CB desert sled - Page 15

Luke · 01-11-2013, 09:31 AM

Quote:

Originally Posted by DRjoe

It was just an idea for if you had the swing arm angle where you wanted it but if you want a more progressive shock action and and more anti squat then moving the shock mounts will certainly solve all those at once.

Have you had a look at tony foales book and suspension program? Its a great read and the program really helps with working out suspension geometry.
There is also a program for push bikes that helped me a lot to work out the rear suspension on my project bike, I think it was called linkage but I'm not 100% sure.

I've been borrowing Foales' book for almost a year now, should probably just go and buy my own copy. I wrote some of my own software to figure out linkages and levers and mounting points, but it's always going to be garbage in garbage out.

What did you end up setting the rake to on your drz fork build? I like the idea of just copying the drz rake since the offset (and trail) are already set on the forks but I can only find one second hand source for the rake (27.6 degrees). I can slide the forks to give +/- half a degree on the rake, but would like to start out as close to right as possible.

DRjoe · 01-11-2013, 03:21 PM

I like you tried to copy the drz rake but ended up setting it less than the drz because it the bike just handled better.
I'm not sure what I ended up with, I'll measure if later and get back to you.

With my dr the biggest factor for improving the handling was increasing the swing arm angle and getting rid of some squat, The dr has very flat swing arm compared to other dirt bikes.

Have you seen the article tony did about rake v trail
He experimented with the rake in a bike by reducing it in stages all the way back to 0 degrees the whole time he kept the trail the same.
The result was quite interesting. He found stability was not changed as long as trail was kept the similar.
There where other effects like less front end dive and the steering was not effected by terrain so much.

Luke · 01-11-2013, 04:48 PM

Yes, I just re-read it last night :)

For those reading along, this one:
http://www.tonyfoale.com/Articles/RakeEx/RakeEx.htm

That'd be great if you could measure what you ended up with. That'd make a great starting point. Especially since the more I research the DRZ geometry, the more numbers I get. On the upside, I've been measuring other bikes and it seems that the rake is always* measured with the suspension fully extended. That makes things simpler. If it's true.

*well, on 3 of 3.

DRjoe · 01-12-2013, 01:00 AM

I'll measure it tomorrow.

To be honest I think I fluked the geometry on the dr.
It was pretty good at the first attempt but I felt it needed less rake but I couldn't get any less without major operation.
After a while I thought just for an experiment I would drop the forks back down the triples and increase the rake slightly.
Low and behold it handled even better, its more stable and turns quicker.
After that I decided that the next bike I would make any thing to do with the bikes suspension and steering geometry adjustable because the chances of getting it spot on first time is slim even if you do copy another bike.

I think power, weight, centre of gravity, gearing and riding position has got more to do with a bikes handling than I first thought.

Luke · 01-12-2013, 08:57 AM

I get what you're saying about adjustability. I just may end up making the rear frame totally adjustable. As it is, I should have at least made the top shock mounts eccentric, as that would give an easy inch or so of adjustability. I might still do that.

I went over to a friend's place last night and measured the rake on his DRZ, and got a different number than any of the published ones. Oops. Then I noticed he had street tires on it, so I measured the axle heights. It turns out that the different tires change the rake by almost a full degree, so maybe I'm just obsessing at this point.

LC Garage · 01-12-2013, 09:20 AM

[QUOTE=so maybe I'm just obsessing at this point.[/QUOTE]

DRjoe · 01-12-2013, 12:15 PM

Quote:

Originally Posted by Luke

so I measured the axle heights. It turns out that the different tires change the rake by almost a full degree, so maybe I'm just obsessing at this point.

Uh maybe just slightly.

Next you'll be worrying about how many tacos you eat before the start of the race, you wouldn't want to move the centre of gravity buy over eating.

oregoncoast · 01-12-2013, 04:59 PM

Quote:

Originally Posted by Luke

maybe I'm just obsessing at this point.

Ya think??

Luke, you have 105 days until the starting line. 105 days. Just build a damn dirt bike...stop engineering a freaking masterpiece!! We still need to test the shit out of that thing!! You have less than 3 weeks left to have the bike running and rideable;; according to the schedule you told me

I need a drink....maybe you can build us a still so we can make our own whiskey while you're in the fabricating mood....

Just kidding...looks great! Now how about turning that inline four into a rotary engine for the race?? I mean, you have the lathe all warmed up...shouldn't be too tough....

TwinDuro · 01-12-2013, 06:33 PM

Quote:

Originally Posted by oregoncoast

Just kidding...looks great! Now how about turning that inline four into a rotary engine for the race?? I mean, you have the lathe all warmed up...shouldn't be too tough....

Hmm... A rotary powered desert sled? That sounds like fun!

Except for the blown rotor seals just south of El Arco.

LC Garage · 01-12-2013, 06:52 PM

A quick progress report and pics from today, Luke and Al will add more later, I'm sure!

Stator cover is off to make an adapter or shim, in order to mate the two dissimilar gasket surfaces;

Shim is progressing;

Shim finished, now to shim brush pack;

Brush pack is held in by two small bolts, removed those (after this pic was taken) and it appears no special shim will be required, just two small matching washers;

Custom footpeg mounts in progress;

Measure once, drill twice??

Doesn't the kick starter go in here somewhere?

Progress seems to create debris fields;

Progress!!!

sailah · 01-12-2013, 08:07 PM

Sweet, that seat looks a little hard

Luke · 01-12-2013, 08:34 PM

Quote:

Originally Posted by sailah

Sweet, that seat looks a little hard

It's a 'stock' seat. From what I've read it's supposed to be like that.

Ladybug0048 · 01-12-2013, 08:40 PM

You're going to get splinters in your butt - - -

TwinDuro · 01-12-2013, 09:52 PM

Quote:

Originally Posted by Luke

It's a 'stock' seat. From what I've read it's supposed to be like that.

Not if I have anything to do with it!

That seat will be like a La-Z-Boy attached to a cruise missile; horrifying but somewhat comfortable...

Luke · 01-12-2013, 10:47 PM

While Rick was working on the stator cover adapter, Allan and I worked on the frame.

First up was to mount the motor properly and measure the space for the airbox (no change, it's still tight) then make a wooden cradle for holding the frame on the jack.

There was more measuring done on the frame just because.

Then we made some footpeg brackets. They're not quite right, but they're close enough: we needed to see how far forward the top shock mounts could go without hitting the rider's leg. We also needed to see that the footpegs cleared the other bits: exhaust, shifter, kickstart lever. Well 2 of 3 is going to have to do for now. Besides, the kickstarter is just a backup anyway.

01-12-2013, 09:20 AM	#216
LC Garage On Any Sunday Joined: Mar 2011 Location: Columbia County Oddometer: 581	[QUOTE=so maybe I'm just obsessing at this point.[/QUOTE] __________________ "Nothing can stop us but fear and common sense”

01-12-2013, 06:52 PM	#220
LC Garage On Any Sunday Joined: Mar 2011 Location: Columbia County Oddometer: 581	Progress Pics A quick progress report and pics from today, Luke and Al will add more later, I'm sure! Stator cover is off to make an adapter or shim, in order to mate the two dissimilar gasket surfaces; Shim is progressing; Shim finished, now to shim brush pack; Brush pack is held in by two small bolts, removed those (after this pic was taken) and it appears no special shim will be required, just two small matching washers; Custom footpeg mounts in progress; Measure once, drill twice?? Doesn't the kick starter go in here somewhere? Progress seems to create debris fields; Progress!!! __________________ "Nothing can stop us but fear and common sense”

01-12-2013, 08:07 PM	#221
sailah Lampin' it Joined: Aug 2005 Location: Turning expensive metal into scrap Oddometer: 4,139	Sweet, that seat looks a little hard __________________ We're not out here to rough it. We're here to smooth it . Things are rough enough in town. Nessmuk

01-12-2013, 08:40 PM	#223
Ladybug0048 Bug Sister Joined: Nov 2005 Location: Spokane Valley, WA (the dry side of the mountains) Oddometer: 8,587	You're going to get splinters in your butt - - - __________________ 2013 Hells Canyon/Wallowa Valley Gathering: http://www.advrider.com/forums/showthread.php?t=843668 "Always be a first-rate version of yourself, instead of a second-rate version of somebody else." - Judy Garland

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01-11-2013, 03:21 PM	#212
DRjoe Beastly Adventurer Joined: Sep 2007 Location: Sunshine coast qld Oddometer: 4,244	I like you tried to copy the drz rake but ended up setting it less than the drz because it the bike just handled better. I'm not sure what I ended up with, I'll measure if later and get back to you. With my dr the biggest factor for improving the handling was increasing the swing arm angle and getting rid of some squat, The dr has very flat swing arm compared to other dirt bikes. Have you seen the article tony did about rake v trail He experimented with the rake in a bike by reducing it in stages all the way back to 0 degrees the whole time he kept the trail the same. The result was quite interesting. He found stability was not changed as long as trail was kept the similar. There where other effects like less front end dive and the steering was not effected by terrain so much.

01-11-2013, 04:48 PM	#213
Luke ^OP GPoET&P Joined: Aug 2004 Location: Idiotville, OR Oddometer: 3,748	Yes, I just re-read it last night :) For those reading along, this one: http://www.tonyfoale.com/Articles/RakeEx/RakeEx.htm That'd be great if you could measure what you ended up with. That'd make a great starting point. Especially since the more I research the DRZ geometry, the more numbers I get. On the upside, I've been measuring other bikes and it seems that the rake is always* measured with the suspension fully extended. That makes things simpler. If it's true. *well, on 3 of 3.

01-12-2013, 01:00 AM	#214
DRjoe Beastly Adventurer Joined: Sep 2007 Location: Sunshine coast qld Oddometer: 4,244	I'll measure it tomorrow. To be honest I think I fluked the geometry on the dr. It was pretty good at the first attempt but I felt it needed less rake but I couldn't get any less without major operation. After a while I thought just for an experiment I would drop the forks back down the triples and increase the rake slightly. Low and behold it handled even better, its more stable and turns quicker. After that I decided that the next bike I would make any thing to do with the bikes suspension and steering geometry adjustable because the chances of getting it spot on first time is slim even if you do copy another bike. I think power, weight, centre of gravity, gearing and riding position has got more to do with a bikes handling than I first thought.

01-12-2013, 08:57 AM	#215
Luke ^OP GPoET&P Joined: Aug 2004 Location: Idiotville, OR Oddometer: 3,748	I get what you're saying about adjustability. I just may end up making the rear frame totally adjustable. As it is, I should have at least made the top shock mounts eccentric, as that would give an easy inch or so of adjustability. I might still do that. I went over to a friend's place last night and measured the rake on his DRZ, and got a different number than any of the published ones. Oops. Then I noticed he had street tires on it, so I measured the axle heights. It turns out that the different tires change the rake by almost a full degree, so maybe I'm just obsessing at this point.

01-12-2013, 10:47 PM	#225
Luke ^OP GPoET&P Joined: Aug 2004 Location: Idiotville, OR Oddometer: 3,748	While Rick was working on the stator cover adapter, Allan and I worked on the frame. First up was to mount the motor properly and measure the space for the airbox (no change, it's still tight) then make a wooden cradle for holding the frame on the jack. There was more measuring done on the frame just because. Then we made some footpeg brackets. They're not quite right, but they're close enough: we needed to see how far forward the top shock mounts could go without hitting the rider's leg. We also needed to see that the footpegs cleared the other bits: exhaust, shifter, kickstart lever. Well 2 of 3 is going to have to do for now. Besides, the kickstarter is just a backup anyway.