Need Help Choosing Springer length and Rockers

[Tattooo]

The rockers need to be specific to the angle of rake?

Nope your wrong................. Like I said before not unless the rockers are a foot long..............

Your really over thinking all this rake of the frame, length of a front end in relation to the rocker length..........

It's not as complicated as your trying to make it out to be...........

Set your frame at the angle you like, buy a front wheel that you want to run, get a tape measure and have at it............

Stop talking about it and get to work..........

[TriNortchopz]

If ya wanna learn more about rocker design, here ya go, lots of reading on this site:

Chopper Builder's Handbook
Springer Fork Rocker Designs

"...What this article addresses is the specific design considerations for building custom Springer Rockers as a part of fine-tuning the handling characteristics of a typical Springer fork system.
Keep in mind as you read along that what we're going to talk about here applies to Chopper front-ends. By that I mean forks that set on a 35-degree rake or more and forks that are extended at least 6-inches over stock.
Don't try to apply what follows on stock or Bobber type front ends..."


The sketch above shows a fairly typical off-the-shelf Springer setup for a bike having a 45-degree rake angle and running a 21-inch front wheel while the sketch below shows the same hypothetical bike set up to run a Springer using dropped rockers.


Notice the 1.5-inch difference in the location of the wheel pivot point (PR) between the two fork sets and the 3-inch difference in trail. The effective length of the rockers is identical so there is no change in the spring rates for the two different forks even though the 'sword' type dropped rockers look far larger. The forks in the lower sketch will handle significantly better than the forks shown in the upper sketch.

https://www.chopperhandbook.com/rockers.htm

[Booneman]

If ya wanna learn more about rocker design, here ya go, lots of reading on this site:

Chopper Builder's Handbook
Springer Fork Rocker Designs

"...What this article addresses is the specific design considerations for building custom Springer Rockers as a part of fine-tuning the handling characteristics of a typical Springer fork system.
Keep in mind as you read along that what we're going to talk about here applies to Chopper front-ends. By that I mean forks that set on a 35-degree rake or more and forks that are extended at least 6-inches over stock.
Don't try to apply what follows on stock or Bobber type front ends..."

[ATTACH=CONFIG]97847[/ATTACH]
The sketch above shows a fairly typical off-the-shelf Springer setup for a bike having a 45-degree rake angle and running a 21-inch front wheel while the sketch below shows the same hypothetical bike set up to run a Springer using dropped rockers.

[ATTACH=CONFIG]97848[/ATTACH]
Notice the 1.5-inch difference in the location of the wheel pivot point (PR) between the two fork sets and the 3-inch difference in trail. The effective length of the rockers is identical so there is no change in the spring rates for the two different forks even though the 'sword' type dropped rockers look far larger. The forks in the lower sketch will handle significantly better than the forks shown in the upper sketch.

https://www.chopperhandbook.com/rockers.htm

Yeah! Thanks! This is what I think I need. I want to get rockers that will reduce my trail.

[Tattooo]

Yeah! Thanks! This is what I think I need. I want to get rockers that will reduce my trail.

Why?????? Do you have a reason for that statement????????

[TriNortchopz]

Remember back in the hey day (or was it haze-daze...hard to remember, oh da fog...) of chopper building...who thought about trail...that was something rough you rode your bike down, before there were actual roads, if you were asked about your trail, the answer was 'rough and dusty'
...when the neck was just cut from the bottom and a 3-finger rake was built and welded together...like shown in this Big Bike article from 1970: http://www.choppersrule.com/chopper_...rake_neck1.asp (no mention of trail there...)
and the springer legs were cut and lengthened with Ford radius rods or whatever was layin' around...or round steel slugs were screwed into the top of the fork tubes to lengthen 'em...

Wow...are they making them again?!: " These fork tube extensions replace the stock fork tube caps and are made from solid, hi-grade steel with a chrome finish. Available for most 39, 41 and 49mm applications in 2" (5 cm), 4" (10 cm) and 6" (15 cm) length...Fits 39mm forks on 1987 to present Sportster, 1987 thru 1994 FXR and 1992 thru 2005 Dyna": https://catalog.zodiac.nl/en/catalog...be-extensions/

Then there were raked trees and extended tubes, (or fork slugs) stuck on stock bikes with stock rake, like the Allied 10-10 kits:

and negative trail was the result...okay for slow speed but don't hit a bump when flying down the road (further along than just a trail)

Of course the were many manufacturers of extended springers and girders like AEE, Amen, Butts, California Cycle, CCW, Columbus, Cycle Shack, Defiance, Durfee, D&D, Dick Allen, EME, Finch, Franks, Fury, Gyro, Harman, Jammer's, KDM, Ness, P&P, Paughco, Randy's, SIE, SB&F, SugarBear, T&S Sales, Wayne, Wheel Specialties...t name a few...
Then there were highways, and discussions turned to rake and TRAIL (not just a rough and dusty path)...with calculations and generalizations of what is acceptable trail (is that almost a rule - a chopper rule...come on - there ain't no rules!)...so now, through places like The Chopper Handbook, trail is a real thing, a thing to consider, to tune even, to get the best handling for you, for the rake and length of extended front end you got or want. SugarBear has a big rocker thing that is designed on trail:
Figure 16 represents a stylized sketch of what we used to call 'Scimitar' rockers that were popularized in the early sixties and still built today by Sugar Bear and a few others:


This particular chart was set up to determine the rocker geometry for forks where I wanted to maintain 3-inches of trail regardless of what the neck rake angle happened to be. On the full-scale chart it was easy to interpolate down to 1-degree of accuracy.

Those semi-circular arcs you see drawn between the axle and the rear pivot pin hole having nothing to do with the rocker shape but are there just to make it easier to understand what axle locations go with what pivot location...Ironically a guy who actually was really good at mathematics and geometry did the same exact thing but did it empirically by actually building a mockup in his shop consisting of steel bars drilled with dozens of holes. Through trial and error he tried scores of various rocker/rake relationships and physically measured the amount of flop for each and every possible arrangement of parts and hole locations. This guy was Sugar Bear and that's how he came up with his incredible rocker designs.

https://www.chopperhandbook.com/rockers.htm

Handling characteristics involve hundreds of variables as we mentioned earlier and the trail value is but one of those factors. For more definitive information about trail as it effects road bikes I urge you to read the book entitled 'Motorcycle Handling and Chassis Design' by Tony Foale.

For the average Chopper builder Trail is strictly an indicator of relative 'forward' or 'dynamic' stability at various speed ranges and if your bike is within the 2 to 9-inch range you're in the same group as about 98% of all other Chopper owners. https://www.chopperhandbook.com/rake.htm

[Booneman]

Remember back in the hey day (or was it haze-daze...hard to remember, oh da fog...) of chopper building...who thought about trail...that was something rough you rode your bike down, before there were actual roads, if you were asked about your trail, the answer was 'rough and dusty'
...when the neck was just cut from the bottom and a 3-finger rake was built and welded together...like shown in this Big Bike article from 1970: http://www.choppersrule.com/chopper_...rake_neck1.asp (no mention of trail there...)
and the springer legs were cut and lengthened with Ford radius rods or whatever was layin' around...or round steel slugs were screwed into the top of the fork tubes to lengthen 'em...
[ATTACH=CONFIG]97955[/ATTACH]
Wow...are they making them again?!: " These fork tube extensions replace the stock fork tube caps and are made from solid, hi-grade steel with a chrome finish. Available for most 39, 41 and 49mm applications in 2" (5 cm), 4" (10 cm) and 6" (15 cm) length...Fits 39mm forks on 1987 to present Sportster, 1987 thru 1994 FXR and 1992 thru 2005 Dyna": https://catalog.zodiac.nl/en/catalog...be-extensions/

Then there were raked trees and extended tubes, (or fork slugs) stuck on stock bikes with stock rake, like the Allied 10-10 kits:
[ATTACH=CONFIG]97959[/ATTACH]
and negative trail was the result...okay for slow speed but don't hit a bump when flying down the road (further along than just a trail)
[ATTACH=CONFIG]97960[/ATTACH]
Of course the were many manufacturers of extended springers and girders like AEE, Amen, Butts, California Cycle, CCW, Columbus, Cycle Shack, Defiance, Durfee, D&D, Dick Allen, EME, Finch, Franks, Fury, Gyro, Harman, Jammer's, KDM, Ness, P&P, Paughco, Randy's, SIE, SB&F, SugarBear, T&S Sales, Wayne, Wheel Specialties...t name a few...
Then there were highways, and discussions turned to rake and TRAIL (not just a rough and dusty path)...with calculations and generalizations of what is acceptable trail (is that almost a rule - a chopper rule...come on - there ain't no rules!)...so now, through places like The Chopper Handbook, trail is a real thing, a thing to consider, to tune even, to get the best handling for you, for the rake and length of extended front end you got or want. SugarBear has a big rocker thing that is designed on trail:
Figure 16 represents a stylized sketch of what we used to call 'Scimitar' rockers that were popularized in the early sixties and still built today by Sugar Bear and a few others:
[ATTACH=CONFIG]97957[/ATTACH]

This particular chart was set up to determine the rocker geometry for forks where I wanted to maintain 3-inches of trail regardless of what the neck rake angle happened to be. On the full-scale chart it was easy to interpolate down to 1-degree of accuracy.
[ATTACH=CONFIG]97958[/ATTACH]
Those semi-circular arcs you see drawn between the axle and the rear pivot pin hole having nothing to do with the rocker shape but are there just to make it easier to understand what axle locations go with what pivot location...Ironically a guy who actually was really good at mathematics and geometry did the same exact thing but did it empirically by actually building a mockup in his shop consisting of steel bars drilled with dozens of holes. Through trial and error he tried scores of various rocker/rake relationships and physically measured the amount of flop for each and every possible arrangement of parts and hole locations. This guy was Sugar Bear and that's how he came up with his incredible rocker designs.

https://www.chopperhandbook.com/rockers.htm

Handling characteristics involve hundreds of variables as we mentioned earlier and the trail value is but one of those factors. For more definitive information about trail as it effects road bikes I urge you to read the book entitled 'Motorcycle Handling and Chassis Design' by Tony Foale.

For the average Chopper builder Trail is strictly an indicator of relative 'forward' or 'dynamic' stability at various speed ranges and if your bike is within the 2 to 9-inch range you're in the same group as about 98% of all other Chopper owners. https://www.chopperhandbook.com/rake.htm

Thanks for sharing this!

[Booneman]

Why?????? Do you have a reason for that statement????????

Because, I'd like to order parts that are most ideal for my application.

[Tattooo]

Because, I'd like to order parts that are most ideal for my application.

That's not a reason..... And I'm not being a smart ass............

What trail are you shooting for and why do you think that is the best for your application??????

[Booneman]

I'm not sure what springer rocker combination would be best for my application. That's why I ask for some other people's opinions to consider before I order parts.

Trail sits around 10 inches now, so I'd like to cut that number in half at least. I guessing around 4 inches of trail would be more ideal. There are obviously many different rocker configurations.

Trail is not the reason for replacing front end, but while I'm at it, I may as well get a nice handling set up.

It seems you are disregarding the rocker shape/style as not being a factor? From what I can see in diagrams, it is somewhat of a factor.

Please do tell. What fork/rocker length would you put on this bike?

[Tattooo]

Please do tell. What fork/rocker length would you put on this bike?

What I would run really doesn't matter......... I don't have a problem riding any style bike so at this point it's all up to your riding skills??????? You know what your comfortable riding..........

But to answer your question I've NEVER figured trail on any of my bikes that I built from the beginning 45 + years ago............ I just run what looks the best........... I've been very lucky I guess as I've never built an ill riding/handling bike.......

Best of luck finding that allusive sweet spot..............

[Tattooo]

but while I'm at it, I may as well get a nice handling set up.

I missed this the first time I read your post........

If your looking for a handling bike you need to go back to a stock rake frame and front end.......

[TriNortchopz]

Tolle, famous manufacturer of looong tube frontends in Sweden has this info for tech tips on trail (translated from Swedish):



Normalt försprång
Måttet ligger mellan 5-13 cm. Motorcykeln är lättmanövrerad i både höga och låga farter samt att den följer med bra i kurvorna utan att bli överstyrd. Har du mycket brett bak- däck bör du ligga vid den övre gränsen, runt 10-13 cm.

Normal lead
The dimensions are between 5-13 cm. The motorcycle is easily maneuvered in both high and low speeds and that it follows well in the curves without being oversteered. If you have a very wide rear deck, you should lie at the upper limit, around 10-13 cm.

Too much head start
If the dimension is over 13 cm, the mound feels heavy and steady in high speeds straight ahead, but very difficult to maneuver. In a curve, the bike suddenly becomes overpowered and difficult to balance at low speeds. It feels generally tongue-controlled and wants to fall into the curve so you can pick it up.

Too little head start
With too little head start it becomes easy to swing at high speeds, the bike does not control itself. In extreme cases, the lead may be negative (the picture), ie the wheel shaft is in front of the point of the steering head. Should you get high-speed wobble, it is clearly fatal!

https://www.tolle-engineering.se/sv-SE/tekniska-tips/m%C3%A4ta-f%C3%B6rspr%C3%A5ng-20434425

[Booneman]

Tolle, famous manufacturer of looong tube frontends in Sweden has this info for tech tips on trail (translated from Swedish):

[ATTACH=CONFIG]98007[/ATTACH]

Normalt försprång
Måttet ligger mellan 5-13 cm. Motorcykeln är lättmanövrerad i både höga och låga farter samt att den följer med bra i kurvorna utan att bli överstyrd. Har du mycket brett bak- däck bör du ligga vid den övre gränsen, runt 10-13 cm.
[ATTACH=CONFIG]98006[/ATTACH]
Normal lead
The dimensions are between 5-13 cm. The motorcycle is easily maneuvered in both high and low speeds and that it follows well in the curves without being oversteered. If you have a very wide rear deck, you should lie at the upper limit, around 10-13 cm.

Too much head start
If the dimension is over 13 cm, the mound feels heavy and steady in high speeds straight ahead, but very difficult to maneuver. In a curve, the bike suddenly becomes overpowered and difficult to balance at low speeds. It feels generally tongue-controlled and wants to fall into the curve so you can pick it up.

Too little head start
With too little head start it becomes easy to swing at high speeds, the bike does not control itself. In extreme cases, the lead may be negative (the picture), ie the wheel shaft is in front of the point of the steering head. Should you get high-speed wobble, it is clearly fatal!

https://www.tolle-engineering.se/sv-...%A5ng-20434425

I'm in the 25 cm range now, lol. I see they used raked tree in combination with raked neck to get better handling. This is what I would do if I was going with telescopic forks.

I'm guessing there's no need for a raked tree with springer, because you can use different rockers to compensate for excessive trail?

I love the looks of the Sweedish choppers, personally!

Thanks for the info!

[TriNortchopz]

I'm guessing there's no need for a raked tree with springer, because you can use different rockers to compensate for excessive trail?

Can still use raked neck post with your springer to adjust rake and trail.

In the 2008 online Paughco springer catalog, who describe themselves as, "The ultimate in springers since 1969"
they list their long springer with a rake in the neck:

"Springers 15" over stock and longer have 3° stem angles, but
this option is also available on shorter Springers upon request"

https://www.paughco.com/2008-catalog/pdf/SECT01-springers.pdf

Paughco, manufacturers of the most respected and sought after line of custom and OEM style Springer front ends, recently unveiled an entirely new collection of their trend setting tapered leg springers.
Featuring the company’s exclusive, tapered rear legs they are superior in strength and more closely resemble the original factory front ends than any other springer on the market.
These latest custom motorcycle legs are offered in sizes ranging from stock to 24-inches over in increments of 3 inches. Lengths 15-24 inches over are supplied with 3 degrees of additional rake only.

https://ultimatemotorcycling.com/2011/08/12/paughco-tapered-leg-motorcycle-springer/

another way to change rake (and trail) of your frontend is with a raked bearing cup kit;

This 3 degree kit an be used to either increase or decrease rake of all front ends on any Harley Big Twin Frame that uses bearing cups.

https://www.meatballsspringers.com.au/3-degree-neck-cup-bearing-kit/

You can include this in your calculations to change your 45 degree frame rake to 42 or 48 degrees.

[Booneman]

Interesting. I suppose this allows for use of a less "extreme" rocker design than used on the sickle style set up.