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Discussion Starter · #1 ·
G'day Blokes.
I'm not so happy with the way my IKON sprung Bonnie handles the bends.I'm thinking of bolting the Bonnie motor into a XS650 Yamaha frame and turning it into a real cafe racer.Them old 650s were the good gear on the corners.I remember em well!!!!.
Suggestions and comments appreciated.
Catch ya. Macca. :-D :moon:
 

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Never heard that 70's Jap frames was anything special...
(more that they flexed and were prone to wobbling)

What do you mean is wrong with the handling of your Bonnie then?
I agree that it feels very slow handling compared to my SV650, I believe one reason for this is the 19" front wheel.

Do you have standard length rear shocks? Putting on loger rear shocks (e.g. Truxton) will give you more height in the rear and a little less rake at the front.

There's also a thread on here about putting a SV front end on a Bonnie.
 

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On 2007-02-28 06:12, ivar wrote:
Never heard that 70's Jap frames was anything special...
(more that they flexed and were prone to wobbling)

What do you mean is wrong with the handling of your Bonnie then?
I agree that it feels very slow handling compared to my SV650, I believe one reason for this is the 19" front wheel.

Do you have standard length rear shocks? Putting on loger rear shocks (e.g. Truxton) will give you more height in the rear and a little less rake at the front.

There's also a thread on here about putting a SV front end on a Bonnie.
The real issue effecting handling 'quickness' is not the size of the wheel, per se. Rather it is the longer trail on the Bonnie vs. an SV650 (or other more sport oriented bikes). The trail (I hope I get this right, if I screw it up I am sure someone will correct me) is the length of the line on the ground between the location of the center of the wheel and an imaginary line drawn through the pivot point of the steering (center of the head bearing) and parallel to the forks. If I understand this right, there are three things that effect the trail (in decreasing importance):

1) The angle of the steering head (remember the imaginary line is parallel to the forks so the shallower the rake angle the farther that line will be from the center of the wheel when it intersects the ground).
2) The size of the wheel, a taller wheel should result in a larger trail because the imaginary line has more distance to travel and will intersect the ground farther forward.
3) The offset of the top of the forks from the center of the head bearing. This is probably a negligible effect.

A shorter trail creates a quicker turning, less stable bike.

Is any of this helpful? You should be able to calculate how much a smaller wheel will change the trail via simple geometry (the rake angle for all of our bikes is published on the Triumph web site and all of the other parameters can be measured easily). I think (if I remember correctly) Bonnie's have trails of 110mm, Scramblers 105mm, Thruxtons 97mm, and SV650s are in the 80s. I have no idea what the XS650 had for a trail.

I guess I am bored at work today, is any of this helpful?

Fred
 

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I'll pipe in here because I know a little bit about XS frames. I've hardtailed one, and hacked on 2 others.

The XS frame was last made in 1983 I believe, so over 20 years ago. This should be where I say "END OF STORY" but I'll continue.

The bonnie motor is big, and tall, compared to the XS motor. If you've ever pulled an XS 650 motor out of the frame you would know how big of a pain in the ass it is. There are 6 (I think) mounting bolts that hold it in place, 2 in front, 2 plate setups on top, one under the motor, and a bolt at the rear, and 2 plates at the rear, so that's 8 actually...

In order to fit a bonnie motor into the XS frame you'd have to fab all new mounting locations, as well as probably cut/raise the backbone to fit the taller motor.

Are you going to stick with the stock 35mm XS650 forks? I sure wouldn't, so how about a custom front end setup $$$?

The XS rear swingarm sucked the big one, custom bronze bushings cured it a little bit, but it's still a 30-40 year old design....

Is it possible you just have warm fuzzy (hazy) memories about the XS? :hammer: :hammer:
 

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Good explanation Fred. The funny thing is that some folks think the Boonie steers too quickly, and try to slow it down with wide tires; oy! And Sweatmachine, I think you summed up the situation quite well.

A '78 XS-650 was my first bike. I thought it handled pretty darned good, at the time. I could even get the front tire to howl in some corners; they were Continental's I believe.

When I got my second bike, a bevel drive Ducati 900SS, well that propelled my idea of handling into a different universe. But the Duck was a really slow steerer, and it took quite a bit of input to set it up for a corner, but then again you could steer it with the throttle in tight corners.

I sold that Duck to buy a BMW R100RS thinking all expensive bikes would handle as well. Wrong! They didn't nickname the BMW's rubber cows for nothing.

But be that as it may, I can still ride my 30 year old BMW R75/7 significantly faster on the rough and curvy back roads around Northern California than I can my '06 Bonnie. I partially chalk that up to 30 years experience on BMW's and the over-sprung and under-damped shocks on the Bonnie. Beyond that, and with nearly twice the fork and swingarm travel the BMW has in comparison to the Bonnie, plus the lower center of gravity of the BMW, those old airheads are pretty potent backroad weapons.

Maccaoz, I think you've gotten excellent advice from those folks who recommended working to modify what you have, but if you have to have an XS-790 good luck.

[ This message was edited by: Jimbonnie on 2007-02-28 14:52 ]
 

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One of the changes I had done to my T100 recently was to have the front end lowered (by raising the forks in the triple tree). I asked for 1/2", but it looks like maybe 5/8. The difference is subtle, but it's there (a little bit quicker).
 

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I say phoey on the nay-sayers and make it happen. Definitely post pictures and progress reports....
 

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Discussion Starter · #14 ·
G'day Blokes.
Thanks for all the comments and advise,you are all wrong but dont let it worry ya.Just wait untill I get her going(Its a she because its a bitchen bike).I cant wait to stick it up that OZBON in the twisties,when he gets well!!!
MY other project is to turn the R90sBMW into a chopper,Good idea or what????
Catch ya around the traps. Macca. :-D
:wow: :) :moon: :upthumb:
 

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Maccaoz build that thing ride it up to cairns and I will race you up the Gillies range with my Thruxton. After I stop at the top and smoke a ciggie waiting for you we can discuss where you went wrong and if you beat me to the top I will go home get on my Ducati and we will try it again :-D
 

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Sorry, I didn't know I was being salty lately, I wished you guys would have let me know in the past when I wasn't being salty!

Guess being elbow deep in this motor has made me push my sweet side to the back burner for a while. I'll be all smiles when I fire this puppy back up though.
 

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"MY other project is to turn the R90sBMW into a chopper,Good idea or what?"

An excellent idea.! There are far too many R90S's out there and it's getting to the point where I can hardly step out into the street to pick up the paper without getting hit by one. I always thought it would be cool to mount a twin beam Peterbilt headlight on one of them, you know, to make it look cool...
 

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Sweat-

Sweet and salty is what you want...like a Salted Nut Roll!

:-D
 
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