I could use a little education here...and maybe some others could too!
I've looked at (not studied) your site and seen the different compressors listed. From what I've surmised is that all the compressors are basically the same except for volume and pressure. I'm not completely sure if they share the same motor, but those may change also.
For me, its all about how long it takes to air up my tires. I like how you list them by tire size, but I'm the guy who would buy the 37" compressor to fill my 33" tires faster...and have room to grow when its time for new shoes (tires). I also understand the use of a tank and its advantages.
But my question is this... What stand alone compressor gives you the best bang for your buck and why? Is the 450 over the 400 worth the extra bucks? Does it have a better motor or compressor unit? Is the only difference the motor? If you were going to recommend someones FIRST compressor, what would it be?
Dino - KX6D
Those are definitely good questions and I will be glad to answer them all for you. In my answers, I am referring to VIAIR compressors.
All the VIAIR compressors will basically have similar motors, some larger than others as they are designed to run for longer periods of time with less heat generation (referencing the 100% duty cycle). The main difference being the RPM in which they run. This has an effect on the CFM, but so does piston size, etc. They are brush style motors and all (except for the smallest 90 series compressors) have thermal overload protectors built-in. They are direct-driven with no gears and are an oil-less design. All use the same style piston seal, connecting rods, cylinder wall, etc.
The slower running compressors can run much longer, and in some cases continuously, but have a lower CFM rating because of it. The faster compressors can't run as long, before they need to be rested and cooled down, but do offer a higher CFM rating.
Being that all VIAIR compressors have the same basic motors & components, the main things to look at are CFM, pressure and duty cycle. With all of these considered, I believe the best VIAIR compressor for all around use is the 400C, for most people's applications.
Although it has a 33% duty cycle, it can still be ran for up to 20 minutes @ 100 PSI, before needing a rest. Now that being said, all duty cycle ratings are shown using a constant PSI, which is 100 PSI. If you take that 400C with 33% duty, and run it around 50 PSI, you essentially can run that compressor for about 30-35 minutes. This is because it is operating at a lower PSI, not creating as much load on the compressor motor, keeping it cooler and allowing it to run longer before resting.
So, you can actually use a 400C to fill 37" tires, if you are only filling to 30 PSI or so. Because it is a lower pressure, it not only shortens the fill time, but also means the compressor has more duty cycle because it is only filling to 30 PSI. You would not
hit the duty cycle limits before you were done filling all the tires to 30 PSI.
If you are looking to fill 37" tires to 60 PSI, then the 450C would be a better choice, because the actual fill time would be longer, calling for a 100% duty compressor. If that all makes sense. In other words, because a 37" tire to 30 PSI would not take as long to fill vs. a 37" tire to 60 PSI, this means the 400C won't hit it's duty and you can use it for a low pressure 37" (or maybe even 40") tire.
Because we don't know what exact size tire & pressure the compressors will be used for, we try and recommend based on a general consensus. This is why you see the 450C rated for 37" and the 400C rated for 35". But in some cases, like Jeep guys, the 400C will work on 37" tires because of the low pressure usually ran.
I hope this info has helped, and not made it more confusing. Sometimes this info can be confusing, but I tried to explain as best as possible and relate to real-world scenarios. In your case, i think you would be happier with a 400C, even if upgrading to a 37", because of it's speed.