VFR400 NC30 geometry

[Cammo]

Just measured:

My forks measure 475 mm from bottom of triples to axle centre, I have approx 5 mm of fork protruding from the top triple so this is on par with yours.

My swingarm pivot to ground measures 420 mm as the bike sits on the ground, but I've increased the rear ride height be shortening the length of the dog bone link by 5 mm so its a fair bit higher than standard.

Can you measure the distance between the 2 holes on the dog bone link? Stock is 113 mm, shortening to 108 mm (any shorter and it can foul the exhaust) is an effective way to raise the rear but it will increase your shock spring rate a bit.

Edit: my dogbone was actually shortened 8 mm, not 5.

[magg]

405mm swingarm pivot height, 690mm overall length of the assembled fork from the top of the fork tube to the axle centreline.

Also, I have 25mm of front static sag, not 10mm, so the nose of my bike will be lower.

[Bud977]

Thanks Cammo and Magg, that's excellent! So as I suspected, the rear end is too low as my swingarm pivot is 370mm high, compared to your 405-420mm.

I've got to go up 35-50mm. Apparently the linkage ratio is about 3.5:1 so I need to change something by 10-15mm.

I'll check the dogdone length Cammo and advise.

My shock was modified by the previous owner, so I'll have to check the shock length as well.

[Bud977]

I would say the dogbone is 115mm between centres. It's a bit hard to measure on the bike, so I'd say +- 2mm. How did you shorten your dogbone Cammo? Cut and weld?

The shock is about 305mm long when topped out. I read the standard is 310mm, so that could be adding to the problem.

[Cammo]

I would say the dogbone is 115mm between centres. It's a bit hard to measure on the bike, so I'd say +- 2mm. How did you shorten your dogbone Cammo? Cut and weld?

The standard nc30 dogbone length is 113 mm (centre to centre), rvf is 109 mm. To shorten it you just need to weld up the existing holes then drill new ones where you need them (standard and new holes will overlap if you don't weld up the standard hole).

Mine measures 105 mm, any shorter and it might foul on the exhaust.

Doing this would improve your geometry a lot for a track bike.

Have a read through this thread for some good info an pics: viewtopic.php?f=24&t=41759&start=0

[Bud977]

OK, I'll weld up and re-drill the hole in the dogbone. That's easy.

When people talk about changing to the RVF linkage, do they mean just the dogbone/pull arm, or do they mean the triangular rocker, or both?

[28hodge]

TAKEN FROM ANOTHER THREAD

Second thing is that the bush that mounts to the bottom of the shock is solid (the bush doesnt rotate freely inside the rubber section) - the other two bushes in the triangle section rotate freely (with a small amount of resistance) - this probably needs to be replaced right?

This is normal on nc30's, it uses 2 bushes and one solid mount.

RVF400's use a bearing in this mount, it can be fitted to the nc30 linkage if you feel the need.

Basically its better to replace both parts to RVF parts as the RVF triangular section has 3 bearings in it, whereas the nc30's only has 2 bearing and one solid mount.

The push rod/pull arm is a must change in order to help raise the rear, the triangular is a nice addition as its a better part but wont effect the ride height if left, it'll just hinder the operation of the shock a little.

[Bud977]

I see. I'll do the dogbone mod first and see how I go.

[Neosophist]

I see. I'll do the dogbone mod first and see how I go.

Yes that is the main difference, the RC30 and NC35 use a bearing in the lower mount where its a solid rubber block on the 30.

I didnt notice much difference when swapping between them, for the hassle its easier to start with the dogbone.

Your dogbone sounds standrd, must be someething with the rear shock making it low

[Bud977]

I've been working on setting the bike up for a race meeting this weekend. It will be the first thrash in anger for this bike for many a year.

I ended up with a geometry of 25.1° and 98mm of trail. I've found out that these VFRs like a bit of rake.

I achieved this with welding and re-drilling the dogbone to 106mm, fitting Pirelli Supercorsa tyres and this gave a swingarm pivot height of 404mm and a swingarm angle of 11.0°. This is pretty close to your settings Magg.

I have 20mm of static sag at the front and 0mm at the rear. The fork protrusion is 5mm. I can go as far as 24mm, but this was not recommended. I'll check the laden rear sag when I get the bike off the table but I think I'll need to wind off some pre-load.

I changed from a #900 shock spring to an #800 to suit the softer sidewall Pirellis over the stiffer Dunlop slicks.

Well, let's see how it goes over the weekend. It will be a shakedown for the bike after a big clean up, so hopefully it hangs in there and I can fine tune it as I go.

Thanks for all your replies. I'm sure the bike is a lot closer to a good set-up with all your advice and suggestions. That saves a lot of time at the track, and increases the fun factor.