F: Frame Help required measuring coil lengths on AVO coil over rear dampers.

[timetraveller]

Sometime before Xmas Chris Launders bottomed out the rear end of his twin over a particularly severe pothole. Since then Chris has been taking lots of measurements and I have been doing calculations. When Rob Staley developed these units with AVO he produced a spread sheet to work out what springs to use with what weight of riders, possibly with pillion passengers. Our intention is to put an easily consulted table, both one here and in MPH, which riders can consult when setting up their bikes. We have now come up with a table of rider weights and spring compressions but before putting it on here or in MPH it would be good to check the calculations with what people are experiencing in the real world. Therefore this request is for anyone who has a twin with this set up and has the time and patience to make some measurements. Place the bike on the rear stand. Measure the distance, in inches if possible, from the lower edge of the preload adjuster at the bottom end of the spring to the top of the upper spring aluminium stop ring. The measurements that would be useful are bike only, bike with rider seated and feet off floor (we need to know your weight as well) and then finally, if you carry a pillion passenger occasionally, the same measure of spring length with both rider and pillion seated and we need to know the weight of the pillion rider as well.

Thank you in advance.

 

[vibrac]

Always assuming we have the same springs I have changed mine* I have one on the Comet and on the twin changed it up again for the racer) so especially if you inherited the bike and dont know the history it would help if you gave us dimensions of the 'standard' spring wire thickness hopefully unladen length to avoid spurious data
*AVO are just down the road and very accommodating

 

[timetraveller]

The standard spring is 275 lbs/inch. the length from the bottom of the preload ring to the top of the top aluminium ring is 8.55". There are 10 coils with a gap beween the coils of .497", measured at right angles to the wire, not along the length of the damper. Wire diameter is 0.385". Fully sprung seat of course.
The springs are available in 25 lbs/inch steps, 275, 300, 325 etc. Thank you.

 

[Bazlerker]

My Rap is undergoing a partial restoration right now..one of the areas to be addressed are the front and rear springs and dampers - An AVO coilover is being considered as a replacement for the petteford springs and original damper currently fitted …I’ll be watching this thread with interest.

 

[Comet Rider]

Hi Norman,
On my Rap I went to a 350Lb spring after talking to AVO, and you know I'm no lightweight,

Neil

 

[timetraveller]

Yes, Chris has just moved up to the same although I think he is about thrree stones lighter than you. The table we have made starts at 50 kg, 110 lbs, 7.9 stones and goes up to 160 kg, 352 lbs, 25.1 stones so should cover most people. It is just that before making the table widely available I would like to get a few more real world points to check my calculations. I am told that springs up to 400 lbs/inch are available to order.

 

[Michael Vane-Hunt]

I went to a 350 pound spring as the 250 was bottoming out.

 

[oexing]

For extreme potholes there should be a rubber buffer on piston rod - as typically found on other shocks. Otherwise I´d leave the AVO alone when it is allright on your favorite country roads. I´d think the damper should have min. half of total stroke left when all loads are on the bike on wheels at standstill. Or more than half ?? A harder spring that handles even extreme potholes will be way too harsh for most of the time.

Vic

 

[timetraveller]

.Yes Vic, buffers are fitted to the AVO rear coil overs. Two types are available. One increases the resistance to 1,000 lbs over 7 mm of compression and the other to1200 lbs over 10 mm of compression.

 

[Michael Vane-Hunt]

I find the 350 pound spring much better as in more comfortable. I am heavy and usually usually travel with full luggage. Seldom two up but the 350 spring is really needed when I have a pillion.