THE KRAN

Total loss of compression, or Spark

271 posts in this topic

Regarding longer shock on the 2018s, well  that seems that's not the case. 
Just checked 2017 and 2018 RR250 2 stroke parts fiche and the shock rod is  exactly the same (p/n 031.33.015.00. 00 , number 19 on the schematic diagram). 
Now regarding lengthening or lowering the shock. By doing this you alter the ride height of the rear which also means that you modify the front - rear balance. 


That's the whole point, to improve the balance. While the shaft part#s may be the same, as you know it's not the only way to lengthen the shock. I simply shimmed the clevis. If Sachs had a lot of shafts on hand and Beta requested a longer shock, it would be a simple CNC change to the Beta clevis. A different top out plate is also an option. I actually designed one but never had it made as the shim method worked so well.

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3 minutes ago, GP said:

 


That's the whole point, to improve the balance. While the shaft part#s may be the same, as you know it's not the only way to lengthen the shock. I simply shimmed the clevis. If Sachs had a lot of shafts on hand and Beta requested a longer shock, it would be a simple CNC change to the Beta clevis. A different top out plate is also an option. I actually designed one but never had it made as the shim method worked so well.

 

Pictures?

 

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There was nothing left to raise at the time. No more threads. I had RaceTech make me a  rear spring spacer, so now the forks are back down a bit more now.
I find raising the rear up to a point is better, but sometimes the dropping the front works too. 
I am very tall, and the bike sits lower to the ground than other brands,  so I prefer to have as much ground clearance as possible, and have tried it with everything 'up', but it just did not work out. Had to lower the front some too.
I actually test the neutrality of the handling on a empty/vacent house lot; nice and flat. I sit on the seat in a specific place, and execute a turn with power, then apply front brake or chop the throttle to see how it reacts.  I try to get the bikes rear end to come out slowly when the throttle is chopped hard, still in the turn, and the front to not understeer harshly when heavy breaking is applied. Once I find the spot, I get small amounts of over or under steer just by leaning forward or back; I don't have to even move on the seat.  Works really, really well on loose single track where don't have much room to make corrections, or if you cannot use libeal throttle to steer with the rear. Also makes hill climbing much better when I can vary between rear wheel spin and front wheel loft, with very little movement. I just sit on the very front of the seat, and the over/understeer feels just like it did on the flat.
The lack of shock body threads is a common issue with the springs that are available (shorter than usual ? less thread than usual? what ever...)


I'm talking about lengthening the shock, not the preload. 4mm gets you 15 mm at the axel, with less preload required. Sounds like you might like it as it adds a hair of clearance too. FWIW, My '13 shock has more threads than the newer shocks, but neither have been a problem with the Cannon springs.

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Race techs data is incorrect, their recommended springs are the wrong diameter and length. 


Their GV application for the Sachs was wrong too. Had to call and talk to someone with some common sense to get the right #.
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1 hour ago, kawagumby said:

 

I've had that problem once myself...and had to make a shock spacer. But... I found Cannon Racecraft, an outfit that makes custom springs to your spec's.  They have made springs for me that were perfect  - send them the length, width, and rate, and they will provide you with a quality part.  The cost is not outrageous either; the last set of fork springs I had them make (for my '94 KDX) cost about $20 more than the price of a race tech set (which was no longer available).  I've been very happy with them - reasonable turn-around time too.

I went with Diverse Racing. There springs are 8mm longer than the RaceTechs. Still about 8mm shorter than any spring in my shop...

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1 hour ago, Mckay said:

Ok, you talked to the same idiot I did at RT. Put me on a 6.6 too. Thats a freestyle spring. Im now at a 6.0 and EVERYTHING works much better. If they made a 6.2 in the proper length Id go that route. I have about two inches of thread left. Your fighting the same thing I did, until I had my suspension properly done, I had no idea how far off it was. What do you weigh?

I did not end up with the RT spring. I don't listen to the guy who answers the phone. They have some fantastic engineers on staff, but they don't talk on the phone.

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1 hour ago, Mckay said:

Ok, you talked to the same idiot I did at RT. Put me on a 6.6 too. Thats a freestyle spring. Im now at a 6.0 and EVERYTHING works much better. If they made a 6.2 in the proper length Id go that route. I have about two inches of thread left. Your fighting the same thing I did, until I had my suspension properly done, I had no idea how far off it was. What do you weigh?

With my full pack, ready to ride, about 265. More than the bike! 6'4"

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10 minutes ago, THE KRAN said:

With my full pack, ready to ride, about 265. More than the bike! 6'4"

Same as me weight wise. The engineers will talk if you firmly ask but their data is still off. 6.6 spring is putting a hurt on you, especially if your preloaded as much as you said. Ill get the part number of the RT spring that the race team uses, correct length and diameter.  I think I have the Eibach number as well.

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3 minutes ago, Mckay said:

Same as me weight wise. The engineers will talk if you firmly ask but their data is still off. 6.6 spring is putting a hurt on you, especially if your preloaded as much as you said. Ill get the part number of the RT spring that the race team uses, correct length and diameter.  I think I have the Eibach number as well.

I have the sag numbers I need, and I have about 11mm of spring preload right now.  It works really well once it was finally tuned correctly by N2Dirt.

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3 minutes ago, THE KRAN said:

I have the sag numbers I need, and I have about 11mm of spring preload right now.  It works really well once it was finally tuned correctly by N2Dirt.

how can you have 11mm of preload yet be out of threads?

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