Pin drives or 5 stud/brake options - any opinions?

I'm hoping to order a rolling chassis kit soon & need to make some early spec decisions.... Whats the collective opinion on the pros/cons of pin drive wheels vs 5 stud?

Would choosing a pin drive option limit my choice of wheels & brakes?

Ideally I'd like a car with powerful brakes & assume the easiest way to achieve this is go to 17" wheels to allow room for bigger discs?

I'm told the current 'stock' brakes on GTD's are Mustang, are these up to sprint/track-day use?

I think you do not have to make the pin drive choice yet as most folks use pin drive adapters to bolt onto the 5 lug hub.

I'd say no to the must have 17" wheels for good brakes. The RF car uses PBR brakes (Corvette and Mustang Cobra OEM) which are quite good and work with 16" wheels. Other makes use 15" wheels with six pot pistons easily.

Ron

Julian,
The RF GT40 also uses 13" rotors in front and 12" rotors in the rear. The front calipers are 4 piston and the rear are large one piston. This is a standard compitition
system with the kit. RF also offers a full race brake option. Contact Gordon Levy for more details.

Hersh

there are a lot of differences between the RF and GTD. The brake system on the RF was designed for the RF and won't work on a GTD unless some modifications are made.

Gordon,

As I understand the 2001 spec GTD uses Mustang discs (rotors?) & calipers.. I could well be wrong...

I'm not sure about the GTD. The RF uses a propriatary spindle, hub, and control arm assy. the brakes that are used on the RF have custom brakets to fit this system.
If the GTD are using Mustang rotors with off the shelf bearings than I can come up with a system for you be it PBR or Wilwood.

thanks Ron, Hersh,

I assume then the GTD uses the same braking setup as the RF? & this setup is rated for track use, or if not I guess there are uprated items available in the US?.

Interesting to learn about the pin drive option! I was under the impression different hubs would be required.

Are there alot of similarities between the RF & the GTD?

regards,

I believe that GENUINE pin drive hubs are
special/dedicated and expensive.
The adapters that many folks use to convert
to pin drive are a less costly method than ripping off the 5-stud hubs and installing
pin drive hubs. Apparently the adpater strength strength is not
an issue on the street, but I don't know whether they'd pass an SCCA inspection.

MikeD

We race on pin drive all the time. As long as the system is designed and installed properly it isn't an issue.

Hi Julian,
We use pin drives on the GTD we use for Sprints and Hillclimbs which are of a 'bolt together' construction and have had no problems thus far despite some fairly aggressive loading whilst cornering on slicks. I have included two pics below of the pin drives fitted to the monocoque we are currently constructing.

Front Hub with rotor + Alcon 4-pots (15" wheel)


Rear hubs prior to Rotor / AP Caliper fitment.


Hope this is of interest.

regards

Paul Thompson

[ December 27, 2001: Message edited by: P Thompson ]

Hi Julian

If you are intending to do some competition and track work, then it is sensible to consider after market braking systems and ignore standard set ups. Definately try and go four pot calipers. AP are very popular here in UK. On a GTD you can buy a special AP set up specifically put together for the GTD.

You will most likely be looking at getting some brake bells machined for your car specifically and the same may apply to the brackets. But these are one off machine items and in fact are not prohibitively expensive anyway. Then you can bolt on any make of disc you fancy and to suit your exact application.

My way of working out braking requirments are a bit practical but based on what I consider logic. If you can lock up your wheels then your brakes can match the grip level of your tyre plus a bit. If you can't lock up your wheels you need better brakes. On 15 inch rims if you run hot sticky slicks then you may need more braking but only on occasion. If you run 17 inch road tyres then a 15 inch brake set up will easily out match the grip from the tyres. Once you are into locking up your wheels it is up to you as driver to feed in the right amount of braking to stop the car without locking up in the shortest possible distance!

Malcolm

Malcolm,

Yes, I certainley will be doing track days, & therefore need equipment to suit. GTD offer a 'race spec brake system' for £4500 + VAT. I don't know exactly what is included in that kit but the components must be extreemley high quality to demand such a high price.

The 17" wheel option looks favourite, purely to allow the biggest possible disc. Your brake theory makes perfect sense to me & seems the most logical & practical.

I need to find more info from GTD about the brake options they offer, but assuming they are Mustang, these are presumably 15" discs???

Regards,

I do not beleive for an aftermarket brake option you need to go to a manufacturer for it. After all it is only someone elses kit they are supplying with a price adjustment. I suspect that for for your £4500 it is an AP system. Give Roy Lane a call on 01926 403721. He has supplied many AP kits to GTD owners and he knows what he is on about. If you have a weird wheel set up he can also arrange for machining of bells and or adapters for calipers. Better still if you trailer your car to him for measurement or leave it with him and collect with brakes fitted. Could be a £1000 saving there for you depending what you want. AP are certainly a damn good brake system.
If that is too much then get yourself to the Autosport show at the NEC over 11-14th January and talk to loads of other brake suppliers. Wilwood, Alcon, etc etc.
Hope this helps.

Malcolm

I do not beleive for an aftermarket brake option you need to go to a manufacturer for it. After all it is only someone elses kit they are supplying with a price adjustment. I suspect that for for your £4500 it is an AP system. Give Roy Lane a call on 01926 403721. He has supplied many AP kits to GTD owners and he knows what he is on about. If you have a weird wheel set up he can also arrange for machining of bells and or adapters for calipers. Better still if you trailer your car to him for measurement or leave it with him and collect with brakes fitted. Could be a £1000 saving there for you depending what you want. AP are certainly a damn good brake system.
If that is too much then get yourself to the Autosport show at the NEC over 11-14th January and talk to loads of other brake suppliers. Wilwood, Alcon, etc etc.

As to disc sizes, no way could you fit 15 inch discs into even a 17 inch rim, (I stand open to contradiction. I thik the best you get with 17 inch rims is in the region of 14 inch discs bbut that is monster stuff. Almost overkill. For 15 inch rims you can go to about 12 inch discs. I run 305 mm with Alcon 4 pot calipers at the front. At the rear I use a sierra cosworth single pot caliper with a 273mm vented disc. No brake balance bar as I won't fit that until I can have a way of recording brake pressures in place. This set up gives me a very good balance and I do quite ok in competitive events against guys with 4 pot calipers all round. I also pay £22 per rear disc (or at last last time I did!)compared to £150 per big disc at the front.

Hope this helps.

Malcolm

Some of the Cobra guys use these with good success. http://www.cobracountry.com/trigo/home.html

Julian,

5 stud:
doesn't look correct
most dependable (particularly for road use)
least expensive

Pin drive using adapters:
"correct look" until you take off your wheel
Not as dependable
Adds rotating and unsprung weight (the worst place to add it, slows acceleration and susp action).
Further offsets the wheels, affecting suspension geometry. This may or may not be a problem if you can correct with a different offset wheel.
From a mechanical standpoint this is the least desireable setup.
Considerably more Expensive

Pin drive, with true pin drive hubs:
"correct" look
Not quite as dependable, although if the spinner is wired they probably are.
No weight or geometry compromises.
Most expensive.

Mechanically the only reason for pin drives is quick wheel changes which your probably not going to see with a GT40 in this day and age, so aesthetics is the only reason to have them. Are you willing to pay 3-5K more so you don't see those 5 lugs, that's the question.

The original cars had 11" and 12" rotors. Anything over 12" is overkill unless your going to be doing some serious racing. In which case you could go to 13" on the front. Friend of mine vintage races a GT40 he runs 11" no problem. Nascar runs 12.5" on the fronts with different size calipers depending on the venue.

Don't forget bigger brakes adds unsprung and rotating weight so it's a compromise either way. A 13" rotor will typically fit in a 16" wheel depending on the caliper.

For my money the best calipers are the wilwoods, they have the best web site also. A aftermarket vette caliper is 150$ and the 4pot wilwood I got is 100$ plus it looks better than the vette.

One note the original cars didn't have e-brakes. You can set up a e-brake lever under the dash that pulls on the brake pedal, thus elimiating a lot of weight and expense. Don't know about the DOT inspections though.

[ January 03, 2002: Message edited by: Kalun D ]

Kalun D

Don't disagree with 95% of your analysis but would make the following few comments from our practical experience here in UK.

Cost wise the adapters are not overly expensive. Clearly more so than 5 studs and a bit less than single peice axles. However you imply a cost between 3-5K more (assumed in Dollars). I hope that includes the wheels themselves. You need a set of wheels whatever set up you buy so that item could be excluded for comparative purposes. I think Ray charges about £600 (open to correction) for a set of adapters.

Any change to any part of the suspension will as you say give a change in geometry. However I would guess that 99% of replica owners are ameteur drivers and if the changes are slight ie the width of front track is increased by 36mm (a set of adapters) without changing the inset/offset of the wheels to compensate you won't notice the difference. Here there are a number of us who have made our own suspension mods with variuos pick up points etc moving up to 40 mm per side. We are all getting faster as we develop our cars. Some pick up points are suicidal to touch on a GTD eg the trailing links to chassis points but others are open to improvement. I can only assume that this could apply to all replicas out there. Any manufacturer out there who says their set up is perfect for everyone, all conditions and never needs changing is "being commercially minded". With the GTD we don't all agree with Ray! Take Ackerman for instance.....

On the unsprung weight issue, I went to adpaters as there were no single peice axles available at the time. Yes an increase in weight. However my old 3 peice rim wheels are heavy but I saved the weight back with my new wheels as the Phil Schmidt BRMs are very light. Also the weight is brought closer in to the centre so has a lesser effect. Again Joe Average driver will never spot the difference.

How far do you take it? In my book on the McLaren F1 (my dream car of all time) Gordon Murray says the unsprung weight on that car is the same as on a Ford Fiesta! (A chrysler Neon sized car)

I think we have different strata of builder/owners out there on this forum site. Same within our club. Some are purists (did you know its a GTD on the frontcover of Trevor Legates new book?!) and some are custom car guys and some are just speed freaks. Oh and some will just polish their cars. Uuugh! Maybe Ron should get forum members to declare their interests.

Anyway just adding to the debate...

Malcolm

Thanks for your input Malcolm, Kalum. Very interesting reading. With regard to the brakes, I assume that more than adequate braking force can be acheived with 12" rotors & a quality set of calipers.

I hadn't considered the unsprung weight issues before, but would be reluctant to add anything un-necessary in this area.

Obviously 15" wheels are more authentic, but I understand there is a limited tyre choice in this size? Is this the case in the UK?

On the brake issue, I can offer a conversation I had with the US Alcon road racing rep regarding brakes for a race car I am building (not a GT-40). The car will weigh approximately 2600 lbs, front engine but the engine is set back well behind the front axle line. You could consider the car similar to a Trans/Am car if you follow that series but with a '68 Mustang fastback body. I just could not afford to pay $2000 US per caliper for the high end Alcon/Brembo/AP Racing calipers that were marketed toward my application. So after a bit of looking around I noticed that the calipers marketed towards NASCAR were considerably cheaper even when new. NASCAR brakes are usually offered in kits aimed at the various types of tracks. Short track / road race, Intermediate, and Super Speedway. Of these the short track/road race have the most demanding braking requirements and as a result cost the most

The top of the line Alcon short track setup costs $4750 US and includes 4 calipers, 4 rotors, and 4 hats and all the rotor mounting hardware. Of course the hats would be specific to a NASCAR car, just wanted to give an idea of price. Their one step down short track package with titanium pistons is $4100 (F-Type front caliper). However that is still a lot of money. The solution is to look for used calipers from a WC team. I recently paid $245 US for two Alcon F-Type calipers (with Titanium pistons) from a WC team. All they should need is a new set of seals at $5 piece.


Before buying these I talked to the Alcon rep about them and whether or not they would be OK for my application. Since these are designed for NASCAR where they can only use a 15" rim, the max rotor diameter that can be used is 12.625" but 1.38" thick. I was assured by the Alcon rep that I would not run out of brake with this setup. And as a bonus can run regular stock car size rotors (ie cheap) and pads (again cheap). I was a little worried that the rotor would be too small. But he said I would not suffer. Further below is what a Wilwood rep said regarding rotor size:

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>Personally, I feel a 14 inch rotor is ridiculous. Generally you compromise the integrity of the rotor to have it so large and then trying to get the mass (weight) into an acceptable range. I prefer shorter / wider rotors (12" to 13" range) as they tend to be more stable under excessive heat cycling.
Nowadays with al the excess friction potential that the current racing pads have increasing the rotor diameter for torque value is not necessary.

Carl Rupprecht
Sales & Technical Representative
Wilwood Engineering
<HR></BLOCKQUOTE>

Back to the NASCAR calipers, if you are looking at used ones look for Type F for the front, part number CAL6665S05 with Titanium pistons. For the rear the Type H, part number CAL6346. Note neither of these calipers have dust seals on the pistons and therefore probably not a good choice for a car that sees lots of street use.

Question on the pin drive hubs above. What spindle do these require for the full conversion (not the bolt on)? I have been looking at putting pin drive (Centre Lock) hubs on my car, however the only source I have been able to find is Hoerr Racing. They use a common stock car spindle (Howe 5x5 stubby spindle). However to do all 4 corners would be about $4200 US including the nuts. What is the cost for the UK ones?

having experimented a lot with brake systems, here are few of my observations.
Bigger brakes are always better.
Most aftermarket, quality brake systems are lighter than anything stock.
Unsprung weight for an ameture(sp?) driver is not an issue. They can't tell the difference.
PBR's are good street calipers but have limitations at the track.
Alcon and Brembo are great brakes but are very expensive.
I use a lot of the new Wilwood 6 piston billit brake clipers on their new 12.9"X1.25" rotor. It is a wonderful brake system and costs less than a PBR system.
Brake are personal choice and depends on your budget.