Wheels and Rear Clamshell Width

Bart Roberts

Supporter
Since I'm based in the US, I'm looking at Vintage and Trigo for wheels. I have used the Trigo in the past on a Cobra. The Vintage BR are 15x8 and 15x10 with 4 inch backspace. The Trigo are 1/2 inch narrower on both with a 3.6 inch backspace. I'd like to hear comments on those sizes and experiences. Next I have 2 clampshells, After doing research there appears to be 3 common widths of clamshells in the replica world. I have an intermediate with 71 inches wide at the center of the rear wheels and wide rear with about 79 inches wide at the rear wheels. For folks running the wide body rear, do you use wider wheels, more offset or longer control arms to space the wheels out further?
 

Davidmgbv8

Supporter
What chassis are you using? That was the big part of my decision to use Vintage as they could build the wheels to the offset I needed along with the drive pin pattern and diameters. As for me I got advice on my wheel width based on the Southern GT chassis and the bodies they use in England which is wider than a "stock" MK1 road cars. If I had gone with a 9" width on the rear I would not have had to make so many suspension changes.
 

Bart Roberts

Supporter
What chassis are you using? That was the big part of my decision to use Vintage as they could build the wheels to the offset I needed along with the drive pin pattern and diameters. As for me I got advice on my wheel width based on the Southern GT chassis and the bodies they use in England which is wider than a "stock" MK1 road cars. If I had gone with a 9" width on the rear I would not have had to make so many suspension changes.

Thanks and I have a collection of parts. Right now the chassis is a GTD but it is bare, I have to make the suspension arms.
 

Davidmgbv8

Supporter
My body is 68.5" wide I had to narrow the upper and lower arms and bring inboard mounting points to fit a 10" wheel and a 275 tire. If you use SGT/AK40 uprights and spindles Bob at Vintage has the offsets for that from my project. I think figuring out your uprights and backspacing would be the next step.
 

Neil

Supporter
Thanks and I have a collection of parts. Right now the chassis is a GTD but it is bare, I have to make the suspension arms.
Suspension design is not an especially intuitive science. A computer is a big help in analyzing the wheel motion over a wide range of conditions. I used this software to design the F & R geometry on my car- not a GT40: https://www.performancetrends.com/SuspAnzr.htm

It worked well and is relatively easy to use. One of the most valuable aspects of the computer is that you can move points around and actually see the motion that results from those changes. In the case of my rear suspension, I chose a 5-link design based on Porsche 996 rear uprights with all spherical rod end bearings but I found that the original Porsche geometry had bump steer. I was able to move some attachment points just a little to effectively (almost) eliminate it. I think Porsche may have chosen their points as compensating for deflection in their rubber bushings. Without a computer I would have been simply guessing and changing things willy-nilly- probably for the worse.
 

Mike Pass

Supporter
I have a GTD with 10" wide rear wheels with 275/55 X 15 Avon cr6zz tyres. If it will help I can measure the rear clip width and suspension arms and take pics etc.
Cheers
Mike
 

Bart Roberts

Supporter
Suspension design is not an especially intuitive science. A computer is a big help in analyzing the wheel motion over a wide range of conditions. I used this software to design the F & R geometry on my car- not a GT40: https://www.performancetrends.com/SuspAnzr.htm

It worked well and is relatively easy to use. One of the most valuable aspects of the computer is that you can move points around and actually see the motion that results from those changes. In the case of my rear suspension, I chose a 5-link design based on Porsche 996 rear uprights with all spherical rod end bearings but I found that the original Porsche geometry had bump steer. I was able to move some attachment points just a little to effectively (almost) eliminate it. I think Porsche may have chosen their points as compensating for deflection in their rubber bushings. Without a computer I would have been simply guessing and changing things willy-nilly- probably for the worse.

Thanks for the link. I want to look at using mustang 2 spindles so this software can help me. With this I can compare a lot of things but trying to decide between stock height and 2 inch drop spindles. I can simulate both. I'm trying to use components common here in the states.
 

Bart Roberts

Supporter
I have a GTD with 10" wide rear wheels with 275/55 X 15 Avon cr6zz tyres. If it will help I can measure the rear clip width and suspension arms and take pics etc.
Cheers
Mike

Thank you Mike. I may take you up on that. Right now I'm trying to find rear upright drawing or dimensions so I can fabricate some to start the process on the rear. GTFORTE.co.uk is the only place I see them available and everyone has told me not do business with them so feeling a little stuck.
 

Neil

Supporter
Thanks for the link. I want to look at using mustang 2 spindles so this software can help me. With this I can compare a lot of things but trying to decide between stock height and 2 inch drop spindles. I can simulate both. I'm trying to use components common here in the states.
I used the Mustang II as well for my whole front suspension on two cars. Some time ago I had lunch with my car guy buddies and Chuck Weiss joined us. He was the designer of that suspension so I picked his brain while I had the chance. The geometry is very good which accounts for its popularity on race cars, hot rods, & custom cars. Many, many vendors offer versions of that geometry. I used a version from Speedway Motors for my black race car- tubular swaged tubes & spherical rod end bearings all around in the rear. I used the stock no- drop spindles from Shell Valley Cobra since those were forged steel instead of cast. Here is the rear & the front.
 

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FWIW, I designed our front and rear uprights around what I regarded as the optimum geometry and roll center height. Very similar to the original GT. I just compared the Mustang II dropped upright and it's very close to our front upright, geometry-wise.
 

Bart Roberts

Supporter
I used the Mustang II as well for my whole front suspension on two cars. Some time ago I had lunch with my car guy buddies and Chuck Weiss joined us. He was the designer of that suspension so I picked his brain while I had the chance. The geometry is very good which accounts for its popularity on race cars, hot rods, & custom cars. Many, many vendors offer versions of that geometry. I used a version from Speedway Motors for my black race car- tubular swaged tubes & spherical rod end bearings all around in the rear. I used the stock no- drop spindles from Shell Valley Cobra since those were forged steel instead of cast. Here is the rear & the front.

That is very nice. Can you share what front arms you used upper and lower? Is that at afco lower as well. I used to race a local circle track and bought afco arms from speedway many years ago. Lots of choices though and looks like you've already figured it out. Is that your design on the rear upright?
 

Bart Roberts

Supporter
FWIW, I designed our front and rear uprights around what I regarded as the optimum geometry and roll center height. Very similar to the original GT. I just compared the Mustang II dropped upright and it's very close to our front upright, geometry-wise.

Bob thanks for your insight. Any help on rear uprights? I'm searching for general dimensions so I can design with readily available hub bearing assembly like Corvette C5/C6 (or a Ford that is similar) and get away from the older Ford UK stuff that's not very available here in the USA.
 

Neil

Supporter
The front top a-arm is AFCO but I fabricated the lower ones to fit my wheel offset, etc. The photo of the rear suspension is my variation on the Porsche 996. This arrangement is rather odd due to my using Porsche 928 S4 FRONT rotors & calipers on it. Perfect fit but I re-drilled the hubs to fit standard stock car "5 on 5" bolt circle, 5/8" stud pattern.The metric Porsche bolt pattern was very close. I did not want to use magnesium or aluminum wheels on salt and the SCTA rules require genuine racing wheels so 15" dia Bassett steel wheels were a lightweight bargain.
 

Bart Roberts

Supporter
The GTD used Ford Granada Mk3 rear hubs bolted to a fabricated steel upright. I may have a drawing somewhere or I can measure up one of my uprights.
Cheers
Mike

Help on drawings or dimensions on the rear upright would be greatly appreciated. Not looking to copy anything directly as I need dimensions to at least evaluate more currently and USA available bearing assemblies is my actual goal.
 

Mike Pass

Supporter
Here are a few pics of GTD rear suspension uprights and suspension. I would suggest using the Willwood Mustang 2 front uprights as they have better geometry than the the Granada items and are available as standard or with a 2" drop. There is a thread on here about them. They also have a good range of hubs in 4 and 5 bolt and a good range of brake and calliper options for 15" and 17" wheels.
Cheers
Mike
 

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Mike Pass

Supporter
Here is the link to the thread about the Wildwood pro spindle.
I have sent you a PM with a source for GTD rear upright dimensions.
Cheers
Mike
 

Bart Roberts

Supporter
Here are a few pics of GTD rear suspension uprights and suspension. I would suggest using the Willwood Mustang 2 front uprights as they have better geometry than the the Granada items and are available as standard or with a 2" drop. There is a thread on here about them. They also have a good range of hubs in 4 and 5 bolt and a good range of brake and calliper options for 15" and 17" wheels.
Cheers
Mike

Thanks Mike!
 
Just to make you dizzy, this is what I've accumulated over the years of the various wheels we've had to deal with. The wheels are modeled with our suspension and body profiles.
As I remember it, sets/sizes of wheels are in separate layers.
 

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