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Old 11-02-2011, 05:21 AM   #31
sailah
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I use 1" & 1.25" DOM tubing mostly in 0.065" wall. I do have some heavier wall tubing but as I remember back from naval architecture school, the way to decrease weight and maintain strength is to minimize wall thickness (or plating in a boat) and increase the depths of the supporting stringers and frames. I am NOT an engineer so let cosman walk with that one.

I also use those sizes because they match the bending dies I have for my hydraulic tubing bender., which is important in that most of the tube work I use is not straight.

DOM welds nice, finishes nice, esp if you are tigging it.

I have use just regular seamed tubing on the CBR because I needed some heavy stock for the shock brace and I had it on hand.

I've never used cromo tubing, mainly because of the cost and the welding sounds complicated. I'm not building bikes to shave the last couple pounds off, I'm building them to ride and have fun. If someone gave me a good reason to use it I would, but so far the DOM tubing has been great and its what most Harley, rockcrawlers, regular racer types use.
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Old 11-02-2011, 10:09 AM   #32
Lambo
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Tubing

Sailah,

Thanks for the reply, is that 1018 DOM? I am always concerned about weight...thecosman would you weigh in re: 4130?
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Old 11-02-2011, 10:12 AM   #33
Bleached
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Here's a question! Just posted it in my new thread. Post #3 regarding a bushing between the steering stem/top triple.

http://advrider.com/forums/showthread.php?t=738523

Thanks!
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Old 11-02-2011, 10:20 AM   #34
sailah
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Quote:
Originally Posted by Lambo View Post
Sailah,

Thanks for the reply, is that 1018 DOM? I am always concerned about weight...thecosman would you weigh in re: 4130?
Honestly no idea. Probably. I got out from metals depot online. I bought about 10 sticks sy once.
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Old 11-03-2011, 06:11 AM   #35
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Quote:
Originally Posted by Bleached View Post
Here's a question! Just posted it in my new thread. Post #3 regarding a bushing between the steering stem/top triple.

http://advrider.com/forums/showthread.php?t=738523

Thanks!
Instead of turning it down and adding a shim why not tap it for a bolt instead of a nut?
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Old 11-03-2011, 09:10 AM   #36
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Sorry if this is too rinky dink a question for y'all's awesome knowledge, but I figured I'd ask anyway. I want to change a bike from a 16 rear 18 front (rims) to a 18 front 18 rear. I've been told (inter webz) that this will greatly effect the handling of the bike. The only reason I'm doing this is I think it would look better, and I can't leave well enough alone. What do y'all think? Will the handling be 'different', meaning I'll have to get used to it, or will the handling be 'different' I'm going to kill myself? If it matters, the bike in question is a cb250.

( I just re-read what i wrote- seems the kids these days call something 'awesome' if they want to mock it, but i mean 'awesome knowledge' in the 'I'm awed by your knowledge' way! )
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Old 11-03-2011, 12:30 PM   #37
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Thanks! Kinda...........I only have the fuzziest notion as to what trail is, and what changing it will do. Also, what/where exactly would I be measuring? Also also, what does slow my steering down mean? Make it less responsive to inputs?
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Old 11-03-2011, 12:57 PM   #38
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Thanks again! that's just what I'm looking for. you've been very helpful.
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Old 11-04-2011, 10:13 AM   #39
CosentinoEngineering OP
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oops, sorry

Wasn't getting updates form some reason.

For frame tube material there is not much practical difference between CREW, DOM, or 4130. CREW and DOM are plain low carbon steels. For a given diameter and wall thickness all 3 have the same weight and stiffness which is the primary factor in frame design. The main material difference is that the 4130 has a higher yield strength than the other 2 but no material should be subject to stresses near yield in normal operation. Crashing is a different story but then again if you crash you should expect your frame to get bent. I think it was Kevin Cameron who said that his riders could not crash in a controlled enough manner to stay under the 4130's yield point so it was a wash.

With that said, I still like to use 4130 material in my frames. I find the higher quality material has better straightness and profile accuracy mainly due to the fact that it is a more expensive product. It does require care to be taken not to use too much heat when welding so has some drawbacks but they are not insurmountable.

For a beginning welder I would recommend using CREW or DOM. There are much less welding related strength and brittleness issues when compared to 4130 and we all must learn to walk before we can run. Once you've got some fab experience under your belt try some 4130. you may like the better accuracy or may consider the additional price to be a waste and stick to mild steel.


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Old 11-04-2011, 10:23 AM   #40
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rim size

>>Sorry if this is too rinky dink a question for y'all's awesome knowledge, but I figured I'd ask anyway.
>>I want to change a bike from a 16 rear 18 front (rims) to a 18 front 18 rear.

Like they said in school the only bad question is the one you don't ask.

The key to look at here is the overall height of the rim/tire assembly. The 18" tire may have a lower profile than the 16" one so the difference may be less than the rim size.

Swapping out the rear will have less of an effect than changing the front but with no other changes you will have a higher rear ride height which would result in less steering trail which would tend to make the steering feel faster.

If it is a twin shock rear bike you could find slightly shorter shocks to compensate and keep the bike in the same front/rear ride height. Mono shocks are more difficult to do this with but some do have built in ride height adjustment which would come in handy here. You could also drop the forks in the triple clamps but then the entire bike will be higher, may be good, may be bad depending on how tall you are!

Whatever way you go, definitely start slowly and see how differently the bike is behaving so you don't go flying off and hit a car or tree.

This is also a good reference for bike geometry: http://www.tonyfoale.com/Articles/index.htm


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Old 11-07-2011, 12:27 PM   #41
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Rodger that on the whole 'go slow' thing!
Thanks for the encouragement on my 'rinky dink' question. You never know what your going to get on the inter-web, but having read through the thread I had a feeling y'all would be cool.
I've done a good bit of reading and i've come to the conclusion that it'll probably be fine. Still, I'll take it slow.
It is a dual shock setup, with lots of adjustment. That was a good point, and likely to come in handy.
The only real doubt i have at this point is the choice of rims. I have a parts bike for this model (nighthawk 250). My plan is to take the 18, 1.85 front rim and lace the back hub to it. i know that 1.85 is less then idea for a back rim, but lots of well known and popular bikes (cb350 for one) ran this size, so I figured it would be ok. Am i wrong about this?
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Old 11-07-2011, 02:40 PM   #42
CosentinoEngineering OP
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Ivan,

Rim width on the rear is not as important as using the proper width tire for the rim. If you put a wide tire on a narrow rim you will deform the profile and that could result in weird turning behavior. Too narrow a tire on a wide rim may not seat fully and allow it to slip. Don't worry if your front and rear tires are the same size, most bikes have oversized rears that only serve to look cool but in reality make the bike slower turning and sluggish. With a 250 you won't be worrying about spinining the rear up so a smaller tire may make the bike easier to turn with no drawbacks. That does not happen often!


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Old 11-07-2011, 06:45 PM   #43
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great! very encouraging! thanks
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Old 11-13-2011, 03:46 PM   #44
muddriller
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on one hand.....

I need to make a decision about the direction I want to take as I modify a four stroke thumper. My bike, KLX 650R, has a nikasil jug. I can either overbore,and line the cylinder and get a big bore engine( and lose the coated cylinder), or I can get a
high compression piston and a stroker kit. What should I be looking at to help with the decision?

Thanks

Todd
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Old 11-13-2011, 06:15 PM   #45
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should have added....

Expense isn't a big issue. The bike is plated so reliability needs to be considered. Am looking for big horsepower gains and all are invited to comment. Would like to hear from anyone that has done this type of project.

Thanks

Todd
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