Clearance Issues

[Kinetic Analysis]

I'm sure this has been covered, but I'm having some clearance issues on my 390. I put BST wheels on and they are great. Good for 2 seconds. The only problem is now I'm starting to drag the right side T-Rex case cover and the back edge of the belly pan. I'm going to swap out the case cover, but I was wondering if anybody else had suggestions. Dave Moss suggested +3mm in the rear shock height and +1mm in the front which I'm going to do, but the bike turns plenty quick as is...

 

[Formula390]

I'm sure this has been covered, but I'm having some clearance issues on my 390. I put BST wheels on and they are great. Good for 2 seconds. The only problem is now I'm starting to drag the right side T-Rex case cover and the back edge of the belly pan. I'm going to swap out the case cover, but I was wondering if anybody else had suggestions. Dave Moss suggested +3mm in the rear shock height and +1mm in the front which I'm going to do, but the bike turns plenty quick as is...

There are different thoughts on suspension setup, and each rider also has their preferences... but "back in my day" when I was racing, I jacked the rear end up as high as it would go, and lowered the front as low as I could go while I still maintained clearance and straight line stability. Basically I'd drop the front lower and lower and lower until I started to get a high speed wobble at my fastest point on the track (usually just before dropping anchor into T1 and throwing it in to the turn. That gives you your best turn in while still giving you -=*JUST*=- enough stability for your fastest point. I'd usually give myself a LITTLE more margin, just in case I got a good draft (our club raced multiple classes together) and got a pull from one of the bigger bikes going down the straight. That could usually get me a little bit more speed and if I didn't have the chassis setup for it then the draft would end up putting me into the wibbly wobbly zone of things. I just had to have a half thought about turning and the bike would flick in so fast it was shocking, but when you are racing Ultra Lightweight that's what you want. Keeping that bike balanced on the edge of a razor and then fall into the turns. That can freak out somebody who's not expecting it tho... so some riders don't want THAT much geometry... at which point, just raise the front up some, or lower the rear.

 

[simpletty]

I'm sure this has been covered, but I'm having some clearance issues on my 390. I put BST wheels on and they are great. Good for 2 seconds. The only problem is now I'm starting to drag the right side T-Rex case cover and the back edge of the belly pan. I'm going to swap out the case cover, but I was wondering if anybody else had suggestions. Dave Moss suggested +3mm in the rear shock height and +1mm in the front which I'm going to do, but the bike turns plenty quick as is...

View attachment 5024

Ill buy that case cover from ya...

 

[green_bread]

I cant give you exact numbers, but the Dave Moss advice is good advice. Do that, for sure!

Where are your forks in relation to the triple clamp? Are they flush or are the tops of the forks moved down in to the clamp some? What does your rear shock measure, eye to eye, in MM?

 

[Tom]

I dont get it, is this because you can lean mor due to a wider rear tire patch?

Also, if you can comment on how the front tire is affected by the smaller rim width. I've been going between these and the marchesini wheels. The BSTs are way lighter, and the rear is huge, which im assuming allows you to run a much wider rear tire. But the front is almost mountain bike width. Aside from asthetics, would it be possible to run a Marchensini front with the BST rear?

 

[abyzfr6]

Also here.
Rear ohlins-max on length, stock front-flash. 140/70 rear tire.
Going to put front cartridge this week, hope its going to stop.

 

[Formula390]

View attachment 5053
Also here.
Rear ohlins-max on length, stock front-flash. 140/70 rear tire.
Going to put front cartridge this week, hope its going to stop.

The Ohlins can only go as far as 309mm (300mm + 9mm at max extension) which is IMHO still short of where it should be. The JRi shock has 12mm of additional ride height. With running the 140/70 you are getting a little more rear height over the stock 150/60 rear tire size, so that's helping you some. The big problem you are facing here is that the KT303 has always been too short so one of the issues is clearance, and has pretty much always just been a "cost of business" with running the KT303 on the track. You could try to fitting a 150/70, as that would get you a little more ride height over your 140/70. You can also try to raise the front end some. It may also be that you need to step up on your spring size and move up to the next larger spring, and then adjust your damping to account for it. The KT303 has a bit of a bother here as well, as it doesn't have as much range of an effective adjustment range as the JRi has. Not quite as many tire choices, but still some good options are out there in both Race and DOT/Supersport tire sizes.

Full disclosure: I sell and support the JRi shock, and do NOT sell (or even go NEAR) the KT303. The issues I have with the KT303 stem from the problems with the shocks clearance, effective range of damping adjutability, the shim stacks, and the primary seal is the for that. I don't sell anything I don't believe in. I wanted the Ohlins shock for the RC to be a success, but sadly Ohlins chose to build the KT303 to a price point and consider it an entry level budget aftermarket shock. They failed in their initial understanding of the RC market and rider base, and have never revised the design to account for the (ahem) more mature rider base vs the rest of the 300 market which is primarily owned almost in entirety by a younger less experienced demographic. Try hanging out on the Ninja400 forum, just for 5 minutes, and see if your head doesn't start to explode.

 

[abyzfr6]

Matt, thank you for the post. I got the FKS507 front cartridge for the RC390.
I does not fit the RC, it's for the Duke above 2017 model. Damn!

Ive intalled z750 springs and put 80w90 oil in it for now.

 

[hvlmike]

There are different thoughts on suspension setup, and each rider also has their preferences... but "back in my day" when I was racing, I jacked the rear end up as high as it would go, and lowered the front as low as I could go while I still maintained clearance and straight line stability. Basically I'd drop the front lower and lower and lower until I started to get a high speed wobble at my fastest point on the track (usually just before dropping anchor into T1 and throwing it in to the turn. That gives you your best turn in while still giving you -=*JUST*=- enough stability for your fastest point. I'd usually give myself a LITTLE more margin, just in case I got a good draft (our club raced multiple classes together) and got a pull from one of the bigger bikes going down the straight. That could usually get me a little bit more speed and if I didn't have the chassis setup for it then the draft would end up putting me into the wibbly wobbly zone of things. I just had to have a half thought about turning and the bike would flick in so fast it was shocking, but when you are racing Ultra Lightweight that's what you want. Keeping that bike balanced on the edge of a razor and then fall into the turns. That can freak out somebody who's not expecting it tho... so some riders don't want THAT much geometry... at which point, just raise the front up some, or lower the rear.

A couple years ago I bought a Ninja 650 lap record setting race bike from a friend. It was set up the same way! ride height pretty much maxed out on the rear...lower in front...very quick turn in. At the time I thought WTF?..but guess that's how the fast guys do it! lol

 

[Snapcase716]

Hey so,, I just got a 2015 rc390 and it has the kt303 on the rear, I am currently awaiting cartridges for the front but this thing seems a little butched. I know basics of setting static sag and a 25-30mm rear sag height. And usually a little more on the front (30-35?) i can do a basic susp setup for track. Literally watching Dave moss vids! I was wondering tho, because I’ve never considered this, what is the stock ride height supposed to be ? And from what points does it get measured for front and rear? I’m looking for a baseline to start with this bike. I see you’re not a fan of the kt303 but for now it’s what I have. See I noticed my rear has 0 sag it’s super tight and so I started loosening the spring and the whole shock moved which was when I realized I have a ride height adjustment on this bad boy, and the jamb nut for it was loose so who knows where it’s at?! I’m just looking to start at what would be considered a good baseline and go from there? Any help is appreciated,!

 

[yowsaboss]

but "back in my day" when I was racing, I jacked the rear end up as high as it would go, and lowered the front as low as I could go while I still maintained clearance and straight line stability. Basically I'd drop the front lower and lower and lower until I started to get a high speed wobble at my fastest point on the track (usually just before dropping anchor into T1 and throwing it in to the turn. That gives you your best turn in while still giving you -=*JUST*=- enough stability for your fastest point.

Fully agree, that's always been my strategy for small bikes. "Jack it up until it wiggles, then take it back 1/2 turn!"