http://www.balloonbikes.com/template...r/grafik-1.jpg

Hi,

I have no doubts they can work up to 100psi but the physics of a 1.5" tyre
don't change with the numbers printed on the sidewalls. 100psi is 6.9 bar
which is rock hard for a 1.5" tyre, no doubt they'll have low rolling resistance.

The implication the chances of a bent rim or pinch flats increase at 50psi
is just plain wrong IMO, that implies 100psi is somehow optimum, and
my research and experience indicates
its way too high for a 1.5" tyre.

(The research indicates optimum tyre pressures are inversely related
to the tyre width, are about the same for a given width, and you gain
little with much higher pressures, except on very smooth tarmac, the
rest of the time the teeth rattling ride actually slows you down.)

The pressure needed to avoid pinch flats depends on the tyre
width and not much else, its not related to tyre pressure ratings.
(Unless the tyre is very heavily loaded, so they would matter.)

On my (non suspended) folder 50psi in 1.75" tyres is way too hard for
the front, probably about right for the rear (weight dependent), still
experimenting with the front, I think about 35psi goes with 50psi rear.
(I'm average weight). 1.5" tyre pressures would be somewhat higher.

I don't think its goofy to run your tyres at the best all round pressures,
what is goofy to me is the "harder is always better" school of thought.

rgds, sreten.

As your graph shows the important thing is to have enough pressure.
Then I'd say the better the surfaces you ride on, up the pressure more.
Better riding technique on poor roads allows you to run higher pressures.

I agree that it isn't goofy to run tires 'at the best all round pressures' but I think it's goofy to base optimum tire pressures on size alone especially when tire sizes can vary between manufacturers... my 20"X1.50" Kenda Kwests are narrower than my 20"X1.50" Schwalbe Marathons. There's also more than size to take into consideration like the rubber compound, tire wall thicknesses and carcass construction.

**UPDATE**
Incidentally, the Schwalbe Marathons have a suggested pressure range of 55-100psi yet are as wide as some cheap Kenda 20"X1.75" I have lying around. Now, srtn, I would have to ask you, who's suggestion do you think I would trust... yours or the designer/manufacturer of the tire?

the chart that you referenced is for balloon tires. the recent discussion was regarding narrow high pressure tires. these tires (primo comets, for example) were designed and formulated to be inflated to high pressures to reduce rolling resistance for smaller wheels. that is the purpose.

http://bikeforums.net/attachment.php...hmentid=300997

Hi,

I'm not suggesting you can simply calculate optimum tyre
pressures, but you can calculate / find ballpark numbers,
and pressures way off that are very low or usually very high.

You can find graphs for 15% tyre drop for different loads
and different tyre widths. The article states around 15%
was found to be ~ optimum. Some may prefer more
(lower pressure), some may prefer less (higher pressure),
but the general gist is for a lot more you lose far too
much in rolling resistance, and for a lot less you lose a
lot of comfort for some advantage on smooth but lose
out on rougher surfaces, the harder the tyre the more
easily you lose out on less than smooth surfaces.

Smaller wheels deform more than bigger wheels so
probably for folders the optimum is lower than 15%,
assuming rolling resistance is sidewall deformation.

I imagine having 100psi in a 1.5" front tyre on my
bike would be horrible, 50psi and 1.75" was too
hard and bouncy for the roads that I ride on.

I've got my back tyre near its (low) maximum
and set the front so it seems a little harder
over bumps and ripples, 20-25% lower.

Good tyre pressures are a compromise.

I'm just implying if I fitted 1.5" tyres to my
bike and pumped them both up to 100psi
because that is the max on the sidewalls,
I'd basically be losing out overall compared
to a more considered approach to settings.

rgds, sreten.

Hi,

I think its pretty clear who you should want to trust.

My observations are me trying to work things out, and
I certainly don't want them taken on trust, they are
food for thought and your own experimentation.

rgds, sreten.

Hi,

Whilst that graph compares a balloon tyre to a more typical tyre,
the same sort of thing applies to a typical tyre and very narrow
tyres, narrow tyres need very high pressures to avoid the sort
of things you were talking about, pinch flats etc.

I wouldn't call 1.5" "narrow" but they are labelled "recumbant"
tyres, which is pretty specialised compared to my prosaic folder.

rgds, sreten.

http://www.bikequarterly.com/images/TireDrop.pdf
http://janheine.wordpress.com/2012/0...ance-of-tires/
http://www.biketinker.com/2010/bike-...-for-bicycles/

quoting myself... sad.

I've heard they're quite susceptible to punctures.

big apples have thin stretchy sidewalls. although i've never experienced it, i can see how sidewall punctures could be fairly likely. if you are looking for a wide (1.9 +) high pressure tire that is super rugged, i would suggest the maxxis hookworm. sounds like an intestinal parasite, but is actually a very nice riding and aesthetically pleasing tire with wrap-around tread. comparatively heavy though..

http://bikeforums.net/attachment.php...hmentid=301033

Hi,

No. I quite agree. I just needed some input for sensible experimentation.
The eyeopener was to run the front and rear at different pressures and
now I'm just pumping up the tyres to what seems good, not a psi number.

The theory helped in why I didn't like both tyres at maximum pressure.

rgds, sreten.

Back in the late 70s I would inflate the tires of my air-cooled (rear-engined) VW bug (per spec) at about 18 psi front and 30 psi rear... because the weight bias of the car and the tire technology of the time dictated that. So yes, I agree that weight bias is a factor in what the working psi of a tire should be. But spec'd psi numbers have their place if not to at least offer a starting point from which to work from.

This is the same setup I run on my Moulton APB. The Marathon Plus's are very puncture resistant and a very long lasting tyre.
Highly recommended! I run them at about 50 psi. Very comfortable. Enjoy the Big Apples Elvis - they are what I'll be putting on my Surly Ogre that I'm currently building up as a long distance tourer.

also, the overdrive elite is maxxis answer to the schwalbe marathon. its a great tire:

http://www.ebay.com/itm/Maxxis-20X1-...item5d39d60d07

http://www.77bike.com/bbs/attachment...ce083e2f2b.jpg

http://www.77bike.com/bbs/attachment...b76d71274e.jpg

http://www.77bike.com/bbs/attachment...00d214434b.jpg

Good luck rebuilding your Raleigh 20. I rebuilt one a few years ago. I brazed on pegs for cantis. These days I might use V brakes, but my limited experience with drum brakes has been such that I would not use them. What are you doing with the headset? Mine had a plastic sleeve on top. I measured carefully and had the head tube trimmed for a real headset. I also installed real dropouts front and rear and made mine a derailleur bike. I put the front derailleur on a plate extending aft to allow for the low chain line of 20” wheels. I spread the rear dropouts to 135 and use MTB hubs. The 20” wheels are 406 with aluminum rims on Deore XT hubs. I also cut the bottom bracket and installed a normal 68mm BB. Someday I may get around to painting it.

I am a Clyde and I only inflate my 20x1.5" tires to 65 psi or so (rear). At the moment I am using Greenspeed Scorcher and they are the fastest I have found.

My approach is quite unscientific, i.e. 'If this tyre was the sole of a shoe, would I walk around town in them without worrying about my feet being mangled?'... ;)

http://www.chainreactioncycles.com/M...?ModelID=94600

Hi,

Just because I like trusting my instincts, after doing some
research, I've ordered one for the rear wheel of my cheap
folder, I hope the picture is right, the description wrong.

The current tyres are "superdiamonds" aka "wandakings"
and look very similar to the Kenda Konnect BMX tyres.

Not saying its going to be ideal, but it seems good value.

rgds, sreten.

According to the site the Schwalbe Tracer's maximum load rating is "70". I wonder what unit that is because if it's pineapples, I'm getting a set for my trailer.

Hi,

I know its a trailer tyre but for a 20" rear tyre under £10,
I haven't found anything likely to be better than fitted.

I think just used as a rear tyre it could be very good value.

rgds, sreten.

Hi,

I'd assume that is Kg,
bar rating is 1.5 to 3.5 according the the UK site :
http://www.schwalbe.co.uk/special-purpose/tracer/

rgds, sreten.

My current tyres are max 3 bar, max 65 Kg.

that's 70IPU (International Potato Units)

http://bikeforums.net/attachment.php...hmentid=301354

That's a little odd to suddenly throw in an Irish unit of measurement.

My Pilots arrived yesterday. They look great. I bought lightly used rims on ebay, and they weigh only 300 grams each. The tires are light, too. This will be a FAST Twenty! Too bad I didn't see those Schwalbes before, because I could have saved a lot of money, but that's OK.

ClemY, this is my second Raleigh Twenty project. The first one I did way back in 1980. After I was done, I still didn't like it and gave it away. I put a Sturmey Archer S5 (5-speed) hub on it. I also used drop bars, alloy rims, BMX tires, and I don't remember what.

This time, I got a threadless 1" headset on rhm's advice.

I used this drum brake hub on a Surly Cross Check, and it was an excellent brake. Control is excellent, and so is stopping power. Plus, in the rain and snow, it won't be any worse, except for my tires' traction on the ground. I shouldn't need to maintain this hub for another 30 years.

Mrs 'you have more photos of your bike than you have of me' Shumaker's cute new bike comes sensibly equipped with 2.125 Big Apples (she won't ride a folder) - http://www.fahrrad-xxl.de/shop/media...g-2012-1-2.jpg. She has a deep-seated fear of tramlining a wheel - and that can't happen with fat tyres.

I couldn't be happier with them, they have improved the handling of my bike no end. 30 psi seems to be the sweet spot.

When I rebuilt the Raleigh 20 I left on the flat bars. It is for my wife and her sister when she comes to visit. You are having a better time with the drum than I ever did. I have a Maxicar drum tandem wheel and an Aria drum, neither of which is strong enough to use as a main brake. While I was putting descent dropouts in the fork, I also built up the unicrown area with more brass. It just looked too insubstantial to me.