Very long story how I got here but have R4J frame and 5K swing arm and rear caliper/holder. There is no lug to attach rear brake torque arm above the swing arm pivot on frame but there does seem to be one below. so looking for a setup to mount caliper below swing arm. Was thinking of an RS125 caliper, holder and torque arm. Is there something that will work?

Alternatively would it be easier to just get the R4J swing arm. I do have the caliper carrier that fits that swingarm, but i think the caliper itself is different but should not be hard to find. Is the 5K swingarm noticeably stronger for racetrack use with slicks?

Short and easy answer is to source a 1988 swingarm.

Whatever else you do is obviously going to require some form of fabrication. Depending on the condition/use of your bike, I'd consider welding a lug on the frame for the R5K torque arm. In standard form I would say the 1989 swingarm is indeed stiffer than the 1988.

The 88 swingarm was modified for F3 by welding in 4 gussets around the shock cavity, to strengthen it. (The 89 got a new swingarm with enlarged cast section.)


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Thanks Andy. That is helpful.

If you do go for the Rs125 caliper you will have to weld a lug on the bottom of the arm for the torque arm, done this on a 21, Dan at Gecko imports use to sell the conversion kit, but don't think he does any more, Tyga do an under caliper mount for the 21, but not sure if they do for the 18 models, might be worth an enquiry. But as Andy said might be easier to get another swing arm, I wouldn't have thought 18 arms were going to cost an arm and a leg. ps, RS250 nf5 calipers are the same as 125.
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Thanks Les.

supplementary question: are the R4J and R5K rear calipers interchangeable? I know they have different part numbers. the R5K does not look like it will fit on the R4J carrier.

No, the calipers are different. You will need an 88 caliper for the 88 carrier.
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grrrr. Not what i wanted to hear but thanks a ton Andy.

tleighbell wrote:
grrrr. Not what i wanted to hear but thanks a ton Andy.

Weld a lug on the frame for the R5K torque arm then!
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Yeah, except my guy who is doing the work for me is concerned it may not clear the tire. Using a 165/55 Dunlop slick. I would think it must be possible to shift the torque arm outwards enough to clear the tire, yes?

To be honest, I don't know. I've never seen the point of slicks on an NSR, so never tried it, especially when Supercorsas are available in 110 & 150 sizes. However, I'm not very fast, so they're more than capable of out-performing me! I can't see any problem with spacing the torque arm out a few mm though. You won't know until you offer it all up though.

You'll probably find the chain interfering with the tyre is more of a problem than the tyre touching the torque arm, when squeezing an oversized tyre onto an narrow NSR rim. I've seen MC21s with marred 165 slicks before.

Just saying too, we ran Supercorsas on the NSR500s too, and never had anyone complain. Well, John McGuinness did comment that the rear on one of them needed replacing, but he has the qualifications to!




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LOL thanks again Andy. good points. I am certain to be slower than you so maybe supercorsas will solve all problems.

Been doing trackdays for years on NSR's and never found the need for slicks, always used supercorsas, the trouble with slicks, unless you are a reasonably fast club racer at least, you wont be able to keep enough heat in them to perform properly. Even my son who was a national and international racer doesn't even bother with them when he takes my RS250 out for a spin occasionly.
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Thinking about it, I seem to recall even Racer38's NF5 had a little bit of marring on his rear slick. I think it's very tight, even on the RS, let alone the NSR.

If slicks are your thing, by all means go for it. But I reckon you'd be surprised by the Pirellis. The first time we wheeled the NSR500Vs out with them people laughed. They soon changed their tune though!

*Disclaimer time: I just thought... I'm not sure if you have an 18" rear wheel still, or changed/changing to 17". I don't think there's an 18" Supercorsa available. In fact, I am certain there isn't. Sorry.
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Thanks Andy and Les. Not married to slicks, i am certainly not faster than you or your offspring. Plus i would prefer to use the right sized tires. and yes, i do have the 17" rear wheel so no problem.

Thanks again both, really appreciate all your input.

No, really, my ambition far outweighs my talent! I was OK-ish a few years back, but a lack of seat time over recent years has knocked me back a long way.

My claim to fame however, is when at the Rockingham track briefing the instructor asked "has anyone not been here before? Has anyone not done a track day before?". I was the only one who put my hand up (it was an invitation event, so everyone else there was seasoned!), and he asked what I was riding... "an NSR500". Caused a bit of stir!
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