I am doing a Speedway disc brake conversion on my dropped stock 40 Ford axle. This kit increases the width by 3/4 inch per side. Can anyone with experience with this tell me what wheel backspacing and or offset seems to work best. I am thinking I want a 4 1/2 inch to 5 inch wide wheel only. I have GM power steering and will run 15 inch wheels and aboaut a 195 X 75 tire. Open to comments for '40 guys. Many thanks.
I run disks on both of mine (40 coupe and 41 pickup). When ordering the front wheels, I try for those with maximum back spacing. If I recall correctly (it has been some years) the front wheels on the pickup are 15 x 5 with 3 inch backspacing. Work fine with the 165R15 tires I run. I doubt that stepping up a little on tire size would make it a problem.
What's the kingpin to kingpin on your dropped stock axle? If it's not stretched back out to the 48" stock width, you will be totally fine. I'm running that on my '40 coupe. I've got some 15x5 American TTO's and 165R15's.
I haven't ran mine yet, (1939 dlx) but the combination that I went with was 15 x 5" rim, 2 1/2" offset, 165 tire, magnum 4" drop (narrowed). I removed the disc and went with the lincoln brake for the same reason you listed. The challenge is if you increase the backspacing, you may start to rub on the inside (frame/splash guards) area. I should be back up and running in about 2 months based on other changes, so like I said I haven't road tested this combination yet, but I understand you concern.
have done several with the magnum axle--have used both 15x5 and 15x6 with those size tires. The critical measurement is from the mounting surface to the lip on the outside--no more than 3 1/8. A centered 5" wheel measures this but be sure to ck before buying.
I followed his rule on my 40 SD with a Magnum axle, 185x70x15 tires on a 15x 5 rim and they fit perfect. A dropped stock axle is probably a safe bet with this set up. You can make a jig and measure the correct offset also. Lynn
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