samedi 10 décembre 2016

Accessoire - suspension

Un article intéressant d'un proprio australien et spécialiste des amortisseurs. Il prêche pour sa paroisse mais je pense que les données parlent quand même d'elles-mêmes.

Le Sag pour un pilote sur une AT devrait être de 65.4mm. Un pilote de 90kg sans bagages arrive déjà à 83mm en full preload et avec bagages à 118mm (passager). Incroyable. Comment Honda peut laisser passer ça et comment la presse et les "spécialistes" ne peuvent pas le voir et le dire?

Comme quoi, les suspensions sont ce qu'elles sont mais si vous sortez du moule des 70-80kg et si vous faites un peu plus d'off-road que la moyenne, il faudra passer par la case remplacement ou recondionnement. Je l'ai fait pour la DRZ et c'est une machine incroyable maintenant dans le terrain.

Leur guide pour le règlage

The Africa Twin has a cult following that most motorcycle makers can only dream of. With a string of Dakar wins in the late 80's (back when it was actually run from Paris to Dakar), the original was a seriously capable offroader, built to cope with anything.

The new AT has an engine to die for. The suspension, initially rumored to be off the CRF450R turns out to be more 1980's and early 1990's technology. Typical rider reports are initially great, then when pushed the suspension gets out of it's depth quickly.

We have been working with a few experienced AT owners developing settings both on the road, trail and on the dyno. Our settings will allow you to ride at speed with safety while retaining the plush feel and allowing for luggage.

The USD Showa 45mm forks have been given a workout on the road, trail and desert. We have a great bank of settings for the fork.
Fork Revalve & Service. Send us the forks & shock, plus info on your height, weight, ability, terrain, and your complaints. We will give you back the customised results from our settings bank and experience.

The stock 46mm Showa shock is not a bad unit but set up very lightly for road touring with an emphasis on comfort. Although the shock spring rate (8.3kg/mm) is OK for an 85kg rider, the shock spring preload needs to be increased dramatically to help keep the ride height up. We have done some experimenting with stock preload, see below.

For those of you who haven't read our setup guide, (and you really should) here are the basics of sag.

If you have the bike up on a lift, the suspension is "topping out", completely hanging free. This is called the free length and it's as long as your suspension gets.

Now if you put the bike back on the ground, the suspension will drop a little due to the weight of the bike. The amount it drops is called static sag.

And if you then sit on the bike, the suspension will drop some more due to your weight. Even further if you carry a lot of gear. The amount that the suspension has dropped from the free length is called the rider sag.

A "classic" sag setting is 10% shock travel for static sag and 30% shock travel for rider sag, so here are the numbers for the CRF1000F: a total of 218mm shock travel, so an ideal static sag of 21.8mm and an ideal rider sag of 65.4mm.

So, as you can see from the graphs, the sag from stock is massive! With no preload on it, the rear suspension is almost a third of the way through it's travel before anyone even sits on the bike. When it's weighted up, with so much less shock travel to absorb any big ruts and thumps, the shock skips around and gets harsh quickly. We have added a spacer/collar to the spring to increase the initial pre-load, and now it's much closer to classic ride height numbers, leaving more shock absorber travel.

We've been testing the damping too, which is light on both rebound and compression, but especially on low speed rebound. As you can see from the Africa Twin's Suspension Dyno runs above (rebound adjuster at 5 clicks out for all these tests), we have marked (with a red cross) 40kg @ 25mm/s as the absolute minimum we want to see for rebound on any suspensions. At 40 degrees it is only just covered, but once you are at or above 60, the rebound has dramatically faded. While this dampening loss is reasonably big, it's the fact that we start with barley enough that makes it a problem. Why do manufacturers do this? My theory is everyone wants a nice bouncy plush feeling bike on the showroom floor.

Showa Shock Revalve. We revalve your stock Showa shock, to suit your riding and your weight. This is the result of exhaustive testing and shock dyno testing. Every shock is tested to ensure it meets our standards.

The stock spring is 8.3kg/mm. We have 8.0,8.5,9.0 and 9.5kg/mm springs in stock. As our spring is 10mm longer, inital preload is added, making your hydraulic preload adjuster more useful (you don't have to have it on full hard all the time). 8.5kg is suitable for up to 110kg inc luggage, 9.0kg/mm 110-160kg and 9.5kg/mm for over 150kg.

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