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Nunn shall pass
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Discussion Starter · #1 ·
A long shot, I know, but it's worth a crack...

I'm looking for a formula to determine what change in wheelbase a sprocket size change will give me. I know I can fit sprockets and measure, but a) the bike is not stored at my house, and b) I don't yet own all of the possible sprocket combinations, and don't want to waste money on stuff I may not need. As for why...

I've taken to using the Pirelli 180/60 slicks on my 08 R6, but find that the 15/46 sprocket combination, which is pretty much perfect for Assen with these tyres, means my chain is either too short to allow the warmers to fit between the tyre and top of the swing arm, or too long with the added links. I'm looking at mixing up the gearing using a 16/48, or even a 17/52 if needed. The added benefit of being able to work this out in advance will be when I visit other circuits, I can find the right gearing without having to increase or decrease the wheelbase too much.

With the two extra chain links in now to fit the 180/60 rear, the bike feels a lot harder to turn. The front is already pretty low, and I'm scraping my toes in at least three corners, so not keen to lower any further (scraping your toe in the 200+km/h Hoge Heide corner is interesting...)

Any help would be appreciated
 

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From what I have heard direct from a couple crew chiefs mouths was wheelbase isnt a huge factor to sweat on those bikes (2008+). Most prefer it slightly longer for stability. If you notice 1-1.5" wheelbase then you have something wrong elsewhere. Even at the swingarm max the axle to axle measurement is ~55.5"
 

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If you add a tooth you're looking at about a 10-20mm difference. It all really depends on how tight your chain is, if it's new (will stretch), and if you also plan to adjust your rear shock height as well. But there isn't much of a set formula to go by because there are so many factors that can affect the adjustment of the chain length/tightness.

I run between a 15/49 at the short tracks and a 16/47 for Road America which equates to a 1 tooth difference. I can definitely feel the difference in turn-in and mid corner stability but it isn't necessarily drastic. If you're comfortable with the wheel base you currently have then just choose whatever sprocket set you prefer and add a link to the chain for every tooth that is added overall.
 

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Nunn shall pass
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Discussion Starter · #4 ·
Cool, thanks for the tips. Even just knowing that it's 10 to 20mm per tooth is helpful. I tried running a 47 tooth rear for a while, and think I could feel a difference in turn in, so will do some sums to see what I can do.

I think ride height needs to be looked at as well. My pegs are as high as they go, and I'm scraping my toes in some corners. This isn't great when one of those corners is the 5th gear Hoge Heide. I probably need to hang off the bike a bit more, but we'll see...

I'll report back on progress, although it could be a while - winter is coming
 

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Nunn shall pass
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Discussion Starter · #6 ·
This site may have what you're looking for....

http://www.gearingcommander.com/
Well, I'm a ****ing idiot. Have been looking at that site since Friday working on sprocket combinations, and didn't think to look if it has such a feature. Which, of course, it does. And, I've been using the site on and off for years. Duh, gee George!

Thanks for pointing it out to me :)
 

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Go fast or die slow.
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180/60 rear is heavyer then the 180/55, but it should balance out by beeing a taller and sharper profiled tyre.

Why are you continuing to lower it? To make the bike easyer to turn?
Are you using the full fork travel?
If not,
Are you running more oil then 103mm with the oem cartridge? If so, take it down to 103mm again.
If the forks are stock

Check your compression settings and soften it.
The more travel you use the sharper your steering angle will be and it makes for a quicker turn in.

Check your rebound adjustments also, thighting it by a few clicks will make the bike want to turn in with more ease as the frontend wont bounce back at you as fast.


If you use the stock shock it not much you can do about adjusting the ride hight, you can add shims to the top mount.
You can also adjust the ridehight with adding more preload on the spring.


Another thing you change when you move the rear wheel is the ride hight, this will also alter how the bike feels into and out of corners.

The further back the rear wheel is, the taler the rear ridehight will be.
 

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Seen this discussed by a graves suspension tech in graves' forum before. They change gearing sometimes for handling purposes.
 

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Nunn shall pass
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Discussion Starter · #9 ·
Locci, thanks for the tips, I'll take what you say into account. I'm not trying to lower either end, I'm just trying to shorten the wheelbase as best I can. Ideally, I need both ends higher, to deal with the previously noted scraping of toes in fast and slow corners - turn 1 at Assen (Haarbocht) in particular is where I need to fix this, as it's affecting my confidence.

In the end, my goal is to have as fast a turning bike as I can. Last time I rode at Assen, I worked my arse off for some very average times. Much of that is down to a lack of testicular fortitude under brakes and corner speed, but some of it is due to having to work hard to turn the bike. A suspension tech session would probably help, but I'm still far too slow for suspension tweaking to make much of a difference, what I'm trying to fix here is a heavy feeling bike, not find that 1 or 2 seconds that keep me from the front (more like 10 at the moment!).

Oh, and I found one minor area of improvement last time out - I backed off the steering damper a bit. I normally have it pretty stiff, an old habit from my 400 racing days at Broadford in Aus. I tried backing off as far as I could, and found it a little easier to turn. But I still worked hard.

Appreciate the comments, keep 'em coming!
 

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Scraping toes says to me you need to put them up on the pegs more. Could just be a bad foot position you e become used to. Plenty of guys can almost elbow drag without touching their toes. Even with non adjustable pegs like woodcraft.

And yes spend the $ for a suspension session. I was amazed how much better a r6 feels with high end suspension set up correctly feels over stock. Night and day.
 

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Discussion Starter · #11 ·
Scraping toes says to me you need to put them up on the pegs more. Could just be a bad foot position you e become used to. Plenty of guys can almost elbow drag without touching their toes. Even with non adjustable pegs like woodcraft.

And yes spend the $ for a suspension session. I was amazed how much better a r6 feels with high end suspension set up correctly feels over stock. Night and day.
I know this is long dead, but it turned up in a search I was running, and I think it's poor form to not follow up on your own posts...

After losing a tooth from third gear at Hockenheim in August, I took the bike to get it fixed. The shop I went to run two R6s at the pointy end of the OW Cup, the amateur competition I race here in the Netherlands, and they were shocked at how badly my suspension was set up. Too much oil in the forks, a and settings all over the place. I got it back and took it to Spa, and it was amazing, the difference was incredible - I'd actually considered giving up as I was not having fun riding, but after a couple of dry sessions, I was back in love with the track, and just loving riding again. Here's the video - note the oil all the way through Eau Rouge :(

https://www.youtube.com/watch?v=AHbO560i-wg
 

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I try to keep my wheelbase as close as possible to the standard chain length from the Gearing commander website. I run the 180/60 tyres and the easiest way I found to work with the bike was to put an extra 2 links into the chain (now 116 links) and I use 16/48 for tracks with long straights like Aragon and 15/48 for shorter tracks like Jerez, Donington, Cadwell Park etc.

By just changing the front sprocket the wheelbase stays virtually the same but I needed the longer chain to accommodate the 160/60 tyre and 48 tooth sprocket.
 
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