Wombat Rear Axle

[dirty_rat]

Very good points Max. Too many times people think bigger is better, etc., instead of looking at what their actual goal is. My son-in-law and I recently competed in at AHRMA race in Florida. The track was VERY muddy for practice. I have a chain guard on my Rat and my son-in-law does NOT have a chain guard on his Super Combat. After practice my chain, sprockets and shifter case was fine. My son-in-laws was packed with mud in the chain, the sprockets and the shifter case. It was so bad the rear wheel almost wouldn't turn because the mud had made the chain so tight (hitting a good jump with no play in the chain could have easily broken the transmission, etc.) Once the chain, sprockets and case was cleaned out, the chain re-gained it's proper slack. Just a word of caution about running a bike without a chain guard.

[hodakamax]

Ah, the discussion has begun. I should also note that I try not to do mud as I grow older and that my pant leg was chewed off while testing my 94A in tennis shoes. I'm looking at some ways on my new project to build a safety type chain guard even though it don't have room for the mud guard part. Safety first! (and not wearing boots was dumb on my part).

Max

[---]

Max, if you don't know when and why it is necessary to spin a tire, I can't help you. I thought you rode flat track. Are you going to tell me you never, ever, spun a tire racing flat track?

[hodakamax]

I guess I just had too much horsepower to prevent wheel spin.

[Bill2001]

I love spirited discussions.

I'll see who the tires work out with my riding. Which, as I see it, is turning out to be a low-key trials enduro. No racing, just an easy mosey through Southeast forest backcountry.

The wheel is moved over less than 1/10". The sprockets seem to line up well enough. If there is a problem, I can reposition the chain guard. Or shim the sprocket on the cush hub. Or go back to stock tire sizes.

The rationale for the wider tires from the previous owner was the same as Max's-- riding in muddy ruts is easier.

--Bill

[hodakamax]

Even in flat tracking spinning is a necessary component but traction is what wins the race. We still want more traction, not less. Remember, slipping tires=lost energy. This is why in flat track braking is done by sliding (negative energy) to slow down. On acceleration traction is needed to apply the power to the track. We used the largest tire and even sharpened edges and opened spaces with razor blades to increase traction before and after each race even on new tires. The front wheel was a spool and you could just turn it around but the back either needed sharpened or replaced if we weren't getting enough traction for the conditions. Sharp tires were a major factor in that type of racing.

Your turn--

Max

[hodakamax]

OK, let's try it another way since I'm not getting much discussion. Why would we want to spin the rear tire? Steering situations come to mind when watching a rally car spinning everywhere they go. Perhaps we need to spin to kick out the back end as to set up for a corner but that is generally done with braking (which is negative spinning of sorts). Maybe we need to spin to throw more roost on our opponents although bigger tires throw more material which brings us back to needing more power. Maybe (and probably is) the reason is that there can't be much more fun than spinning the rear around in circles throwing roost everywhere and having a good time. I guess Greg and I are both right in that motorcycles are supposed to be fun and spinning is part of the fun. I was just trying to make a point when Greg said my 94 didn't need a big tire.

Maxie

PS--And there is the old saying that weenie motors require weenie tires. Maybe it was Clarence who said that. Not sure though.

[Bullfrog]

So consider this - when spinning and stepped out to the side, the rear tire is pushing the motorcycle toward the center of the turn AND traveling smoothly along the sweep of the turn. It could simply NOT do both if it had perfect traction (no slipping of any sort relative to the ground).
Ed

[hodakamax]

Hmm---Good point Ed, yet another reason for spinning. Ed's point also summarizes what is happening to a flat track bike. Centrifugal force is pushing you to the outside and after a point both front and back begin to slip. Adding power adds to the traction loss but changes the thrust vector to the inside of the turn. All fun!

[hodakamax]

After all this discussion the bottom line is still slipping tires=lost energy. Spinning is just lost traction. Even though a flat tracker or any racer takes advantage of this through braking and thrust vectoring it's still lost energy. The fastest way from A to B is to put the power to the ground. Even though the flat tracker is spinning for thrust vectoring, we are still trying to put energy into the bike through traction. And it is just a discussion, not an argument. Kinda fun. (and I was bored.)

Max

[Bill2001]

And in a semi-urelated note, on my Wombat 94, the Front tire is a 3.25x21 instead of the stock 2.75x21. Same deal as the rear-- the PO the wider tire floats through muddy ruts better than a narrow tire. Makes sense. And the "trend" nowadays is for tires to be oversize for "that look". (insert "rolleyes"). I reality, what should this do to (for) the handling?

On the rear tire, I'm thinking I can modify the chainguard mounting to move it 1/10" leftward and so I can eliminate that extra washer in the axle stack. I'll do it next time I have the rear wheel off.

--Bill