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Will a 2mm offset difference for aftermarket wheels make a difference?

korkiley

Member
Dec 3, 2013
18
10
South Burlington, VT USA
I just ordered 18x8.5 Storm Grey Enkei Tuning TS-5 and

235/45R18 Michelin X-Ice Xi3 from tirerack.com for my model 3 AWD as my winter tire/wheel set. With those wheels my choices were either, 18X8.5 with 38mm offset or 18X8 with 40mm offset. I liked the fact that the 18X8.5s were the same as the OEMs but was a bit concerned with the 2mm difference in offset after reading this article. I read somewhere that the specs should be within 3% and the 2mm difference reprsents a 5% difference. Could that difference possible affect handling or alignment?
 

kbecks13

Active Member
Dec 27, 2017
1,916
2,280
SoCal
You're fine with the 38mm, stock for RWD and AWD cars is +40 so the wheels will sit 2mm slightly outboard and actually look a little better too ;)

I'm running 33mm wheels on a P3D (stock is 35mm) so i'm basically in the same situation, but with 9.5" wide wheels instead. Tons of clearance so no worries rubbing.

For completeness, you are slightly changing the scrub radius but it's such a minimal change that i wouldn't worry about it at all.
 
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korkiley

Member
Dec 3, 2013
18
10
South Burlington, VT USA
Within 3% is a guideline on rolling diameter, not offset
Thanks. The discussion where I saw the 3% guideline wasn't clear exactly what they were referring to. I wasn't sure so thank you for setting me straight. I guess the 3% on tire diameter makes more sense--so a tire that is 26.3" like the Michelin X-ICE XI3S I have on order could safely go to 26.3 + 3% = 27"? After that, the car might have problems adjusting calculations to that diameter and maybe there could be rubbing at extreme suspension compression or steering radius?
 

korkiley

Member
Dec 3, 2013
18
10
South Burlington, VT USA
You're fine with the 38mm, stock for RWD and AWD cars is +40 so the wheels will sit 2mm slightly outboard and actually look a little better too ;)

I'm running 33mm wheels on a P3D (stock is 35mm) so i'm basically in the same situation, but with 9.5" wide wheels instead. Tons of clearance so no worries rubbing.

For completeness, you are slightly changing the scrub radius but it's such a minimal change that i wouldn't worry about it at all.

Judging by the number of modifications you've made to your P3D+, you must know what you are talking about : ) I don't understand why people think additional poke looks better? I guess it's a young people's thing. I'm 74 so well past that stage--but not far enough past not to appreciate the performance of my M3 AWD. I grew up with a Morgan +4 and a couple of Porches in the 60s. I'll never forget how those Porches felt and handled. Of course when you're comparing to VW Beetles and Microbuses and a 57 ford wagon--OK, and a Morgan, the contrast was pretty stark. As well as the model 3 handles, the feel isn't as inspiring as I remember those Porches being.

Just out of curiosity. Do you know of any guidelines for offset modification?
 

kbecks13

Active Member
Dec 27, 2017
1,916
2,280
SoCal
Judging by the number of modifications you've made to your P3D+, you must know what you are talking about : ) I don't understand why people think additional poke looks better? I guess it's a young people's thing. I'm 74 so well past that stage--but not far enough past not to appreciate the performance of my M3 AWD. I grew up with a Morgan +4 and a couple of Porches in the 60s. I'll never forget how those Porches felt and handled. Of course when you're comparing to VW Beetles and Microbuses and a 57 ford wagon--OK, and a Morgan, the contrast was pretty stark. As well as the model 3 handles, the feel isn't as inspiring as I remember those Porches being.

The "poke" fad can definitely get out of hand, for me it's really about making the wheels flush with the wheel well and NOT poking out. The stock wheel/tire fitment leaves the tires sucked into the wheel well for aerodynamic reasons though it doesn't look the best, but its a super minor detail anyway.

Offset modification is something you shouldn't really dabble with too much since it can impact scrub radius, but such a small change (2mm) isn't really worth fretting about. Also since you're keeping 8.5" wide wheels you won't rub at all.

I use this online tool to help check clearances before i ordered my wheels since they are so wide compared to stock, haven't had any rubbing during track days and sporty driving. A few others are running 9.5" wheels with 265 wide tires as well.

Calculator for offset/clearance: Rim & Tire Size Calculator. Custom Offsets
 
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korkiley

Member
Dec 3, 2013
18
10
South Burlington, VT USA
The "poke" fad can definitely get out of hand, for me it's really about making the wheels flush with the wheel well and NOT poking out. The stock wheel/tire fitment leaves the tires sucked into the wheel well for aerodynamic reasons though it doesn't look the best, but its a super minor detail anyway.

Offset modification is something you shouldn't really dabble with too much since it can impact scrub radius, but such a small change (2mm) isn't really worth fretting about. Also since you're keeping 8.5" wide wheels you won't rub at all.

I use this online tool to help check clearances before i ordered my wheels since they are so wide compared to stock, haven't had any rubbing during track days and sporty driving. A few others are running 9.5" wheels with 265 wide tires as well.

Calculator for offset/clearance: Rim & Tire Size Calculator. Custom Offsets

Great information! I love the Rim & Tire Size Calculator and I love what it says about my 2mm offset differential, "Almost no difference"!
 

dfwatt

Active Member
Sep 24, 2018
3,134
5,148
FL
You're fine with the 38mm, stock for RWD and AWD cars is +40 so the wheels will sit 2mm slightly outboard and actually look a little better too ;)

I'm running 33mm wheels on a P3D (stock is 35mm) so i'm basically in the same situation, but with 9.5" wide wheels instead. Tons of clearance so no worries rubbing.

For completeness, you are slightly changing the scrub radius but it's such a minimal change that i wouldn't worry about it at all.

So Kbecks are you talking about tons of clearance with your set up? I'm thinking of trying to get a 20 by 9.5 in at 40 mm offset but with aftermarket rotors. Which means that it would be 2 mm inboard from your current setup with a 265 / 30 - 20 Pilot Sport 4S. If you've got ample clearance that means I should be good with the aftermarket rotors and 40 mm at 9.5. Does that sound right to you? When I do the measurement it seems close. I've got about 19 mm of space right now between the side wall and the front spindle. But that's with 38 mm offset and the stock 235 Tire, and I'm going to eat up about 15 to 16 mm of that space with a 1 inch wider tire and moving the wheel inboard 2 mm. Also again on aftermarket Racing brake rotors. Once I buy the vs forged I own them whether they fit or not with the 265. How much clearance have you got between the inside of your tire and that front spindle?
 
Last edited:

kbecks13

Active Member
Dec 27, 2017
1,916
2,280
SoCal
So Kbecks are you talking about tons of clearance with your set up?

Not really tons, not sure on a specific number but id say around 5mm. It also depends on the tire you're running (like specific brand/model) since they are not all equal in dimensions, tire rack has some good data. Also, i think you could always add a slim spacer if necessary so that might give some peace of mind
 

dfwatt

Active Member
Sep 24, 2018
3,134
5,148
FL
Not really tons, not sure on a specific number but id say around 5mm. It also depends on the tire you're running (like specific brand/model) since they are not all equal in dimensions, tire rack has some good data. Also, i think you could always add a slim spacer if necessary so that might give some peace of mind

Thanks Kbecks. That should be enough. I just want to end up with at least two mm of clearance. I suppose if the 265 don't fit I can always just put the stock tires back on and I'm sure they'll be okay.
 

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