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pinjas
08-07-2015, 11:32 PM
Hello,

Apologies if this is an incorrect section for this topic. Some trikes appear to have their wheels further forward than others. Some seem to have the wheels closer to the riders hips and others closer to the riders knees.

What are the pros and cons to having wheels further forward compared to further back on the frame?

Thanks

Petone_NZ
08-08-2015, 03:23 AM
With a trike (tadpole or delta) there's a "triangle of stability" formed by connecting the ground contact patches of the three tyres. As long as the centre of gravity remains within that triangle then the trike stays upright. but if the CoG moves outside the triangle (e.g. during cornering) then the trike will tip - or possibly slide, depending on height of CoG.

If a tadpole front axle line is closer to the rider then the CoG is closer to the wide end of the triangle - so it would have to move further laterally before reaching tipping point. Thus (for any givern track width) the closer the front axle is to the rider, the more lateral stability there is.

But as the front axle line moves further forward away from the rider, there is less chance of lifting the back wheel under heavy braking - and thus losing directional control.

The compromise is balancing lateral stability v longitudinal/braking stability. There's probably no "one best answer" that will suit all tadpole trikes ... you'll need to balance these two factors for your own design and weight. Widening track will also increase lateral stability.

If you go for a quad design instead of a tadpole then the "triangle of stability" becomes a "rectangle of stability" and the front axle can be as far forward as you like without affecting lateral stability. This also introduces drivetrain complications and extra weight (compared to a tadpole), plus in some jurisdictions a
"bicycle" cannot have four wheels.

MrIdaho
08-08-2015, 09:35 AM
a picture is worth a 1000 words and Google is a great tool

www.google.com/search?q=calculating+center+of+gravity+on+a+trike&rlz=1C1AOYE_enUS532US623&espv=2&biw=1440&bih=763&site=webhp&tbm=isch&tbo=u&source=univ&sa=X&ved=0CC4QsARqFQoTCM2hlNbLmccCFUGUiAodXUwMwA&dpr=1

pinjas
08-08-2015, 11:11 AM
Super interesting, excellent explanations, thanks.

Ticktock
08-09-2015, 09:03 AM
HI,
Petone has hit the nail on the head! Its all a trade off. There is no one answer for all conditions. The best overall starting point , if you don't k ow that you need anything different , is to design for equeal load on all wheels. (for a tadpole trike--different answer for a delta trike).
And it is surprising how many places will stop a four wheel "bicycle", despite all the envioroment advantages.
Steve G
Beijing

Twinkle
08-09-2015, 03:01 PM
I run 3 e-trikes and a couple of pedal tadpoles all with straight booms with 42" ish wheelbase and 32 " track without a problem see the voyager and 20/20 e-trikes in the newsletters or the transportable .
All ride well and using the 20" rear wheel on 3 out of 4 of those trikes allow the trike to fit in the rear of the estate car without dismantling

Any longer wheelbase will cause you problems with the back of the leg hitting the cross boom whilst pedaling . All corner well and the weight distribution is about 55 rear 45 front .

regards emma

LongRider
08-09-2015, 08:15 PM
Funny no one has mentioned that (from what I've read) the optimum weight distribution for a tadpole trike is 30/70 -- that is 30 percent of the weight resting on the back drive wheel and 70 percent (35 percent on each) distributed between the two front wheels. The position of the front wheels can greatly effect this...

Twinkle
08-10-2015, 03:43 AM
Funny no one has mentioned that (from what I've read) the optimum weight distribution for a tadpole trike is 30/70 -- that is 30 percent of the weight resting on the back drive wheel and 70 percent (35 percent on each) distributed between the two front wheels. The position of the front wheels can greatly effect this...


it might be optimum BUT when you brake hard all the weight comes off the back ( weight transfer ) and the back brake will lock up and skid OR the hard braking will actually lifts the rear wheel off the ground , which l can assure you is a frightening experience .

On an average "UK built/grown adult " the legs each weigh about 24 b and arms 12 lbs each with the body and head making up the rest , thus it is THE POSITION OF THE RIDER / luggage carried that dictates the overall loading of the trike and that is why it is difficult to design in this parameter ,

My thoughts on this idea is as long as the weight is far enough behind the front wheels to give good handling and that the weight transfer during very hard braking is still behind the front wheels you won't go far wrong .

As Petone stated ; the Centre of gravity in effect should be as low as possible and just far enough behind the widest point on a tadpole inside the triiangle of staboilty where weight transfer will not have too much effect on hard high speed braking and handling .

regards emma.

ken will
08-10-2015, 07:14 AM
A few more points to ponder:

If you are tall with a big chest, head and shoulders more weight will transfer forward when braking.
If you are short with a large % of your weight in the butt :stooge_curly: and lead acid batteries mounted low ...much less weight will transfer forward during braking.

If your riding style includes sharp, high speed turns a little more weight between the front wheels works.

Keeping the weight as low as possible is always a good idea

LongRider
08-10-2015, 11:10 AM
it might be optimum BUT when you brake hard all the weight comes off the back ( weight transfer ) and the back brake will lock up and skid OR the hard braking will actually lifts the rear wheel off the ground , which l can assure you is a frightening experience .
regards emma.

I always thought that having a rear brake (for anything other than a parking brake) was not the best idea on a tadpole trike -- being that it can contribute to less than stable handling. Also how can a rear wheel that has had all the weight come off it lock up and skid??? Another reason for not having a brake on it. My zwei pfennigs...

Twinkle
08-10-2015, 01:13 PM
I always thought that having a rear brake (for anything other than a parking brake) was not the best idea on a tadpole trike -- being that it can contribute to less than stable handling. Also how can a rear wheel that has had all the weight come off it lock up and skid??? Another reason for not having a brake on it. My zwei pfennigs...

Unfortunately

:thinking2:



:taz:

The UK has something called the EAPC regulations that regulates the conditions and use of electrically assisted pedal cycles and some "not knowing individual " who probably has never riding a bike ( or trike ) in their life has decreed that the rear brake of a eapc should not only be fitted but be capable of stopping the as said vehicle in a certain distance at a specified MPH . In "being a responsible and law abiding UK citizen " , we have managed to not only fit a rear brake but get it just within the stopping distance ,
The over enthusiastic use of a pair of 180mm front brakes can still lift the rear wheel off the ground just for the effect though .

These regs also govern when to put the brakes and how !!!!!! ( not quite word perfect )

Just at the point where the weight is transferring to the front wheels by the use of the front brakes the rear wheel will just lock up .

But

It does really nice tailslides when done on loose gravel and grass , believe me

ALOOB I know but then you have to humour these law making bods that in general talk a load of of B****S.

regards emma