Stability Issues

[Hendo]

As someone new to the ST, Iam after some advice on stability issues i may have, a few times whilst travelling at 90-100 km/h on the freeway I have experienced a slight twitching sensation through the bike. it doesnt appear to constant just occasionly. At the time i was lightly loaded. ie just me on the bike. I personally think it is a tyre problem as suggested by my local bike shop.Pressures were 36 psi on front and 41psi on rear.
 For some reason there is a Bridegestone BT023 120/70 on the front and an Pirrelli Angel 170/60 on the rear, both appear in good condition though  there is some centre tyre wear on the rear, but not the worst I have ridden on. I am currently thinking of replacing the rear with a BT 23 soon. 

Do all you experts think this is a good idea, and is there anything else that i should double check?

There also seems to be some conjecture as to which tyre size should be on the bike? what would people recommend for the rear 160/70 or 170/60?

Cheers,

Hendo

[Hendo]

Forgot to mention the bike is a 97 ST1100.
 

[alans1100]

Ok

You don't say if you have an ABS model or not so:

1100  Front 110/80 ZR 18 is standard & 36 psi
          Rear  160/70 ZR 17 is standard & 42 psi

The 1100ABS has a 120/70 ZR 18 which will also fit the standard but speedo error will occur (more than usual)

The 170/60 tyre which is a slightly wider tyre and a lower profile will fit the 1100 but the motor will rev a little faster for any given speed compared to the OEM and it's better to fit this tyre if no OEM tyre is available rather than the 160/60 (weight rating is to low) tyre.

Not knowing to much about the Pirrelli tyre myself but you must fit tyres of the same type to both wheels. e.g. 2 x radials or 2 x cross plies,

[StinkyPete]

I'd start by checking tyre pressures, wheel balance and head bearings.

[Streak]

Do all you experts think this is a good idea, and is there anything else that i should double check?

There also seems to be some conjecture as to which tyre size should be on the bike? what would people recommend for the rear 160/70 or 170/60?

I have run the Bridgestone Battle Axe 023's on my 1996 ST1100 since i have owned it, have been excellent, and never an issue, when i bought my bike, i actually replaced both front and rear tyres, i wanted to start the bike fresh with me, not have someone elses Tyre wear being my problem.....

Front is a 110/80/18

Rear is a 160/70/17

the vibration is not something i have experienced, but i think pete is heading down the right track.

[Brock]

Wheel balance, tyre pressures, headstem bearings will give you a constant problem. You issue, sounds lik,e a dirty air problem.

This means minor turbulence from vehicles around you, and little wind gusts and so on. The ST has a lot of surface area that can act like a sail, the best thing to do is relax and go with the flow. The gyro action of the wheels means that the bike will self adjust for these things, (probably what you are feeling)

[saaz]

Agree with Pete. Do the basics first.  When the head bearings get worn and notchy it can lead to an unstable feeling, or if the bearings are loose or over tightened.  Vibration is often a tyre balance problem, or if one of the tyres has not seated properly on the rim and is out of round.

 I have run 120 fronts on a non-abs bike with no problems, and mostly run a 170 rear as the tyre selection is greater.  Either of those brand of tyres are quite ok.  It is possible that there is a mismatch between the tyres that becomes more obvious with wear.  In a straight line even with well worn tyres the bike should be stable - it is a feature of the ST1100!  It is usually when cornering to notice worn tyres more.

[Chops]

I recently bought a 96 ST1100
It had a weave when I test rode it at most speeds but on checking the service history I put it down to tyres as they were over  10 years old although still with plenty of tread maybe that's why the bloke that test rode it before me didn't buy it.
I freshened the bike with new pads fluids and a new set of BT023's now it rides like a new one have only done 4000 Ks on these tyres so far but showing no sign of wear.
Jake Wilson has these tyres for $297 a pair delivered to your door in a few days.

[Wombat]

I will have to tend towards Brocks idea. It may be wind  turbulance. I find the same on open roads with breaks between trees or behind trucks. KISS principle applies here. Go for a couple of rides and take note where it happens. I am doing the same as a lot of owners in that i am going thru the bike and renewing or updating the maintenance so I have a good base to start from. Anyway I think we need a new Emocian as a Two Cent piece for my input. 

 

[jimwilly]

I think it probably is wind catching the screen and bike, when I bought  my 1300 changing from a honda blackbird I noticed what seemed to be a surge or buffeting, I quickly realised this was just the screen catching a croos wind, I put the screen down and bike handled perfectly.

[Gatey]

I'm going to add two thoughts of my own. Jim has just touched on one.

First thing is tyre pressure though. 36psi is low. Jack that up to 40psi. It will stop the wall walking on lateral ridges in the road surface which is part of what you might be feeling..

The other thing is wind on and around the edges of the screen.
 My TDM has the stock short screen and I'm out in the wind from ribs up. All my upper body is effected at once by cross winds, turbulence following traffic and so on.
I noticed that with a screen on the ST only some parts of my arms are exposed to outside influences. These buffet my elbows on occasion and that's directly transferred to the bars...here's the rub. This is only noticeable when I'm in heavy freeway traffic for example...ie under a bit of added stress. I noticed I tense up in the wrists and elbows. Wind effect on my body round the edges of the screen exasperates this situation.
So like Brock said relax a bit.

You get the same effect by stiffening /locking your elbow. Every bump and ripple will make the bike feel like its possessed by a cat devil..