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Center Hub Steering
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swaybar2002



Joined: 26 Jan 2005
Posts: 380
Location: Central Pa.

PostPosted: Wed Feb 02, 2005 12:09 pm    Post subject: Center Hub Steering Reply with quote

Seems as though many HPS rigs run a center hub (or center point) steering on the front end. What is the main advantage of this system over a leading link?
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Claude Stanley

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bmcsheehy



Joined: 22 Jan 2005
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PostPosted: Wed Feb 02, 2005 1:09 pm    Post subject: Reply with quote

The advantages of CHS (Center Hub Steering)?
I would guess and say rigidity and strength. Not relying on steering head bearings to support the load or weight of the sidecar. It doesnít feel like the front end or forks are going to break off around hard corners. It accomplishes the same thing as a leading link as far as trail goes. One of the things I like is the steering is disconnected from the suspension. It steers with the same amount of effort now matter what the road or driving conditions are. Of course the faster your going around corners the harder it is to hold on, but thatís true with everything, right?

Can anyone else relate?
What do you like about CHS?
Poke
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docmike



Joined: 27 Jan 2005
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PostPosted: Wed Feb 02, 2005 1:47 pm    Post subject: Reply with quote

Another advantage would be that the tire stays flatter on the road, maintaining the same contact patch as the front end turns. On a LL the tire comes up slightly on edge when turned.

Which brings up another question, some CHS are not true CHS, the steering axis is offset to the left. Is this just for ease of manufacturing, or is there some reason to have some camber on the front wheel? Would the camber make a difference if the sidecar wheel steered?

Enquiring minds want to know.

Have to go to work now
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sidebike



Joined: 22 Jan 2005
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Location: Cabot Trail, Cape Breton Island Nova Scotia

PostPosted: Wed Feb 02, 2005 2:02 pm    Post subject: Re: Center Hub Steering Reply with quote

swaybar2002 wrote:
Seems as though many HPS rigs run a center hub (or center point) steering on the front end. What is the main advantage of this system over a leading link?


One of the advantages of hub center steering is the contact patch.



EML GL1800 GT Twin chassis. The front end of the bike typical of stock front forks or leading links. It would be riding on the edge of the tire.
The front wheel on the sidecar is flat on the ground typical of Hub Center Steering
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bmcsheehy



Joined: 22 Jan 2005
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PostPosted: Wed Feb 02, 2005 2:31 pm    Post subject: Reply with quote

Well I can tell you first hand, itís not easy to get everything inside the wheel. Thinking I think thatís why they do it . If the upper pivot is on the outside of the wheel and the lower pivot is inside the wheel so if you draw a line through the pivots the line would be in the center of the tire where it meet the road but not through the middle of the wheel/tire, then this is not true CHS. True CHS, looking from the front of the bike, is when the pivots are in line vertically and centered on the wheel /tire, if you draw a line through the pivot points it would be lined up in the middle of the wheel/tire. They donít both have to be inside the wheel either, some manufacturers put one above the wheel and one inside the wheel. Not sure if this would be considered true CHS.
I donít know if I explained this properly, I can see it in my head, might have lost something in the translation.
Someone please correct me if I'm wrong.
Does one work better that the other, I donít know. I have true CHS and love it.
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Bill
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swaybar2002



Joined: 26 Jan 2005
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Location: Central Pa.

PostPosted: Wed Feb 02, 2005 3:05 pm    Post subject: Reply with quote

Doc mike wrote:
...SNIP... some CHS are not true CHS, the steering axis is offset to the left. Is this just for ease of manufacturing, or is there some reason to have some camber on the front wheel?

Would the camber make a difference if the sidecar wheel steered?
============================================================================================

If you mean where the ball joints are placed quite a few things come into play. Some have utilized the term 'center point' in lieu of 'center hub' when referring to this method of steering. For what it's worth I feel this is probably the more correct term if we were to speak in an all inclusive manner. Sometimes we hear the term 'true center hub'...more on that later.
One goal when designing a center point or center hub steering (CHS) is to eliminate any scrub radius at the contact patch of the tire. Scrub radius is a tern which defines how far the centerline of the steering axis is offset from the center of the tire at ground level. If we look at many front ends we will find that the ball joints are not in line, above one another, when viewed fron the front. The upper ball joint is typically futher away from the centerline of the tire than the lower one. This offset angle is what is known as 'KINGPIN INCLINATION'. (Note that if a kingpin was being used instead of ball joints it would be on an angle as well.)
Looking at the front of the rig towards the rear...If we were to draw an imaginary line from the upper ball joint down through the lower one and then on down to ground level and were to draw another line straight down through the center of the tire..and if these lines did not intersect at the ground level the difference would be the SCRUB RADIUS.If they intersected at ground level there would be a zero scrub radius.
On a car with two wheels steering a SCRUB RADIUS is not too critical as one tire will counteract the other tire. On an outfit if there is a SCRUB RADIUS it will cause the rig to pull one way or the other. If this pull was adjusted out in some fashion other than getting rid of the SCRUB RADIUS the pull may go away but with the cost of drasticalluy increased tire wear.
So...it is best to not have a scrub radius to begin with.
If we think about all of this we will see that on a rig that has a kingpin or offset ball joints creating a kingpin inclination it will be much more difficult to vary tire diameters or rim sizes. Both of these factors will create a SCRUB RADIUS and cause the handling to suffer. Measures can be taken to prevent this such as adding or taking away spacer plates (really the front wheel backspace should be initiall designed in so spacers can be added OR REMOVED when tire diameters are reduced or increased..if the front end was designed without this adjustment an owner may have to get a new wheel with a different backspace when going to another tire size with a larger diameter..bummer..and costly!).
How can this concern be over come? Some rigs today are being constructed with both ball joints directly above one another and in the center of the wheel when viewed from the front. This is 'TRUE HUB CENTER STEERING'. No kingpin inclination to deal with and tire diameter can be varied with no concerns. Of course with this system the ball joints must remain in the center of the wheel. Wheel width, if changed would require a different back space or spacers but this system still allows more variation with tire sizes than the other system. It is possible on some rigs to adjust the ball joints in and out slightly to take care of this concern as well.In those cases the ball joints may consist of heavy duty tie rod ends being used as ball joints.
There is more but I guess I HAVE BEEN TOO LONG WINDED ALREADY.
Guess I better leave the steering sidecar wheel answers to someone else (Roger?? Ralph????). MY FOOT IS IN MY MOUTH TOO MUCH OF THE TIME ANYHOW.
Blah Blah Blah
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Claude Stanley

Founder: Internet Sidecar Owners Klub
http://autos.groups.yahoo.com/group/SCT/

2007
I.S.O.K Sidecar RON-DEE-VOO III ..
First full weekend in August!! Thursday through Sunday!!
Weikert, Pa ..more details coming


Last edited by swaybar2002 on Wed Feb 02, 2005 3:10 pm; edited 1 time in total
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swaybar2002



Joined: 26 Jan 2005
Posts: 380
Location: Central Pa.

PostPosted: Wed Feb 02, 2005 3:06 pm    Post subject: Reply with quote

Embarassed post came up twice..tried to delte one but can't..sorry
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Claude Stanley

Founder: Internet Sidecar Owners Klub
http://autos.groups.yahoo.com/group/SCT/

2007
I.S.O.K Sidecar RON-DEE-VOO III ..
First full weekend in August!! Thursday through Sunday!!
Weikert, Pa ..more details coming
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bmcsheehy



Joined: 22 Jan 2005
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PostPosted: Wed Feb 02, 2005 3:22 pm    Post subject: Reply with quote

Claude,
Sounds good.
3 Stars
Clapping
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Bill
High Performance Sidecaring... ...There is nothing "HACKED" about it.
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Powersl@ve



Joined: 31 Jan 2005
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Location: Netherlands

PostPosted: Wed Feb 02, 2005 4:05 pm    Post subject: Reply with quote

docmike wrote:
Another advantage would be that the tire stays flatter on the road, maintaining the same contact patch as the front end turns. On a LL the tire comes up slightly on edge when turned.

Which brings up another question, some CHS are not true CHS, the steering axis is offset to the left. Is this just for ease of manufacturing, or is there some reason to have some camber on the front wheel? Would the camber make a difference if the sidecar wheel steered?


That the tire keeps a complete contact with the road is true, it improves grip but at a slower speed it steers a lot less easy, you really have to put in a lot of arm power around slow corners.

As far as I know the wheel is placed a little to the left to improve a staight line stability.
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bmcsheehy



Joined: 22 Jan 2005
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PostPosted: Wed Feb 02, 2005 4:19 pm    Post subject: Reply with quote

Just one of many excuses I use for not going to the gym. Smile
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Bill
High Performance Sidecaring... ...There is nothing "HACKED" about it.
2006 ZX-14 / HANNIGAN HP.
2011 Concourse / California Friendship III.
1936 Ford Fordoor Humpback
www.Yankee-Engineering.com
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swaybar2002



Joined: 26 Jan 2005
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Location: Central Pa.

PostPosted: Wed Feb 02, 2005 4:47 pm    Post subject: Reply with quote

The thing that changes camber when the wheel is turned is the amount of caster in the front end. (It seems we should talk 'caster' instead of trail with a center hub set up. Is this agreed?)
Anyhow, I believe most are running between 6 and 9 degrees caster on their rigs. (Comments welcome).
Now I have a question. When the ball joints are viewed from the sidecar side is the upper ball joint further back, towards the bike, than the lower one??
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Claude Stanley

Founder: Internet Sidecar Owners Klub
http://autos.groups.yahoo.com/group/SCT/

2007
I.S.O.K Sidecar RON-DEE-VOO III ..
First full weekend in August!! Thursday through Sunday!!
Weikert, Pa ..more details coming
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docmike



Joined: 27 Jan 2005
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Location: Eastern NC

PostPosted: Wed Feb 02, 2005 6:03 pm    Post subject: Reply with quote

From what I've seen the upper ball joint is further back than the bottom.

And don't worry about being long winded, the more I listen (read) the more I learn.
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93 BMW K1100RS / EML Speed 2000
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docmike



Joined: 27 Jan 2005
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PostPosted: Wed Feb 02, 2005 6:03 pm    Post subject: Reply with quote

From what I've seen the upper ball joint is further back than the bottom.

And don't worry about being long winded, the more I listen (read) the more I learn.
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93 BMW K1100RS / EML Speed 2000
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67 Triumph 650 chopper
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Powersl@ve



Joined: 31 Jan 2005
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PostPosted: Wed Feb 02, 2005 7:42 pm    Post subject: Reply with quote

We heard you the first time.... Wink Very Happy
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bmcsheehy



Joined: 22 Jan 2005
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PostPosted: Wed Feb 02, 2005 8:29 pm    Post subject: Reply with quote

swaybar2002 wrote:
The thing that changes camber when the wheel is turned is the amount of caster in the front end. (It seems we should talk 'caster' instead of trail with a center hub set up. Is this agreed?)
Anyhow, I believe most are running between 6 and 9 degrees caster on their rigs. (Comments welcome).
Now I have a question. When the ball joints are viewed from the sidecar side is the upper ball joint further back, towards the bike, than the lower one??


No I don't agree about calling it caster. I run about 9 degrees trail and zero degree caster. My understanding is caster is the angle left to right and trail is created front to back.
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Bill
High Performance Sidecaring... ...There is nothing "HACKED" about it.
2006 ZX-14 / HANNIGAN HP.
2011 Concourse / California Friendship III.
1936 Ford Fordoor Humpback
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