Tyre size advice please!

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area51
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Joined: Mon Apr 16, 2012 10:47 pm

Tyre size advice please!

Unread post by area51 » Mon Jul 16, 2012 9:24 pm

I'm just starting to re commision a 1987 kawasaki gpz 550..the stock front tyre size is 100/90 x 18. I have a new battleaxe bt45 to match the rear but its 100/80 x 18.
are there any reasons apart from speedo overreading maybe that would advise against fitting this new tyre to the front of my bike?

Its been as long time since i had much to do with modern tyre sizes and am unsure if its a good thing or a bad thing to go down a size on profile.
1987 kawasaki gpz 550 unitrack
RICK

The Mighty Gusset

Re: Tyre size advice please!

Unread post by The Mighty Gusset » Mon Jul 16, 2012 9:49 pm

That's a tricky one these days, although they are nominally the same, tyre sizes and profiles differ greatly from one manufacturer to another.
What do Bridgestone say ?
For what it's worth, if they're a matching pair of tyres, and not stupidly inappropriate sizes for your bike, then you're probably Ok.

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area51
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Joined: Mon Apr 16, 2012 10:47 pm

Re: Tyre size advice please!

Unread post by area51 » Mon Jul 16, 2012 10:24 pm

Hi gus..the rear is a bt45 120/80 x18 which is standard size for a rear at that age. I think the lower profile tyre used to be a go faster dodge to make it steer quicker but I could be wrong or even have it back to front as its a long time since I was involved with mucking up perfectly good bikes in the persuit of going faster!
1987 kawasaki gpz 550 unitrack
RICK

The Mighty Gusset

Re: Tyre size advice please!

Unread post by The Mighty Gusset » Mon Jul 16, 2012 10:42 pm

What are you going to do with the tyre if you don't fit it ?
If you do fit it, the worst that can happen is that you don't like the way it handles and decide to sling it in favour of something else.

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Hooli
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Location: Doncaster

Re: Tyre size advice please!

Unread post by Hooli » Tue Jul 17, 2012 11:53 am

I believe your right, it'll just make it turn in faster.
Classics ain't built in Metric

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area51
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Re: Tyre size advice please!

Unread post by area51 » Tue Jul 17, 2012 11:29 pm

I even phoned bridgestones tech department today..what a total waste of time!
Wouldnt comment on which tyre they would recommend or why. didnt know what effects a reduction in sidewall profile might have.
not sure he'd ever actually seen a motorcycle tyre before.
or a motorcycle for that matter.

It seems it should be okay to use unless anyone can come up with a credible reason why not...
1987 kawasaki gpz 550 unitrack
RICK

Coxy
Posts: 202
Joined: Sun Mar 29, 2009 11:05 am
Location: Sydney Australia

Re: Tyre size advice please!

Unread post by Coxy » Thu Aug 09, 2012 10:34 pm

Originals were 90 profile going down to an 80 profile front and rear will lower the gearing affect the speedo reading and lose some ground clearance but otherwise not adversly affect the bikes handling or rideability,These bikes were not really lacking in ground clearance when new so it should be OK .

The Unitrack GPz 550 was a great Toy to ride when New and I was working for Kawasaki Australia Tech Services Department,though even when new they were lacking somewhat in rear shock damping,So if having it replaced or rebuilt remember that point.

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