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Discussion in 'Thumpers' started by ferdiepick, Mar 18, 2017.
Everything you said is correct. If they weren't so expensive I would try one.
Think of ot like this...
The first and every mm of my front spring requires 8.5Newtons to compress it. So, if I sit on the bike and 'pre-load' the front spring by say 30mm snd you come along and try to push the front down, you will have to apply 8.5 Newtons for every mm you want to lower the front.
So, that initial 30mm of compression does not alter the spring rate, 'rate' being something per something else. In this case pounds per inch or Kgs per mm or Newtons per mm.You still need 8.5 Newtons for the last mm of travel just like the first mm of travel.
Apply that logic to the rear where you have mechanical pre-load snd you still need the same weight to deflect the rear by it's last mm as to deflect it by its first mm. Pre-load leaves the 'rate' the same.
And 'pre-load' means before you apply the load...Simples!
I borrowed this from www.qa1.net
It’s the best explanation I have seen on spring rates.
“Spring rate refers to the amount of weight that is needed to compress a spring one inch. If the rate of the spring is linear, its rate is not affected by the load that is put on the spring. For example, say you have a 200 lb. per inch spring - it will compress 1" when a 200 lb. load is placed onto the spring. If another 200 lbs. is put onto the spring, the spring will compress another inch. At this point the load on the spring is 400 lbs. The rate of the spring, however, remains constant at 200 lbs. per inch.”
Its only in recent years that I have fully understood suspension as its only recently that I have needed to think about it. Read on and see if anyone can identify with this tale of miss guided youth.
I started motorcycling in the 1960s on my BSA A10 and Gold Star DBD34. Front suspension boinged up and down and there was nothing to think about or adjust. All your thoughts were directed at fixing numerous oil leaks, new badges for your barbour jacket and washing your white silk scarf and sea boot socks. - and boiling your rear chain on your mothers cooker then hanging it on her washing line as the hot gloop dripped off.
Now at the back end things were so complicated - you had two shocks that each had a cam so you could set pre load in three positions. Of course no one knew it was pre load, we knew that by squashing the spring you were making it firmer. So the C spanner would come out and the shocks were wound up to the 'firmest' cam. Then we would bounce up and down declaring that it was now much stiffer. Off we would go delighted that the stiffer spring had transformed the bike, it no longer wallowed and would do over a ton on a bend. Others agreed as they too preferred a stiffer back end. and all had a home made C spanner.
Fast forward 40 years. To learn about suspension you no longer needed to sit in the reference section of the library. You have the internet and forums,
So now I find myself looking for unsuspecting mates who I can trick into talking suspension. Hoping that they will casually mention stiffening up their suspension and then gotcha - lets go for a pint and talk springs and dampers . Then when my mate decides he wants to go home I point out that by the way, dampening is applying moisture, damping is whats going on as you bounce up and down.
Had to visualize that. As our shocks have ~100mm of stroke, curves move apart much more than in my calculation done above with 70mm.
At full stroke that's ~8% more force on the 70N spring over the 65 but only 2% more that the preloaded spring needs for full compression.
And here it's only a swap from a 65N/mm to a 70N/mm spring, but full 10mm of preload (that's a lot in my opinion).
Things get more obvious when swapping to a 75N/mm spring, and comparing to 5mm preload.
P.S. That does not take any linkage progression into the equation.
oMMo: I'm under the impression that the ratio of wheel travel to shock travel is about 4:1. I don't think what you show does not take this into account.
No, an Ohlins shock for the Rally is spec'd with 102mm of stroke length.
So the overall rate is only around 2.6 : 1.
(It's not linear)
Found another site stating 84mm stroke length for the 250 L, which has less rear wheel travel and a shorter shock.
oMMo: That 84 stroke for the CRF-L sounds about right. The manual says it's travel is 240. That gives a 2.86 ratio. Thanks for the stroke data. Rally travel is 264.... I have both models. The CRF-L suspension has very different links. I read that 4:1 ratio somewhere.....or just calculated wrong. In Japan they make the "LD" model Rally that has CRF-L links and shock with lower seat height. I have those bits on back order and will be converting my Rally soon. It's suspension may have (technically) more travel than my "L" but when you ride both bikes side by side you realize the stock Rally mushy suspension is just unacceptable, and my old short legs will appreciate the reduced seat height.
And just don't get me started on those who think that a 'shock-absorber' absorbs shocks...
Springs absorb the shock. Try riding without one to see how long your fillings and your spine lasts.
The things most folks (and a whole pile of car and bike accessory manufacturers and sellers) refer to as 'shock-absorbers' are of course dampers. Try riding with a knackered one and see how soft and boingy your ride is.
So, springs absorb the shock and dampers control the oscillations of the spring.
So what the hell is a 'coil over shock-absorber'? Two coils, one outside the other?
Like I say, don't get me started
I get adverts for a digital suspension tuning device below this thread now.
I don't see the ads but if its for the Slacker, I have that. Works great but pricey.
I thought it about time we had a photo ...
My weight-saving GPR silencer finally arrived from deepest, darkest Italy yesterday. There were none in UK stock when I ordered it and it turned out there were none in Italy either. So, this one was made just for me, how special does that make me feel...the fancy swing tag on the link pipe was a stock one but the one on the silencer actually had my name on it.
It's a smart bit of kit with everything you need to fit it, including a spring puller to fit the two springs that hold the silencer to the link pipe. However, although the pipe and silencer were a perfect fit to both the header pipe and the frame, it was pretty obvious that no-one at the factory had ever fitted one to a Rally, or even to an L and it took some jiggery-pokery with the original nuts and bolts and the ones supplied with the kit to get everything fitted correctly.
Once fitted it looks really good and the model I chose, the Furore in matt black, has a similar appearance to the much larger stock item.
The silencer weighed in at 2Kgs and the stainless link pipe and fittings took it to 2.6Kgs. That makes it exactly half the weight of the original which was 5.2Kgs including a spattering of mud
Here's the finished article...
...but of course, the unasked question is, what does it sound like?
Well, it has way more 'presence' than the (in my opinion, over silenced) stock one and I would describe it's tone as fruity and sporty. It is louder than the stock silencer for sure but not offensively so and is fully road legal in the EU and built to Evo 4 spec.
It's only had a spin to the end of the drive so far so I'll come back with my on-the-road impressions later. Brian
'19 rally getting me out camping with my old man! Nothing like a bonfire with cheap trashy beer and shootin the shit till dark 30 just to get out of the house. Free campsite off the St Croix River and fire wood laying around everywhere to boot!
Worn/scratched side panels/fairings:
Hi All, I'm interested in buying the Rally, but I've read that the rider's knees tend to rub against the side panels under the tank and seat and badly scratch them over time. The following screenshot taken from a YouTube review seems to confirm this. What are your experiences? Are you protecting your panels with protective foil, etc.?
Thank god for that
Those are not 'wear' marks, those are deep scratches and they are all coming up from below and in front. That bike has either been dropped or ridden through hell and back with the rider standing on the seat
All legs rub panels on all bikes, nakeds apart, but I've never seen anything like that on any of the high-milers in here. If those 'are' wear marks, that guy must be wearing steel armour on his legs...
Those scratches look to be a lot more severe than the common haze blemish caused by dust on your knees.
I ride a lot of dusty roads with my knees dug into the tank. I even ride with armored pants with big knee pads that make contact with the tank area. I've hardly caused a small blemish where my knees dig in. One could put 3M clear bra film there (which will also blemish) but it's a dual sport, I dont care as much about cosmetics.
OzzyRider: While cruising around on a Rally specific website in Japan for accessories there were knee pads to protect that area of the bike's cosmetic plastic. If you wish to protect it 3M and other companies make thin plastic sheets that go over auto paint to protect against stone chips
You don't buy a off-road/adventure bike and expect it to stay cosmetically like new, a couple of adventures on that one I'm sure.