18" -> 17", BT090s -> slicks, suspension and geometry?

[StrayAlien]

Hi all,

Having recently snaffled myself an nice RVF 17" rear, I am keen to give the world of slicks a go.

I have a 94 NC30. 18" rear, stock front. The bike already has the rear suspension 'welded dog-bone' mod where one of the holes in the dog bone is welded up and a new hole created at an offset. I have also snaffled a proper RVF dogbone and linkage in case I need it.

The rear eccentric is near the bottom, so the rear is already quite raised.

Rear shock is a rebuilt stocker and the front forks have had "internal modifications", but are the later model NC30 cartridge ones. They are not lowered in the clamps.

It has lived its life on BT090s I think. The bike feels very well sorted.

I understand a change from road tyres to slicks can often mean suspension changes, and of course the change to 18" to 17" means geometry changes.

As I said, the bike feels well sorted so I am looking for advice on what to expect (if anything) and what to do about it.

If the answer is "don't be concerned", then great. Cool. However, all advice welcome, including preferences of slick.

Greg.

[RonniB]

you will get better grip from the slick, no doubt.

Slicks as you and I can buy, are divided in two categories:

Old school 250GP style slicks, like the 165wide bridgestones and dunlops

Modern 160wide slicks for trackday bikes.

The first kind are very grippy, but require a bit of force to keep heat in them, the second kind are more like a modern sports road tire, just with more grip and slightly longer warm-up

Both really needs warmers, the first kind the most.

When you fit the 17" you will need to restore rideheight on the linkage or shock (if lenght adjustable), don't be tempted to lower the front, it will hurt your front wheel clearence. Save that adjustment for when you feel quicker steering is needed and then only drop the forks up 5-6mm to avoid clearence issues.

Raising the rear is fairly harmless compared the bigger bikes, they have to worry about chain pull effects, but with 60-65bhp, that really isn't much of an issue. And you gain road clearence and a higher CoG which helps to reduce required lean for a given speed a little.

But again, only change geometry if you feel that you need. And only bother with slicks, if you feel you are just about to excede the 090s, if you don't get small slides front and back now, you will only get a mental advantage (but that could be important enough on it's own), because you will not generate enough heat/force to keep the slicks in their optimum range. But upgrading the rear shock to a aftermarket one will give an instant improvement that can be felt, and in turn give you the possibility to use the slicks to their potential.

Ronni

p.s. I like the BT003, great tire, sits between a 090 and a slick performance-wise, a michelin power one or pirelli supercorsa would be almost the same. As for slicks, the pirelli diablo superbike is very good, so is the michelin power one slick (but I only tried them on a 600)

[Cammo]

But again, only change geometry if you feel that you need. And only bother with slicks, if you feel you are just about to excede the 090s, if you don't get small slides front and back now, you will only get a mental advantage (but that could be important enough on it's own)

Good advice.

I ran slicks a couple of times on my racebike and the main advantage I found was the mental edge. Their extra grip gives a wider margin for error and as a result I pushed a fair bit harder than I was comfortable doing with 090's. Plus the fact that I'd always wanted to try them - the grip and feel is pretty amazing.

It's easiest in Oz to get the 250gp slicks (even for 18" rim). The bridgestone 165 slicks are the favourite amongst Oz 400 racers (some use dunlops). The 165 size makes the profile a bit strange on a 4.5" rim but it never bothered me and apparently not many others. I never had any worries keeping them at optimum temp and I'm not uber-fast.

I would leave the geometry as is until you've tried the 17" rear in your current setup.

[StrayAlien]

Thanks guys, great info. I didn't think you could get slicks for these 18" rims (hence getting the RVF 17"). But, as these 090s seems to last so darn long (shouts of joy from the crowd), and I have a fresh new set just arrived, I'll be on the 090s for a bit yet.

Another question though. What cold temp would you run the BO090s at on a dry track at (say) 25c. I use tyre wamers.

[RonniB]

Why bother with cold pressures if you put on warmers? Bridgestone advice that you run their tyres at 34psi hot and with warmers fittet you should have the hottest tyres straight out of the warmers (I know I do, can't really keep them at 70-80c continuesly by riding them. And I found that the road legal tyres, really prefers around 50-60c).

- Put on warmers, leave for at least an hour.
- Check/adjust pressure 5 min before you go out.
- Kit up.
- Turn off warmers, and take them off.
- Ride....
- (When back) Check temp, then pressure, write down.
- Put on warmers, turn on warmers.
- Take your kit off.

That is my usual checklist

But if you really want to know, I have usually set my cold pressures at 29psi front and back..

[StrayAlien]

Thanks,

'Scuse if my question re cold tyres seems a bit naive, but I have often wondered why people use that metric - it seems odd when hot pressures are the ones that matter, but ... I never seem to hear people talking about 'hot' pressure, only 'cold' pressure. Might be the move from discussing stuff for road bikes at the track to discussing races bikes at the track. Lots to learn.

But again, great advice, thank you.

Greg.

[RonniB]

Not naive at all, how would you know! In race paddocks I only ever heard about hot pressures, mostly because it a more or less constant from track to track and in different weather conditions.

Cold pressures varies because people, some unknowingly, are chasing the "constant" hot pressure in different conditions.
Hot pressures are different from make to make, since it's much about the tyre construction and what parameters they are meant to work under; pressure, temp, flexibility and load.

Ronni

[999Gomerz]

Keep your 18 rim for wets. Bridgestone make good wets and in an 18 rear.
For slicks I would suggest bridgestne ycy or metzler k1 motard rear. For the front the metzler k1 is great and well priced. The ntec is good but uses a harder carcass and you will not get enough heat in it and thus will feel vague.
I would not use the bridgestone front. The Metz is the same as a pirelli sc1 but cheaper. The Metz rear will last longer than the bridge and you won't feel any grip difference.
I would use 32-34 hot in the front and 28 in the rear with bridge and 2.2 bar for the Metz (sorry don't know imp conversion for this one. I use metric gauge for bike) check tyre pressure before leaving and as soon as possible when return. You are looking for the front to maintain the same pressure and the rear to gain a few psi. If it is to low on return then drop hot pressure for next session. And vice versa.
Re geometry I think your rear is too low and your front too high, try my spare shock. You will like it.
You can get metzler slicks from paul free and bridge stones from mark lemont.

The threaded tyres last forever because there is not as much grip in them kind of like that k2 rear I have that you said I laid a blackey with. That thing will last forever but doesn't have grip on the little 400.