Metric tire sizes for 1979 R65

[Dustit]

 Tire size fit on early (1979) R65 . I have an understanding of the ht. differential and the problems related to the center stand when using metric tires. Would using a 100/90 /18 on the front and a 120/90/18 rear
 be a fit as far as clearance work out ?  Bigger is not always better , what will fit ? Maybe 110/90/18 rear for better handling.

[mrclubike]

I think the most popular frt size is 90/90 but 100/90 does work
The most popular rear seems to be the 4.00-18 most tires are still available in that size.
If you go to the wider rear you may have to install the wider axle spacer.
Problem with that is it causes the rear brake shoes to hang slightly out of the drum. It also changes the mesh of the hub splines. You will also have to let the air out of the tire to get it out.
If I remember correctly  my bike had a 120/90 on it when I got it and I removed it and the spacer
It is just the front that is rare in the old 3,25-18  
3.25- 19 are still common just not the 18 inch at least in the USA  
The other guys around here are very experienced  with this and will chime in

[georgesgiralt]

100/90 front will make your bike heavy and not easy to corner.
A lot of tires are available in 4.00 rear size but not all of them are born equal. Some are wider than other and will fit with difficulties.
I now run Heidenau tires (k34 front in 3.25S18 ) and K36 rear in 4.00H18) which are both cheap and very good. So do not overlook them. They give the bike an original look and that is a cherry on the cake.
Bear in mind that the pressure given in 1979  are a pure joke now. So inflate your rubber in today's values which are way over the old values....

[mrclubike]

I really wanted to try a set of  Heidenau tires but here in the States they were the most expensive tire on the list.
I opted for MADE IN ENGLAND Avon AM26
Being parcel to everything made in the USA or the UK (except for motorcycles)
Before that I ran Metzeler's Lasertecs but they followed the rain groves really bad.
The Metzeler's I only got 5000 miles out of the rears but I think I was running the pressure way to low. Because I was using the old pressures  listed in the manual. The Avon's  are wearing much better using the Avon website  pressure.
The Michelin Pilot Activ's  are very popular on the R65-R45

[marcmax]

I am on my second set of Bridgestone BT45's. I have an LS and the rims are slightly wider so I have no problem with a 100/90 front and a 120/90 rear. The rear clears the swingarm just barely but has never been a problem.

[Bob_Roller]

I used Metzeler 120 rear tires and it was a pain to get the rear wheel on and off the bike ,

Had to deflate the tire to remove or install it .

I now use a 4.00 size rear tire .

Getting too wide of a front tire can cause mounting issues, last time I had a front tire replaced, I was told, a 90/100 would be a better choice next time .

[Barry]

A 79 R65 has less clearance than post 81 bikes so try and use tires that are known to fit on the 78-80 models. You will still need to deflate almost regardless of what you choose.  Pretty much all 120 rears simply won't fit. Anything that has a fitted and inflated width of 120mm or over will rub on the swinging arm. 110’s are OK but you will lose 20mm in diameter over a stock 4.00 tire. I can tell you that 4.00 Pirelli City Demons and 4.00 Michelin M45's are fine at 115mm but still need deflation to get past the brake shoes.

The wider spacer mentioned part no 36312301737 is only 1.5 mm wider so that will allow a 3mm wider tire and that won't be enough for some of the 120's.  As has been said they are not an ideal solution.

[Dustit]

 Thanks for all the reply's , any and all info is helpful.  I purchased the bike with the tires that are on it . Metzeler 90/90 up front and a Metzeler Marthon 4.00 on the rear. The rear tire  width is 123.40 mm (4.87 in.) and far to large . I have two other 18 in. wheeled bikes one running Avon Road Rider 90/90/18 up front and 100/90/18 rear ( 1975 S3 Kawasaki). My 1977 RD400 has Pirelli Strada  90/90/18 front and and a 4.00/18 rear . I have installed Shinko 712 tires on two other bikes in the past and for just under $100.00 for the pair , wanted to use them on my R65. But---  the front not available in any thing smaller than the 100/90/18 . Diameter - 25.08 width - 3.98 . The ht. on the rear would all so affect the cornering and turn in  .  A rear 110/90/18 Shinko Diameter 25.79 Width 4.29.