47-55.1 C4 Vette sub frame & running 4 of the same wheel?

[JDarby]

All of you C4 corvette subframe guys attention:

Is it possible to run the same rims on all 4 corners?

I am being told NO and before I lay down the $ I want to make damn sure that is the case.

1955 GMC-100 1st series and I am using Wheel Smith for my step by step wheel measurements. I increased my front cylinders to C5-6 calipers.

running 17" x 7" wide wheel my front will need 1" spacer with a 5.5" Backspace

running 17" x 7 wide wheel my rear will need 1/2" spacer with a 3.5" Backspace

All you FlatOut suspension guys if you have any wisdom you can share with me please do

I am wanting to run smoothies on all 4 with a spare,
Thanks for your advice,
Jeff

[dsraven]

if you want the steering and front suspension geometry to work properly for alignment purposes you can't really change too much from the stock outside diameter of tire and offset. this is because the steering is set up so the steering axis (a line drawn between the upper and lower ball joints and terminating at the ground undere the tire) is supposed to end up in the middle of the tire contact patch where it touches the pavement. if the wheels offset too much one way or the other, or the tire outside diameter changes too much, then the steering can be twitchy or will tend to follow every crack in the road.scrub radius is something that this affects and racers have been playing with these settings for years.
maybe this will help?

https://www.wheel-size.com/calc/

[fauXGT]

Was it Flatout that said staggered front to rear?
Odd, being the stock C4 use same wheel for front and rear. And my understanding is if Flatout suspension is welded in correctly to AD stock frame, it has the same footprint as a stock C4.
And I may have ordered slightly too wide a wheel (16 x 8 4.25" backspacing), but all the same. I checked several sites, including here that said 8" is the max that will fit on stock AD.

[fauXGT]

And spacers are usually a no-no... especially if you are ordering custom wheels that can be set to proper backspacing.

[dsraven]

yup, not a big fan of spacers either. just buy the correct wheel for the backspacing you need and go from there.
personally, i like all 4 wheels and tires to be the same size and offset. any wheel, any location. I realize that for some applications this is impossible due to how the vehicle was built. hopefully, when the project was being built, the rake angle desired was taken into account so that, at this stage, the tire diameters can be chosen to keep the rake angle, which affects the IFS steering geometry, can be kept within the limits of being correct. if you do a little research into the effects of changing wheel offsets on the steering end of the vehicle you will see that changing the scrub radius can really affect how the vehicle drives.

https://www.motor.com/magazine-summa...drive%20design.

[JDarby]

I wish now that I could buy all 4 corners the same but at the time when I was thinking about my stopping power I wasn't thinking about my wheels!

The bigger caliper up front is causing the wheel pain I am having at the moment.

Bigger calipers means spacers if I want to run smoothies and I do!

Dsraven your motor.com/ magazine article did help clear the air about scrub radius .

I wish I had a simulator where I could feel how my truck would ride under certain situations ie, Tire size, wheel size , off set size's (wheel) etc!

I want the function and the fit and the looks to all be spot on!!!

[dsraven]

How does your desired tire outside diameter compare to the original tire diameter that came on the IFS you are using. Keeping that diameter along with an original donor IFS offset would keep alignment as intended. Changes to that will, of course, change how the alignment will need to be set up to keep it driving straight down the road. An alignment tech who knows his stuff would be an asset. The normal corner garage alignment shop would possibly not have a clue what to do for specs because it wouldnt come up in thedata base.

[fauXGT]

Changing the front to rear footprint of the tires can cause odd steering issues such as over/under steer. The geometry of the front a-arm lengths and wheel offsets and turning all work together. It would be a big disappointment to put in all this effort of the entire build to try to make it better than 1950's stock only to have it be worse and hate the way it drives.
Now up/down suspension travel can be adjusted with quality coilovers, but turning is in the hands of the geometry gods.

[leegreen]

if you can figure out how to use it there are suspension modeling tools online

this is a very long link:

https://vsusp.com/#0.8%26project_nam...ll_center.y%7D

[JDarby]

That is one doozie of a simulation!
Could take me years to understand that one

[JDarby]

Originally Posted by fauXGT

Changing the front to rear footprint of the tires can cause odd steering issues such as over/under steer. The geometry of the front a-arm lengths and wheel offsets and turning all work together. It would be a big disappointment to put in all this effort of the entire build to try to make it better than 1950's stock only to have it be worse and hate the way it drives.
Now up/down suspension travel can be adjusted with quality coilovers, but turning is in the hands of the geometry gods.

Yes,I understand that forever moving forward my alignment will be C4 Corvette Please

[dsraven]

its only gonna be true c4 specs if the IFS is installed just like it would be in the c4 and has the same tire OD and wheel offset.

[JDarby]

With 17x 7 it's as close as I can get to corvette spec as I can, including spacers and backspacing all around!

[JDarby]

Originally Posted by dsraven

How does your desired tire outside diameter compare to the original tire diameter that came on the IFS you are using. Keeping that diameter along with an original donor IFS offset would keep alignment as intended. Changes to that will, of course, change how the alignment will need to be set up to keep it driving straight down the road. An alignment tech who knows his stuff would be an asset. The normal corner garage alignment shop would possibly not have a clue what to do for specs because it wouldnt come up in thedata base.

C4 vette's did run 17" x 8.5/9.5 thru 88-96 front and rear.
So from that stand point I should be ok ?

I have searched the Performance Plus Tire Store of S. Cal data base and
and they have very few Billet being one that offers a 5.5" backspace
and a 3.5 backspace out of stock for $1000.00 ea.

This make's the Wheel Smith seem like a bargain at about 1/2 the $!
I just want this truck to ride as best as it can and that would be like a vette
at this stage!

[JDarby]

Originally Posted by fauXGT

Was it Flatout that said staggered front to rear?
Odd, being the stock C4 use same wheel for front and rear. And my understanding is if Flatout suspension is welded in correctly to AD stock frame, it has the same footprint as a stock C4.
And I may have ordered slightly too wide a wheel (16 x 8 4.25" backspacing), but all the same. I checked several sites, including here that said 8" is the max that will fit on stock AD.

When will your wheels be in hand?

[dsraven]

ok, let me just say that the diameter of the wheel has a little to do with the set up in that the wheel needs to clear the brakes and have the proper backand front spacing that works with the tire outside diameter in order to get the tire contact patch with the road in the correct spot with regards to the rest of the IFS set up. if you think about it you will see what i mean. you could install an 18 inch wheel with a smaller sidewall and end up at the same outside diameter of tire. it is not so much the diameter of the wheel as it is the outside diameter of the tire that is going to affect the alignment. if the offset of the stock wheel, and the outside diameter of the stock tire, are kept to be within reason with the new wheel and tire choice then the alignment and driveability of the truck would be like the original donor car. if you run a taller or shorter tire that the donor or use spacers or a large offset whels to get the wheel further outward in order to get the tire/wheel opening/stance look you want then the alignment is going to be significantly different than the stock donor was and so a difference in alignment and driveability is going to come along for the ride.if you spend some time with the scrub radius link I posted earlier you will see how the different offsets and tire outside diameters will affect the alignment geometry and may have an adverse affect on the driveability. yes, guys do it, yes they will all say it drives like a race car. they just won't tell you the negatives. not all race cars are a dream to drive until they are set up correctly. personally, I would stick with the stock donor wheel offsets and tire outside diameters in order to have the alignment correct because I hate having to herd the vehicle down the road, be affected by every crack or groove in the road surface and never being able to take my eyes off the road for a second to check the radio station or whats in the field next to the road etc etc. change the scrub radius=change how it drives. maybe better, maybe worse. read up on how scrub radius affects steering feedback for a little better idea. talk to a front end alignment guy, do some research before you spend money.
remember, wheel diameter is less important that tire outside diameter. it all works together, wheel outside diameter-wheel offset for the backside AND the front side, rake angle the front end was set up for (which is affected by different outside diameter tires on the front versus the rear).
don't take my word for it, ask a seasoned front end guy who knows, not the wheel salesman, not the tire salesman, not the guy at the car show who has a corvette IFS in his truck that he spent big bucks on, with wheel spacers and big offsets and who says it's the best thing ever but won't look you in the eye when he says that. the front end alignment guy in the know is who to talk to. one from a chassis building shop would be good likely because they would likely have done a few vette suspensions and would know the ins and outs.
just my 2 cents. build it right the first time.

[fauXGT]

I found rebuilt stock C4 calipers with slotted rotors and carbon ceramic pads. The 15" rollers clear. The 16 x 8 took almost a year to get being it was in the middle of covid. I have only hung it on the truck, but still working on finish paint. Hopefully later this summer. I have a rare S-15 truck 2WD that the manufacturer put AWD wheels on it for a dealer demo. They had to put spacers on the front to push them out to be flush like the AWD trucks. It looks great, but it has a bit of a delayed oversteer when cornering. You turn into the corner smoothly, but a little more turning and it goes into an oversteer. For a sport truck, thats kinda scary. been to several alignment shops and none can make it any better.
Just saying that I think it is easier to keep all the wheels the same, being C4s are all the same. No different stagger front to rear.