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-   -   Improving handling at higher speeds??? (http://www.horizonsunlimited.com/hubb/yamaha-tech/improving-handling-at-higher-speeds-37397)

Tenere Tom 27 Aug 2008 20:43

Improving handling at higher speeds???
 
I don't know if it's just the way my suspension is set (a bit on the soft side) on my latest ('84) XT600 but at speeds over 55 - 60 mph the rear feels 'odd and a bit vague' and the front feels like it's ready to take off due to the wind under the front fender.

I'm going to increase the pre-load on the rear a bit and maybe pump up the front forks - What should it be at in psi???

What else can be done to make it at least 'feel' a bit more stable???

oldbmw 27 Aug 2008 21:25

What are you carrying ? my BMW gets wobbly if the rear end is overloaded.

Tenere Tom 27 Aug 2008 22:02

Quote:

Originally Posted by oldbmw (Post 204155)
What are you carrying ? my BMW gets wobbly if the rear end is overloaded.

Just me!!!

I'm not on knobblies either so I can't blame them:(

xtfrog 27 Aug 2008 22:06

Yamaha manual for the '84 bike says 8 psi in the forks

Warthog 27 Aug 2008 22:09

Could your shock be dead?

Once the damping is gone, your bike will feel wallowy and vague.

The spring could also be tired.

Is it an import? Some grey imports from another market sometimes have weaker springs (eg some Japanese home market 400s had lighter springs asn generally the Japanese are a bit slighter than a lardy Westerner!!)

Brian Williams 28 Aug 2008 00:04

Try fitting a lower front mudguard, Acerbis do one that will fit. Stiffer 'progressive' fork springs. What Tyre pressure are you running at ?

mollydog 28 Aug 2008 00:19

But the basics should be addressed first.

Tenere Tom 28 Aug 2008 20:57

Thanks for all the tips and advice guys!!!

The bike IS an import my docs say it was first registered in the UK in 2001 - the bike is a 1984.

When the rear wheel is lifted off the ground there is free up/down movement - before the suspension comes into play, this will be worn suspension bushes.
What is acceptable free movement???

I am going to be giving the suspension a good check over this weekend and I'm going to firm up the rear and check the pressure of the forks.

Warthog 28 Aug 2008 22:09

Quote:

Originally Posted by Tenere Tom (Post 204327)
Thanks for all the tips and advice guys!!!

The bike IS an import my docs say it was first registered in the UK in 2001 - the bike is a 1984.

When the rear wheel is lifted off the ground there is free up/down movement - before the suspension comes into play, this will be worn suspension bushes.
What is acceptable free movement???

I am going to be giving the suspension a good check over this weekend and I'm going to firm up the rear and check the pressure of the forks.

I would say you should have no play in the swingarm's arc other than the movement of the shock's own piston. If you do I expect it is bushes or the roller bearings in the shock linkage (do XTs have one, or does the shock bolt straight to the swingarm?). It could even be play in the swingarm bearings.

If you stand the bike upright, knock the sidestand up and hold the bike at the back: use your weight to compress the rear shock - sort of drop your upper body weight onto the back of the bike to give the shock a sudden increase in load.

If the shcok compresses immediately or, more importantly, springs back immediately, without any restriction, then the compression is gone and that will hamper you bike's handling: if a rebuild is not an option (rarely is on stock shocks) then a new one is the only option, unless you want to chance a Breaker's Yard.

If its the only glitch with a 24 year old bike, I still think you got a nice ride....

Tenere Tom 29 Aug 2008 19:59

What I meant by 'free play' in the rear suspension was - If you get the rear wheel off the ground (use the side stand if you don't have a jack) and lift the wheel (you might need a hand) and I guarantee there will be a bit of free movement before the suspension would come into play.

I may do a poll to see how this differs with the age of our XT's.

mollydog 29 Aug 2008 20:13

OK, I think I get what you mean.

angustoyou 30 Aug 2008 21:55

First things first, set the tyre pressures for fast riding. (2.1 bar front and rear, I think, from the top of my head). The difference will be huge. Make sure the tyres are cold (unridden) when you check the pressures, as heat in the tyre will give differing pressures, depending on the temperature.

Wether you think so or not, over 50mph on a trail bike is fast riding. The standard tyre pressures are a compromise for on and off road use.

Tenere Tom 31 Aug 2008 20:24

I guess I'm just used to going quick - 60mph isn't quick for a bike:(

A smaller front fender would help - or a steering damper

I'm going to replace by rear suspension bushes soon - is there an upgrade? needle rollers???????

angustoyou 31 Aug 2008 21:48

Quote:

Originally Posted by Tenere Tom (Post 204682)
I guess I'm just used to going quick - 60mph isn't quick for a bike:(

On tarmac that's true, off road it's pretty swift! :mchappy:

When I first tried an XT, I was suprised at how stable it was on the road (up to about 80 mph, on dual purpose tyres, as a first impression). I was expecting a bit of nervousness at speed. I've since changed to knobblies, at normal pressures, as I wanted the off road performance, and over 60 mph on the road it's a lot vaguer now, and does weave a bit.

I upped the pressures for a 60 mile 2 up road trip, and it was ok still. (At very sensible speeds) :innocent:

The other half blagged a lift home, allowing me to blast the 60 miles home 1 up, without dropping the pressures, and even on the knobblies the handling was much improved.

A weave is usualy indicative of softness on the suspension and / or tyres.

I had a 350 YPVS way back when, which had oversize tyres fitted, which weaved horribly cranked over at 80+. Going back to standard tyre sizes, and upping the preload on the rear shock cured that problem (but not the tank slappers!):helpsmilie:

If you are on the generous side, this will make the softness symptons worse.

It's pretty hard to test the shock, without replacing it, but after the tyre pressures / sizes, that's where I would spend my money.

A steering damper is to absorb rapid oscilation, as in a tank slapper, I don't think it will stop a weave. That would be my last resort.

Mark 3 Sep 2008 12:40

Sounds like head race bearings to me
 
Hi Tom,

My money would be on the headraces being either worn or too tight / loose, when mine became loose I had a weave starting to develop at about 60 pmh. It also caused front brake judder . Be aware that when you tighted the bolt at the top of the stearing stem it further tightens the stearing bearings that you have just spent an age getting just right! You have to set the stearing bearing slightly loose using the castlenated nut to allow for this.

"When the rear wheel is lifted off the ground there is free up/down movement - before the suspension comes into play, this will be worn suspension bushes.
What is acceptable free movement???" - One British MOT tester that he would fail a bike if it had more than 3mm free play, another passed by bike with 5mm, saying so long as it moved smoothly, no nasty noises then upto about 8 or 10mm was acceptable. A friend has now just become an MOT inspector and tells me their rules only allow an 'advisor' for excessive free play here, cannot be failed on it. Personally I think about 5mm is the most I would accept before I started investigating where trhe ware is. I don't believe that play here will cause the symptom you describe though.

Hope tha's some help

Mark


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