Effect of steering head angle?

Discussion in 'Hacks' started by iantochips, Dec 28, 2012.

  1. iantochips

    iantochips Been here awhile

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    I'm in the process of drawing the leading legs conversion for my VL1500/Dnepr sidecar. In deciding on trail reduction I began to wonder about the effect of the 1500's chopperesque steering head angle.

    As a solo the thing has real enthusiasm for going straight on in any corner- needing muscular counter steering to deflect it from its course. This is I think the combined effect of its humungous 300kg weight and considerable wheelbase as well. What is the effect of this angle when going round a corner upright though?

    I'm guessing its long wheelbase and rearward weight distribution means, like old Harleys apparently, I can get away with less sidecar wheel lead? I'm thinking 15% max. I am struggling though to get my head around the amount of trail reduction, and whether there's any significant interaction with the steering head angle. I'm a fairly small older guy and I don't want too much of a workout when I'm out riding. It's all twisties around here!

    Is the steering head angle not relevant with an outfit- we all know it makes a tremendous difference to a solo- it's why a Ducati is so much fun, and why I'm putting a third wheel on the Suzuki!
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  2. claude

    claude Sidecar Jockey

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    Take a look at the picture of trail measurment in the link below and you will see how steering head angle affects trail. Reducing trail is what makes steering easier.
    http://sidestrider.com/leadingfork.html
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  3. leejosepho

    leejosepho Sure, I can do that!

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    The closer the tire's contact patch gets to the line coming down from the steering head, the easier the turning will be.

    My bike's weight and length are nearly identical to the FXRS Low Rider I used to have, and I would guess my rig's total weight is now around 750 lbs. It is also fairly wide, and I only have 3" lead for the chair wheel. However, my design is such that at least 80% (my own estimate) of my passenger's weight always remains on the back axles.

    Others here know far more than I, but I would say "No." The angle gives you some trail, and you are simply going to reduce that trail by moving the axle forward a bit rather than pointing the steering head "more down". :huh

    Surely it is at some point somewhere, but moving the axle forward a bit seems to be quite sufficient for many folks! Nevertheless, I am also a bit like you might be and can occasionally over-think things a bit.
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  4. claude

    claude Sidecar Jockey

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    Study the picture in the link I posted carefully.

    Steering head angle can affect trail. Rarely do people change the steering head angle as modifying or replacing the triple trees or other methods are more simple in most cases. Exception being the BMW telelever bikes which is a little different story.
    A smaller rolling diameter front wheel and tiore will reduce trail some also.
    Some bikes allow simple fork swaps that move th eaxle forward.
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  5. iantochips

    iantochips Been here awhile

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    Thanks for the thoughtful and helpful replies. No other sidecar pilots for miles around here so nobody to shoot the breeze with apart from here.

    I think I get the geometry of the trail figure completely, and I certainly plead guilty to thinking too much! One of my schoolteachers told me that 45 years ago...

    I can see how changing the angle would certainly alter trail, and I understand that, as long as the steering stem is parallel to the fork tubes (and the headstock unmodified) then trail is fixed , and the only practical option is to modify the yokes (sorry, triple trees), make leading legs, or change to leading links. My question was more to do with whether the shallow steering head angle ( and its strong self centering effect on a solo bike) had a similar effect on an outfit, meaning perhaps that a bit more trail reduction might be a good idea?

    Some trail is obviously a necessary component for stability- otherwise there is no castor effect at all! I've been thinking of perhaps 2" as starting figure?

    I'm very interested in your 3" wheel lead leejosepho- I can foresee getting the same kind of weight distribution with my outfit. It does seem to have advantages in terms of less sidecar wheel tyre scrub- but does it work under fairly enthusiastic cornering? We live in a hilly area with lots of beautifully surfaced bends and I've never entirely got rid of the hooligan in me even as I approach my sixth decade!

    The other issue is how differently it would handle without a passenger set up this way? I anticipate probably a car battery in the boot and a luggage rack on the back, all adding to the rearward weight bias.

    Nearly time to fire up the welder....
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  6. claude

    claude Sidecar Jockey

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  7. iantochips

    iantochips Been here awhile

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    Thanks Claude, what a fascinating link! I had a GSA1150 as a solo for a couple of years and was amazed by its neutral steering and uncanny stability.

    Tony Foale's final comment about variations in trail making little difference clearly points to a big gap between 2 and 3 wheeled behaviour.

    Food for thought. It's bed time here in Portugal so I'll have another look in the morning and get my head around it. Thanks again.
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  8. claude

    claude Sidecar Jockey

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    Read it all very carefully my friend. Everything is related and one change changes other things as you will see. Reducung trail can be done in various ways as noted previously. Reducing trail is done to ease the steering effort. Other things can ease steering also such as wider bars, less wheel lead, narrower track width and tire choices to a certain degree. EVERYTHING is a compromise in one way or another.
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  9. iantochips

    iantochips Been here awhile

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    I've read it several times.......

    I understand the compromise in an asymmetrical 3 wheeler much better now! I'm still struggling to finalize some figures which will be hard to change post welding.

    I found in another thread the suggestion that cruisers should have their trail reduced by two thirds- seem reasonable to you experts?

    I don't think I'll go too low on the sidecar wheel lead despite my rearward weight distribution- I'm thinking to make it adjustable if possible and play between 6 and 10".

    Have to bite the bullet and grind some metal shortly. I'll keep you all posted.
    #9