Using the proper forks?

[projectxs650]

I want to double check on something. So i have a 72 frame, and i'm shopping around for some forks, I've heard that 71' and 72' had different forks than the following years.

So for example: lets just say i get forks off a 76, could i use a it on my 72 frame? what year would the triple tree have to be?

 

[projectxs650]

looking for some answers asap

 

[Beau]

I may be wrong, but I thought the steerer tubes were compatible with all years.

I know some of the early ones had a little longer steerer tube but I'm not sure if it really makes a difference as long as you use the proper parts for that fork.

Buy a complete fork and put in taper bearings and you should be good.

 

[jamesgs4]

70-73 bikes have a shorter neck than 74+, so the trees between them do not swap directly. 70-76 used 34mm tubes, and 77-84 used 35mm tubes. Also brake setups differed between the years. Your best bet would be a set of 72 or 73 trees, with tubes and brakes from 72-76. If you upgrade to 35mm, you have stem length differences that need machining or spacers to make them work.

 

[projectxs650]

70-73 bikes have a shorter neck than 74+, so the trees between them do not swap directly. 70-76 used 34mm tubes, and 77-84 used 35mm tubes. Also brake setups differed between the years. Your best bet would be a set of 72 or 73 trees, with tubes and brakes from 72-76. If you upgrade to 35mm, you have stem length differences that need machining or spacers to make them work.

Great info, well thats good to know with my frames neck i could always add spacers to make it fit better. As opposed to trying to make it shorter : /

How much of a difference is it between years? hopefully not more than a quarter of inch or something?

 

[nj1639]

The '77 xs750 triple tree has a shorter neck than the later xs650's....been wondering if it's the same as the early, '70 to '73 650's. It would make a heck of a difference as the 750 has the 36mm tubes. I happen to have a 750 neck stem in the barn somewheres, could measure it....

 

[XSLeo]

I have a 75 XS650 tree, the stem measures 8 7/8 inches from where the bearing seats to the top of the tree.
I have a 79 XS1100 tree, the stem measures 8 1/4 inches from the bearing seat to the top of the tree.
If any one has a 70-73 tree and can give us the stem measurement, it might help.
Thanks.

 

[nj1639]

I measured the '77 xs750 stem and it's also 8 1/4"....same as the 1100. It sorely would be nice to know what the length is on the '70 to '73's, could help out as the xs750's- mebbe the 1100's forks are about an inch longer than the xs650's and maybe around the stock length of the tx's.
Inner species frankenbiken yo.

 

[XSLeo]

I did a few more measurements on the XS1100 forks. Length from center of axle to top of tube 31 1/4 inches, 37 mm tubes.
I measured the 75 forks, length 29 5/8 inches. The 79 set on the 75 with the better springs, length 30 even, the set on the 82 parts bike, 29 7/8 inches.
Looks like the 73-76 34 mm forks were a bit shorter than the later 35 mm forks, 1/4 inch.
The XS1100 forks are 1 1/4 inch longer than the 77 up forks and 1 1/2 longer than the early forks.
The 70-72 forks may measure different. Can someone who has a 70-72 forks measure them and post the specs?
I got the XS1100 forks before I realized they were different size tubes. 37 mm. I got them so I could use the later single piston calipers for the dual disc front brake. I got an XS1100 set of trees and I haven't tried them yet. Need to swap stems. They do have tapered roller bearings on the XS1100 trees. The offset is about 5/8 inch less than the XS650 tree. The top tree is flat. The top tree has solid mounted bars. I might try building a top tree out of flat aluminum stock. This way I could use rubber mount risers.
We'll see when I get the stems swapped, maybe the vibration from solid mount bars will be ok.

 

[projectxs650]

Anyone know if a 21'' wheel will be fine in stock forks? or will it be cutting it close?

 

[XSLeo]

A 21 inch wheel and tire have pretty much the same overall height as the 19 wheel and tire. Either one works.
A MH90-21 stands about 26 inches tall. A 2.75 inch wide tire.
A MJ90-21 stands 26.5 tall. A 3.00 inch wide tire.
A 100/90-19 is 26 inches tall. A 3.50 wide tire.
A 110/90-19 is 26.7 tall. A 4.00 wide tire.
The difference is at most 3/4 inch.

 

[projectxs650]

A 21 inch wheel and tire have pretty much the same overall height as the 19 wheel and tire. Either one works.
A MH90-21 stands about 26 inches tall. A 2.75 inch wide tire.
A MJ90-21 stands 26.5 tall. A 3.00 inch wide tire.
A 100/90-19 is 26 inches tall. A 3.50 wide tire.
A 110/90-19 is 26.7 tall. A 4.00 wide tire.
The difference is at most 3/4 inch.

perfect!

 

[XSLeo]

Put the 21 on with your fender,I doubt it will hit the fender. If it does you can elongate the fender mount holes and raise the fender a bit.
Being a narrower tire the only place it can hit is on the fender.