Does anybody know how a 17/43 gear ratio would perform on a kdx? There is a company that makes them listed in Dennis Kirk. I know it would give me HUGE top-end speed. But, does anybody know exactly or any info at all on sprockets?
I think anything larger than a 14 or 15 tooth front would interfere with the case and side cover in front of the countershaft. You would definitely have to remove the case guard which could be expensive if you threw the chain. The KDX probably shares the same countershaft splines with some street bike that will fit the 17t, so it is listed in the catalog as fitting a KDX.
Tall gears will only give you huge top speed if your motor has enough power to pull the gearing. Dirt bikes have horrible aerodynamics and KDX's don't make big power, so you might not increase your top speed very much even with a 15 front. IMO, there is no way a stock KDX would rev out in 6th gear with 17/43 gears.
When I had a '90 dual sported KDX200, I would run 14/48 gears on road rides and 12/48 in the woods. The differences were pronounced - tall gearing kills your acceleration when you are riding at normal trail speeds.
Thanks Dirt Bike Dave! I liked your advice. You do make sense. I'm going to do a 15/43 gears instead or maybe 15/45. Could you tell me what size chain I would need?
I would hate to guess wrong on the chain length - sprocket changes certainly make a difference. I'm not sure if taking two teeth off one sprocket and adding two to the other would even things out allowing, you to keep your stock chain length.
I also had a dual sported KDX250 - running a 13t front sprocket allowed me to shorten the chain and wheelbase (that bike needed it) for trail riding. On dual sport rides, I ran a longer chain with a bigger front sprocket (14 or 15 tooth, depending on the ride). With the 14t and longer chain, I had the tire all the way back for additonal stability on the road.
You are talking about making a pretty large change - you might want to just change the front sprocket one or two teeth at first, and see if that is enough. It might save you some money on expensive chains and rear sprockets.
If you are planning on lots of high speed running, it makes sense to lenghten the wheelbase if you can.
dirt bike dave, i don't think i would have to even change the chain because if i did 15/45, then i'm going up 2 on front and down 2 on rear from stock. So, since it's an even change in teeth up front & rear then it shouldn't make a difference.
That is a huge jump in your final drive ratio! Are you asking this cause you want to actually attempt it or just curious if it is possible? I changed one tooth on my C/S sprocket (effectively like changing 3 on the back) and it made a huge difference on my bike, like 10 mph off the top speed. You are effectively wanting to have the effect of changing to a 16 tooth smaller rear sprocket (counting the change in front and back) Im not sure the KDX engine is strong enough to pull that especially on the start. You may end up doing 120 mph, but it will take you 5 minutes to get there. To sum it up, if you want a fast bike, get a fast bike. a KX 500 should have enough speed for you.
wood_rider1, yeah I am just curious if it's possible. But, hey, I really did see it in Dennis Kirk. So, it must fit, and it must perform, but maybe it's strictly desert racing? I have a Pro Circuit pipe on mine. I know FMF makes a Rev/Desert pipe for the kdx, also.
hi im runin a 15/48 with a o-ring chain rk of course well i got fmf fatty pips jetted and modified airbox weisco piston and a la sleeve and it flys pulls wheels throuh 4th gear with just the throttle and the gears dont feel to low like they did with the 13/47