Help, things arent adding up with wheels and brakes

[munkeyboi]

Howday all,

Me again, and asking for help.
So i've got (I Think) A TZR 125 1989 - It Says 2rk on the frame,
now the service manual says this about the wheels and tyres;

http://davedamunkey.no-ip.com/1.jpg


http://davedamunkey.no-ip.com/2.jpg
So not the tyre sizes depending on the model and also the rear wheel should have a drum brake.

Well my bike frame says 2rk, yet the rear wheel has a disc brake.
The tyres fitted on it now are;
MT75
Front - 90/80 17 46p
Rear - 110/80 18 58h

WTF is going on? Nothing matches and i have no idea what tyres are gonna be compatible with it.

[Lateshift]

That just looks to me like someone has used a newer rear wheel and done a drum to disk conversion.

Probably done you a favour to be honest because the benefit of having a slightly wider and lower profile rear tyre can only be a good thing :)

Given that the newer models rear wheel was 2.50 wide instead of 2.15 this has allowed a slightly wider tyre, hence the 110/80/18 instead of the original 100/90/18

Even on car tyres there is enough room to normally go one up or one down without having to change the actual wheel ;)

But to answer the question the original 100/90/18 should still fit, i personnally would stay with the slightly wider 110 though ;)

[munkeyboi]

Hiya mate,

do you think the front wheel has changed, the reason i ask is the disc pads are dependant on age of bike and wheel size, so i want to make sure i get the correct ones.

And what does the letter at the end of the tyre type mean?

cheers
David

[Lateshift]

again going by the front tyre size it would appear that you have the front wheel off the newer model too, now if the manual is correct then the newer disc had a thicker cross section, ideally i would say look for a part number on the disc to try and check, at least then you could match it up for definite, failing that try to see if the pads have got a part number, lastly see if there is any difference between the old pad part number and the new one, its quite conceivable that they kept the same pad and caliper but just stuck on a newer disc ;)

lastly the numbers and letters on the tyres are as follows

110/80/18 58H

110 being 110mm across the width of the tread
80 being a sidewall profile height of 80% of the 110mm width
18 being the diameter in inches of the wheel itself
58 being the load indicator (need a table for that, however 58 = 236kg)
H being the speed rating, H is rated to 130mph

:)

[munkeyboi]

Soooo, last question on wheels and tyres.

What are the biggest size i can safely put on it?
I'm thinking fat tyres would look better

Cheers

david

[Lateshift]

thats a tough one to be honest and you can normally only find that out from someone who spends their time working with tyres and rims.

however there will be a maximum tyre size and a minimum tyre size for that wheel, i would imagine an email to Yamaha would answer the question as its them that make/design/use the rim and would therefore know what was the largest tyre that could safely put on.

As a general rule if its anything like cars you can normally go one (in some cases 2) widths up and one width down, go any wider and it overhangs the rim itself and becomes dangerous.

I reckon at a squeeze you may get a 120 on it, but have a look at trying to find out what the TZR racers use in the Yamaha past masters etc in Bemsee, they are normally standard type bikes with slicks etc on so it should give you a rough idea ;)

[munkeyboi]

Thanks again for the reply mate,

I'll try to contact yamaha or do a poll in the forum, find out the biggest on a TZR.

Sorry to bug ya, but i thought of two more questions.
I have MT75 tubless tyres (aparently) I've got a slow puncture on the front, would that be easy and cheap to fix myself or would i have to pay to have it done. I was quoted £37 but they can't do it til next.

Secondly, since my rear tyre is fatter than the factory one, should the rear pressue be more than the manual says, currently 28?

Sorry I'm a noob when it comes to bikes, gimmie a PC any day and I'll run rings around anyone, but i got the manual, i'm doing small bits and pieces myself. The boy will learn one day.

Cheers

David
Aka Munkeyboi

[Lateshift]

The pressure is a question of "does it feel right?" as long as you do not exceed the maximum rating on the tyre then it will be okay, its more a case of trial and error because a tyre pressure that works for you may not work for me due to weight of rider etc, however a quick look on the tyre manufacturer website may give you the answer to that ;)

As far as the puncture goes, £37 seems a bit steep for just puncture repair, if its a slow one and its "repairable" you can normally get that done for £20 all in.

Personnally if you know what you are doing, you can get tyre repair plugs that last well, but its down to whether or not you can manage the job yourself, it may well be easier to find a place that would do it for you and cheaper ;)

It also helps if you put a rough location of where you are from in your profile so at least people who know your area can then give you some free directions to who they have used ;)

[munkeyboi]

Hey,

Thanks again for the reply

I've edited my profile, location now says North London.
I've never had to fix a tyre before, but i don't mind trying.
It can't be that hard, I mean, some of the mechanics i've met in my life aren't the brightest crayons in the box, no offence meant, merely observations.


cheers

David