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Old 02-06-09, 11:51 AM   #1
stratman
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Dahon Jack sizing

Hi folks,

Following excellent advice on this forum I'm probably going to buy a Dahon Jack soon. Their sizing is S, M, L. Which I think corresponds to 16", 18", 20". According to their charts I should get a Medium.

In bare feet I'm 5'10" and my inseam is 33".

Comfort is my main concern, so I'll want at least the option of adjust handlebars to a more sitting up position. This is far more important than being able to get a head down racer posture.

Is the Medium still the best option? I'm assuming that raising the handlebars (and dropping the saddle?) is the way to get the posture I want.

I'm probably going to do this on an internet purchase, so don't think I'll have the chance to try the two sizes out.

Many thanks, the stratster
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Old 02-06-09, 02:46 PM   #2
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18". I'm about 3/4 inch taller, and my Cadenza fits me perfectly. I have my bars almost at the top of the stem, which leaves me pretty much upright, might try lowering them as I do want that 'head down posture' from time to time.
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Old 02-06-09, 06:23 PM   #3
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Stratman, you're around the height where either size would be acceptable, but the medium size will likely be the better fit.

I'm 5'9", 32.7" inseam. I can ride bikes between 17.5"-20" nicely, but occasionally 20" bikes leave me stretched a bit past my comfortable riding position. I suspect you may be a close story.
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Old 02-06-09, 08:31 PM   #4
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My Large Dahon Matrix felt (and, I think, was) a little smaller than non-folding bikes of the same nominal dimension. IMHO it's worth trying to find a couple to ride before making the purchase.
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Old 02-06-09, 10:56 PM   #5
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33" is your cycling inseam? You may not have enough seatpost extension on Medium Jack if so. I have 34.5" cycling inseam and have little seatpost room to spare on large jack. See thread on dahon forums where I asked same questions before buying.

http://www.dahon.com/forum/index.php...+jack+seatpost
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Old 02-07-09, 04:15 AM   #6
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Originally Posted by jagatron View Post
33" is your cycling inseam? You may not have enough seatpost extension on Medium Jack if so. I have 34.5" cycling inseam and have little seatpost room to spare on large jack. See thread on dahon forums where I asked same questions before buying.

http://www.dahon.com/forum/index.php...+jack+seatpost
Thanks.

In bare feet from floor to underside of crotch (hard up against it, where the top of a saddle would be!) is 33 inches. Is that the right way of measuring?

I've got a newish non folding 26" wheel. At first the saddle was a bit low. Even though I didn't need to, I sometimes stood up just to 'stretch my legs'. I suppose that gives me an idea. I'll keep adjusting that until I find a comfortable position, then measure the dimensions that count. BB to top of saddle, saddle to handlebars. I guess crank length ought to come into the equation. Then whichever Jack can be set up to give me the same dimensions is the one I want, I suppose.

I'm 50 and not going to be racing this. An upright position that keeps weight off my wrists is important, as is legs at almost full extension at the bottom of the travel. I think there's about 2 inches of adjustability in the handlebar stem.

Cheers, his stratness
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Old 02-07-09, 04:29 AM   #7
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OK. looking at the specs on Dahon's site, and the pictures, it looks like the top of the seat tube is very low, so even on the large I'll be able to get the saddle as low as I might want, whereas the danger is that with the medium I might not be able to get it as high as I want.

The Saddle to Handlebar distance doesn't seem to change much. In which case the only other variable is can I get the bars higher than the saddle enough to get the 'upright' position I want. But presumably (?) the relative distance off the ground of the bars/saddle is the same for the medium and large. What I mean is everything is higher on the large than it is on the medium, saddle/bars or whatever. So I can achieve the same sort of 'upright' or if I want it 'heads down' position on the large as I can on the medium. What will change is my leg length - i.e. saddle to pedal distance.

Am I thinking right here?

I'm not particularly worried about the slightly larger folded size of a large. This is a big folder, there's no way round that.
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Old 02-07-09, 05:09 AM   #8
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Originally Posted by stratman View Post
OK. looking at the specs on Dahon's site, and the pictures, it looks like the top of the seat tube is very low, so even on the large I'll be able to get the saddle as low as I might
I think that it basically has the effective top tube length of normally a bike one size smaller - I just measured two frames for comparison. A Nashbar 19" frame has a 22" effective top tube. The 20" jack has a 22". The poster from that other forum said a medium sized frame has a 20.5" effective top tube.

But the inseam will determine it for you - from the calculations I did, I think you'll be at the limit if not over the limit for the medium. So no choice.. it's already a 400mm equivalent seatpost. At 34.5", I have exactly 1 inch left before the maximum length.

Yes, you're measuring the inseam the "cycling" way - same method I use.

Go for the bike.. I've seen the ebay.co.uk 220 GBP price as well.. (the 18" was GBP, I was going to buy another for a friend). Normally only the US gets the good deals.

Last edited by jagatron; 02-07-09 at 05:14 AM.
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Old 02-07-09, 05:25 AM   #9
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Thanks very much for the advice.

It looks like the large would be better for leg length, yes?

If it turns out the bars are a bit to far away or too low, I could always replace them with something higher/nearer. Or infact with a greater sweep. I've got a far better chance of altering bars to suit than I have of changing the frame size, presumably.

I have an old Raleigh that I was given that has dead straight bars and I feel the strain immediately. Playing the banjo puts enough strain on my wrists already!! Never mind my ears (and the rest of the band, for that matter!). So buying high bars with a far bigger sweep (as in Pashley style) is something I am thinking of doing anyway.

Though I did read some advice somewhere that if in doubt get a smaller frame cause they're easier to 'make bigger'. Don't know how good that advice is.
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Old 02-08-09, 04:23 AM   #10
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Originally Posted by stratman View Post
It looks like the large would be better for leg length, yes?
Yes, the large will give you exactly 2" more room for leg length.

Normally you could "make a frame larger" (taller) by getting a larger seatpost.. but that's not so possible when you're already at the limit with a very long seatpost. These posts are already very long.

Yes, you can do some things to get the handlebars closer to you : different handlebars (like trekking), or shorten the stem. But the stem part is complicated since what comes with it is the particular NVO style, and it's not cheap to replace that with a shorter one.

For mine, I'm interested in doing what Sheldon brown has done here (I want a little less reach now too)

http://www.sheldonbrown.com/handsup.html

Threadless Without Spacers

Which will allow doing what the NVO does without its proprietary shim which opens up the availability of all stems.
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