back spacing question

[1969 Project]

I don't currently have my truck to measure... so my question is, Does anyone know if a a 20x10 with a 5.5 BS on 275/45/20 tire will work on a 69 with 4'6 drop? I tried to do a search but can't find a definite answer.

[Jcfcamaro]

Google it and most likely this site will pop up with results.

[AussieinNC]

I believe anything over 8 1/2" - 9" width will have clearance issues on bed side areas.

6" drop will also need adjustable panhard bar...

otherwise the axle will be forced out of alignment...

[Boog]

http://67-72chevytrucks.com/vboard/s...d.php?t=743765

[1969 Project]

Yes, i have an adjustable panhard bar. I was also worried about the bed side. The rims I currently have are really close on the inner and I cant remember off the top of my head what backspacing I went with. the place where i want to order my rims from swears that the 5.5 will work but I am not sure that is totally true. I am only asking because these will be custom built and I want to be sure they fit the first time. Thanks for the replies!

[AussieinNC]

How long before you can get to your truck?

I wouldnt order anything custom without measuring the clearance at ten times....

[Boog]

Your truck could have the narrow axle or the wider axle. There is about 1 1/2" difference in width.

[1969 Project]

It will be about a week before I get the truck back. There is a deal on the wheels and it is due to expire. I believe I have the narrower rear end as the PO swapped it out. I found this out when I did the 6 to 5 lug conversion the axles were 17 spline. The guy I am ordering my rims from said the front on a 20x8.5 with a 5.25 BS and rear 20x10 with a 5.5 BS will work but I am thinking that the 5.5BS may be to close to the bed side.I would hate to have to get spacers.

[AussieinNC]

There are two different wheel mount to wheel mount dimensions:

The 70 1/2 and earlier width is 62-3/8" from wheel mount to wheel mount.

The 70 1/2 and later width is 63-3/4" from wheel mount to wheel mount.

So there is 1 3/8" difference in the width possible.

Half that and we get 5/8" loss possible clearance if the rear end is the narrower style (early)....

So do math...Internal short cross sill measure 50", you have two 5 1/2" backspaced wheels = 11" making a total of 61"...minimum axle flange to flange is 62 3/8"...leaving only 1 3/8" split to get each side clearance of only 5/8""....this is without any overhang of the wheel housings....

Even if you had the later wider rear axle, it is still too close to call.

I simply cant see 5 1/2" backspace working unless you make changes to the bed and the wheel housings.

I would not be ordering special wheels without making certain that they will not only fit, but will have sufficient clearance especially on the bed side area.

I wont run anything less than 2" clearance unless you have replaced the panhard bar with solid rod end to absolutely control sideways movement of the rear end.

Better to be safe than wrecked and out of pocket...

[4oldcars]

Try this: rimsntires.com/specspro.jsp

[1969 Project]

Thanks! Most came up with a 5" BS. I am curious... would BS also depend on the style of the wheel?

[AussieinNC]

Backspace is defined as the distance between the wheel flange mounting surface and the outside of the tire mount bead.

It does not include any allowance for tire bulge outside of the bead.

[1969 Project]

I have confirmed that my Foose in the rear are in fact 5.5 BS so I should be good. Yes, the bulge from my tire is what makes it a close fit but it works. My truck should be finished getting painted next week and my rims are out 6-9 weeks so i'll be sure to post some pics when she's all finished. The paint guy is pretty cool so Ihave been stopping by frequently to check out the progress and I have been like a little kid at the candy store lately. lol Thanks everyone for the replies and advice!

[Mike C]

I would think the 5.5" bs would work on the 10" rim on a fleetside truck even with the narrower axle.

17x9 on my 69 short step with the wider axle and 5" backspacce works. But the fleetside gives you quite a bit more room on the inside.

Worse case scenario is you buy a later axle which may or may not work out being cheaper than buyin new wheels.

[Trackman101]

Tiresize.com is a great website to figure this stuff out.

[Robznob11]

For what its worth i run a 15x12 with 6.5 bs and 15" wide drag radials and they clear the outters but inner tubs needed to be wider. No I have since made room on the outer edge but its because i now have bags and i already had a 3" body drop. A stock truck with a narrow rear like yours should have shod have no outer lip issues even with a 6" drop. The longer panard bar will also help in the side to side movement..