Rear wheel slip, was this "shaft effect"

[wabill]

Last June, when my FJR had only a few hundred miles on her, I rode over the N. Cascades Hwy to Winthrop and experienced what felt like the rear wheel sliding out in tight curves. I put the blame on "New Tires" or maybe because they were Metzelers rather than Dunlops like on my Triumph.

Yesterday I did the same ride again but now with a bit over 7500 miles on the tires. Also hadn't noticed any sort of slippage while riding in N Mex last month. Mid way through a right hander and carrying a good line I put the power to her and felt the rear slide out what felt like at least a 1/2 foot. The roadway was smooth asphalt paving with proper camber.

It wasn't a problem but it dawned on me that this may have something to do with the bike being shaft driven instead of chain or belt. Am I on the right track?

This is a pic taken on the road this past summer.

 

[wheatonFJR]

Sounds like grip between the tire and the road to me...not a question of how the power was delivered to the rear wheel...

 

[Burnspot]

+1 Yea, sounds like a grip issue rather than driveline lash. I've never experienced driveline lash being a factor in such a situation, just a pure power overcoming available grip thing most likely.

 

[Cowcop]

Pavements may look alike, but everywhere can be different. Temperature, compaction and humidity can all have some say in how a tire grips the road. Suggest this is your event rather that any shaft issues.

Maybe you were practicing for Motogp!

 

[Fred W]

I think what you are asking is if the drive shaft's torque effect on the suspension (aka Shaft Effect or Shaft Jacking) might be contributing to the rear tire slippage, right? It is pretty well known that, as you apply power the shaft's torque will (slightly) raise the rear end (increases clearance and quickens steering) but will also stiffen the rear suspension a bit. So theoretically, if a corner was particularly bumpy, it might cause the rear wheel to skip somewhat more when under power.

But in your case, you said the road was smooth, so I don't really think this is what's happening. I'm inclined to agree with the others that you are just exceeding the limits of traction available to you. There is a finite amount of traction available in a given contact patch. You can use it for cornering or for acceleration or for braking. When trying to do multiple things simultaneously you can easily exceed the amount of traction available.

 

[charismaticmegafauna]

The above replies are 'right-on', IMO.

"Shaft effect" relates to the geometry involved in driving the rear-wheel and the pinion gear's tendency toward wanting to climb up or down the crown-wheel. Yamaha appears to have been fairly successful in designing-out shaft-effect, on the FJR, by adherence to good geometry? Some manufacturers employ double sets of "knuckles" (U-joints) and other apparatus to keep shaft-effect at-bay.

To a lesser extent, all rear drives (including chain and belt) exert a force on the suspension when power is applied (either positive or negative power...).

Think 'parallelogram'...

 

[Bungie]

Last June, when my FJR had only a few hundred miles on her, I rode over the N. Cascades Hwy to Winthrop and experienced what felt like the rear wheel sliding out in tight curves. I put the blame on "New Tires" or maybe because they were Metzelers rather than Dunlops like on my Triumph.

My new favourite scenic road. I *SO* wanted to ride this one again in Sept. And Winthrop is a hoot!

Anyway, that road just isn't that tight if I recall correctly. Are you sure you didn't rolloff and then abruptly get back on it hard? Effectively shocking the tire?

 

[wabill]

I think what you are asking is if the drive shaft's torque effect on the suspension (aka Shaft Effect or Shaft Jacking) might be contributing to the rear tire slippage, right? It is pretty well known that, as you apply power the shaft's torque will (slightly) raise the rear end (increases clearance and quickens steering) but will also stiffen the rear suspension a bit. So theoretically, if a corner was particularly bumpy, it might cause the rear wheel to skip somewhat more when under power.

But in your case, you said the road was smooth, so I don't really think this is what's happening. I'm inclined to agree with the others that you are just exceeding the limits of traction available to you. There is a finite amount of traction available in a given contact patch. You can use it for cornering or for acceleration or for braking. When trying to do multiple things simultaneously you can easily exceed the amount of traction available.

That's the effect I was wondering about as to being the cause of traction lose at throttle roll-on. Riding the same road on my Speed3 holds like it was glued with Dunlop RoadSmarts. So, after exiting the corner the thought hit me that it may be due to Shaft Jacking so I thought to ask here about it.

It's too late this year to check out results on a warm pavement. I have dropped tire pressure 10% and see how that effects the handling.

 

[HotRodZilla]

Just FYI, I run RoadSmarts front and rear. To prevent cupping and funny wear, I have been running 42 in the front and 43 in the rear. I have never had an issue with the tires slipping, and I don't take it as easy as I should sometimes. You may want to change tire brands if you are getting that much slip.

The only tire I ever had slip on this bike was the rear BT021 I ran for a while. Other than that, the bike runs pretty solid, even when I gas it in the turn just for fun.

 

[Fred W]

Probably a good move this time of year. The lower tire pressure will help get the tire warmed up a bit more quickly and hold the higher temps in lower ambients.

One thing to keep in mind when comparing the FJR with another (sportier) bike is to compare the weights of the two bikes. If all other parameters are equal (not really all that likely, but if they were) then a heavier bike will use up more of the available contact patch traction in just getting around the corner. The added heft will generate more lateral force, which is translated to the tires, so at the same speed and lean angles will put more force on that patch of friction between tire and tar.

Edit - Of course, HRZ is spot on with the tire question. There is a world of difference in the available traction from one tahr to the next.

 

[wabill]

Probably a good move this time of year. The lower tire pressure will help get the tire warmed up a bit more quickly and hold the higher temps in lower ambients.

One thing to keep in mind when comparing the FJR with another (sportier) bike is to compare the weights of the two bikes. If all other parameters are equal (not really all that likely, but if they were) then a heavier bike will use up more of the available contact patch traction in just getting around the corner. The added heft will generate more lateral force, which is translated to the tires, so at the same speed and lean angles will put more force on that patch of friction between tire and tar.

Edit - Of course, HRZ is spot on with the tire question. There is a world of difference in the available traction from one tahr to the next.

See, I was screwed up a bit on the weight issue. I was thinking that the heavier bike would be applying more downward force on the tire thus reducing slip. Next trip over I'll be ready to do a better analysis of what's going on with the bike and tires..

Hey, I might have missed seeing some stuff on the road to account for the one slip on this ride or maybe the little elephants wet themselves as the road came close.(humor)

HRZ, it's good to hear that someone else is running Roadsmarts. I'm really pleased with them on the other bike and would like to use them on the FJR when the present tires are worn.

 

[Gerry.GEG]

Last June, when my FJR had only a few hundred miles on her, I rode over the N. Cascades Hwy to Winthrop and experienced what felt like the rear wheel sliding out in tight curves. I put the blame on "New Tires" or maybe because they were Metzelers rather than Dunlops like on my Triumph.

Yesterday I did the same ride again but now with a bit over 7500 miles on the tires. Also hadn't noticed any sort of slippage while riding in N Mex last month. Mid way through a right hander and carrying a good line I put the power to her and felt the rear slide out what felt like at least a 1/2 foot. The roadway was smooth asphalt paving with proper camber.

It wasn't a problem but it dawned on me that this may have something to do with the bike being shaft driven instead of chain or belt. Am I on the right track?

This is a pic taken on the road this past summer.

'don't know how much this helps but, my '08 came with the worst Metzler tires. I just wore them out and had slipage several times, and never felt confident.

+1 for crappy tires. PR2's make mine feel like a different bike.

 

[RossKean]

Probably a good move this time of year. The lower tire pressure will help get the tire warmed up a bit more quickly and hold the higher temps in lower ambients.

One thing to keep in mind when comparing the FJR with another (sportier) bike is to compare the weights of the two bikes. If all other parameters are equal (not really all that likely, but if they were) then a heavier bike will use up more of the available contact patch traction in just getting around the corner. The added heft will generate more lateral force, which is translated to the tires, so at the same speed and lean angles will put more force on that patch of friction between tire and tar.

Edit - Of course, HRZ is spot on with the tire question. There is a world of difference in the available traction from one tahr to the next.

See, I was screwed up a bit on the weight issue. I was thinking that the heavier bike would be applying more downward force on the tire thus reducing slip. Next trip over I'll be ready to do a better analysis of what's going on with the bike and tires..

Hey, I might have missed seeing some stuff on the road to account for the one slip on this ride or maybe the little elephants wet themselves as the road came close.(humor)

HRZ, it's good to hear that someone else is running Roadsmarts. I'm really pleased with them on the other bike and would like to use them on the FJR when the present tires are worn.

I had new Roadsmarts on the bike when I bought it (used) this spring. They were good tires in terms of ride and control but didn't last very long for me. (YMMV) Didn't get much more than 5000 miles out of them and by comparison, I got more than twice the mileage out of a set of Michelin PR2's. Riding conditions were not the same but, based on the current set of PR2's, they are also going to last a lot longer than the Roadsmarts did for me. Just so this doesn't turn completely into a tire brand-bashing thread, the FJR is a heavy bike and there is a LOT of lateral force on the rubber during cornering. I think you will be pleased with the improvement when you switch to one of the favored tires as discussed in painful detail in the NEPRT section - you won't see a lot of people excited about the Metzelers. There is also the matter of getting used to a heavier machine. By contrast, I came from a Yamaha Venture and the FJR feels like a (very powerful) bicycle in terms of handling.

Ross

 

[wabill]

Hey, I might have missed seeing some stuff on the road to account for the one slip on this ride or maybe the little elephants wet themselves as the road came close.(humor)

HRZ, it's good to hear that someone else is running Roadsmarts. I'm really pleased with them on the other bike and would like to use them on the FJR when the present tires are worn.

The Elephants.

 

[dustyrains]

Tar snakes. Slippery when hot or wet.

 

[Fred W]

See, I was screwed up a bit on the weight issue. I was thinking that the heavier bike would be applying more downward force on the tire thus reducing slip.

You aren't really "screwed up" on that. When the bike is vertical and rolling along in a straight line, any additional weight will increase the friction, and therefore available traction due to GRAVITY (Not just a good idea, it's the Law!!).

However when cornering that same added weight will generate greater lateral force loads that use up the available traction, and can result in slip. And when accelerating the engine's force has to propel that added weight, so more force needs to be translated through the contact patch to achieve a given acceleration rate.

Our FJRs do have a pretty darned powerful engine. It doesn't accelerate (or corner, or brake) like a race replica, liter bike, and arguably the biggest single reason (there are others) is the big girl's heft. It is prudent to be as smooth as possible with the throttle (and brakes) when cornering.

 

[LAF]

I have shunned Metz 880 tires for life. On the LT they were the most slippery tires I ever rode on, and in rain a nightmare. While they were the mileage king on the LT they were unsafe, and when they cupped/feathered the front would howl like a banshee. The extra mileage was not worth the risk of sliding out. Never would I run a 880 again.

 

[pcrdude]

'don't know how much this helps but, my '08 came with the worst Metzler tires. I just wore them out and had slipage several times, and never felt confident.
+1 for crappy tires. PR2's make mine feel like a different bike.

This is exactly my experience with Z6 and then PR2.

 

[lnewlf]

You want to experience shaft drive effect? ride a Sazook GS850 in the twisties. I put 40K on one and can tell you the FJR has zero SDE. SDE is up and down on the ass end as the throttle is rolled on and off and weave in the bars on the front end. Used to pin the throttle and ride the rear brake to lock up the suspension on the GS Hippo. I wonder at the complex swingarms on the Concourse and BMW's considering how Momaha has cured the prob with a long arm and a damper in the tranny. A sliding rear is usually related to crappy tires or your right wrist. Agree with the consensus on the PR2's, if the pavement is good they won't let go and they are fun to drift.