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Home Forums Sidecars Sidecar setup Reducing Trail – Leading legs

This topic contains 20 replies, has 5 voices, and was last updated by  Eddieb 2 months, 2 weeks ago.

Viewing 15 posts - 1 through 15 (of 21 total)
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  • #5717

    Eddieb
    Keymaster
    • Location: Hamilton, New Zealand
    • Bike: Suzuki DR650 ADV
    • Rank: 1200cc Rider

    Trail reduction assists with the effort required to steer a sidecar and can be achieved in a number of ways. The usual method is to fit a pair of leading link forks, which entirely replace your existing forks.

    These 2 diagrams show how trail it is measured, and how leading link forks reduce trail.

    traildiagramleadinglinktrail

    Another option is leading legs, plates fitted to your existing forks that place the front wheel further forward that their standard position. This interests me and might be something I look at if I decide the R80 steering is too heavy.

    Leading legs on a Suzuki Vstrom 1000

    DSCF1201

    Other side

    HackFrontLow

    On a Yamaha XS650

    Kawasaki Vulcan

    kawasakivulcanleadinglegs

    #5831

    Alan Morrison
    Participant
    • Location:
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    • Rank: 50cc Rider

    Hi interesting photos. Have a sidecar which was to go onto an nv750 honda, but have now purchased a 1200 goldwing and will fit the sidecar to this.Would the leadibng forks be any advantage.

    #5851

    Eddieb
    Keymaster
    • Location: Hamilton, New Zealand
    • Bike: Suzuki DR650 ADV
    • Rank: 1200cc Rider

    I think that depends how how your sidecar handles, if the steering is really heavy and/or has issues with steering wobbles if may help.

    I haven’t investigated it fully myself yet, there’s still much to learn.

    #5853

    Chris DuPont
    Participant
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    • Rank: 50cc Rider

    The advantage of the NV750 Honda is the front axle is in front of the fork sliders , not at the bottom of the slider ! Hence the trail has been adjusted already as the bike is deemed a Cruiser style bike. The leading link style forks will assist if the steering is hard to turn lock to lock when just moving at low ground speed. I have found mine needed a steering damper ( Volkswagon type purchased on trademe from a wrecker , as new for approx. $28 ! ( don’t pay $200/300 for genuine sports bike damper as they don’t have enough travel ! ) The damper was only fitted after the guy doing the WOF at the local garage complained that the bike ” shakes it’s head” between 15 & 30km ground speed. I could control the head shake by pushing onto each handgrip as I accelerated , but this becomes tedious on a long trip. And now there is no headshake what so ever ! Just my 2 cent’s worth. Chris DuPont Incedently I am adapting a Watsonian car to a Suzuki Cavalecade , which is the Suzi copy of the Goldwing.

    #22553

    Ken Moncrieff
    Participant
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    • Rank: 50cc Rider

    I have had made a set of leading legs via water jet cutting of 12.9mm T6 alloy plate. Have seen many types of leading legs but none for a 1981 to 1996 BMW twin. What should be the maximum trail reduction in mms.
    possible for such a model BMW. Any Ideas?

    #22558

    Eddieb
    Keymaster
    • Location: Hamilton, New Zealand
    • Bike: Suzuki DR650 ADV
    • Rank: 1200cc Rider

    Hi @ken_moncrieff, post a pic of your leading legs up.

    I guess there’s probably a engineering equation but I’ve no idea sorry. @stephen-clark is currently rebuilding his (my old) airhead setup and may have some thoughts on what is ideal.

    #22951

    Ken Moncrieff
    Participant
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    • Rank: 50cc Rider

    THis set is my latest effort. On BMW’s from 1981 to 1986, the teles have a bulge at the bottom which can foul the disc bolts and event the disc itself. That means only two locations for the axle are available to move it forward to reduce the trail effectively. I tried the 52mm forward position, but that still made it heavy to steer but better. I then decided to go to 83 mm. 9to the front side of the bulge) That has been a success but it also needed bracing to prevent fork flexing on hard reght hand corners. This bracing has fixed that problem. Now it’s like having power steering.

    Attachments:
    #24815

    Box.a.Bits
    Participant
    • Location: Wellington
    • Bike: BMW Supertanker, R80 & Velorex Sidecar, Gilera Runner ST200
    • Rank: 1000cc Rider

    @ken_moncrieff, looks good (& strong). Just a few questions.

    1. How are the spoked wheels working out for you? I busted the spokes out of my sidecar wheel, so have preferred cast since. However on my next sidecar project I’ll have cross laced wheels.
    2. What’s the sidecar?
    3. Have you calculated how much trail is left?
    4. Have you talked about the mod with your local certifier?

    I had an R80 Mono with even more trail (at least your fork legs had leading axles). We raked out the forks (notionally 3 degrees) to achieve less trail. Still a heavy steerer, but a lot better than stock.

    The monos have a bigger fork tube, have a 25mm axle, & have an integral brace at the mudguard, but I still had issues with flex under hard cornering (which caused the brake pistons to be driven back into the callipers – exciting times). They just aren’t set up for the lateral forces a sidecar can generate.

    #24816

    Ken Moncrieff
    Participant
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    • Rank: 50cc Rider

    Mine has a smaller alloy sidecar wheel so there is no problem there.

    The sidecar is a copy of an English Squire sp2 or sp3 made under licence I believe, in South Africa in 1975. I bought it from an older guy who brought it with him here as a new BMW R75/5 outfit many years ago.. I don’t know how he ever steered it tho’.

    As for the trail, I’m not sure what it is for a standard R75/7 but it must be a lot, so what’s left I have no idea. I’ve found that even with this 83mm trail reduction, it handles and tracks so well. I can drive easily “hands off” at 110 k/hr with no wobbles and steering damper off. It just tracks true and corners both ways very well. It has only 15mm toe-in on the sidecar wheel and about 310mm lead ahead of the back axle. (I do carry 30 litres of water as ballast when I don’t have a passenger in the sidecar)

    Yes. for the 52 mm set I made which were certified by our local transport department. He has yet to certify this increased trail reduction set at 83mm. That should happen next week if possible.

    This bike has a set of 1981/82 forks fitted to it by the previous owner in Victoria. That’s why the brakes are twin Brembos on these model forks from a CS model I believe. It really does drive so well, it’s like having power steering now compared to the first set I hand-made. This set is also made from T6, 12.9mm structural alloy and cut by water-jet cutters from a template made for the job.

    I could not find any firm anywhere in the World which makes leading legs for this model group of BMW front forks to buy outright, so it became a do it yourself project,and it’s taken me over a year to perfect these now after making many model templates out of 10mm craftwood to get it just right before going to the steel or alloy cutting system to make them. To fit them to the forks properly, it’s necessary to shave 1mm off the inside of the bulge on the bottom of the tellies to clear the brake disc on both sides in its new position. Several other factors are also involved with the leg plates and axle/hub spacers to get it just right for minimum clearance of the hub and discs and anchoring the calipers in their new position. That was no easy task. New and longer steel brake lines had to be made as well.

    Also, I’ve braced the rear sub-frame of my bike between the rear shockies under the seat and under the bike between the pillion foot-rest mounts for extra rigidity and strength for connecting the sidecar to the bike.

    #24822

    Ken Moncrieff
    Participant
    • Location:
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    • Rank: 50cc Rider

    I might add that although I don’t know the bike’s exact amount of solo trail, my rough attempts at working it out suggested it to be from 110 to 120mm. There certainly is a fair bit left even when the leading legs are in place.

    #24940

    Eddieb
    Keymaster
    • Location: Hamilton, New Zealand
    • Bike: Suzuki DR650 ADV
    • Rank: 1200cc Rider

    Triple Tree set-up, that changes the angle of the fork by 5 degrees bringing the front wheel forward by 2 inches, for sidecar units.
    Available by Lovekraft Motor Werks in Fort Worth, Texas. For more info call: Dominic Velasquez, (USA)469-831-2944 or check out their website: https://www.lovekraftmotorwerks.com.

    #25037

    Eddieb
    Keymaster
    • Location: Hamilton, New Zealand
    • Bike: Suzuki DR650 ADV
    • Rank: 1200cc Rider

    Here’s another option to reducing trail, though I don’t know if it would pass an engineering assessment in NZ. Check out the fork clamps.

    #25846

    Eddieb
    Keymaster
    • Location: Hamilton, New Zealand
    • Bike: Suzuki DR650 ADV
    • Rank: 1200cc Rider

    DMC Sidecars in the US have just made a set of leading legs for a BMW K1200R

    #25852

    Ken Moncrieff
    Participant
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    • Bike:
    • Rank: 50cc Rider

    That set on a K model looks impressive, I wonder how they lock the legs to the hollow axle? And how much do they reduce the trail by?

    I have had a similar problem with hard right hand corners, and have decided to add a stiffening brace, a bit like an incomplete fixed swinging arm to lock both leading legs/forks together to make it all more rigid and non–flexing. Seems to have worked quite well now.(see attachment).

    Re. triple tree angle changes, Do you know of any who make ones with a 7 degree change in the USA? I’ve heard that they are available but can’t find them.
    Also do you have the email address of any firm in England which make leading legs I had one but have lost it.

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    #25894

    Ken Moncrieff
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    • Rank: 50cc Rider

    This reply may be too late if you don’t have the R 80 any more, but by fitting the brace to my leading legs on my R model to stiffen it all, the problem with the front brakes on tight right hand corners is no longer a problem.
    I’m not sure if it comes from the forks/L.legs flexing or from the wheel bearings allowing the discs to mis-align a bit. esp. if they are tapered rollers.
    I’ve used 20mm/2mm square steel tube, well re-enforced with gussets in both corners. I could have used 25mm/3mm tube which would have been even stronger but heavier. If I was fitting such a U-shaped brace to a K model BMW, I’d certainly use the 25mm square tube.

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