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billy the kidd
08-17-2013, 07:14 AM
if i convert to disk brakes on front of my 57 wagon will my back space on the wheels stay the same and if not how do i get it.thank you

NickP
08-17-2013, 08:03 AM
Back space is a static function of the wheel itself. Going from drum with a flange wall thickness of about .09 to a wall thickness of 3/16" to 1/4" (depending on brand) will push the tire/wheel combo outward by the difference of the two. Your biggest concern is to determine clearance for the caliper to the wheel dependent upon your selection of disc kit.

Maddog
08-17-2013, 05:15 PM
The answer you need is knowing how much the disc brake kit you want to buy will move the wheels out, they all move the wheels out, some more then others. Keep in mind some of the vendors don't know and some lie about this issue. The second thing to consider is if the wheels you want to run will fit the disc brake kit. Tell us which kit and I/we can tell you how much it will move out and what wheels will fit.

chevynut
08-17-2013, 09:39 PM
IMO the real question is....why do you care? If your car is at stock height, it may not even cause any issues. If it's lowered, it depends on how much it's lowered. It has been stated that most disc brake kits move the wheels out 3/8" or so. Some claim not to move them out at all. The late 60's Chevelle/Nova/Camaro discs move them out about 7/8" per side.

Whether you'll have any problems also depends on what wheels and tire size you have now.

To give you any more feedback on your question, we need more information.

warren57
04-07-2015, 07:23 PM
Cnut- you watching tonight? I need a little advise on front wheels.
Want to use a standard torque thrust II wheel. 15x6 their spec shows 3 -1/4" BS with -6mm offset.
Would like to use a 215 60 15 tire.
I have stock spindles with the Large Chevelle calipers.
I measured from face of the mounting surface back to the caliper casting and it measures 1"
Stock springs and ride height.
That enough info for you to give me an educated guess?

Trying to get wheels bought tomorrow, so if any way possible I could use your help tonight. Sorry for the short notice.
American Racing said " no problem" by it sounded like their standard answer for everything!
Thanks
Warren

chevynut
04-07-2015, 08:36 PM
Hi Warren, glad to see you back.

With the Chevelle discs I believe you gain 7/8" per side so the mounting surface width should be about 61" (59.25+.875+.875). The -6mm offset should put the center of the tires (front track) at really close to 61.5". Now if you add a 215 tire which is 8.46" you're at 69.96" or darn near 70". IMO that's way too wide.

Is your car lowered at all? Even if it's not, the tire is likely to rub if you're turned hard and hit a good dip. Those Chevelle discs really cause wheel/tire fitment issues.

warren57
04-07-2015, 09:14 PM
Ok, here's the problem, many wheels in 6" aren't made with 4" bs. But let's think about this, if I went to a 7" wheel with 4" bs, that would put about 3" from mounting surface to fender (without rubber).
If I use a 6" wheel with 3-1/4" bs, that would give me about 2-3/4" from mounting surface to fender, or slightly less tha using a 7" wheel with 4" bs.
I took off 7" wheels with 4" bs and they didn't seem to have an issue.
Am I looking at this wrong?
I don't see how you can narrow up the width a whole lot? The disk brake kit certainly nearly eliminates using many wheels except something custom???
So let me change my question, what is better with this tire selection, a 6" wheel with 3- 1/4" bs, or a 7" wheel with 4" bs?
Or do both suck? Ha ha
Using your old tire calc chart. Looked like .02" (basically no) clearance if we use a width of 62" with 215 tires. If we use a width of 61" we have a .52" clearance.
Some help if I go to 205 60 15 tires. With these at 62" I have .21" clearance and at 61" about .71" clearance.
I will for sure go to 205 tires in lieu of 215's

Thanks

warren57
04-07-2015, 09:23 PM
Hey one more question, what would the rear width be with standard differential housing, drum brakes, using 7 " rims with 4" bs, 245 60 15 tires. Narrower than the anticipated front of 70", about the same or wider?
Using your old tire calc chart it looks like clearance is good, 1.18 in and .93 out.
I'm guessing overall width is 60" for stock differential plus a10" tire for a total of around 70" wide. Just about equal to the front calcs above?

chevynut
04-08-2015, 08:21 AM
But let's think about this, if I went to a 7" wheel with 4" bs, that would put about 3" from mounting surface to fender (without rubber).

No, a 7" wheel is 8" wide at the flanges so 4" backspace is a zero offset wheel. It would also have 4" frontspacing.


If I use a 6" wheel with 3-1/4" bs, that would give me about 2-3/4" from mounting surface to fender, or slightly less tha using a 7" wheel with 4" bs.

Again, your 6" wheel is actually 7" wide to the lip. zero offset would be 3 1/2". That wheel is about 1/4" negative offset. If your 7" wheels with 4" backspacing worked, that's 4" frontspacing. So 3 1/2" backspacing on a 6" wheel would give you the same track. The wheels you're proposing move the center of the tire outboard.


I don't see how you can narrow up the width a whole lot? The disk brake kit certainly nearly eliminates using many wheels except something custom???

There are disc brake kits that give you zero offset from stock. What you really need to know is what the wheel mounting surface width is with YOUR kit. I assumed you used the Chevelle setup which moves the wheels out 7/8" per side, but maybe your kit doesn't do that. It's futile to go through these calculations unless you know the mounting surface width.


So let me change my question, what is better with this tire selection, a 6" wheel with 3- 1/4" bs, or a 7" wheel with 4" bs?
Or do both suck? Ha ha

The 6" wheel with 3 1/4" backspacing has -1/4" offset, meaning the center of the wheel is outboard of the mounting surface. The 7" wheel with 4" backspacing. has zero offset, so the wheel is centered at the wheel mounting surface. Therefore, using the same tire, the 7" wheel is better as far as fender clearance.

warren57
04-08-2015, 08:49 AM
so, if a 6" wheel is 7" over the bead, then at 3-1/4" bs would put the inward edge 3-1/4" in from the mounting surface. Thus giving you 3-3/4" outward.
A 7" wheel is 8" over the bead, then a 4" bs would put 4" inward from the mounting surface and 4" outward, or 1/4" less clearance to the fender than the 6" wheel.
Correct?
I measured my disk kit, I am sitting at 61" wide to the mounting surfaces.
Using your tire/wheel calc program. Using a 6" wheel, 3-1/4" bs and 205 tires, I should expect .71" clearance. Now should I be plugging in a 6" wheel or should I be plugging in the 7" (over the bead) size?
If I use 7" width and the same bs the program says .21" clearance.
Pretty close, but considering wagon front coil height and stock spindles, it may work. Don't have any other option. Guess I'll give it a try. If it's to close, the fix would be a 0 clearance kit and I can make that change easy enough. All it take is dollars!!!
Thanks

chevynut
04-08-2015, 09:01 AM
Warren, you're not concerned about the edge of the wheel...you're concerned about the center of the wheel, which determines where the edge of the tire is. If the wheel center moves, the tire moves.

This can get a little confusing, as you can see. That's why I designed the calculator to calculate the track based on wheel mounting width and backspacing or offset, and the clearances depend on tire size, not wheel size. Actually I use offset for the calculations, even if the user enters backspacing.

warren57
04-08-2015, 09:21 AM
Edited my last post, see if that makes sense.
And yes it gets a bit confusing!!!!
Thanks

chevynut
04-08-2015, 09:37 AM
so, if a 6" wheel is 7" over the bead, then at 3-1/4" bs would put the inward edge 3-1/4" in from the mounting surface. Thus giving you 3-3/4" outward.

Yes, that's correct.


A 7" wheel is 8" over the bead, then a 4" bs would put 4" inward from the mounting surface and 4" outward, or 1/4" less clearance to the fender than the 6" wheel.
Correct?

Yes, that is correct.

However, the edge of the wheel isn't the issue, as I already explained. It's the edge of the tire that matters. So you have to find the CENTER of the wheel, and calculate where the edge of the tire is from that.

The 6" wheel you are talking about has 1/4" negative offset, and the 7" wheel has zero offset. So the 6" wheel center is further outboard, making the same tire on the 6" wheel closer to the fender.


I measured my disk kit, I am sitting at 61" wide to the mounting surfaces.

That's what I thought you should get. ;)


Using your tire/wheel calc program. Using a 6" wheel, 3-1/4" bs and 205 tires, I should expect .71" clearance. Now should I be plugging in a 6" wheel or should I be plugging in the 7" (over the bead) size?

The calculator says to plug in the nominal wheel size. So if it's a 7x15, you'd plug in 7". That's what my original spreadsheet says. I didn't do the online version of the calculator but the guy who did it used my formulas after asking for my permission.


If I use 7" width and the same bs the program says .21" clearance.

Yes, but the backspacing on the 7" wheel you've been talking about is different. To avoid confusion, imo it's always better to talk offset. Offset is independent of wheel width.


Pretty close, but considering wagon front coil height and stock spindles, it may work. Don't have any other option. Guess I'll give it a try. If it's to close, the fix would be a 0 clearance kit and I can make that change easy enough. All it take is dollars!!!
Thanks

If your car is stock height or higher, you shouldn't have much of an issue since the fender lip is over the top of the tire. IMO sometimes it looks funny when the tires stick out that far. And if you're turning hard and hit a big dip, you could have rubbing issues. I think there's a disc brake kit for a stock spindle that has a lot less offset than the Chevelle setup, and that's what I'd probably do if you want to pull the tires in further.

chevynut
04-08-2015, 09:48 AM
Your tires are going to be 70" wide outside and the fender lips are around 71", I believe. The calculator makes an assumption on your fender lip width, and you should measure your own car to be sure. The best way to do that is with plumb bobs and marks on the floor.

With a car that's lowered, or that's likely to see dips on hard turns, like turning into a driveway, I usually recommend that the front tires are no more than about 67.5" outside to outside. Some guys have had success at 68" but it depends on how much the car is lowered.

warren57
04-08-2015, 04:47 PM
Reading your post gave me a flashback to the mid 70's. We all bought Chevy short bed 4x4 trucks, put 1200 15 tires on them with the deepest reversed wheels we could get. The tires had to be sticking out past the fenders by 3-4". Then we stuck on the deepest tread knobby tire we could find.
And we thought they looked great, high and wide!
Now look, everything is down in the weeds, not a look I care for! And the 60's Impalas are down in the weeds with 20" tires reversed ans far as possible.... I call them inside out tires! Stick on gold spoke wheels and you really have something.... I'm just not sure what it is you've got!
Thanks for your pointers on wheels and tires, I'll keep you posted on what I decide and how it works out...

warren57
04-13-2015, 07:44 PM
well, here they are. All is well

chevynut
04-13-2015, 08:28 PM
Looks good Warren.

warren57
04-13-2015, 08:57 PM
Thank you

567chevys
04-15-2015, 12:11 PM
Looking good Warren ,
Is that the car that had the 454 in it ?

Thanks Sid