Yamaha TRX850 Enthusiasts Forum

Ok ... I might take a bite on this YZF 750 rear conversion....

Couple of questions :

1) Is it worth it?? Does the braced swing arm offer any significant advantage over the std TRX jobbie??

2) Will it fit - without too much pissing about ..!

TIA

Greg

Mate,

Main advantage I could see when I looked at this was that the YZF rear wheel will slot straight in, so giving you a 5.5" rim which will take a 180 tyre, but it's easy enuf to put the yzf wheel in the standard swingarm which is what I'm gonna do.

The brace on the YZF swinger adds some 'bling' but probably no real benefit. I think the swinger is aluminium, so may be lighter?

Not sure if the standard TRX shock fits or not? May also need the YZF rear brake caliper?

Couple of questions :

1) Is it worth it?? Does the braced swing arm offer any significant advantage over the std TRX jobbie??

2) Will it fit - without too much pissing about ..!

1) No - the standard item is more than strong enough. YZF may be lighter (but I doubt it and even if it is the rim and tyre will take any gain away) and arguably looks better - that's it

2) If you have a complete YZF rear end, it'll bolt straight in leaving you only chain alignment to worry about (which I understand can be done by simply flipping the standard front sprocket).

Main advantage I could see when I looked at this was that the YZF rear wheel will slot straight in, so giving you a 5.5" rim which will take a 180 tyre, but it's easy enuf to put the yzf wheel in the standard swingarm which is what I'm gonna do.

Personally I don't see having a 180 section tyre as an advantage and you most certainly don't need it to handle the power of the TRX. That said, you do get greater tyre choice with a 180 section.

phuk72 wrote: 1) No - the standard item is more than strong enough. YZF may be lighter (but I doubt it and even if it is the rim and tyre will take any gain away) and arguably looks better - that's it

How the phuk can it possibly be lighter? It's basically the same arm with a phuking great big brace on it....

Saying that; Personally I think it's a worth while conversion. You gain a wider (see what I did there) choice of modern tyres and the stiffer swingarm certainly wont harm the handling.... Plus it looks great!

I'm with Honk, the TRX swingarm is an unbraced version of the YZF, or vice versa if you want to be a pedant. Therefore the YZF jobbie will be at least a half kilogram heavier and the wheel is probably a few hundred grams heavier as well. Also the 180 rear tyre will slow down the steering and as it's not necessary due to a severe lack of power, I don't think the conversion is worth it unless you're simply going for the looks and bling factor.

Tyre choice... well Michelin, Bridgestone and Pirelli do 160s and 170s in most of their range with Bridgestone doing a really good all round and track day tyre in the 170/60x17 BT12SS, which when measured across the shoulders is the same width as the original 160 Macadam!

I don't think you'd find much if any difference in handling from the stiffer arm unless you have gusseted the frame, mounted some serious forks and can hold the throttle wide open flat out in fifth with your knee on the ground. The stock arm is pretty stiff to begin with. I chose the YZF wheel only, simply for the tire choice and I've been more than happy. Four hours flat out in an Endurance race and never had a problem with grip. I've also found the wider rear helps you hold a tighter line and with these new generation tires there is little to no change in 'flickability'.

Flipping the REAR sproket around will align the chain.

For what it would cost me to get a YZF arm over here (not many sold in Japan) I would be much better off spending the money on a shock.

Yamaha R1 2000 swingarm conversion. 190 tyre

Dont attempt this conversion. Took too many hours to do right. Altho it does line up correctly and feels much more comfortable than standard.

It is currently ~50mm longer on the wheel base now. Ive also adapted a R1 shock and spring and made custom parts to keep the "spring compression ratio" the same. That was actually the biggest problem. Other than the chain alignment, swingarm offset (yes its offset slightly) changed wheel, thus a new chain pitch and custom sprocket (front and rear). Brake actually bolted straight up to the piston luckily.. But i prefer the trx stock brake over my new R1 brake.

You like polishing then

Was it your hand that went into the tank

But i prefer the trx stock brake over my new R1 brake.

Why?

R1 swingarm is 12mm wider (completed with pivot pin and covers) than a trx, thus, the frame mount where it bolts in needed to be widened accordingly.

Spring/shock mounts are different, so needed to adapt accordingly (R1 eye-eye, trx uses yoke style)

bottom wishbone is too short (R1 and trx) and needed to fabricate a new one, i still have drawings for this.. From memory i made it 190mm centres.. id need to double check that.

Rear pivot triangle was off on the ratio. Meaning when everything was mounted, the spring is "tuned" (factory) for a "if wheel axle moves up X ammount, i move up 1/5 of X" so i needed to make a new pivot knuckle for this part.

TRX wheel does actually fit in. Disk brake is out of allignment and wheel is offset by 13mm to the chain side. I could have compensated, but instead opted to go for the whole R1 rear wheel aswell for the larger tyre.

Sprocket selection for the R1 wheel is limited. Let me explain. It uses a 520 pitch chain, while the TRX uses 525 (memory) size. Thus, i needed to go from a 110 link 525 to a 134 link 520. The chain is actually ~400g lighter. I also went from a 17t/39t combo to a 17t/42t combo. Ive done this for the "responsive" aspect as my only local riding track (theres only one in the state where i live) is a short tight track which prefers more punchy gears.

Front sprocket needed to be "dished" to space it out to fit. I did this by getting my old sprocket and cutting off all the teeth, and most of the diameter so i was left with a big washer with the drive spline in the centre. I then aligned the new gear and the old one, welded them together, put it all in the lathe, cut the old gear so it was thinner. Then bored out part of the new one so i can still get the lock nut and lock washer to fit while maintaining chain alignment.

because of the new larger rear sprocket, the big bolt in frame section, that the swingarm bolts to, needed to be machined so the chain had clearance and didnt rub nor make any noise.

Under load (accel) the chain will naturally bend INTO the swingarm, and under braking it will straighten up, this was also a slight issue, but so far no problems or tell-tale "gash" marks on the swingarm..

Imagine it as being a plate / saucer previously, now it looks more like a bowl shape.. If that makes sence.

In the polished pic, please note there is a TRX polished wheel there. I still have a set (with tyres) of TRX polished wheels that is 100% useless to me now.. I actually gave them away to someone.

After riding a 190 tyre, i know that 180 is more sensible. Ive noticed the bike is more stable at higher speeds (200km/h) and i believe it is for 2 reasons:
longer wheel base
new forks / front end

Only thing that "slows" steering in my opinion, is not setting your steering damper correctly.

Anything else you would like to know ?

PS: i have a photo archive of most of the work ive done.. I do all the work myself, and it has been done over a 7 week period.. I first rode it in the last week of december.

There is still much more to do. But i have it in a "ridable" condition.



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EDIT
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My tank is non dented, it just bad lighting / photography on my part.



In an "almost finished" state.. Getting suspension set, and was waiting on braided brake lines to be delivered. Few other odds n sods.

IM sorry, to answer your question originally:

R1 brake feels like im using a wooden disk.. Its a "race" brake and isnt ment for "stopping" as much as really "controlling cornering speed".

TRX brake was very definate and responsive (i rebuild every mechanical thing i get. Soon as i got my bike (4yo, 30,000km daily rider) i did brakes, lines, forks, new tyres, all seals, etc)

I was able to control corner speed on a track much easier than with my new R1 brake.. Saying this, i dont currently have a braided line on the rear. This isnt to say the R1 brake ISNT good. Some ppl want this aspect to be able to "ride the brake" and not wash off speed in a corner. Its just something im not used to. Its all personal.

What a bike...you must have been a blur in the workshop to achieve all that in 7 weeks!

You ride it daily and keep it looking like that?? I'm assuming you live somwehere they don;t use salt on the roads in winter



G

winter is never below 25degC..

Within that 7 weeks was finding out about things i overlooked. If you provide me the parts, or you want me to source them, and allow some time.. 2 weeks and i can have it fitted as you see now (please exclude polishing time, and a few other tweaks you cant actually see).

Cluster is about to get a revamp. Note that the R1 wheel DOESNT drive speedo anymore. And double bubble screen, steering damper, few other custom things.

Ill possibly post some pics on new dash if / when i can get on a computer. Im more worried about family and riding rather than posting pics.

Sorry if i sound a bit obnoxious, im not trying too.. Could be im lost in english.

Lost in English? You must be from Queensland...

Seriously though, welcome to the forum and where are you located?

heh. im not a banana bender.

stop stalking me.

This was my 1st attempt.. It was mearly a challenge for me to see what i could come up with




I only did this to sus out how solid it could be made and how much space i had in the rear.

It does fit and if anything its possibly too stiff.. Letting the tyre down 2psi would be optimal, or the usual 5psi difference for track would work well. (cold tyre should be 5psi less than a hot tyre straight after a session, IF you dont have a tyre warmer.. helps you get balance)

I made this in a little over a day for fun.

Nice welds!

What's a tire warmer, btw?

I'm jealous of anyobne who can weld aluminium...

How about posting a 'Beginners Guide' for me !!

G