)
 

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Wilder Tires

I hope I never see a Giulia on "dubs".
 

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Good on both counts lockem. Thanks for that. I took to calling the finder design "cowling" style when we were discussing mud flaps. I'm afraid a good stock spec winter set is still to pricey for me this year. Maybe on clearance? But those tires above look great! Also love the rimsntires site. Great software and I used it on my 348 and 360 wheel and tire swaps/upgrades/spacers ;) Tire Rack and Ricambi helped too.
 
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