Blathering on about VSS and rotations per mile

[ButterSmooth]

I'm reasonably sure that VSS uses the rotor pulses to determine the vehicle stability status. So in selecting new tires, I wanted to keep the front to back ratio of revs per mile about the same as stock. Without extensive testing of various tires, it seems the most pertinent and useful spec provided by most manufacturers is the number of rotations per mile. I was surprised that the size specifications often conflicted with the revs per mile and sometimes with the manufacturers stated tire diameter.

As an example, the Kenda 165/55R15s are larger in diameter than the Vredestein 165/60R15 tires and rotate less (24”/23.9” - 876.9/ 884.6). So, tires size calculators may lead you astray when selecting tires, if you're your goal is keeping nanny happy.

I think overall that these size differences are in the noise. With pulse count difference caused by inflation/wear/load and count differences in the front caused by cornering, nanny must have a pretty loose tolerance for wheel speed difference. Therefore, this is mostly a mental game and leads to such blathering.

[Steve W.]

You have pretty much hit that nail on the thumb.

Once Nanny sees that all wheels are turning, she doesn't care too much that the fronts are now turning 0.93% faster, due to your new tires. What WILL matter is that she will see that one front wheel is only turning half as fast, due to a skid.

I don't think Nanny will mind what you put on, as there is sufficient tolerance in the system for any tire that you can fit.

.

[JayBros]

VSS also uses a yaw sensor.

[ButterSmooth]

VSS also uses a yaw sensor.

Yaw rate doesn't impact tire selection, so for my purposes it was ignored. A wise man would have ignored it all...

[BajaRon]

Bottom line is, the VSS, as far as tire rotation goes, is very forgiving. I don't think you'll be able to fit tires that will give you a problem. What the VSS system is primarily looking for is sudden, and fairly drastic, changes in rotational speeds between wheels. Like one wheel quickly going much slower (locking up) or much faster (spinning) in relationship to the the other tires. It is not all that concerned with a continual and constant discrepancy between the front and rear wheels. Though I think that if you put 2 very different tire sizes on the front the VSS would cry 'Foul' pretty quickly. But who would do that?

[Peter Aawen]

The Nanny IS fairly forgiving, but also very capable once she kicks in! And BajaRon is absolutely right about not being able to even fit tires (without mods to the fenders etc) that'll give the Nanny a problem!

However, if you push the smaller limit of fittable tire sizes on one end and push the larger limit on the other, then the extra 'angle of attack/departure' & the rotational variations that can introduce that might be a little closer to her 'acceptable extremes', teamed with any aggressive or sudden accel/brake &/or direction changes can make the Nanny sit up & take notice juuust a little earlier than you might expect! Similarly, if you put a really sticky tread on one end & a not so sticky tread on the other end, the Nanny will probably take notice earlier on than she would if you had similar grip levels at each end. Heck, the Nanny can usually & pretty safely manage just one tire suddenly deflating & becoming a pretty much useless rim diameter appendage that's barely keeping the important metal bits off the ground, just so long as you don't try any really aggressive evasion manoeuvres once that's happened!! Even running overly sticky track tires on one end & a 'suddenly flat' OE Spec Kenda on the other is within the Nanny's capability!!

So all up, once you remove the seriously limiting factor of the OE Spec Kendas, the Nanny's more than capable of handling any of the 'different tires' stuff many worry about, and even if you do push the limits with your tires on one end but not the other, or have a catastrophic failure in one (or more) tires, it's more than likely that she'll do pretty well looking after you - but she can't fix 'stupid' or deliberate attempts to over-ride her/her inputs (have you seen that 'flipping' vid? Or the 'rolled in reverse' vid?? ) So whatever tires you put on once you toss the Kendas, once you learn/re-learn where their limits and her limits are & try to ryde smoothly within them, if necessary using your weight to balance things out &/or conteract any sudden actions, she really won't intervene all that much or in such an uncomfortable way UNLESS there REALLY IS some reason for said intervention!! But if you think about it a little, maybe try to work out what caused that intervention, then you can use those interventions to improve your ryding skills!

The engineering & design concepts that've gone into our Spyder/Rykers really are generally pretty well up there....(shame about the Kendas tho!) In most cases, it's just the implementation, delivery, &/or fit & finish that occasionally leaves something to be desired - and once identified, that's often not helped at all by the lack of customer service ethics at the particular dealer or sometimes in BRP itself! But they are wonderful machines, and if you've got a good one & make a little effort to learn how to ride your particular machine, they really can & do deliver those Miles of Smiles we talk about so often!

[ButterSmooth]

...
However, if you push the smaller limit of fittable tire sizes on one end and push the larger limit on the other, then the extra 'angle of attack/departure' & the rotational variations that can introduce that might be a little closer to her 'acceptable extremes', teamed with any aggressive or sudden accel/brake &/or direction changes can make the Nanny sit up & take notice juuust a little earlier than you might expect! ...

With my new tires the rotational ratio, front to rear, will be about .45% different than the stock Kendas. Both are A traction rating -- Nanny won't have a clue...

[Peter Aawen]

...... Both are A traction rating -- Nanny won't have a clue...

Yup!

But I bet you notice the difference! . .

[glennm]

Since we are blathering on......

When I had the new rear tire fitted and after resetting the pressure I took it for a short run. The rear felt somewhat squishy. Only a short run so I left it at that as I knew the fronts would be in within the week. Hankooks all round by the way K425 front, K435 rear (very limited selection over here).

Fitted up the fronts and again another short ride and everything felt squishy front & rear. A little off putting to be honest. Running 20 front and 22 rear and yes I will be playing more with the pressures once I get my TPMS. The squishyness made me think I needed a few more psi than Mike and Peter generally recommend. Decided to put more Ks on before being too concerned about it.

Took her out for longer runs without getting too aggressive as I thought (was hoping) the tires just needed some time to settle in.

The last run was through some tight twisties including hairpins and it felt much better. By this time I had about 200 Ks on them.

Once the border opened I rode back home a distance of some 250 Ks. The bike felt well planted and I did not notice any of the squishyness like before.

The front especially really hangs on now with none of the drifting sensation of the Kendas in tight turns and the rear simply follows.

Sorry for the long lead in but is it me getting used to the new tires or is it due to the tires "running in"? Both?

[Steve W.]

You are getting used to having some REAL tires on there.

Enjoy.

Now that you are more acustomed to the "squishiness", try lowering the front pressure to 17. Might feel a bit more "squishy", but still a LOT more traction than stock and a smoother ride, too.

.

[BLUEKNIGHT911]

Since we are blathering on......

When I had the new rear tire fitted and after resetting the pressure I took it for a short run. The rear felt somewhat squishy. Only a short run so I left it at that as I knew the fronts would be in within the week. Hankooks all round by the way K425 front, K435 rear (very limited selection over here).

Fitted up the fronts and again another short ride and everything felt squishy front & rear. A little off putting to be honest. Running 20 front and 22 rear and yes I will be playing more with the pressures once I get my TPMS. The squishyness made me think I needed a few more psi than Mike and Peter generally recommend. Decided to put more Ks on before being too concerned about it.

Took her out for longer runs without getting too aggressive as I thought (was hoping) the tires just needed some time to settle in.

The last run was through some tight twisties including hairpins and it felt much better. By this time I had about 200 Ks on them.

Once the border opened I rode back home a distance of some 250 Ks. The bike felt well planted and I did not notice any of the squishyness like before.

The front especially really hangs on now with none of the drifting sensation of the Kendas in tight turns and the rear simply follows.

Sorry for the long lead in but is it me getting used to the new tires or is it due to the tires "running in"? Both?

Hi, I'm Mike ( of Mike & Peter )..... I have different Auto tires that I use 17 psi front and 18 psi rear .... they have not felt " Squishy or Squirrely " to me. I have a 14 RT weigh 168 lbs and ride solo. I've said in the past ( many, many times ) that tires are part of the suspension system, and Auto tires on veh's that weigh much, much less ( ie Spyders ) need much less psi to function at their Optimum, especially if the road is wet. .... Mike

[glennm]

Thanks Mike and Steve. Just me I guess. Checked yesterday with the new tpms and it indicates15/16 front and 18 rear so will put a pound or 2 in the fronts and see how I go.

[BLUEKNIGHT911]

Thanks Mike and Steve. Just me I guess. Checked yesterday with the new tpms and it indicates15/16 front and 18 rear so will put a pound or 2 in the fronts and see how I go.

I didn't want to get too long winded in my comments .... I said 17 psi for my fronts, I use that because I like to drive Fast & Hard in the twistie's. If my ride for the day is more relaxed, I'll drop the fronts to 15psi. .... it provides a more comfortable ride , and it's still safely on the Rim .... Mike

[glennm]

I didn't want to get too long winded in my comments .... I said 17 psi for my fronts, I use that because I like to drive Fast & Hard in the twistie's. If my ride for the day is more relaxed, I'll drop the fronts to 15psi. .... it provides a more comfortable ride , and it's still safely on the Rim .... Mike

Excellent thanks for the extra info. As I mentioned on the trip home it felt really good so will see how it goes in some of the tighter stuff. So far mostly straight stuff with the border restrictions as my favourite back roads are a no go other than for locals.

[Steve W.]

We don't bother tuning the pressure for every ride. After all, if we start out just intending to cruise (with lower "comfort" pressures), then find a twisty road, will we be safe attacking the road with the lower pressures? With that in mind, I just set front and rear to the same 18 psi. Easier to remember, still plenty comfortable, have not had any problem in the curves.

.

[BLUEKNIGHT911]

We don't bother tuning the pressure for every ride. After all, if we start out just intending to cruise (with lower "comfort" pressures), then find a twisty road, will we be safe attacking the road with the lower pressures? With that in mind, I just set front and rear to the same 18 psi. Easier to remember, still plenty comfortable, have not had any problem in the curves.

.

Using or lowering your PSI's ..... It depends on what the PSI is lowered to .... example ( mea culpa first ) I actually rode with only 6 PSI ( leaking valve stem ) in my rear Hydro-edge for at least 15 miles .... I thought it felt a bit squirrely in twisties sections of road, I was on gravel which does not provide the same grip as on pavement .... I stopped to check it tho and discovered the low psi .... immed. drove slowly to an Air station and filled it. ..... So my tire didn't lose the Bead Seal and I doubt a higher PSI would either ...... I advocate for using lower PSI's on Spyders using Auto tires but there is limit that I don't recommend and that would be 14 psi ( just to be safe ..... Mike