Jenny, that's very interesting. But there is still a spring in the left fork, and the rate of that spring affects the front suspension as the whole, doesn't it? So why not to change that spring in conjunction with the right leg fork spring as well? When I fitted the hyperpro spring only on the right leg, the bike was still front diving, and with both springs it is not.
so you are saying that if the axle rod is not sliding properly due to the both fork extending in a different manner, it is not a problem, one can just force that rod anyway? doesn't it create some kind of stress on the axle?
I do have crf and because it was too soft, first i installed ohlins spring on the right fork, but since it was not enough, I fitted an additional spring in the empty left leg, from Race Tech, and it fixed the problem.
and one more thing - in which way these two systems differ - RR and hypepro? one just changing the right leg spring, and the other, the changing both?
Hi Kris - it depends on what you've changed the spring rate to - if the spring in the right hand leg is now stiffer than before (and stiffer than the one in the left leg), then the left leg spring isn't going to have any effect on the rate of the new [main] spring.
Traditional fork design (with a pair of springs) typically changes the rate of both springs [equally] as the load was shared between the two legs - but in modern USD designs, this isn't necessarily the case anymore (such as the CRF250L example I mentioned above, there is only one spring, in one leg only).
I don't know what spring rate Hyperpro are using in their kit, but it's possible [particularly if they are progressive rate] that the reason you felt your front end still diving with only one of their springs installed was because the initial rate was still very soft (and needed to be boosted by having their other spring installed) - as I say, the OEM left hand spring is really only there as a 'helper' for the main spring - so it's possible that Hyperpro have decided to share the spring load across two springs, rather than one (as per the OEM set-up and the RR upgraded parts), which is why yours still felt soft until you'd changed both springs.
There is nothing wrong with using their 'shared load' approach of course - however, as you experienced, it is very tricky for someone in their garage to disassemble the left hand internal assembly compared to the right hand side - something I presume Hyperpro didn't full consider perhaps?
As for your forks sliding at 'different rates', unless you have some kind of bushing or alignment issue, it should not make any difference - the forks tubes are designed to slide up and down with no discernible resistance, and the axle diameter of a USD fork braces the two lower [stanchion] parts anyway - this is one of the reasons why USD forks tend to have much larger diameter axles than older conventional forks used to have (which also sometimes had additional braces of course). As I say, there will be no discernible stress on the axle unless you are suffering stiction or an alignment issue with the fork legs/bushes.
Regarding your CRF front end - I can only imagine that the fork kit you initially fitted (in just one leg) did not have a sufficiently high enough spring rate for your intended application. I have a friend with a CRF250L rally with the Ohlins shock and fork kit, and that is very nicely dialled in - plush, but will little dive when you start to press on.
Your final question I hope I have answered already in my description above - basically the Rally-Raid fork kit replaces the OEM main spring with a stiffer rate spring - which essentially overrides any effect from the left hand OEM 'helper' spring, making the contents of the left leg essentially redundant with regard to the actual support and springing of the front end.
With the main spring rate now correct (ie not too soft as many people feel the OEM set-up is), you can dial in the sag correctly using the RR preload cap on that main spring, and set your oil weight [viscosity] and volume to suit your preference - for info. TracTive [who developed the front and rear suspension with Rally-Raid] felt that although still quite rudimentary, the OEM damping control was actually pretty good - certainly once their revised main spring was installed and the oil weight changed to match.
Certainly from my own perspective, I would have to agree - while I never covered many miles on an OEM set-up, the RR LEVEL 1 kit (that is standard travel and ride height) I have on my own bike feels very well composed over all surfaces. It's a pretty simple (and easy to fit) solution.
Hope that clarifies things a bit!