Does tire size play a big role?
Ever since i switched to these 45 series tires i've had vibration at high speeds. I'm going to have the balance checked on them tomorrow but i was curious to know.

 

bump.

 

Yes it does. The smaller the tire the faster your DS will spin and the more likely/sooner it will fail. It's not so much speed of your vehicle but the speed of your DS and that's relative to the combination of your tire size, tranny gears and rear end gears.
I was able to go 120ish before I started noticing issues with my DS but that was due to my 3.23 gears(which let me drive faster while keeping DS speed down) and my tires size which were a bit bigger.

 

Okay that's what I thought. My tires were 1 ounce off balance but still getting vibration. with my 55 series i could do 120+ and never feel vibration. with the 45 series i feel vibration starting at about 95-100 ish.

what's a DS cost now days? (i have a 2 piece)

 

Do a key word search on Google with the following:
- Driveshaft
- Critical speed
- Pinion angle
- Harmonics
- Vibration
- Balanced
- Phased

 

Here is a link to a driveshaft critical speed calculator. You will need some detailed measurements and physical properties, but this will give you the exact RPM that a shaft will start to whip itself into scrap.

Keep in mind that if you accelerate through the critical speed fast enough, you get another RPM operating range (before the next harmonic) where the shaft will stabilize. At the next harmonic, the shaft will again go critical, and if held at the critical speed, will self destruct.

 

anybody know the thickness and material of the stock aluminum shaft?

 

The shaft on my truck (04 RCSB) is roughly 58"-60" or so and has never blown at 130mph, and I have done it many many times. It doesn't even vibrate.... What truck has a 80 something inch long shaft? Crew cab? Heck, I don't think my shaft is alluminum, it's steel. WTF?

 

trucks with short shafts including the two piece guys didn't get aluminum.

 

Okay, I don't know if that is good or bad, but at least mine has been good so far. Got 60,000 on it though, I will probably want to put new U-joints in it soon. I know their is a difference in weight, between steel shaft, and alluminum shafts, but what power gains are there really? I would think it would be marginal at best to go from a steel shaft to alluminum shaft. Maybe I am wrong? Is there a company selling aftermarket shafts that are balanced well for RCSB trucks?