phil74501

I have an 85.5 944. What is the original wheel size on one of these? Mine has 16 inchers on it. I know they aren't the original wheels. Also what effect does that have on the speedometer? It seems like it's reading low. And what does the 15x7 mean? I know 15 is the width but what is the 7? Thanks

apierce918

original tires on it were 215/60/VR15's speedometer indifferences will depend on the tires you have, if you havea lower profile tire with... it could cancel out. find out what the outer circumference would be of your tires compared to stock.

original tires had a 79 inch circumference.

if you had for instance, a 225/50/16 tire, the cirumfrance would be 78 inches, and speedo change would be hardly noticeable, but maybe 1 or 2 mph lower

15x7 stands for 15" diameter, and 7" wide

phil74501

I'm not sure what the current ones are. Just that they are 16"s. I know the wheels are BBS. You can see them in the pic I have on my profile. What I was wanting to make sure of was that 15" wheels would fit.

apierce918

yea, i believe original would have been phonedial 15x7 all around. and they would fit fine.

phil74501

I checked they are 225/50/zr16's. I found some 15 inch wheels are Porsche wheels and are cheap.

apierce918

man, that was a pretty good guess i had then huh

phil74501

Yep pretty good guess. I found 4 of the newer phone dial models for less than $400. They look to be in pretty good shape.

tifosiman

That was "Standard", not necessarily "Original" in the case of the initial poster's car. It was possible to order the car with 16" wheels (fuchs). A check of the option#'s on the decal in trunk will verify if the car came with the 16's or not.

Scott at Team Harco

Make sure they are the right offset. Your car (85.5) uses the early offset wheels (23.3 mm). The late offset wheels are 52.3 mm.

I would guess that if you are not aware that 15 x 7 define the diameter and width, respectively, you may have a little trouble with offset. Take a look here, if you need help understanding 'offset': http://www.tirerack.com/wheels/tech/...jsp?techid=101

Edit: to fix offset #s

Scott at Team Harco

Actually, a smaller diameter (circumference, radius, etc) will produce a higher speed reading on the speedometer than actual vehicle speed. Conversely, a larger diameter tire will produce a lower reading on the speedometer. Naturally, the odometer will also reflect this same error.

I run 225/50R15 tires. These tires have a circumference of about 75 inches. The original 215/60R15 tires have a circumference of about 79 inches. The difference is about 5%. My actual speedo/ odo error is closer to 10%.

Note that percentage is used here, because stating a specific mph difference is not necessarily accurate. Claiming the speedo reads "5 mph high" is only true for a small range on the speedometer (for example from 40 - 50 mph).

To help simplify this - realize that the smaller tire must rotate several more times per mile than the larger tire. Each of these rotations is counted (pulses per unit time) by the speedo gear and 'interpreted' by the gauge. If you get more pulses from the sending unit per mile then it will be reflected as a higher value on the speedometer. The speedometer has been calibrated to expect a certain number of rotations per mile. If the tires on the vehicle cause a deviation from this calibrated amount - a certain percentage of error is introduced. Note this is tire dependent - not wheel dependent (as was questioned in the first post).

Sorry for the physics lesson - but this is almost a daily science project for me.

phil74501

It says the offset is 52.3mm. Guess they won't fit. I found them on Ebay for $300. If anyone wants the link let me know.

Andial951

check here

http://www.connact.com/~kgross/FAQ/944faq13.html