Headtube Angle

Going to build a longer down tube for the new one. The stock one is just too short for me. Curious about thoughts on what angle for the headtube to go for. The Folder measures at 30 degrees and the new one at 40 degrees. If anyone has a different ride and is able to measure it; it'd be interesting to know(Libre for example). Or the Sysmic. GT-Race, Apexx.

30 deg. is about the limit for a peter lynn buggy. Anything steeper and you may find the steering a bit nervous which is probably why they've changed them toward 40 deg. I think I used somewhere around 35 on my buggy. Of course you may find perfection at 38.2 deg. Fibonacci

With the two forks I have; the axle is just lined up in line on the same plane as the head bolt.



If I just make a really long down tube; the side rails will be touching the ground because of the strange angle out the front of the side tubes for the down tube.

I may make a 2 piece(simpler):



I like the look of the 3 piece though. Might make both?

The important thing is to keep the same profile as the original. Looking from the side of the front of the buggy, thats the profile. You can do most anything you want to the bug if you keep it all in proportion to the original. If you extend the side rail back 1 foot, you need to extend the front the same. This is about TUNING THE BUGGY, which is another story.
As long as the front fork is not changed from the original angle you can do anything to the down tube you want. It can angle up or down, left or right, twist left with an up and twist to the left with a down, as long as the front fork remains the same angle. If you increase the thickness of the down tube you can reduce the height of the tube itself which will allow the angle of the down tube at the side rail to change and still retain the strength to work at the new angle.

In all fairness to the issue at hand, you are asking about 2 entirely different buggy designs. The PL is one design and the Libre is another design as with the Sysmic, Apexx, and other full size bugs.
The Libre comes in 4 sizes, the PL is one size. Your comparing apples and oranges. The full size bugs have a basically level down tube where it connects to the side rails which aids in tuning the bug for big pilots or long legs. They also have extension parts for extending the side rail back to the axle to help balance (tune) the bug.

I have extension blocks and axle cambers on my Libre along with a longer down tube, all were needed to tune the bug for my style of riding. They are all packed away for the trip to WBB so a picture is not going to happen for a week or so, unless I can find one.
Or you can do this VVVVVVVVV

Been looking online for formula's to determine angles. Math is not my strong point. I'm trying to determine the angle of the top of the top tube that connects to the head tube like I have physically measured on what I have.

Anyone good at this?



(credit of image goes to Popeye)

Don't know how much help this will be but I'll kick in my 2 cents. If your keeping your same fork I would make a simple jig. Could be made out of plywood or whatever you have on hand. First remove downtube from fork and from siderails. Now put some boards under the front of the siderails to prop them up so their in the position you want. Now put your fork in the simple jig you made to hold it at your desired head tube angle,,,,30,35 deg. whatever. Now just work toward connecting the two. Remember all bisected angles are half the desired angle,,,if you want 110 deg somewhere then you set your miter saw to 55 on both cuts. Hope that helps

Quote: Originally posted by Blitzhound

If you're going to build a whole new down tube you need to understand things like Rake and Trail and understand how these two things affect handling and performance. It's not just a Matter of angles. I am an Engineer. This is what I do. If you're just looking to make a longer down tube and using the same fork. Why not simply extend the one you already have. Simply cut the end of the tube if it's not already open. Insert a tight fitting sleeve andbutton weld it in. An extension of the same size as the current tube slides over the sleeve button weld it in place. Then a butt weld along the seam and it will be as strong if not stronger then the original. BOOM DONE!

Problem is the point where the extended piece is welded on and bolts to the side rails Keon the ground or very close. That's why you can't buy a longer down tube from PL.
The Libre Sprinter and V-max are very similar but less dramatic in height.

Took some pictures for fun.
With the stock tube all the way in:


With it shoved all the way in:


All the way out:


With it out to the last bolt just showing the side rails on the ground and oddly the HT angle is 50 degrees:


With it clamped up to my old Folder DT to double the length. HT angle is now 30 instead of 40:







And note how it lowers the side rails and doesn't make the result like this:





Now with it clamped up over/under. At the long setting; HT is 38 and shorter it's 40.









Notice the clever fitment of the 3 pieces:

Quote: Originally posted by kteguru

Don't know how much help this will be but I'll kick in my 2 cents. If your keeping your same fork I would make a simple jig. Could be made out of plywood or whatever you have on hand. First remove downtube from fork and from siderails. Now put some boards under the front of the siderails to prop them up so their in the position you want. Now put your fork in the simple jig you made to hold it at your desired head tube angle,,,,30,35 deg. whatever. Now just work toward connecting the two. Remember all bisected angles are half the desired angle,,,if you want 110 deg somewhere then you set your miter saw to 55 on both cuts. Hope that helps

Thanks for the idea. I'll most likely do it this way.

Ok; this is just a mockup to give me something to work with. It's sold as 2"x2" but it's really 1.5"x1.5" which is what the down tube is(40mm).

Any of the three pieces can be of any length. I'm wondering which ones to lengthen or shorten for better load handling or strength or even just for better aesthetics.

The front piece is 5" total length and only 3" measured from the back of the fork to the end.

The middle piece is 9". The back piece is 8" total length. 3" protruding from the side plates. The side plates are 5" and I have the piece flush with the back.

Bent one up out of aluminum just to see. Don't mind the yellow paint; that's the metal places doing.



At a bit of a stand still due to selecting tubing/pipe for the head tube. I know of Popeyes method of using two pieces of pipe. I planned on doing that; but I'm not really finding available sizes needed to do that. Then I was going to get some say 2" OD with 1/4" wall thickness and mill out the seat for the bearing. I have a drill/mill. Still need to figure out the method of cutting the pipe. A 42mm bearing is 1.654".

So I clamp the tube or pipe vertical to the table. Now use an end mill(of what size?) or boring bar? Or something else?

Also the metal at the actual store was only .50 cents an inch. The online price is high.

Took so long because it seemed like I waited a month for the boring head to show up. Tomorrow I test it:




I know the welds are pitifully ugly. Takes a lot of skill to make them look good.

I did a bunch of welding on a 3' piece of 1/8" material to dial in the machine. Hammered the pieces over to see if it held. Sawed through the welds to look at the bead from the side.








It's been over 5 years since I last did any welding. Last time it was exhaust tubing for a turbo kit using .023 wire and shielding gas. I remember it being easy. Well it was just a leased bottle and I turned it back in. This time I wanted to try flux core. Totally different animal. Much more challenging.

And don't worry about that poor drill press table. It cleans up nicely. It's just for wood anyways and I didn't drill those holes into it either.

Bought it used long ago and it was made long ago.