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      04-03-2021, 07:55 PM   #23
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Quote:
Originally Posted by YWGT3 View Post
P ZERO (PZ4) NERO
215/45R20 95W XL
245/40R20 99W XL
Just curious were these BMW star marked i.e. homologated tires?
Also are you sure they were Nero? I am not aware there is such a model as PZ4 Nero.

Jeff
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      04-04-2021, 10:13 AM   #24
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Originally Posted by YWGT3 View Post
Noise is in-discernable in contrast to the OEM Potenzas. Too early to tell on the tread life (less than 2,000 driven miles). However, as for performance, I notice the P-zeros are a bit stickier, leaning closer toward the handling characteristics of the Michelin Pilot Supersports, which are outfitted on my 650i GC and Merc CL63.
thanks for the feedback on the P Zeros. I might try them. I am looking for something a bit stickier. Got to be careful it does not get too noisy, though. Sticky can mean noisy.

I am just now starting my tire search and typed in my car's stock tire size at Tirerack.com and found that, indeed the only two summer-ey performance tires are the Bridgestone S001 and the Perelli P Zero, both a tread wear rating of 280, not any sort of track-day tire for sure. Given the car's nature, though, I am not sure it needs anything much more sticky, but still I was put off by the lack of choices.

I am playing around with buying forged rims which should be lighter, given the 625 wheels have been quoted to me as being 24 lbs front and 25 rear, by people who are selling and shipping them refurbished. (on Realoem.com BMW lists the 625 as being "forged"... interesting--because, they are heavy pigs)

The issue is: if one goes with a wider, but forged rim, then the rim's width starts to add weight, again. And most forgings in a 20" block do not come as narrow as 7.5", so you are forced to go wider. And if one goes to a wider tire, or a smaller 19" AND wider tire, then, again, the tires get heavier. You might end up with a wash, compared to stock weight.

I spent a couple of hours looking online last night, using this tool. Play around with it and it will start to make sense, what it offers. Another forum member posted it, for which I am grateful. Look at the offset graphic down lower. Its very useful.

https://www.willtheyfit.com/index.ph...8-5&offset2=40

The biggest issue with finding an assortment of tires is the fact that the rims are staggered and also, not super wide. It has to be a staggered setup that is supported by, say, some very popular performance car, and then you will get lots of performance options, and, our staggered setup is not supported by anything but the i8, it seems. Even a modified staggered setup of 20x8.5" rim in front and 20x9.5" rim in back has its challenges finding stickier tire choices. But I did find some in a 220 tread wear rating.

I found that if I were willing to put a non-staggered rim setup of 8.5" 20" forged rim on the front AND back (like the Japanese performance cars of the 1990s), suddenly, one more sticky choice was available. I could do this tire:

https://www.tirerack.com/tires/tires...omCompare1=yes

which is a decently track-day sticky tire, if I wanted. You keep the rim width in back (no one is really losing traction there, anyway), and get a 1" wider rim in front, which is the most embarrassing spot on the "rim width scale", for most. And can get turn-in.

be careful with the offset in the front if you go wider on a rim. I put my car up on an alignment rack, got under there and inspected, and made some movies (not edited yet). Turned the wheel really tight and looked for clearance in front and back. The bottom line is. You are clear to put a good extra inch or more of wideness (and extra rim and tire weight...) tucked into the back. In the front, you have barely the thickness of my first finger, stuffed in between the tire and the suspension upright. Its not much more than 12mm worth of clearance before you rub--up at the top. So you have to be willing to offset the wheel out--towards the fender, as well. My finger was stuffed tight in there. Measure from top of knuckle to bottom, not side-to side, on the finger. Not a ton of space.

I know you could park your car on the ground and turn your wheel tight to one side and stuff your hand in there yourself, reach up towards the top of the tire. You will feel it. I will try to put various objects in there until I can find something that fits and is the right size, and then I will measure it.



for this test, one could jack the car up and do it carefully. the car does not need to be on the ground, at resting stance.
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      04-04-2021, 05:30 PM   #25
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IMO the best affordable option is 516 rims w Michelin PS4 235/40 front, 265/35 rear.

The only other high performance set up is BBS F-IR, at $2k per...
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      04-04-2021, 08:21 PM   #26
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Quote:
Originally Posted by stressdoc View Post
IMO the best affordable option is 516 rims w Michelin PS4 235/40 front, 265/35 rear.

The only other high performance set up is BBS F-IR, at $2k per...
true...unless you have something custom-carved out of a forged billet, which I was thinking, or have something spun via Flow forming. After you said this about the BMW 516 rims, I looked all over the web, at brochures, Realoem.com, talking to vendors who ship refurbished rims, I cannot get the weight of a 516.

Where can I read about the 516 weight?

were you talking about Pilot Sport 4? I can't find either of those tire sizes in a 20" on their website.

https://www.michelinman.com/tires/pi...t-sport-4.html

but I can find those sizes in a Pilot Sport 4-S

https://www.michelinman.com/tires/pi...-sport-4s.html

Last edited by mws; 04-04-2021 at 08:29 PM.. Reason: clarification
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      04-05-2021, 08:08 AM   #27
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Hmm, was thinking about going 245 PS4S Front and 275 Rear. Is that too wide then? On the 444 turbine wheel i might add.
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      04-05-2021, 10:35 AM   #28
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Originally Posted by Byhlinder View Post
Hmm, was thinking about going 245 PS4S Front and 275 Rear. Is that too wide then? On the 444 turbine wheel i might add.
well, in order to find out which width and profile (tire height from the wheel) you might choose, its time to learn how this website works and why. it's pretty easy, once you get past how busy it looks.

https://www.willtheyfit.com/index.ph...8-5&offset2=40

you type in your stock wheel and tire size is on the left. You type in what you "think" you want on the right. Then look at the chart called "Your Results--Old, New"

you want to compare wheel diameter and speedometer error. (even for front tires, it might mess with the ABS sensor) Almost never will going from one tire to the next, give you the "exact" same diameter or speedometer results. That's hot-rodding. Nothing you can do about it. We all live with it. So, how much discrepancy are you willing to go with?

on this website, it only compares one size to your new choice. It cannot do fronts and rears, so open another window and do the rear tires, for instance.

what you may find is, (I have not tried this, this is for the sake of argument) instead of say a 275/40, you might need to go to a 275/35 to get the right size, and one 275 is too large in diameter compared to stock and one is too small. So, then you play with 265s (if they are available, 265s are not very standard) and see if you can get closer.

now, to answer your question directly. Once you have found a tire diameter that looks OK, will that 245 fit on a 7.5" front rim, for instance.

245 is in mm, and the rim is measured in inches. There is a rule of thumb which people might break, but generally you do not want to go a whole lot more than 1', maybe 1.5" at the very most in tire width over your rim width. on a 7.5" I would not want a tire much wider than 8.5". 215mm / 25.4= 8.45". Its right at that 1" oversize mark I mentioned. BMW did the right thing.

A 245/25.4 = 9.64" tire you are trying to put on a 7.5" rim. more than 2". Have guys done it? Maybe (probably using spacers, see below). Would I do it? no. Also, if you read above, the post with the pictures there is only 12mm or so clearance between the stock 215 tire and the front suspension. if the 245mm tire is sitting on the rim as centered (which it is) that only gives you 12mm to stick out on each side, and it will touch the suspension. 12mm+12mm is about an inch of tire width. You want to add two inches to your width.

unless you get custom rims that set the tire out towards the fender, or buy 1" spacers (or bigger!), I imagine your 245 would not fit on a stock front rim because it will not just rub, but seriously interfere with the stock suspension upright.

one word of warning:

when I shop for aftermarket wheels and tires I have my own priorities: 1] losing weight on each corner, to help with acceleration, in all situations, (and handling) 2] the tread wear rating, to get less slippage and cornering (the lower number the better, but---they die quicker and need replacing--I am looking for something below 180. stocks are 280) and for me, 3] then, maybe extra wide rim and tire for looks and cornering, and maybe some traction capability.

bigger, wider tires on the same stock rim weigh more. They will look cooler, but they weigh more and they "will" effect your acceleration, especially on a car with a 228 hp rear motor and 141 hp front. Dragy can prove that out. And the track guy will point out, heavier whees and tires effect the way the car reacts on bumps and in corners. If all you care to do is cruise and pose, then who cares, right? I am not judging, here. Its a valid reason to own the car.

you can easily verify the weight by looking up your stock tire on tirerack.com and clicking into the information and finding it, then comparing to your proposed choice and comparing the weight. And compare the tread wear rating, while you are at it.

You could end up with a heavier, and less high-performing tire. Looks cool? maybe. Slows your car down? in that case, for sure. You can measure it with Dragy and if it's more than a few pounds each tire or tire and wheel, I have had cars where I actually feel it, as well. I know this because I have done all this, more than once, and there's plenty of write ups on it, and physics to back it up.

to solve that weight issue I am looking at having some forged or flow-formed rims made. if you made custom rims that are the exact same size as stock, you could stand to lose 3-4-5 lbs per corner, which is huge(!!) if you stick with the same tires.

problem is you can't have those made, at least, not in front: most forgers do not have 7.5" billets to cut into a rim. They start at 8.5". And, most people, me included (I like to pose sometimes too), are not going to pay $300-600 minimum to have someone custom make a 7.5" wide 20" rim, even if the company had billets that size.

Now you have a wider, somewhat lighter, but (dang it!) not AS much lighter rim, because it has more metal on it. You could have lost 3-5 lbs going forged for 7.5"x20, but an 8.5"x20 might weigh 1-2 pounds more than a 7.5x20 forged. Couple that with a wider heavier tire? You would need to do the math. Might be lucky to lose 1 pound, maybe 2, or hopefully not go over the stock weight.
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      04-05-2021, 11:42 AM   #29
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Have you looked at the ac-schnitzer rims. I found a tweet that ac-schnitzer Europe was selling rims a while back for i8s at 50% off.

https://twitter.com/acschnitzer/stat...159872?lang=en

Not sure if it still applies....
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      04-05-2021, 04:58 PM   #30
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Bridgestone 980AS

I run a square setup 245's all around to reduce understeer. My i8 is my daily so I put 980AS on it and I love them. I run a 3MM spacer and titanium wheel bots to offset the weight of the spacers and slightly heavier tires. Car is wonderful!
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      04-06-2021, 10:45 PM   #31
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Quote:
Originally Posted by MGRMLN View Post
I run a square setup 245's all around to reduce understeer. My i8 is my daily so I put 980AS on it and I love them. I run a 3MM spacer and titanium wheel bots to offset the weight of the spacers and slightly heavier tires. Car is wonderful!
interesting, I was thinking of running square 245s, but with aftermarket 8.5" forged wheels, all around.

you are running square with stocker rims and spacers in front to avoid the rubbing I was mentioning?
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      04-07-2021, 12:15 PM   #32
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Totally agree with MWS comments on unsprung weight. I was disappointed that CF composites were not on the LCI. But the 516s are at least a small improvement.

It is very difficult to find aftermarket rims for the i8 that are lower weight than the stock rims.

Titanium lugs help a little bit, I got them and saved several ounces per wheel.

The i8 tire set-up is consistent with the difficult trade-offs between Eco and performance. Hence there is some room for performance enhancement at minor reduction in efficiency.
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      04-13-2021, 07:41 PM   #33
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If anyone can find a link that shows the weight of a BMW 516 rim. Please send it to me. I only found one that says it weighs 8 kg which seems suspicious.
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      09-30-2021, 10:27 PM   #34
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Quote:
Originally Posted by mws View Post
I found that if I were willing to put a non-staggered rim setup of 8.5" 20" forged rim on the front AND back (like the Japanese performance cars of the 1990s), suddenly, one more sticky choice was available. I could do this tire:

https://www.tirerack.com/tires/tires...omCompare1=yes

which is a decently track-day sticky tire, if I wanted. You keep the rim width in back (no one is really losing traction there, anyway), and get a 1" wider rim in front, which is the most embarrassing spot on the "rim width scale", for most. And can get turn-in.
I am going to look into a square rim setup with 245/20s all around.
but....
this tire suggestion from me turns out to be a monumentally bad idea, now that I am resuming this train of thought and working on a custom-made lightweight set of forged rims and tires. These tires are BHPs. (Big Heavy Pigs). The stock 245 Bridgestones in back weigh 24 lbs, according to Tirerack.com.

https://www.tirerack.com/tires/tires...mpulse%20World

These RE050As I brought up, are indeed, very sticky BUT HEAVY!!! 30 lbs each. On a car with such HP challenges already, it is a horrible idea. (and they are only W rated, up to 168 MPH, more on that later)

I have started to look into tire weights, compared to the UTG (stickiness) rating. Having a hard time coming below 220, which is the Pirelli P Zero, which are also 24 lbs for a 245, and not just any P Zero. There appears to be a special one made for cars such as the i8.

Not this P Zero, it is 25 lbs

https://www.tirerack.com/tires/tires...mTireCompare=Y

you want this P Zero which is 24 lbs.

https://www.tirerack.com/tires/tires...mTireCompare=Y

there are also two different Potenza S001s, one is 28 lbs and Y-rated, for a 245 and the one we use is 24 and W-rated. Unless you feel the need to go 186+ miles per hour, the W-rated one is lighter and quicker.

also, I weighed my actual tires/wheels with a hanging scale, they were 45.5 lbs front, 49 rear. If the tires are indeed the weights tire rack.com says they are, then -21 and -24 respectively and you should have 24.5 front and 25 lbs rear for the wheels. It would be nice to get 20x8.5" forged wheels in the 18-19 lb range. I think that is possible (if you choose a simple spoke design). I had some VS Forged VS01s made in 20x9" front and 20x10.5" in back and they were a mere 20.2 lbs and 21.6 lbs (this was for a Jag). So, rims that are less wide, and similar style, might weigh less. Probably not more.

and talking this Square idea all the way through. Lets say we end up with 24 lb tires all around and 19 lb rims? That's 43lbs.

front was 45.5 and rear was 49. So the only big winner for weight savings, is the rear. The front electric motor is the one challenged in this whole equation. The last thing I want to do is make things worse for the electric motor, which this does not do..... but also, not spend a bunch of money and not really "help" the front, either. Losing 1.5 lbs of moment arm weight on the front to help the electric motor is not much. Maybe I should toss out the Square notion and use the 20/215 lighter tires in front, even on a slighty wider rim, if I can get someone to make a 20x8" forged front.

I am not doing this for looks or stance. I want to lose some weight. Turns out BMW already helped us out by selecting the lightest possible tires, so the only place to lose the weight is the wheels.

Last edited by mws; 09-30-2021 at 10:36 PM..
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