Fork Sag on Banana Forks

[Supergrandad]

Question for you guys with banana forks on trials bikes. I have a 66 Greeves Anglian with the banana foks and 2 shock absorbers that have no adjustment. The damping seems good and it rides well but I might like a little less sag. It currently has about 1.5 inch what is normal for these forks.
Ken

[IanCordes]

Do you know the free length, and spring rate of the spring dampers?

[Supergrandad]

Do you know the free length, and spring rate of the spring dampers?

The free length between bearing surfaces of bolt holes is 37cm and No I do not know the spring rate.
Have you a special formula.

[Phil Hyde]

Bananas

I have Banana forks on my TFS. I run slightly longer units on the front with spring poundage rates to take account of the machine weight and rider.

So, without rider, sat at rest both front and rear units should not move. Rider on, a small amount of travel. This permits the front wheel to remain in contact longer. The remaining travel in the units is there to take up bumps and weight transfer of the rider.

As we are talking trials machines the tyre pressures should not be overlooked. 3-4 psi in the rear and 9 in the front. These settings have served me well for many years in hundreds of trials.

Speak to Norman Blakemore he has helped me out more than once and also sells reasonable units. USUAL DISCLAIMER.

[IanCordes]

The original Girling spec for them was:- overall free length 13.9"; spring free length 9.4" and spring rate 54lb. I believe some riders prefer a lower spring rate, say 45lb.

Obviously the spring rate will affect the sag, as will your weight; but whilst you probably know the latter, you don't know the former, so that is not too much help!

Is the issue you have with the sag that it appears to droop the front end too much? If yours are a touch shorter, then the sag will have that effect.

The reason I mention it is because I have looked into buying springs for my banana forks recently, but it seems a bit tricky to find some of the correct length. Too long or too short will of course adversely affect the steering geometry.

Having said all that, I am a bit puzzled by your 37cm, which is 14 1/2". Probably best remove one of the shocks and measure it.

Ian

[Supergrandad]

The original Girling spec for them was:- overall free length 13.9"; spring free length 9.4" and spring rate 54lb. I believe some riders prefer a lower spring rate, say 45lb.

Obviously the spring rate will affect the sag, as will your weight; but whilst you probably know the latter, you don't know the former, so that is not too much help!

Is the issue you have with the sag that it appears to droop the front end too much? If yours are a touch shorter, then the sag will have that effect.

The reason I mention it is because I have looked into buying springs for my banana forks recently, but it seems a bit tricky to find some of the correct length. Too long or too short will of course adversely affect the steering geometry.

Having said all that, I am a bit puzzled by your 37cm, which is 14 1/2". Probably best remove one of the shocks and measure it.

Ian

Cheers for reply Ian, Interesting your planning/thinking of changing your spring rate. I think I know the answer to my question having been riding for many years on and off road I have a good understanding of Pre Load, Rebound and Sag. If I put things this way it is easier to understand what I want to reduce. Let say I want to open my throttle to lift my front wheel in the air, currently the first thing that happens is the 1.5 inch of sag has to be taken up before we have lift off. I think this needs to be similar to the rear =1/2 to 3/4inch of sag. Agree with you I do not know my spring rate but I think it is too soft. I have only just obtained this machine and have ridden it once in a trial, we did quite well. It is certainly very different to my other Anglian with the Ceriani forks. I will call in and have a chat with NJB shocks. Norman is a great chap and I am sure we can easy sort some different springs or maybe even get something new that will be better fit for purpose.
Ken Carroll

[Supergrandad]

I have Banana forks on my TFS. I run slightly longer units on the front with spring poundage rates to take account of the machine weight and rider.

So, without rider, sat at rest both front and rear units should not move. Rider on, a small amount of travel. This permits the front wheel to remain in contact longer. The remaining travel in the units is there to take up bumps and weight transfer of the rider.

As we are talking trials machines the tyre pressures should not be overlooked. 3-4 psi in the rear and 9 in the front. These settings have served me well for many years in hundreds of trials.

Speak to Norman Blakemore he has helped me out more than once and also sells reasonable units. USUAL DISCLAIMER.

Thanks for reply cheers Ken

[IanCordes]

Ken. In a nutshell, the only thing which will reduce static sag is to increase the spring rate. Adjustable pre-load on your shocks would help you play around with it, to get it to your liking. It looks from the photos as though the current shocks are plenty long enough, as the front end sits quite high. It may be just the angle of the photo though.

Good luck with it.

Ian

[Brian Thompson]

A few additional thoughts.....

Just thought I'd chip in with a couple of thoughts, first on terminology.....

Static sag = sag without rider.

Rider sag = sag with rider on board (the important figure.)

Adjusting the spring pre-load will not affect spring rate, just the ride height.

A good rule of thumb/starting point for rider sag is around 1/3 total suspension movement.

If the spring rate is 'in the ball park', fine tuning of the ride height on non-adjustable units could be achieved with the fabrication/turning of a pair of hollow 'top hat' spacers fitted above the springs, with the thickness of the 'rim/flange' setting the amount of preload/ride height. Original Girling gas shocks employed the 'finned' "cooling" rings for this purpose....add or remove to increase/decrease.

Happy fine tuning Ken, and update us on progress!

Brian.

[IanCordes]

Quite right Brian.

[Supergrandad]

Just thought I'd chip in with a couple of thoughts, first on terminology.....

Static sag = sag without rider.

Rider sag = sag with rider on board (the important figure.)

Adjusting the spring pre-load will not affect spring rate, just the ride height.

A good rule of thumb/starting point for rider sag is around 1/3 total suspension movement.

If the spring rate is 'in the ball park', fine tuning of the ride height on non-adjustable units could be achieved with the fabrication/turning of a pair of hollow 'top hat' spacers fitted above the springs, with the thickness of the 'rim/flange' setting the amount of preload/ride height. Original Girling gas shocks employed the 'finned' "cooling" rings for this purpose....add or remove to increase/decrease.

Happy fine tuning Ken, and update us on progress!

Brian.

Will do Brian, all good fun and not that costly to have a play. I do have a couple of top hats knocking about. Thanks for replying. Ken