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Soft Sand & Tires
I have a 1997 Cannondale hybrid I use for beach crusing ONLY and I want
to make it the most efficient for getting through soft wet and semi wet sand which is like ridding through glue (good workout for the knees though). I am constantly is my lowest gear and when I get a little wind in my face and the sand is real soft it stops me in my tracks. I've ordered a new cassette with larger sprocket but I want to get new tires(I have 700c's, 38mm front and a 42mm rear now( not knobbies but some tread). I'd like to get a pair of 47mm wide slicks. The problem is the rear tire will fit between the chain stays(frame) but with only a mm or 2 of space to spare. If my wheel were to go a little untrue or the tire gets slightly deformed it might rub against the chain stays. Is there a minimum amount of space between the tire and the stays that you go by? COULD I FILE DOWN THE CHAIN STAYS A LITTLE? Are the chain stays hollow or are they solid aluminum? Do you think these 47mm's are the best choice or should I just stay with 42's? Should I get a little tread for the front tire? And finally, what pressure should I fill them to to get the lowest rolling resistance for wet sand?. I weigh 200lbs? I have read Sheldon's site on tires and I'm not sure what he means by "Narrow" back. How much narrower? This is from Sheldon's site. Hope he doesn't mind me posting it here. · Off-Road Issues Bikes that are used some of the time on loose surfaces often benefit from a wider front tire, with a fairly agressive tread, coupled with a somewhat narrower, smoother rear tire. The wide, knobby front tire will provide the all-important front wheel traction. If your front tire skids, it almost always leads to a crash. For riding in soft conditions, such as sand or mud, a wide front tire is essential. If the front tire sinks in and gets bogged down, you're stuck. If the front tire rolls through a soft patch OK, you can generally power the rear through to follow it. The narrower, smoother rear tire will have lower rolling resistance. Since most of the weight is carried by the rear tire, rolling resistance is more important on the rear than the front. If the rear tire slips, in most cases the worst that will happen is that you'll have to get off and walk http://www.sheldonbrown.com/tires.html One last thing, here's the tires I'm looking at. Harris doesn't have 700 x 47 on their site. They are hard to find. http://www.bicycletires.com/tek9.asp...cific=joopdpg8 Thanks |
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#2
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Soft Sand & Tires
John wrote:
I have a 1997 Cannondale hybrid I use for beach crusing ONLY and I want to make it the most efficient for getting through soft wet and semi wet sand .... (I have 700c's, 38mm front and a 42mm rear now( not knobbies but some tread). I'd like to get a pair of 47mm wide slicks. The problem is the rear tire will fit between the chain stays(frame) but with only a mm or 2 of space to spare. The Michelin Transworld City 700x47 is a street tire with a very tall casing for its width. That is, it has an oval cross section with the short axis across the width of the tire. Since it's not even close to an actual 47mm wide, it fits in frames that other tires of similar outer diameter will not. OTOH, it will need more tire pressure to resist rolling off the rim than a tire with a short profile would need. You can probably get away with a tire that leaves just 2mm of clearance on each side, but it might rub occasionally when you're really honking on the bike. 3mm per side is a much safer bet. COULD I FILE DOWN THE CHAIN STAYS A LITTLE? Are the chain stays hollow or are they solid aluminum? Do not, under any circumstances, file your frame. It's made of thin aluminum and you will destroy it before you get any meaningful change in tire clearance. I have increased tire clearance on frames before by using a ball peen hammer as a punch, but I wouldn't recommend it in your case. Just live with the tire clearance you have, or get a mountain bike with lots of room for fat tires. Do you think thesee 47mm's are the best choice or should I just stay with 42's? Fatter is better, as long as it fits without problems. Should I get a little tread for the front tire? It won't make any difference in soft sand, in my experience. And finally, what pressure should I fill them to to get the lowest rolling resistance for wet sand?. The lower the pressure, the easier it will be for you. Every little bit helps a /lot/. Bring a frame pump and gauge with you and experiment to see what you can get away with. On sand, you'll be able to run pressures that would almost guarantee pinch flats if used on pavement. How low you can go is directly related to your weight and the tires' width. You should be able to use at least 20% lower pressure in the front than in the rear, for the same size tire. I have read Sheldon's site on tires and I'm not sure what he means by "Narrow" back. How much narrower? This is from Sheldon's site. Hope he doesn't mind me posting it here. For sand, you really and truly just want to use the widest tires you can. If you get a "twenty-niner" suspension-corrected fork (or a suspension fork), you'll be able to use the colossal 700x60 Schwalbe Big Apple in the front. That would be an excellent choice. 30 psi is plenty for that tire on a soft surface, and you may be able to use much less than that. http://harriscyclery.net/site/page.c...=49&SKU=FK0004 http://www.unicycle.com/shopping/shopexd.asp?id=674 Chalo Colina |
#3
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Soft Sand & Tires
Chalo wrote: snip For sand, you really and truly just want to use the widest tires you can. If you get a "twenty-niner" suspension-corrected fork (or a suspension fork), you'll be able to use the colossal 700x60 Schwalbe Big Apple in the front. That would be an excellent choice. 30 psi is plenty for that tire on a soft surface, and you may be able to use much less than that. http://harriscyclery.net/site/page.c...=49&SKU=FK0004 http://www.unicycle.com/shopping/shopexd.asp?id=674 Chalo Colina I'll ditto Chalo. Fatter floats better. If you want to give up on the Cannondale, this is the fattest: http://www.hanebrink.net/etb/index.html Jeff |
#4
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Soft Sand & Tires
"Chalo" wrote: (clip) The lower the pressure, the easier it will be for you. Every little bit helps a /lot/. (clip) ^^^^^^^^^^^^^^^^ By lowering the pressure, you are causing the tire to bulge to a width which would not fit between the chainstays or fork, but, since the wide part stays at the bottom, you can get away with it. As Chalo says, on sand, pinch flats are not a problem. And also. since traction is so poor, the side forces on the bead are not likely to pull the tire off the rim. You will probably find that it is best to run the tires almost flat. (Don't forget to add air if you leave the sand, though.) |
#5
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Soft Sand & Tires
Thanks for your imput Chalo wrote: The Michelin Transworld City 700x47 is a street tire with a very tall casing for its width. That is, it has an oval cross section with the short axis across the width of the tire. Since it's not even close to an actual 47mm wide, it fits in frames that other tires of similar outer diameter will not. Interesting, it got me thinking if the tires I have on now are really the width that they claim to be. I measured them and found out they are not. The 38mm is really only 34mm and the 42mm is really only 38mm wide. Both are different make tires. Is this common for tires to be a shorter width then they're marked for? John |
#6
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Soft Sand & Tires
John wrote: Interesting, it got me thinking if the tires I have on now are really the width that they claim to be. I measured them and found out they are not. The 38mm is really only 34mm and the 42mm is really only 38mm wide. Both are different make tires. Is this common for tires to be a shorter width then they're marked for? John Measured width in bicycle tires is tricky. To some degree, the tire's width depends on which rim the tire is mounted on. If the rim is on the narrow side, the tire will measure narrower than its nominal width. The marked width *should* be the width of the flattened-out casing, measured bead-to-bead, divided by 2.5. I *think* this is the ISO/ETRTO method of determining a given tire's width. I've never been able to turn up a reference to this standard, though. Of course, the manufacturer could simply be untruthful: http://www.sheldonbrown.com/tire_sizing.html#dishonest Jeff |
#7
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Soft Sand & Tires
John wrote:
Interesting, it got me thinking if the tires I have on now are really the width that they claim to be. I measured them and found out they are not. The 38mm is really only 34mm and the 42mm is really only 38mm wide. Both are different make tires. Is this common for tires to be a shorter width then they're marked for? It's very common. So common, in fact, that the only way to know for sure what size your tire will be is to mount one, inflate it, and measure it. It's a decent rule of thumb, in my observation, to assume that a given tire is one size category smaller than claimed, e.g. "35mm" is actually about 32mm, "38mm" is more like 35mm, etc. Probably three out of every four tires I've tried come out that way. Chalo Colina |
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