Forum Replies Created
March 30, 2020 at 11:57 pm #32910
Here’s a picie of one of the calipers before fitting it. The large threaded collars provide adjustment for the floating process….usually about 1-1.5 mm of float is enough. High temperature 0 rings on either side of each cliper arm, allow for a bit of extra float to absorb any back pressure on the caliper pistons, thus avoiding a loss of “pedal” after taking sharp corners. ( ie what is termed “brake pushback” often found with some leading legs.
Attachments:June 2, 2018 at 11:53 pm #26890
Since my last posting on these leading legs, I’ve abandoned that lower brace because of the extra weight and its poor looks, with a perfect brake mounting system. That is, full floating mountings for the brake calipers. The brakes now work perfectly under all heavy right or left-hand cornering driving.
The legs have since been approved and certified by our State Transport Department engineers.May 31, 2018 at 2:30 am #26870
Here are some other pics.May 17, 2018 at 1:52 am #26751
Since my last posting re that brace I’d fitted, I didn’t like its looks much or its extra weight to the suspension and have now discarded it.
Instead I’ve made both brake calipers “full floating” on their 10mm bolt mountings which has solved the “loss of pedal” problem on hard right hand corners, completely, and the whole system is now working perfectly under all conditions.March 11, 2018 at 9:12 pm #25894
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.March 6, 2018 at 7:45 pm #25852
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.
Attachments:February 7, 2018 at 3:29 pm #24822
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.February 7, 2018 at 1:43 am #24816
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.February 6, 2018 at 2:38 pm #22951
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:February 4, 2018 at 1:19 am #22553
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?