K100 GSXR conversion questions

[Max]

Hi all how is every one doing?. I have been building a 1985 k100 rs since March this year and have been messing around trying to get a GSXR 750 front end to fit and have a few questions. I have turned down and pressed in the original BMW stem tube into the GSXR tree and just wondered if this will be safe enough to take the load or should I get a solid bar made up?. Also with the GSXR front wheel what would be my options regarding tires as I want the old cafe style look. I was told having the GSXR front wheel will limit my choice in tires but do not understand why? Can any one help answer this or give a suggestion on tires. I am a great mechanic/fabricartor/painter but know nothing about tires and am struggling to get a definitive answer, even my local bike shop could not help. Any advice would be greatly appreciated

[Laitch]

Considering the effects upon me of age, gravity and observation of human behavior, I'm doing pretty good. How long did it take you to attain greatness as a mechanic?

[Max]

3 years at collage and a further 10 years in the trade 👍 Thanks for asking

[Laitch]

Part of the instruction in university and trade was to machine a part—for example, a BMW stem tube— to a spec that you want so it can be used in an assembly of your choice then determine afterward by asking around on the Internet whether it would be safe enough to take the load?

[Max]

You must have gone to a different university than me then but am happy to take on any advice from you as you seem so knolagable. I did not realise I would be tested in my knolagable and skill from simply coming onto this site but I guess there is always one that feels threatened by other people's skill set. I agree that stating I am great was the wrong use of word, competent would have been a better word to use, I apologise and bow to to you greatness if you could answer my questions?

[Barry in IN]

I only spent two years in college then the next 31 as an aircraft mechanic.  I wish I could be “knolagable” enough, whatever that is, to achieve greatness too.   
Maybe I could get there by stripping pieces and parts off of perfectly good motorcycles.   That’s OK, I’ll do without. 

Why am I being so harsh? 
Because you took a vital structural part and reduced its thickness and therefore strength.   Doing it without knowing how much difference that will make is one thing.   What makes it worse is you did this to a hidden area, where it won’t be apparent to the next owner.   The only way they will know is if you tell them.  Maybe you plan to do that.  Maybe you will drop dead tomorrow and the bike will be sold by someone else. 

Start trimming on the steering knuckles of a 35 year old car, then go on a car forum and ask opinions.  See how well that goes over.

And this was all done as part of making the motorcycle look different to meet a style fad.   Well, that makes it all worth it. 

[Max]

Fine I will turn down a solid bar to fit, can any one answer the tire question?

[Barry in IN]

Lots of tire threads here.   I like the Michelin Pilot Activ. 
Since you want tires based on “that old cafe look” rather than performance, I’m not sure if you’ll find the info you want here. 

[Max]

But why will I be limited to what tire will fit the rim, size is obvious but I was told radial tires will not fit the rim but could not be given an answer as to why?. This is all becoming to much of a headache and am just going to refit the standard front end at this rate

[K1300S]

"But why will I be limited to what tire will fit the rim".  huh?   maybe there is an english translation issue here, but of course you are limited to what tire will fit the rim.  if it doesn't fit, you can't put it on.


is the tire thing a trick question?  why wouldn't whatever size tire that came on the gsxr fit the gsxr rim?  there must be a zillion tires for that bike.  you aren't looking for a tire to fit an old k bike, you are looking for a gsxr tire.  or did i miss something?

[Max]

I want an old style cafe tire fitted onto a modern rim, I was told this cannot be done and had no explanation why. I just wanted to know the reason is all but starting to wish I never asked

[Barry in IN]

I don’t know what size rim you have, but I know many BMW K-series ones are in a size that radials aren’t made in.  That may be part of it.

[Laitch]

I want an old style cafe tire fitted onto a modern rim, I was told this cannot be done and had no explanation why.

If by old style you mean narrow, one reason might be the Gixxer rims are too wide for narrow tire beads to seat securely on them. The Gixxer is designed with radials in mind—wide ones, especially the rear tire. An additional reason might be the diameter of old style tires tends to be greater than Gixxer rims.

The early K model tires look more like the BSA and Triumph tires of yore.

[johnny]

greetings...

before f-ing with tiors you oughtta square away that bung... proally will fixt the handling...

click on this link... perhaps you can getts you that hemorrhoid hanging off the bung of that blue 750... that will offset that abortion of a head job you performed on that hundert rs...

j o

[Laitch]

Maybe it's time to head out for bratwurst with espresso and gelato chasers.

[Max]

I thought that the wheel rim was too shallow to take the tire to seal onto but they are exactly the same, the GSXR rim is slightly wider but still do not understand why this will be a problem as tires can stretch or get a slightly wider tire.

[Max]

I'm just going to re fit the standard front end and address the GSXR front end at a later date, I like a challenge but also want to use the bike before winter hits

[Barry in IN]

Well at least you planned it out well.   

[johnny]

greetings...

i guess you learnt everything except common sense... guess common sense aints all that common...

j o

[Laitch]

I thought that the wheel rim was too shallow to take the tire to seal onto but they are exactly the same, the GSXR rim is slightly wider but still do not understand why this will be a problem as tires can stretch or get a slightly wider tire.

There is data available that a uni-educated person should have found before now even using a clapped-out Mac in need of an upgrade it can't support.

Here's a table that shows minimum to maximum rim width for sizes of tires. This isn't the only table on the Web but its color caught my eye. Gixxers have rims typically 1.5 inches or more than the maximum width for narrow tires, despite what you might think. Although these tires might have been called balloon tires when they had tubes in an earlier and simpler motorcycle age, they are not balloons.

[NickHeijman]

My plan was to follow this topic, because i'm planning to do a USD swap over winter or beginning of next year. The GIXXER 750 front had my attention, however it looks like every one here is giving Max a roast.

@Max, I looking over the internet and it seems that the ZX7R front end will fit with the original ZX7R Triple and triple top. The length of the stem is about the same. So you will be on the safe side in that case. Furthermore google around, several guys have done the R1 fork and a GIXXER750 front swap and left some nice details and information.

Hope you will figure it out before I do so I can take your notes as well :)

Cheers and best luck,
Nick

[CG_3D]

Don't use the BMW stem you turned down. You have thinned out a hollow tube which takes a shear load on the front of the bike.  I don't remember the exact difference from a 750 to a 1000 if any (google 'gsxr fork matrix') but Cognito Moto make a GSXR to K100 stem. For $140 save yourself a headache.

Also look at the tire size you have on the GSXR wheel you have. The GSXR wheel isn't that unusual. If it's say a 180/55-17, then you look for tires the same size to start. - 17 being the wheel diameter. 180 is the section width in mm and the 55 is the sidewall height as a percentage of the width. Therefore you could look for all available tires at that size. You could look at 190 wide perhaps. Maybe a 60 sidewall...Depends on the look and what is available.

[CG_3D]

Re-read above and want to add, not sure what exactly you are thinking as being a 'cafe racer style' tire, but most vintage style tires are tube type vs modern sport or touring type tires which are most commonly tubeless.... you can technically run a tube type tire on a 'tubeless' rim (like the gsxr). There are mixed opinions on running a 'tube only' tire without an inner tube on a 'tubeless' (sealed) rim. You can, of course run an inner tube on a tubeless rim... Google is your friend. ....

[johnny]

greetings...

here is a 6 ply with nice steering tread...


AIRTRAC.jpg (14.67 kB . 320x320 - viewed 880 times)

j o

[Barry in IN]

“Like” ^