Girodisc 2pc 348-355 Front rotors released

What are these "custom" brackets you speak of?? Are you using stock 355 calipers??

 

FBB
I have a line on some white 355 challenge rims that i'd like to put on my '91 348tb, and fit them with R-rubber for track days. I'm on my 3rd season of track days, and would describe myself as an aggressive intermediate, getting about 85-90% out of the car.

I am currently running 18" Modena rims & michelin PS2 (275/35 & 225/40) At threshold braking at the end of the 2 straightaways, the rear end tends to be a bit skittish - it's not breaking loose, but it's not confidince inspiring. These braking zones are from about 130mph down to 70, and 110 mph down to 65.

Would grippier rubber warrant brake upgrades, or should I leave the brakes alone?

Is is possible that I need to adjust the a brake bias? Is that adjustment possible with the 348?

Thanks

 

You can't adjust bias on that car with a knob or anything. You could try different pad compounds to do that however. What pads are you running now?

What have you got for suspension? If you are getting faster and faster as you improve your driving, the front is diving more and more because of higher top speeds on the straights and then more aggressive braking at later markers. My guess is stiffening the front would probably help settle the car down at this point. R-compound tires are only going to make this problem worse. Search for what others are running for spring rates and compare that to what you have. Putting less aggressive pads in the rear to solve your problem means your lap times will increase....

FWIW

Martin
Girodisc

 

If the problem is initial instability under brakes that becomes more tollerable as speed comes off, raise the nose by a turn on the front shock collars. If the instability persists all the way down, drop the rear by 1 or 2 turns on the shock collars. {both are temporary fixes}

Next time you go for tires, choose the 275/40ZR18s at the rear, then set the rear ride height at 186mm +/-5mm; road surface to center of rear a-arm bolt at chassis pick up point.

225/40ZR18 are correct at the front (set ride height to 166mm +/- 5mm)

 

Thanks,
I got new pads all around and new front rotors last winter. After bedding them in, I noticed the rear being more twitchy under heavy braking than it was before. It's stayed consistently twitchy all summer.

I'll have to dig to find out the specifics of the new pads.

 

It's the initial instability.

With the PS2's, I was under the impression that the 275/35 was closer to stock diameter. Not so?

Any sizing recommendations for R-compound rubber?

 

Follow the previous post to address the initial instability under brakes. (i.e raise the nose)

F355 original tires
225/40ZR18 rolling diameter 25.08
265/40ZR18 rolling diameter 26.34 *

F348 original tires
215/50ZR17 rolling diameter 25.46
255/45ZR17 rolling diameter 26.04

Compare 275 tires
275/35ZR18 rolling diameter 25.58
275/40ZR18 rolling diameter 26.66

So the front end was dropped (25.46-25.08)=0.38 and the rear end was dropped (26.04-25.58)=0.46. So in reference to the F348 original chassis setup, the 275/35 is a closer match {so you were right}, while in reference to a F355 the 275/40 is the closer match.

To address the rear being dropped more than the front 1.5-2 turns up on the rear shock collars will put the rake back where it belongs. Start with 1.0 turns and see if you like the direction it moves the handling.

(*) many of the tire manufactures of this particular sized tire use 26.1" for the rolling diameter. The 26.34 is a calculation:: (265*0.4*2/25.4)+18

 

Make that the front was dropped by 0.38/2 = 0.19
and the rear was dropped by 0.46/2 = 0.23
for a difference of 0.04

At this point, I would just leave it aloone if it feels good.

 

I still need a set of these rotors and have been hoping Daniel will find it in his heart to sell me a set .....

 

That's what I think i will do, just leave it alone. It's only the initial instability under heavy braking that spooks me. Everything else seems to be terrific behaviour. Corner entry is fine, very stable mid-corner with gentle throttle (sometimes moderate) I only get understeer if I push too hard mid-corner. I don't trail-brake, so I always try to pick up some speed through the corner. A little throttle lift in the corner will tighten the line. All in all I think it has good balance.

So next year I hope to get some slicks to see what it can do.

FBB says the stock brakes can handle the slicks, so I'll find out firsthand.

Too bad it has to wait until next year, but it's snowing already.

 

What a bummer. I was really hoping to get these.

Placed the order on July 18 and paid instantly via paypal.

Was advised on July 20 that they are not in stock but could ship "mid next week" (week of July 26).

I agreed to wait an extra week.

When nothing shipped that week I contacted Johann (person who replied initially) to find out the status and was informed on July 29 that they can now only ship second week of August (week of Aug 9).

Fine, I agreed to wait yet again.

Well, the second week of August has come and gone and I have not heard a peep from them, even after sending several additional email asking for the status.

The thing is, I need new discs for my 348 and I am done waiting. I'll get the HE one's from Daniel now.

Really disappointed in the less than stellar customer service. Too bad, this looked like a nice product.

I initiated the paypal dispute today to ask for my money back on Aug 23 (an action that I indicated I would take in an email to Johann last week Thursday if I would not hear back from them).

Better luck next time, I guess.

Kai