Testarossa Lowering and Rear Track Width Change

This (moving the rear tire centerline ~60mm more outboard) would be a bit ballsy IMO. The good news is that on the TR design, they added a chamfered spacer between the outer bearing inner race and the sub axle = this allowed them to add a big radius to where the stub axle diameter changes from the outer bearing ID to the much larger diameter of the mounting flange. This greatly reduces the chance of the stub axle fatigue fracturing there like it can on a 308 that has no radius there (but it still increases the shear and moment loads on the stub axle at that junction).

The bad news is that moving the tire centerline 60mm more outboard greatly increases the radial loading on both bearings. In the stock design, the large bearing is located almost on the tire centerline (but is still slightly outboard of the tire centerline) so takes most of the radial load, and the inner bearing has a much lower load so can be much smaller bearing. Here are the numbers just scaling the rear suspension drawing in the TR WSM:

Stock Rear TR Wheels
F tire = radial load on tire
F outer bearing = 0.93 F tire
F inner bearing = 0.07 F tire

When you move the rear tire centerline 60mm more outboard, now both bearings are well inboard of the tire centerline (this is known as an "overhung" loading), and the bearing loads are:

Using ET=0 offset wheels at TR rear
F tire = radial load on tire
F outer bearing = 1.54 F tire
F inner bearing = -0.54 F tire

It's not like the rear wheel bearings would fail on day 1, but both will have much shorter lives. Bearing life is inversely proportional to the cube of the load so increasing the outer bearing load by ~65% drops the life by a factor of about 4X. Can't really apply this life change estimate to the inner bearing because the stock loading is so low, but I'd be more concerned about this smaller inner bearing because its load went from about 7% of the (stock) larger outer bearing load (almost nothing) to about 60% of the (stock) larger outer bearing load (a significant load).

What would be your plan for the rear fenders? Moving the rear wheel centerline out 60mm + using a wider wheel moves the outboard edge of the tire out a boatload -- some sort of flared fenders?

 

If you mean TR coil-over shocks with a threaded, adjustable lower spring perch to change the coachwork elevation, I've never seen anything available to just buy and ready to use. My memory is that two companies can/have rebuilt people's TR Koni shocks and added a threaded lower spring perch to the shock case as part of the rebuilding process:

Carobu Engineering: http://www.carobu.com

Truechoice Motorsports (in Ohio, but not sure they still exist or do this anymore)

If you do a search on "Koni adjustable" in the TR/512TR/512M section, you should get some prior threads. I think your only (reasonable) option is to find a Koni rebuilder who can do the modification to add the threaded lower spring perch when the shocks are disassembled for the rebuild. IIRC, there should be a thread where Steve Jenkins changed his 512TR to Penske shocks with this feature (but that's some serious $s and still required some special engineering/fab work).

Those example are visually outrageous (and undriveable at those ride heights -- airbag suspension down at minimum?), but, to really be properly functional, you'd need to do something more serious like widen the frame rails (to move the whole rear upright more outboard) and get longer driveshafts.

PS Another minor downside of changing the rear trackwidth by just changing the wheel offset is that the wheel spring rate will be reduced so you'd have to get stiffer springs just to keep the same wheel spring rate.

 

I see you are from Germany.TUV will never allow a thing like this...moving to JAPAN is an option

 

Stefan,
Changes like that will destroy your pocketbook, ride quality, handling, resale value and change the car from a classic, to a rather silly looking ‘boy racer’. You will not enjoy the result.

The TR will never be a nimble race car. It is heavy in the rear with a high cg. Ferrari was designing a classy, comfortable and fast GT. They succeeded. The proposed changes will destroy all that is desirable about the TR and create a true Frankinarri.

If you want to truly muck about with a car, get an early (pre ‘73) corvette. Dump a big crate motor in it, lighten it up and move weight down and to the rear. Freshen up the driveline with the wide array of aftermarket parts. It’ll be a hoot and faster/better handling than a Frankinarri.

Just a cautionary opinion.