[pawn]

Can anyone tell me what a CB 450 frame tubing diameter is? Specifically I'm planning to rid myself of the stock hoop under the seat and weld in a loop so I can make a very flat seat.

thanks

 

[tbpmusic]

The two frame tubes that run rearward under the seat are about 25mm.
The main tube that runs rearward under the tank is at least 51mm in the narrowest spot.

Both measurements will vary a bit, as there are all sorts of gussets welded on them.

 

[66Sprint]

Two points.... The upright "hoop" as you call it is only a bit < 3/4" above the apex of wheel/tire travel...If your "flat" seat sits appreciably lower than the "hoop" did, the wheel can literally wedge and stop against its bottom side........ Longer shocks could help minimise this.......
Second point.....Why can't you just measure the tube diameter of YOUR frame?...I don't get it!....

 

[pawn]

thanks. You're saying the wheel travel will come close to that hoop? I really didn't think it was that close since under the fender (when it was on on my bike) there was plenty of space between metal and tire. Also, yes, I have lowered suspension in the rear which means stiffer and less travel. I didn't think it would have a possibility of the wheel traveling between the frame all the way up to hit a seat pan. Am I really that off in my vision of what goes on when I hit a bump?

I can't measure it because it's under a lot of things right now and I can't get to it in my shed. There's fiberglass curing on a buck on the bike, a lawnmower in the way, and I don't have a compass, or a caliper to get an exact measurement, and I didn't want to use a simple ruler in case I measure wrong. I figured it wouldn't hurt to ask on here.

 

[tbpmusic]

thanks. You're saying the wheel travel will come close to that hoop?

It's very common for bigger than stock tires to rub under a 450 rear fender, so yes it is closer than you might think.
May not look like it when it's up on the stand, but under load it will rub at times.
Better the fender than your butt, eh??

But it's your bike, so just tell us about it and post some photos.....

 

[pawn]

I want to do a seat like the one in the pic in the link below:

http://4.bp.blogspot.com/_hKkYZ9GWzKA/S ... urBrat.jpg


as for my bike...nothing special. Picked up the CB450 almost two months ago for $500. Cleaned the carbs and set the time as per your instructions from another thread, and it runs very well. Stock everything aside from the new rear suspension. Going to run straight pipes wrapped. My stock mufflers are all but swiss cheese and don't really baffle much of the sound. Maybe eventually I will have a pipe with a washer for back pressure welded up and couple that with the header, but for now I think the header's going to have to do. I'm trying to do this as cheaply as possible because I'm getting married shortly, and need all my money for the honeymoon. I don't have any pics of it though unfortunately. Since I have no internet at home (personal choice...i get enough of it at work) I can't really upload any images and it's kind of a hassle to bring my camera in...and to top if off my work Mac has a busted usb port so I can't even use m'damn thumb drive. Some day as soon as possible I'll throw some photos up. Most likely after I get the front brake, seat, and handlebar, taillight, and license plate bracket mount situated.

 

[66Sprint]

If you look closely, you can see that bike's owner has re-fabricated an upward loop (out of tubing).....Plus those shocks appear to be longer than stock, and set at a more severe angle, which means the swingarm was lengthened too....... I kinda like the "dragster" look though..... Steve

 

[pawn]

even so, look at that fender...it can't be more than an inch away from the tire, so you'd assume he's rubbing fender on a regular basis. I doubt that the hoop is as high as the stock hoop. I'm not sure if I set my suspension to it's hardest setting that I would have a problem with wheelbite. But I will certainly take that into account and test it out before I do any real welding.

 

[tbpmusic]

Try it - if it's too low you can always cut it out and do something else....

Wow, that would put a "skid mark" on your shorts pretty good......