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Posted by: larryM Dec 20 2017, 02:41 PM

just curious

- for those who are running staggered rear/front wheels on flared cars - AND who have also run all-same size - without modifying the other suspension factors ?

what are your comparative experiences & tho'ts about any handling benefits or detriments, given that our cars are quite well F/R weight balanced

street vs AX vs track???? - 3 distinctly different ways we "use" the cars

i know the "le mans" cars used stagger, .... did the rallye cars such as monte-carlo, or many of the other racers back in the 70-73 period (does the Roy Smith "racing 914's" book give us that info??

- iirc the factory FIA spec GT wheel was 15x7 all around (fuchs 8x15 were not made then), and the "gt" cars at RRV all were running 15x8s iirc - historic venue rules being a factor concerning plus sizes

(fwiw imle - staggered sizes limit ability to cross rotate for tire wear for non-directional street tires on my car with competition neg-camber alignment - i did run staggered sizes when racing, but never all-same, so can't say if it might have made any difference - & can't say i can tell any difference when "canyon carving" on street tires either way)

i posted a similar Q on pelican, but those opinions are mostly about 911s which are notoriously in need of such "help" - (i owned a swb 911 - know all about that evil)
http://forums.pelicanparts.com/porsche-911-technical-forum/979556-why-stagger-frt-r-wheel-tire-sizes.html

Posted by: 914Toy Dec 20 2017, 03:47 PM

QUOTE(larryM @ Dec 20 2017, 12:41 PM)

just curious

- for those who are running staggered rear/front wheels on flared cars - AND who have also run all-same size - without modifying the other suspension factors ?

what are your comparative experiences & tho'ts about any handling benefits or detriments, given that our cars are quite well F/R weight balanced

street vs AX vs track???? - 3 distinctly different ways we "use" the cars

i know the "le mans" cars used stagger, .... did the rallye cars such as monte-carlo, or many of the other racers back in the 70-73 period (does the Roy Smith "racing 914's" book give us that info??

- iirc the factory FIA spec GT wheel was 15x7 all around (fuchs 8x15 were not made then), and the "gt" cars at RRV all were running 15x8s iirc - historic venue rules being a factor concerning plus sizes

(fwiw imle - staggered sizes limit ability to cross rotate for tire wear for non-directional street tires on my car with competition neg-camber alignment - i did run staggered sizes when racing, but never all-same, so can't say if it might have made any difference - & can't say i can tell any difference when "canyon carving" on street tires either way)

i posted a similar Q on pelican, but those opinions are mostly about 911s which are notoriously in need of such "help" - (i owned a swb 911 - know all about that evil)
http://forums.pelicanparts.com/porsche-911-technical-forum/979556-why-stagger-frt-r-wheel-tire-sizes.html

Posted by: jd74914 Dec 20 2017, 03:57 PM

I'm not sure there is an issue running the same sizes-until tire temperatures get out of whack. Even street tires have an idea tire temperature for best rubber grip. When the tires are cold, having extra wide stuff in the back probably doesn't make a difference since friction coefficient is overall insensitive to surface area. As you really work the tires (staying at the edges of that friction circle Bill is talking about), you're adding energy to the carcass. A wider tire can handle that energy addition better because it has more mass and more surface area to dissipate energy. There should be a perfect front and rear tire size to keep the tire temperatures acceptable for the compound.

For a street car, you're probably never really working the tires so I bet it doesn't matter. But perhaps if you are really driving for a bit there could be a definitive benefit?

Posted by: brant Dec 20 2017, 04:00 PM

I believe the lemans cars actually used 6inch wheels with a 1 inch spacer

sure by the later 70's wider wheels were common
but in the early 70's they were not

I think I have an FIA appendix J at home for the lemans cars
its in german... but has all of the black and white photo's of what the FIA
ACTUALLY accepted in 1970

brant

Posted by: mepstein Dec 20 2017, 04:01 PM

Some unverified thoughts:
7” on the front will steer lighter than an 8”
8” on the back for the 3.2 engine
Definitely looks good
Our tires tend to age out before worn out

Eric Shea told me to do it that way

Posted by: Mark Henry Dec 20 2017, 04:54 PM

Mid engine car I was always told there wasn't much if any advantage.
I can see the lighter steering, but wouldn't that be more a low speed advantage?

BTW I asked the same thing back in early 2000.

Posted by: Chris914n6 Dec 20 2017, 05:54 PM

The car is balanced with same size tires.

Fatter rears are to compensate for more HP.

The harder steering is more a factor of the spacers pushing the wheel centers out than 20mm more tire.

I've currently running stock Boxsters. 16x6 w/205 and 16x7 w/225. When I need to replace the tires I've been considering 225/45 on a set of Euromeister 17x7 just to get the natural balance back. 200hp isn't swinging the rear out like a Mustang.

Posted by: larryM Dec 23 2017, 12:20 AM

The Info for Sports Purposes document 4890.20-200-03-72 (see page 33-35) shows the 914/6 (on all 4, not staggered) 6"x15 for rallye, with tires spec 185/70-15;

and 7"x15 wheels for racing with racing tires spec 4.75/10.00-15 (same as on 917 www.flickr.com/photos/wbaiv/6252749070)

Info Sports Purposes to 1972 -
https://www.dropbox.com/home/914-6-GT%20historical%20docs?preview=Info+Sports+Purposes+2nd+edition+to+1972_english.pdf (on my dropbox pages)

- the 914/6 (flared GT) was spec'd for 21mm spacers with the 6's, and 27F/35mmR for the 7's (... also spec'd long studs & steel lugnuts for racing)

as a general rule - 7x15's were the FIA homologation spec as seen in the "factory docs"

let's also remember that the "Porsche spec performance tire" of 1970 was a 185/70xVR15 for both the 911 & 914/6

- IIRC the Sunoco GT used wider non-Fuchs (minilite?) rear wheels 'cuz ther was no 8" Fuchs then (the French car Ranson Webster now owns & races 9140430457 - had them when i saw it in his showroom a few yrs ago; at RRV it had fuchs on back! http://www.914-6-club.de/PorscheClubs/pc_914-6/pc_main.nsf/web/6C658A1CD38926C4C1257F0D00721E76?OpenDocument&tabnr=2)

SCCA GCR up to 1972, generally allowed 1" wider than FIA spec; so 8x15 would have been period OK; in the 1972 GCR they went up to 1.5" wider, but limited overall track width in both cases ... "1971 GCR stock 914/6 spec was 6x15" .... 53.58 frt, 54.41 rear track width" - on some cars, careful selection of width/backspace can yield wider wheels & slightly more contact patch

- so that's probably why most vintage/historic groups & PCA allow up to 8x15's - but no x16 dia

HMSA (& other Steve Earle venues) upon petition, allowed 914/6's pure slicks on x15s (see Jon Wactor 9140430375 and Eddie Arrowsmith both running Goodyear cantilevers) because the 4.75/10's were allowed per factory 4890.20-200-03-72

the 1972 m471 "USA dealer option" only suggested 6x15's (pic) below

fwiw - to corroborate a comment above: circa 1993 Ken Mack founder of Sportech in Campbell who was a credible 914/6 racer for some yrs, said "7x16 with 225/50 frt, 8x16 rear with 245/45" so i b'ot a set of 16" BBS-RA from him to that end - obviously not "period correct" -he aligned my car to comp'tn spec & i have never changed that

(still have the wheels) - dunno if it made a diff since i never ran anything else after that (ran 8x15/9x15 BBS before that - also vintage incorrect, but scca scrutineers never looked at 'em except to see if the steel lugnuts were tight) & i also converted my frt-susp to 911 SC with underslung swayvbar on advise of another P-car guru

i currently run 4 7x16 fuchs with A/S3s all around - (let's me cross rotate for better street tire wear cuz the comp'tn negative camber is an issue, as another above post suggests) - i briefly tried 8x16 rear fuchs with 245/45 last yr, it "felt different" but the like-new Fusions were 10yrs old, so my seat-of-pants opinion is irrelevant; (i dismounted 'em & you can have 'em for free at my gate zip 95635)

- back to the original question - do any of us have experience that suggests wider rear wheels & fatter-lower-profile tires make any difference on (any) 914?


yes - i have copies of all this historic stuff - but am finding it is difficult to scan & convert some of 'em to something i can post -

Posted by: larryM Dec 23 2017, 12:21 AM

QUOTE(Mark Henry @ Dec 20 2017, 02:54 PM)

Posted by: mlindner Dec 23 2017, 05:17 AM

QUOTE(larryM @ Dec 23 2017, 12:20 AM)

The Info for Sports Purposes document 4890.20-200-03-72 (see page 33-35) shows the 914/6 (on all 4, not staggered) 6"x15 for rallye, with tires spec 185/70-15;

and 7"x15 wheels for racing with racing tires spec 4.75/10.00-15 (same as on 917 www.flickr.com/photos/wbaiv/6252749070)

Info Sports Purposes to 1972 -
https://www.dropbox.com/home/914-6-GT%20historical%20docs?preview=Info+Sports+Purposes+2nd+edition+to+1972_english.pdf (on my dropbox pages)

- the 914/6 (flared GT) was spec'd for 21mm spacers with the 6's, and 27F/35mmR for the 7's (... also spec'd long studs & steel lugnuts for racing)

as a general rule - 7x15's were the FIA homologation spec as seen in the "factory docs"

let's also remember that the "Porsche spec performance tire" of 1970 was a 185/70xVR15 for both the 911 & 914/6

Wow, thats a lot of nice information larrym. Thanks for sharing. Mark
- IIRC the Sunoco GT used wider non-Fuchs (minilite?) rear wheels 'cuz ther was no 8" Fuchs then (the French car Ranson Webster now owns & races 9140430457 - had them when i saw it in his showroom a few yrs ago; at RRV it had fuchs on back! http://www.914-6-club.de/PorscheClubs/pc_914-6/pc_main.nsf/web/6C658A1CD38926C4C1257F0D00721E76?OpenDocument&tabnr=2)

SCCA GCR up to 1972, generally allowed 1" wider than FIA spec; so 8x15 would have been period OK; in the 1972 GCR they went up to 1.5" wider, but limited overall track width in both cases ... "1971 GCR stock 914/6 spec was 6x15" .... 53.58 frt, 54.41 rear track width" - on some cars, careful selection of width/backspace can yield wider wheels & slightly more contact patch

- so that's probably why most vintage/historic groups & PCA allow up to 8x15's - but no x16 dia

HMSA (& other Steve Earle venues) upon petition, allowed 914/6's pure slicks on x15s (see Jon Wactor 9140430375 and Eddie Arrowsmith both running Goodyear cantilevers) because the 4.75/10's were allowed per factory 4890.20-200-03-72

the 1972 m471 "USA dealer option" only suggested 6x15's (pic) below

fwiw - to corroborate a comment above: circa 1993 Ken Mack founder of Sportech in Campbell who was a credible 914/6 racer for some yrs, said "7x16 with 225/50 frt, 8x16 rear with 245/45" so i b'ot a set of 16" BBS-RA from him to that end - obviously not "period correct" -he aligned my car to comp'tn spec & i have never changed that

(still have the wheels) - dunno if it made a diff since i never ran anything else after that (ran 8x15/9x15 BBS before that - also vintage incorrect, but scca scrutineers never looked at 'em except to see if the steel lugnuts were tight) & i also converted my frt-susp to 911 SC with underslung swayvbar on advise of another P-car guru

i currently run 4 7x16 fuchs with A/S3s all around - (let's me cross rotate for better street tire wear cuz the comp'tn negative camber is an issue, as another above post suggests) - i briefly tried 8x16 rear fuchs with 245/45 last yr, it "felt different" but the like-new Fusions were 10yrs old, so my seat-of-pants opinion is irrelevant; (i dismounted 'em & you can have 'em for free at my gate zip 95635)

- back to the original question - do any of us have experience that suggests wider rear wheels & fatter-lower-profile tires make any difference on (any) 914?


yes - i have copies of all this historic stuff - but am finding it is difficult to scan & convert some of 'em to something i can post -

Posted by: mlindner Dec 23 2017, 05:19 AM

LarryM, wow thats a lot of great information. Thanks for sharing. Best, Mark

Posted by: Mark Henry Dec 23 2017, 09:43 AM

QUOTE(larryM @ Dec 23 2017, 01:21 AM)

QUOTE(Mark Henry @ Dec 20 2017, 02:54 PM)

Mid engine car I was always told there wasn't much if any advantage.
I can see the lighter steering, but wouldn't that be more a low speed advantage?

BTW I asked the same thing back in early 2000.

got a link to that - might be interesting to review the comments