Tire Sizes

Since I have my rear end apart, I thought I might change out the chen-shin 120/90-18 rear tire (Front is a new-enough-to-still-have-the-nubbies Dunlop K70).

Now, seeing that the rear is not the true stock size (4.00H-18) and noticing that the chain guard looks to have been rubbing, I have the following questions for those who may have been down this road before me:

Would a 110/90-18 be closer to the original 4.00H-18?
Is it worth the trouble finding a 4.00H-18? I have found a few, but it severely limits one's choices, though it looks like Metzler has just such an animal for under $100.
It is a crime worthy of my physical punishment (when the bike self-implodes) to run different manufacture tires front & rear?

I would rather not swap the front, as it is practically new.

Congratulations, you just stumped me with a KZ750 twin question :ohmy:

All my 750 twins have 16" rear wheels (Morris Mags or 80 G model drum brake mags), so I don't have a clue about 18" rear wheels on the 750 twin.

Really? :ohmy: The FSM says:

Front: 3.25H-19 4PR
Rear: 4.00H-18 4PR

I have noticed that most of the wheels out on ebay for KZ's, including twins, are 16in. But the book (Covers 76-79) states 18in. I never thought much about it till just now, since it matches what's on the bike.

Let's see if I can go two-for-two. I have grokked what the 3.25 and the 4.00 are (Width). The "H" is speed rating, and the 18 & 19 are rim sizes. What is the "4PR" bit about?

Four ply rated?

Complete tire info explanation, along with conversion chart

76-79 KZ750 twins were originally equipped with 18" rear and 19" front, there was a Dealer installed Morris Mag option that was 16" rear and 19" front.

I used the brake pedal and swing arm from a 1980 KZ750 G to install the 750 G's mag wheels on my 79, the 79 swingarm is on one of my 80 G models that is getting the Morris Mags. My 750 twins are all confused

Oh yeah, in answer to your original question, the above link says a 4.00x18 is the same size as a 110/90/18

Post edited by: steell, at: 2007/02/15 21:38

Don't know about the 18" vs 16" thing, but a 110 is closer to a 400-18 for sure. I went from a 120/90-18 to a 110/90-18 because I wanted back to original size tires. Every brand is different is the major problem though. I used to run 130/90-18 Pirelly (however it's spelled), and they were smaller diameter as well as less wide than a 120/90-18 Dunlop K591. Last tire I got was a Dunlop 404 I think, which is a pretty cheap tire and the 110/90-18 is really small in that brand. I wish there was more uniform across the board sizes among the brands. I went to buy tires for my truck and a 235/85-16 is just that. Every brand nearly identical for the most part, but not on motorcycles.

Thanks for the link steell, that is what I needed!

Interesting that various manufactures are different physical sizes for the same "size" (geez,that just does not read well...). I looked online at Bridgestones Bt45's, since the manual calls for Bridgestone Super Speed 21's (not made anymore), then Dunlop D404, Michelin M50, Continental K112, and Metzler Lazertechs. Now I wonder about actual size.

Crikey, why make it so difficult? Might as well stamp them "Approximately" whatever size...

I may just putt it down to the bike shop once I get her together, and have 'em put on what they got handy...:blush:

EsaPro wrote:

I looked online at Bridgestones Bt45's, since the manual calls for Bridgestone Super Speed 21's (not made anymore), then Dunlop D404, Michelin M50, Continental K112, and Metzler Lazertechs.

Careful: you don't want a radial tire back there, not with a bias front. I think at least a couple there are.

I'd go Dunlop bias ply, even though I run Pirelli. Ron named a couple of different Dunlop #s that should work.

Most of the manufacturer's websites have the actual width and diameters listed for each model of tire they make.