Lowering the sub frame

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#1
I have read nearly every were that racers and average joes lower there sub-frames 5mm and I was wondering how this is done and if it really makes a differnce like in the stadium style woops? I have a 02 KX 250 and i have read that people make bottom hole oblong to lower the rear, looking at it on my KX it does not seem like it can go much lower with out cutting and rewelding. also what about the silencer mounting wont this affect how the silencer mounts?
 

Faded

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#2
I would think you'd have to be pretty intimate with your bike to notice a 5mm lower seat height. That's only 0.2", I would think that there wouldn't be enough change in height to worry about your silencer not lining up correctly. Just in case you can loosen all your pipe/silencer bolts and wait to tighten them until you've installed your modded subframe. An alternative route might be using an electric carving knife and some sand paper on the seat foam and carfully remove your 5mm from there. Either way, good luck.
 

Rcannon

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#3
Faded, the 5mm being on an angle might be noticed more, right? If I tried to remove foam from my YZ seat, I might as well just sit on the bare fender. There must be a foam shortage in Japan.
 
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#4
I am talking about the 5mm from making the mounting hole oblong witch equals more at the rear fender. and I am a short guyso I already moded the seat Its mor of a Freestyle seat but at least I can flat foot the ground now.
 

Faded

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#5
Originally posted by Rcannon
Faded, the 5mm being on an angle might be noticed more, right?
Right. If I get time I could take some rough measurements and make a drawing and see exactly what lowering the mounting holes 5mm would do to actual seat height. I still think that there would be enough play in the pipe/silencer mounting arangement to allow for this. Unbolt the silencer and see how far down it sags from the original mounting location and this should give you an idea of how low you can go. I'm not too familiar with your bikes, but on my CR I think I remeber there being some room to work with, I'll have to check it out over the weekend.
 

marcusgunby

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#6
Its about 15mm at the back if you drop the mounts 5mm.It makes a big difference-i just did my 04RM 125 and i have put it back to std, as the distance from the rear of the seat to standing became too much and i couldnt stand as well.
 

Studboy

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#7
Originally posted by Rcannon
...I might as well just sit on the bare fender. There must be a foam shortage in Japan.
No,  only Yamaha's supply was cut short.  ;)

Honda, Suzuki, and Kawasaki still seem to have some seat foam on their bikes.
 

darringer

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#9
I shortened my subframe by re-drilling the holes in the lower subframe as close to the welds as I could get. I then welded up the original holes and ground the subframe down to match the frame. To make the silencer fit all I had to do was loosen all of the pipe mounts and move the pipe around until everything lined up. A small hassle but not that difficult. Doing this with shaving my seat made a HUGE difference. The rear of the seat and the fender are about 1 1/2" lower. It's much more comfortable in turns and I'm more confident trail riding and hill climbing as now I can dab my foot with more authority.
 

los36

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#10
Do any of you guys that have shortened your subframe have trouble with the rear tire hitting the fender too often or too hard? I would like to lower the rear of my RM a bit, but the tire already hits the fender often enough. It seems like when you would really bottom-out (like landing from a big jump) this would cause some trouble.
 

DougRoost

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#11
I have the same question as los since I'd heard this was more of a KTM mod. Reason supposedly being there is some room between the rear fender and tire on KTMs but not the Japanese MXers. Haven't done this to mine but should consider it.
 

darringer

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#12
I haven't had too much of a problem with the tire rubbing the fender. It does hit it, but I don't feel it. I only notice the black marks on the fender. On my CR, there was a small gap between the seat and fender, so when I replaced the fender I drilled it to fit snug with the seat, thus picking up about 1/2" clearance that was lost with the shortened subframe.
 

los36

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#15
I have not lowered my 02 RM and i get solid contact with the rear fender. The black marks are as wide as the entire center knob on a Dunlop 756.