FT: Frame (Twin) Suspension and Handling Upgrades

[Speedtwin]

Rapide Touring,
I am happy to report that the conversion to an AVO front damper and rear coil over shock with a 275 spring has gone very well.
I am fat at the moment and was a little worried about the spring weight as being too light at 275.

The addition of the Norman Walker steering damper to a refreshed front end has been fantastic made all the difference.
I tested the bike with some very hard riding on a local circuit to log the suspension movement during an open track day.
Undulating hilly circuit lots of high speed bend and a few bumpy bits good mimic for road racing set ups.

Results of the logging are mixed, not great as the loggers are designed for interrogation of telescopic race forks and rear shocks.

Rear logs are okay they enabled me to dial in the rear shock, which is running with minimal preload 7 inches, for road use and three clicks on the damping which gives a positive feel, soft for touring, road use tyres are firmly in contact with the road feeling through the seat is lovely.
Only use this setting if you are a chubster..

Front logs showed some weird results the local suspension guru looked at the results and shook his head.
All we got that made sense was the front damper movement and reaction times which again were very positive I have it set at two clicks very slow damping and it works well.
Tracking the front axle was interesting but useless and failed to give a clear result only the horizontal movement looked right.
The long eye bolts seem to be the best length for me and the AVO front damper.
A fixed ortho logger camera packed in and was not working on the day it is the best way to capture all the front movements.
We stick little targets on all the moving bits and it watches these and records them in UHD high speed.
Worked on the race bikes did not work on the Vincent maybe not six volt compatible........

Suspension Yoda was very impressed with the steering damper set up, clicked at exactly mid way for normal road use it showed positive reaction speed and force and is working very well.
Dialed up on the track was very good, small section over two rises were the front goes light it paid for itself.
I can not recommend these enough we all should have one safety first.
With the damper dialed down the same rises as same speed resulted in a noticeable head shake not a full on tank slapper but I suspect if pushed slightly harder that was in the post.
Speaking of Post what is going on with Pat my stuff from the VOC Spares is taking forever...

So some 150 miles of road riding later and it is like riding a sofa rather than one of those dodgy beds of a feather type..
Wheels are in contact with the road all the time, ride is positive handling is good, feels planted.
Running modern tread pattern modern compound Avon Roadrider two tyres.
Riding very sensibly on the road, I am still getting used to and dialing in my clutch adjustment, changes up the box is great down the box not so great think it is me, not the bike.
Any suggestions welcomed.

Thanks to Norman for all his help and his lovely steering damper, AVO for their units priced very reasonably,(freeset Neil please) and all of you who advised I think I am there or thereabouts.

I plan to do the same but firmer on the Comet before I go track day riding.
Had a lovely day out with our friends from K-Tech and Ohlins who all loved footering about with the bike.
"How old is it?"
"Feks sake".

Oh and we got some bikes ready for the Manx which was nice.
I will not be going back to the rock this year as I will be in the Hebrides on the Rapide turning oil into smoke and petrol into noise.
Al

 

[timetraveller]

Very interesting and thanks for letting us all know the results of scientific testing. I wonder whether the results for the front are due to the original girdrauic geometry. This means that the wheel has to go forwards when deflecting upwards over a bump before it starts to go backwards. It is this problem which causes the front suspension to lock up when braking hard with the bike trying to ride up over the front end. If you are in a position to repeat these tests then I would be prepared to LEND you a JE steering stem, the different springs and the brackets to allow you to fit the same hydraulic steering damper to the new stem. I will pay postage from here and all I ask is that the parts are returned in as new condition and that you let us all know the results.
The amount of steering damping you use is interesting. Most people who have them use a few clicks up from the softest setting but there is one very experienced Vincenteer who uses the system at about half the full setting. He finds that better for him on his Shadow.

 

[Speedtwin]

Yes it appears that the front wheel moves forward and up at the same time over a bump in an arc as you noted, this was with original geometry.
On fall away it appears to return on the same arc.

When braking the movement was noted to cease at the point the brake was applied.
The detail was poor but he thought the suspension was not returning as it did with no brake on.
Advice was try to ride out the bumps, be careful heavy braking know your limitations brake before cornering avoid brake correction in bumpy bends.
Never brake on fork fall away as the bike will want to ride over as you say.

One interesting thing was hammering into a bend and braking late the fork almost wanted to oscillate the wheel this was apparent with the steering damper turned off.
Turned on and set just over half way this was corrected.



Yoda had said that some subtle changes to the rake could improve this.
Would not be drawn on which way shorter or longer or more attack.

What I failed to mention is I am running twin springs in both spring boxes he had remarked that it would maybe be better to run a softer set up on the front, spring wise maybe one outer on one side and the twins in the other side.
My travel on the spring boxes marked at max compression was 30mm or just over an inch measured from the bottom of the outer box cover.
Al

 

[timetraveller]

With the JE set up the movement of the spring bozes is 3 inches plus. To enable the full amount of this one has to shorten the inner and outer spring boxes to ensure that they do not clash and limit the total movement. The upwards and downwards movement has to be the same as this is controlled by the upper and lower links. This is a measured path of the front wheel spindle by me when setting up and testing the system. The squares on the graph paper are one inch squares.

 

[highbury731]

Just to make sure I have done the correct amount of shortening of spring-boxes, can you tell me the required length, from bolt centre to end of the box, please.
Paul

 

[Speedtwin]

Nice one how did the bike handle after the alterations Norman?

 

[timetraveller]

Please don't take my word for it. Just about every Vincent which is being raced at the moment with the standard front end has the JE stem, or in the USA, a similar design by Dave Dunfey. Greg Brillus in Australia has either sold or fitted between 50 and 60. The Tilleys from south Wales who are long distance riders find it a vast improvement and have posted a video of the new forks movement. Chris Launders from south Yorkshire has also been impressed by the handling and has posted his video of the fork movement. The chap who was racing Patrick Godet's Flash on the Isle of Man a few years ago had one on his bike and, if I remember correctly, was the fastest Vincent around the course ever. So much has been written about it on this forum that I could not expect any one to read all of it but when you are back at home and have spare hour or two it would be worth browsing. Try searching under 'modified steering heads. I have sold about 300 now and have another twenty on order for machining now. This is all for zero profit as I was so impressed by the system when I finally understood what John Emmanuel had designed, and having had a tank slapper at 100 mph many years ago while racing at Cadwell Park that it seemed to me that this was such an improvement to the safety of Vins that it was worth getting involved. I never thought that it would take so much time and that so many would be used. JE's design solves the handling as far as it can. The improvement to the comfort comes from my own design efforts and those of Hadranuk, on here, who persuaded AVO to do the development work on their dampers and Greg Brillus in Oz who came up with the idea of replacing the Oilite bushes in the eccentrics with ball races on the replacement concentrics.


As for the length of the spring boxes, the question by highbury731; the problem here is that not all spring boxes are the same. No surprise there then. In particular the part at the top of the outer can be noticeably different from bike to bike. I have measured an outer one which I believe is unmodified from new and it is 12.25" from the bolt centre to the bottom of the tube. I recommend cutting off three quarters of an inch to a full inch off both the inner and outer tubes. There is a way to check but it is tedious. Remove both front springs and then ensure that the inners will go all the way into the outers, replace the boxes. Leave the springs out. Move the forks from max high to max low and look at the distance between the bottom of the outer tube and the part of the blade forging to which the inner tube connects. If the tubes are too long then there will be a clash between the outer tube and the fork blade at that point. The total movement is controlled by the combined length of the damper and the lower eyebolts and it is important that the longer eyebolts are used with the AVO damper to ensure that the forks are in the correct part of their movement range. I would point out that Greg in Australia prefers to use stronger springs than most people over here find comfortable. He uses the 45 lbs/inch springs and a softer damper. I tried supplying those to people several years ago and when used with an AVO damper all the middle to lower weight riders found that combination too hard. I supply the 45 lbs/inch springs to all riders of twins over eighteen stones and one rider who is about 21 stones also packs the stronger springs with about half an inch of solid material. For Comets, lighter riders or even stripped down for racing Comets I supply springs from 30 lbs/inch and then 33 and 36 lbs/inch springs as the weight of the bike and rider increases.

 

[timetraveller]

This is a message for the chap who asked if I could replace his concentrics for the JE mod intended for use with the Oilte bushses for the later type which are used with ball races. I have now sourced what you need. The reason for this message I cannot find either an email or PM from you so need to know who you are and are you still interested.

 

[Chris Launders]

Yes it appears that the front wheel moves forward and up at the same time over a bump in an arc as you noted, this was with original geometry.
On fall away it appears to return on the same arc.

When braking the movement was noted to cease at the point the brake was applied.
The detail was poor but he thought the suspension was not returning as it did with no brake on.
Advice was try to ride out the bumps, be careful heavy braking know your limitations brake before cornering avoid brake correction in bumpy bends.
Never brake on fork fall away as the bike will want to ride over as you say.

One interesting thing was hammering into a bend and braking late the fork almost wanted to oscillate the wheel this was apparent with the steering damper turned off.
Turned on and set just over half way this was corrected.



Yoda had said that some subtle changes to the rake could improve this.
Would not be drawn on which way shorter or longer or more attack.

What I failed to mention is I am running twin springs in both spring boxes he had remarked that it would maybe be better to run a softer set up on the front, spring wise maybe one outer on one side and the twins in the other side.
My travel on the spring boxes marked at max compression was 30mm or just over an inch measured from the bottom of the outer box cover.
Al

If you want to see how the forks behave with the JE stem, AVO damper and springs to suit I made a video of mine, taken from the crash bar, ignore the rattles and vibration at speed, you will need to view it more than once taking note of the road condition, fork movement and bike stability. Chris.

 

[timetraveller]

To see how the system smooths out the bumps look at the movement of the concentric against the passing road side vegetation.