FF: Forks Modified Steering Stem

[BigEd]

Suspension set up can be quite complicated even on a "relatively" simple machine like a Vincent. It can also counter intuitive where you think that one end, "A" has a problem but in fact altering the other end, "B", improves "A" and vice-versa.
Great to hear that Martyn is out on his Comet again and enjoying the improvements to his ride.

 

[timetraveller]

Chrislaun also found the same thing while road testing the new front ends. He does some quite serious riding over serious bumps at high speed and once he had the front end to his liking he found the rear end to be spoiling the ride. For those who are waiting for the new front ends I can report that machining of the parts is well underway but I haven't got any parts yet. Following the road tests from the Southern Hemisphere I am considering offering different spring for different bikes. For example 33 lbs/inch for Comets, 36 lbs/inch for twins which will continue to use the Oilite bushes at the rear of the lower link and 45 lbs/inch for twins which will use Greg's ball race mod which seems to reduce the front end friction by an unexpected amount. The stronger springs would have two inches of preload rather than three inches with the weaker springs. Your thoughts please gentlemen.

 

[Tom Walker]

I have just read the whole thread, and I must say that the idea of optimizing girder type forks to the extent where they work very well as a way of suspending the front of a motorcycle is fascinating, and has really got the old grey cells working. Talk about the appliance of science!
I was just going to mention that cutting coils off a spring to shorten it will change its rate, which may need to be taken into account. Im sure thats like teaching Granma to suck eggs, but I have been there....

 

[Martyn Goodwin]

..... The extra freedom of the forks does take a little getting use to, I must admit to trying to grab the damper knob a few times, and quickly realize that does nothing anymore.

What damper knob? LOL

Martyn

 

[Martyn Goodwin]

I now have had my first 'real' ride on the new suspension after first switching to a fully suspended seat. Bit like great wine - just gets better and better. To get the maximium benefit of the upgrade to the front suspension you really need to move to a fully suspended seat.

It acheives two things - both IMHO both good. First up is provides a degree of isolation to your back and backside from road shocks as the seat is no longer connected rigidly to the up down motion of the rear wheel. Second - and more inportantly it reduces the unsprung weight (by the total weight of rider and pillon) that the rear suspension needs to deal with; as a result the rear damper - whatevey you use - has a much easier life and actually has a chance to do its job.

Yesterday I covered a wisker over 170 miles, mostly in hilly country. As I noted earlier I found that I was unintentionaly cornering at higher speeds than before the changes plus I found that the brakes were more effective and overall the bike was way more stable - at all speeds. Within the 170 miles was around 8 miles of unsealed road with a fine gravel surface. Even on the gravel the bikes handling and feeling of ride security was greatly improved with the suspension actually managing the varing surface. With the original suspension setup on unmade roads there was a lot of wheel hop and side stepping - with the new setup these spincter tightening effects were all but absent.

Moving to a fully suspended seat is not just a matter of removing the rear FT94 friction struts and replacing them with a straight strut from the seat to a suspended part of the bike. Do this and you may well have serious issues. You need to ensure at least 2 things. 1. that there is no new stress applied to the seat frame and second, that there is no way that any part of the rear suspension can hit against the new seat strut you plan on installing. There will be a detailed article on this in OVR within a next few months. Just to keep you alert to the problems - here is a photo of what happened to a seat frame after a 'simple' strut was used to effect a fully suspended seat. Not nice.

Martyn

 

[BigEd]

I now have had my first 'real' ride on the new suspension after first switching to a fully suspended seat. Bit like great wine - just gets better and better. To get the maximum benefit of the upgrade to the front suspension you really need to move to a fully suspended seat.
It achieves two things - both IMHO both good. First up is provides a degree of isolation to your back and backside from road shocks as the seat is no longer connected rigidly to the up down motion of the rear wheel. Second - and more importantly it reduces the unsprung weight (by the total weight of rider and pillion) that the rear suspension needs to deal with; as a result the rear damper - whatever you use - has a much easier life and actually has a chance to do its job. .............
Martyn

Dear Martyn,
Great feedback on the benefits of the suspension modifications. The fully sprung seat mod does reduce unsprung weight but I query your statement that it is reduced "by the total weight of the rider and pillion". I believe that as a rule of thumb with the standard seat stay setup the pillion receives approximately half of the suspension travel enjoyed by the rider. The rider is already more or less fully sprung.
With the standard seat stays the rear springs usually cope reasonably well with the additional weight of a pillion as only half the pillion's weight is sprung. With the fully floating seat and a pillion I found that the AVO monoshock was of great benefit as I could wind in some spring pre-load to compensate for the greater weight. (Hastily adding that the greater weight is beautifully formed and in wonderful proportion or so she tells me.)

 

[Martyn Goodwin]

Dear Martyn,
Great feedback on the benefits of the suspension modifications. The fully sprung seat mod does reduce unsprung weight but I query your statement that it is reduced "by the total weight of the rider and pillion". I believe that as a rule of thumb with the standard seat stay setup the pillion receives approximately half of the suspension travel enjoyed by the rider. The rider is already more or less fully sprung.
With the standard seat stays the rear springs usually cope reasonably well with the additional weight of a pillion as only half the pillion's weight is sprung. With the fully floating seat and a pillion I found that the AVO monoshock was of great benefit as I could wind in some spring pre-load to compensate for the greater weight. (Hastily adding that the greater weight is beautifully formed and in wonderful proportion or so she tells me.)

Ok Ok... It was a generalisation. BUT it IS reduced!

 

[BigEd]

Ok Ok... It was a generalisation. BUT it IS reduced!

Dear Martyn,
My comment wasn't meant as any kind of criticism. I was just trying to point out that getting the spring rate right improves the ride quality and that going "fully floating" introduces another factor especially when you need to carry a passenger and.or luggage.

 

[Martyn Goodwin]

Dear Martyn,
My comment wasn't meant as any kind of criticism. I was just trying to point out that getting the spring rate right improves the ride quality and that going "fully floating" introduces another factor especially when you need to carry a passenger and.or luggage.

NFW !

 

[Martyn Goodwin]

Moving to a fully suspended seat is not just a matter of removing the rear FT94 friction struts and replacing them with a straight strut from the seat to a suspended part of the bike. Do this and you may well have serious issues. You need to ensure at least 2 things. 1. that there is no new stress applied to the seat frame and second, that there is no way that any part of the rear suspension can hit against the new seat strut you plan on installing. View attachment 15952

For those wanting to know how I addressed these two issues, here is a photo

Martyn