Dirt bike tower thingy

**pete-blen** · 12th September 2013, 10:48

I needed a way of getting the dirt bikes around..
No room for a trailer & the cars not big enough for
a bike rack across the back...
So I put this togeather at work...
The only real pain is takeing the chain off/on the bike..
there will be 4 tie downs & 2 wheel straps to hold it in..
The pull is on the wheel as it fits down in the frame...

It just plugs into the fitting bolted to the tow bar with 2
1" bars with 10mm cross pins to hold it in... 1min to put
it on/off...

**Gremlin** · 12th September 2013, 12:06

Surely rear tyre wear is fast enough already? Guess it depends how far you need to move it.

Have you ever considered a slightly heavier BMW GS adventure bike? It's road legal, so you can ride on the road too.

**fridayflash** · 12th September 2013, 12:22

pretty trick bit of engineering there

ya reckon itd be no good running the chain on it..as in spinning the counter shaft?

**scott411** · 12th September 2013, 13:11

i can't imagine thats wonderful on the gearbox either, having it spinning that quick behind a car, tyre wear would have to be an issue as well, knobblys dont like tarseal

**pete-blen** · 12th September 2013, 13:15

Originally Posted by Gremlin

Surely rear tyre wear is fast enough already? Guess it depends how far you need to move it.

Have you ever considered a slightly heavier BMW GS adventure bike? It's road legal, so you can ride on the road too.

Was waiting for the tyre wear comments.....

Now here's how I veiw the tyre wear issue...
Rideing the bike under it's own power would wear more rubber than towing it with out any drive force
or rider weight on the tyre... ..... They are Dot rated tyres as the bike has rego & wof...

Originally Posted by fridayflash

pretty trick bit of engineering there

ya reckon itd be no good running the chain on it..as in spinning the counter shaft?

I wouldn't like to try... the chain slack would also be on the top instead of the bottom..

**haydes55** · 12th September 2013, 16:40

Originally Posted by pete-blen

..... They are Dot rated tyres as the bike has rego & wof...

That was going to be my question, being basically a trailer in the eyes of the law, this could only be done with a WOF'd bike.

**Jay GTI** · 12th September 2013, 17:06

Originally Posted by pete-blen

Was waiting for the tyre wear comments.....

Now here's how I veiw the tyre wear issue...
Rideing the bike under it's own power would wear more rubber than towing it with out any drive force
or rider weight on the tyre...

But the tyre would also be put under quite a different load than it is designed for. When cornering at speed, there will be a lot more lateral load and as the bike will be upright, it's not going to put the same forces on the tyre as a leaned over bike being held at constant throttle. Not saying it's going to suddenly start lurching sideways and tearing knobs off the tyre, but it won't be the load you'd imagine just because there's no drive or weight on it.

**pete-blen** · 12th September 2013, 17:17

Originally Posted by Jay GTI

But the tyre would also be put under quite a different load than it is designed for. When cornering at speed, there will be a lot more lateral load and as the bike will be upright, it's not going to put the same forces on the tyre as a leaned over bike being held at constant throttle. Not saying it's going to suddenly start lurching sideways and tearing knobs off the tyre, but it won't be the load you'd imagine just because there's no drive or weight on it.

I think you are grasping at straws a bit here...
But the real good thing is..they haven't stoped makeing tyres..

**Motu** · 12th September 2013, 17:25

There will some forces acting on it for sure. Many years ago (mid '70's) we tried to tow a husky behind a Mini - first we put the front wheel in the boot, then took the front wheel off and tried with just the forks. But no matter how tight we wrenched it down, soon as we turned a corner the bike fell over....we ended up taking the wheels off and the seats out of the Mini and putting it in the back. That won't happen with this rack because the bike is being held tight, but those forces will still be there twisting the bike where it was never designed to be twisted.

**pete-blen** · 12th September 2013, 17:42

Originally Posted by Motu

There will some forces acting on it for sure. Many years ago (mid '70's) we tried to tow a husky behind a Mini - first we put the front wheel in the boot, then took the front wheel off and tried with just the forks. But no matter how tight we wrenched it down, soon as we turned a corner the bike fell over....we ended up taking the wheels off and the seats out of the Mini and putting it in the back. That won't happen with this rack because the bike is being held tight, but those forces will still be there twisting the bike where it was never designed to be twisted.

I realize there are forces at play...
I couldn't design them all out...
If yer look at it you will see the up/down pivot point of the front axle
& tie down lower mounts are in line.. to stop the tie downs wanting to change
length / forks compressing , exspanding as the bike moves up/down

It would be possable to make the bike lean into the corners...
muliply the body roll of the car in the oppisite direction..
But really how complex do yer go ?