So what's the deal with wheels?
01-20-2010, 09:06 PM
#31
massive thread dig, but only cos i have a question and i used search and found this thread!!
whats a good size track tyre for 16" 7's and 8's? car is a street '86944 n/a.
thanks
currently have street tyres (bridgestone g3's), 205/55/r16's and 225/50/r16's at factory pressures.
whats a good size track tyre for 16" 7's and 8's? car is a street '86944 n/a.
thanks
currently have street tyres (bridgestone g3's), 205/55/r16's and 225/50/r16's at factory pressures.
For track, 225-50-16 front and 245-45-16 rear; 205's are just too small for track duty imho. Some folks run 8's front and rear (245-45-16s all around) However, finding the tires you want in 16" rim sizes can be hard. You could also run 225's all around on the rims you have.
01-20-2010, 09:54 PM
#33
Addict
Rennlist Member
Rennlist Member
Porsche put 15" rims on most of there 944s. Lots of people like to buy aftermarket rims and such, many times 16" or so. Ive even seen big old dubs on a 44.
So my question is what kind of advantages do rim size give you? what are the advantages to having bigger rims. Handling, acceleration? Do they degrade the performance?
If Porsche put 15s on them I'm sure thats the optimal size for a well rounded car, but if I put wider ones one will my handling go up? even if acceleration goes down.
So my question is what kind of advantages do rim size give you? what are the advantages to having bigger rims. Handling, acceleration? Do they degrade the performance?
If Porsche put 15s on them I'm sure thats the optimal size for a well rounded car, but if I put wider ones one will my handling go up? even if acceleration goes down.
Not sure about the "Porsche put 15" rims on most of their 944's" thing.
Mine came stock with 16" wheels.......I believe all the S2's did.
I also believe all the later Turbo cars were 16".
All the 968's were 16" as well
01-21-2010, 01:00 AM
#34
Advanced
Join Date: Mar 2007
Posts: 68
Likes: 0
Received 0 Likes
on
0 Posts
15" rims were standard on the base 944 and at least the 87S. Probably 88S as well. 16" rims were a $2,000+/- option in 87 on both the basic 944 and the S. I looked at alot of cars at dealers in 1987 when I got mine. My memory says not too many basic 944's had 16" rims, but I think they were common on S's. 16" rims were standard on turbo's and S2's.
Norm
Norm
01-21-2010, 03:41 AM
#35
Instructor
Join Date: Sep 2009
Location: Miami
Posts: 242
Likes: 0
Received 0 Likes
on
0 Posts
01-22-2010, 06:49 AM
#36
Team Owner
Join Date: Oct 2009
Location: one thousand, five hundred miles north of Ft. Lauderdale for the summer.
Posts: 28,705
Received 212 Likes
on
153 Posts
You're not going to find many Y rated tires in 15 or 16 inch sizes... the reason why Porsche and Ferrari were the first to go to larger rims, beginning with the 959 and F-40 was probably for 2 primary reasons.
1. as Dunlop and Pirelli were developing run-flat tires, they had also been working for quite some time on tires that could be driven in excess of 186 mph without failure... it soon, became clear, that a higher pressure would be required to maintain less tire deformity between the rim and the road. a stiffer tire with a flatter shape and more air would decrease the ratio of the volume of air located near the "bulge" vs. the total volume of air in the tire, as tire pressure was increased.
the bulge represents a bubble of air running at a higher pressure than the air surrounding it, and because this bubble is rushing around the tire, and the super-compressed molecules are slamming into the sides of the tire, THIS MAKES A LOT OF HEAT...
so then, the idea is to have a smaller bubble of air running through the tire - and this means, not only that there's going to be less of a difference in pressures between the bubble and the rest of the tire, but this difference is going to be seen in the form of LESS HEAT !!
this allowed the margin of safety (stable operating temperature of the tire compounds) to be pushed past 180 mph... but, in order to maintain the correct outside diameter (24.5-26 inches), and keep the total amount of rubber that would be in contact with the road (correct shaped contact patch) at a maximum, a conventional rim size of 15 or 16 inches would not fit the demands of the design engineers, so the 17 inch rim was introduced for the 1988 model years. it just so happened that in creating the perfect tire and wheel combination, it allowed for a second benefit -
2. being able to run bigger brakes...
the perfect combination for the Porsche 944/968 running on the street with big brakesis is a 17" or 18" rim, a 225 to 255 mm tire in front and about a 245 to 295 mm tire in the back. if you want big brakes, and the best possible handling, you need to go to a larger diameter rim. but not exceed about 25.7" for the outside diameter of the tire. it's also good to run less tire stagger than Porsche uses in the 911.
ex: 245-35-18 on 8.5" rims in the front and maybe 275-35-18 on 10" rims in the rear.
as far as all the other factors you guys are talking about... you have wheel/tires and suspension setups that make great track times regardless of what diameter tires are being run. this suggests that additional body roll can be made to be less of negative factor than we would expect. a smaller rim tire with a relatively large diameter and can handle a greater load... it may dissipate more heat. and because the tire is more forgiving, it's likely to have a longer tread life. it's as much a persional choice as anything else. you have 15" and 16" wheels on 944s that look spectacular, and there's 18" wheels that look only marginally better.
you can always find used 15" and 16" tires for pennies. just my 0.02.
1. as Dunlop and Pirelli were developing run-flat tires, they had also been working for quite some time on tires that could be driven in excess of 186 mph without failure... it soon, became clear, that a higher pressure would be required to maintain less tire deformity between the rim and the road. a stiffer tire with a flatter shape and more air would decrease the ratio of the volume of air located near the "bulge" vs. the total volume of air in the tire, as tire pressure was increased.
the bulge represents a bubble of air running at a higher pressure than the air surrounding it, and because this bubble is rushing around the tire, and the super-compressed molecules are slamming into the sides of the tire, THIS MAKES A LOT OF HEAT...
so then, the idea is to have a smaller bubble of air running through the tire - and this means, not only that there's going to be less of a difference in pressures between the bubble and the rest of the tire, but this difference is going to be seen in the form of LESS HEAT !!
this allowed the margin of safety (stable operating temperature of the tire compounds) to be pushed past 180 mph... but, in order to maintain the correct outside diameter (24.5-26 inches), and keep the total amount of rubber that would be in contact with the road (correct shaped contact patch) at a maximum, a conventional rim size of 15 or 16 inches would not fit the demands of the design engineers, so the 17 inch rim was introduced for the 1988 model years. it just so happened that in creating the perfect tire and wheel combination, it allowed for a second benefit -
2. being able to run bigger brakes...
the perfect combination for the Porsche 944/968 running on the street with big brakesis is a 17" or 18" rim, a 225 to 255 mm tire in front and about a 245 to 295 mm tire in the back. if you want big brakes, and the best possible handling, you need to go to a larger diameter rim. but not exceed about 25.7" for the outside diameter of the tire. it's also good to run less tire stagger than Porsche uses in the 911.
ex: 245-35-18 on 8.5" rims in the front and maybe 275-35-18 on 10" rims in the rear.
as far as all the other factors you guys are talking about... you have wheel/tires and suspension setups that make great track times regardless of what diameter tires are being run. this suggests that additional body roll can be made to be less of negative factor than we would expect. a smaller rim tire with a relatively large diameter and can handle a greater load... it may dissipate more heat. and because the tire is more forgiving, it's likely to have a longer tread life. it's as much a persional choice as anything else. you have 15" and 16" wheels on 944s that look spectacular, and there's 18" wheels that look only marginally better.
you can always find used 15" and 16" tires for pennies. just my 0.02.
01-22-2010, 10:35 AM
#37
Drifting
Join Date: Jan 2008
Location: Suburban DC
Posts: 2,641
Likes: 0
Received 0 Likes
on
0 Posts
01-22-2010, 11:51 AM
#38
Race Car
Tire size is a concern and I think the critical component is the overall outside diameter. It is important to maintain this as for the said gearing and such, but larger dia. wheels require more offset to maintain proper geometry. As for racing the tire size and wheel diameter has a lot to do with temp. stability as much as anything else(odurandina states this well). Also larger wheels and tires wreak havoc on stock suspension. Bigger wheels and tires have limited benefits sans cosmetics, and are more of a detriment, especially beyond the stock diameter. As for unsprung weight, bigger wheels/tires can be anchors, and if the wheels are to light you run into a bunch of other problems. I have 16" Boxster wheels on my 924S and they work very well, but 17"s would kill it.
