Frame Head Angle for stability at speed

[outofsquare]

Been reading some really intresting posts of custom frames people have either changed existing frames or made from scratch to create their own optimal set up, and can not really find any info on the head angle they have used, for instance one would think that as the bikes speed would increase a bikes stability would come into play more and it would need to be ajusted to accomodate this, the bike Im converting for my first ever Mid Mount E Bike has an head angle of 71 degrees, this will be fine as Im staying totally within the laws & top speed is only 25 km/hr, I was thinking that you would probably need to be around 64 - 68 degrees to create high speed stability.

Am I thinking about this area completeley wrong, as the posot I heave read about frames being chopped up, or new ones from scratch to create a custom build seems to have no alterations to accomodate faster speed stability, as I am thinking of building my own frame from scratch for my second build I feel this could be a valid area I would have to consider, or does the head angle have not as much affect on stability as possible other modifications.

Anyway hope this post has some merit & all could educate me about my query.

Cheers All

Tom

 

[2moto]

It certainly is a good thing to think about these things. IMHO, there a lots of death traps at the speeds some of them go.

While head angle has a great influence, it is actually the trail that is the variable that determines the stability of a two wheeled vehicle. Here is probably the foremost experiment done on this subject: http://www.tonyfoale.com/Articles/RakeEx/RakeEx.htm

While it was done on a motorcycle, it directly translates to bicycles. On a bicycle it is the combination of the front fork geometry and rake angle that determine the trail figure. Here is another decent write-up directly related to bicycle and gives example figures for trail dimension at speeds: http://www.calfeedesign.com/tech-papers/geometry-of-bike-handling/

Having designed a good number of frames from bicycles to road racing motorcycles, I know from experience that getting this right makes a huge difference. That is not to say there are plenty of other influencing factor, such as frame stiffness, etc.

 

[outofsquare]

Hi 2moto,

Excellent links you have given me, I am trying to understand the trail factor, and you have sure pointed me in the right direction, I have been playing around with the Bike Forest frame design software (its a free on line frame design program) & it does work out trail figure and give you this info, just have to get my head around how to transfer the trail figure into a understandable answer that makes sense to me & what it actually means.

In the past I have had bikes that worked quite well at speed but where a pig at low speed input, especially in turn scenario at low speed, I'm just trying to educate myself about frame building & the parameters that have to be considered when designing a purpose built frame, it will not be for some time before I am willing to give it a go, but when I do, I want to ensure I have the info that is going to make the frame worthy of something when I finish it.

Thanks 2moto

Tom

 

[2moto]

No worries, Tom. Just shout if you want any further help. If you want to read some of the theory behind it, I can highl recommend this book: http://www.tonyfoale.com/book.htm . Not cheap, but the best money you can spend if you're going to design and build your own frames. Obviously, pedal bikes will have additional critical areas, such everything involving the crank geometry, assuming your e-bike will actually have pedals. :wink:

 

[outofsquare]

Appreciate your offer 2moto, will take you up on that, its turning out to be a very interesting fact finding scenario, and I now see how important trail is, will be interesting to see if any forum members post their finding's and what head angle & trail they used with the outcome they experienced, I might try to design a head tube which is adjustable so I can play around with the angle & test, this will make it easy for me to change the angle which in turn will alter the trail and quickly do a real case scenario test on the road, and then I can see how the handling characteristic s has altered, once I have it feeling how I like it I can build the actual frame set with my desired geometry as I know how it will act on the road, probably the long way around it, but it might be the easiest & clearest way for me.

Lots of ground work I need to do before I even go down this path

Cheers

Tom

 

[dogman dan]

A good topic to research before getting out a welder for sure. In general though, if modifying an existing frame, try to keep the head angle same as it was, including avoiding installing forks that make it much taller than it was.

Keep the forks and head angles the same, and lengthen the wheelbase is generally the best idea IMO. If lengthening, then raising the rear can compensate for longer forks returning the original angles the bike came with. This is what i did with my longtail, welding two frames into one bike. I measured the height of the bb from the ground, then cut the second frame such that when welded on, the bb was still the exact same distance above the ground. The result is 3 feet longer, but no change to the steering geometry. It rides real nice.

 

[2moto]

The problem with the lengthening the wheelbase is that it tends to become "slow" steering. Plus, unless you pay attention to the trail figure, lengthening the wheelbase doens't solve the stability problem. I do agree that I would not try to change the steering tube angle, though. There are several fairly easy ways to increase trail (if that's the issue), such as:

http://www.eandsweb.com/me/pics/bikes/104_0474.JPG

Remember that some frames are just too flimsy to provide adequate stiffness for speeds above say 30-35 MPH. No changes to geometry will solve that.

 

[agniusm]

This is the area i think center-hub steering comes with its benefits. You can have this adjusted on the system to your preferences if done right. I am yet to see if i am right or wrong with the concept i am working on.

 

[2moto]

I disagree, I am afraid. Hub center steering has no advantage over conventional forks in terms of setting trail and head angle. It's just a different (and considerably more complicated) way of doing it. That is not to say that hub centre steering doesn't have its benefits, but making it easier to set/adjust trail/head angle isn't one of them.

 

[amberwolf]

I might try to design a head tube which is adjustable so I can play around with the angle & test,

I'd had a plan to do that:
http://www.endless-sphere.com/forums/viewtopic.php?f=2&t=24034
but I never got any farther than that thread. Too many projects.