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I've never known much about those multi-pumps. I just have a shock pump that I leave at home or in the truck while I'm on the ride and carry CO2 with me on the trail for the tires. Never had the need to pump up my shocks while riding, and not a fan of frame pumps because of their size and weight.
 

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Discussion Starter · #3 ·
Yea, had a situation today, where I let out to much air from the fork, and it was a little to soft for the rest of the ride. Would have loved to have a pump on the trail to add more air. Doesnt happen often that I need one, but figure Im gonna do a 100 miler later this year, and it might be nice to have in case I need to change air pressures at some point in the race.
 

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Shock pumps and tire pumps serve two different purposes. It would be great to have an all-in-one that works great for all, but it would be difficult to achieve... Tire pumps pump volume, while shock pumps are designed for high pressure. As of now, it is best to carry both or have lots of patience (and arm endurance) and carry a shock pump...
 

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it would take a loong time to pump up a tire with that, but it would serve to function as both. Topeak makes a similar item.
The only problem with use as a shock pump is that the accuracy of the dial isn't going to be as compared to a dial with a range of say 150-250 vs 0-300.
 

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Discussion Starter · #6 ·
jrabikerepair said:
Shock pumps and tire pumps serve two different purposes. It would be great to have an all-in-one that works great for all, but it would be difficult to achieve... Tire pumps pump volume, while shock pumps are designed for high pressure. As of now, it is best to carry both or have lots of patience (and arm endurance) and carry a shock pump...
Both pumps would do the same thing, as the other poster posted. It WOULD take a while to pump up a tire with a shock pump, as the volume of the compressed air is small, BUT they both do the same thing, and eventually will reach the same pressure. To say that one cannot function as the other, is incorrect.

Imagine some gas inside a piston. If you compress the piston, the volume will decrease, and the pressure will increase correspondingly.
 

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I should have reworded what I said. I apologize.
It would be very difficult to correctly add air to a shock with a tire pump. The pressures needed for many shocks are at or above the pressure limit of many tire pumps.
I understand they both pump air, but the volume and pressure of air created by each type of pump is too different to effectively make an all-in-one pump.
 

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Discussion Starter · #9 ·
The overall pressures should be the same, its just how fast they can get there.Of course at some point in time, you need to be able to compress enough volume to overcome the pressure already in the fork/shock/tire, etc.

I think Boyles Law would apply here.

A low volume pump, such as a shock pump will allow finer degree of pressure differences since it cant compress or reduce as large a volume of air, and in turn wont produce as much pressure.

A tire pump on the other hand, will compress more at a given time, meaning that it can reduce the volume of air more, leading to more pressure out.

I think that both pumps would reach the same outcome. I would probably assume that the designers of such pumps would be able to "valve" the pump to allow the user to switch between two settings that would allow tire inflation or a shock/fork inflation. Or maybe the valving is internal and dependent on the pressure it sees. When it sees a low pressure such as a bike tire 2-50 psi, it behaves one way, and when it sees a high pressure such as 100-140 psi for a shock or fork, it would behave another way?

Who knows?

Ok wierd, just found this thread on a google search, but didnt find it using the search on the forum???

http://forums.mtbr.com/showthread.php?p=4111138
 

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I have that exact same pump and carry it in my kit. It has two modes: high pressure, low volume (for shock inflation) and low pressure, high volume (for tires). All it takes is a twist of the knob on the end of the pump handle.

It works decently for shocks, though I would like it if the gauge had more graduations to be more precise.

It will inflate tires, but in 'V' mode, it still takes a while because it has such a short body and stroke.

I carry it in my hydration pack.
 
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