Good rake/trail/geometry resources?

ILoveThumpers

ILoveThumpers

Everywhere is thumpers!
Hello!

I'm planning some changes to my GN that will drastically change the geometry of the suspension. Shortening the forks, moving them up in the trees, larger rear wheel which necessitates longer shocks.

So while I'm not in love with the handling of the GN currently (it's chopper-ish) I don't want to create an unsafe condition by making these changes without some knowledge of what it's going to do.

So are there any good resources (here or not... wherever) about the geometry issues that you use for guidance? Please share!

-Deek
 
Be Careful! there are slotsof places out there. here is one.

http://www.chopperhandbook.com/rake.htm
 
AlphaDogChoppers said:
Sounds like you are on the path to creating a tank-slappin' death trap.
Click to expand...

That's why I'm asking for resources here. I'm not interested in dying via concrete so I want to do it right.

The bike has 29.5 deg rake and 4.06" trail stock, so I have some room to breathe.

-Deek
 
AlphaDogChoppers said:
No. Really, you don't.
Click to expand...

Yeeeeaaahhhhhh...

The rake and trail can't just be changed willy nilly. The entire motorcyxle needs to work as one unit. Change one thing, something else will likely need to be modified.

http://item.mobileweb.ebay.com/viewitem?sbk=1&nav=SEARCH&itemId=370825345758

Great resource ^^^^. Buy it. Read it. Love it.
 
AlphaDogChoppers said:
Looks useful, I may buy it, although I could probably write that book. ;)
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Man... And for half a minute I was beginning to think I liked you. That's gotta stop happening... Hahaha...
 
I didn't give you enough information for that kind of "OH MY GOD YOU'RE GOING TO DIEEEEEE" reaction. For fucks sake all I did was ask for resources and you're berating me for even THINKING about changing ANYTHING to do with geometry.

Next time I'll leave out ALL the details. Would that work better for you?

Wheel is larger, tire is smaller: diameter is the same.
Rear shocks will be 0.5 inches longer; the difference in rake is less than 0.5 degree.
Shortening the shocks will change the wheelbase by about an inch and the rake by about another degree.
I haven't done the trail calculations yet, but I will.

I'm NOT going about this willy-nilly and I haven't made a single fucking change to my bike yet. I have that book plus two others on reserve at our local library.

Now I'll be happy to share what I learn here but if this is the reaction I'm going to get, fuck it.

-Deek
 
ILoveThumpers said:
I didn't give you enough information for that kind of "OH MY GOD YOU'RE GOING TO DIEEEEEE" reaction. For fucks sake all I did was ask for resources and you're berating me for even THINKING about changing ANYTHING to do with geometry.

Next time I'll leave out ALL the details. Would that work better for you?

Wheel is larger, tire is smaller: diameter is the same.
Rear shocks will be 0.5 inches longer; the difference in rake is less than 0.5 degree.
Shortening the shocks will change the wheelbase by about an inch and the rake by about another degree.
I haven't done the trail calculations yet, but I will.

I'm NOT going about this willy-nilly and I haven't made a single fucking change to my bike yet. I have that book plus two others on reserve at our local library.

Now I'll be happy to share what I learn here but if this is the reaction I'm going to get, fuck it.

-Deek
Click to expand...

Ooooo K. Chill out man. You asked a question, gave slightly vague information and got a response that

WAS MEANT TO HELP YOU AND KEEP YOU SAFE.

Don't want or like the help you get when YOU ask for it, than ignore it. I apologize for attempting to help you find the answers ina fashion that upset your delicate sensibilities. Won't ever happen again.
 
AlphaDogChoppers said:
You said it yourself: "will drastically change the geometry of the suspension."

Longer shocks, AND larger rear tire, AND shorter forks, AND move the forks up in the trees.

I wasn't kidding or exaggerating. You are on the path to build a death trap. I don't need no fuckin' rake and trail calculator to figure that one out.

Here's a good one anyway:
http://www.rbracing-rsr.com/advchoppercalc.html
Click to expand...

I like that link, but let's avoid generalities please. My bike has larger rear wheel, longer shocks, smaller front wheel and shorter forks and was fine at just over 100 mph with steering damper at second notch. Admittedly I did measure rake before and after to determine what the changes might do to stability. I really need new triples with less offset but it's within limits (just).

That link is a great place for the OP to determine what his bike will change from and to. Thanks for the link.
 
These questions were on my mind too. I saw the subject line and was interested. Good links posted that I will look into for my own knowledge. Sounds like Deek is wanting to do the right homework before the mods.


Deek, leather up man, they just want to help. I look forward to reading your research and frame calcs.
 
I'm just not used to this overabundance of concern, I guess. "Be safe" is fine but discouragement with no motive is pointless. I thought I made clear that I wanted to do it right and intended on doing it safe, but maybe not.

I was purposefully vague in my original post; I wasn't asking advice on a specific bike/setup, etc. just for what resources people might use. Next time I'll leave out all details unless they're necessary. I tried that once but that didn't work out either. Maybe back to lurking for me...

-Deek
 
Yeah, sorry... in a mood today.

I'm in for the long haul; this project has me more excited than any I've ever started before so bear with me if you can. Or block me if I'm too much of a cunt for you to stand some day. ;D

Sorry again. And thanks for the links, everyone. The information soak has begun...

-Deek
 
Started a build thread... here's the beginning of the geometry discussion: http://www.dotheton.com/forum/index.php?topic=52764.msg590580#msg590580

-Deek
 
AlphaDogChoppers said:
Looks useful, I may buy it, although I could probably write that book. ;)
Click to expand...

I just started my first book....
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should finish reading it this year....
 
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