Making a Cushier Cush Drive

[Greg Field]

All of that is true, but many people do brutally use engine braking to slow their bikes.

 

My point was simply that it is quite possible to add shock loads to your splines and clutch plates during engine braking that are every bit as large as those applied by the engine

[Guest ratchethack]

Aye. I've seen it done improperly and even dangerously many times -- most notably on "Goose Gaggle" road trips. I figure if a sloppy, Neanderthal downshift is severe enough to chirp the rear tire (as all too often witnessed by Yours Truly), it's even harder on the splines than acceleration wear, and well past unacceptable for long-term practice without considerable downside consequences. . .

[mike wilson]

Aye. I've seen it done improperly and even dangerously many times -- most notably on "Goose Gaggle" road trips. I figure if it's severe enough to chirp the rear tire with a sloppy, Neanderthal downshift (as all too often witnessed by Yours Truly), it's even harder on the splines than acceleration wear, and well past unacceptable for long-term practice without considerable downside consequences. . .

 

Not only the splines. If the preceding (the clutch dump) downshift has been done without at least some attempt to match shaft speeds, then "the dogs have been taken for a walk" as one of my more colourful mentors was wont to say.

[dlaing]

Dave:

 

On a V11, are you more likely to exceed the traction available to your tire by:

 

1) Cranking on the throttle

 

2) Downshifting and dumping the clutch with the throttle off.

 

Personal experience has shown me that #2 is more likely.

Yes, but that is because of the balance of weight.

Which is more likely to lock up a wheel, the big dual disks up front or the little disk in the rear?

You can generate far more decelerative force with the front brake before the front wheel exceeds traction than you can at the rear, atleast when going forward....

In forward motion it is possible to lift the front tire. The amount of force at the splines when poppin a wheelie is far greater than the amount of force when exceeding traction on a downshift.

I am not saying it is fine continuously do merciless high rpm downshift clutch dumps, I am just saying that popping wheelies or just accelerating hard will do more damage to the splines, and that you should have fewer holes drilled in your acceleration cush than the one compressed during deceleration.

[Greg Field]

Throttle and downshifting act on the same wheel, so the comparison is valid. If one can break traction but not the other, it tells which is the more violent force.

[GuzziMoto]

No, I have to agree with dlang. The rear tire is easier to break traction during decel not because the engine can develop more force on compression braking then acceleration (if that were true it would be sad) but because the rear tire unloads during decel and has less grip (further reducing the loads on the drive train).

[Greg Field]

If one is not using the front brake, and the wheel locks instantly upon clutch release, why and when does this "unloading" occur?

[pasotibbs]

No, I have to agree with dlang. The rear tire is easier to break traction during decel not because the engine can develop more force on compression braking then acceleration (if that were true it would be sad) but because the rear tire unloads during decel and has less grip (further reducing the loads on the drive train).

I agree also rear wheel drive cars can easily lock up the rear during extreme down shifts,going from 4th to 2nd worked really well for my friend in his Opel Ascona , but would almost certainly just over rev a front wheel drive car.

But with regard to Guzzi's, I haven't had a problem with the V11 but my mates LM2 has caught me out a couple of times I think mainly due to the slower gear selection that the older bikes prefer(I needed to keep the revs up longer between the gears) and both times I wasn't on the brakes much but just slowing down.

[GuzziMoto]

If one is not using the front brake, and the wheel locks instantly upon clutch release, why and when does this "unloading" occur?

 

Right before the wheel locks up.

Look at it this way, the rear brake can lock the rear tire much easier then the front brake can lock the front tire. Does this mean that the rear brake has more power then the front brake?

[Guest ratchethack]

Ah, Winter. . .

 

 

The annual return of thrashing through the frosty, dark and frozen thickets of amorphous, entangled variables far too unquantifiable for rational analysis. . .

 

Keyboards clack, whilst Guzzi's hibernate. . .

[Greg Field]

Right before the wheel locks up.

Look at it this way, the rear brake can lock the rear tire much easier then the front brake can lock the front tire. Does this mean that the rear brake has more power then the front brake?

 

If you're coasting at 40 mph, downshift twice, and dump the clutch, locking the rear wheel, when does the weight transfer occur? It doesn't.

 

Now, coast at 40 mph, downshift as many times as you want and try with engine power to break traction on the rear tire on a stock-ish V11. You won't.

 

What does this tell you?

[gavo]

If you're coasting at 40 mph, downshift twice, and dump the clutch, locking the rear wheel, when does the weight transfer occur? It doesn't.

 

Now, coast at 40 mph, downshift as many times as you want and try with engine power to break traction on the rear tire on a stock-ish V11. You won't.

 

What does this tell you?

 

errr motorcycling not 4 you

[GuzziMoto]

If you're coasting at 40 mph, downshift twice, and dump the clutch, locking the rear wheel, when does the weight transfer occur? It doesn't.

 

Now, coast at 40 mph, downshift as many times as you want and try with engine power to break traction on the rear tire on a stock-ish V11. You won't.

 

What does this tell you?

 

The "motorcycling's not for you" line was funny. But the weight transfer happens the moment the rear tire tries to slow the bike down, which is a fraction of a second before the rear tire locks up. If you want to compare the two with your scenario, that's fine. But a more comparable version of the acceleration side would be the opposite of your deceleration example. So, start off slow (or better yet from a stand still), rev the motor up with the bike in first or second gear (depending on how fast your going or if your standing still). You never said what gear you are atarting in, I'll assume you did not start in top gear. Now dump the clutch. If you don't wreck right then and there the rear tire will be "breaking traction" so much that there is smoke coming off it. Now, unless you know how to do a burn out already I would not suggest you try to do this based on what I have posted because that was an example to make a point and not meant as a tutorial on doing burnouts. But what it comes down to is this, a Guzzi motor makes something to the tune of 70 ft/lbs of torque in acceleration. It makes a fraction of that in deceleration. Ham fisted clutch work in either direction is a bad thing, and it may be more common in deceleration, but the possible loads in acceleration are many times higher then the possible loads in deceleration due to the many times greater availability of torque and traction.

[Greg Field]

If you had seen as many hammered splines as I have seen, you might think differently . . .

[dlaing]

If you had seen as many hammered splines as I have seen, you might think differently . . .

So, you see the splines feathering off more in the direction of deceleration damage. Very interesting.

The physical difference in torque between acceleration and deceleration does not support that so, it must be some other factors at work.

One thing I did not consider is that damaging effect of pure steady torque is not helped by a cush but impacts are helped by a cush.

In the real world, the torque is not purely steady but is dynamically changing.

Even though we may be getting 70 pounds of rear wheel torque accelerating, and maybe 10 pounds decelerating, the deceleration may have more impact due to factors like momentum.

A 70 pound hammer swung at 5MPH will do much less damage than a 10 pound hammer at 100MPH.

So, something must be creating significantly more velocity in the decelerative direction. (or the number of impacts may be greater)

But what creates the higher velocity?