I tore the ntx suspension down looking for improvement the other day and found the following:
The front springs are both the same .85kg/mm 30.5mm i.d. 41mm o.d. x 447mm long, this is good news plenty of spring available, I replaced mine with a set of traxxion dyn. omni springs 1.0kg/mm. there is no need to go looking for unobtainable Marz parts. Sonic springs (great springs) have rates up to 1.2kg/mm. BUT!!!! With the Rake of this fork (if the rear sag is right) YOU WILL NEVER go above 1.05kg/mm EVER if you do the fork will act like it is solid!
EVEN if loaded with 500lb 1.05 is stiff if the back end is good and correct.
Fork cartridges: rebound side is ok...not great but at least it controls oil through the whole stroke and will work as intended( it is a sealed cartridge and not re-valveable)
The COMPRESSION cart. is basically total crap, it is not re-valveable, and due to a series of holes down the sides of the cartridge body does not control the oil at all during the first 4/5ths of the stroke. The adjuster only controls compression at the bottom 40mm of stroke, ie it is acting like an adjustable bottoming valve...not compression adjustment. The only good thing about this cart. is you could set it so that it will never bottom...
going up very slightly to 10w in the compression side helps, but is a bit heavy in the rebound side.
The front end fix is carts from Traxxion Dynamics (ak-20) you will lose 5mm stroke with them. You will really never notice this as it will be hidden in the loss of 5mm of top out. Or Matris Cartridges I have zero experience with these but from what matris tells me they also lose 5mm in top out. This is really not a big deal as the top out in this fork is very stiff and short.
The Matris cart also is supposed to have a bottoming valve as well at the conventional valves but I have not seen one in person to evaluate.
NOW on TO THE REAR:
THIS IS IMPORTANT!!!!!!!!!!!!!!
There is a limit to the spring rate of a 2.25" (60mm) i.d. shock spring that will fit in the damn frame!!!!! and that is 83-84mm o.d.
Factory spring is 56mm id x 80.6mm od 185mm long with a rate of 610lb/in or 11 kg/mm.
So what does this mean? if you build a Penske shock ( they use a 2.25 id spring) the max rate you can use is 800lb or 850(maybe it will probably touch)
Who knows what id Matris uses if it is std 60mm id you may get a shock that does not fit if the rate is high, My email to them about the spring id and wire dia. got no response.
56mm id springs are not really std. (thanks guys)
The good news is that even though the stock Sachs, is very mid Sachs range for their line, it is a very very well built shock (sachs has one of the best floating piston designs out there) and is re-valveable and re-buildable, without issue.
Now the good spring news you can use without issue 60mm id springs on the Sachs shock up to 800lb-850(maybe), or if you need a bit more YOU CAN use a HYPER COIL / Traxxion Dynamics Gold Wing shock spring....the down side is they are only avail in 1000, 1100, 1200 lb. so you have a gap right where a lot of folks will fall. The wing spring is 1" short but a spacer takes care of the problem....so why do this work?
The spring wind is a very open coil, and when you orient the open areas rotationally on the shock body correctly they will miss the frame and swing arm. (the frame and swing arm are in the spaces between the coils) This will not work with the penske as its coil density is higher. It is also very slightly smaller on the id.
Properly done the Sachs can be very good for about $350,
I used 5 wt oil for the re-build.
There is a possibility that a 50mm id spring may work on a penske but they have neither confirmed or denied it, Any way you slice it the penske rear (unless you are under 250) with gear and luggage looks like a really really custom build, (maybe using one of their car shock bodies) this was a suggestion straight from Penske.
I am looking for more hard information (numbers sizes)
By the way I actually had a Penske springs at every rate they make to check the fit, that is how the dia problem showed up.
My set up is actually good (bike sag in rear 8mm, front 15mm, rider sag rear 42mm, front 47mm) it is stiff but not punishing, very good if the roads are good to decent and on good gravel, it would be a bit stiff for non-aggressive, touring on really bad roads.
A quick check to see if the stance is right and the chassis balance is good on the ntx, is if the tires front and rear are both used equally (scorp trail) the stance is right, if there is a lot of side on the front and the rear is to the edge, the rear is really soft, and the bike is flying nose high, the same cond. kicks in when the front is goofy soft, and plowing like mad.
The front springs are both the same .85kg/mm 30.5mm i.d. 41mm o.d. x 447mm long, this is good news plenty of spring available, I replaced mine with a set of traxxion dyn. omni springs 1.0kg/mm. there is no need to go looking for unobtainable Marz parts. Sonic springs (great springs) have rates up to 1.2kg/mm. BUT!!!! With the Rake of this fork (if the rear sag is right) YOU WILL NEVER go above 1.05kg/mm EVER if you do the fork will act like it is solid!
EVEN if loaded with 500lb 1.05 is stiff if the back end is good and correct.
Fork cartridges: rebound side is ok...not great but at least it controls oil through the whole stroke and will work as intended( it is a sealed cartridge and not re-valveable)
The COMPRESSION cart. is basically total crap, it is not re-valveable, and due to a series of holes down the sides of the cartridge body does not control the oil at all during the first 4/5ths of the stroke. The adjuster only controls compression at the bottom 40mm of stroke, ie it is acting like an adjustable bottoming valve...not compression adjustment. The only good thing about this cart. is you could set it so that it will never bottom...
going up very slightly to 10w in the compression side helps, but is a bit heavy in the rebound side.
The front end fix is carts from Traxxion Dynamics (ak-20) you will lose 5mm stroke with them. You will really never notice this as it will be hidden in the loss of 5mm of top out. Or Matris Cartridges I have zero experience with these but from what matris tells me they also lose 5mm in top out. This is really not a big deal as the top out in this fork is very stiff and short.
The Matris cart also is supposed to have a bottoming valve as well at the conventional valves but I have not seen one in person to evaluate.
NOW on TO THE REAR:
THIS IS IMPORTANT!!!!!!!!!!!!!!
There is a limit to the spring rate of a 2.25" (60mm) i.d. shock spring that will fit in the damn frame!!!!! and that is 83-84mm o.d.
Factory spring is 56mm id x 80.6mm od 185mm long with a rate of 610lb/in or 11 kg/mm.
So what does this mean? if you build a Penske shock ( they use a 2.25 id spring) the max rate you can use is 800lb or 850(maybe it will probably touch)
Who knows what id Matris uses if it is std 60mm id you may get a shock that does not fit if the rate is high, My email to them about the spring id and wire dia. got no response.
56mm id springs are not really std. (thanks guys)
The good news is that even though the stock Sachs, is very mid Sachs range for their line, it is a very very well built shock (sachs has one of the best floating piston designs out there) and is re-valveable and re-buildable, without issue.
Now the good spring news you can use without issue 60mm id springs on the Sachs shock up to 800lb-850(maybe), or if you need a bit more YOU CAN use a HYPER COIL / Traxxion Dynamics Gold Wing shock spring....the down side is they are only avail in 1000, 1100, 1200 lb. so you have a gap right where a lot of folks will fall. The wing spring is 1" short but a spacer takes care of the problem....so why do this work?
The spring wind is a very open coil, and when you orient the open areas rotationally on the shock body correctly they will miss the frame and swing arm. (the frame and swing arm are in the spaces between the coils) This will not work with the penske as its coil density is higher. It is also very slightly smaller on the id.
Properly done the Sachs can be very good for about $350,
I used 5 wt oil for the re-build.
There is a possibility that a 50mm id spring may work on a penske but they have neither confirmed or denied it, Any way you slice it the penske rear (unless you are under 250) with gear and luggage looks like a really really custom build, (maybe using one of their car shock bodies) this was a suggestion straight from Penske.
I am looking for more hard information (numbers sizes)
By the way I actually had a Penske springs at every rate they make to check the fit, that is how the dia problem showed up.
My set up is actually good (bike sag in rear 8mm, front 15mm, rider sag rear 42mm, front 47mm) it is stiff but not punishing, very good if the roads are good to decent and on good gravel, it would be a bit stiff for non-aggressive, touring on really bad roads.
A quick check to see if the stance is right and the chassis balance is good on the ntx, is if the tires front and rear are both used equally (scorp trail) the stance is right, if there is a lot of side on the front and the rear is to the edge, the rear is really soft, and the bike is flying nose high, the same cond. kicks in when the front is goofy soft, and plowing like mad.
