YZF/THUNDERACE SWINGARM CONVERSION

[drix]

Took my measurements today using the string method mentioned above and here they are...

Setup: complete YZF750 front / complete Tunderace rear
Tyre size: 120/70 and 180/55

Gap at the front left - between string and rim edge: 40mm
Gap at the front right - between string and rim edge: 46mm

So I have a 6mm difference and looking at the clearance available at the rear wheel, I'll go with amending the front wheel spacers... adding a 3mm spacers between the speedo drive/fork leg and shaving off 3mm from the spacer on the other side. Worth mentioning that when I replaced my front wheel bearings, I had Kayla make a +1mm YZF spacer as the original one (made by Kayla too) was a wee bit short for some reason.

I'll try to take a pic of the rear end/chain as the above wheel misalignment won't detract the fact that the chain doesn't look quite straight between front and rear sprockets!

[Con Rod]

If you have a 180 rear and a 120 front your measurements of 40mm and 46 cannot be correct.

As the rear wheel is only 60mm wider than the front the total of your left and right measurements must be 60mm

[drix]

If you have a 180 rear and a 120 front your measurements of 40mm and 46 cannot be correct.

As the rear wheel is only 60mm wider than the front the total of your left and right measurements must be 60mm

I've measured at the front rim edge rather tyre edge which is probably why the measures are not as you'd expect. Will try again but measuring on the front tyre edge later today or at the weekend.

[Con Rod]

ah yes sorry, this makes more sense

[cobbadiggabuddyblooo]

Here's what I've learnt from fitting another front rim with wider hub on my bike and may be useful if your choosing to off centre the front wheel between the forks.
Bluespots have an 8mm gap for the disc to run in. So 5mm is taken up with the disc.
So you have 1.5mm of movement unil you find the disc sitting against the caliper body so you will need to take material off your caliper and space the other caliper to fit.
You will then find your front wheel off centre to the stem and the forks . I don't think you'll find a motorcycle in production that utilised this thinking.
Same with the option of offsetting the rear wheel in the swingarm.
That's why you find some rims have offset centres to suit the needs of the design.
I'm not telling anyone how to do their mods but just letting you know what I've leart from the challenges I've experienced from changing forks , suspension and wheels to my own TRX.
Just something to be aware of if you do choose this option.

[alextrx850]

Brian, how does the wheel become off centered to,the steering stem and the centre line of the machine when all is being suggested is to reposition the front calipers to the disc ?...did I miss something there ?
The centre line of any vehicle must be valued as to maintain stability, which is the direction of many to have the YZF rear wheel in track with the trx front.
I don't doubt the YZF rear might be a little off the centre line as compared to a trx as they were manufactured as two different machines, but if it is a concern , then the ideas and photos posted are on the money.
I was one of the early ones to just whack a yzf rear on and go for it....never knew it might have a little out.
Too busy having fun.
Handy this forum having so many different minds to point out options.

[cobbadiggabuddyblooo]

My understanding with DRIX in the UK and his suggestion to just offset the wheel spacers to re align the front wheel with the rear, effectively offsetting the wheel from centre between the forks unless I have misunderstood his interpretation on his suggestion to deal with the issue of a the rear yzf750 swingarm alignment.

" Gap at the front left - between string and rim edge: 40mm
Gap at the front right - between string and rim edge: 46mm

So I have a 6mm difference and looking at the clearance available at the rear wheel, I'll go with amending the front wheel spacers... adding a 3mm spacers between the speedo drive/fork leg and shaving off 3mm from the spacer on the other side."

If i have read this wrong my apologies..

[drix]

You have read right Cobba, my initial and quick thought was to shift the front wheel +3mm to the right and job done.

The other option here would be to shift the rear wheel +3mm to the left... considering how close my chain currently runs to left edge of the rear tire, I'd need to shift that too with a offset front sprocket suggested in this very topic and potentially an offset rear sprocket to get the chain alignment right.

I now get the point, reading Alextrx850's comment, about getting the wheel aligned and getting them in turn aligned with the center line of the TRX. The question being which wheel is in line with the center line of bike... front, rear or neither of them? I would think the front one would be in line with the frame (assuming the forks are dead straight) thus making my initial idea of shifting the front wheel to the right a little daft and defeating the purpose.

I'll retake some proper measurements from tire edge to tire edge first though.

[alextrx850]

My understanding with DRIX in the UK and his suggestion to just offset the wheel spacers to re align the front wheel with the rear, effectively offsetting the wheel from centre between the forks unless I have misunderstood his interpretation on his suggestion to deal with the issue of a the rear yzf750 swingarm alignment.

" Gap at the front left - between string and rim edge: 40mm
Gap at the front right - between string and rim edge: 46mm

So I have a 6mm difference and looking at the clearance available at the rear wheel, I'll go with amending the front wheel spacers... adding a 3mm spacers between the speedo drive/fork leg and shaving off 3mm from the spacer on the other side."

If i have read this wrong my apologies..

This is really good thought swapping, I would have thought the mass rotational forces being the wheels would be best used in the line of most balance advantage..,which is the vertical centre line and the line of travel direction for the machine..
And assuming the forks and the frame are straight, so should be the wheel centres. ( ever followed a crabbing truck or dirt bike ?)..and fair enough Brian to space the front over to track the rear...but I'd offer to space the rear into line more so for what it's worth.
The big clincher....now that we have all the wheels centered and tracking to the centre line of the bike and all...we now go and add a single sided exhaust and heavy end can....do we ride with one butt cheek the other way ?..
Good topic.

[cobbadiggabuddyblooo]

..[/quote]
..and fair enough Brian to space the front over to track the rear...but I'd offer to space the rear into line more so for what it's worth.

Good topic.[/quote]

I never suggested this Alex ,
I was merely making DRIX aware of as he put it," his initial and quick thought"
( and we have all been guilty of that. )
and how this will place the front wheel off centre and this is not a practiced design on motorcycles for a good reason with my quote.
"You will then find your front wheel off centre to the stem and the forks.
I don't think you will find a motorcycle in production that utilises this thinking. "
Also if you choose to initiate this option , their are other factors that come into play like the disc and caliper alignment.

Addressing the problem at hand which is the swing arm alignment would be the easiest way to deal with this challenge but this is my opinion.
I'm sure we would all agree, changing the front to align things it gets your wheels inline may not be the best approach at the detriment of geometry and other alignment issues...
Keeping the rear wheel central to the swing arm is commonplace on motorcycles and again for good reason, so this is why I would suggest if you take the 5mm needed from the swing arm and the dog bone mount on the swing arm and just space the other sides accordingly.
The only problem that may have to be considered is the exhaust link pipe clearance on the bracing and this may not impact on all exhaust systems used with the YZF combination, but if it is the case it would be cheap and easy to address I'm sure .
No extra cost needed for sprockets as you can use your std sprockets, The only costs being two pieces of machining on the swing arm itself.
Wheels and sprocket will be inline, so cost savings also as no wheel spacers need to be machined up .
I'm sure if you look at the cost of machining the swing arm compared to costs of offset sprocket and wheel spacers plus machining the caliper mount..it will be a worthwhile option in my eyes .
If you choose to use a 520 chain conversion there are no special sprockets that need to be manufactured too as all these are easily sourced and readily available and will work to your advantage too with gains in the narrower width rollers if your worried about chain/tyre clearance.
So there are a number of ways to approach this but it seems logical to address the original problem at hand ..The swing arm.
All I ask if for those to look at all options and the actions these will impact on the rest of the geometry and mechanics on the bike itself, and everyone has their own choice in life on the road they choose to go down..
Good weather for the Anzac service this morning too I might add..
LEST WE FORGET

[drix]

Swingarm mod sounds more straight forward indeed. This mod would even more so require an offset front sprocket as per the start of this topic however... As 3mm would be shaved off the left side of the swingarm pivot axel thus impacting chain alignment even more than it currently is. Simple enough still though once you get the offset right

[cobbadiggabuddyblooo]

But you need to go to the right ( rear brake pedal side) with the swing arm for alignment to the front wheel and this will being your sprockets into line also.
Conrod chose the option to offset the wheel within the swing arm to the right for wheel alignment and to get the sprocket within 1 or 2 mm, but as mentioned this means machining new wheel spacers and machining the brake caliper mount .

I feel you have your left and rights mixed up DRIX.
heavy nite last nite??? We are all only human mate..
When you took your measurements with the string ,is your left facing the bike from the front or as sitting on the bike???
Bit like stage left and Front of house left.. both left but from a different view


A little research you may find a front sprocket that gives you the exact sprocket alignment too as the shaft pattern is a common one in amongst Honda , Suzuki and Kawasaki too as I found out when searching for a 520 conversion.

Here is how Conrod approached it
QUOTE

" By removing the 4mm spacer from the right of the swingarm pivot and adding it to the left I have moved the swing arm 4mm to the right.

You will now have a gap of 35mm on the left and 25mm on the right (from 39 / 21 previously).

But the front and rear wheel will still be 5mm out of alignment.

To address this you can now move the wheel 5mm to the right.

This can be done, as I did by shaving 5mm off of the rear calliper bracket and adding a 5mm spacer on the left.

This is good as it will bring the wheels into alignment without causing any clearance issues with the shock linkages, pipes and hangers.

It will mean the chain wont sit right on the guide again. This can be addressed by adjusting the guide or sprockets. "

Note... machining the swing arm pivot on the RHS 5mm and not the wheel also keeps your chain guide inline so another thing not to worry about..
This is within 1mm of the 6mm extra offset front sprockets on offer to deal with this.
That extra offset also puts just a little more load because it sits a little further down the shaft and onto the front shaft bearing too with the leverage factor..

[dixonj]

Cobba, take it your not a fan of the offset sprocket set up. It is a simple removable option.

[drix]

My left and right is when sitting on bike if I remember correctly... too lil time and too many things to do hence (lucky the missus is away at the mo so it's one thing less to worry about! ) so I'll be taking the measurements again over the weekend to get it right before shaving off anything from swingarms etc!

So at the front wheel, a gap of 40mm on the left and 46mm on the right (when sitting on the bike) means that I have to shift the rear swingarm 3mm to its left (again when you sit on the bike) to get the wheels aligned... thus accentuating the chain misalignment hence the offset front sprocket need. The same operation has to take place on the shock linkage too.

[cobbadiggabuddyblooo]

Cobba, take it your not a fan of the offset sprocket set up. It is a simple removable option.

Looking at chain alignment alone...yes it has it's merits for a " simple and removable option" but only addresses one of the problems associated with fitting a swing arm not specifically designed for a TRX850.
As i said .. each to their own,
If esthetics is the only reason for fitting a YZF swing arm as it is for some, it would be cheaper to just weld your own bracing to the original swing arm and fit a 180 tyre to a 5" std trx rim.