Bobs 2024 Build Off Build

[bob58o]

This is beginning to look like something.
This is the basic shape I find pleasing to gaze upon.

 

[Denny]

But you won’t find it pleasing to ride. It’s too low.

 

[bob58o]

Seat height is 21” off the ground, which is about 4.5” higher than this folding chair I’m using for reference.

 

[bob58o]

My weight multiplied by the height of my belly button plus the engine’s weight multiplied the height of its belly button divided by the combined weights of both belly buttons puts center of mass at 24” above the ground.

24” vertical center of mass is 1/2 of the 48” wheel base.

 

[Denny]

Look at how tall off road dirt bikes are and tell me center of gravity matters. It doesn’t. Now center of weight distribution front to rear, that’s what matters.

 

[bob58o]

Quick guesstimates
1.75” Offset
27.5 degree rake

Me thinks that will give about 3” of trail. Give or take an inch; 2-4” of trail seems about right for this geometry.

 

[Rat]

Look at how tall off road dirt bikes are and tell me center of gravity matters. It doesn’t. Now center of weight distribution front to rear, that’s what matters.

He isn't getting it. Even having spent nearly my hole life as a 2wheeled terror... I don't think I can get it to sink in that COG is an irrelevant matter for his project due to its lack of weight alone.


Having a low center of gravity only matters for bikes in ONE aspect... Cruisers, as in Heavy Highway Haulers.
No one wants to hold an 1800lb fully dressed out Harley with a high COG upright for long at a red light, and forget trying to get something like that moving because the low speed corective wobble would lay you down if the red light didn't

Now you take something that has a curb value of 500lbs or less it becomes completely irrelevant how top heavy it is or is not because it becomes more manageable.

The other factor in this is the naturally occuring gyroscopic effect of the wheels in motion, a large bike takes a lot more to control at lower speeds and it would be devastatingly worse if they had a high COG. The gyroscopic forces seem somewhat delayed when you're talking about a full dresser, but their wheel and sire sizes are a factor in that to an extent.

Dirtbikes and dualsports are designed around high travel suspension and tend to have larger diameter wheels and heavier tires than said cruisers but more noticeable the rear wheel is nearly ALWAYS a size smaller diameter, and a size wider than what ever is on the front.

So where they weigh so much less and are therefore already easier to control at low speeds already before the gyroscopic forces take over trying to keep them upright (which is significantly sooner) they tend to accelerate a lot quicker (a factor if weight and gearing) that yet again having a top heavy COG is irrelevant by design.

These are all the same factors that make a 1999 Ford Exploder such an easy rollover risk taking corners too hard. They were too tall, too heavy, with suspension that was too soft... AKA high COG and heavy.

You could put an 18" lift on a 1985 Subaru Brat and most likely still not be able to roll it over easily...Why? Because they are light as hell coming in around 2300lbs max.

In short Heavy= Low and Lightweight= who cares

 

[ezcome-ezgo]

Graph paper negates all arguments.

 

[bob58o]

If vertical COG doesn’t matter, then it doesn’t matter.
The position of seat height is not just determined by one thing. It’s a multi-dimensional seat.

Butt to handlebar distance and angle.
Frame design simplicity.
Length of forks.
3-tree offset.
Desired amount of trail.

as EZ^2 stated, Graph paper wields tyrannical authority.

 

[bob58o]

The front is Honda Z50 style
About 600mm to top of seat?
About 24”

A Z50 stretched 14”.
With 10” diameter front wheel.
About 12” rear diameter tire.
About 16” front diameter tire.

 

[ezcome-ezgo]

Graph paper wields tyrannical authority

The awe of it's sovereignty demands submissiveness.

 

[ezcome-ezgo]

Honda Z50 style

Many meticulous Japanese engineers devoted their careers - nay their lives - to the development of this product. Yet another carefully thought out detail that cannot be ignored.

 

[Denny]

Many meticulous Japanese engineers devoted their careers - nay their lives - to the development of this product. Yet another carefully thought out detail that cannot be ignored.

Actually it all started off as a kiddie ride on a merry go round that didn’t go up or down. True story! That’s how Honda ended up in the mini-bike business.

 

[bob58o]

It seems the green zone is the area in question.

From 495mm (19.5”) to 590mm (23.25”) on the Z50

585mm (23”) to 660mm (26”) on the G212ATT

The Z50 image (and the weight of my mason jar) suggests I’m too high already.

But the Graph Paper has spoken.
If you dare to continue this blasphemous conversation you do so at your peril. The wrath of the Paper is swift and merciless.

 

[Evanguy]

i may of missed it but are you running a bypass or second throttle body on that bad boy? the SC shouldn't be under vacuum, that's why you see so many failures with these most run them with a draw though and no bypass or second throttle body causing the vacuum at idle to drain the oil and just generally hard on them.

 

[bob58o]

16.9” Front Tire
12.3” Rear Tire.

This measurement was slightly better because I measured. How many inches of phone charging cable is the circumference of your tires?

53” of charging cable.

 

[bob58o]

i may of missed it but are you running a bypass or second throttle body on that bad boy? the SC shouldn't be under vacuum, that's why you see so many failures with these most run them with a draw though and no bypass or second throttle body causing the vacuum at idle to drain the oil and just generally hard on them.

Ask Denny. He’s been telling me for years I don’t need a bypass set up.

 

[Evanguy]

Ask Denny. He’s been telling me for years I don’t need a bypass set up.

ill see the answer when he replies i guess, the only setups I've seen without a bypass fail very quickly. and i don't think I've ever seen a factory setup without one on anything.

its going to cause insane heat that isnt needed, there is only downfalls and zero advantage

the extra throttle body helps with the life of the charger due to the lack of vacuum but doesn't help wit the heat. the bypass valve is the answer to both

 

[bob58o]

ill see the answer when he replies i guess, the only setups I've seen without a bypass fail very quickly. and i don't think I've ever seen a factory setup without one on anything.

its going to cause insane heat that isnt needed, there is only downfalls and zero advantage

the extra throttle body helps with the life of the charger due to the lack of vacuum but doesn't help wit the heat. the bypass valve is the answer to both

The original plan was to try to set up a Greddy type blow off valve to be used as a recirculating bypass under vacuum.

 

[bob58o]

I played around with a few different set ups.
Recirculating bypass.
Intercooler.