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Discussion Starter · #1 ·
I'm sure I read they should be, but I'm not sure if that is only model 2s with PP. Here's my front...
1951

and the rear...
1952
 

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Well this clears up a lot of confusion for me. I was sure the tyres were the same but saw people talking about different sizes.. What would the reason be to use a wider rim on the back? the contact patch will be unchanged?
 

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Discussion Starter · #6 ·
Pressures, according to the notice on drivers door frame is same back and front.
 

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I have no idea why the wheels are different widths. I don't know if it is a performance/contact thing, or if it is a clearance/offset thing. Perhaps someone on this forum has a better idea? My understanding is that it is not super uncommon to have wider rims in the back. But why?


Edit:

Here is an explanation, although I'm still somewhat confused.

 

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It's quite common for heavy and powerful vehicles to have slightly wider rear wheels as it helps with the balance of the car and means it will understeer on the limit, rather than trying to swap ends.
 

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You might well find the track is wider at the rear too, for the same reasons.
 

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It's quite common for heavy and powerful vehicles to have slightly wider rear wheels as it helps with the balance of the car and means it will understeer on the limit, rather than trying to swap ends.
As your post is the only one I can find that specifically suggests a reason for the unusual rim offset, I am posting here, although there is also a discussion at Polestar 2 Aftermarket Wheels where members are discussing alternative, aftermarket dimensions.

Your answer sounds like a very good reason for not messing with the OEM rim dimensions, and, unless someone can point to a proof that same rims front and rear is a safe solution, I will personally be very careful about making any changes. Especially in the winter when we must drive in slippery conditions.

In Norway, where we use a separate set of winter wheels, we have a popular aftermarket rim and tire provider which has published the following.

Quote:
UNNECESSARY ENERGY REQUIRED WHEEL SET UP ON POLESTAR 2. SMARTER SOLUTION WITH THE SAME WHEELS FRONT AND REAR
Polestar is delivered with 245 / 45R19 and the same tire dimension front and rear. Nevertheless, the rim layout has been changed to 19x8.5 front and 19x9 rear. 19x9 is very unfavorable and in fact the maximum allowable width to the tire dimension. The STRO standard that the Norwegian Public Roads Administration follows recommends 19x8 as the most correct for the tire, and we also recommend 19x8 based on how we measure the tire against the rim. 19x9 gives rim edge outside the tire side, and the rim is very easily damaged in contact with curbs. 19x9 is also far heavier than 19x8, and reduces the range unnecessarily much. We believe that Polestar should not have been type approved with 19x9 rims at the rear, based on the principle that the same tire dimension front / rear should have the same rim dimension front / rear. Changing wheels thus becomes a challenge in avoiding confusing the wheels. 19x9 and 20x9 are still within legal data and the STRO norm, but not most recommended. Our recommendations below are approved according to legal data, and you are also product insured with Megahjul as an extra solid guarantee for our recommendations. Change of ET from h.h.v. ET53 and ET50 to 45.5 do not affect wear of wheel bearings and warranty on the car is not affected. It is also not allowed for car dealers to claim otherwise.

Polestar-2-rim recommendations:
Polestar-2-felger-anbefalinger


Does anyone have any comments on the above, and would it be appropriate to publish a warning on the site about the potential risks of messing with rim sizes?

Noob and prospective Polestar 2 (Non-PP) owner.
 

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I had a BMW 3 series with different size tyres front and rear.
I thought the PS had different size rims in order to get clearance to the brake calipers?
 

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The different rims are present on both the PP and non-PP editions and are to do with rim width (ie nothing to do with caliper clearance), rear rims being about 2.5 cm wider than the fronts, but fitted with the same tires, so no difference regarding tread footprint. Megahjul, which is a Norwegian, EV specialist tire distributor and fitter, published the above article in Norwegian. Before ordering winter tires, I'm trying to get a clear idea of how safe it would be to go for Megahjul's probably more efficient recommendation.
 

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Ok, ok, ok. First, the rear rims are not that much heavier than the front. I bought a spare set of rims for a winter wheel set and weighed them myself. They're about 2 pounds heavier.

Yes, you're more likely to curb the rear rims.

I think this has been done for two reasons: a slight performance advantage in the curves and better aesthetics.

I'm speculating about the performance, but it makes sense to me... The sidewalls on the rear wheels are angled outward a bit more from the contact patch to the rim. Under lateral load during cornering, some load can travel through the sidewall to the rim more directly due to this. Thus the sidewall would "feel" stiffer to the car. This effect would be similar to using more camber, but without all the problems associated with increased camber.

I don't think any of this has any major effect on safety or performance... We're dabbling about in minor differences.

So I wouldn't sweat it, especially for a winter wheel set. If you get proper caliper clearance, I see no problem at all using the same rims front and back.
 

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I've got some information on the PP OEM rims. These are my best shot at the dimensions, but note that I'm using woodworking tools for measuring them.

Rear rims:

29 lbs 10 oz +/- 2 oz (29.6 +/- 0.1 lb)
Rim width, face of flange to face of flange: 251 +/- 1 mm (9.88 in)
Rim width, inside flange to inside flange: 228 +/- 2 mm (8.98 in) Note that the flanges are tapered, so the measurement is approximate.
Outside diameter (from flange tip to flange tip): 548 +/- 1 mm
Inside diameter, just inside face that faces inwards towards the center of the car: 498 +/- 1 mm.
Inside diameter, just inside of the faced hub: 466 +/- 1 mm.
Depth, face of rim to face of machined hub face: 180 +/- 1mm.
Offset: 54.5 +/- 1 mm.

Front rims:

27 lbs 12 oz +/- 2 oz (27.8 +/- 0.1 lb)
Rim width, face of flange to face of flange: 225 +/- 1 mm (8.86 in)
Rim width, inside flange to inside flange: 205 +/- 2 mm (8.07 in) Note that the flanges are tapered, so the measurement is approximate.
Outside diameter (from flange tip to flange tip): 548 +/- 1 mm
Inside diameter, just inside face that faces inwards towards the center of the car: 498 +/- 1 mm.
Inside diameter, just inside of the faced hub: 466 +/- 1 mm.
Depth, face of rim to face of machined hub face: 165 +/- 1mm.
Offset: 52.8 +/- 1 mm.
 

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The tires are "squared" (same size front and rear) purely for range purposes, is my guess.

Given the weight, and a desire for decent handling, Polestar probably originally intended to ship the car with staggered tires. But wider tires would be a hit to range, so they opted to square the tires to the smaller size intended for the fronts.

If you don't care about losing a few miles/km of range, you can step the rears up to 255/40 or 265/35 for the rears on the 20" rims. 265 is the widest you should do on a 9" rim.
 

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Ok, ok, ok. First, the rear rims are not that much heavier than the front. I bought a spare set of rims for a winter wheel set and weighed them myself. They're about 2 pounds heavier.

Yes, you're more likely to curb the rear rims.

I think this has been done for two reasons: a slight performance advantage in the curves and better aesthetics.

I'm speculating about the performance, but it makes sense to me... The sidewalls on the rear wheels are angled outward a bit more from the contact patch to the rim. Under lateral load during cornering, some load can travel through the sidewall to the rim more directly due to this. Thus the sidewall would "feel" stiffer to the car. This effect would be similar to using more camber, but without all the problems associated with increased camber.

I don't think any of this has any major effect on safety or performance... We're dabbling about in minor differences.

So I wouldn't sweat it, especially for a winter wheel set. If you get proper caliper clearance, I see no problem at all using the same rims front and back.
Thanks Prof. for well-reasoned reply.

I should add that one of the (main?) reasons that I want to buy a Polestar is that I drove one on extremely slippery roads last winter (OEM non-PP standard winter wheels) and was blown away by how well the car handled, drifting gently and very neutrally out when it lost grip. I don't want to change anything that would risk different or unexpected behavior on the slippery winter roads that we sometimes get over here. On the other hand, the weight and curbing arguments of Megahjul are compelling, so cheaper, lighter (10.2kg / 22 pounds 8 ounces) , quieter winter wheels that are less susceptible to curbing would be a good choice if the car still handles neutrally.

Any thoughts on 18" vs 19" for winter use?
 
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