[craigawoodman]

I love the 911 Sport Classic (but am massively amused and puzzled at the price). One aspect I like is the Fuchs (or replica) Fuchs rims. This listing is on e-Bay;



http://www.ebay.com.au/itm/Porsche-new-1...2c5d30b736



They only make 8.5" and 11" widths. To run an 11" width, you will need to mount something like a 285 to 315 width tyre. The offset will push the rim to the outer edges of the bodywork, but be relatively neutral (according to my calculator) on the inside strut.



Has anyone run an 11" rim on a 968 and if so, what offset and tyre width. Will this fit, or would it possibly need machining to make it fit?



Thanks,



Craig

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[DaveN]

Price certainly puzzles me too, I would expect new (Genuine) 19" Fuchs to be around 3K on eBay. I have entertained 19" wheels on my car due to greater selection but everyone has advised against it. Clearance, very low profile tires required, rock hard ride and there is a picture here in a previous post and the car just doesn't look right with 19s. Too blingy, almost SUV look. IMHO.

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[blau]

Looks like the price on that ebay auction is for ONE 19x11 wheel. Not for a set...

Personally, I think a 19" wheels is going to create a very rough ride, and overfill the wheel arches...but to each his own!

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[bombfactory]

I have a set of 19's for my E36 M3 - had to use fairly low profile tires to get close to the stock overall diameter: 225/35-19 front, 255-30-19 rear Toyo Proxes T1R. The ride was not harsh at all. I think today's ultra-low profile tires are designed with softer sidewalls to provide a decent ride. Of course that still doesn't change how 19's look on a 968. I'm still on the fence - I've only seen pics so far. Once I see some in real life I'll decide if I want to give them a try, as there are a lot of really nice looking 19" factory Porsche wheels out there.

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[Cloud9...68]

I suspect the car's suspension needs to be tuned to accept ultra-low profile tires in order to maintain an acceptable ride. I would think that just slapping a set on a 968 would make for a very harsh ride. But that may or may not be an issue for Craig (OP).

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[craigawoodman]

I am potentially in agreement on the 19" rim size issue - but there seems to be very little being made in 18" anymore. I have a friend who has an old 911 on 15" rims and there is only one R-spec tyre available in Australia in his sizes. Has 18" rims been left behind.



Same for 17" rims - there is little development of new tyres for this size, with most development now switching to 19" predominately plus support for 18" rims.



Where are the photo's of a 968 on 19"s? I have seen a 944 - but it did not look good (or is it just that we are not used to it - remember when 17" rims were OMG and expensive for tyres) - (I can remember when 15" rims and 60 profile tyres were cutting edge, 50 section was only for super exotica).



The auction is for a set (2x 8.5" and 2x 11"). It is worth noting that the rims on the 911 Sport Classic were not Fuchs rims - they were Italian version and not forged.



Has anyone fitted an 11" rim with similar offsets to a 968?

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[bombfactory]

I've posted this pic before but can't remember where, so here you go:



   



I think these look damn good with the car lowered down like that. Most Porsche people hate the 'lobster claw' wheels, but I really dig 'em. If I ever go 19 inch these will be what I get. They are available in 8" and 10" from the Boxster/Cayman S. I'm also curious if 11's will fit on the rear, and what offset and tire is needed for that.

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[tamathumper]

Having been a lobster fisherman, I'd love to have them just to tell people what they are, mounted on my red car <img src="/forum/images/smilies/968/smile.gif" class="smilie" alt="" />



But I'd need 18's - the idea of 19's still scares me.

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[flash]

the physics need to be carefully considered here - more contact patch and stickier tires mean more strain on suspension components - mass and where it is also plays into this equation - outer rim mass has a huge effect on the rest of the suspension



check the rim weight and the tire weight and compare to stock numbers - consider what you have done to beef p the hub, bearings, lugs and suspension mounting points - that will tell you a lot about how big you can go, be it width, diameter, or offset

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[Cloud9...68]

"I can remember when 15" rims and 60 profile tyres were cutting edge, 50 section was only for super exotica"





So can I! The extent to which enormous diameter wheels have caught on, given all their disadvantages (ride quality, weight, risk of damage by potholes, cost, etc.). I still think 17" is the perfect size, but I'm also dismayed as the lack of tire choice in that size. Maybe ever-stricter fuel economy standards will restore some sanity to wheel diameter availability.





[size="2"][color="#1c2837"]I'm probably going to end up with a set of 18" wheels for the track, and would like a set of 17" (or even 16") for the street to soften up the ride a bit, and even more in fantasy-land, I'm toying with the idea of a centerlock conversion to minimize the hassle of taking the wheels on and off and the track, but there's no way 17" or 16" wheels will be available with a centerlock option.[/color][/size]

[size="2"][color="#1c2837"]

[/color][/size]

[size="2"][color="#1c2837"]Sorry, I'm being of absolutely no help with the question about the 11" wide wheels on the back.[/color][/size]

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[craigawoodman]

Flash,



A smaller diameter rim will alway assist acceleration and braking due to its lower polar moment on inertia being closer to the centre line. A large diameter rim takes the rim base further away from the rim (assuming the same rolling diameters - the tread and belt package stays the same and rubber sidewall is replaced by alloy spokes).



So the bearing and brakes will cop a bit more - but as long as the overall weight is similar - the rest should be ok.



The challenge will be when you have to move to 19's to simply keep current tyre tech on your car.



Remember when a 75 section tyre was a comfort tyre and a 65 section was a performance tyre. Now a 45 section is a comfort tyre. THe use of kevlar and aramide for belting has allowed greater sidewall flex - but beware potholes and your rims.



My wife's A5 convertible has 18" rims and 45 section tyres as a "comfort" option rather than the options 19" rims and 35 series performance option. Go figure.



I think that even on 18" rims - the front when on 40 section rubber look too thick compared to the rears and 35 section rubber.



Oh - by re-looking at the eBay ad, I actually think the rims are priced individually - so OUCH on the pricing. If it was for four rims I was a potential starter - but each ? ? ?

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[flash]

tire is heavier than aluminum, so it's not straight trade - depending on the wheel and tire, you could go up or down, but the mass location can change, and hence so would the momentum factors



on a track car, i would go with the smallest diameter possible and keep the profile of the tire as small as possible,without causing you to lose access to top speed desired - this will lower the gearing and give better acceleration - this works well on most tracks - basically though you have to gauge the tire diameter by the max speed you will be going - if you will only go 140, then you have a good amount you can decrease diameter - if you will hit 150, then not so much



on the british cars we changed rear differential gearing on a track by track basis - not so easy on the 968

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[benspeeder]

Figured I'd chime in on my race wheels - they cracked and are being fixed by Kodiak. So I had to run my93 Cup (93 Cup (Cup 2)) stock rims - Kodiaks were 245-45-16 front 275-45-16 rear



Stock was 245-45-17 front and 275-45-17 rear.



The weight difference between the sets were 51 pounds! So at a rotating mass weight impact of 8 to 1 my motor was pulling an extra 400 lbs. I could tell the difference in throttle response <img src="/forum/images/smilies/968/sad.gif" class="smilie" alt="" />



The weight of the wheels and tires really matters!

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[bombfactory]

I've heard before that a larger diameter tire/wheel package puts more stress on a car's hub components, but is this only due to additional weight? I'm not understanding how wheel diameter comes into play here. If two cars are both cornering at the same speed and lateral G load, and one car is running 17's and the other is on 19's (same overall tire diameter though), aren't the hubs on both cars seeing the same amount of stress?

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[DaveN]

The farther away from the axis the greater the moment of rotational force/ and therefore stress on the centre. Even if they weight the same (doubtful) there will be more metal in the outside rim and therefore more force transmitted to the centre. Consider a spinning bicycle wheel, smaller wheel requires less force to change it's angular plane than a slightly larger one. The opposite happens in a car, changes to the outside happen first though.

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[bombfactory]

I can see how a larger diameter wheel will put more stress on the hub during straight line acceleration and braking - a wheel with more weight distributed towards the outside takes more energy to change its rotational speed - I can't imagine the stress difference at the hub is very significant though, radially.



What my physics-challenged brain is having trouble grasping is how an increase in wheel diameter, but not an increase in overall tire diameter, puts more stress laterally on the hub during cornering. The length of the 'lever' transmitting force to the hub - in this case the distance from the center of the hub to the contact patch, right? - stays the same, so what (assuming for this exercise both wheels, say a 17 and a 19, have the same overall weight) causes the added stress?

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[Cloud9...68]

I would assume it's because in most cases, a larger diameter (and definitely a wider) wheel will weigh more than a smaller-diameter one.

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[craigawoodman]

The load on the hub is due to the higher rotational moment of interia. Consider how hard it is to rotate a bmx wheel (not very). If you were to take the same wheel diameter (or radius) and significantly increase the weight around the outer edge - then try to rotate the wheel again, it would take significantly more energy/effort to get it to the same rotational speed.



Without going back and consulting reference books (which is hard because they are in a container somewhere being shipped), I am not sure if the variance is a factor of mass by radius (or radius squared).



Similarly, if you try to turn a wheel, the bigger the polar moment of interia, the higher the forces required to overcome the gyroscopic forces - which are all reacted back through the hub.



So the harder it is to accelerate the wheel/rim and brake it, turn it, etc - all of which is fed back through the hub/suspension to the chassis. Larger diameter rim - higher forces.

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[bombfactory]

I'd be interested in knowing the actual numbers for each particular increase in wheel diameter. There must be something to it if Porsche lists certain larger wheel sizes as prohibited on certain Porsche cars.

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[Cloud9...68]

"on a track car, i would go with the smallest diameter possible and keep the profile of the tire as small as possible,without causing you to lose access to top speed desired - this will lower the gearing and give better acceleration - this works well on most tracks - basically though you have to gauge the tire diameter by the max speed you will be going - if you will only go 140, then you have a good amount you can decrease diameter - if you will hit 150, then not so much"



I was struck by this comment, as it appears that all cars, including track cars, are moving in the opposite direction, with enormous wheel diameters and rubber-band thin sidewalls. Seems that rotation moment of inertia is being traded off for minimization of sidewall flex.

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