Gum's CRUMPTON UL 4.40kg, 9.70lbs

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nicrump
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by nicrump

bikemaniack wrote:The frame is only few grams heavier than the frame from "World lightest bike" project.


but clearly has at least 4cm more head tube and seat tube to fit Gum.
Last edited by nicrump on Fri Jan 20, 2012 4:55 pm, edited 1 time in total.

nicrump
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by nicrump

The main thing that is different about this frame than what I have done with ULs in the past is the main tubes. They are Isogrid of which you can google for more details but essentially the ID has a +/- grid of bundled tow which do the bulk of the work. The grid enables a much much thinner tube wall. The tube walls are 57% thinner than the thinnest tube wall i have ever used in the past. While you do rob peter to pay paul, paul gets a tad less and the excess loss is enjoyed in overall weigh reduction. While a 57% reduction in wall sounds fragile, it sorta is but not really. The grid is tight and very stable. If one damages the tube wall say to an focused impact, the grid will likely survive and prevent crack propagation. The main purpose of the wall(or skin) is to transfer load form grid to grid. These are the lightest tubes the Isogrid guys have made to date.

As far as I know, we are teh first to do tube-to-tube building with this stuff. You usually see it in Ti lugged frames form teh likes of Holland, Santana and the old Titus. Here is a pic of the inside surface of an Isogrid tube.

Image

by Weenie


artray
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by artray

nicrump wrote:The main thing that is different about this frame than what I have done with ULs in the past is the main tubes. They are Isogrid of which you can google for more details but essentially the ID has a +/- grid of bundled tow which do the bulk of the work. The grid enables a much much thinner tube wall. The tube walls are 57% thinner than the thinnest tube wall i have ever used in the past. While you do rob peter to pay paul, paul gets a tad less and the excess loss is enjoyed in overall weigh reduction. While a 57% reduction in wall sounds fragile, it sorta is but not really. The grid is tight and very stable. If one damages the tube wall say to an focused impact, the grid will likely survive and prevent crack propagation. The main purpose of the wall(or skin) is to transfer load form grid to grid. These are the lightest tubes the Isogrid guys have made to date.

As far as I know, we are teh first to do tube-to-tube building with this stuff. You usually see it in Ti lugged frames form teh likes of Holland, Santana and the old Titus. Here is a pic of the inside surface of an Isogrid tube.

Image

Hi Nick. Is it possible to replace a top tube or down tube on a bike that is already light and make it lighter using the isogrid ? My bike frame weighs around 770/780 grms. Say I replaced two of my main tubes would i get a significant weight loss. I know it depends on the weight of my tubes but im sure you could make a decent guess .

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Fuchspk
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by Fuchspk

Like I said, I understand why you have them like this.
And they are not bad.

But I think it would be better to switch them around 90 degrees
Keep them quite short in the front and an long angel at the back and the fibers in 45degree.

I am on my phone right now but can make a sketch next time on the computer to show how it if you want.

And please,do not take it the wrong way, I do not mean to put that frame "down"
It is just something I was thinking about :)

nicrump
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by nicrump

don't judge these by this single angle pic. they are flat on housing entry and tapered at the back slightly shallower than the sides. they are co-molded in place at the same time the joints are cured. they are not secondarily bonded. The design was driven by bench tests.

there are many aspects to keeping these things on the tube and in the case of these tubes, I mentioned earlier how thin they are, with a smaller foot print the tube can become excessively distorted under a heavy load at the stop. like so many things in designing a carbon frame, surface area is boss.


Fuchspk wrote:Like I said, I understand why you have them like this.
And they are not bad.

But I think it would be better to switch them around 90 degrees
Keep them quite short in the front and an long angel at the back and the fibers in 45degree.

I am on my phone right now but can make a sketch next time on the computer to show how it if you want.

And please,do not take it the wrong way, I do not mean to put that frame "down"
It is just something I was thinking about :)

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kgt
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by kgt

nicrump wrote:Image

Nice engineering! :thumbup:

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Fuchspk
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by Fuchspk

Okej,maybe that was the problem. On the pic they seem to be very wide but short.

Always kinda difficult to judge thinks on the internet.


Quick question, these special tubing, isn't this "just" a special kind of filament tubing? Looks cool for sure.

nicrump
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by nicrump

an isogrid marketing video. not very technical but go to 2:00 min in and keep watching. in my case, no Ti at the ends. Just a carbon tube.

http://www.youtube.com/watch?v=uwAT4SzqrVI" onclick="window.open(this.href);return false;

gumgardner
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by gumgardner

fallen86 wrote:with all the razor-blade work you do on your components i would have guessed you'd go with a nude carbon finish instead of a matte black... 30 grams in paint? blasphemy! :evil:


I spoke with Nick today and he thought it was best to go with the clear coat. Not only for the finishing 'look', but also because it'll add some protection against strand fraying since only small amounts of "glue" is used. Something like that.

Nick strongly recommended the coating, so I'm going with it. He knows much more than me.

mises
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by mises

Does it use a Deda rear triangle?

Thenewguy11
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by Thenewguy11

Whoa, another gum thread that I have to follow. Crumpton bikes are just ridiculously nice. One of these days . . .

nicrump
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by nicrump

artray wrote:Hi Nick. Is it possible to replace a top tube or down tube on a bike that is already light and make it lighter using the isogrid ? My bike frame weighs around 770/780 grms. Say I replaced two of my main tubes would i get a significant weight loss. I know it depends on the weight of my tubes but im sure you could make a decent guess .


may be possible depending on the frame but not a service that I offer.

justkeepedaling
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by justkeepedaling

Very nice, a bit lighter than a R5 CA (after clearcoat), but probably a little bit less stiff and a bit more fragile. Still, it's going to have that nice custom feel and that light weight.

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split
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by split

Hmmm, how many pages can we get this to before the bike reveal?
S P L I T: 2010 Meivici: 14.4 lbs | 2003 Odile: 19 lbs | Hunter Cycles Cyclocross: 17 lbs | 2013 Dundee Cycles Jewell 29er: 17 lbs

gumgardner
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by gumgardner

I could get it real high if you want to see the components that are going on :mrgreen:

by Weenie


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