Put some 'meats' on the rear of the 924S..

Schumi · 10:02 PM

So as some may know the 924S comes with 6" wide phone dials instead of 7" wide like most 944's. Why this is I do not know, as the 7" wides fit just fine. I'm guessing it was because Porsche had a bunch of them left over from the first series 928 or something.

So I picked up a set of 4 7" wide phone dials on the cheap for track wheels not too long ago. They have some shot sport tires on them.

Being curious as I am, I threw two of them on the rear my 924S street car today, leaving the 6" wide wheels on the front (with 205/60/15). The rears have 215/60/15. They fill out the rear fenders much much better and make the rear look of the car pretty nice. Looks like a lot of tire under there.

I took it out for a drive and could immediately feel a difference, even with the shot Yokohama AVS tires on the rear. They must have some grip left in them. The rear end felt sluggish to respons and the car initially understeered. I knew this would happen, everyone claims this... but I didn't realize how pronounced it would be. It was very noticeable. That is, until those tires gave it up and the rear started sliding around.

The weight difference of the wheel/tire combo is also very significant. I would say that there is about a 5-6 pound difference between the 205 size tire on the 6" rim and the 215 size tire on the 7" rim. This is significant as it is not just unsprung mass but also rotating mass, and on a lightweight car with very little horsepower it makes a huge difference.

My front fenders are rolled and the 7"ers would fit in the front too, but I didn't try it out. I've come to the conclusion that the 6" wide wheel with a 205 tire is plenty of tire for the car's weight and power, and that going to a 7" with a 215 or even a 225 would actually make the car slower in all cases, handling wise and straight line acceleration.

I also suspect that it's possible that if the 944-spec 924S's could use the 6" rim (in the rules it states a 7" rim is required, and it would be needed to fit the spec tire) and fit a 205 width Toyo on them that they, with comparable setup, would be quicker, just based on the unsprund rotating mass reduction, along with the reduction in polar moment of inertia of the car. The car doesn't need the extra tire to put down power, and a 205 is sufficient width with those Toyos to provide enough contact patch to transmit the longitudinal forces (if the setup is correct - meaning optimal pressures and camber). This of course, is again not currently permitted in the rules, but if it would it would just add to the already good list of reasons the 924S can be, IMO, the car to have in 944-spec. It's the lightest chassis, the short 5th gear, the smaller frontal area, the lower overall Cd, et etc.

Just figured I'd write about my thoughts on that. That's what my race engineer habits can deduce from 10 minutes of driving back to back on two sets of crappy, worn out tires. YMMV.

JHinOH · JHinOH's Garage

I run a 205/50/15 on all 4 corners for street/auto-x and 225/45/15 R-compound for the track. Very happy with both set ups and the 225/45 is so short it lowers the gearing to help a little with acceleration. It just means the speedo is about 4mph off. I'll probably pick up another set of 15x7 phones for backup soon too.

Rasta Monsta · Rasta Monsta's Garage

Meats? How about 8s. . .

Schumi · 07-31-2009, 07:41 AM

The rear fender of the 924S is definately not filled out by the stock wheel/tire combo.

Why this is I never understood, as the 944's fenders are much wider and the 7's oder them look fine. I guess the hub spacing is that different? I'm not aware of how the rear 924S hub/brake spacing differs from the 944, but I know that the wheel offsets are the same.

Porsche 924 · Porsche 924's Garage

Meats??? hows bout 245/45/16

Schumi · 07-31-2009, 08:12 AM

Porsche 924-

what sizes are you running up front?

The Glademister · The Glademister's Garage

I've tried several wheel/tire combos for auto cross. I eventually was able to get the 16" phone dials off a 944S I owned and put Hancook Ventus RS-2 in 205x50 front and 225x45 rear. The 16" wheels are 7" wide fronts and 8" wide rears. The overall diameter for the two tire sizes is the same. I've got the 924S lowered all the way in the rear and 1.5" lowering springs in the front. Good clearance in the rear with 1 degree neg. camber but I'm really close the the springs in the front with 3.5 degree neg. camber. I like the Hancook's grip at 40-42 PSI. They suite the street tire class I'm racing in with my local club well. The car is chipped and has a 3-bar FPR with some real HP improvement from stock. I was having serious launch grip problems with the stock 15x7 wheels. The larger contact patch has definitely improved that.

Porsche 924 · Porsche 924's Garage

205/55/16

The Glademister · The Glademister's Garage

Photos of the above mentioned wheels and tires...

onZedge · 07-31-2009, 02:39 PM

For the 924S:
6x15 "phone dial" all around was factory stock
7x15 "phone dial" rears was a factory option
6x16 "man hole covers" all around was also a factory option
No other "standard" fatory options were available

miester: Thanks for the picture with 6&7x16's. I always wondered how they would look...

Rasta Monsta · Rasta Monsta's Garage

Hey Glade, yer ass is looking a little high. . .

flosho · 07-31-2009, 05:27 PM

255/40/17 in the rear...

The Glademister · The Glademister's Garage

Quote:

Originally Posted by Rasta Monsta

Hey Glade, yer ass is looking a little high. . .

Rasta, dude it won't go no lower unless I re-bias the torsion bar (major PITA). Might have something to do with those Koni sports. Feels good on the track though.

944Spec_bound · 08-02-2009, 02:20 PM

Quote:

Originally Posted by Schumi

I also suspect that it's possible that if the 944-spec 924S's could use the 6" rim (in the rules it states a 7" rim is required, and it would be needed to fit the spec tire) and fit a 205 width Toyo on them that they, with comparable setup, would be quicker, just based on the unsprund rotating mass reduction, along with the reduction in polar moment of inertia of the car. The car doesn't need the extra tire to put down power, and a 205 is sufficient width with those Toyos to provide enough contact patch to transmit the longitudinal forces (if the setup is correct - meaning optimal pressures and camber). This of course, is again not currently permitted in the rules, but if it would it would just add to the already good list of reasons the 924S can be, IMO, the car to have in 944-spec. It's the lightest chassis, the short 5th gear, the smaller frontal area, the lower overall Cd, et etc.

Just figured I'd write about my thoughts on that. That's what my race engineer habits can deduce from 10 minutes of driving back to back on two sets of crappy, worn out tires. YMMV.

Whoosh...
That was the sound of most of that going over my head.

I'm not used to talking with someone who actually knows why the car sticks or not.
I just know wider tires look more macho.

Porsche 924 · Porsche 924's Garage

just some more pics

Rasta Monsta · Rasta Monsta's Garage

Nice car! Love the 924 pRon!

rickharrison · 08-05-2009, 05:59 AM

hey Porsche 924...I've never seen that rear black valance...looks really nice on the '24!

Details?

Porsche 924 · Porsche 924's Garage

Thanks,
and a friend sold it to me he said that he had bought it for his 944 and when he got it he found it a bit to small for his 944 and aparantly it was for a 924, u can ask him where he got it his name is "drift a 944" in pelican.
Send him a private message asking him where he got it.
Cuz I got no idea.
And thanks again.