2.50 x 18 Rim

750TT

750TT

Full member
Location
Canary Islands
Hi.
I want to mount a 2.50 rim (replica Borrani, Sanremo, etc.) on my 230mm Laverda drum. Should the rim have any special characteristic in the angle of the perforations or is a standard 36 spokes valid?
Regards
 
From memory I would say that the rim is best to have deep dimples to allow the nipples to seat properly as the spokes can have quite a steep angle. I fitted numerous wider Borrani rims to Lav rear drums and made a tool to relieve the seat for the nipple.
 
750TT said:
Hi.
I want to mount a 2.50 rim (replica Borrani, Sanremo, etc.) on my 230mm Laverda drum. Should the rim have any special characteristic in the angle of the perforations or is a standard 36 spokes valid?
Regards
Click to expand...
I assume you mean non-drilled rim?! As mentioned, the acute angle will determine what sort of dimple you need.
 
Or you can go to a 3.0 rear rim if you want, that's the biggest flanged rim type they make. I have one on my 3c and that allows a 140 rear tyre to fit. There are a couple of high-performance 140 rear tyres available, one from Bridgestone that I use. As mentioned the replica rims have a smaller dimple that struggles to allow the hole to be drilled to suit the correct spoke angle, finding a Wheel Wright that has the skill to do short spokes in that specific pattern required is not easy to find.
 
I ordered a drilled 3.00 Morad from Central Wheel to suit my 3c with twin leader rear brake maybe 15 years ago before I learned how problematic this could be. They're pretty experienced so I expected a good result. What I got was drillings that didn't work well, maybe they didn't know how big the hub is, or maybe they didn't know the modern dimples are smaller than the original rims. That rim lasted for a good 10 years before the spokes started pulling through the rim. I ordered an undrilled replacement and found a Wheel Wright who did the drilling and spoking, its not your typical spoke pattern as well. That's a compromise to get a good spoke angle that seats well on the dimple. It's critical to find the right bloke to get the best result. There are a couple of ways that the spokes can be bent to fit the hub and pass by other spokes as well.
 
Vince said:
I ordered a drilled 3.00 Morad from Central Wheel to suit my 3c with twin leader rear brake maybe 15 years ago before I learned how problematic this could be. They're pretty experienced so I expected a good result. What I got was drillings that didn't work well, maybe they didn't know how big the hub is, or maybe they didn't know the modern dimples are smaller than the original rims. That rim lasted for a good 10 years before the spokes started pulling through the rim. I ordered an undrilled replacement and found a Wheel Wright who did the drilling and spoking, its not your typical spoke pattern as well. That's a compromise to get a good spoke angle that seats well on the dimple. It's critical to find the right bloke to get the best result. There are a couple of ways that the spokes can be bent to fit the hub and pass by other spokes as well.
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Thanks,Vince
 
750TT said:
Hi.I was actually looking for the experience of some of the members, to get a pre-drilled one adapted to this drum.
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All the anecdotal evidence I'm aware of, in nearly 50 years around Laverdas, has warned against pre-drilled rims.
I'm guessing, on the Canaries, wheel builders are thin on the ground.
I had a 3" rim fitted to my 3cE's rear hub by Alf Hagon, back in '91, and have had no problems from it.
Might be worth sending the wheel to a recommended wheel builder to be done.
 
The Sock said:
All the anecdotal evidence I'm aware of, in nearly 50 years around Laverdas, has warned against pre-drilled rims.
I'm guessing, on the Canaries, wheel builders are thin on the ground.
I had a 3" rim fitted to my 3cE's rear hub by Alf Hagon, back in '91, and have had no problems from it.
Might be worth sending the wheel to a recommended wheel builder to be done.
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You have understood my doubts, there are no close or cheap solutions here.;)
 
750TT said:
You have understood my doubts, there are no close or cheap solutions here.;)
Click to expand...
Maybe not cheaper, but a sort of work-around...

Are we talking front or rear wheel here? I'm suspecting rear.

The front is actually no problem at all, Laverda used a conventional spoke pattern and the dimples of modern rims are quite adequate for the required spoke angles. The rear uses a different pattern, which is a little stronger, but, in truth, technical overkill.

I also had a 3.00" inch rear (Akront) laced to the drum of my 3C many, many years ago. The dimples were far too shallow to accomodate the Laverda spoke pattern, so the wheelwright resorted to the more normal pattern as used in the front wheels and drilled the rim accordingly. Suffice to say, it held up well to all I could throw at it during my carefree and daring younger years. It has since moved on and is currently fitted to another 3C, is used regularly and still offers sterling service. See pic, St Avold ca. 1983-84.

IIrc, to offset the "missing" strength of the spoke pattern, the wheelwright used thicker spokes, 4 (4.5?)mm. I specified stainless steel at the time, turned out I had loads of problems with the disc front wheel, which were later solved by a switch to cast (Suzuki) wheels!

FWIW, the SFC750 and SFC1000 both use a conventional spoke pattern in the rear wheels with disc hubs, with longer (weaker) spokes at that!

piet
sav15.jpeg
 
Mine is also an Akront, laced with 4.5mm spokes, in the Laverda style.
Takes the spokes to the edge of the dimples, but works fine for 95+ BHP and up to a 140/70 rear tyre for the last 33 years

2021 05 29 Power Station 1.jpgIMG_7639.JPG
 
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The Sock said:
Mine is also an Akront, laced with 4.5mm spokes, in the Laverda style.
Takes the spokes to the edge of the dimples, but works fine for 95+ BHP and up to a 140/70 rear tyre for the last 33 years

View attachment 94111View attachment 94112
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Not really Hamish.

The original Laverda rear drum wheels had the spokes "cross" adjacent spokes 3 times. What you have there is the conventional 2-cross pattern (bound to be a technical term, but I'm not familiar with it), same as mine. This pattern is also used for the front drum wheels. It is also the most common/universal pattern of all for spoked wheels.

Most alloy rim dimples are just too shallow to cater for the acute angle that is required for the 3-cross pattern, the old Borranis were only just adequate. Even on those, the spokes exit at the very edge of the dimples and the spoke nipples have a reduced bearing area on the inside of the rim.

It all works, sort of... but isn't quite ideal.

piet
 
And that's what I meant by the number of spoke bends where they connect with the hub and pass other spokes. That 3 cross lace complicates the job a hell of a lot and scares off a lot of wheelwrights.
 
Peter Williams of Norton fame said that shorter spokes can be too rigid leading to breakage. I’ve wondered if Laverda used the 3 cross pattern on the drum rear wheel to give a longer spoke which can flex a bit and handle the extra stress of being the drive wheel.
 
Normski said:
Peter Williams of Norton fame said that shorter spokes can be too rigid leading to breakage. I’ve wondered if Laverda used the 3 cross pattern on the drum rear wheel to give a longer spoke which can flex a bit and handle the extra stress of being the drive wheel.
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Short, rigid spokes may show up shortcomings in the flange of the hub, or even in the actual strength of the rim material. Don't think flexy wheels are desirable in any way, which Peter Williams proved to the world as one of the most prolific developers of cast alloy wheels.

The 3-cross pattern places the spoke at more of a tangent to the hub, allowing for greater forces to pass through it under acceleration or braking. Through the change of direction, it also reduces forces at the bore in the hub flange. Yamaha developed tangentially spoked hubs in various off-roaders in the 80-90s as engine power rose and disc brakes were introduced.

piet
 
A simple way of explaining the benefit of the 3-cross is to imagine the hub twisting inside the wheel. The most direct line from hub to rim is going to offer the best transfer of force (there's no doubt a term in physics for the angle of the tangent). Even on a bicycle, the drive side spokes will always be tangentially configured, whereas the non-drive can be radially laced.
 
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