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27.5 degrees 3.98 inches
23.6 degrees 3.8 inches
23 degrees 2.48 inches

Those are for my bikes BMW, MV and Montesa, note the MV has almost the same as the trials bike, those bikes are both kick ass responsive as the numbers would imply,
the beemer is a sport touring bike, handling is perfect suited to the autobahn but limited to period design tires just like your bike.


... shortening a suspensions travel on a road bike is completely contrary to a motorcycles safe handling, performance wise it's just dumb if you're planning to give a fast motorcycle about the same usable suspension travel as a honda 90 step through, makes no sense unless you're going to ride it at scooter speed.
+ no way an informed motorcycle mechanic is going to sign off on that modification, you need to find one that doesn't have a clue :|

Hey, you want to try a trials bike? that would be good for a laugh
 

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Discussion Starter #82 (Edited)
alright I measured everything out more precisely. Accommodated for the grade on my driveway as well. Here is the numbers:

Rake: 27.2°
Tire Radius: 25.795" (110/90/R18)
Triple Clamp Offset: 2.375"
Fork Length: 29" 3/4

Using the https://www.rbracing-rsr.com/rakeandtrail.html calculator that leave:

Trail:3.96"

Me being not so trusting of random calculators online, I did pull out my trusty laser meter and double checked that the trail is indeed ~4.0".

Also played around with the fork to see how much travel it actually has rough measurement is 3" (which is consistent with what everyone is saying would happen)

Now where all that leave me, is essentially with a front end that should be about as stable as the above mentioned BMW example by TrialsRider. With about 3" of travel, and not the stiffest of springs. Certainly not a knee dropping, corner carving with confidence, beast of a machine. But also not an unstable death trap.

Now I would like to hear people's opinion of what the handling characteristics of a machine with roughly the specs above? (I would like to hear the actual technical aspects not just "its shit" type answers.)

Also the forks currently sit 2" above the top yoke. Since I am planning on putting clip-ons, that does leave me with that room of adjust-ability. So given that currently is how the forks were originally mounted, i could slide the forks down and have them "flush" with the yoke. Which would put the rake and fork length roughly at the stock amount, minus the travel of course. Either way there is options.

What is people's opinion of those steering dampeners? (not sure what they are actually called, the little mini hydraulic actuator that connects to the fork and make the turning action much smoother and gradual.)
 

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When you calculated fork length, did you subtract the 2" that are sticking up above the triple clamp?

How much of the 3" of travel are going to be taken up by the sag with you and the weight of the bike on it?Usually, you would set up the sag to be between 1" to 1.5"......so now how much travel do you think you have?

Also remember, that trail decreases when the fork compresses....like when you hit the brakes, or hit a bump, or sit on the bike. So when Granny pulls her Buick out in front of you and you hit the brakes, if you are bottomed out with no suspension give, and your trail goes to the region of shopping cart wheel...... that is NOT a good time to discover how unstable the front end is.
 

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Discussion Starter #84
Yes the fork length is measured from the top of the top yoke to the center of the front wheel axle. (aka. excluding the top 2"). I agree with all that you have pointed out about the forks characteristics under static load, and heavy breaking.
 

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Sounds like the axle is offset forward on the fork leg and that is messing up your measurements.
What's the rake angle measured at the steering head,
what's the trail using a line through the steering head bearing to the ground and then from that to the bottom of the tire contact patch?
 

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.. I agree with all that you have pointed out about the forks characteristics under static load, and heavy breaking.
add:
Compression through corners, reaction to bumps, resistance to head shake (rigidity of the entire assembly), steering dampener is a nice add on.
 

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OK Sparky,
Here is a reasonable suggestion for you. Given that you don't have enough experience to make any reasonable assumptions and that you have been given plenty of advice on here that ranges from very wrong to maybe right based on their assumptions, here is what you have to do. Return your forks to stock with the appropriate amount of appropriate oil in them and put them in the stock location.. Then once you get the bike up and running, ride it a while and make the adjustments as needed. Right now, you don't know what to do. Based on my experience, what you have now is a recipe for disaster with respect to handling, compliance and ground clearance.
 

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it's going to bottom out hard and often. when it does, the only suspension you have left is the tyre. hitting bumps under braking is when it will be most unstable, and it'll probably bounce off bumps as there's no suspension left.

get a big piece of steel, put it on the concrete and hit it hard with a hammer. that's what it sounds and feels like, and if you have mechanical sympathy, it'll make your skin crawl.
 

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Discussion Starter #91
Sounds like the axle is offset forward on the fork leg and that is messing up your measurements.
What's the rake angle measured at the steering head,
what's the trail using a line through the steering head bearing to the ground and then from that to the bottom of the tire contact patch?
The axle is not offset forward, it sits at the bottom of the fork. The 27.2° of rake is the measurement at the steering head. As i mentioned the trail both with the calculator online and with manually measuring the trail on the ground by comparing the bottom of the contact point of the tire with the projected straight line from the steering head is roughly ~4".

So in terms of riding the bike with the stock setup. When i bought the motorcycle i rode it for about 2.5 hours straight on country roads. Varying speeds. When i bought it the stock forks were slid up roughly 2 inches. Effectively leaving the rake/trail at about the same position as now. Big differences was the preserved full travel of the fork. They did need new fork seals, and had lost a good amount of oil already. So i did feel the thunks of the fork bottoming out.
 

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... had lost a good amount of oil already. So i did feel the thunks of the fork bottoming out.
Low oil level will not bottom out your suspension you will only lose dampening, too Much oil will bottom out suspension when it hydraulics.

... if you heard a thud when it bottomed out that was because something was hitting and that would have to relate to the yokes being slid down too far on the stanchions. The springs are what carry the weight and hold the suspension extended :/ the oil produces some compression dampening, but if the shock absorber runs dry air offers little resistance, uncontrolled travel in that part happens.



We just got 2 inches of wet snow here :| that is going to put a damper on Woody's demo day tomorrow :( sure hope it melts by morning
 

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Discussion Starter #94
Ait cool, so i thought about it, what i'll do is spend the winter disassembling this sucker and learning how things work. So far I've learned quite a bit from you guys. So thank you for that. I'll see what i might do come spring time. I would ideally get another v45/v65 Sabre in a much better condition and continue my build on that, using the current thing as a parts bike. Thinking about the work that needs to go into this one to get it to an operational level especially with the small dent in the frame kind of deterred me from it. The engine case i am not too worried about because i could always buy another engine or new set of crank cases. Yes its a lot of work to dismantle and reassemble it but its not that bad. The frame though, there is no repairing that other then cutting that piece off and welding a new one. That seems like a terrible idea as it will effect the balance, and structural integrity of the frame.

Given that this project has turned form building something that works, to a science experiment for learning. What would the masses suggest for any actual project bike. I do like the v4s from honda, as they are truly unique, in sound, performance, and engineering. I do want to hear your opinions for the best bike to use for a project. Things to consider I guess would be the performance of the machine, the complexity, the deviation from that classic horizontal line stance... like what makes that bike better? I see that functionality is important for all so I would assume "because it looks better" type answers should be held back.
 

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alright I measured everything out more precisely. Accommodated for the grade on my driveway as well. Here is the numbers:

Rake: 27.2°
Tire Radius: 25.795" (110/90/R18)
Triple Clamp Offset: 2.375"
Fork Length: 29" 3/4

Using the https://www.rbracing-rsr.com/rakeandtrail.html calculator that leave:

Trail:3.96"

Now where all that leave me, is essentially with a front end that should be about as stable as the above mentioned BMW example by TrialsRider. With about 3" of travel, and not the stiffest of springs. Certainly not a knee dropping, corner carving with confidence, beast of a machine. But also not an unstable death trap.

Now I would like to hear people's opinion of what the handling characteristics of a machine with roughly the specs above? (I would like to hear the actual technical aspects not just "its shit" type answers.)
I haven't read the whole thread, just a couple short pages.
based on the numbers, it sounds like a fine front end set up for a good sport tourer. Provided the measurements are accurate. However, you cannot escape the fact that at a wheelbase of 61.5 inches, it is never going to change directions quickly or easily. Depending on what you are used to or what you want, this may or may not matter. Coming off Harley's you may be pleasantly surprised. If you were riding supersports and wanted a throwback racer, you might be disappointed.
3" for front end travel is not good though and would be my biggest concern. Death trap right there. Think about sag taking up 1-1.5 inches, that leaves 1.5 inches of compression. No way. EDIT- 8ball already pointed this out....


That's the thing with those pretty bikes, most aren't really rideable.
 

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Yep, this is very much a form follows function forum, but that is what makes it unique.

I'm sure there are other forums where they get all cranked up over stationary riderless artistic impressions of a real motorcycle and buzz terms like "classic horizontal line stance" or "boneline" actually means something to somebody, in this place it's a bit of a joke to draw imaginary lines through a motorcycle and call them important. example: How to Build a Café Racer ? BikeBound What I see first is a set of tires that still have the little tiny hairs still on them confirming this is just yet another unridden indoor art project.

If you want advice on how to make a motorcycle go this is the place, if you want to wax poetic about imaginary lines photoshopped on a picture of a riderless bike :/ not so much.

Complexity is not something you want in your first motorcycle, 4 cylinders fed by 4 carburetors is a good example of complexity.
Frames themselves are rarely to never balanced as such and repairing one isn't a huge problem, welding without creating stress fractures or weak spots on a frame constructed of relatively unknown, used materials is a huge challenge.
 

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What you want to do with the bike, how big you are, the project budget, parts support, your skill set, all help determine where to start.
 

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Just a hunch, check out 1970's 2-strokes ;)
example: Yamaha 350 cc everybody will notice it, motor performance will scare the crap out of you, easy to work on, easy to modify, the bike is already low, stock frame and suspension is scary if you push it hard, but I suspect you will never ride it fast enough to matter. Buy one that is pristine stock as possible and has been stored in the back of a heated garage, not some cafe project.
... if that's not enough bike for you then look at a Suzuki T500
 
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