What's everyone running for wheels and tire size on their race cars?

Do you go with a staggered setup or square?

What size wheel?

What size tire?

What do you run for rains?

So far I've tried

15x8&9 with 245x40x15 DOT comp tires on all four corners Maxxis Victra RC-1

16x10 with slicks on all four corners. Dunlop 265x60x16 slicks


I'm most likely going to run 16x8&9 next weekend with 245x45x16 on all four corners with RA-1s.

I've got some 15x9&11 that I may try down the road with my local club

and when I run COTA with SVRA later this year I'll have to go to 15x8 on all 4.

I'm new to this car and am still learning it and learning to race.

I'm running 16x11 front and 16x12.5 rear with slicks 23.5x10.5-16 front and 25.5x12.5-16 rear. Have been running Goodyear, switching to Hoosier now that Goodyears aren't available anymore. I'm doing track days and club racing, so no rules limitations. I've found the car to be very balanced with this setup.

Scott

For what its worth and realizing this might not apply to you depending on what limitations you have by class rules - I run 17's (R7)- its a better performance tire size and the selection is excellent. The worst size for available tires is probably 16's - started with them and quickly switched. I hope to be able to eventually run square with 275/35-17 - time will tell...

F: 24/40-17 (7)
R: 275/35-17 (9)

Tony

Click to view attachment

I'm running 15x7 205/60/15 front and 15x8 225/50/15 rear with RA-1s and loving it. I also have a set of 16x7 205/55/16 and 16x8 225/50/16 using 888s. Can't get the 205/55/16 in 888s now. Don't like this combo too much.

Click to view attachment

What are you running for a front spoiler/splitter up front? My car came with a rear spoiler similar to yours but was missing it's front. I pulled it off since I'm running just the normal 6-gt front bumper setup and was concerned about balance.

Thanks for the datapoint.

I'm running in the rain it looks like this weekend so trying the Ra-1 toyos and mounted on 16x8&9 fuchs. 245x45x16 all the way around.

That car looks like its all business!

Fuchs 16x8 front with Hoosier 245/45/16 and 16x9 rear with 274/45/16.Click to view attachment

Wow... That's beautiful!

Here are some before and after front spoiler photos. Same piece of fiberglass, just repaired..the beauty of glass.... This setup is very stable for me at high speeds.

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Regarding the spoilers, splitters, spoiler and wings....

My on-track experience leads me to believe:
1) The duckbill spoiler is of no tangible performance value but it does greatly help the aesthetics of the rear on a 914. That air is dead as dead as can be...
2) The spoiler is a decent place to mount brake cooling ducts but not much else..it increases drag vs a stock valance. The increased stability is probably a function of the car being slowed down due to the increased vertical surface area. I run this air-dam too...
3) A wing needs to be way the hell up there to grab clean air - the bottom of my wing is 1" (and should be higher) above the highest point of the roof line.
4) An actual splitter must be able to support at least 250 pounds of direct vertical force to remain stable at speed. My first effort fractured at 160 mph (mid-corner T9 RA) and I thought I had lost a wheel!!! IF you install one - bring it back all the way to the front suspension cross-member - there is more to aero than just the leading edge reveal.

Not meant to offend and step on toes - just sharing what I have learned...

T

For posterity here are a few shots of my car in different configurations.

15x8&9 fuch/minilite

16x10 on all four corners in current silver and past green with front/rear spoiler.Click to view attachmentClick to view attachmentClick to view attachment
Click to view attachmentClick to view attachmentClick to view attachment[attachmentid=617
350]Click to view attachment

striking teener...

T

...so in your opinion, do you think that a little ducktail spoiler could be run without a front spoiler? ...sure cannot do that on a 911. I'm talking about one like on the yellow car or the one you can barely see on my the green version of my car in the photo above.

Spoiler or splitter? If you are referring to a splitter as a spoiler - no you can not but if you just mean a spoiler as an airdam - yes. PM me with your contact info if you want to discuss this - far easier and more precise.

Tony

Tony, I will P.M. you. to attempt to be clear, I was curious about running a ducktail spoiler meaning the little rear spoiler like on the yellow car or the green version of my car with a standard GT front air dam like on the silver version of my car. I chose to remove my rear tail since I didn't have any aero up front.

LOL. Yes. You can run that with no front-aero all day. I hadn't had my cup of coffee this morning yet!

T

thread kinda morphed from tires to aero, but I think it's worth noting that in sanctioned racing, one would be rules-limited to tire size and aero (among other things).

For instance, when I raced BMWCCA in Mod class, the wing height was limited to no higher than horizontal with the roofline.

Otherwise, I think Cracker's observations are correct when restrictions don't apply

Yes for sure rules will dictate. I'm looking at SVRA tire rules and really not sure what I will run when I run with that club. Here is what they say:

Group 8 - Molded Treaded Tires
Minimum aspect ratio of 45, except
certain car Make and Models, which
have specific tire requirements listed
in their Supplemental Regulations,
tread depth—no less than 2/32”
remaining, at all times, over 75% of
the tire.
Wheels may be of an alternate
material but must be of period
design. They must be the correct
diameter and width as specified
within the Supplemental Regulations
of the Make and Model.
Tires may not extend beyond the
fender opening at the highest point
of the tire.
Approved tires:

There are no specific sizes listed because of the large diversity of Group 8 cars.
All Group 8 cars must use similar sized tires to what was used in the day, which is pre 1973.
Using oversized tires is unacceptable and when in question, SVRA’s determination shall be
the final word.

Avon: ACB9, ACB10, CR6Z
Goodyear Eagle: 5.50/15 G12 or G12A
Hoosier: Street TD & Speedster
Any Treaded, DOT approved Tires with a UTQG of 100 or greater with appropriate
Speed Rating and a minimum Aspect Ratio of 45
Note: Group 8 must use approved full molded treaded tires, regardless of what
specification tires a car may have competed with in a prior race series.
For Toyo RA1’s and Nitto NT01’s, please see page 6 of this document

Curious how your splitter performs. I'm designing one for my car and I also have a Sheridan standard widebody. I hap planned on using five supports but it appears as if your not using any. Riveted to the lower lip and attached to the pan about midway to through the wheels?
Has the Sheridan glass cracked any on ya?
TY
D

I don't mind bouncing between aero and wheel/tire so hope nobody else does.

Spoke with SVRA today and R888R are not on endangered list yet so should be able to run those in 2018. I'm going to try 225x50x15 on front and 235x50x15 on rear when I run SVRA and probably my local club too.

My car is a little more street than track, so I wanted something with a little better treadwear. I went with the BFG rival s 1.5 (200 tw) 225/45 15 rear and 205/50 15 fronts. So far I like them and they seem to hook almost as good as the Nitto NT-01 (100 tw). They give really good feedback, the 205 works well on a 7" rim and 225 is great on an 8".

Click to view attachment

I love those 16x10's they look great on a flared car! Who makes those?

These were made by HRE.

Now with 15x8 & 9 Fuchs with 245x40x15 and 275x35x15 Hoosier R7 tires.Click to view attachment

What about for street tyres on 15 x 7 and 15 x 8" Fuchs? (slight thread hijack)

The one's I show in post #21 are street legal on 15x7 and 15x8 fuchs. If you want something taller with better tread wear Kumho still has an option available (Ecsta AST). If you want stock size original style tires you can get those too, but I'm not sure where.

Thanks.
What size are the Kumhos? And also what were the original tyre sizes for 15x 7 and 8s?
Cheers
Craig

Kumho's are 225/50/15 and 205/55/15 they are different model tires, but I think they were close enough both ecsta series and 400 tw. Stock I believe was one more tire size up, closer to a 25" diameter.

225-
https://www.tirerack.com/tires/tires.jsp?ti...rtnum=25HR5EAST

205-
https://www.tirerack.com/tires/tires.jsp?ti...romCompare1=yes

225/45 front
245/40 rear
Advan Ao48

The advan rubber is kinda loud on my 2.0 / 4 cylinder car. But on my GT. the road noise from rolling rubber is not noticeable at all. Very very sticky , wen heated up. A great tire.

OOPS !

225/45/17
245/40/17

Yokohama

Luv the tread look ....
3.2
Carbureted twin plug
Street car. Drives , like a race car.

Looking good, are those the Rota Fox Wheels? If you lower the car anymore do the front tires rub? That was a problem I had with my 17's.

Is that the 6" or 8" Sheridan spoiler?

Had it on the track yet? Mine came with supports, but I havent tried it on the track with or without.

4 inch Sheridan rear wing .
And
Yes to Fox wheels ....

17x7 front
17x9 rear

On this car I had 15x11 Real Racing Wheels with 275/45/15 Hoosier A6s.

It will be the same on this new project when I widen these barrels in a couple of weeks

Old-ish thread brought back but nothing wrong with that IMO...

While I have no 'scientific evidence' I am leaning with Tony that the Sheridan (or similar) ducktail spoilers have little to no effect. I just removed the 6" one from my car as I never really liked the looks and it had some annoying gelcoat surface defects as well. If anything, I 'may' have noticed a slight increase in stability in Turn 8 at Big Willow. But I seldom drive this car at Big Willow...it's a car for short technical tracks.

Just looking at the car's profile and windshield angle it seems logical that's a dead/negative pressure area as the airflow over the body is going up and out...same reason we have no positive cooling airflow thru our engine lids/grills.

Now I'm bummed my GT lid and paint are drilled and scarred but f/g is relatively easy to fix vs metal...

I definitely DO notice a difference running the deeper Sheridan front spoiler/splitter vs. the two shorter spoilers I've got. The (negative) impact on brake cooling is immediately evident and ducts are mandatory with that one.

I have seen Trekkor's running his car at Thunderhill in the rain and could see the difference in the air movement behind his car (with duckbill) and another similarly setup car but without the duckbill. The interesting thing I noted was the swirl of air behind the cars (the rain and mist behind the cars was very visible). No duckbill resulted in a swirl of air providing lift to the rear of the car. The one with the duckbill showed that same swirl of air but nearly 3 feet behind the car, thus not contributing to lift at the rear of the car. I wish I could find the video.

I'm no aero expert
but Tony is!!!!

I think the car designers only had rudimentary aero in mind when they designed the car and the dead space is hard to over come with the roof line.

most classes will not allow the change
but the old PCA classes did....
this is how the aero was improved by a local 914 race shop (AJRS) on many of the PCA club race cars 15 years ago....

they changed the roof line to improve the high speed aero
they used clear lexan to build a square duct to get air into the electric fan shrouds for engine cooling....

notice the windshield is layed back... and the base of the windshield covers the cowl vents as it is moved forward all the way to the edge of the front trunk.

I'd agree that the small spoilers on the rear don't do a whole lot. It should make some difference, but you won't notice a large difference.

As for raking the windshield ... I make that mod to my car when I first built it. I can tell you it's a complete pain in the butt. There is a lot more work than you'd think. I eventually put a low windscreen on the car.

One comment on the car pictured above. The work appears nicely done, but I'd venture to say that the way it was done - raking back the windshield and lowering the front of the roof but leaving the rear of the roof at the regular height - probably doesn't yield much aero gain if any. You need to lower the rear of the roof too. In fact, the way this car was done may well make the turbulence over the engine and rear decklid worse.

Ideally there would be a hatch of some kind over the rear deck area to smooth the airflow. But then I guess it wouldn't be a 914 anymore!

I think he cleaned up the cooling air and still has good downforce front and rear

They built approximately 5 like this with good result and many class records in the day

I am replying to this 5 year old post, as I think it may still do others some good with their aero. Aside from access to a wind tunnel, this is by far the best way to find out where to tune your aero goodies.

Get some of your wife's favorite yarn and cut it into 3" pieces. Use scotch tape to tape a hundred or so all over your car. Set up as many GoPro cameras as possible. Use your GoPros, use your buddies, bug your third cousin, just get several of them. Attach to outside car, pointing to the main areas you have taped the yarn (you can always repeat this with the camera looking at other areas), to find out what the air at body panels is doing, and use that info to tune your aero goodies.

Check this video: Video of Aero with yarn

I have the little brother to this car. Same builder, same roof mods. Haven't had it out enough to comment on it' performance, but according to the logbooks it took a couple of podiums in the day. Ran GT5S class.