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Old 04-20-2010, 06:39 AM   #1 (permalink)
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Rake and trail explained.

Your front suspension geometry is defined by the following six variables which are defined as:

OFFSET: Centerline of the top steering neck to the centerline of the top of the fork tubes.

RAKE: The angle in degrees of the steering neck from the vertical cord.

FORK LENGTH: The distance between the top of the fork tubes to the centerline of the axle.

DIAMETER: The diameter of the front tire.

TRAIL: The distance defined by the vertical line from axle to ground and the intersection of centerline of the steering neck and ground.

RAKED TRIPLE TREES: In order to bring trail figures back into line, triple trees with raked steering stems can be used. Usually adjustable in 3, 5, 7 degrees of rake.

HOW TO MEASURE CORRECT TRAIL

Raise the bike to an upright position, using a tape measure, hold the tape straight down from the front axle to the floor. Put a mark on the floor at that point. Then place the tape parallel to the steering neck, following the angle of the steering neck all the way up to the floor. Put a mark here also. Now measure the distance between the two marks and you have your trail measurement. It should read between 2 and 4 inches. Note: If your bike is equipped with a rear suspension, have someone sit on the seat when you make the measurements to simulate your actual riding condition.

TOO LITTLE OR NEGATIVE TRAIL

With too little or negative trail (steering axle mark behind the front axle mark), the bike will handle with unbelievable ease at low speeds, but will be completely out of balance at high speed. It will easily develop a fatal high-speed wobble. EXTREMELY DANGEROUS!

NORMAL TRAIL

Normal trail is somewhere between 2 and 4 inches. The bike will handle easily at both high and low speeds. Flowing smoothly through curves without swaying or wobbling. If you use a very fat rear tire, you should keep the trail as close to 4 inches as possible.

TOO MUCH TRAIL

If the trail is more than 4 inches the bike will handle sluggishly at high speeds. It will seem almost too steady. You will have trouble balancing the bike at lower speeds or on winding roads. It will feel generally sluggish and clumsy.


Good site for a calculator: RB Racing Rake and Trail Calculator
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Old 04-20-2010, 06:43 AM   #2 (permalink)
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thanks for the post -up Dave. does this have anything to do with our phone conversation yesterday evening?
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Old 04-20-2010, 06:50 AM   #3 (permalink)
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Originally Posted by Rockerbox1 View Post
thanks for the post -up Dave. does this have anything to do with our phone conversation yesterday evening?
Well....kinda. That and 2 other forum questions regarding how to measure rake and trail, or how lowering a bike effects it, this morning.

It's good information to know, or at least to have if ya need it.
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Old 06-04-2010, 07:31 PM   #4 (permalink)
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hello Dave63,
Doo yoiu know how far of a rake you can put on stock frame with stock forks. I run an 09 fatboy and want to stretch it out just a bit. Thought a raked triple tree might be the answer
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Old 06-04-2010, 07:57 PM   #5 (permalink)
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The farthest that HD uses is the Rocker (and maybe one other) which is 32* neck and I wanna say another 2*-3* on the trees. I could be wrong....

Personally, I wouldn't go much farther then 5* over stock, and even at that, you should have some inch+ stanchions to account for the front dropping, because of the rake.

I gotta admit, I don't really know enough about raking a bike to tell you what's gonna handle good, or make you wish you didn't do it.....
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Old 06-05-2010, 04:41 PM   #6 (permalink)
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So, Dave.........

I'm following, somewhat, and then i'm confused.

I am jonesin in a big way to go wide 41mm on my 93 Dyna Lowrider. But i want more than just a wide glide look. I'd like to stretch it a tad, not too much, and keep the front end at the same height. This is done by increasing the rake degrees AND the length of the fork. So i't would be impossible to restore the trail unless you repositioned where the axle is mounted, like positioning it in front of the off-set centerline. Am i right? If so, does the after market set-ups make this correction or are you stuck with increased trail?

I noticed springer forks position the axle farther out. I didn't notice any non-springer sliders with that correction.

I ride/race mountain bikes. A general rule was, increasing the fork length 1" slackened the bike angle about 1 degree. I'd guess it wouldn't make a diff with a motor bike. Jeezus just tell me what to buy!
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Old 06-05-2010, 05:31 PM   #7 (permalink)
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Originally Posted by Phast Phil View Post
I'm following, somewhat, and then i'm confused.

I am jonesin in a big way to go wide 41mm on my 93 Dyna Lowrider. But i want more than just a wide glide look. I'd like to stretch it a tad, not too much, and keep the front end at the same height. This is done by increasing the rake degrees AND the length of the fork. So i't would be impossible to restore the trail unless you repositioned where the axle is mounted, like positioning it in front of the off-set centerline. Am i right? If so, does the after market set-ups make this correction or are you stuck with increased trail?

I noticed springer forks position the axle farther out. I didn't notice any non-springer sliders with that correction.

I ride/race mountain bikes. A general rule was, increasing the fork length 1" slackened the bike angle about 1 degree. I'd guess it wouldn't make a diff with a motor bike. Jeezus just tell me what to buy!
A 1993 Dyna SG/Lowrider have a 28* rake. This is about 4* less then most other Harleys, and 2* less then the FLT in that year.

If you add a WG (41mm) 0* front fork set up like I did, it's going to be about 1.5" longer in the front, then your stock 39mm set up out of the box.

This is also going to lift your front up a little, making your kickstand seem shorter due to the added fork length. (with 0* trees)

I ended up lowering my front end 1.5" (Progressive lowering springs), setting the front back down, bringing my trail number back down.

What you could do (but adds to expense) is find HD OEM trees with the 3* rake added into them, or get aftermarket trees with a 3*-4*+ rake and add the OEM 41mm lower legs/stanchions to them. Anything more, and you'll likely have to start adding stanchion length, to being front ride height back to level.

With the added OEM forks being about 1.5" longer, with the added rake in the trees, it'll balance out with the rake and fork length, making the bike sit level, but giving you a more stretched out look.

As for adding 1" of fork length = 1* ( not sure if you're referring to trail or rake) it's going to vary, as Harleys vary in fork length and tire height, and those are both integral parts of the mathametical equasion.

You wouldn't be able to maintain the same trail, as extending rake and fork length automatically extends trail.

Extending the forks will change front ride height, which affects trail, but not going to get you back to the original numbers, unless you started to raise the rear ride height (as in a sportbike) lowering the trail numbers again.

Extending (raising) rake decreases a bike's ability to turn, however, makes it feel more stable on the roadway at speeds.

Hope some of this helps.............

Here's a pic of my bike, with a 1999 Fatboy WG 41mm front fork set up (0* rake trees, with the FLSTF being a 32* frame rake), on a 28* Dyna frame, with a 1.5" front fork drop.

If you imagine lengthening the forks and moving the trees out farther rakes, you can see the bike extend.....


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Old 06-05-2010, 06:30 PM   #8 (permalink)
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So fxdl has a shorter fork than the fxdwg. You explained what i might find if i use HD forks with 0* rake. So when an aftermarket maker says "stock length" they mean wide glide specs. I get it. So, i'll need to actually measure my front end and compare it to specs of new forks (and possibly go with 4* rake). I'm not even sure if fxdl and fxdwg and sg's wheels are the same size. Homework sucks but must be done. The link you posted earlier with the conversion table might get some play. Guess i have to get my ass off of the couch now!

Have any recommendations as far as after market 41mm forks?

Thanks a lot Dave. You been very helpful.

BTW, nice bike (super glide?). And that lowering kit brought it back to stock level? Oh, the possibilities.
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Old 06-05-2010, 07:19 PM   #9 (permalink)
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Quote:
Originally Posted by Phast Phil View Post
So fxdl has a shorter fork than the fxdwg. You explained what i might find if i use HD forks with 0* rake. So when an aftermarket maker says "stock length" they mean wide glide specs. I get it. So, i'll need to actually measure my front end and compare it to specs of new forks (and possibly go with 4* rake). I'm not even sure if fxdl and fxdwg and sg's wheels are the same size. Homework sucks but must be done. The link you posted earlier with the conversion table might get some play. Guess i have to get my ass off of the couch now!

Have any recommendations as far as after market 41mm forks?

Thanks a lot Dave. You been very helpful.

BTW, nice bike (super glide?). And that lowering kit brought it back to stock level? Oh, the possibilities.

FXD has a shorter fork then the FXWG: Yes, but only when mounted. (Keeping in mind that some 39mm forks are shorter then others, based on model they were off of.) You can have a 39mm fork on a XL1200 that will be longer then a set from an 883-Low, which is shorter by build.

The big difference is the 39mm narrowglide forks hold the fork in the trees with 2 pinch bolts, (2 each side, one top and one bottom) and the stanchions are flush with the TOPS of the upper tree.

On the 39mm, the Stanchion goes completely through the top tree and large nut only holds fork internals in:



The 41mm wideglide fork stanchion and lower leg can be the same length as the 39mm fork, however, the stanchions stop at the BOTTOM of the top tree, and are held on with a large bolt that holds them to the tree. This mounting position now makes the total length 1.5" taller, due to the stanchion mounting position, in comparision.

The 41mm forks stop at bottom of top tree and have a cap with a stud on it and a threaded hole in the stud. The stud slides up into the tree and the bolt/cap holds it in the tree.



Fxd also has a 39mm narrowglide fork, where as the WG has a 41 mm wideglide fork.

FXDL has a 19" narrowglide hub.

FXWG has a 21" wideglide hub, which is wider, requiring a wider fork stance. The only way to use a narrowglide wheel on a wideglide fork is with an adaptor to space the rotor out to the wideglide hub position, and wheel spacers to match the narrower hub stance.

See the large round rotor spacer in the wideglide conversion kit?



You can also buy a wideglide conversion kit, that has new trees, spacers, but maintains your original stanchions and lower legs. I used one of these on my bike, with a wideglide 21" front wheel for 2 years, as seen here. These were just my old FXD forks, with triple tree kit.



Here it is, with the 39mm forks, and a 19" narrowglide wheel (Sportster and FXD models only) with the whole kit, rotor spacers included. Note the large fender spacers they give you to mount your narrowglide front fender to a wideglide stance fork!!






I have no clue as to who makes good aftermarket WG forks...

I used a set of OEM forks, and found (read:Swapmeets) all the parts I needed and matched years to maintain brake caliper fitment and axle fitment. (3/4" axle and bearings)

My bike started life as a 1995 FXD superglide... The fender was off in this picfor a minor paint repair, but the stance was what I was trying to show. I love the "no fender look" but not practical for the time I've spent riding in the rain....
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Old 06-07-2010, 12:50 PM   #10 (permalink)
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Just to make sure we beat this to death, I was advised to NOT do a tree rake to correct extra fork length but instead to use a raked headset cup kit.
If the 41mm's i install are longer the trail will not be affected, but the level of the bike front would be raised. To level it back off a 3* headset cup would actually increase trail (to about 6.2") where a raked tree kit would decrease trail making the bike less stable at speed.
Increased trail in the 6" range, quick steering maneuvers would suffer, however. Head-ons might just get more difficult to twitch away from!

It's all about style though!
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