FF: Forks Modified Steering Stem

[greg brillus]

Thanks Mac, that's a good description..........Like I said, I had proved this to myself using a spare front springbox as a jig and a set of scales to measure the differences from one spring to another. On the spring I had used earlier, I checked the spring before and after I had chopped 3 inches off it.

 

[davidd]

McVette makes a good point and it is often easy to get lost or turned around when talking about these things. Anyone should feel free to ask for an explanation.

Many years ago when I was doing the initial testing I came to the point where I had to try many different spring rates to get a feel for the range of rates I should order for the short springs. To keep it all straight I made a table to record the spring rate of a Thornton spring that was cut off at various lengths. As you can see from the table, the shorter the spring is cut the higher the spring rate:

David

 

[vibrac]

So the 1/2" of broom handle mod beloved by us old racers of the sixties was pre loading the standard spring by 30lbs (1st table post #401) and the other beloved mod of yester-year was to fit Pettiford springs at the rear to increase ground clearance. is science catching up with rule of thumb or not?

 

[Bill Thomas]

But even useing David/T.T. white (strong springs ) I still have to put Coins/Broom handle packers in the spring boxes on a standard set up. Or it sits much to low . Cheers Bill.

 

[timetraveller]

Are you sure about that Bill? Remember that the whole point of David's springs was to move the steering head downwards so that the bottom link was slightly up at the front with the rider seated. Don't tell me that you packed it up to bring it back to the original height!!

 

[Bill Thomas]

Yes I know that, But without packers the Engine is on the floor !!, As you say you can fit the spring by hand but that is no good for my bikes, Which are Standard twin and Comet, I think I have about 1.1/4" packers, Sitting on it with these in the lower link is about level, I am happy with that, And when the weather gets better, I am going to put an inner valve spring under the shroud of the standard front damper on the Comet, Which needs a bit more bounce !.
Cheers Bill.

 

[Chris Launders]

If you put a valve spring on the damper aren't you going to limit the travel on it by the spring getting coil bound before the end of the damper travel ?

 

[vibrac]

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....

 

[greg brillus]

The installation of the short springs was always going to be a compromise, whereas the new stem returns the position of the ride height back to normal. In fact because I also fitted a Thornton coilover on the rear when I rebuilt my bike last year, the overall ride height of the bike is much taller than standard. To give you some idea, I had to cut and lengthen my Kawasaki side stand by 35 mm to get the bike sitting back at the right angle when resting on the stand.

 

[Bill Thomas]

If you put a valve spring on the damper aren't you going to limit the travel on it by the spring getting coil bound before the end of the damper travel ?

Hello Chris, Not by much, It's only the inner spring, And I thought we all agreed, there is too much movment , It's just a bit of Fun, Bill.