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Downgrading to 17” wheels

 
Old 12-20-2006, 05:32 AM
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leosayer
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Default Downgrading to 17” wheels

Hi there, I have a 1996 C2 with H&R coilovers and 18” turbo twist wheels. The suspension is firm, but a great trade-off between comfort and handling.

I’m in the early stages of ownership just making sure the car is set up perfectly. I’m not after ultimate grip or the best looking car, but I do want the best handling car I can get, my driving is weekends blasts and track days, it is not a daily driver.

From looking around, I’ve found that my wheels are relatively heavy and, for example 17” Sports Classics are 3.2kg/7lb lighter at the rear and 2.7kg/6lb lighter at the front. Overall, that’s a fairly significant 12kg/26lb saving in unsprung weight.

Has anyone made this transition? Is it money well spent? Do the lighter wheels make any noticeable difference to the drive?
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Old 12-20-2006, 07:44 AM
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993inNC
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I now run a set of 996TT hollow spoke wheels and they are MUCH lighter than even the 993 hollow twists. I could definately feel a difference in how fast the car got up to speed, vs. with the old 993 wheels......big difference. Have not done the 17's but know guys at the track do because the size difference changes the circum. of the wheel which effectively changes your gear ratios and makes the car quicker off the corners. Having driven Silverstone (if you're running there) I would stick with what would get you the higher top speed.
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Old 12-20-2006, 08:58 AM
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Chris- I'd be curious to know the weights of 996 hollow spokes.

Leo- Alot of folks use 17" on the track, as Chris pointed out. Have you already lowered to the low end of the ROW Sport range and corner balanced with a full alignment, including K toe?

BTW- Shameless plug- I'm selling a set of 17" Cup II 7's and 9's with P Zero Assymetrico's with 8/32" remaining. PM me for addtl details if you're interested.

-Jim
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Old 12-20-2006, 09:17 AM
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leosayer
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Hey Chris, my avatar pic was taken at Silverstone!

By moving to 17" I expect to keep the same rolling radius so I don't expect any difference to top speed, just ride and handling.

I may indeed keep the 18" for track and use 17" for the road.

According to my info, the 17" Sports Classics are almost as light as 964RS magnesium wheels. See here for wheel weights (I don't know how accurate):
http://www.944racing.de/felgengewichte.html

My car is now much lower than the M030 kit that it had when I bought it, the H&Rs are a matched kit of springs and dampers and they were fitted and aligned by JZ Machtech, probably the top Porsche garage in the UK.
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Old 12-20-2006, 11:10 AM
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clib
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That difference in weights seems higher than I recall (if comparing stock cup wheels to 18in hollow spoke at least) I was using this link:

http://members.rennlist.org/911pcars/WheelWts.html

My buddy and I have almost exactly the same set up with PSS9 suspension, same ride height etc. The only difference is I have the stock 17in. cup wheels and he has the 18in. hollow twists. There is some minor differences - mostly my steering is slightly quicker just off-center - on certain roads it can even feel 'twitchy' in comparison to the larger diameter wheels which I always attributed to more rotating mass at a further distance from the hub (moment of inertia I believe its called): whether what I feel is real or just in my head is debatable. I find the 17 in wheels more fun to drive, but honestly its a subtle difference.

bill
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Old 12-20-2006, 11:16 AM
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Originally Posted by clib
That difference in weights seems higher than I recall (if comparing stock cup wheels to 18in hollow spoke at least) I was using this link:

http://members.rennlist.org/911pcars/WheelWts.html

My buddy and I have almost exactly the same set up with PSS9 suspension, same ride height etc. The only difference is I have the stock 17in. cup wheels and he has the 18in. hollow twists. There is some minor differences - mostly my steering is slightly quicker just off-center - on certain roads it can even feel 'twitchy' in comparison to the larger diameter wheels which I always attributed to more rotating mass at a further distance from the hub (moment of inertia I believe its called): whether what I feel is real or just in my head is debatable. I find the 17 in wheels more fun to drive, but honestly its a subtle difference.

bill
Do you have a pic of your car with the 17s?

TIA
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Old 12-20-2006, 11:54 AM
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RallyJon
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Interestingly, if you search on Tirerack, the 17" tire sizes for 993s are within a lb or two of the 18" tire sizes. I guess less sidewall rubber more or less makes up for the increase in tread rubber.
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Old 12-20-2006, 12:28 PM
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993inNC
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Originally Posted by leosayer
Hey Chris, my avatar pic was taken at Silverstone!

By moving to 17" I expect to keep the same rolling radius so I don't expect any difference to top speed, just ride and handling.

I may indeed keep the 18" for track and use 17" for the road.

According to my info, the 17" Sports Classics are almost as light as 964RS magnesium wheels. See here for wheel weights (I don't know how accurate):
http://www.944racing.de/felgengewichte.html

My car is now much lower than the M030 kit that it had when I bought it, the H&Rs are a matched kit of springs and dampers and they were fitted and aligned by JZ Machtech, probably the top Porsche garage in the UK.
That track was fun......didn't get enough time there tho I did the driver's experience with the F355, Carrera and Audi TT 3.2......what a blast
If you go with a small series tire, it will reduce your gear ratios and make a world of difference.
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Old 12-20-2006, 12:39 PM
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Thanks for the post LeoS and the feedback everyone... I have been so busy thinking I must upgrade to 18's (cause that is one of the mods we do) that I did not stop to think my 17's might just be fine for the type of driving I am doing.
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Old 12-20-2006, 01:26 PM
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Edward
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Honestly, suspension/tire widths/etc. being equal, I doubt there is much real-world difference between 17 and 18. I think perhaps a verrry good/seasoned driver can exploit the latter's advantages in a track setting, but for street use, even aggressive canyon runs, there just isn't enough of a performance delta to spend a thought on. Barring super-heavy crap wheels, shod the ones that you think are the best looking.

Edward
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Old 12-20-2006, 01:29 PM
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Chris: Im sporting OEM 17" and kind of arrived at the same conclusion as you. Although I really like the looks of the aftermarket 18", Ive done the cost benefit analysis many times and have not been convinced to make the move yet. Plus the previous owner lowered the car with Eibach springs so Im thinking that Im asking for trouble increasing wheel OD. No complaints with handing at the track or street although I would like to cure a little understeer with some wider front tires - with the stock 7.5, not sure how wide I can go. When it comes time to buy new tires, Ill search and have my answer.
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Old 12-20-2006, 01:56 PM
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I'm keeping my 17's on my daily driver for the simple reason the more compliant sidewalls will spare the mechanical components of the suspension some wear and tear. YMMV.
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Old 12-20-2006, 02:05 PM
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Thinks 17s might be my next mod...call me crazy buy I find 18s look kinda big. and if 17s are lighter...woo hoo... and cheaper.. ..with no ill effects sounds like a must do...
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Old 12-20-2006, 02:21 PM
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993inNC
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Originally Posted by Edward
Honestly, suspension/tire widths/etc. being equal, I doubt there is much real-world difference between 17 and 18. I think perhaps a verrry good/seasoned driver can exploit the latter's advantages in a track setting, but for street use, even aggressive canyon runs, there just isn't enough of a performance delta to spend a thought on. Barring super-heavy crap wheels, shod the ones that you think are the best looking.

Edward
I'm not sure I agree (with all due respect). I've been smoked by NA 993's with 17's and can only attribute (having spoken with the driver - also an instructor in my group) that the 17's with a low profile tire allow for a decreased gear ratio which tends to help on tracks where our normal gearing is to tall for one gear and to short for the other. The 17's provide the happy medium and really seem to help launch off the turns......

I for one have never tried it, but it upsets me to get beat like that with equal cars Having experienced the effects is my only knowledge so ........
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Old 12-20-2006, 02:53 PM
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If you like the look of 18" wheels but are concerned about weight, I understand that the Carrera II wheel (the 18" wheel for the MY 2002 and later 996) is quite light and looks great and is not too expensive.
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