Have 78 Elky. Plan on 2" drop spindals want to go with 17"x8" Centerline Galaxy wheels. Just need to know what backspacing. Tires will be Firestone Firehawk SZ50 EP 205/40ZR17

A 4 or 4 1/2 would be the best. The tire you want to run sounds a little small. The smallest I have run is a 215/45R17, and that was with about 3 1/2" of drop.

A 4 or 4 1/2 would be the best. The tire you want to run sounds a little small. The smallest I have run is a 215/45R17, and that was with about 3 1/2" of drop.I'm only going to run a 1.5" or a 2" drop at the most.

Don't forget you'll need to re-calibrate the Speedometer, probably new drive and driven gears depending on the overall diameter of the wheels/tires.

Don't forget you'll need to re-calibrate the Speedometer, probably new drive and driven gears depending on the overall diameter of the wheels/tires.Not a problem, the speedo doesn't work right now, so I'll do all that at the same time. 8)

If that is all you are lowering it, I would go with a 245/45R17. It will fill the fenderwell better. The added width will also help your handling, and the extra sidewall will help protect those new rims.

where do u go to get your spedo calibrated and mechanic shop a tranny shop or what?

where do u go to get your spedo calibrated and mechanic shop a tranny shop or what? I would think most tranny shops could do it for you.

is it expensive?

VERY FEW shops can calibrate a speedo, you'll probably need to ask around. I live near the largest cities in the state and there are only 2 shops within 50 miles that do speedo work and they don't advertise. Ask a few of the local shops where they would send it.

the website for TCI transmissions has a speedometer calculator, enter your rear end gear, tire diameter, and plug in a drive gear and it'll give you a driven gear number. if you don't know your drive gear number just look at the chart for your tranny and start plugging some in until you get it as close as you want, then buy both the drive and driven gears and a new clip, they're pretty inexpensive and not that hard to change.