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I'm switching to road cycling. My diminutive and portable pump will likely be a pain to get 120psi. Rather than get a foot pump with either a built-in or an external pressure gauge, I'm thinking of simply getting a pump for car tires that doubles as bike tire pump.

Despite the brand of the model I'm considering, it doesn't actually include batteries.

Powered tire inflation pump

I have two questions.

  1. Is this feasible? Can one fit a Presta valve on a pump such as the one pictured? A Presta valve is not listed among its paraphernalia. (I'm assuming the Schrader valve is identical on cars and bikes.)

The upper limit of pressure of the pump pictured is 120psi. This matches the needed pressure for the road bike tire. But it would have been nice if the pump were to exceed it ever so slightly.

  1. Would a pump rated at 120psi be sufficient for a tire needing 120psi? Or, conversely, is it a big deal if a road bike tire is inflated at only 115psi (because the upper limit is a theoretical, not actual, upper limit)?
  • The main issues are how accurately it gauges the pressure and how rapidly it inflates. The pictured pump will PROBABLY be OK for bike tires (except perhaps for really narrow tires). But it's impossible to say for sure. (Note that that Schrader valve is standard on virtually all automobile tires.) As to 120 PSI precisely, being 5-10 pounds under is generally not a big issue, plus you can always "top off" with a hand pump. – Daniel R Hicks Apr 3 at 19:52
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    @Swifty lol.. I'm switching from mountain/hybrid cycling. But there I never needed to understand the numbers on tires, since they last forever. With road cycling I understand that it's a major weak point that needs special attention. And the measurements for replacing them is the first question. Understanding the measurements is of course a separate issue/question. – Sam Apr 3 at 20:18
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    @Sam cool cool, I guess you can think of mtb tyres as 'wide', hybrid tyres as medium and road bike tyres as 'narrow' - they're getting wider with fashion but now are between 23mm wide and 28mm wide inclusive. Bike tyres are described by their inner diameter in mm then their width in mm, so 622-28 would be a road tyre which is 28 mm across. Almost all road bike tyres are used on 622mm rims, so only the width need typically be mentioned – Swifty Apr 3 at 20:21
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    @Sam the set and forget tyre inflators are a bad idea for bikes. They don't measure the pressure continuously but deliver air into an assumed large volume, pausing every few seconds to measure. When you put a small volume on there, the pressure in the tyre can get way over the setpoint in that few seconds. – Chris H Apr 3 at 20:23
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    Inflating road bike tires with a good track pump does not take a huge effort, and would seem to be simpler than a powered unit, and you will not have to screw around with schrader to presta conversions. – Argenti Apparatus Apr 3 at 22:29
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There's a lot going on in this question!

The pump pictured seems to be intended for car tyres, with Schrader valves, which can be considered high volume, low pressure.

A 120 psi road bike tyre can be considered low volume, high pressure, and will typically take a Presta valve to suit this status and the rim's valve hole. You can get adapters for pumping up your road bike tyre, but a cycling specific pump won't need this.

That said, 120 psi for a road bike tyre is considered excessive these days, it should be tailored to your weight and 100 psi is a bit of a ceiling for optimal rolling resistance (fashion alert). So its certainly no big deal if you only hit 115 psi, but I would be sceptical of the pump getting close to it's maximum rating. I imagine your portable hand pump is rated 100+ psi and probably v hard work to get even close, hence looking for an alternative.

By far the best thing to do is do like all the other cyclists who have solved this problem already and buy a quality, cycling specific track pump, not a car specific pump. For a road tyre it takes about the same time (# of strokes) to inflate even up to 120 psi, because of the low volume. It actually takes longer to inflate a large volume (26x2.35) mountain bike tyre up to pressure at 30 psi!

The upper limit of a bicycle tyre is the limit below which the manufacturer promises the tyre will not explode off the rim while you cycle along. Most riders should use less than the maximum for comfort and rolling efficiency; generally only riders at the heaviest end of the design weight will need to inflate their tyres to the maximum.

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  • Re "It actually takes several times longer ..": Thank you. That is precisely the problem I'm trying to solve. I expected the opposite. That reaching 120psi would take four times (divided by the volume ratio) what it takes to inflate a mountain/hybrid tire. – Sam Apr 3 at 20:21
  • @Sam ah, well the problem may not be there at all. It can take a bit more force on the pump in the last few strokes to hit 120 psi, but there are far fewer strokes to get there at all, for a narrow tyre. That added force is where a track pump excels, I can't imagine inflating a tyre without one – Swifty Apr 3 at 20:23
  • It takes much more than four times longer to get to 120 psi than 30 psi. Those are gauge numbers (in excess of the 14.7 psi of the atmosphere) so you are actually going from 45 psia (absolute,including the 14.7) to 135 psia. However, you start with a cylinder at 14.7 psia and have to compress it to match the tire pressure. The remaining stroke of the piston sets how much gas goes into the tire each stroke. That is very small when you are at the upper limit of the pump. – Ross Millikan Apr 3 at 23:33
  • @Sam, I revisited the numbers, "several times longer" was a poor estimate on my part, but there is no extra time to inflate a narrow tyre even with a high pressure, because the tyre volume is so much smaller. I just did this practically with 4 different tyres, the 2 road and one basic mtb tyres took a comparable number of strokes ~30(road just edged less) and the larger (tubeless) mtb tyre took 44 strokes (it measures 61 mm across). – Swifty Apr 4 at 9:25
  • @Sam re your comment, if it were to take four times (divided by the volume ratio), but the volume ratio is around 4, then it takes the same time(!) This is borne out in my test, and just doing the maths on Torus shapes, a mtb tyre has 3.5 - 5 times the theoretical volume of a road tyre. – Swifty Apr 4 at 9:55
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Buy a floor pump, also known as a track pump, instead of an automotive accessory.

A track pump will take about the same time to top up your tires as a small car compressor, and has an advantage of not needing electricity at all.

You still need the on-bike pump for punctures while riding, but in the garage at home a track pump works very well. I ended up carrying a smaller track pump on my bike instead of a minipump.

Do get one with a gauge - doesn't matter if its analogue or digital but estimating tyre pressure by squeeze isn't ideal. A track pump will last you decades, where the small tyre pumps tend to fail in a few years.

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Incidentally - I've tried to use my big track pump to add some air to a car tyre, and after 10 minutes I'd raised it from 20 PSI to 22 PSI. If you want to inflate car tyres as well, get both. One pump will not do both jobs well.

My car tyre compressor stalls out at around 70 PSI despite being "rated" for 175 PSI - there is no way it can pump up a road tyre and if I did, would have to finish it off with the hand pump anyway.

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I have one of such compressors for car use and of course I have used it on my bikes.

However, I only use it on MTB bikes which I inflate to 40 psi at most. I Do not own a road bike but some slick tires sometimes inflated up to 60 PSI. For MTB tires the compressor is slow enough to allow very accurate pressure control.

The problem I have faced is that as the pressure increases, so does the load on the compressor's motor, in turn the amperage it consumes and that heats the connector. The connector heated enough to blow a thermal fuse in the cigarette lighter socket (I could replace only recently). I is a design flaw in an otherwise very capable compressor.

For Car tires I have no trouble at all since they are used at 33 psi in my case. (Small pickup truck or smaller) For such uses it does heat up, but not as much.

In conclusion, depending on the design of the compressor you acquire, it may not be worth the hassle that it could cause if it damaged your vehicle's socket. Most small cars do not use high pressure tires, and even though the compressor's seller may label it as capable of achieving 150 psi I seriously doubt they actually test the product to such extents (I have seen ones with a depiction of it being used to inflate a tractor tire as tall as an adult, but the construction quality was very cheap, thin cable, lousy connector.)

A proper track pump is way less hassle in practice. There are pumps more suitable for road tires and other are better for MTB, and there are even dual volume pumps. Having the proper valve chuck is faster than dealing with adaptors every time.

A pump can also be used away from the car. I have been to events where I have to park away from the start/finish area or the area where one could perform last minute calibration or puncture repair. I've also have been in the situation where the adjacent cars are too close to allow for the bike to be close enough to operate the compressor on it.

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The valve connection is simple, there are adapters for Schrader on Presta, some cycle pumps have these as standard. Your LBS may sell these as extras as well.

Problem would be pressure. Does the pump really deliver the indicated pressure.If the max. pressure delivered by pump is 120psi and your tyre needs more you can't just let it run for a longer time to fill in more air.

The opposite may be more problematic. If your pump delivers a large volume quickly and your tyre only requires 90psi, you may easily over-inflate it because when stopping the pump there is always a delay. If there is a pressure activated switch to turn off the pump at a preset, is that one accurate and consistent. So you'd need a precise gauge anyway.

A track pump with a manometer, activated by muscle power is the better solution for cycle tyres. The pressure is easier to control and the required volume of air is small enough not to call for a motor-driven pump. A further advantage is that the possible pressure is often higher than 120psi.

However, if you use tubeless tyres you may need a more sophisticated hand pump, one with a storage tank that is brought to pressure prior to inflating the tyre. It is then connected to the valve and the air is released to the tyre in one explosive go to seat the tyre bead in the rim.

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