Backspacing?

Doug Rahn wrote:Here's what I've drawn up so far, just need to verify the tires will have enough clearance from the fender lip. I'll definitely be ordering gun drilled axles to cut down the weight.

Screen Shot

Doug, just curious as to why you aren't running the pinion centerline on the centerline of the chassis? Is the engine and trans off-set also?
Rob

whatbumper wrote:

jbozzelle wrote:

whatbumper wrote:I would go 3.5". Used wheels all day everyday. plus if you ever decide on beadlocks you can not beadlock a 7.5" bs.

Why?

it is how the inside of the wheel is made. most wheels you can't get the tire on and off the wheel because of this. there are very few wheels that will take a double beadlock with that much backspace.

http://www.cwibeadlock.com/TechSpecs.htm

that aint no lie! i have 5"B/S i think,the last set of goodyears had to be cut off! it's like 5"of bead on the back of the wheel.f***ked up deal.IMO

Heck why not just go no backspacing at all that way you can just unbolt them and they will fall off......


Doug I see you have your frame rails set at 22 inches, I thought about that also but the chassis guys said not to go that narrow said sometimes it makes the 4 link or ladders a little more unstable, they all suggested 24 minimum outside. just something to think about.

the Coug wrote:Doug I see you have your frame rails set at 22 inches, I thought about that also but the chassis guys said not to go that narrow said sometimes it makes the 4 link or ladders a little more unstable, they all suggested 24 minimum outside. just something to think about.

I think that's more of an old wives tale now days on a lot of cars. That's because of stronger anti-rolls (for the 4-link) and stronger ladder bars out there. A lot of the newer narrow body cars running 33.5 & 34.5 tires can have the 4-link brackets on centers a lot narrower than 24" with no problems. On some of them the 4-link brackets sit so close to either side of the thirdmember that sometimes it becomes a pain to change gears out. It's common to see some 4-link centers out there around the 16-18" range now days with 14-16" wide rear frame rails on some of the faster cars.

What I find interesting on some of the newer cars fitting assorted SFI cage specs is how many different round tube rear frame design/layouts there are out there (from main hoop back) in relation to the top of the 4-link bracket placement. Some guys are starting the rear frame tubes directly over the top of each 4-link bracket assembly. While others start these bars moved inward to the inner side of the top of the 4-link bracket assembly. This gives the tire sidewall a little more body roll/tire shake sidewall "flap" room inside the wheel tubs, and more clearance for the top of the housing bracket.

Double frame rail placement (next to the driver) is another thing that you see many different ways of doing things. Some guys install the double frame rails as close to in-line with the top of the 4-link brackets as possible, while others place the double frame rails much closer together giving a little less support for the top of the 4-link, but giving the driver more room .

whatbumper wrote:http://www.cwibeadlock.com/TechSpecs.htm

CWI"s beadlock conversion is great. They do an excellent job & the turn around is damn quick considering the labor involved. You would think all that cutting/welding on a "finished" rim would cause warpage problems, but the 16x16 rims CWI did for a friend came back perfect & spun dead-nuts straight.

Their ring with all the lightening holes is still amazingly rigid too.

Doug,
I didn't see that the disc brake hat thickness was taken into account. These vary some between the brands, but I allow 1/4" to 3/8" per side for these. So this will shorten your flange to flange distance by 1/2" to 3/4" to keep your wheels at the same location.

The pinion offset looks like it is 2" from the center of the rear frame. If you are not centering this then the number is usually 1" from the center to keep it lined up with the factory offset of the engine.

The rear frame rails on the SFI25.3 Maverick that I built are 22" outside to outside and it has the ART antiroll bar with the 1 1/2" tube and it doesn't have body roll.

Good eye 85Monte. Strange rotors aren't near as thick as the aluminum hat rotors.

85montess wrote:Doug,
I didn't see that the disc brake hat thickness was taken into account. These vary some between the brands, but I allow 1/4" to 3/8" per side for these. So this will shorten your flange to flange distance by 1/2" to 3/4" to keep your wheels at the same location.

The pinion offset looks like it is 2" from the center of the rear frame. If you are not centering this then the number is usually 1" from the center to keep it lined up with the factory offset of the engine.

The rear frame rails on the SFI25.3 Maverick that I built are 22" outside to outside and it has the ART antiroll bar with the 1 1/2" tube and it doesn't have body roll.

I took into account the hat thickness, you just can't see it in that photo zoomed that far out. My hats are .180 thick and all of my dimensions are from axle flange to axle flange. When you capture a screen shot and put it in .jpg or .bmp photo format you lose a lot of resolution. The offset on my current 9" rear is 2" as is the 8.8 I have sitting in my shop, the engine and transmission are also offset 2" to the right and the driveshaft is smack down the middle if the tunnel .

I've been working on the side view drawing some more this morning, this is what I have so far. Still tweaking and a lot more to draw to connect it up to my current roll cage! Here's a screen shot.

Doug Rahn wrote:I've been working on the side view drawing some more this morning, this is what I have so far. Still tweaking and a lot more to draw to connect it up to my current roll cage!

My first guess is that it's a Chris Alston layout? If so his 4-link brackets do have a pretty good design for a layout based on all the bolts being 5/8" OD on his basic chassis bracket. I think he also has a chassis bracket with 1/2" top holes. The one thing I do dislike on a lot of these chassis kits is when they put the rear frame/trunk floor (behind the rear housing) so low/close to the ground. True, doing it this way makes tons of room for a giant fuel cell in the back. But it also kills a bunch of wheelie bar height room under the car. The 2x3 tubing by it's nature also takes up a bunch of room too. Since your car already has round tubing in the front of the car, why not go with round in the back of the chassis too? To be SFI 25.5 legal the rear main frame round tubing can be as small as 1-1/2" OD x .108" ms/.065" cm (running from the main hoop crossmember to rear bumper).

Does look like a damn interesting drawing/design program.

Good eye Dave. It's their Eliminator II rear clip. I found a drawing that had some of the dimensions on it and I filled in the rest. I thought the wheelie bars might be tight too, but I drew those in and it looks okay. I have considered round tube, but I haven't made up my mind yet .

85montess wrote:The pinion offset looks like it is 2" from the center of the rear frame. If you are not centering this then the number is usually 1" from the center to keep it lined up with the factory offset of the engine.

85montess, I owe you an apology. I am such a dumb ass . I told Mike about this the other day, laughing the whole time. I was out in the shop last weekend taking some other measurements, and thought I would check the width I need one more time just for peace of mine. Well you where right, it's one inch. Then I tried to figure out how in the hell I came up with two inches. Then it dawned on me I forgot I was measuring from the 1" mark on my tape measure and forgot to subtract that, which is usually what I do since tape measures are known to be off if you use the catch tab on the end. Plus I was reading the tape upside down . I'm such a dumb ass! Don't say a word about being old Mikey .

Doug don't feel like a big dumb ass I have done the same thing a few times yes it make you feel stupid sometimes.