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rake and trail flat track #203951
03/19/06 3:46 pm
03/19/06 3:46 pm
Joined: Aug 2005
Posts: 189
easley south carolina
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bsadb Offline OP
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bsadb  Offline OP
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Joined: Aug 2005
Posts: 189
easley south carolina
Kboyd was just asking questions about round track tires. My question is rake angle and trail for a trackmaster frame. What is the proper shock and fork legnth for a trackmaster?
There is a flat track in SC now and I'd love to try it.


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Re: rake and trail flat track #203952
03/20/06 5:45 pm
03/20/06 5:45 pm
Joined: Jun 2004
Posts: 1,115
Kansas
kboyd Offline
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kboyd  Offline
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Joined: Jun 2004
Posts: 1,115
Kansas
I ended up talking to a couple of experienced flattrackers/tuners and got some advice on the suspension subject. I didn't realize just how secretive folks can be about flattrack suspension, its like "I'd tell you, but then I'd have to kill you!"....

Anyway, the rear shocks should be 13", but 12.5" to 13.5" will do, depending on shock sag under rider weight and front end rake/trail. Choose shock springs (usually around 70 to 80 lbs depending on your weight) that sag about 25% of their travel under rider weight (or 1" of the 4" of travel), making sure that the swingarm does not go negative under heavy load!

Steering head angle should be 26 degrees, the front forks should be about 30", and if my memory is correct the springs should be around 23# for flattrack. I'll check that number when I get home.

So set your rear shock length to get your swingarm angle, then adjust front fork height to achieve correct trail (end result of neck rake, neck height, axle position on forks, etc). This is an over-simplification, but that's the basic procedure as I was told.

I have now dispatched the Flattrack Suspension Secret Society goons to your house... they should be there any moment to drink all your beer and give really bad setup advice!

Good luck,
Kyle


Kyle#44x

1969 T100R Daytona
1979 Powroll Honda XR250 "Dallas Baker" flattracker
1975 XL350 project bike
Re: rake and trail flat track #203953
04/14/06 1:36 am
04/14/06 1:36 am
Joined: Mar 2006
Posts: 19
atlanta
ambivolent Offline
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ambivolent  Offline
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Joined: Mar 2006
Posts: 19
atlanta
i was talking to my dad who was sponsored by yamaha back in the day and he said 28 to 20 degrees was a good rake angle to use on the bike and extending the swingarm about 1-2 inches helps handling while sliding in the corners


"Chrome dont get you home!"
Re: rake and trail flat track #203954
04/14/06 5:40 pm
04/14/06 5:40 pm
Joined: Aug 2001
Posts: 1,897
Elko, Nevada USA
dave - NV Offline

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dave - NV  Offline

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Joined: Aug 2001
Posts: 1,897
Elko, Nevada USA
Some chassis "set up", info you may/may not find useful. Certainly not 'pro level' but ...

Just out of curiosity I had son Joel measure the rake @ 22 on their (Richard's Racing) newest/latest/greatest C&J framed Rotax powered dirt tracker. Steep eh? I don't have this bike's trail but can get it from him. This bike chassis is fairly easily tuned with an adjustable length Penske rear single shock and adjustable offset/trail triple trees. And natch the Yam R6 fork tubes can be slid up/down in the clamps. We'll see.

This is a bit steeper than our Goldie rigid Sonic Weld tracker @25 rake with 3.67" trail. We have the Cerriani rr fork tubes slid up as high as is safe for tire clearance at full compression. And have fitted modified rear axle plates raising the rear end ~ 1/2" above OEM SW plates. I really dislike the way the GS feels at 'putt speed', as it's as wiggly and sensitive as a trials or speedway bike seems to me. But the front tire does stay hooked better than many/most and Joel likes it.

Front tire traction is 'everything' you know, as it will determine your corner entry speed. Being able to control a sliding and tucking in front end in the corners before needing to back off the gas is a key to going fast. But you all knew that ...

There's not been a problem (so far) with head shake with the GS even on rough tracks. But in my estimation the bike needs more trail to be safer which I want to experiment with, 'someday' ... sheeze.

Here's a 'plug and play' trail calculator on the Net.
http://www.rbracing-rsr.com/advchoppercalc.html

have fun, go fast, don't skin yer knees!


Dave - NV
Re: rake and trail flat track #203955
04/19/06 4:18 pm
04/19/06 4:18 pm
Joined: Jun 2004
Posts: 1,115
Kansas
kboyd Offline
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kboyd  Offline
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Joined: Jun 2004
Posts: 1,115
Kansas
Thanks for posting that cxalculator Dave!

U-D-Man...

I'm still trying to get the flattracker done, but took time off it to get my Tri 500 on the road. Have you seen the gas prices lately! Yikes...

I'm becoming less fond of the 2-stroke motor.. It just doesn't feel right to a 4-stroke fanatic. I liked it a lot better when rebuilding the top end (read as- "el cheapo"). Oh well.. I was building a 500 twin for it anyway, now I'm giving it a bit more priority than before!

Kyle


Kyle#44x

1969 T100R Daytona
1979 Powroll Honda XR250 "Dallas Baker" flattracker
1975 XL350 project bike
Re: rake and trail flat track #203956
05/19/06 1:47 pm
05/19/06 1:47 pm
Joined: Jun 2004
Posts: 1,115
Kansas
kboyd Offline
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kboyd  Offline
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Joined: Jun 2004
Posts: 1,115
Kansas
I just had to make a correction in the spring rate for fork springs that I posted above. I got dislexic I guess... 23lbs should be 32-34lbs for most vintage flattrack... I was looking over my notes and figured I'd better post the right info.

Kyle


Kyle#44x

1969 T100R Daytona
1979 Powroll Honda XR250 "Dallas Baker" flattracker
1975 XL350 project bike

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