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lowmass

18' 450 sxf sprocket size vs chain adjustment

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Posted (edited)

So I would like a bit more thrust/ faster tach,  through low- mid range  than stock so I bought a 49 tooth rear sprocket. stock is 48

2 problems

1- with this gearing you have to run a bit longer chain and the rear wheel ends up so far back on swing arm that there is only about 1/16-1/8 inch of adjustment left. Once the chain wears in a bit there might be one , maybe two adjustments, then its throw chain away and get a new one. Ouch. Is this why KTM made the adjustment slots longer on newer models?

2- not sure yet as I haven't ridden BUT this is almost a 1/2- 3/4 inch change in wheel base ( longer). Will be interesting to see how this effects handling as suspension is dialed in with rear wheel in mid area of adjustment slot, and this chassis is critical of SAG. 

 

Anyone have experience here?  I suspect a 50 tooth would give a bit more adjustment range BUT I also suspect 2 teeth on rear would be too much. I like the stock gearing but its a bit less responsive than I like down there.

A "1/2" link would put wheel in right place BUT I havent seen those used in decades and I use O ring chains so maybe even harder to find?

I have a 2 stroke air filter cage ( no screen) to try, and will cut some holes in air box cover. maybe that with the stock gearing will do it?? 

Edited by lowmass

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Faster turn throttle cam and aggressive map ?

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Posted (edited)

tryed larger throttle cam but no change. Apparently I dont have a problem turning wrist.   Its more to do with way it builds power. Its just a tad slow to go through the low - mid

The "aggressive" map helps just a bit BUT not quite what looking for.

 

Edited by lowmass

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If you like the rear a little further forward you can turn the axle blocks around. I did this to get the rear wheel in a more neutral position when I made the jump to 49T

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Posted (edited)
1 hour ago, BDubb106 said:

If you like the rear a little further forward you can turn the axle blocks around. I did this to get the rear wheel in a more neutral position when I made the jump to 49T

Im confused by this. the distance the axle needs to be to get proper chain tension is a fixed position based on chain length. anything that changes the axle position changes chain tension???

 

OR are you saying theirs extra room in the axle slot in forward direction when blocks turned that will allow use of standard chain length with 49T ?

Edited by lowmass

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I feel that if you are finding that 1/2" one way or another from your axle position "sweet spot" gives you grief, you may be a bit more sensitive to bike setup than most . If anything, just go slightly long to begin with and then pull a link after the initial stretch... Should get you ballpark, no? Also fwiw, I was running a 50t to get more pull off the bottom but felt I ran through each gear a little quick so I recently switched to a 49t & am much happier with it.

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Posted (edited)

yea the 49 seemed the right guess, will see. I like the stock gearing but as said just a tad more response would be good

The plan was to remove some links after initial wear in BUT it is sooo tight all the way forward, AND sooo little adjustment left going rear ward with longer chain needed for 49T , that I suspect will have to run chain ridiculous loose for a while till wore in enough to remove links and goto forward position.

 

 

 

Edited by lowmass
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2 hours ago, lowmass said:

Im confused by this. the distance the axle needs to be to get proper chain tension is a fixed position based on chain length. anything that changes the axle position changes chain tension???

 

OR are you saying theirs extra room in the axle slot in forward direction when blocks turned that will allow use of standard chain length with 49T ?

Correct... I think I may have said it backwards. I am confused now... lol. I will have a peak tonight and post back.

Also, 49T is night and day better than the stock 48. I also tried a 50T. I loved it in the woods (the tighter, the better it worked) and hated it on the track. 

Edited by BDubb106
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Posted (edited)

OK so BDubb made me look a bit stupid ha, yes just turn the axle blocks around.

Went to track yesterday. Only change was 49T rear. As expected it was a small BUT noticeable change. Most noticed was seat bounce stuff and jumps. What was a bit tricky to get right with the 48T ( slower accel), was now easier with 49T. In fact I found myself over jumping quite a bit. Also a bit easier to "save"it in a rut turn where you didn't have quite enough momentum to keep bike pressed against wall.And the 49T didn't run out of steam early, at least not on this track which had some serious speed sections as well as tight twisty. 

Motor "character" really didn't change at all. Its still very linear, But now it will squirt a bit quicker.

plan to try the 2 stroke filter cage and the air box mods next week

That said I was having trouble in corners getting bike to settle and at turn entrance. I struggled to get it to start a carve. Rear wheel is now about 1/4 inch farther forward than it was with 48T so not sure how this effected things. It seemed to want to be more rear wheel steer/ slid .  Will have to sort that out at some point and to be honest I was off a bit that day so unsure. Its possible I wasn't aggressive enough that day to load front well at turn entrance.

But with wheel farther forward there is less weight on front so........more time needed to sort out

Edited by lowmass
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Try 1-2 mm more on the fork in the clamps to load the wheel more

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just rechecked sag. I messed up here , it was at 99 rather than 105.

the trouble I had with front end loading was really more of a front end push freakin me out at turn entrance,   I think? ha

anyway this was likley most of issue . Will see next time out

interesting it seemed a rear wheel bike set up like that. Like you had to get back on the chassis more to balance it out

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If the chain has reached the limit of adjustment and not worn out. Remove a link.

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OK so BDubb made me look a bit stupid ha, yes just turn the axle blocks around.
Went to track yesterday. Only change was 49T rear. As expected it was a small BUT noticeable change. Most noticed was seat bounce stuff and jumps. What was a bit tricky to get right with the 48T ( slower accel), was now easier with 49T. In fact I found myself over jumping quite a bit. Also a bit easier to "save"it in a rut turn where you didn't have quite enough momentum to keep bike pressed against wall.And the 49T didn't run out of steam early, at least not on this track which had some serious speed sections as well as tight twisty. 
Motor "character" really didn't change at all. Its still very linear, But now it will squirt a bit quicker.
plan to try the 2 stroke filter cage and the air box mods next week
That said I was having trouble in corners getting bike to settle and at turn entrance. I struggled to get it to start a carve. Rear wheel is now about 1/4 inch farther forward than it was with 48T so not sure how this effected things. It seemed to want to be more rear wheel steer/ slid .  Will have to sort that out at some point and to be honest I was off a bit that day so unsure. Its possible I wasn't aggressive enough that day to load front well at turn entrance.
But with wheel farther forward there is less weight on front so........more time needed to sort out

Those were my findings exactly with the switch so it is not just you. Give it a ride or two until the chain settles in and you will be able to bump it back a bit. I don’t notice any of those quirks that come from moving the wheel forward anymore.

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just rechecked sag. I messed up here , it was at 99 rather than 105.

the trouble I had with front end loading was really more of a front end push freakin me out at turn entrance,   I think? ha

anyway this was likley most of issue . Will see next time out

interesting it seemed a rear wheel bike set up like that. Like you had to get back on the chassis more to balance it out

I’m a tall guy so I didn’t notice that because my weight is naturally towards the rear. I did however notice the front getting twitchy on really high speed sections with the rear forward. I’ll be interested to hear you thoughts once you get that sag fixed. As I said earlier, I was able to bump the rear back after a ride or two which settled the bike back down for me. It was very uncomfortable for those 2 rides though.

 

If the chain has reached the limit of adjustment and not worn out. Remove a link.

That will move the rear forward even more... which will only make his problems worse.

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The sag difference sounded like the issue

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Ok so reset SAG to 105 and spent some time on home track.

MUCH better ha. No more knife and push at turn entrance. Can ride more aggressively and the overall balance is much better. 

I did notice a bit more stability in choppy fast sections as well. The chassis was more forgiving here with 105 SAG. 

When I first set up this bike I noticed that getting within 1-2 mm of 105 was critical. i dont know how I missed that when I put the 49T sprocket on? Maybe I just didnt do it and thought I did ha.

 

BTW this was a lesson in how our perception can really confuse suspension set up. With the axle moved forward the rear was raised 5mm , and weight bias moved a tic to the rear. This making the front dive too much , BUT, my thoughts were that I couldn't get the front to settle into the turn making me think the front was stiff. Opposites !

Seems what was happening was the front would dive too much when brakes first applied, then I would let up on them before I got chassis settled into turn which allowed front to rise a bit right about when you want it lowest.

 

 

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Hmm, I would have expected you to experience a little twitchy feeling to the front end on really high speed stuff with the rear forward. I know I did. The bike did corner much more precisely though. Took much less input to keep the bike in a rut. Maybe it was in my head after all though. Moving the rear axle back 1/8" after the initial chain break in and all my symptoms were gone. 

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yes it was twitchy with axle forward

and yes once in the rut it followed it well

the problem was at turn entrance and just before. The bike was diving too much. perhaps could have added front compression and or slide tubes down in clamps and to be honest I may try that sometime as having the rear at 100mm SAG gave a noticeable increase in rear absorption ( less ridding the shock bumper).

But this would make an already tall bike even taller. Might be a good setup for a mud day with the extra weight?

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That will move the rear forward even more... which will only make his problems worse.

That was a fix for your throwing new chains away when they reach the end on the adjustment range.

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