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Discussion summary
YOUR RESEARCHAcceleration for 18" vs 19" Wheels
Leading reported evidence
Replace stock 18" oem wheels
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Performed · outcome unconfirmed · Original poster
I have recently replaced the stock 18" oem wheels with some inexpensive aftermarket 19" and found the acceleration significantly slower at every gear levels due to the weight issue.
Leading evidence: 'Replace stock 18" oem wheels' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, the most frequently mentioned possible cause is 'rolling diameter' (1 discussions; 0 report identifying it and 1 suggest it). The most frequently discussed action is 'Adjust larger diameter' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Suggestion
Does the Turbo have the capability to adjust for the larger diameter?
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Suspected cause
It's probably not the weight, it's most likely the rolling diameter.
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Suspected cause
As long as he is relatively close say with in a few percent then it is more than likely a rotating mass issue.
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Suggestion · Original poster
Either move back to 18" wheels or replace my 19" with lighter wheels to make the weight equivalent to the 18" OEM.
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Performed · outcome unconfirmed · Original poster
I have recently replaced the stock 18" oem wheels with some inexpensive aftermarket 19" and found the acceleration significantly slower at every gear levels due to the weight issue.
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0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suggestion
If you used any of the car systems then you need to take into account that tires with 5% bigger circumference also mean the speed meter (and mpg meter etc) is underreporting by that amount.
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I have recently replaced the stock 18" oem wheels with some inexpensive aftermarket 19" and found the acceleration significantly slower at every gear levels due to the weight issue. I initially thought only the low gears would be impacted and there shouldn't be an issue once the car has built up the momentum. I was apparently wrong.
Now I have two alternatives to move on. Either move back to 18" wheels or replace my 19" with lighter wheels to make the weight equivalent to the 18" OEM.
I then wonder if anyone would know the difference on the acceleration between the 18" and 19" wheels assuming their width and weights are identical?
I am struggling between moving back to 18" and buying lighter 19" wheels. Both are costly options though.
I've been in the same shoes as you and can confirm that there is a SLIGHT difference I've noticed when moving from 19"s to MK.2 OEM 18"s lights. There is some difference but sometimes it's brain that wants to belive something
I have some lightweight 19" wheels that I am looking to sell if you are interested. (Fikse mach v). Pretty much like these except 19" with proper backspacing.
http://www.bimmerboost.com/images/im...010/10/265.jpg
It's probably not the weight, it's most likely the rolling diameter. Just look up the old vs new tire sizes on tire rack and post the difference in diameter. Lighter 19s won't solve the issue. But you can always get light 18s and have the best of both worlds.
definitely not rolling diameter unless he put huge *** tires on there which i doubt. As long as he is relatively close say with in a few percent then it is more than likely a rotating mass issue.
I just figured out it's a combo of weight and rolling diameter. I had 225/40-18 & 295/30-18. When moving to 235/35-19 & 295/30-19, the front wheel is half an inch and rear one full inch bigger.
[OLD]
Front: 44.1 lbs; diam 25.09
PS2 225/40ZR18 92Y XL BSW 22.0 lbs
Turbo II 18x8 22.1 lbs
Rear: 54 lbs; diam 24.97
PS2 295/30ZR18 98Y XL BSW 27.5 lbs
Turbo II 18x11 26.5 lbs
[NEW]
Front: 50 lbs; diam 25.48
PSS 235/35R19 91Y XL BSW 24.0 lbs
Wheel est 26.0 lbs
Rear: 58 lbs; diam 25.97
PSS 295/30ZR19 100Y XL BSW 28.1 lbs
Wheel est 29.9 lbs
Now I am planning to move back to 18" PS2 with OZ Alleggerita hlt as the front 18x8 weights only 17.4 lbs and rear 18x11 at only 22 lbs. I'll be, however, glad to know if there are other brands/ models with a better cost/ weight ratio.
I truly appreciate all your inputs.
Sales call. I accidentally bought two set of my02 lightweight 5 spokes and I need to sell one of them. Don't ask me how. It was stupid and I wasn't paying attention.
OP, the OZ Alegrita are a nice set of lightweight wheels. You might look into the Pilot Super Sport tires though. They are less expensive and better performers than the PS2.
Does the Turbo have the capability to adjust for the larger diameter? The NA doesn't, which is why those of us who want our speedo to be semi-accurate run tires with shorter sidewalls - to keep the OD roughly the same. I suspect that if you'd selected a tire that accommodated the 19" wheel but kept the OD close to stock, you would not have noticed the difference or that it would at least have been less pronounced.
This is one of the few shortcomings about the 996 that surprised me. Even my antiquated 1996 Corvette is programmable via OBD-II to correct for a change in gearing, tire circumference, etc.
How did you measure your speed in the acceleration tests, anyway?
If you used any of the car systems then you need to take into account that tires with 5% bigger circumference also mean the speed meter (and mpg meter etc) is underreporting by that amount.
You can't really work of the generic tire specs. The outside circumference should be taken from the actual product page from the manufacturer. The interpretation of some of these numbers isn't even across manufacturers.
In any case, if you would just go to 295/25/19 in the rear they won't interfere with gear/drive/speed ratio anymore, and move the mass a bit inwards.
Changing your rolling diameter by an inch is no small amount. It's like changing your final drive ratio by 0.5. It is a substantial change to your actual gearing. Measurements differ between manufactures but 1" rolling diameter is no incremental measurement. The other thing to note is how adding rotating mass affects acceleration. From a dead stop you have to get that mass moving. But once it's turning (and the faster it goes) the less it matters. You could change nothing but make the rear wheel 10lbs heavier and you won't notice *much* in acceleration difference from 30-100. It will hurt shock performance and braking and acceleration to extent and I want to be clear that unsprung weight is bad but not likely what the OP is dealing with.
I have made a decision to move back to 18" but an new issue pops up. The OZ rims I am interested in have different offsets from the OEMs. The front OEM is 18x8 ET50 while the front OZ is 18x8.5 ET40, I figured out that the front wheel will move out for around 16mm. While the rear OZ has the exact measurement 18x11 ET45 as the OEM, that means I need to add a 15mm spacer to balance the look of the front/ rear wheel.
I know adding spacer will increase the load of the axle and thus slower acceleration again. Just that each OZ rim is around 4 lbs lighter than OEM, that translates to a drop of 16 lbs unsprung weight or around 64 lbs load yet may not be enough for compensation. I really hate spending all the money but getting no result by end of the day. Now I start to wonder if I should just stick to the OEMs. I aware a lot of modded 996tt do stay with OEM wheels and there must be a very good reason behind. Now I start to understand more...
You should not have a problem getting front or rear wheels with factory offsets if you keep looking around or try another manufacture of a similar looking wheel.
A spacer does not increase axle load in any way that will affect acceleration. If you're worried about the mass of the spacers, you needn't be - aluminum spacers are relatively light and the spacer mass is near the center of the hub. You can find aluminum spacers that are skeletonized to reduce weight; if you know anyone with a water jet or a CNC mill, you can skeletonize your own spacers to minimize the weight further, although this is complete overkill in my opinion.
A Chipotle burrito and a Diet Coke will add more weight to your car than the rear spacers will.
