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Front Tyre Scrubbing - Understeer


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Hi there,

I have been having a problem with cornering and I though I would try you guys to see if I get some sensible suggestions as to how to handle it.

 

first some paremeters

 

Bike: kwaka zx14 2008se

tyres: michelan PR2's

Tyre pressure 40psi

 

The problem only seems to happen when I am pushing my zx14 through a set of twisties fairly hard (double indicated +10km/hr). I sometimes feel the front end starting to slide just a little bit, it makes a kind of crackling sound and it kind of feels like a car does when it understeers....

 

Im wondering what Im doing wrong. In my mind tyres are designed by people who are a lot clever'er than me to work together as a pair so Im thinking that the rear should be letting go first. Is this the case ??

 

Im hoping the minister for war and finance will be getting me a CSS level 1 course for my birthday (she asked me this morning if it was covered by my insurance co as 'rider training', which it is) so its definately on the cards. is this a prob they will be able to fix @ level 1 ??

 

any thoughts on tyre choice, pressure, what I should be doing with my body position, throttle etc ?

 

any input would be appreciated

 

thanks in advance

 

OZ

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Hi Oz

It could be all sorts of things but if you'r erunning 40psi front and rear then that sounds wrong. I'm not so familiar with really big bikes so check with Michelin but I would think that 36psi front 42psi rear is right. If a tyre is too hard it'll want to let go more as it won't absorb the bumps. The other thing is suspension set-up, a hard front/soft rear wouldn't help though really you need a nice balanced set-up rather than just get stuck in and make random adjustments. Finally throttle control would probably help you out, what are you doing at the point the front is pushing? CSS level 1 teaches you this in the first session (and you'd be surprised how many people don't know good throttle control, although nearly all of them think they do).

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Hi there,

I have been having a problem with cornering and I though I would try you guys to see if I get some sensible suggestions as to how to handle it.

 

first some paremeters

 

Bike: kwaka zx14 2008se

tyres: michelan PR2's

Tyre pressure 40psi

 

The problem only seems to happen when I am pushing my zx14 through a set of twisties fairly hard (double indicated +10km/hr). I sometimes feel the front end starting to slide just a little bit, it makes a kind of crackling sound and it kind of feels like a car does when it understeers....

 

Im wondering what Im doing wrong. In my mind tyres are designed by people who are a lot clever'er than me to work together as a pair so Im thinking that the rear should be letting go first. Is this the case ??

 

Im hoping the minister for war and finance will be getting me a CSS level 1 course for my birthday (she asked me this morning if it was covered by my insurance co as 'rider training', which it is) so its definately on the cards. is this a prob they will be able to fix @ level 1 ??

 

any thoughts on tyre choice, pressure, what I should be doing with my body position, throttle etc ?

 

any input would be appreciated

 

thanks in advance

 

OZ

Hi OZ,

 

It's hard to tell without having seen you ride the bike nor seen the tyres, as there could be several things.

1) How much wear is there on the front tyre? It could simply be that you're scrubbing off speed with the front, from the classic "fast in, slow out" riding style. Going in slower, not scrubbing off so much seed with thr front, should help both on the front understeering, but also allow you to get a better drive out.

2) If you're riding with hang-out, the bike could be reacting to some involuntary rider input as you move from side to side.

3) The suspension could be set up incorrectly for your riding style and body weight.

4) Those 40 psi's sound like an awful lot to me, especially if it's the front tyre.

 

A simple thing is to take a look at your tyre pressure. What is the recommended tyre pressure in the bike's manual? and what does Michelin recommend for your bike?.

The recommended pressures for my R1 roadbike are 33 front and 36 rear, but your bike is heavier than mine.

 

Try lowering the tyre pressure to 36 psi - this will allows the tyre to move around a little more, causing it to be warmer, which should make it more sticky. You will find that the bike feels a bit "squirmy" until the tyre has properly heated up, but stick better after that. If it helps, you might even want to try 33 psi.

 

As for the rear tyre breaking away first: not necessarily. The tyres deal with very different loads under different situations. Under which situations would the rear break away? - and in which situations the front?

 

Best regards,

 

Kai

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OZ,

 

The numbers on the tire and in the manual are Cover Your Ass numbers: What would the bike need with 2 large people, saddle bags full of beer, smoking hot day, what should we put in their? We have had bias tires take that much with 700/800/900 pound bikes, but 40 seems pretty high to us. At the schools where we have these kinds of bikes, we do 36 on the really heavy bikes.

 

Stuman has ridden a Concourse, I'm going to ask him. Also, don't know that particular tire.

 

Stuman, what would you ran for maximum traction?

 

CF

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G'day Oz, good on you for noticing the problem, a lot of riders have no idea what the bike is doing under them... good signs mate!

 

It seems a couple of common themes are emerging: One is riding technique changes may help with your handling problem, which we can't really change from here without decent feedback, the other, is tyre pressure which you can easily make changes and try.

 

So let's go with the tyres. Out here in Oz we recommend, then set the road bike tyres to 30PSI front and rear... on Busa's and 14's we'd give it an extra few PSI. Considering you'd always set the track PSI lower than the road (on license keeping speeds) I'd suggest you give the PSI change a shot but not go quite as low as 30...yet.

 

Pilot Road 2's are a brilliant tyre, they're not soft in the sidewall so you can run the lower pressures without concern.

 

 

Make sense so far?

 

Starting out does it make sense to go with the three recommendations above of 36PSI?

 

You can then try the twisties and feel (once warm) how it goes. Then repeat using a figure lower than 36PSI.

 

Let us know how you get along, you might be in for a big surprise at how well your Kwack handles.

 

P.s. 36PSI is the pressure when the tyres are cold... i.e. buy or borrow a good brand tyre gauge (don't trust servos!) and check it at home before the ride to know whether you need to add 1,2,3 etc PSI when you get to the air pump.

 

Cheers

JasonBW

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Just talked with Will:

 

Large sport bikes (Busa, ZX-14, etc.) 34-36 front, 30-34 rear. If it goes bigger, like ST-1100, then add a few more pounds.

 

CF

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Just talked with Will:

 

Large sport bikes (Busa, ZX-14, etc.) 34-36 front, 30-34 rear. If it goes bigger, like ST-1100, then add a few more pounds.

 

CF

 

 

Hey oz this is OZ, its my name not yours!!!!! biggrin.gif about the tires I ride the same pressure as I do on the track 30 front and rear (COLD), like everyone says a couple more for a heavier bikes is the G O. Cobie mentioned (another thread that I cant find) that he rides the same presurres as track to road as being why would you want a smaller contact patch on the road than on the track? made sense and my tire wear isnt much different.

 

40 sounds way too high to me is that hot or cold? No ones asked yet if that is your HOT or COLD pressure so can you clarify that for me

 

Cheers Bud see ya round tha traps

 

Dylan

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I ride a Concourse 14 on the street with Pilot Road tires. Recommended tire pressure for the bike is 41 front and rear. This is way too much for aggressive riding in the twisties.

 

For your bike I would probably go to 34 front 36 rear and see if that makes an improvement. I run 36 front and rear on my Concourse when riding in the twisties and 41 f/r when commuting to work.

 

I suspect you have too much pressure in your front tire and that would cause what you are feeling. Also making sure your relaxed on the bars would probably help a great deal.

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I ride a Concourse 14 on the street with Pilot Road tires. Recommended tire pressure for the bike is 41 front and rear. This is way too much for aggressive riding in the twisties.

 

For your bike I would probably go to 34 front 36 rear and see if that makes an improvement. I run 36 front and rear on my Concourse when riding in the twisties and 41 f/r when commuting to work.

 

I suspect you have too much pressure in your front tire and that would cause what you are feeling. Also making sure your relaxed on the bars would probably help a great deal.

 

 

Hey blokes, thanks for the feedback smile.gif

 

The kwaka manual recommends 42 psi front and rear ! This seemed a little high for me too, so I dropped it a couple of pounds.

 

when setting up for a ride through the twisties I will drop it a couple of pounds more to start with and see how that goes.

 

As for measuring tyre pressure, I went and spent $20 on a digital gauge (which I keep in my pocket) and I always measure cold.

 

a mate told me about 'the funky chicken' last year...... and am a big fan of the manouver even though it is hard to look cool while your doing it.

 

I have been reading up on the forums and yeah, the standad suspension is set up of a 75kg (165 pound) jockey and not a 'generously proportioned' fella like myself (weigh in @ 115kg (253 pound) in full gear) so it is hidiously undersprung..... I hope to drop the bike into PTR racing for suspension tuning and a trip on the suspension dyno later this year.

 

Im loving the bike though and have done a little over 52,000km in the 20 months I have owned it.

 

thanks again blokes

 

OZ(johnno)

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Nice k's there Johnno... for the other folk that's a decent 20,000 mi a year! Iron Butt award category methinks!

 

Would be great if you can get some k's riding to one of our schools, you'll get to experiences some decent tech that could well revolutionise your riding, just mention to the minister about how great riding skills can save your bacon :)

 

If anyone is wondering how to really do funky chicken, see a great article here: link... :) or do a quick search here for the Relax drill.

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Undersprung front sounds like a problem too. Soft springs can give the feel of a slide (at either end). Stiffer ones will make a big difference, the SV650 used to have pathetic fork springs even for my miserable 65kg/140lb/10 stone let alone bigger blokes. The damping is pretty crude too, but the worst of it is the spring weight.

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[...]

Im wondering what Im doing wrong. In my mind tyres are designed by people who are a lot clever'er than me to work together as a pair so Im thinking that the rear should be letting go first. Is this the case ??

 

If you are off-throttle in the turn, or not on-throttle enough, the front will typically be the first to start sliding. If you are on throttle too much in the turn the rear will be the first to start sliding. If you have the throttle slightly on, and very gradually rolling on more and more, causing the bike to speed up very gradually throughout the turn, THEN the traction will be balanced front to rear.

 

So it's not just about the tires being matched, you have to match the LOAD on the tires with proper throttle control, along with the funky chicken.

 

KHP and others already got into this stuff but it seems the tire pressure and suspension has gotten a lot more attention.

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