Brake Offset For Floater Rear for wheel BS

[CampbellshotrodsAZ]

I'm in the process of finalizing my order for my Billet Specialities Forged wheels, and have one last detail I'm trying to figure out. I'm going to get the Speedway Engineering Grand National floater rear through RSRT, and I guess Speedway hasn't been quick to returning answers. I figured I'd ask if anyone has any actual experience or measurements to help me get a ballpark BS figured out. I'll be running the Grand National floater, and I guess the Wilwood brake package I'll be running won't utilize a traditional rotor hat type assembly, but mount to the floater hub itself, and place the rotor in towards the center of the rearend more? I just would like to know what this offset is around, roughly. I'd like a deep wheel, but I don't want it deep enough to where the brakes end up outside of the wheel entirely, potentially becoming an issue with the wheelwells/suspension! I'm thinking if I could get a rough backspacing to where the brake rotors are just barely inside the wheel, that should give me a good balance of cooling/clearance.

And FYI, wheels will be ordered first, then I'll mock the wheels in the vehicle and finalize the width of the rearend, and get it built.

[dontlifttoshift]

I would consider 6" backspace, minimum. 7" backspace would give you some room.

[csouth]

What width are the wheels?

[CampbellshotrodsAZ]

What width are the wheels?
18x12, and these are the new Concave Pro-Touring line, so a 6" would look a little positive offset-wise, though the backspace would be centered.


I would consider 6" backspace, minimum. 7" backspace would give you some room.
Great, thanks for your input. I was thinking something around 5-6" before I took into account the brakes. If I do 6" that should be safe, and it'll be the same BS as the front, which would have my rears look 3" deeper. Not as much as I'd wanted, but it'll be fine.

[sccacuda]

You can go as little as 3" or so. The caliper mounts either front or rear, so not really an issue with wheel well. If your using a separate e-brake caliper, then you'll have an issue. Here is how mine is set up. Brakes in the air for cooling and rear narrow to loose weight.


https://static1.pt-content.com/images/pt/2015/07/IMG_2478_zpsaoxdxzun-1.jpg (http://s1060.photobucket.com/user/340cuda/media/IMG_2478_zpsaoxdxzun.jpg.html)

[CampbellshotrodsAZ]

Thanks for the pic! It looks pretty cool, but now that's making me think about another factor... the Ridetech 4 link! The coilovers in the Cuda look to be inboard a bit. The Ridetech lower mounts look to be a little more outboard, and not too far from the backing plate, basically inline with where the factor leaf is now. I'm not as much worried about the wheel with the Ridetech suspension, but if I go with too small of a backspace with the floater rear, I'm worried I might run into issues with the brake to coilover clearance, if I go with too narrow of a rearend. So maybe I'll have to go with a 6" backspace like I thought, instead of too deep. If I compare to the 18x9.5 (5" BS) Boss 338's I had before, that would mean my new rearend would be 1.5" (2.0" to be safe) narrower per side. Guessing I'll need to do some more investigating and try Speedway again, knowing that exact brake offset would be nice.

From the Ridetech install instructions.
https://static1.pt-content.com/images/noimg.gif (http://s26.photobucket.com/user/blazinred87/media/Ridetech_zpsvmtafl2v.png.html)

[CampbellshotrodsAZ]

http://1speedway.com/index.php?route=information/information&information_id=8

I did find the above link that might have helped a little. Then compared to the Mod-lite hub, which is similar to the Grand National dimensionally, except the Mod-lite page shows the brake adapter.
http://1speedway.com/index.php?route=product/product&path=69&product_id=75

Using the above link to the measurement page, it looks like I might be safe to assume that the mounting flange to the rotor center is going to be around the "G" measurement, or around 3", give or take 1", which no matter what would put the brakes into the wheel with a 6" BS. It looks like the factory GM drum brake offset is around 2.75", so the floater doesn't really put the brakes much further inboard of the drum backing plates than I thought.

Maybe I'm overthinking it. But it looks like if I use a 5" BS wheel, and use the "G" measurement from Speedway (just over 3") to place my rotor, and worst case, assume it mounts to the front face, that would put the back face of the rotor around 4.25" from the hub (1.25" rotor) at the WORST CASE, or pretty much have the rotor 0.75" within the wheel. So it looks like I may be making a mountain out of a molehill. So now I'm thinking 5" would be just fine with this latest scenario, any input? If the hub offset is less, it'll be inside the wheel more, no big deal, it'll be completely shrouded by the front wheels.

[sccacuda]

Floater hubs are pretty much standard for brake mounting. This is how it would mount in relation to the hub:

https://static1.pt-content.com/images/pt/2013/03/file_zpsd599def3-1.jpg (http://s1060.photobucket.com/user/340cuda/media/file_zpsd599def3.jpg.html)

If you know how far back on the hub the mount is, the brake adapter to rotor plate is 5/16" thick. This distance will be how far the rotor mounts behind the hub mounts, if that makes since. That should let you calculate where the calipers will be.

You rotor will mount to the rear of the hubs:

https://static1.pt-content.com/images/pt/2013/03/file_zpsaf39ecc8-1.jpg (http://s1060.photobucket.com/user/340cuda/media/file_zpsaf39ecc8.jpg.html)

BTW, if you haven't got them, my rear brakes are for sale. New, just mockup. GT 48 rotors.

[CampbellshotrodsAZ]

Wow, thank you for those pictures Craig, it's definitely the most I've seen of the floater hub assembly, still a new thing for me! And pretty close on my assumptions, add in the 5/16" mount plate, then my rotor would still be within 0.375" of the wheel, roughly. Now if only Speedway would answer their phones, I'd be golden! I'd imagine that they are probably at PRI this week though.

And I haven't bought my brakes yet, those look similar to what I want to run. Those the 12.19", or 12.88"? I'm still a ways away unfortunately, I'm scrambling as it is to get my wheels, minitubs, and rearend ordered near the same time.

[sccacuda]

The rear calipers are Wilwood 120-8063's and the rotors are Wilwood 160-2541's with the GN hub adaptor. 12.72" diameter, 1.25 wide, spec-37 iron.

[TheJDMan]

Wow, thank you for those pictures Craig, it's definitely the most I've seen of the floater hub assembly, still a new thing for me! And pretty close on my assumptions, add in the 5/16" mount plate, then my rotor would still be within 0.375" of the wheel, roughly.

Josh,
I have read your posts several times and I'm still not sure I understand exactly what your concern is. I also don't understand what you mean by the above comment about the rotor being .375" from the wheel?. Are you wanting to mount the calipers inside the wheel BS or are you concerned about the caliper clearing the body or shocks or the back side of the wheel center? To be honest, I did not spend too much time worrying about the brakes when I built my wheel/axle configuration because I pretty much knew what I needed to fit and where. My wheels/tires were my first purchase, and I specified 18x12 5.6"bs which gave me the outer lip I wanted. From there, I mocked the wheels up under the car and measured the exact WMS to WMS dimension I needed for the axle width which in my case was 57". Once the axle was mounted in the car then I was able to determine where I wanted to mount the rear brakes. With a floater you have brake rotor mounting options. By that I mean you can mount the rotors on either the outboard side or the inboard side of the rotor adapter. This basically gives you about 1/2" to play with. In the photo above Craig mounted his rotors on the inboard side of the rotor adapter. I mounted my rotor on the outboard side of the adapter which locates my rotor 1/2" further outboard on the axle compared to Craig's setup. You can also clock the calipers either in front or rear of the axle it just depends on what packages best for your installation. I guess the point I'm trying to make is that once your wheel/axle package is in place you still have options on where you locate your brakes relative to the wheels, body and suspension.


https://static1.pt-content.com/images/pt/2015/12/camaro13011220001-1.jpg

[CampbellshotrodsAZ]

Thank you for your input Steve, good to know about the flexibility in mounting these pieces of the puzzle together.

And I did hear back from Ron, who talked with Speedway at PRI. I was informed that the distance from the WMS to the innermost face of the caliper is 6.5", meaning a 6.5" BS would totally enclose the caliper within the wheel. I then decided upon a 5.0" BS, so I'll have 1.5" of caliper poking out of the inner wheel face, which won't be an issue with clearance, and allow the depth wheel I want. I was going to have the brackets welded onto the rearend, but after reading your post Steve, I might have them left off, and do it myself so I can clock it if needed. Or I'll get the minitubs in and make sure clearances are good and have Speedway do it. Either way, it's going to be a busy couple of months! Wheels are ordered as of today, so I have 5-6 weeks to install the DSE minitubs, so when the wheels get in I'll get tires mounted so I can measure rearend width and get that ordered, then I can get my Ridetech 4-link ordered so it can all go together sometime around March!

[dontlifttoshift]

If WMS to inside of caliper = 6.5"

Wheel Back Spacing = 5"

Tire Back spacing (assuming 315 on an 11" wheel) = 5.25"

We will make another assumption, that you will allow 1" of clearance between the tire and the framerail.

WMS to frame rail - WMS to caliper = clearance at caliper

(5.25" + 1") - 6.5" = -.25" In other words, your caliper will not clear the frame rail.

What am I missing?

[CampbellshotrodsAZ]

(5.25" + 1") - 6.5" = -.25" In other words, your caliper will not clear the frame rail.


I've never hard calculated the frame rail into this equation. But it's not directly flush side to side with the wheelwell, and it's cut up high enough in the rear of the wheelwell to where if the caliper were to come to the height of the frame rail, the rearend would have to be hard bottomed out against the frame rail. I don't see that being an issue.

[Ron Sutton]

Hey Guys,

Quick guidelines for Speedway Floater Rear Ends with RSRT 13.06" x 1.25" Superlite 4P Brakes:
A. The WMS-to-WMS of a floater rear end needs to be a minimum of 15" wider than the frame rails, so you have 1" of clearance between the caliper & frame rails.
B. We can "clock" the calipers at any position from 9 o'clock to 3 o'clock. Or said another way, from 90° in front of the housing to 90° behind the housing.
C. Our standard mounting position is 10 o'clock to the front. This is equal to 60° rotation forward from the top, or 30° rotated up from the 90° position, however you like to think of it.
D. We routinely mount the brakes in front, so there is no interference with rear mounted shocks, Watt's links. etc.
E. We can make the rearend narrower than the 15"+ number above ... as long as we're clocking the calipers to provide clearance from the frame rails.
F. If the caliper is mounted under the frame rails ... we need a minimum of 2" clearance from the caliper to the frame rail for track cars with race suspensions, and 3" for cars with soft rear springs.
G. FYI: The actual travel of the rear suspension with our modern High Travel/Low Roll Set-ups ... is 3/4" or less either direction. The "High Travel" is in the front, not the rear. The "Low Roll" is why the rear suspension travels so little.
H. The actual travel of the rear suspension with a conventional Low Travel/High Roll Set-ups ... can be up to 2"+ in either direction. The "Low Travel" is in the front, not the rear. The "High Roll" is why the rear suspension travels so much.

If you're planning to run Wilwood rear brakes ... with parking brake ... the above does NOT apply. The major differences are:
1. These are 12.88" x .81 narrow rotor brakes. The caliper mounts 1-1/8" farther inside.
2. So ... The WMS-to-WMS of a floater rear end needs to be a minimum of 17.25" wider than the frame rails, so you have 1" of clearance between the caliper & frame rails.
3. If you're running leaf springs, we need to make sure the parking brake cable bracket has enough clearance, because it is located farther inward than the caliper.
4. The bracket places the calipers at 9 o'clock, in front of the housing.

:cheers:

[dontlifttoshift]

I've never hard calculated the frame rail into this equation. But it's not directly flush side to side with the wheelwell, and it's cut up high enough in the rear of the wheelwell to where if the caliper were to come to the height of the frame rail, the rearend would have to be hard bottomed out against the frame rail. I don't see that being an issue.

....but there is mini tubs in the future? So now your inner wheel house is flush with your frame rail. Is this the 2nd gen? If the caliper mounts in the front, you will have a clearance issue, if you mount it to the rear it will be tight for clearance.

I am looking at this situation like this, not enough clearance is a problem. Too much clearance is _not_ a problem. I will always choose the path of "not a problem"......I'm just lazy like that.

[CampbellshotrodsAZ]

....but there is mini tubs in the future? So now your inner wheel house is flush with your frame rail. Is this the 2nd gen? If the caliper mounts in the front, you will have a clearance issue, if you mount it to the rear it will be tight for clearance.


From the videos I've seen, and the photos from various build ups, the minitubs are not flush with the frame rails. In the rear there appears to be 1-2" of clearance from the frame rail to the minitub. And yes, I'm planning to clock these towards the rear. I figure there is going to be moderate clearance (0.5-1.0") with the 18x12's with a 335 since people do these all the time, then the next (and only) interference would be the wheel tubs, if at all. If that's the case, I can clearance the wheel tub as necessary, it's only sheetmetal, but I don't think that'll be necessary, we are only talking caliper protrusion of 1.25" max (assuming 0.25" tire width).

[TheJDMan]

Not sure what happened with my post above, my floater pic did not display so I went back and fixed the link, seems to be working now. I have my brakes clocked at approximately 2oclock to the rear looking from the driver side. In this position the inboard side of the calipers clear the frame rails by 7/8" per side but I have been told the C6Z06 calipers are a little wider than most. When ordering the rear end I would have the suspension brackets all welded on because they need to be in known specific locations. But I think I would prefer to leave the caliper mounts off until I had the rear end actually installed in the car so you can determine the best location for your build. Just keeps your brake mounting options open.

[CampbellshotrodsAZ]

Thanks for the pic Steve. It looks like the 1st gen minitub pretty much fits flush against the frame rails, from everything I've seen the 2nd gens don't seem to be the same way, it looks like there's 1.5-2.0" between the rails and the tubs, but that's only an estimate. I'll find out soon enough! No matter what, with the little caliper protrusion I have, nothing is impossible to fix, though I don't believe it to be an issue.