FF: Forks Modified Steering Stem

[greg brillus]

There is a lot of things to answer here.......Ok first Bruce......Yes the upper link was what I was looking at, and its movement over bumps whilst braking quite heavily was near locked in that position. I think some are confusing the movement of the bike itself verses the movement of the forks. Remember there is a huge visual difference from these forks over telescopics. I feel you can jack up the rear of the bike as much as you like, only you need to make allowances for extra slack in the drive chain. I along with other racers have done this simply to gain extra ground clearance, and even so, I still ground the lower corner of my primary cover whilst coming around turn 12 at Phillip Island which is a very fast corner. I am actually interested to know how many of you reading this actually have this modified stem kit on your bikes........? As there seems to be a lot of guessing and surmising as to the fore's and against's of it all. The one thing that it proves beyond any doubt is that there are plenty who would like to do "Something" about bad handling, or who are aiming for a better and generally "Softer ride" which is a good thing, but my only advice is, this is not like hotting up an engine, or putting larger carburetors on, where the results are generally "Known" it is a common thing that carrying out a supposed "Upgrade" can and often leads to disappointment often for reasons the owner chose himself based on the opinion's of others or what they read in a magazine. Suspension upgrades to Vincent motorcycles is nothing new, people have been trying to improve it for years. I have had the benefit of using at least one of these stem kits in the racer since 2014, for those who don't know, I have bought 9 of these kits so far. Does that tell you something........ Regarding Nigel's comments, if you change the seat to fully sprung, the comfort at the rear will improve greatly, though the spring rate at the rear may need changing to stronger springs. It is possible to stretch standard springs, but that's another story.

 

[davidd]

I have just completed fitting two discs on the front wheel of my Rapide. They seem to work very well.
I haven't noticed the front end snapping to full extension. (I'll take more notice next time out.) I have Rob's degressive spring fitted to the Girdraulics so perhaps they are preventing it.

Eddy,

The digressive springs like the short spring or the steering stem mod should de-link the brakes and suspension.

On the use of Thorntons on the rear, no one I know has had a problem with the rear damper. I have to assume there was air in the shock and I am always very careful when I change the oil to top up the shock without air.

On extending the rear suspension. The Reg Bolton mod to create ground clearance and steepen the rake angle has been used successfully by me, Carleton Palmer and the Horners. It is difficult to see why Chris should run across such a problem, but I am inclined to believe that something else was also at play that may have caused a problem.

On a longer damper, see above. I believe that Horners used a longer damper on their Goodwood Rapide to get the faster handling needed for a competitive edge. It may not be greeted enthusiastically because most street riders do not feel the need.

On Nigel using Thornton springs on the rear. I did this and had the springs cock in the spring boxes. While not causing the bike to crash, it was disconcerting and caused me to develop my own Thornton coil over. Now that Thornton has offered them, I will use the coil over Thornton on the rear. I think for touring the springing offered on the Series D shock is the best, but Thornton will not do the things that Works is happy to do and I don't see a solution to that problem other than making sure your spring boxes do not cock.

On fully sprung seats, it is the best way to go for both solo and double. The Factory did so on Flash prototypes and the TT Flashes with no downside reported.

On interesting party tricks, at Pat Manning's annual party there are usually a dozen or so Vincent owners. With lots of bikes around I take one of the bike with stock Girdraulics and grab the grips and pull it up to full extension. At full extension, I grab the front brake. As long as I hold the brake the Girdraulic is seized. I climb on the bike and rest my knee on the oil cap. I then bounce up and down with all my weight over the handlebars. Nothing happens. There is no movement of the suspension. I then release the front brake and the fork finally drops from full extension. This has surprised many veteran Vincent men. Tom Kerr once dropped to his knees and said "Do that again." I then do the same with a Vincent with my short springs. I heft up the front to full extension, grab the brake and it unceremoniously drops back to its normal position. Even if it is a party trick, I want my front end to work at least as well as all the other non Vincents in the driveway.

Here is a photo of Carleton's two championship racers at Deland, Florida. Note that the Flash on the right has the Reg Bolton extension plate bolted on as well as a set of Thornton rear springs. Look at the angle of the RFM and the rake angle of the fork and I think the changed attitude of the bike is obvious. He won three national championships with this bike alone.

David

 

[Chris Launders]

Hi David
The RFM pivot was 1.5" higher than normal (I measured 3 others locally) and with the sidecar springs it didn't hardly move with a rider on board, all I did was fit allegedly pettiford copy springs and wind the eyes back in and that transformed it, nothing else was touched, in fact, shortly after he sold it to me and I've done 10k before fitting one of the modified steering stems.
Chris.

 

[vibrac]

I started with some incredibly long Petteford springs and I was not aware they had a negative effect on handling, unless you include falling over when parking on a slope because I could not reach the ground.

I agree about Pettifords they were the rage of the paddock back in the VOC club racing days I don't think raising the back end to the extent that they do would be detrimenta but you certainly need some stand extensions when you use them

 

[greg brillus]

The rear springs seem to be too short standard and the pettifords too long, you really only need a spring another inch or so longer. A lot of springs I have checked and replaced on solo bikes have been sidecar springs, I assumed they were installed because that's possibly all that was left in the parts bin long after the factory closed.

 

[timetraveller]

A comment for Nigel Spaxman above; have you considered the new AVO coil over damper? I have one on the shelf ready to fit when the bike goes back together and it seems like a well made item. Chris# experience with the AVO on the front suggests that they work well. I have no connection with the company.

 

[hadronuk]

From memory, the specification for Petteford springs is standard +1". My new ones from the spares co were more like +2.5".
Easy to shrink. Clamp spring fully closed on threaded studding, heat with hot air gun, leave to cool. Don't overdo it!!

AVO will produce an extra long rear coilover or damper if anyone wants one.

 

[hadronuk]

From memory, the specification for Petteford springs is standard +1". My new ones from the spares co were more like +2.5".
Easy to shrink. Clamp spring fully closed on threaded studding, heat with hot air gun, leave to cool. Don't overdo it!!

PS don't heat the whole spring. Just get part really hot, leave to cool. CHECK LENGTH! Repeat on different part of spring if more needed.
Stretching can be done (yes I overdid the shrinking) but tricky.

 

[Bill Thomas]

I had my first tank slapper on my outfit in 1965 , After shutting off hard = forks compressed !!, I was young and riding silly. Cheers Bill.

 

[Oldhaven]

At the risk of getting too far behind the front end discussion, I would be interested in knowing the real world average height and range for the rear frame member pivot, and I know Dave Hills always asks for this when he makes a center stand and uses a standard method for measuring. Realizing that B and C will have different numbers and that different springs and wheels affect this number, it would still be interesting, especially if sorted by model. I don't know if Dave is on the forum, but maybe someone close could ask if he has looked at this. Mine is 12 3/4 inches, rather tall for a B, I think, but that is with a Thornton coil over, 21" front and a Thornton rear with David's long rear springs
Also, for information, the full installed length of a rear non coil over Thornton on my B Rapide from UFM spindle center to RFM center is 10 3/4 inches when on the Hills stand and the rear wheel off the ground with a spring preload. I don't recall that it gets much less when I sit on it off the stand, but I can't measure that right now.

A moderator can move this if necessary to its own topic, but as in previous suspension threads this all seems to be related in ways to handling, comfort, and safety issues.

Ron