XS11 to thunderbolt trail affects

[joep7]

I am in the process of swapping my forks for a cartridge style off of a Buell thunderbolt.

They are about 2 inches shorter and a 1 inch smaller rim. Based on a trail calculator I should be going from the stock 5.66 in trail to about 5.1. Rear will be getting a matching 17 rim.

That should be stable enough at speed right? Seems to be within safe tolerances and should possible even improve steering a bit.

[skids]

I am no expert in this, but even raising your fork tubes in the triple tree clamps can make a marked difference. I know this isn't the same thing that you are talking about, but small changes in the geometry can make a difference and you are talkin big differences I think.

[TopCatGr58]

Hey Joep7,

You will still have quite a bit of trail there, and these things are heavy steering to begin with. I'm running about 2" of trail due to my bent frame/neck that I wasn't aware of for 10 years after a bad front ender. It's quite stable at speeds, and is VERY easy to turn! It almost likes to OVERSTEER but I've gotten used to it. SO...with ~5" of trail, you should be more than stable, and might get a little less required effort in steering as well.

T.C.

[Eveready1100]

Joep, before you do anything permanent to the front of your bike, try dropping your original forks 2 inches up through the triple clamps (maybe 1/2" more to emulate the smaller wheel) and check your clearance.
It'd be pointless swapping front ends to improve the ride and handling if you can't lean it into the turns.

[joep7]

Hey Joep7,

You will still have quite a bit of trail there, and these things are heavy steering to begin with. I'm running about 2" of trail due to my bent frame/neck that I wasn't aware of for 10 years after a bad front ender. It's quite stable at speeds, and is VERY easy to turn! It almost likes to OVERSTEER but I've gotten used to it. SO...with ~5" of trail, you should be more than stable, and might get a little less required effort in steering as well.

T.C.

Well I am machining new triple clamps anyway so maybe by changing the offset I can get it down to like a trail of 4. How far is too far?

[joep7]

Joep, before you do anything permanent to the front of your bike, try dropping your original forks 2 inches up through the triple clamps (maybe 1/2" more to emulate the smaller wheel) and check your clearance.
It'd be pointless swapping front ends to improve the ride and handling if you can't lean it into the turns.

Not possible unfortunately due to the fact that this was the bike that had a bad 2nd gear fix which caused the motor to seize between 1st and 2nd gear. Everything is torn apart on it. :/

[TopCatGr58]

Well I am machining new triple clamps anyway so maybe by changing the offset I can get it down to like a trail of 4. How far is too far?

Hey there,

I'm no engineer. I will say that 2" seems a bit too far as I stated because of the oversteer, and even though it's fairly stable up to about 90 mph, it does seem a little wiggly above that, but part of that is also the aerodynamics due to my square edged saddlebags.

I don't know what the value/trail is when folks swap the special TT onto a Standard frame/forks....the offset is closer to the steering neck on the Special TT's vs. the Standards. Fred might know the value, he's talked and promoted this type of mod for lightening the steering for folks with sidecar hacks.

If you're really good at math, then it might be simply extrapolated by knowing/measuring the amount of offset of the Specials TT's vs. the Standard TT's and then just calculate the resultant different location of the standard front wheel, forks, and axle, and figure out the trail amount then.

Folks have stated that the OEM value is ~6". And these bikes were built/designed for SPEED, and I would think for stabilty and safety at that speed, and so I would think Yamaha would have set it at that for a reason, but we also know how they OVERENGINEERED a lot of what went into the XS11, and so perhaps they also overhedged the trail amount to be on the safer/more stable side vs. manueravability??

I know sport bikes have much smaller trail values, but they also have dampening rods attached to the steering components!

T.C.

[skids]

Hey, where is that free-body diagram for engineering? Just kidding. There is a lot of engineering involved just to get into the ballpark before the trial-and error tests. But...you will soon know if you nailed it. Good luck man!

[joep7]

Hey there,

I'm no engineer. I will say that 2" seems a bit too far as I stated because of the oversteer, and even though it's fairly stable up to about 90 mph, it does seem a little wiggly above that, but part of that is also the aerodynamics due to my square edged saddlebags.

I don't know what the value/trail is when folks swap the special TT onto a Standard frame/forks....the offset is closer to the steering neck on the Special TT's vs. the Standards. Fred might know the value, he's talked and promoted this type of mod for lightening the steering for folks with sidecar hacks.

If you're really good at math, then it might be simply extrapolated by knowing/measuring the amount of offset of the Specials TT's vs. the Standard TT's and then just calculate the resultant different location of the standard front wheel, forks, and axle, and figure out the trail amount then.

Folks have stated that the OEM value is ~6". And these bikes were built/designed for SPEED, and I would think for stabilty and safety at that speed, and so I would think Yamaha would have set it at that for a reason, but we also know how they OVERENGINEERED a lot of what went into the XS11, and so perhaps they also overhedged the trail amount to be on the safer/more stable side vs. manueravability??

I know sport bikes have much smaller trail values, but they also have dampening rods attached to the steering components!

T.C.

Good info thanks.

I moved it from the 1.25ish offset stock to 1.5. Hopefully thats not to much. Moves my trail to about 4.85.

[joep7]

Here are some drawings I did. Offset of 40mm.







Will have my boss look at them tomorrow to see what he thinks as far as machinability.

[fredintoon]

'treeswapping

I don't know what the value/trail is when folks swap the special TT onto a Standard frame/forks....the offset is closer to the steering neck on the Special TT's vs. the Standards. Fred might know the value, he's talked and promoted this type of mod for lightening the steering for folks with sidecar hacks.

Hi TC,
The different look of Standards and Specials is mainly cosmetic, both bikes have exactly the same rake and trail.
My Clymers ain't handy right now but my memory sez rake is 29º and trail is 5.3" on both bikes.
What happens when you put the longer reach Standard 'trees on a Special is that the fork tubes get moved forward which reduces the Special's trail by ~2"
Which lightens the steering which is a good thing on a sidecar rig.
What happens when you go t'other way and put the Special's shorter reach 'trees on a Standard is that the fork tubes get moved back which increases the Standard's trail by ~2".
Which will develop your shoulders like Atlas if you ride it like that.

[Eveready1100]

Joep,
I just went into the garage and measured my bike to give you some point of reference to what I was talking about. With it sitting level on the ground, I have roughly 8 inches of clearance to the lowest point under the motor, and I'm running 14" shocks on the rear that lifts the bike a fair bit as well. Simulated dropping the front and ended up with that lowest point dropping to just over 6 inches.
Now comes the interesting bit........
Got a sheet of plywood and rested the bottom edge against the outer edge of the tyres and leant the sheet up against the bike which resulted in a lean angle of only about 20 degrees from vertical before hitting hard points.
So are you looking at putting a sidecar on it??

[joep7]

Joep,
I just went into the garage and measured my bike to give you some point of reference to what I was talking about. With it sitting level on the ground, I have roughly 8 inches of clearance to the lowest point under the motor, and I'm running 14" shocks on the rear that lifts the bike a fair bit as well. Simulated dropping the front and ended up with that lowest point dropping to just over 6 inches.
Now comes the interesting bit........
Got a sheet of plywood and rested the bottom edge against the outer edge of the tyres and leant the sheet up against the bike which resulted in a lean angle of only about 20 degrees from vertical before hitting hard points.
So are you looking at putting a sidecar on it??

That bad huh? What does it start hitting at a 20 degree lean?

[WMarshy]

That bad huh? What does it start hitting at a 20 degree lean?

Pegs are first to touch down but they fold back so no worry there. Next is the lever arm on the left side of the center stand followed by the center stands foot on the right side. Beyond that I am unsure. I guess if I took off my center stand I could find out but wont happen until next year.

[joep7]

ok good to know. I think I am going to try to raise the rear a bit. If I need to I may make fork extenders like xschop did. Tho I dont think he ever ended up needing them.