Frame Geometry for the 350X, 250R and XR600

[bkm]

I wasn't planning on posting anything about this for a while as I'm giving myself two years to complete this and wasn't even planning to start for another few months, but seeing as I have a lot of questions and issues to deal with I figure this thread is as good a place as any to start asking them.

So this is what I want to turn into a trike. I've had my eye out for the right donor bike for a while now and this one came up the other day for the right price and in the right condition. I'm hoping to do this build in a way that if I do have to throw in the towel at some point I'll still be able to make it back into a bike, but if not and it does become a trike I'll have lots of spare parts for my other girls.

Attachment 247416
Attachment 247417

The rake looks to be about 2° less than my TRI-Z which should be easy enough to adjust with the rear shock location if that ends up being the desired rake angle. However I'm planning to use the KTM WP forks which are easy to shorten, but have a leading axle vs the trailing axle on the TRI -Z.

The biggest investment aside from the price of the bike is going to be the front and, so I want to make sure I get it as close to perfect as possible on the first try.

I spoke with a buddy who used to be a regular on here they gave me a few recommendations four guys that might be interested in building my triple tree. I plan to start contacting them early next year, but hope to have some idea what it is I'm looking for before I start bothering them with questions.

I think I'm going to build the swingarm myself, but I need to decide which carrier and axle I'll be using. The KTM quad swingarm would be the ultimate way to go, but it uses a link shock system and I would prefer to keep the PDS set up as it will facilitate ease of height adjustment as well as simplify setting up the shock. I really like the ATC style swing arms that clamp onto the carriers, but I've never taken a good look at how the brake carrier works on that setup. I also want to make sure I choose something that has wheels and axles readily available.

Tons to think about and learn (we can't all be as smart as Dude) may as well start now.

Look into the honda 450r rear setup. It's similar to the 250r, but parts are cheaper and available. I have a 04/05 450r swingarm I'll trade you for some black dirtbike wheels if you'd like?

[El Camexican]

Me likes that idea kemosabe

[BOB MARLIN]

Getting back to the original purpose of this thread---------

Frame geometry is one thing, but getting the "Rake and Trail" right is the important part of getting something to steer right. On a trike you want to keep the "Trail" part of the equation short, no matter what "Rake" you end up with.

[El Camexican]

I'll leave you scientists alone.

Promises, promises….

[El Camexican]

I'm being directly addressed. And now you're trolling.

Send me the ticket.

[BOB MARLIN]

At one time, I read a thread where someone had scoped out the different rake angles and trail numbers for various trikes. I think it might have been Jason Hall-not sure. And it may have even been on the other 3 wheeler site before it went down (the old .org site). You might try to search here or even on the old site (it kinda still works) for that thread.

When I did my 450 conversion I measured the rake angle on one of my 350x's and I think it was close to about 23 deg. and the trail was around 3.5". I think the 350x handles the best out of all the trikes so that's what I shot for when I built the 450. I had to play with the numbers on the triples I built, and lower the rear top shock mount to try to get there. I still couldn't get to my target numbers but I was able to get it close enough to work well.

[El Camexican]

At one time, I read a thread where someone had scoped out the different rake angles and trail numbers for various trikes. I think it might have been Jason Hall-not sure. And it may have even been on the other 3 wheeler site before it went down (the old .org site). You might try to search here or even on the old site (it kinda still works) for that thread.

When I did my 450 conversion I measured the rake angle on one of my 350x's and I think it was close to about 23 deg. and the trail was around 3.5". I think the 350x handles the best out of all the trikes so that's what I shot for when I built the 450. I had to play with the numbers on the triples I built, and lower the rear top shock mount to try to get there. I still couldn't get to my target numbers but I was able to get it close enough to work well.

I posted a link to a thread in post #2 of this thread that might be the one you're referring to. It's a good read.

[BOB MARLIN]

I read that thread a couple times before I started my project and it was a big help in making me understand what effects steering and why. The funny thing is I remember kacey bringing that missile out to the invasion and saying the steering was way too twitchy. I believe its because the missile is using trike geometry in a two wheel configuration. The same is true when you use a two wheeler frame for a trike, but in reverse, the steering gets "heavy" instead of twitchy.

[El Camexican]

Here’s what I come up with so far.

1985 TRI-Z 250 (with 4” over swing-arm and forks extended ½” above the clamps)

Head Rake ......... 20 deg.
Fork Rake ...........26 deg.
Fork Length………..31.1”
F. Tire Dia…………24”
Wheel Base .........?
Dry weight ...........?
Wet weight ......... ?
Wet bias .............F ? / R ?
Bias percentage ... F ? / R ?
Axle position .......Trailing
Triple tree angle ...6 deg. staggered
Swing Arm length…?
Calculated Trail Neg. - .15” (guesstimate this would be about positive .6” if stock swing-arm was used)

1998/2003 KTM 250/300/380

Head Rake ......... 25 deg.
Fork Rake ...........25 deg.
Fork Length………..35.75”
F. Tire Dia…………28”
Wheel Base .........?
Dry weight ...........?
Wet weight ......... ?
Wet bias .............F ? / R ?
Bias percentage ... F ? / R ?
Axle position .......Leading
Triple tree angle ...0 deg.
Swing Arm length…?
Calculated Trail Pos. 5.98”

I’m wondering if a set of Halls USD triple trees is angled like the stockers? If he uses a zero angle and retains the same 1” offset and all other variables are the same that would make the trail positive 3.3” VS negative less than 1” on the stocker I would think that would dramatically change how the trike handles and likely for the better based on the comments I've seen.

[El Camexican]

Yout tri-z without a doubt does not have negative trail.

According to this it does http://www.carbonfibervalvecovers.co...ake_trail.html

It wouldn't if not for the added length of the swing-arm and the forks being above the top of the triple tree. As well, the measurements were taken in a static position. Adding a rider would also put it back into positive territory as it's is only .15" negative as it sits.

On the topic there was a study done in the UK in which a BMW was set up with an adjustable rake and they tested it to the point of having the forks vertical. See below.


https://www.tonyfoale.com/Articles/RakeEx/RakeEx.htm

[El Camexican]

Let me put it another way; the CL of the steering head intersects almost perfectly with vertical line of the axle, so I don't understand how that can equate to several inches of trail.