Tyre size

[b_racuda]

I know that there has been allready a old topic from tyres. But I still have few things to ask:

- if I want to change the profile from 90 to 80 is that ok? (I now have 100/80 18" rear and 90/90 18" front)
- is 130/80 18 too wide for Vision?
- If I change rear tyre size from stock 100/90 18" to 120/80 18" is it better to change also the front tyre to 110/80 18"?

Why I am changing the tyres, well my front tyre body is damaged. There is higher point at one point and the tyre is bouncing when riding. Currently I am having Bridgestone Battlax BT45 tyres but thinking to change to Avon Roadrider AM26.  I like to have wider tyres just because they look better :)

[The Prophet of Doom]

Bigger tyres DO look better.

I've not seen 80 profile tyres here - other people may be able to answer first hand. I'm running 120/90 and 110/90 BT45 but had to remove the front mudguard to make it fit. I think a 130/90 might just fit with the exhaust system replaced with Macs, Predator or SpecII.

Physical tyre widths and heights change a lot between manufacturers, so what works for Bridgestone won't necessarily work with Avons.  Tell the shop you are unsure it will fit and see if they will swap if it doesn't.  Mine was happy to do this, but charged me an extra $10 to balance again.

I do like the BT45, but never tried Avons

[b_racuda]

Thanks POD, do you think 120/80 rear and 100/80 front will work? I mean that the handling is ok with that setup? I don't want to remove the mudguard and maybe the 120 is also enough :)

POD I also looked your rims at the going racing topic and i have to also paint mine to black. In my opinion they look far better in black. I remember that you powdercoated them? Did you have to remove parts before putting them to oven?

[The Prophet of Doom]

The 120/80 100/80 will fit because the 120/90 100/90 do.  Can't comment on handling - It all gets a bit complex because you are changing your centre of gravity, your steering geometry, your gearing... 

I don't regret the black rims, I think they look better in real life than in the pics, though I should have clearcoated them also..  When you powdercoat you sandblast the rims and them cook them at 200 degrees so you need to drop out your bearings, spacers and remove balance weights.  I tapped them out and the tyre shop pressed the new one in for free since they supplied them.

[b_racuda]

I did a little search from the internet and in the Europe XZ550 came with the rear tyre size 4.25/85 H18 so that is 120/90 18" in the metric system (correct if wrong). I also measured the side clearance between the current tyre 100/80 18" and the closest point and it was 20mm. The closest point was the left side of the swingarm.

Widht:
So if calculating that 130/80 18" is 30mm wider than my current tyre so with 130 wide tyre there is 15mm extra width to both sides --> so it should fit with 5mm clearance on the left side.

Diameter:
The diameter of tyre+rim is changing from the 617,2mm to 665,2mm so the diameter of 130/80 is 48mm larger than in 100/80 (18"=457,2mm and 130/100*80=104mm*2=208mm --> 208+457,2=665,2mm).

So:
90/90 diameter is 619,2mm
100/80 diameter is 617,2mm
100/90 diameter is 637,2mm
110/80 diameter is 633,2mm
110/90 diameter is 655,2mm
120/80 diameter is 649,2mm
120/90 diameter is 673,2mm
130/80 diameter is 665,2mm
130/90 diameter is 691,2mm


So if the 120/90 (4.25/85) was original size in Europe should 130/80 also fit but it is very tight with the side clearance! I don't know how much the tyre is changing the shape when the weight is on the bike and you are cornering.

The riding height:
Original setup Europe 619,2mm front and 673,2mm rear (90/90 and 120/90)
New setup 1 617,2mm front and 665,2mm rear (100/80 and 130/80) front is 2mm lower and rear is 8mm lower
New setup 2 637,2mm front and 665,2mm rear (100/90 and 130/80) front is 18mm higher and rear is 8mm lower
New setup 3 633,2mm front and 665,2mm rear (110/80 and 130/80) front is 14mm higher and rear is 8mm lower
Original setup USA 637,2mm front and 655,2mm rear (100/90 and 110/90) front is 18mm higher and rear is 18mm lower (than in Europe)
My current setup 619,2mm front and 617,2mm rear (90/90 and 100/80) front is the same as original and rear is 56mm lower

According to this the riding height was different in the Europe and in the USA and my current setup is wrong. Maybe the "new setup 1" is the closest to stock

EDIT: of course the ride height is not the same as the diameter for the whole tyre...

[The Prophet of Doom]

4.25 is inches - that's less than 110mm

[b_racuda]

I just used some chart table to convert the size (http://www.mccookracing.com/ "Tire Sizes and Conversion Chart")

[b_racuda]

I understood that you can't convert the low profile inches directly, as 4.25/85 is low profile. I believe that the true widht it is between 110 and 120.

I also found old topic where there was conversation with this same thing http://ridersofvision.net/rovforum/index.php?topic=8787.0

[dpequip]

Back in the day when these were bikes were brand new the max tire we could put in were 100/90 in the front and 120/80 in the rear.  These were on USA Spec models.  As a previous poster mentioned 110 series will not clear the existing front fender.  130 series will not clear in the rear.  One other thing to remember with tires is that they grow as speed increases.  Especially bias ply tires.  Tires may have adequate clearance under zero speed static conditions but may contact hard parts at speed and cause tire chunking.

[QBS]

Back in the day I put a 130 on the back of my '83 and went Ducati hunting.  Found a gaggle of three and couldn't catch them because my bike wouldn't exceed 85 indicated mph.  How puzzling and maybe life saving.  Later I noticed that the center of my new tire was showing a very strange wear pattern, kind of polished with chunks for tread missing.  Then I noticed that the inside of the swing arm yoke area was also highly polished.  I gave up on being a boy racer and replaced the 130 with a stock size tire and have bee very happy since then.  That happened about 20 years ago.

[PHM]

I am running Pirelli Sport Demon on my 1983.  On the front 110/90-18, I was able to use the front fender. All I did was with the four mounting bolts just grind the head of the bolts a bit. The heads of the bolts rubbed until I took off that small amount of bolt head and now fits like a charm.  On the rear I am running 120/90-18.  This set up fills it out perfect.  No ride or wear troubles, and they look great...Paul

[PHM]

Thinking back I may of also filed (dremel tool grinding disk) the mounting bracket the wraps around the inner part of the fender a bit.  All I know is it took limited work for my front fender to work.  I thought at first it would not, but it did and fills it in nicely...Paul

[dpequip]

QBS that is exactly what happens.  When I worked at a Yamaha dealer I saw that several times on a Vision and RZ 350 that the owners insisted could run a 130 tire.  Glad that it didn't have a bad end for you.  It kind of blows my mind that the front tire on my Bandit 1200 is the same width as the Vision rear. ;).  Motorcycle tires and suspension have some a long way in 30+ years.