FF: Forks Modified Steering Stem

[Bill Thomas]

Bill you are beyond help! At least I have the good sense to keep fairly quiet while the good gents finish their deliberations and I can find the pennies to purchase the resultant improvements you on the other hand force them to spend hours over their Excel sheets trying to see how wrong you are.
Either that or you had far too much christmas pud. You need to get back into shape as I remember you (see picture) Incidentally I dont see any piles of coins on your bike here....

Hello Vibrac, I think I am going MAD !!.
Not coins in the Commando Forks, But long bits of threaded hex', The Vin' Engine is too heavy so I had to do a JOB on them also !!.
I just can't stop playing !!.
I don't have a clue what they are talking about, So I am trying to keep out of it, But I had to say something when you started on about Broom Handles !!,
Excel Sheets ! I thought they were BED SHEETS !!
And my Standard Twin also has the long rear springs !. Cheers Bill.

 

[Martyn Goodwin]

Blimy! if its better than Bramptons I had better start getting interested: any photos?

Better than Bramptons!!!! Who is foolish enough to think they are shake free?

Take a look at this - Its Marcus's Brampton equiped twin having a MASSIVE headshake.

Was only good luck that kept the bike and rider undamaged!!!

 

[Martyn Goodwin]

Better than Bramptons!!!! Who is foolish enough to think they are shake free?

Take a look at this - Its Marcus's Brampton equiped twin having a MASSIVE headshake.

Was only good luck that kept the bike and rider undamaged!!!

Its at the 3 minute 20 second mark that the "fun" occures

 

[greg brillus]

It just proves that any bike given the right circumstances can shake its head. My guess is there is more to that than meets the eye.......Something loose or similar. Chris, if you are back on the forum, can you tell me if your suspension is topped out without you astride the bike, this with the pair of 36 lb springs installed, cheers.............Greg.

 

[davidd]

It looks like a good example of how lightening the front end just by changing riders can have a dramatic affect on the propensity to wobble. I think with the high weight on the rear might be creating the problem for the lighter rider. The heavier rider blows right through with no issue.

David

 

[timetraveller]

Greg, I can answer your question. Recall that the idea is that without the rider the lower link is slightly down at the front. The exact angle is controlled by the length of the damper and the eye bolts. So at that stage the suspension is 'topped out'. When the rider is seated then the front is pushed down just enough so that the lower link is now up at the front. That total movement should be about half an inch. This is the best compromise that I could come up with to combine travel and comfort with the limited amount of movement possible with the fork design. The spring rate and the pre-load were worked out for Chris' weight. Lighter riders might well find that less pre-load is needed. We cannot go for lighter springs as the forks would bottom out at the other end of their travel.

 

[greg brillus]

My guestimate is that the unladen bike ( for a twin) needs to have approximately not more than 200 Lb.'s of spring loading at rest. I proved this over the week end by installing one of my springs on one side rated at 50 Lb.'s with 2 inches of pre-load (100 lb.'s loading). And on the other, one of the 36 lb springs, which at 3 inches of pre-load is 108 lb.'s. At this set up the suspension was quite definitely "Topped out" Ok then I removed the 36 temporarily and cut 1 inch off its length (I'm getting pretty good at this) thus lowering the pre-load to 2 inches and a total of 172 Lb.'s combined. This now has the bike not topped out and after I sat on the machine the front shocker had used about 15 mm of travel. I also tried the two 33 lb. springs which seemed ok at first, but I found the front end would pretty much bottom out under hard braking, maybe ok on a single with light rider, I'm not sure. I don't feel that having the front end near topped out with the bike on its stand is a good idea, as it means the front end is going to hammer away at the shock absorber very time the front end becomes light over certain road conditions. I definitely feel that there is a limitation to how soft you can go, and slight variances of spring rates makes little to nil difference at all. The twins definitely reach a point where going too soft has no effect other than bottoming out. And the singles are much smoother which I guess is to be expected from their lighter weight. I had hoped to get my twin as "Soft a feel" as the singles, but after testing with numerous springs, this seems unlikely. But I will say that I am most happy now, and the spring set up I have is about as good as it gets from my testing. The only major change would be to go to a fully sprung rear seat, to maximize on the comfort at the rear. But that's another story. Cheers for now.............Greg.

 

[vibrac]

Dont forget the riders feedback. Years ago at Silverstone I had great fun on the twin through corrams curve on the Rapide twin (broom handle modified)
I consulted Ron Kemp of course 'grip the tank with your knees and let your hands relax" , he said. it worked
The advice was repeated to me by an old Australian in 1999 when I was about to lead group 2 out for the closed roads lap and I voiced my misgivings about the bumpy road through schoolhouse towards Ramsey. He also added "dont be clever on the road out of Ramsey towards the hairpin- nobody does that fast on a Vincent" - he was right!

 

[Chris Launders]

Hi Greg, I use a Hill's style centre stand so there is virtually no weight on the front end and it is topped out as would be expected, if I drop it on to it's wheels which is the same as using a rear stand I have 1/4" of sag and 1/2" when sat on it.

I have realised that I did not reset my cable tie last time I had chance to get out on it, so my saying it was still using all the travel with the damper at 1/2 and 3/4 was not valid, I'll just have to try again.

Chris.

 

[greg brillus]

You blokes and your bits of broom stick................I can only imagine that the only reason for that was to gain more ground clearance, luckily for me I was able to do it in other ways. I seriously don't know how you guy's didn't kill yourselves........... I guess for every lucky one there was an unlucky one. Chris the other thing too is that the springs do settle somewhat after some use. I'm not convinced about the theory that you make the most of every mm of suspension travel by using overly soft springs. When you are getting along at speed and need to stop in a hurry, you still need some suspension travel in reserve or else the opposite happens to what we were trying to avoid in the first place. The suspension is never going to match a modern bike simply due to the lack of travel. But it can be made much better than standard, and the twins are never going to feel as good as the singles due to the extra weight of the machine, it is actually quite noticeable. Having said all that........I thoroughly enjoy riding my twin now. And I have two Shadows in the workshop undergoing the same surgery as we speak.