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1997 Boxster with 18" wheels


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Yes, I know. You can only use 18 inchers on Boxsters from 1998 on. BUT, I hear of a lot of guys doing it and I want to know if anyone has ACTUALLY HEARD of any problems with it. I bought my 97 a little less than a year ago, and it had 18 inch tires already. The fronts were new, and I changed the rears the same week that I bought it, which cost some big bucks. I then found out that 18 inch tires are a no-no. It looks beautiful with the 18 inch turbos, and it will hurt like hell to change them, but I really don't want to risk my life on it. Yes, I know they did some reinforcements and stuff on the car in 1998. I'm also a little dense on this...can there possible so much difference of a stress factor between a 17" wheel and a 18"??? My car is only street and NEVER beaten nor driven more than (normally) 200 miles a month.

Addition 9 Jul 06: To confuse things more, I've been using the calculations on the The Tire Rack page, and the total height of a 205/55 16 inch is 24.87 inches while the height of a 225/40 18 inch is 25 inches!!!! What possible reason can there be? Please, someone shed light on this humble soul. :(

Edited by bigdog
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  • 2 weeks later...
Yes, I know. You can only use 18 inchers on Boxsters from 1998 on. BUT, I hear of a lot of guys doing it and I want to know if anyone has ACTUALLY HEARD of any problems with it. I bought my 97 a little less than a year ago, and it had 18 inch tires already. The fronts were new, and I changed the rears the same week that I bought it, which cost some big bucks. I then found out that 18 inch tires are a no-no. It looks beautiful with the 18 inch turbos, and it will hurt like hell to change them, but I really don't want to risk my life on it. Yes, I know they did some reinforcements and stuff on the car in 1998. I'm also a little dense on this...can there possible so much difference of a stress factor between a 17" wheel and a 18"??? My car is only street and NEVER beaten nor driven more than (normally) 200 miles a month.

Addition 9 Jul 06: To confuse things more, I've been using the calculations on the The Tire Rack page, and the total height of a 205/55 16 inch is 24.87 inches while the height of a 225/40 18 inch is 25 inches!!!! What possible reason can there be? Please, someone shed light on this humble soul. :(

The figures mean:

225 = width of tire

40 = 40% of width is side wall height

18 = fits 18inch diameter rims

So if you do the maths, the two different sets of tire/rim combo results in slightly different overall diameter. This is completely normal and expected. Your speedo will most likely be more accurate if you increase your tire diameter/height as most Boxster speedos, certainly mine, overreads actual speed by around 7%.

As for putting 18s on a 97, I've been wondering the same thing. I have been trying to find photos of the rear suspension/chassis setup of a later model car to compare it to my 97 model. Haven't found a good one yet.

But there are people on this forum that uses >17inch rims on a MY97, I can't remember who.

My thoughts would be that the reduced side wall on a 18 inch setup results in less cushioning of vibration and this does something to the (?fragile) suspension/chassis setup somehow. Although, if this is true, then Porsche really hasn't made the Boxster a very tolerant car from an engineering perspective. But I suppose the reliability of Boxsters is an entirely different can of worms.

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Thanks for your ideas on the subject. Seems you're about as frustrated as I am on the whole deal. Like I said, I can get a set of 16"wheels, buy 55/ 225 and it's as big as a 18" 35/205. Well, anyway, I've got someone who's going to trade out his 17" for my 18" tires and wheels. I'm pretty much losing out all around. I'd just like someone to explain clearly why a 18" wheel is so much of a problem. I haven't had any explainations on it, so I guess it's kinda like religion. You just believe what you're told and that's that. Thanks again.

Edited by bigdog
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Have you been to the Tech Q&A section of www.pca.org? I think there were some explainations given in a few of the posts by a Porsche mastertech although they weren't really specific enough (like saying which beam/strut/chassis is not strong enough to support what) IMO.

Do you have 18 inch turbo wheels or 18 inch turbo tech wheels? Are they genuine? I would love to know how much the rear 18 inchers weigh if you get a chance to weigh them when you take them off for the trade.

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I read the piece by the PCA about a dozen times, and it does say that you can't put 18 inchers, because of reinforcement issues. Sorry Jinster, but the same day I read your message, the wheels were shipped. Can tell you that they were very heavy with the tires. The turbos are original and have the Porsche numbers inside. Although, I think that they are a "old" style as I've seen newer ones that are alot different. I liked these because they reminded me of the old Muscle Car days.

post-7250-1153670213_thumb.jpgpost-7250-1153670784_thumb.jpg

Edited by bigdog
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  • 2 months later...

I run 18's on my MY97. I dont race it on track, I do ride it a bit hard near the mountain roads, but not too hard. The car seems fine. It looks great (Carrera 5 spoke) light wheel (atleast in my mind). Check my garage for pics.

I also had read that there was a reason not to put 18's but I figured that if I did not change the overall volume of the 17 with the 18's it would be fine, I also looked for what I thought were the lightest wheels.

I say put 18's, its much nicer and car gets a slight mean look.

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Let me know when your cars falls apart so I can come over and look at it. :P

In the 7 plus years I have been around there are 1997 owners with 18" wheels. I have not seen a problem being reported on the message boards. In fact, there is a 1997 guy on Rennlist with a 3.4 conversion and 18" wheels. Porsche did not approve a 3.4 conversion either.

There are newer 986 owners with 19" wheels. Porsche never had or approved a 19" wheels for the 986.

I have a 1997. When I spoke to Peter Smith years ago about this subject he asked (as a joke) if I drove on cobble stone roads.

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Let me know when your cars falls apart so I can come over and look at it. :P

In the 7 plus years I have been around there are 1997 owners with 18" wheels. I have not seen a problem being reported on the message boards. In fact, there is a 1997 guy on Rennlist with a 3.4 conversion and 18" wheels. Porsche did not approve a 3.4 conversion either.

There are newer 986 owners with 19" wheels. Porsche never had or approved a 19" wheels for the 986.

I have a 1997. When I spoke to Peter Smith years ago about this subject he asked (as a joke) if I drove on cobble stone roads.

Hehe, nicely put, TP. Puts things in perspective.

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  • 1 month later...

yeah, I can understand the frustration since Porsche hasn't offered any real explaination other than 'don't do it'.

I was fishing for a clearer answer when I posted that question on the PCA tech Q&A site a couple years ago. I was really hoping the reply would come from someone involved in chassis design or development at Porsche, not just speculation from the PCA rep's.

My hunch says there were durability issues with the first-year design that were detected too late to revise in time for the launch of the car. This implies the design is marginal as-is to Porsche's internal requirements & the recommendation is intended to prevent additional stress from larger wheel / tire. My next hunch is that the durability cycle is more severe than most of us will encounter with the car (hence the cobble stone road comment from Peter Smith) & using the larger wheels will not result in failure under 'normal' use. Until the D&R activity speaks up, we'll probably never know..

Edited by ToSi
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