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Frame Geometry
- Thread starter M5-
- Start date
P
A little off topic but I think panthera is using the powerdynamo ignition. It quits sparking once it's been wet and your engine temp gets to around 180F. Learned the hard way. Twice.
I carry a spare one wired up and ready to go in my truck.
There are ways around it. If anyone wants to use that ignition for its 80w, I can explain to them in depth.
I carry a spare one wired up and ready to go in my truck.
There are ways around it. If anyone wants to use that ignition for its 80w, I can explain to them in depth.
P
The simple way is to weld ears to your spindle to allow it to be moved further back. Vey simple and effective in comparison to the major mods proposed here.:face-icon-small-coo
Spindle trail/negative caster
Just a thought. No doubt mounting the spindle in a position that moves the ski pivot point (ski bolt) rearward of axle shaft (negative caster) could improve trail manners. But, as the ski pivot point is moved rearward the spindle starts to work as a lever to bend, rather than compress, the forks when resistance at the ski is encountered. Maybe that's why the manufactures limit trail in the design of the spindles? You have to mod spindles to get more trail. Anyone suffer bent forks with increased trail/negative caster? Question is how much trail is to much. I like the geometry of the sx that requires less trail/negative caster to achieve improved trail manners.
Just a thought. No doubt mounting the spindle in a position that moves the ski pivot point (ski bolt) rearward of axle shaft (negative caster) could improve trail manners. But, as the ski pivot point is moved rearward the spindle starts to work as a lever to bend, rather than compress, the forks when resistance at the ski is encountered. Maybe that's why the manufactures limit trail in the design of the spindles? You have to mod spindles to get more trail. Anyone suffer bent forks with increased trail/negative caster? Question is how much trail is to much. I like the geometry of the sx that requires less trail/negative caster to achieve improved trail manners.
M
So looking at other conversions, the KTM 250 and 350 frames are a non-starter because of the design of the frame cradle. The 450 frames are all deeper and will take the CR500 motor almost directly. Interestingly from what I have found so far the rake on most KTMs whether SX or EXC or XC-f is 26.5 degrees.
One other reason for looking at this build is newer kits don't have fit kits for the old CR steel frame. I made my own for the TS but I'm thinking good luck for any other brand.
M5
One other reason for looking at this build is newer kits don't have fit kits for the old CR steel frame. I made my own for the TS but I'm thinking good luck for any other brand.
M5
dooman92 ,
Here's a set back used on the heavy weights , 400 plus #s and the only thing I've ever bent was the frame when I broad sided a bank coming out of a creek bottom at a clip that threw me . The frame tweeked so bad I had to kick the ski straight and ride out with no steering .
The set back makes a huge difference in steering on hard pack but is horrible in any deep snow , whole lot of force on it . Works great for newbies .
Had this posted in another thread and yes I keep repeating myself but it's how these kits mount the spindle to the forks that cause the damage . Sure glad I'm not shelling out a grand because I could of bought a new bike for as many times I put the skis under a tree , off a rock etc etc .
Must have something to do with the old patent or something , or ignorance .
Here's a set back used on the heavy weights , 400 plus #s and the only thing I've ever bent was the frame when I broad sided a bank coming out of a creek bottom at a clip that threw me . The frame tweeked so bad I had to kick the ski straight and ride out with no steering .
The set back makes a huge difference in steering on hard pack but is horrible in any deep snow , whole lot of force on it . Works great for newbies .
Had this posted in another thread and yes I keep repeating myself but it's how these kits mount the spindle to the forks that cause the damage . Sure glad I'm not shelling out a grand because I could of bought a new bike for as many times I put the skis under a tree , off a rock etc etc .
Must have something to do with the old patent or something , or ignorance .
G
16 wr450 is 36.75-37” or so ski bolt to swingarm bolt centers
About 45” ski bolt center to driveshaft center with Snowtech MX kit.
Snowtech old non adjustable spindle has 2.75” of trail
One other note if it is on the stand or compressed changes the measurements a lot. With just the sag it drops to 36” front axle to swingarm. Be sure to note how you are measuring
About 45” ski bolt center to driveshaft center with Snowtech MX kit.
Snowtech old non adjustable spindle has 2.75” of trail
One other note if it is on the stand or compressed changes the measurements a lot. With just the sag it drops to 36” front axle to swingarm. Be sure to note how you are measuring
M
This is maybe a better article about all the factors coming into play. Its more than trail and rake. I'm not an MX racer so I have never paid much attention to this stuff but I can see how it would be huge if you were racing. Wheels vs skis, the ski is like a bike with a flat tire, hard to make it handle.
https://motocrossactionmag.com/ten-things-about-triple-clamp-offset/
M5
https://motocrossactionmag.com/ten-things-about-triple-clamp-offset/
M5
Is it possible the whole reason why these kits mount the spindle so far forward is because the manufactures believe this is what needs to be done because the ski has so much resistance ?
And if that's the case holy crap are these guys missing the boat .
Nice article
And if that's the case holy crap are these guys missing the boat .
Nice article
Spindle trail/negative caster
Hawkster, I don't know sh** about the hawk thingy may or may not be relevant.
But, back to excessive trail. Take a look at the bent forks in photo 1 page 1 of the Aro spindle post/discussion. Saundet's post (#13). That photo shows lots of trailing (appears maybe close to 3") and the resulting bent forks. The energy that is transferred to the forks is attempting to bend rather than compress the forks which is what happened there. Why did those forks bend when they should have compressed and absorbed that impact?
Hawkster, I don't know sh** about the hawk thingy may or may not be relevant.
But, back to excessive trail. Take a look at the bent forks in photo 1 page 1 of the Aro spindle post/discussion. Saundet's post (#13). That photo shows lots of trailing (appears maybe close to 3") and the resulting bent forks. The energy that is transferred to the forks is attempting to bend rather than compress the forks which is what happened there. Why did those forks bend when they should have compressed and absorbed that impact?
LOL , neither do I
It has to have something to do with the way the spindle is mounted .
I've been asking why is it that the forks are not turned 180 degrees ?
Also why are they clamping to the tube ?
Why not to the housing/axle holder ?
That tube was never designed to be mounted to ?
Not to mention it could help lower the bikes .
If anything guys should be hammering the crap out of the stem bearings .
Somebody please give me a reason why all of them are doing what they are doing ?
It has to have something to do with the way the spindle is mounted .
I've been asking why is it that the forks are not turned 180 degrees ?
Also why are they clamping to the tube ?
Why not to the housing/axle holder ?
That tube was never designed to be mounted to ?
Not to mention it could help lower the bikes .
If anything guys should be hammering the crap out of the stem bearings .
Somebody please give me a reason why all of them are doing what they are doing ?
E
The main reason they are doing it this way is because it is a bike conversion not a ground up correct design. The spindle length and trail are needed because it is a dirt bike converted to snow.
Shortening the spindle would be way stronger and I've always wanted to hack it in half but then the ski would smash my pipe and the rest of the chassis wouldn't match at all.
Shortening the spindle would be way stronger and I've always wanted to hack it in half but then the ski would smash my pipe and the rest of the chassis wouldn't match at all.
M
OK so update. It appears as if KTM is fairly uniform and has been forever in their head angles. So it makes no difference between an SX or an EXC or an XCF they are all the same. So the 250 and 350 SX frames are a non starter because the frame cradle isn't deep enough and needs to be modified for the CR500 motor. The 450 XCF/EXC frames have a deeper frame cradle which makes the swap super easy. I found a cheap deal on a 450 frame so I picked it up.
Next is the triple clamps. I want this thing to turn like crazy, I don't care about high speed straight line stability. My understanding is that a lower fork offset will make it turn faster and also have less trail which may reduce stability, I don't care too much about high speed as I don't really do that much. Older KTM fork clamps were adjustable from 18mm to 20mm of offset. The newer triples seem to have 21.5mm. There are tons of triple clamps for sale of all vintages its just a matter of picking the right ones.
Old or new? I'm just concerning myself with the frame right now. Its a PDS frame and I can modify the shock mount or do whatever I like as it wont ever see wheels. I'm not sure what kit it will get but it wont be the LT TS that's on the 500 now.
M5
Next is the triple clamps. I want this thing to turn like crazy, I don't care about high speed straight line stability. My understanding is that a lower fork offset will make it turn faster and also have less trail which may reduce stability, I don't care too much about high speed as I don't really do that much. Older KTM fork clamps were adjustable from 18mm to 20mm of offset. The newer triples seem to have 21.5mm. There are tons of triple clamps for sale of all vintages its just a matter of picking the right ones.
Old or new? I'm just concerning myself with the frame right now. Its a PDS frame and I can modify the shock mount or do whatever I like as it wont ever see wheels. I'm not sure what kit it will get but it wont be the LT TS that's on the 500 now.
M5
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There is a set of 14mm clamps on ktmtalk right now.
M
I can't seem to find them, got a link?
M5
M5
hey Paul
do you think any of the fatigue has to do with the power delivery of the cr ?
i was think about this the other day
my turbo sled beats me up more than stocker
with the extra hp
do you think any of the fatigue has to do with the power delivery of the cr ?
i was think about this the other day
my turbo sled beats me up more than stocker
with the extra hp
M
No I don't think that's it. My YZ is close power wise to the CR, its the kit and the frame geometry. I rode the CR yesterday and it's the wheelbase that makes it tough to ride. The turning circle is huge because of the forks. Its a great climber and cruiser but its not very turny.
M5
Here's what I am looking for:
14mm Top clamp 54801034014
14mm Bottom clamp 54801032014
From 2003 125 SX SXS
200 EXC MXC SX
250 SX SXS
2004 125 SX SXS
200 SX
M5
Here's what I am looking for:
14mm Top clamp 54801034014
14mm Bottom clamp 54801032014
From 2003 125 SX SXS
200 EXC MXC SX
250 SX SXS
2004 125 SX SXS
200 SX
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D
When ice racing bikes on the ice in a class that does not allow modified frames, forks or triple clamps, some guys do exactly that, they rotate the forks so the axle is behind tightening the steering geometry
D
I will say that a CR500 power delivery is drastically different, it makes it 60 HP by 6000 rpm , from 2500 to 6000, and comes on like king kong compared to a 60HP 4 stroke, climbing from 4000 to 10,000 rpm, suspension squat from the 500 power delivery requires a much stiffer shock spring, I would guess a strutless bike still would want to squat out the skid more than a 4 stroke does, causing alot of suspension movement for and aft on and off the throttle. When I put my cr500, and 625 motors in my pDS frame we tossed the progressive spring for a straight rate 7.7 kg/mm spring so it wouldnt squat so hard under power and would actually steer still with the throttle open.
