Confusion about the multiple tyre designations

[iansoady]

Please forgive the lengthy introduction - I will get to the point!

I've been a casual cyclist for many years, usually on our annual caravan journeys to France. Since having a replacement knee some years ago I found my existing bike (a Saracen mountain bike) hard work as my knee wouldn't bend far enough to pedal properly. My brother, who is far more au fait with these things than I am. pointed out that MTBs have a higher bottom bracket therefore if the saddle was low enough to reach the ground the pedals were too high. Obvious when you think of it.

So I (and my wife who has a similar problem) donated our bikes to the Re-Cycle scheme and I've bought a fairly well used Dawes Mojave. I realise this is far from state of the art but it is so much easier on the knees - I may even be tempted to do more cycling in this country!

Now to the point. This bike has 700 x 35C tyres with Presta valves. I've replaced the rear, which was showing signs of heavy wear, and have bought a Schrader adapter to inflate it via a foot pump. However, my Schrader pressure gauges fail to work with these adapters. Is there a special pressure gauge for these valves?

I've had old British motorcycles for the last 50-odd years so am very familiar with mechanics in general but the specifics of pedal cycles seem to have moved on dramatically since my teenage years. When I last looked at wheels and tyres they were either 26" or 27", and this 700C stuff has me rather confused.

Anyway, many thanks for bearing with me (if you have indeed) and thanks for any pointers.

[mjr]

Ignore everything except ISO sizes. All others are confusion, especially things like 700x28C and 700x35C because the C denotes a width anyway!
https://www.cyclinguk.org/cyclists-libr ... tyre-sizes

I've been a casual cyclist for many years, usually on our annual caravan journeys to France. Since having a replacement knee some years ago I found my existing bike (a Saracen mountain bike) hard work as my knee wouldn't bend far enough to pedal properly. My brother, who is far more au fait with these things than I am. pointed out that MTBs have a higher bottom bracket therefore if the saddle was low enough to reach the ground the pedals were too high. Obvious when you think of it.

So I (and my wife who has a similar problem) donated our bikes to the Re-Cycle scheme and [...]

Did you try just raising the saddle to the correct height?

Now to the point. This bike has 700 x 35C tyres with Presta valves. I've replaced the rear, which was showing signs of heavy wear, and have bought a Schrader adapter to inflate it via a foot pump. However, my Schrader pressure gauges fail to work with these adapters. Is there a special pressure gauge for these valves?

Presta pressure gauges exist, but it's generally better to use a pump with a gauge built in IMO.

[iansoady]

Did you try just raising the saddle to the correct height?

Yes I did and spent many happy hours fiddling with it. If it was high enough to let my knee articulate properly I couldn't reach the ground so often dismounted in an untidy heap; if low enough to get my toes on the ground I could only pedal by having my instep on the pedal rather than the ball of my foot as I was taught many many years ago.

The Dawes is definitely far more comfortable and even my first attempts are far better. I looked at elevation drawings and the bottom bracket is 66mm lower than a line through the wheel axles rather than the MTB being approximately on that line hence definitely nearer the ground.

[Mick F]

This bike has 700 x 35C tyres with Presta valves. I've replaced the rear, which was showing signs of heavy wear, and have bought a Schrader adapter to inflate it via a foot pump. However, my Schrader pressure gauges fail to work with these adapters. Is there a special pressure gauge for these valves?

Yes there is.

There's loads of them out there.
Some do both Presta + Schrader, and some just Presta.

Just Google "bicycle pressure gauge" or pop into your local bike shop or Halfords.

[simonhill]

Basically you set your saddle height in relation to the pedals, not to whether you can touch the ground. I suggest you Google how to set up your saddle height and position. Probably easier than me trying to explain.

I wonder if that old Saracen was one of the early hand made 531 frames. I had one for many years, an original Kili Flyer.

[iansoady]

Yeah, but for those of us who are older and less flexible, touching the ground is quite handy.....

When I was a teenager I did know how to set up seat / pedals etc but losing some of the flexibility in my knee just made life more difficult. I even tried shorter pedal cranks on the Saracen which helped a bit but not enough.

The Saracen was an early 2000s model I think with an alloy frame and cheap front suspension.

[mjr]

Yeah, but for those of us who are older and less flexible, touching the ground is quite handy.....

You're not supposed to touch the ground while you ride When you do need to touch it, you either tilt the bike or hop off the pedal (or cheat like I do by holding posts or putting feet on fence rails to avoid getting off when waiting at junctions)... but I suspect the bike was even higher than a plain MTB to cope with the suspension and sometimes there are just bikes you don't get on with, I know.

Just wondered, that was all. It read like you'd gone straight from "this bike is too high" to "new bike!" pretty quickly. Glad you gave it a chance.

[iansoady]

I'd actually had the Saracen for about 10 years (since before my op) so think it had a very decent chance! My wife had had hers (Dawes Watoga) for about 20 years so they'd earned their keep if only for a few miles at a time along French lanes. Remember that our use is very low energy / short distance so convenience is a higher priority than it would be for many other people who live in the saddle.

For us casual riders, it is handy to be able to get on and off without contortions. I was finding with the Saracen I could only get off it by lying the bike on its side which, although I'm usually immune to what other people think, did feel a bit amateurish.

Many thanks for all the responses by the way.

[thelawnet]

I'd actually had the Saracen for about 10 years (since before my op) so think it had a very decent chance! My wife had had hers (Dawes Watoga) for about 20 years so they'd earned their keep if only for a few miles at a time along French lanes. Remember that our use is very low energy / short distance so convenience is a higher priority than it would be for many other people who live in the saddle.

For us casual riders, it is handy to be able to get on and off without contortions. I was finding with the Saracen I could only get off it by lying the bike on its side which, although I'm usually immune to what other people think, did feel a bit amateurish.

Many thanks for all the responses by the way.

It depends if you have mobility issues but generally you just sort of lean the bike over at a slight angle from the vertical and get over it that way, and when you are stopped at lights and want to put your foot down likewise just lean slightly and put your foot on the ground. (The top tube will need to be lower than your inside leg, but the saddle should be quite a bit higher) Obviously if you are wearing a hooped dress that might be trickier.

[thelawnet]

Now to the point. This bike has 700 x 35C tyres with Presta valves. I've replaced the rear, which was showing signs of heavy wear, and have bought a Schrader adapter to inflate it via a foot pump. However, my Schrader pressure gauges fail to work with these adapters. Is there a special pressure gauge for these valves?

A pressure gauge might fit Schrader, Pressure or both. Not special particularly.

Generally you will want to use a pump like this for inflating bike tyres.

https://www.wiggle.co.uk/lifeline-essential-track-pump/ Built in gauge, plenty of puff, two heads for either type.

I've had old British motorcycles for the last 50-odd years so am very familiar with mechanics in general but the specifics of pedal cycles seem to have moved on dramatically since my teenage years. When I last looked at wheels and tyres they were either 26" or 27", and this 700C stuff has me rather confused.
.

27" is almost the same size as 700c.

current 26" is a 559mm (22" ) rim, though there are other obsolete sizes calling themselves 26"
700c is a 622mm (24.5" rim)
27" was 630mm (24.8" rim)

If you put a 1.1" tyre on a 24.8" rim you end up with 27". If you put a knobbly 2" tyre on a 22" tyre you end up with a 26".

If you put a knobbly 2.25" tyre on the 24.5" rim you end up with 29", and that's what they call 622mm/24.5" rims with knobbly tyres on, even though they may be a bit more or less than that. It's the same rim diameter as a 700c, but 700c implies a narrower road-type tyre, not a knobbly one.

Basically if you buy tyres based on rim size it's the safest way.

[mjr]

26" is a 534mm (21" ) rim

Not the full story - 26" can be loads of things up to at least 597mm. See the link I posted in the first reply.

[thelawnet]

26" is a 534mm (21" ) rim

Not the full story - 26" can be loads of things up to at least 597mm. See the link I posted in the first reply.

yes I have edited that a bit now.

here's another page on the same https://www.sheldonbrown.com/26.html

[RickH]

If you have difficulty reaching the ground when you stop, you may be able to fit one of these new fangled dropper seatpost (that are getting popular with mountainbiker) to gracefully lower (& raise again) the saddle at the press of a button. The proviso are that your frame takes a wide enough seatpost (I think 27.2mm is the smallest) & you have enough seatpost showing (a modern sloping tob tube frame is more likely to have enough clearance that a traditional horizontal top tube frame.

[Brucey]

27" is almost the same size as 700c.

strictly speaking that is true but it implies that you might be able to swap tyres; you can't. BTW it is '700C' not '700c'

current 26" is a 559mm (22" ) rim, though there are other obsolete sizes calling themselves 26"

of the many 26" sizes only a couple are obsolete. The others are still being used. They all use different rims including those with 559, 571, 584, 590, 597mm bead seat diameter (BSD). The thing that makes them all 26" wheels is that when they are fitted with the intended (original) sizes of tyre, the rolling diameter is 26".

FWIW rim BSD values are difficult to measure directly (*); quoting BSD values in inches for bicycle rims is pretty much a waste of time; the BSD value in mm is mainly useful because it is also written on the tyres and tubes that you buy; unlike in car and motorcycle tyres a BSD size in inches is not usually marked on tyres and tubes for bicycles, so quoting those sizes in inches is just going to confuse people.

This page is what CUK presently offer;

https://www.cyclinguk.org/cyclists-library/components/wheels-tyres/tyre-sizes

which sadly (and amazingly) is both incomplete and contains multiple redundant entries, as well as numerous typographic errors. "Could do better".

https://web.archive.org/web/20160221203327/http://www.harwoodcycles.com:80/tyre_size.htm

If you are interested in the historical development of tyre sizes these pages are worth a read;

http://www.oldbike.eu/museum/tyres/pneumatic-tyres/the-pneumatic-tyre/

http://www.oldbike.eu/museum/bike-i-d/bicycle-tyre-sizes-conversion-chart/



All modern tyres and rims are based on the 'wire edged' designs in the chart above. These rims and tyres were popularised (but not strictly invented) by Dunlop. Most of the above sizes are still in use.

(*) in the 1911 chart it suggests that you measure the external size of the rim to see what size the rim really is. This is still reasonable advice.

Rim OD - (9/16" or ~14mm ) =~ BSD value.

Thus a 700C (622) rim usually measures ~636mm OD.

cheers

[foxyrider]

Yeah, but for those of us who are older and less flexible, touching the ground is quite handy.....

When I was a teenager I did know how to set up seat / pedals etc but losing some of the flexibility in my knee just made life more difficult. I even tried shorter pedal cranks on the Saracen which helped a bit but not enough.

The Saracen was an early 2000s model I think with an alloy frame and cheap front suspension.

But you missed the point, you don't set the saddle so you can touch the floor but so your legs articulate properly. On an ATB this will often mean you can't comfortably touch the floor whilst on the saddle, however, if the bike is the right size you should be able to comfortably stand over the frame with feet flat on the ground, yep you come off the saddle when you stop.

Not your fault if you were unaware of this but any half decent bike shop could have advised on that.

FWIW my Airnimal folder has a high BB too, I can tab a curb but have to come off the saddle if the floor is flat about.