Steve Lavigne

I've been planning on buying some track wheels for my '86 944 turbo and have been wondering about wheel diameter. So far, I see it like this:

The wheel diameter should be as small as possible in order to reduce intertia in the wheel assembly. Additionally, small wheel diameter will allow a small tire diameter which will further reduce intertia and shorten the rear final drive ratio. With this in mind, the wheel must be large enough to clear the caliper/rotor.

I am wondering what role the caliper/rotor to wheel clearance will have in brake cooling. Secondly, how does the diameter of a tire affect the contact patch.

Anyone have any experience using late 80's vintage 16" BBS 3 piece wheels and Big Red calipers? Do they fit?

I suppose another issue is tire availability. It appears that there are fairly wide sizes available in 16" Hoosier DOT tires. Additionally, there seems to be a large selection of wide 16" race (non DOT) tires.

-Steve
'86 944 turbo

Danno

You have to quantify this instead of throwing out a blanket black&white qualitative statement. What is the weight of your stock wheels and tire combo (tire weight counts too)? Aftermarket 3-piece wheels in 17/18" sizes can actually be lighter than your stock wheels (Lindsey RR-10s are 14/15lbs, 3-4lbs lighter than PhoneDials).



Since the tires are at the outermost part of the rotating assembly, they make a bigger difference than wheels. Hoosiers race tires are 3-8lbs lighter than street tires for the same size.





Not much as contact-patch area is dictated by tire-pressure. But there are some minor effects of diameter differences. In general, larger-diameter tires have more grip, smaller-diameters less.



One thing you might want to consider is that tire compound makes a BIGGER DIFFERENCE than anything else. A supper-soft DOT tire with a treadwear rating of 60 or less have a greater impact than ANY diameter or weight differences on a street tire.





Yup, you'll need 16x10/12" wheels too. Check out these recent threads:

Biggest, widest tires/wheels on 1987 944???

Max rear tire width on 944T 951

adrian jaye

Hi Steve,

There's a lot more to changing wheels/tyre combinations than meets the eye.

Simply cos they look good, or are bigger (or smaller) has a knock on effect on a load of thing's.

Things I can think of at the moment (depending on what wheel/tyre combo you use could be)

* Speedo inaccuracies
* Alligment / Tracking problems
* Stress and strain on suspension components
* Stress and strain on bushes/bearing's

When any car is designed, the designer takes into account what use the car is going to be used for, driveability, longeveity, fuel consumption, "SAFETY", looks, etc.

He tries to build in a certain ammount of "Idiot" factor cos he knows someone's going to play around with it.

The 944 has been described as the most perfectly balanced car.

Start to play around with any part and you shift the balance of what that car was desinged to do and safely !

I would seek proper proffesional advice from a person who is competant to work on Porsches (preferably for a living) and who's willing to g'tee that "what ever fix" you want to try is a: going to work b: not adversley effect the car c: invalidate any insurances and more important be SAFE

just my 2c's

respect

Adrian

trebor_quitman

I can't speak from experiance, but I believe that big reds will require 17's for the caliper to clear. Any info for/against this statement?

Steve Lavigne

Obviously a different weight wheel or tire will have an affect on this. Also, it is obvious that the outermost parts have the most affect on moment of inertia.

I am talking hypothetically here, for a race situation. I did not mention this before, but I am assuming similar construction wheels and tires. Also, assuming similar sidewall height. Going from a phone dial in one situation to a magesium wheel in another will throw it out whack. Also, having a racing slick, as opposed to a dot competition tire, or a ice racing tire will cause a huge difference. Let's assume that these issues will be the same regardless of diameter.

The negatives to this seems to be a minor loss of grip, as Danno confirmed. Also, a possible loss of some brake cooling, which I still can't confirm. I suppose the lower moment of intertia would also increase the likelihood of wheel lockup and wheelspin.

An additional item on the plus side, depending on how the PCA rules on 944 ride height are worded, it is possible that smaller diameter wheels and tires could allow a lower ride height, which could reduce drag.

I guess the one thing I haven't really explored would be how a lower spindle height would affect the roll center.

I suppose just like anything in racing/tracking, it is a matter of finding the right compromise. I refuse to go with 17" wheels just because that is what Fikse and Kinesis are selling me. Besides, if I can save money and get better performance, I am all for that.

On the practical side of things, I was hoping to pick up a couple of sets of late 80's 16" BBS 3 piece wheels on the cheap. I figure I need at least one set with Porsche centers, and one or two more to get the correct wheel halves. I could use some dye penetrant on the wheel centers and halves and come up with some max width combinations. (Right now, I am thinking 10.25" in front and 11" in back, but I need to do some actual measuring). Then, come up with some saleable wheel combinations and sell the remaining sets. I don't have any experience with these wheels, but have heard they are very strong, but I have not heard anything about their weight. I assume they have forged aluminum centers and spun aluminum outers.

I read in a previous thread that it may be possible that 16" modular wheels may clear big red calipers. I am wondering if this is true for BBS 16" wheels. I suppose this also depends on whether you use using any spacers between the caliper adapters and the caliper itself, which is a discussion for an entirely different thread.

It seems that this could be a cheap, and even optimal setup for track wheels.

Steve Lavigne

'86 944 turbo

IceShark

Yes, Roberto, big reds do require 17" wheels. You could fit them in 16" with something unusual I suspose but would have to put on a smaller disk which would sort of defeat the whole point.

Steve Lavigne

My phone dials could fit 350 mm rotors. The problem with this would be that I need calipers around the rotors so that I can stop.

Unless you are talking about using some kind of spacer with the caliper to change its radial location, disc size isn't the issue. I don't have any direct experience with big red calipers.

I just did some quick and dirty measurements of my early offset 16" phone dials. They have an ID of 15.5", and an ID of 14" near the mounting face. This 14" ID seems to carry about .5" from the mounting surface toward the wheel face. The stock caliper appears to require about a 13 3/4" clearance, and sticks out about .5" beyond the hub face. This .5" seems to jive with something I saw on the Fikse site about Porsche caliper clearance.

Anyone have any measurements for caliper clearance on big reds? I suppose this could depend on who made your spindle/caliper adapter. Also, anyone have the ID measurements for a late 80's vintage BBS 16" 3 piece wheel handy? ...I can dream can't I!

-Steve

'86 944 turbo

trebor_quitman

My phone dials could fit 350 mm rotors. The problem with this would be that I need calipers around the rotors so that I can stop.

Thanks

trebor_quitman

I can see it now, The new Wave in fashion.

Do you want style in your street machine? Well we at "Ricers are Us" found that those useless calipers get in the way of the bigger disk look. Pluss you'll never have to clean brake dust off of your rims again!" Rotors come in hot pink, neon blue, lime green and several other awesome colors that would have never lasted before

It's too funny.

Bolkboy7

My question is can you buy phone dials from Porsche or any other dealer? I have Fuch wheels and i find the look of phone dials much better. Thanks

trebor_quitman

Bolkboy7,

Where abouts in Indiana are your from? I'm an ex Marion Resident.

booster

Bolkboy7 I bet there are lot's of people that would trade their phone dial's for your Fuch's....I like the Fuch's much better than phone dial's their lighter than phone dial also, they were a expensive option on the 944's.

ModusPonens

If you reduce the diameter of the tire you will increase force and acceleration but you will redline faster in each gear; so a smaller diameter tire = faster but more shifting.