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I was shopping around for a tire air inflator for my car, and noticed that for a Viair 84/85P Model, it can pump 31" inch tires but has a work pressure of 60 PSI, compared to the 70/74P Model, which can pump 80 PSI, but are only rated for 225/60R18 sized tires. It seems as though with this product modeling, it's inferring that size affects the working PSI of the device. This is just my guess though.

I figured that it doesn't matter what the tire size is, because the size wouldn't affect the PSI. It will still take the same amount of effort to push 35 PSI in bike tire as it would a car tire, right? Not necessarily the same amount of energy, but in terms of effort, shouldn't it be the same? The only thing I can think of, where the tire size affects the air compressors operation, is that the device would have to sustain pushing 35 PSI for longer periods, because the size is larger, but why would that make any difference? Shouldn't an air compressor be able to sustain pushing 35 PSI for a prolonged period of time?

I must be missing something.

Narcotixs
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1 Answers1

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Checking the spec sheet on line it appears the duty cycle of the Viair 84/85P Model is only 20 minutes. This is the reason for the tire size limitations. Basically they are trading off a low performance long running duty cycle for short term performance. You have to ask if you want a pump that will take 60 minutes to fill a tire, but could do it all day or a pump that can fill up a tire in 20 minutes but then has to cool down before the next 20 minute cycle.

mikes
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