Backspacing?

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?

plus you have shorter axles and housing................less weight.


There is no real need for the backspacing to be in the center of the rim, The wheels are plenty stout enough..............seen many a way faster cars than use with offset bs and never hurt anything.

Using a shallow backspace rim with this current proposed upgrade will allow you to go even bigger/wider in the future (like say a 16x16) without having to narrow the housing again. Along that same thinking it's an idea to place the new back-half frame rails & tubs in far enough (and high enough) to accept even bigger tires in the future.

DILLIGASDAVE wrote:Using a shallow backspace rim with this current proposed upgrade will allow you to go even bigger/wider in the future (like say a 16x16) without having to narrow the housing again. Along that same thinking it's an idea to place the new back-half frame rails & tubs in far enough (and high enough) to accept even bigger tires in the future.

Dave, that's definitely true after I finished this drawing. Every size tire I stuck on there fit with no problem. I especially like the Hoosier 18400, it's the only one I see that's available in three different compounds (D05, D06, & C07). So that gives you more options. I know some are thinking, why the odd ball axle dimensions in the drawing. The overall width is based on the amount of clearance between the tire and inner fender lip. What I'll do is round it off the the next lower number. In the current revision the overall axle flange to flange distance is 34.888", the final distance would be 34.75" and still leave plenty of room everywhere plus make it easier on the builder of the axle. I have the car up on my lift right now, so today I'll go out and drop plumb lines from the car and plot the whole thing on the floor of my shop to verify my drawing and make any changes if necessary.

Doug, keep in mind the Hoosiers have a LOT more sidewall bulge than any other tire. I don't know if the cross section dimensions actually reflect this.

Also, the wheel manufacturers don't all use the same BS dimensions. Some go to the 1/2", I think some go to the 1/4" or 3/8". Just suggesting you decide what wheel you want before setting your plans in stone.

The shallow BS is a major deal for tire removal. This '57 Ford chassis car I've been working on is a nightmare. Between the lack of fender opening height from the factory, and almost middle BS 14" wide wheels, I have to take the shocks loose, let the rear hang, and jack the chassis up until it is practically above the tire, just to get the tire/wheel off. Pobably have to take the driveshaft loose also, when it gets one in it.

bosshoss wrote:Doug I believe the general consensus is that the shorter the axles the lower the rotating weight and total weight of the rearend as well. That being said I think the most common backspacing will be in the 3.5- 5.5 range. If you go with 3.5 and leave an extra couple of inches on each side to the frame rails then you have the option of going to a bigger wheel tire combo later by increasing the back spacing.

I think a lot of guys opt for the big Chevy bolt pattern as well. That way the wheels resale value may be higher.

dkp

X2, I'm of the school that wheel and tire weigh less than diff and axles. The last door slammer that I built ('72 F-100 Short Bed, T/S class, Tube Chassis, 4-link, strut) I used a 4 3/8" BS on a 15"X15" rim with a 5 on 5" pattern. My feelings are that if you need more rear weight bias then you can balast to it.
Rob

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.