Weight reduction: Running out of ideas.

[69427]

How wide a rear tire can you run with the C4 rear suspension and stock '69 bodywork?

Cheers,
Matt

Presently I'm running some C5Z wheels (10.5" width) with 285/18 tires on the rear. I could have fit some 295/18 tires there, but the incremental price difference was too damn high for just 10 mm of additional tread.

I have some 315/16 tires on my C4 that I've been meaning to try on the 69 when I get a free moment from other more "important" projects.

Wow, I'm surprised. That's quite wide considering. Did you notch the frame at all the gain that tire width, or does the C4 knuckle and links give you more room?

Regards,
Matt

I didn't notch the frame as the inner wheelwell bodywork is basically on the same vertical plane as the frame rail, and I would have had to also cut and modify the bodywork. My intention at the start of the suspension conversion was to leave the bodywork unmodified.
The two trailing links are set inward substantially compared to the original C3 trailing arm, allowing the wheel/tire to pretty much set inward pretty close to the frame rail and inner bodywork.

 

[Bad Bird]

Thanks for the feedback.

I completely understand the desire to leave the bodywork alone of a '69. Not much looks as good. They can get a little tire challenged though with the stock bodywork.

 

[69427]

Thanks for the feedback.

I completely understand the desire to leave the bodywork alone of a '69. Not much looks as good. They can get a little tire challenged though with the stock bodywork.

You're certainly correct there. That's half the reason why I've been trying to take weight out of the car (the other half obviously is acceleration and braking). A bunch of years ago I took a few driving schools that used Formula Ford cars. IIRC the tires on those cars were about 195 or 205 mm width. I thought at the time that that sure was a skinny tire for what is supposed to be an actual competition vehicle, but after driving the car the first time I got a quick appreciation of the advantages of low vehicle weight (IIRC, FF cars were about 900 pounds). Those cars will brake hard and corner damn well. (My car is about three times as heavy as a FF, but only has about about 40% more tire. )

 

[mrvette]

Thanks for the feedback.

I completely understand the desire to leave the bodywork alone of a '69. Not much looks as good. They can get a little tire challenged though with the stock bodywork.

You're certainly correct there. That's half the reason why I've been trying to take weight out of the car (the other half obviously is acceleration and braking). A bunch of years ago I took a few driving schools that used Formula Ford cars. IIRC the tires on those cars were about 195 or 205 mm width. I thought at the time that that sure was a skinny tire for what is supposed to be an actual competition vehicle, but after driving the car the first time I got a quick appreciation of the advantages of low vehicle weight (IIRC, FF cars were about 900 pounds). Those cars will brake hard and corner damn well. (My car is about three times as heavy as a FF, but only has about about 40% more tire. )

My '72 had the later shark flares spliced on to the body by previous owners I did not notice it until parking next to a stone stock '72 and take a tape to the fenders they measure like a '78+ so that enables my 9.5" '89 vette wheels/tires are 50 series....

 

[redvetracr]

Thanks for the feedback.

I completely understand the desire to leave the bodywork alone of a '69. Not much looks as good. They can get a little tire challenged though with the stock bodywork.

thats why GM developed the L-88 fender flare and what looks better than a lowered 69 with L-88 fender flares?....maybe one with L-88 flares and FIA headlights?

 

[mrvette]

I would love to lower my car almost 2" worth, but these dip shit roads around here I"d be dragging pipes, if not more....it's as if they WANT to make the roads shitty, and so I even got pissed enough to call the County roads dept, seems all the NOT NECESSARY road resurfacing is done by some stupid committee and none of them come out to actually LOOK and drive the roads....:bonkers: typical dumb assed .gov :flash:

 

[vette427sbc]

So Ive got my C4 D44 separated from the rest of the suspension... The diff and batwing are light as a feather compared to the C3 iron diff (I guess no real surprise here) I really need to get a scale in my shop to start weighing things like this. I can easily pick it up and my gym equipment has a considerable amount of dust on it :crap:
Point is, its more than just a few lbs and you wont have to mess around with the C4 batwing to C3 diff plate.

 

[69427]

So Ive got my C4 D44 separated from the rest of the suspension... The diff and batwing are light as a feather compared to the C3 iron diff (I guess no real surprise here) I really need to get a scale in my shop to start weighing things like this. I can easily pick it up and my gym equipment has a considerable amount of dust on it :crap:
Point is, its more than just a few lbs and you wont have to mess around with the C4 batwing to C3 diff plate.

IIRC, one of the reasons I didn't go with a C4 D44 was the physical size/shape of that unit (the other reasons were price, and the supply of various ratio C3 differentials I had laying around). It looked to me like the C4 unit might not fit the back of the tunnel without some cutting and glassing. I didn't mind cutting up the spare '69 frame I had, but I didn't want to cut up any bodywork for this suspension conversion. (And at this point, I'd be on the hook for another set of custom width halfshafts ($$) if I changed to a different differential.)

Make sure you start a build thread when you start installing that setup. :thumbs:

 

[rtj]

I know it won't help you 69427, but thought this belonged in this thread.

Duntov motors, not cheap:

Aluminum Diff Cover

Although heavy, the iron differential cover is low and almost all the way back . That makes the differential cover about the last part of your racing Corvette to replace with a lighter piece. However, this part was available from the factory for Corvette racers back in 1963, Part # 0228635. If you want to be both trick and period correct, get one of these. We sand cast these covers in 356-T6 aluminum using an original GM wooden plug. It comes with a gasket. This cover accommodates the 1963-1977 2.25 inch rear leaf spring. If you are running a later model 2.5 inch rear spring, this cover won't work.

Free Freight

 

[69427]

Front crossmember

Started cutting and drilling some material for a new front crossmember in aluminum. Planning on a couple geometry tweaks while I'm at it. IIRC, the present steel crossmember is about 35# (I need to weigh it again). I'm taking it out at the moment, and I'll make a small jig with it to make sure I get everything lined up okay before I weld up the new one. Looking for 5-10 pounds less weight off the front end.

 

[phantomjock]

Ohhhh, More info PLEASE...
Dropped Spindles? Ball Joints?
New Upper mount locations (like the chevele mods) etc?
New Upper Control Arms -similar to SPCs - or SPCs?
New Lower Control Arms?
New Uprights - C5/C6? The GXR equivalents?
New Bearings?

Oh, so many choices - Please share...

Cheers - Jim

 

[rtj]

http://sriiimotorsports.com/196382corvette.html

At the bottom of the page these guys show a tubular steel conversion cross member for a c3.

 

[rtj]

Can't be too heavy.

 

[mrvette]

Those modifications are so damn beautiful, I just want to run away and cry......

:hissyfit::ill:

 

[1Michel]

that would certainly be an improvement but, would the frame still twist like a wet noodle?

I dont know, for not much more I would go for a full tube frame and get the suspension parts one by one if I have to.

 

[rtj]

that would certainly be an improvement but, would the frame still twist like a wet noodle?

I dont know, for not much more I would go for a full tube frame and get the suspension parts one by one if I have to.

8000$ for the tube chassis. This steel cross member would likely twist less than one made from aluminum. It might weigh less too.

 

[mrvette]

that would certainly be an improvement but, would the frame still twist like a wet noodle?

I dont know, for not much more I would go for a full tube frame and get the suspension parts one by one if I have to.

8000$ for the tube chassis. This steel cross member would likely twist less than one made from aluminum. It might weigh less too.

Gopher it, I give you a grand for what you have.....:drink::crylol:

 

[rtj]

I think this must have been recently released.



Hurst 530-491-0500 - Hurst Pro Billet Speedway Super Shifter Details

Pro Billet Speedway Super Shifter


Advanced Linkage System
Low Mounting Proximity
Heat Treated Heavy-Duty Machine Composition
Lubrication Management System
All Grade 8 Hardware Predrilled
Shifter Can Be Tailored
Weight-Saving Materials
Space-Age Coatings

 

[69427]

that would certainly be an improvement but, would the frame still twist like a wet noodle?

I dont know, for not much more I would go for a full tube frame and get the suspension parts one by one if I have to.

It's the area between the axles that resists the torsion, not the crossmember. The crossmember/axle area is just where the forces are inputted into the frame.

 

[69427]

After a few busted up knuckles I got the crossmember pulled out. I tried to not disturb any more items than I had to in the removal. (The rack bracket bolts to the crossmember so that the rack location can be changed without removing or altering the crossmember.)



The "original" crossmember is a bolt-in unit so I could modify or replace it for any of a multitude of reasons, and not be stuck with the first pass geometry if it had been welded in. The new crossmember will have a few tweaks to change the geometry, in an effort to get a bit better front grip in mid-speed corners. A few pounds less weight on the front tires is also a goal.



The dimensions and wall thicknesses are larger than the steel crossmember specs to retain sufficient strength and safety.