SP: Spring Boxes (Rear) Replace Rear "76 Koni" Damper on Series B (2501)? Advise please

[Albervin]

TT. I have, as you may know,I have a modified coil over damper on the front of my B Rapide. The spring is 135lbs as opposed to the original 150lbs +. On my C Shadow I have single Series D springs and a Koni damper. I would say the C set up was absolutely wonderful in the UK but I have not tested it yet in Oz. IF it is found wanting I would fit a firmer damper rather than stiffer springs as a first fix.Second fix would be spring spacers and last fix stiffer springs. One issue I want to avoid is dreaded topping/bottoming of the movement.

 

[bmetcalf]

A bit OT, but diesel on the road isn't talked about much here in the US. The bad car drivers must be overwhelming enough that a mere slippery road is nothin'?

 

[greg brillus]

Its all about available travel........The Vincent does not have much front or rear.......If you have a small amount of travel then the way to control it is with strong springs, or else it will readily bottom........I choose the strongest of the range of springs in the front end, as using the weaker springs bottom too easily........remember the 45 lb springs are way softer than the stock Vincent springs. To use a strong/stiff shock absorber is the wrong way to fix the problem as you are using the shock absorber to "Mask" the spring strength.......If you read up on bike suspension from the guru's they all say that you should use as strong a spring that will do the job with minimal pre load as is possible and a shocker unit that will control the spring oscillations without limiting the behavior of the springs.........I have ridden Comets that have had the modified front end done, using the AVO damper up front, the fork action was way too rigid, with no suppleness at all........The back end is no different, you have to increase the suspension travel there to get a softer ride, this generally means the rear chain looks like it will fall off with the bike unladen.......Of course the fully sprung rear seat is the real answer there. There are limits to what can be done, folk who really struggle with it have mostly given up on old bikes and ride their electric start BMW's now........well that's what I've seen here locally anyway.

 

[timetraveller]

I really can't argue with any of that. However, empirical testing by the feel on ones rear is that the stronger 45 lbs/inch springs are too stiff for most mid weight people for comfort on the road. The JE modification gives 3" of movement on the front, provided that one shortens the spring boxes by about an inch. The Series 'D' s with the original Armstrong damper have about 7" at the rear. Remarkable for the time. If the AVO coil over rear unit is used then it has about 3" of movement built into the damper (it is a sod to check) which would give about 4.5" for the wheel. Medium weight people to whom I have provided 45 lbs/in spring for the front have asked to exchange them for the 36 s. This is with the AVO turned down to almost its minimum setting. There are a couple of videos of front fork movement over typical UK roads on the forum so people can judge for themselves. Possibly there is some difference between the comfort expectations between hard riding Aussies and the European and Americans. I have no good ideas as to why there are two schools of thought on this but I am happy to supply what either group wants.

 

[greg brillus]

I guess everyone has to work out what works for them........My take on it is that if you give people some options they will generally get it wrong, because they don't know what is right or wrong........How many Vincent's out there have poor brakes and yet the owners seem to live with it. I prefer to carry out the entire front end re work myself rather than let others finish the assembly themselves, as some of the ones I've seen have been completely wrong........I have found that all the springs that I have installed have needed to be cut shorter by about 20 to 25 mm in overall length to stop it from being topped out.

 

[ClassicBiker]

A bit OT, but diesel on the road isn't talked about much here in the US. The bad car drivers must be overwhelming enough that a mere slippery road is nothin'?

I think you are absolutely right there, Bruce.
Steven

 

[Chris Launders]

While doing some of the spring and damper testing for the modified steering stem I found the Koni damper to be one of the worst, I tried several varying from brand new to ones that had been on bikes for decades but they all exhibited the same problem in being too stiff initally, so on finely rutted roads, small corrugations or broken up surface they transmitted it all to the rider, but on the larger bumps, speed humps, pot holes and emergency stops though they were fine.
I found the dampers I tried could be divided into three groups, the Thornton and AVO were best, then the Armstrong and Vincent (although I have no idea if that was standard) and finally the Koni.
They ALL gave pretty much the same performance on bigger impacts (pot holes, speed humps and emergency stops) it was the operation on the small stuff that was the major difference.

 

[timetraveller]

One thing to note is that the original Vincent and Armstrong damper had the same resistance to movement in both the compression and extension modes. This is no longer thought to be the best way to use damping. To simplify, it is now thought that one needs to have much less resistance to movement in compression than in extension. I do not know about the Thorntons but if it is true that they are no longer available it is irrelevant anyway. Konis might be the same story but I have heard that IKON still produce the same or a similar product. They could be approached if anyone was interested. The AVO damper was developed specifically for Vincents with Rob Staley (Hadronuk) acting as the Vincent input side of the project. it is a modern damper and although it is possible that for racing there might be better, more adjustable and much more expensive dampers available they seem to be very good for Vincents in general. For those who doubt, find the videos by either Chris Launders of Chris and Tracey Tilley on this forum. The suppleness of the front suspension is transformed.

 

[ClassicBiker]

With regards to the Ikon. I asked in another thread if anyone was using them. I received a couple of replies indicating some had good experience with them. The reason I had asked was I had stumbled across this,

76-1239 Shock Absorber

76-1239 Ikon's 76-1239 is a specialized version of the 76-series shock that was developed for Vincent motorcycles, which utilize the same single shock front and rear. Ikon's 76-1239 features an appearance much more like that of the original shock with an aluminium body & black dust cover...

www.ikonshocksusa.com

at the time I asked, a couple of months ago, they were still in stock. Looking today they are not. I had been considering buying them once we were in the new year and fitting them for the 2021 riding season, if such a thing comes into existence. Looks like I will have to contact them and see what they are planning on doing.