Can I Mix RIM widths on back of 911?

Restoring a 996 and discovered the previous owner had different rims on nearly every tire. I've corrected the front and they are all good now and mounting 225/35/18 tires on 18x8 rims However on the back I have NOT been able to find another (matching) 18x10" rim as yet but do have an 18x9 available. That being the case, I would have to run it with an 18x9" rim and a 18x10" rim on the back and mount matching tires of 285/30/18 tires on both which is in spec for both rims. Bottom line, the rims will be 1" in width different but the tires identical. In researching I am getting conflicting opinions if this is ok Has anyone experience this or have knowledge of good or bad? This car would be a weekend driven vehicle.

I think you worry too much! No way you will be able to tell the difference.

Bad, you know it........no explanation required......just be search harder for a 10 inch wheel. Or post the wheel you need someone may have one in thee basement

Quotes source post: 20063896

Well, to start with you're using the wrong Porsche recommended size. IIRR,,, Suppose to be 225/40_18, not 35. rear size is 285/30_18 Second, using different width rear rims, even with the same tires is not recommended. Different width wheels will probably make the tire have a different contact patch with road, different handling characteristics and maybe even a different diameter. Granted these might be small differences. Maybe noticeable problems doing this mismatch, maybe not, maybe she pulls/wanders to one side, maybe not...? Bottom line, if thats all you have, then by all means mount em up and enjoy your car while looking for the correct size rims. But if you're buying this mismatch, I'd pass on that purchase and wait for the right wheel match up for sure.... jmho

Quotes source post: 20063939

I checked multiple sites for OEM rim size and tire size based on my year make and model and there were two options on the VIN Given what was on the car the closest match to what was on the car out of the two options was below: REAR: Factory Part Number 99636214050 Wheel Size18 X 10 Bolt Pattern5 X 130 Offset.65 Tire: 285/30/18 rear FRONT: Factory Part Number 9963213650 Wheel Size18 X 8 Bolt Pattern5 X 130 Offset.52 Tire: 225/35/18 front My thoughts are that I will use it with the 10" and 9" on the rim, using the car periodically until I can obtain a 10" matching rim Aside from a small difference in RIM WEIGHT I think I should be ok with same size tires. This is the RIM I'm looking for, I have found a couple but they are in Europe or very expensive here. Im sure something used will show up at some point.

The 9 inch rim is likely a front wheel and will have wrong offset. I would go with a set of 17" wheels before I'd mix like you are thinking. They're less expensive and tires cost less as well. Also ditto on the front wheel size, 225/35 is too small. 225/40-18 or 235/40-18 is what you need up there. 996 Porsches can be cheap to buy, but they're never cheap to fix.

Another option is to buy a less desirable set, like stock 17s with good tires, and then you can patiently find a good deal on your missing rim. As for driving on a miss-matched set, my opinion, you can� but I certainly wouldn�t. Think of it like driving on a spare at best.

Yeah i wouldn't drive with different width rear wheels. Its bound to make a bit of a difference as the wheel will be a little narrower than the other and also have a slightly higher sidewall. Wont be crazy dangerous but potentially could make it a bit snappy with the handling in one direction compared to the other. You will have to decide whether that extra risk is really worth it. Wheel looks like a factory GT3 rim, so wont be easy to find. I run the GT3 option 235/40 fronts and 295/30 rears as below:

You probably have a 996 Boxster rear wheel at 9" wide. Bad idea to run 2 different wheels on the same axle, as the others already said. 225/40R18 is the correct front tyre size, no doubt about that. Check your tyre pressure placard inside the frunk lid.

For sure it will get you to the grocery store just fine. Don't run it hard that way and keep keep looking or get an alternative set of 10-in rims. The nines are boxster and a 285 will be pretty fat on those but again, you're just getting groceries until something better comes along.

Yep, your all just repeating whats running in my brain, ya can...but. I'll return the 9 " and bite the bullet on a matching 10" rim. Found one for $600. I hate to pay that much but I suppose in the big picture its a drop in the bucket. Thanks for all the input!

Found the manual with the tire and rim specs. Fortunately I ordered the correct configuration. I was able to find 2 matching 18"x10" rims. It was $$$ but they are near perfect and from what I was told, they are getting very rare, so I figured I may as well bite the bullet and get it over with. One time my tire guys screwed up and put the exact same tire on the back but without telling me, one of them had a different speed rating. I didnt get 2 miles, tool a ramp and nearly lost control. I had to eyeball the tires for 10 minutes before I realized there was a difference, and that tiny difference was enough to make it nearly uncontrollable. They gave me a bit of a hard time to exchange it, saying it shouldnt matter, but I told them I would do a charge back if necessary, and they relented. That was the last time I dealt with them.

With it being a C4, you just need to make sure your rotational % is within 3% front to rear. This is where you can run into an issue if they are not (risk heating up the front differential). You can find rims all day long on FB Market place or here in the classified.....just be sure you have the correct tire size.

So glad I decided to go with the new back rims at the right size. Car is starting to look really nice and I'm becoming more confident with the restoration. This is my first time restoring a car since I was in my teens, so I'm a little nervous, but its coming along well and my mechanical skills are coming back to me. Spent 20 years in technology and CIO in banking, so this is my first time getting my hands dirty, and it feels GREAT! Its given me the confidence to work on my 2013 and repair a number of things instead of paying $200 an hour at my Porsche shop. I'm loving the savings and the FUN working on my babe! New tires arrived today, rims will be here late next week, and now I'm working on the interior with new leather and some upgrades. I'm starting to see the light at the end of the tunnel and its looking good. If anyone wants to see the restoration you can go here: https://rennlist.com/forums/996-foru...ggestions.html

Kudos to you for doing the resurrection project, you will become very intimate with the 996 doing this exercise that will increase your joy of ownership !!! I would also suggest a little " knuckle blood sacrifice to the Porsche Gods" ......they will reward you ten fold ......

Quotes source post: 20068022

Not seldomly tyre manufacturers offer a variant of tyre by simply assigning it the next lower speed rating to what is otherwise an identical tyre. They can sell that at a slightly lower price point with no other effort than replacing the placard that carries the speed index in the tyre mold at time of manufacture. As such I highly doubt that it was the cause of the loss of control. Nonetheless getting it replaced by them was the right thing to do, as is getting two identical, 10" wide rear wheels on your 996!

Quotes source post: 20070538

I'm 99% certain that was the only difference. They were Michelin Sport 4 and if I recall correctly the speed/load rating was 102y on one and 92y on the other. If you look here you will see exactly what I'm talking about, same tire but different ratings: https://www.tires-easy.com/tires/mic...SAAEgIAdvD_BwE I was so puzzled I called Michelin support and talked to their tech department. They told me that yes it does matter, and that certain tires of the exact model are made with different speed/load ratings for different vehicles (BMW MERCEDES etc). He said that its the way the interior of the tire reinforcement is done, and that it will effect the tires different as they rotate at high speed. It was perfectly fine in a straight line, but if I suddenly accelerated it would pull HARD right, and on a ramp it became almost uncontrollable. It was that big a difference. Michelin was very helpful, if anyone ever needs their tech support this is how to contact them: https://www.michelinman.com/auto/assistance/contact

You spoke to the right people, that's for sure and what they said is, obviously, correct. Not trying to be clever and you did write you're not entirely sure of your recollection but contrary to your initial post, the difference between the two tyres according to the digit-letter combo in your reply shows that it wasn't the speed index, (designated by the letter) but the load index (designated by the double digit number) that differed between the two tyres. A different load rating requires a different build-up of the tyre. OTOH, a difference of 10 between 2 load indeces does not exist either for a given tyre size and speed index. It can only differ by 4 between two versions of a passenger tyre, where one has a standard load rating and the other has an 'extra load' rating, designated by XL in the tyre spec. (I'm leaving out HL/high load passenger tyres here). Having different (OE) spec of the same tyre makes it a different tyre as Michelin explained and it is denoted by the OEM's chosen code or symbol (BMW spec is designated by a 5 pointed star for instance) on the side wall for identification purposes. What I'm trying to say is that the cause for your on-ramp experience was most probably the tyre but in that case, it wasn't due to the different speed rating left to right but due to something else being different too between both tyres. Be it load rating, OE-spec or both. With my reply I do not mean to criticise but to inform, others mostly.

Quotes source post: 20071826

whew! sounds like you are far more an expert on this subject than me. You're right, I'm not 100% sure, it was at least 4 years ago, but that was the best of my recollection. You're also right that I may have used incorrect terminology. But I do remember that it was such a minor (visually) difference in the two tires both of which were Michelin Sport 4 that it took me awhile to identify the differences. In the end what I can say is that the instability was so significant it made me pull off the interstate to inspect the tires. Once that tire was replaced it was perfect handling. I might have pictures still of the tire, I'll try to find it and if I do I will post it here. I dont mind your "interrogation", nothing wrong with getting the facts right and I appreciate the commentary.

well its all done, everything is updated to 225/40 ZR 18 front on 8x18 rims 285/30 ZR 18 rear 10x18 rims Car drives amazing, very happy! new rear rims!

That's good news to read, very happy for you! Enjoy!