Hard riding; are girder always as harsh?

[Maurice Sanders]

Hello all club members

I have a 1936 Flying Squirrel which is one of the joys of my life. During lockdown it’s given me hours of pleasure for which I am truly grateful. I’m not going to pretend it’s totally sorted. Can an old bike be described in this way? But it’s running really well – lucky me. The only thing that takes the edge off the experience is the harshness of feedback from the front forks. The handling is superb but I’ve got to point of avoiding some roads because of the shaking my arms get when hitting a rough stretch. Obviously I’m getting older but I don’t remember this before and I’m wondering if there’s something wrong. I’ve checked everything I can think of. Everything that should be greased is greased and the spring  seems intact. No obvious play in linkages and tyre has miles left in it. Adjusting the steering damper makes no difference. I’ve experimented with tyre pressures going down to 19psi but to no avail. My other bikes all have teles and I wonder if girders do give a harsher ride but why haven’t I noticed this before? Any advice from members would be appreciated. Stay safe.

Maurice Sanders

[dave bushell]

Steering head  bearings ok?

[PhilCrowder]

If adjusting the damper makes no difference, check the friction discs. If they get grease in they become less effective.. Try new ones in clean conditions. Some people have strange ideas about the material to make discs from.

[Maurice Sanders]

Thanks for all the useful comments. I hadn’t considered bearings. As a matter of interest what would members recommend as tyre pressure back and front. I have to admit to be surprised when changing the front tyre pressure – mid 20s to 19 – didn’t seem to make a lot of difference. Perhaps my pressure gauge needs looking at!

Regards

[Stan Thomas]

Hi Maurice,

As you say “there is no obvious play in the linkages” might be a clue to your problem – so first question – does grease easily extrude from between the forks and their linkages?

If not, there are four spindles passing through the fork links with two thrust washers either side. Check that at these can be just turned by hand – if not, the forks will have a stiff and “jerky” motion. (but they are difficult to adjust to get just right)!

Now!  Has anyone changed the main spring??

Known only to 3.74% of motorcyclists, they have different rates, dependant upon the weight of the machine.  If your forks seem “solid” you could have too higher rate spring fitted.

However, the problem is not steering head bearings – but as Phil says, it could be greasy friction disks creating a greater initial force required to overcome the  “sticktion” (i.e. the initial movement from static  inherent with this type of damping design).

[dave bushell]

The reason I suggested head bearings Stan, was because some years ago I was riding my 1938 Prototype Clubman Scott quite fast over a not too smooth a track at a Beaulieu Motor Museum show and the girder forks started juddering quite badly as if they we’re bottoming out, especially when braking. No problems on normal roads. When I got home and checked them out, I found the forks and spring were ok but a fair amount of play had developed in the head bearings. Bearings and cups were replaced and the problem disappeared.

Dave

[BRIAN MARSHALL]

It might have a sidecar use rated spring. Measure the diameter of one of the coils using a digital caliper or something similar, and tell us the size. We can then compare it to the spring in a known good-handling bike.

[Maurice Sanders]

How interesting. You guys know some stuff. Just back from the garage and the spring measures 8.5mm on the calliper  about halfway down its length. Will drag the bike out into the sunshine tomorrow to check the spindles  as Stan suggested. Will report back on that. Thanks for all your help so far: I’ve learnt a lot.

Kind regards

Maurice

 

 

[Stan Thomas]

Hi Maurice,

Thank you for those few kind words – Brian is one of the 3.74% I mentioned in my earlier post!

Now, How long have you owned the bike?  Why I ask is that it is not unknown for a seller to tighten up the fork spindles to hide the wear, so a lot will depend upon what you find tomorrow.

What area do you hale from?  There’s a company in the West Midlands who overhaulsd girder forks but will not sell the parts (the miserable git)  – but don’t fret they are not that difficult to do yourself if you have access to a lathe  to make the bushes etc. and a liquid reamer to fit them.

Keep us posted.

Stan.

 

 

 

[Martin Heckscher]

Hi Maurice,

I’ve just re-read your original post – and there is no question in my mind that on a bumpy road you are always going to get a much rougher ride with girders than with telescopic forks. There may be nothing wrong with your forks. A rigid rear end doesn’t do much for comfort either of course.

Poor fork spindle adjustment is unlikely to result in a rougher ride but it will adversely affect the handling and roadholding. Regular checking is essential, as is lubrication or your spindles will wear rapidly. There is plenty of source material on how to maintain your girder forks in period publications.

Good luck

Martin

 

[PhilCrowder]

Martin I think his experience suggests that it appeared different from before. It may not be , but as you say there are plenty of articles on how to maintain girder forks.  You should try the ride on cyclemotors which seem much better on balloon tyres. These days avoiding potholes is a national sport.     I am just getting a Cyc Auto back together, that has blade type girder forks .    Still looking for a 300 cc lightweight. !!!!!

[Martin Heckscher]

Sorry Phil, you are of course absolutely right, Maurice did indeed report a deterioration, though he didn’t tell us over how long a period this had occurred.

As Stan points out, if the fork spindle adjustment is too tight this would make the ride quality worse – but I would expect it also to have a negative effect on the handling, and as Maurice tells us that it is superb, this is unlikely to be the cause of the harsh ride.

I still think that teles generally deliver a smoother ride over rough roads.

Martin

 

 

 

[Stan Thomas]

This is turning into quite some debate Martin!!

You are right that teles give a smother ride, principally because the damping medium (oil) provides a far higher restitutional capability than a friction damper, which requires a greater  force to start it moving than once that is achieved – hence friction dampers have a far greater degree of “jerkyness” in operation by comparison.

Also, a further factor is the ratio of the unsprung mass (front wheel and movable portion of the forks) to the to sprung weight (that portion of the rest of the bike acting as a downward force on the front wheel), which in a girder fork set up is higher.

Simply put, it is the ability of the forks to respond to road surface irregularities whilst also controling the rebound characteristics of the suspension medium – which is better for teles than girders as you say.  Its called the co-efficient of restitution.

Now, about the Parker sun probe. …………………..

Stan.

Stan.

• This reply was modified 3 years, 2 months ago by Stan Thomas.

[PhilCrowder]

I presently only have one bike with telescopic forks. either normal or upside down ones. I don’t ride much but my first Triumph had girders which I replaced with Matchless Teles. Its  64years since and I think it might have been an improvement. I did use to make F1 shock absorber parts , they were searching for improved damping in both directions,and adjustable at that. So whilst its quite obvious that hydraulic damping is superior to friction, it will depend on other things if handling is to also be considered. A pair of good Girders might well be better than some tubular based teles. I think that Vincent’s were girders with hydraulic damping. I can also possibly claim to have straightened more telescopic forks in York than the rest put together. Only repaired perhaps 10 girders of which the Scott which is neither was in its original brazing a bit suspect.  My first Norton  had girders , I was just glad to get it to run and it took me 10  miles to get it out of first gear !

[Maurice Sanders]

Wow! I am finding this discussion fascinating although I freely admit I’m out of my depth. I have tried to cover the points raised in correspondence so far and I’m starting to think that the linkages may be at least part of the problem. Thanks for the pointers Stan. One of them seemed a little stiff so I’ve tried to bed them in as much as possible without really knowing what ‘bedding in’ means. Spindles have been degreased and movement when pushed against front brake seems normal. What I could really do with is something like an exploded diagram with some indication of what would be a satisfactory set up. The point Brian raised about spring rating is a very interesting one. I have just refurbished the telescopic forks on my 1948 Ariel NG. First year of teles with no drain plugs and steel stanchions. I was struck by how much less robust the springs are compared to the Scott but of course there are two of them. But it was noticeable before I did the strip down to find a bit of treacle in each leg just how poor the suspension was. Stan is absolutely right: the fork oil seems to do much of the work and the bike is now transformed. I am starting to wonder if the improvement in the Ariel has coloured my perception of the Scott. However, I still believe that I have not got the set up on the Scott forks right and welcome all the help I get on this.

So,how about this for a theory. There is a problem with the linkages ( or spring rating) on the Scott but I had learned to live with it until refurbishing the forks on the Ariel forced the problem to the forefront of my mind by making for an unfavourable comparison. This combined with ever worsening road surfaces has demanded attention which I should have given it before. Plausible theory or psychobabble? I have really valued the thoughts of members so far and would welcome any further comments. The bike will be out on the road today or tomorrow and I’ll report back.

Thanks again

Maurice

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