Author Topic: to brat or not to brat (Read 10308 times)

FunJimmy · « **Reply #25 on:** April 03, 2015, 07:36:44 AM »

Sounds like you've put a fair amount of thought into it. I applaud you for keeping the side covers and airbox.
Will be interesting to see if you can pull off the seat without cutting the frame brace. It's pretty integral to the integrity of the frame but an impediment to the clean slab seat asthetics. If you're fabing up the Brat seat with some padding and comfort (height), could you mix it up a bit and integrate the brace into a small custom made lock box and tail light assembly? It's my opinion that a well crafted seat (of any style) fits the tank correctly too. Just thinking out loud.

FunJimmy · « **Reply #26 on:** April 03, 2015, 07:43:45 AM »

It also looks like you're comfortable with aluminum fabrication too.
Cal has a good point about rear-set location in relationship to comfort.
Pop over to my Interceptor build and look at my rear-sets.
You could easily make the brackets attach to the swingarm and engine bolts as I have. This would allow you to move them considerably further forward but back from stock as well. They don't need to be multi adjustable either. Flat plate aluminum is much simpler anyway.

jvandyke · « **Reply #27 on:** April 04, 2015, 09:52:12 AM »

I think the frame brace has to go, I have saved cutting it as long as possible trying a few ideas but no way to keep it without getting really ugly, going to try to cut carefully so re-welding in the future is possible. Maybe a faux oil cooler tank surrounding the bracket?
Hmmm that would be interesting
http://www.tcbroschoppers.com/electronics-tank-fake-oil-tank.html
Yes, no interest in the "empty middle" thing that's too much form over function for me.

mine isn't really a brat, more of a "resto-mod, tribute bike", little brat, little 50's Vincent, little Honda, just whatever elements I like

crappy artists concept

jvandyke · « **Reply #28 on:** April 04, 2015, 04:00:54 PM »

I'm planning on adding a front fender on the rear wheel. I mocked it up. It'll work. I think. My thoughts on riding position concure with yours. The seat will be far thicker than a a standard brat. Bars and rear set position can be tweaked ad nauseum until it's dialed in. 99% of my rides are 80 miles or less. That's what I'm building for.

jvandyke · « **Reply #29 on:** April 04, 2015, 04:39:01 PM »

How important is that rear hump? I'm thinking not so much given there is a brace running across the frame just in front of the shock mounts. Maybe running 2 up you'd want it. I'm convincing myself it's not super critical.

Retro Rocket · « **Reply #30 on:** April 04, 2015, 06:10:26 PM »

Quote from: jvandyke on April 04, 2015, 04:39:01 PM

How important is that rear hump? I'm thinking not so much given there is a brace running across the frame just in front of the shock mounts. Maybe running 2 up you'd want it. I'm convincing myself it's not super critical.

It is a brace and adds stability and stops flex to the rear of the frame from forces produced by the suspension, its well documented on the forum....

jvandyke · « **Reply #31 on:** April 04, 2015, 06:24:53 PM »

Quote from: Retro Rocket on April 04, 2015, 06:10:26 PM

Quote from: jvandyke on April 04, 2015, 04:39:01 PM
How important is that rear hump? I'm thinking not so much given there is a brace running across the frame just in front of the shock mounts. Maybe running 2 up you'd want it. I'm convincing myself it's not super critical.

It is a brace and adds stability and stops flex to the rear of the frame from forces produced by the suspension, its well documented on the forum....

Sorry, not being clear. I know it's recommended to keep but has anyone (and I did try to search) actually tested rigidity with and without it? Wonder if I could, markers and high speed cameras and lots of bouncing?

jvandyke · « **Reply #32 on:** April 04, 2015, 06:33:09 PM »

There's already a lot of metal tying those rails together (on a 500k anyway)

FunJimmy · « **Reply #33 on:** April 04, 2015, 07:07:50 PM »

His plan looks like he's cutting right behind the shock mounts. That's already a triangulated structure. I doubt there's much to worry about. Furthermore, hoops are pretty insignificant in their structural contributions. They are typically flat, thin wall tubing with a long reach. Better for finishing off the frame than they are at structural duty.

Bootsey · « **Reply #34 on:** April 05, 2015, 02:19:13 AM »

Shouldn't have to worry about getting cold feet with the current rear set setup

Feets007 · « **Reply #35 on:** April 05, 2015, 02:58:28 AM »

Do what makes you want to ride it! If your bike looks like everyone else's is it really yours. I have never met a bike I didn't like, though I have seen things I would change on almost every one I've ever seen.

jvandyke · « **Reply #36 on:** April 05, 2015, 05:08:54 AM »

Quote from: Bootsey on April 05, 2015, 02:19:13 AM

Shouldn't have to worry about getting cold feet with the current rear set setup

No kidding!

Here's a shot with the front fender laying over the back wheel, you can see the frame a little too, so much meat across the gap directly in front of the shock mounts I'm going to see how it seems with out an additional brace first. I've gotta hunt down another fender for the rear. I like that look and than I get a fender back there. Clearance issues may develop I know. New rear shocks may help......anyway. thanks again.

SOHC4 Cafe Racer Fan · « **Reply #37 on:** April 05, 2015, 11:19:59 AM »

Quote from: Feets007 on April 05, 2015, 02:58:28 AM

Do what makes you want to ride it! If your bike looks like everyone else's is it really yours. I have never met a bike I didn't like, though I have seen things I would change on almost every one I've ever seen.

Yeah, NO! Modifying a bike should not be just about aesthetics, but functionality! That cross-member (along with the one in front of the shock mounts) keeps the back frame rails from twisting out of square when the rear suspension exerts force on the frame. Even though the frame is fairly secure, I think it would be a good idea to replace the cross-member with one flush in height to the frame rails toward the rear end. It does not HAVE to be a hoop.

Both Jim and Cal are correct. Can you get away without it? Sure! But I think it would be a good idea to replace the support to preserve structural integrity.

jvandyke · « **Reply #38 on:** April 05, 2015, 01:14:54 PM »

As in most things, it's a compromise, middle ground and all that.

FunJimmy · « **Reply #39 on:** April 05, 2015, 03:14:16 PM »

It would be good if one (or two) of the engineering types would chime in here with some engineering calculus. From what I gather jvandyke is building to resemble the bike shown below and his sketch suggests cutting the frame spars just behind the shock mounts. Depending on the seat length this bike may be a monoposto, sans pillion. That being said, is there any likelihood that the frame would suffer torsional stress as a result of the intended frame mods? Crack out those scientific calculators and let's see the results.

Retro Rocket · « **Reply #40 on:** April 05, 2015, 03:35:10 PM »

Quote from: FunJimmy on April 05, 2015, 03:14:16 PM

It would be good if one (or two) of the engineering types would chime in here with some engineering calculus. From what I gather jvandyke is building to resemble the bike shown below and his sketch suggests cutting the frame spars just behind the shock mounts. Depending on the seat length this bike may be a monoposto, sans pillion. That being said, is there any likelihood that the frame would suffer torsional stress as a result of the intended frame mods? Crack out those scientific calculators and let's see the results.

You don't need an engineer Jim, Its well known in racing circles that the weak point in the back end is the swingarm/ rear shock section, thats an area that usually gets braced with an "X" shaped brace above the swingarm to try and lessen twisting forces in the back end, and small gussets in the corners of the rear triangle, removing any bracing material in the rear will lessen the rigidity and increase twisting... Look at a well braced frame and you'll see what I mean...

I wouldn't remove that brace on a bike I was looking to ride hard, and I would also add some bracing..

FunJimmy · « **Reply #41 on:** April 05, 2015, 04:52:33 PM »

Quote from: Retro Rocket on April 05, 2015, 03:35:10 PM

You don't need an engineer Jim

Don't say that Mick. You know what a sensitive lot they are.
You're absolutely right. Racing will exploit the strengths and weaknesses and I'm sure Buddy will be really pissed with his decision when he's turning some hot laps at the local track. He might even rethink the rattley fender on the back.

Retro Rocket · « **Reply #42 on:** April 05, 2015, 04:55:39 PM »

Quote from: FunJimmy on April 05, 2015, 04:52:33 PM

Quote from: Retro Rocket on April 05, 2015, 03:35:10 PM
You don't need an engineer Jim

Don't say that Mick. You know what a sensitive lot they are.
You're absolutely right. Racing will exploit the strengths and weaknesses and I'm sure Buddy will be really pissed with his decision when he's turning some hot laps at the local track. He might even rethink the rattley fender on the back.

I apologize to any engineers that were offended by the expression of my views.....

jvandyke · « **Reply #43 on:** April 05, 2015, 04:56:40 PM »

yep, that's the "inspiration bike" or one of them anyway, I'm just a layman of course but it sure seems like that stock hump is intended purely as a fender mount, it's thin and so tall it seems ill suited as a torsional brace, not saying it doesn't provide some but it would seem, to me, as untrained and inexperienced as I am, that ditching it wouldn't make much difference, especially on a bike designed to carry two, now only ever carrying one, of course I could be (and often am) dead wrong.
Track? Yeah right. Cruising to the bar with the boys once a week in nice weather, that's it. Some "hot laps' through the countryside once in a while.

Retro Rocket · « **Reply #44 on:** April 05, 2015, 05:02:09 PM »

Quote from: jvandyke on April 05, 2015, 04:56:40 PM

I'm just a layman of course but it sure seems like that stock hump is intended purely as a fender mount, it's thin and so tall it seems ill suited as a torsional brace, not saying it doesn't provide some but it would seem, to me, as untrained and inexperienced as I am, that ditching it wouldn't make much difference, especially on a bike designed to carry two, now only ever carrying one, of course I could be (and often am) dead wrong.
Track? Yeah right. Cruising to the bar with the boys once a week in nice weather, that's it. Some "hot laps' through the countryside once in a while.

Yeah, really, you should be fine if its a bar hopper type bike, it won't ever see the stress some of us inflict on our old machines

I will correct you on the brace though, its a lot stronger than you think, look at its design, rolled edges and raised sections , width and so on, its dual purpose, support and box in the rear frame around the shock mounts and hold the fender, when you remove it, try and twist it, you'll be surprised..

....

FunJimmy · « **Reply #45 on:** April 05, 2015, 07:32:29 PM »

Not the front end or tank that your other inspirations reflect but I love how tidy the rear is.

jvandyke · « **Reply #46 on:** April 05, 2015, 08:12:45 PM »

outstanding stuff, thanks for all the input, will devise a cross brace, can't hurt, only help, something else fun to do!
on vacation now, can't wait to get back and get the thing road worthy and start tweaking, this is my first foray into "customization", till now it's always been maintain
I've never enjoyed a project more and am already scheming on more bikes. (moving into a new place with a shop next fall).

WnRn · « **Reply #47 on:** April 06, 2015, 01:51:33 AM »

Can't wait to see the end product mate.

jvandyke · « **Reply #48 on:** June 05, 2015, 05:50:57 AM »

Sorta done. No seat cover yet, waiting to get a few more rides to be sure the seat design is okay.
Really like it.

Since put side covers on.
Made cell phone holder on 3-D printer to use as speedo. Lots of tweaks to do and seat cover to make but I really like it. Clip ons and rock hard grips are brutal on the hands but that's expected.

jvandyke · « **Reply #49 on:** June 05, 2015, 05:58:47 AM »

Quote from: calj737 on June 05, 2015, 05:57:39 AM

hope you wear asbestos lined socks and shoes while riding. Your feet will get cooked by those pipes.

Yep, designed in feet warmers. All part of the master plan.

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Author Topic: to brat or not to brat (Read 10308 times)