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      08-10-2020, 01:58 PM   #1
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Tires questions on 2019

So I noticed my 2019 has 215 at the front and 245 at the back.
Would it be worthwhile to get 275 35 20 Potenza s001 for the back and move the 245s to the front ? Iím getting used 275s for like 150$ with 7/32.
Planning to take the car lapping at the end of the month
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      08-10-2020, 02:00 PM   #2
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Hoping to not change the OEM mags
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      08-10-2020, 03:54 PM   #3
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Thatís what I did but I used pilot sport 4s
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      08-11-2020, 03:47 PM   #4
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If your goal is to go around the track faster with balanced handling then 245 all around (square) is likely to be your best choice. If you think wider rear tires look better, well that is a different issue.
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      08-11-2020, 04:49 PM   #5
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I run 245 all around in a square setup. Totally eliminated the factory understeer that I disliked with the 215's. I run 3mm spacers all around, to keep the tires away from the front suspension arm. It clears without them but I just wanted to make sure.

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Originally Posted by stressdoc View Post
If your goal is to go around the track faster with balanced handling then 245 all around (square) is likely to be your best choice. If you think wider rear tires look better, well that is a different issue.
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      08-11-2020, 05:29 PM   #6
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Quote:
Originally Posted by stressdoc View Post
If your goal is to go around the track faster with balanced handling then 245 all around (square) is likely to be your best choice. If you think wider rear tires look better, well that is a different issue.
Why is (square) better?
I can’t think of a single high performance car that comes from the manufacturer with the same size tires on the front and rear.

One reason that manufacturers may deliver cars with a staggered tire set up is because
cars that understeer are considered safer than cars that oversteer.

On the i8 by adding the same level of increased grip 245’s front and 275’s rear and keeping the original staggered set up as designed by BMW you maintain the safety of understeer while increasing overall cornering grip which is your goal.

The best handling race cars understeer at the limit.

Unless you prefer another old racing adage....“oversteer is better because you don't see what you're about to hit.”

Last edited by Coastali8; 08-12-2020 at 01:04 PM..
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      08-12-2020, 06:09 AM   #7
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Does a 275 tyre fit on the oem wheels?
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      08-12-2020, 01:08 PM   #8
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Originally Posted by Tazzie View Post
Does a 275 tyre fit on the oem wheels?
Yes.
245/40x20 fit on the front factory wheels and 275/35x20 fit on the rear factory wheels. No spacers needed and no clearance issues.


Disclaimer:
The tire manufacturers recommend a wider wheel for these tire sizes. However some automobile manufacturers have not followed these recommendations when installing tires as original equipment on new cars. Including BMW, Porsche and GM.

Last edited by Coastali8; 08-12-2020 at 01:24 PM..
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      08-13-2020, 03:33 PM   #9
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Ah so I would need to move the rear tires to the front wheels and the add 275s to the rear wheels?

Or just get 245s for the front wheels

I am doing for all 3 reasons, better street driving, better lapping and better appearance (more minor, who am I kidding the car still has kids dropping jaws)
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      08-13-2020, 08:28 PM   #10
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Move the tires.
The wheels are different widths.
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      08-16-2020, 10:09 AM   #11
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If you want better street and track performance then get Michelin PS4s.

275/245 set up adds 3-4lbs per wheel of unsprung weight. This diminishes handling and acceleration.

The stock 245/215 rubber was chosen in part to complement the i8's fuel efficiency / CO2 mission. Many of us prefer a minimal cost in fuel to enhanced performance.

The i8 does not have a powerful engine driving the rear wheels; traction during acceleration is not much of an issue. Power-induced oversteer is not a challenge for the 245s. The relatively skinny 215s on the front, however, are a bit of an Achille's heel for cornering. The car 'pushes' (understeers) at its limits. But unsprung weight is a true enemy of handling, so simply slapping on bigger wider tires involves compromises. There also are issues with the handling software; algorithms are based on stock tires. This is complex - but there is a fair bit of flexibility/adaptability in the system, so small changes do not present problems.

Ideal solutions require extensive comparison tests of the sort that Tire Rack does.

My best guess: If you have $$$ to burn, get superlight rims -- BBS FI-R. Michelin PS4 265 235.

Mixing new tires w used ones is problematic. That said, the $ saving choice is to get two new tires and use the old 245s, either keeping them in back and putting new 245s up front for square set up; or moving old 245s to front and putting 275s on rear. The only real gain here is appearance, if wider tires appeal to you. Your track time would likely be slower. Street feel and steering sluggish.
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      08-16-2020, 11:20 PM   #12
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Iím working on getting a set of used ps4 for 400$CAD - 245/40/20

I was never going to mix different tire brands or significantly different tread depth

stupid other logistical question but is it possible to fit 4 tires inside the backseat and passenger seat of the car for a 20 minute drive?
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      08-19-2020, 03:04 PM   #13
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Ha, good Q, I could not get 4 tires into the car. I drove tires to installer in my 4runner, then went back for i8. I could have done it with the seasucker rack.
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      08-20-2020, 08:53 AM   #14
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Just a thought...
You could save a little money by installing 215/45X20 tires on the rear. That would give you a square set up. I guarantee it would solve the understeer issue and make the car feel even sportier with reduced unsprung weight and who knows... even quicker acceleration.
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      08-20-2020, 01:41 PM   #15
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Iím looking at Firehawk Indy 500 as the super sport deal fell through. I prefer replacing the full set of 4 tires so I can put them back on for the lease return
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      08-26-2020, 02:46 PM   #16
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Quote:
Originally Posted by Coastal i8 View Post
Why is (square) better?
I can’t think of a single high performance car that comes from the manufacturer with the same size tires on the front and rear.

One reason that manufacturers may deliver cars with a staggered tire set up is because
cars that understeer are considered safer than cars that oversteer.

On the i8 by adding the same level of increased grip 245’s front and 275’s rear and keeping the original staggered set up as designed by BMW you maintain the safety of understeer while increasing overall cornering grip which is your goal.

The best handling race cars understeer at the limit.

Unless you prefer another old racing adage....“oversteer is better because you don't see what you're about to hit.”
Easy there. It's for feel. I prefer the feel of a oversteer biased car. My i8 sees no track time and I dislike understeer.
FWIW, the best race cars are balanced.
Another plus, is I can swap back to front to even out wear, again on my street car.
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      08-26-2020, 07:22 PM   #17
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Quote:
Originally Posted by MGRMLN View Post
Easy there. It's for feel. I prefer the feel of a oversteer biased car. My i8 sees no track time and I dislike understeer.
FWIW, the best race cars are balanced.
Another plus, is I can swap back to front to even out wear, again on my street car.
Well...
This is a huge subject and many books and different opinions are available.

In reality there is really no such thing as neutral handling.
The balance of the car changes depending on if your accelerating or braking in a corner and a bunch of other factors. (Body roll, weight shift,- suspension related plus aerodynamics, etc. )

In general though....When the tire grip runs out something has to give. A good driver can keep the car in a relative neutral position through the curve but that is a very narrow place. At some point you will either be in understeer or oversteer because your too fast or turning in too tight for the available grip of your tires. Also... A car that understeers is more stable on a straight line.

Last edited by Coastali8; 08-27-2020 at 11:02 AM..
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      09-05-2020, 02:40 PM   #18
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Quote:
Originally Posted by thesubmitter View Post
Iím looking at Firehawk Indy 500 as the super sport deal fell through. I prefer replacing the full set of 4 tires so I can put them back on for the lease return
Did you end up getting these? if so, how are they? I'm undecided between these and the PS4S..
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