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Illustrated Lecture on Tire Size, Ok, so I'm different!

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Porsche Rescue	Mar 4 2005, 11:10 PM Post #1
Saving and Enjoying Old Porsches Group: Members Posts: 2,978 Joined: 31-December 02 From: Bend, Oregon Member No.: 64 Region Association: None	Members are often asking tire size questions and I usually respond by advising that they stay with something very close to the original equipment size. Unless the car is going to be frequently autocrossed or tracked I believe it is the best way to go. You don't change the gearing, create an inaccurate speedometer, reduce fuel economy or have to worry about clearance issues. Today I replaced the tires on my 914-6 recently acquired from Eric Shea. He sent along a set of OE option 5.5x14" Fuchs ( beautifully polished by Eric). The car came to me with 6x15 Fuchs with 195/50x15 Dunlops. Since the car will be a Sunday driver, cruiser (1000 miles to WCC '05 I hope), and since I bought the car for its originality, I wanted as close to stock tire size as possible. Sixes with the 14" Fuchs had 185x14 tires (same wheel/tire combo available on 911's as the "comfort"option). They are pretty much NLA. Their diameter was 25.6" with a cross section of 7.4". I bought a set of Michelin X 195/75X14's at Costco (used on Toyota Camrys and mini-vans!), diameter 25.4" and cross section 7.7". Close enough. Here is a pic of the 195/50x15's beside the 195/75x14's. The 50 series, even though on a 1 inch taller wheel are nearly 3" shorter with a diameter of 22.7". No wonder gear ratios are changed (maybe a good thing for autocross) speedo is way off and fuel economy suffers. Also, much less cushion and thus harsher ride (but more precise cornering) with the low profile. All of the above applies to 4's as well. They came with 165x15 (as did the six with standard 15" steel wheels) which is exactly the same diameter as my 195/75's. The best modern size which is close is 195/65x15 (25" tall). Attached image(s)

Porsche Rescue	Mar 4 2005, 11:11 PM Post #2
Saving and Enjoying Old Porsches Group: Members Posts: 2,978 Joined: 31-December 02 From: Bend, Oregon Member No.: 64 Region Association: None	Also, I wanted the 1970 look, wheel wells full of rubber. The front is the old 50 series 15, rear is the new 75 series 14. Attached image(s)

redshift	Mar 5 2005, 12:22 AM Post #3
Bless the Hell out of you! Group: Members Posts: 10,926 Joined: 29-June 03 Member No.: 869	Excellent illustration! I agree totally. If I lived on a mountain, I might think it over. (IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif) M

rick 918-S	Mar 5 2005, 12:46 AM Post #4
Hey nice rack! -Celette Group: Members Posts: 20,456 Joined: 30-December 02 From: Now in Superior WI Member No.: 43 Region Association: Northstar Region	See, I like the wheel wells full of rubber look too! (IMG:http://www.914world.com/bbs2/html/emoticons/clap.gif)

MarkV	Mar 5 2005, 12:58 AM Post #5
Fear the Jack Stands Group: Members Posts: 1,493 Joined: 15-January 03 From: Sunny Tucson, AZ Member No.: 154 Region Association: None	50 series tires are extremely short. I am running 205/60-15's on stock 5.5" Fuchs. They are .71" shorter than the stock tires at 24.68" & they run 2.8% faster. (IMG:http://www.914world.com/bbs2/html/emoticons/rocking nana.gif)

Rhodes71/914	Mar 5 2005, 10:30 AM Post #6
Glacier Group: Members Posts: 1,374 Joined: 8-August 04 From: End of the Road, Alaska Member No.: 2,482	I willl be putting on a set of Falken Ziex Ze-512's, size 105/60-15, next week. Should be a lot better than the mis-matched used ones I put on just so I could roll the car around.

Porsche Rescue	Mar 5 2005, 11:24 AM Post #7
Saving and Enjoying Old Porsches Group: Members Posts: 2,978 Joined: 31-December 02 From: Bend, Oregon Member No.: 64 Region Association: None	Your 205/60's will be about .75" smaller in diameter. You will be a little lower geared and your speedo will read about 3% fast. No big deal in trade for more crisp handling and 40mm more tread on the road than stock. I have never had trouble fitting 205's but some cars require massaging the fender lip on one side or the other.

Eric_Shea	Mar 5 2005, 05:54 PM Post #8
PMB Performance Group: Admin Posts: 19,275 Joined: 3-September 03 From: Salt Lake City, UT Member No.: 1,110 Region Association: Rocky Mountains	That looks gay... I should have never sold you that car (IMG:http://www.914world.com/bbs2/html/emoticons/w00t.gif) Seriously, looks REALLY good Jim! (IMG:http://www.914world.com/bbs2/html/emoticons/smilie_pokal.gif) I can't wait to go for a ride. I'll bet it feels a ton different. The car was a drive around town car so with the 195/50's it was actually a ton of fun. I love that profile for a more modern look. It think it's the perfect tire to fit under a stock wheel well for a teener. You do throw off the speedo (but you don't get in trouble with the law) (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif) It was reading about 7mph over best I could judge HOWEVER... those 14's look great on there now. Way ta go.

Aaron Cox	Mar 5 2005, 05:56 PM Post #9
Professional Lawn Dart Group: Retired Admin Posts: 24,541 Joined: 1-February 03 From: OC Member No.: 219 Region Association: Southern California	i like my 205/50's myself.... 10% lower gearing.... great for whoelshots and cornering...... not optimal on the freeway though (IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif) but....my sidewalls dont tuck under in corners! (IMG:http://www.914world.com/bbs2/html/emoticons/laugh.gif)

Rhodes71/914

Mar 5 2005, 07:19 PM

Post #10

Glacier

Group: Members
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From: End of the Road, Alaska
Member No.: 2,482

QUOTE (Rhodes71/914 @ Mar 5 2005, 08:30 AM)

I willl be putting on a set of Falken Ziex Ze-512's, size 105/60-15, next week. Should be a lot better than the mis-matched used ones I put on just so I could roll the car around.

I meant 195/60, I think this should be a good all around size.

Eric_Shea	Mar 5 2005, 10:38 PM Post #11
PMB Performance Group: Admin Posts: 19,275 Joined: 3-September 03 From: Salt Lake City, UT Member No.: 1,110 Region Association: Rocky Mountains	205's didn't fit on that car. (IMG:http://www.914world.com/bbs2/html/emoticons/sad.gif) That's why I endore the 195's. I'd bet they're sure to fit "any" teener. They do have all those nasty side effects that Jim talked about though... speedo off (I think you can get that recalibrated). Fuel and gearing issues... (IMG:http://www.914world.com/bbs2/html/emoticons/huh.gif) I used to use 205/60x15's all around on my stock bodied 71, 911. Almost a perfect match for the stock tire heigth. I tried those on the 914-6 and they rubbed on the rear passengers side.

MattR

Mar 5 2005, 10:43 PM

Post #12

Advanced Member

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From: SF Bay Area
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Region Association: Northern California

QUOTE (Eric_Shea @ Mar 5 2005, 08:38 PM)

205's didn't fit on that car. (IMG:http://www.914world.com/bbs2/html/emoticons/sad.gif)

Someone get the baseball bat, we're gonna roll some fenders (IMG:http://www.914world.com/bbs2/html/emoticons/w00t.gif)

Nice pics! I have 205 50s on the 914, but Ive never driven it, so I cant tell you how they perform... Ive got some 205 60 15s on their way for the 912, but again... on their way, so I cant compare. Im not very useful, am I (IMG:http://www.914world.com/bbs2/html/emoticons/sad.gif)

markb	Mar 6 2005, 01:15 AM Post #13
914less :( Group: Members Posts: 5,449 Joined: 22-January 03 From: Nipomo, CA Member No.: 180 Region Association: Central California	I've got 205 60 15s on the Blue car, but I'm thinking of 205 70 15s for the Black car. Think they'd rub?

Porsche Rescue	Mar 6 2005, 10:16 AM Post #14
Saving and Enjoying Old Porsches Group: Members Posts: 2,978 Joined: 31-December 02 From: Bend, Oregon Member No.: 64 Region Association: None	If the 60's have a little clearance on both sides you should be ok with 70's. The width is the same but the "fat" part of the tire will be a little higher because the tire is taller. Could be close. Diameter will be same as stock so speedo and gearing will be correct.

Rhodes71/914	Mar 6 2005, 10:29 AM Post #15
Glacier Group: Members Posts: 1,374 Joined: 8-August 04 From: End of the Road, Alaska Member No.: 2,482	I have some 205/70's on the back of my 71 and they are real close to the fender, like I can barely get my finger in between. I think they also look big in there.

Aaron Cox	Mar 6 2005, 10:31 AM Post #16
Professional Lawn Dart Group: Retired Admin Posts: 24,541 Joined: 1-February 03 From: OC Member No.: 219 Region Association: Southern California	im telling you....low profile tires TREMENDOUSLY help handling.... if you are worried about rolling diameter, go to a 16" wheel with a 50 or 55 series.....really wakes the car up! (IMG:http://www.914world.com/bbs2/html/emoticons/smilie_pokal.gif) i went the tall tire route.... never again! (IMG:http://www.914world.com/bbs2/html/emoticons/laugh.gif)

DuckRyder	Mar 6 2005, 10:46 AM Post #17
Avatars Mode: OFF because of the recalcitrant few. Group: Benefactors Posts: 767 Joined: 8-January 03 From: Georgia Member No.: 110	Some common ones: Specification Sidewall Radius Diameter Circumference Revolutions Speedometer Odometer Difference 165/80-15 5.2" 12.7" 25.4" 79.8" 794/mi 60MPH 10000mi N/A 185/65-15 4.7" 12.2" 24.5" 76.9" 824/mi 62MPH 10378mi -3.6% 205/60-15 4.8" 12.3" 24.7" 77.6" 817/mi 62MPH 10287mi -2.8% 205/50-15 4.0" 11.5" 23.1" 72.5" 874/mi 66MPH 11007mi -9.1% 195/75-14 5.8" 12.8" 25.5" 80.2" 790/mi 60MPH 9952mi 0.5% From: http://www.powerdog.com/tiresize.cgi I personally kinda like the 185/65/15 on a street car.

Porsche Rescue	Mar 6 2005, 11:01 AM Post #18
Saving and Enjoying Old Porsches Group: Members Posts: 2,978 Joined: 31-December 02 From: Bend, Oregon Member No.: 64 Region Association: None	16's on a 5-lug car are great. You can have best of both worlds. Where do you find sixteens for a 4-lug car?