steering neck angles

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steering neck angles

Postby xlh59 » Thu Jan 10, 2019 4:18 pm

As I never found any information on steering head angles, I thought I might do some measurements and post it here. These values are static angles or frame angles, not considering higher/lower shocks of forks or suspension sag. To know theses values is relevant for anyone interested in front wheel trail, e.g. if you are changing forks or tires.
I took three frames for my measurements:
  • a 59 XLH frame
  • a 52 K-model frame
  • a XLR frame (year unknown)

I took the measurement on the XLH frame to compare with the factory drawing and to verify my measurement method.
  • the 59 frame has the factory drawing 30°
  • the 52 K-model frame has 28° head angle -- I did not expect 2° less rake!
  • the XLR frame has 25° neck angle -- also much less than expected

Especially the XLR frame is a bit surprising, as with the stock (sportster) triple trees the trail would be very short. Maybe this explains why the XLR also used the raked triple trees? Does anyone know what the angle in these raked triple trees is? Another question about the XLR frame came into my mind: Did post 56 KRs also use the "sportster" top motor mount or would there be two different frames available?
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Re: steering neck angles

Postby sportyparts » Thu Jan 10, 2019 10:13 pm

Late 1956 KH model frames used the forged K model top motor. Sportsters used the pressed steel top mount.
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Re: steering neck angles

Postby Ferrous_Head » Thu Jan 10, 2019 10:47 pm

The XLR is a dirt race bike. The reduced trail makes it easier to turn at the expense of straight line high speed stability.
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Re: steering neck angles

Postby Lisa » Thu Jan 10, 2019 11:30 pm

I had a 53 K and it rode goofy felt like it would respond fast like top heavy hard to explain but after riding it for a while you get used to it, because of the angle I guess nothing like my 55 KH 67 and 69 CH it is night and day to explain ?
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Re: steering neck angles

Postby hugoct » Fri Jan 11, 2019 10:31 am

All XLRs except the 1970 use the 52R (heavy) frame.
The steering head casting should have a 57R casting number.
The 58R frame and the late 52R frame are dimensionaly and visually the same.
The difference is the gauge tubing and the reinforcements where the front tubes go into the bottom of the steering head casting.
Can you post a picture of both sides of the steering head casting ?
The non parallel triple clamps change the effective offset of the forks and reduce trail.
The early KRs also used non parallel clamps changing to parallel in 1954.
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Re: steering neck angles

Postby hennesse » Fri Jan 11, 2019 12:51 pm

Here is a visual about trail - and how rake and angled triple trees affect trail. You can see in the image how trail is measured.

More trail results in the reduced ability for either variances in the road surface, or the rider pushing on the handlebars to change the direction of the bike. Choppers have high-speed stability - you can easily do "Look Ma, no hands".

Less trail means enhanced ability for the road surface or rider to change the direction of the bike. Motocross bikes are very manuverable, but you must keep your hands on the handlebars at all times.

trail.jpg
Trail - effect of reduced frame rake and angled triple trees
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Look at the image, and notice what rake and angled triple trees do not only to the trail measurement, but also to the wheelbase of the bike.

The 1952-1953 K had a reduced rake, and angled triple trees. Both things reduce trail, and doing both together make this a very maneuverable bike. Too maneuverable in fact, so in 1954, they increased the frame rake to 29-3/4 degrees. This increased the trail, making the bike less maneuverable, but more stable.

In 1955 (very late 1954) they changed to parallel triple trees. This made the bike even more stable, and even less maneuverable. But these are road bikes, not motocross, so this configuration of rake and triple trees was the best, and pretty much what was used from then on. In 1956, they lowered the frame a little, and increased the rake 1/4-degree to 30 degrees.

One thing you can't easily see in my crude images is the effect on the front of the frame that the rake/triple trees have. The reduced rake causes the front of the frame to rise upwards a little bit. (To visualize, imagine shifting the rake to 0-degrees). The frame is no longer parallel to the ground. The angled triple trees have the opposite effect.

In 1955, the change from angled triple trees to parallel triple trees caused the front of the frame to rise about 1 inch. To bring the frame back to parallel to the ground, they reduced the length of the fork tubes 1 inch.

-----
This is a very complicated subject, since every little change has an effect on everything else. Changing the frame rake changes the wheelbase and changes the height of the front of the frame. Changing the height of the front of the frame actually changes the "effective frame rake" a little. To visualize, imagine a bike with 6-foot over fork tubes. The front of the frame is now so high that if you measure the angle between the frame neck and the ground, it's about 85-degrees !!!

Frame rake and angled triple trees have a big effect on trail. Other things have an effect too. The change from 19" wheels to 18" wheels had a small effect on trail. Other things such as longer/shorter fork tubes, taller/shorter tires. Using a taller front tire than the rear. Not applicable to us are things like offset triple trees - where both the top and bottom of the fork tubes are closer or further away from the frame neck.

I don't know how modern engineers design steering geometry. But back in the early 1950s, Harley engineers used the trial and error method. After lots of errors with the K-models, they finally got back to the same geometry they used with the VLs, Knuckleheads and Panheads. Duh.
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Re: steering neck angles

Postby thefrenchowl » Fri Jan 11, 2019 3:47 pm

Thank you professor,

I'll never guessed all this by meself...

Patrick
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I'm the one who has to die when it's time for me to die so let me live my life the way I want to...
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Re: steering neck angles

Postby xlh59 » Fri Jan 11, 2019 4:50 pm

Its all a bit irritating with the "R" frames ... people are talking about rake, de-rake, light, heavy etc., but no real information available. That was one of my intentions for this post. My "R" frame has no neck casting number, as the neck has been "smoothened" --- what the heck --- why did anyone butcher these frames so badly? At least nothing has been cut away (besides the large tank mounts and - of course - the front seat mounts). Still, I am pretty sure it is a -57R neck.

No double tubes to the neck, pressed steel top mount ... weight is 29lbs

Regarding the rake/trail combinations, a very common figure today is 65°rake (or 25°) and 100mm trail. In the 70s/80s the combination 62° (28°) and 115mm with a 3.25" x 19" front tire was very popular (for fast bikes). So both, the early K-model frame and the "R" frames should have a very nice geometry (assuming sufficient rigidity and good steering damping) -- especially as the wheelbase is very modern.

25years ago I had fitted my XLH with Yamaha FZR forks and new nothing about rake/trail ... the triple trees were much to short and steering hard work; stability was amazing of course.

Lets do some maths:

  • K-model frame rake 62° 60mm triple tree offset 3.5" x 19" tire 108mm trail
  • XLH frame rake 60° 60mm triple tree offset 3.5" x 18" tire 114mm trail
  • XLCH frame rake 60° 60mm triple tree offset 3.25" x 19" tire 118mm trail
  • XLH frame rake 60° 35mm triple trees (FZR) 110/80 x 18" tire 142mm trail
  • "R" frame rake 65° 60mm triple tree offset 3.25" x 19" tire 85mm trail
  • "R" frame rake 65° 60mm triple tree offset 4.0" x 19" tire 94mm trail
  • "R" frame rake 65° 45mm triple tree (ceriani) 3.25" x 19" tire 101mm trail

For clarification and information:
I checked all franme I have ... K-model, 56KR, 59XLH, 59XLCH and XLR and all of them have 20.3mm inner diameter of the downward seat tubes -- this results in 0.1" wall thickness of the tubes. All frames the same! -- Still, the "R" frame is significantly lighter than the others.

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IMG_20190111_190906_887_small.jpg
IMG_20190111_190906_887_small.jpg (470.82 KiB) Viewed 951 times


Cheers!
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Re: steering neck angles

Postby Ferrous_Head » Fri Jan 11, 2019 8:06 pm

Anyone wanting to get a real understanding about frame geometry should consider buying one of Tony Foal's books. (Chassis design).
I read it about 20 years ago. Maybe more.
But it wasn't until I spoke to Mick Dewith a few years ago that the penny really dropped about rakes and trails. Mick builds racing sidecars. he told me his first couple handled "pretty bad". When your building something from scratch it's always possible to build a Frankenstein. (Ask me how I know that) What he told me was the answer was to get as much of the weight as far forward as possible.

When I built my current sidecar I changed the front end geometry radically. I reduced the rake and brought the trail back from 4 inches to 1 inc. That's 100mm down to 25. I know from talking to the F2 guys (and girls) that they run virtually no trail. 10-15mm.

Now before anyone says "Yeah, but that's a sidecar" read what Tony Foal had to say about this. Ans especially what he explains to the reader about telescopic forks. And why we still persevere with this poor designs to this day. Clue, it's just marketing.

Here's a picture of Tony riding his modified BMW to show how "unstable" a bike becomes as you reduce trail towards ZERO.




Image


Most of my point here is for years I couldn't believe GP riders were telling me that decreasing the rake by 1/2 a degree was having a noticeable effect on the bike's handling. But while it was changing the fork geometry it was also affecting the weight distribution. The two combined was being felt by the rider.
"I know only too well the evil that I propose, but my inclinations get the better of me."
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Re: steering neck angles

Postby thefrenchowl » Sat Jan 12, 2019 7:16 am

I think everyone needs to look at reality, ie period photos and stop generating theories from the modified stuff lying today in your garages:

Pohlman factory photos:

52K, photo from November 1951:

Image

1st ever KR, photo from November 1951:

Image

1st ever KRTT, photo from November 1951 (from close look, this is the very same KR above returned to the race dept and fitted with the KRTT stuff):

Image

1st ever KRM, photo mid 1952:

Image

1956 KRTT in Daytona Trim:

Image

1st ever XLR-TT, late 1957:

Image

All have the same steering angle and early K offset.

The 1956 KRTT might has a very slight difference (touch more trail for more Daytona stability in the sand?) but certainly not 5 degrees...

My 66 XLR-TT have had its frame moded as well, so no chance for decent measurements...

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