125 Pit Bike Wheel Upgrade

Weldangrind · 04-03-2009, 01:40 AM

My son was quickly outgrowing his 125, so I picked up a set of larger wheels that took him from a 12 / 14 combo to 14 / 17.

I found a really aggressive rear tire for the new 14" rim (haven't bothered with something better for the front yet). I also took the opportunity to change the gear ratio from the pathetic 37 / 14 setup (2.64:1). Some searching on the JT website revealed that the bolt pattern on the rear wheel matches the early eighties Suzuki RM50. The only drawback is that the RM50 used a 420 chain instead of a 428, but the new RK 420 chain I installed is not likely to break. Some more searching found a Honda front sprocket that fit the countershaft and converted it to 420 to match the new rear. He now has a 45 / 12 setup (3.75:1), and it will climb anything! That little 125 is unstoppable. There was a trade-off in top end speed, but I don't want my fearless 14 year old rocketing through the trails anyway. Hill climbing power is way more important. The 45 tooth rear sprocket is the absolute outer limit within the design of the chain guide. We're leaving it alone now.

I had to trim off the stud that locates the rear brake caliper and weld a new one in that allows the wheel to be adjusted further back. The new aggressive knobby barely clears the swingarm.

This photo shows the new wheels; the larger front rim is the most obvious difference. The only other mod that was needed was to trim 1/2" from the lip of the skidplate and bend it slightly up towards the valve cap for front tire clearance. This photo doesn't show the modified skidplate.

Weldangrind · 06-24-2009, 12:54 AM

Hey NoName,

This is what the crummy number plate used to look like. The new Konker plate you have now is alot cooler.

Cheers!

TurboT · 06-24-2009, 03:32 AM

Gio does make a nice looking MX bike.

Good job!

What does your boy have now, Weldandgrind?

Weldangrind · 06-24-2009, 10:23 AM

For awhile he'll ride my old PE175 Suzuki. He's light enough (even at 6') that the PE will haul him up any hill he wants to climb.

He has a little cash, and he's trying to decide if he wants a better bike or a pick-up.

04-03-2009, 01:40 AM	#1
Weldangrind Join Date: Mar 2009 Location: Sardis, BC, Canada Posts: 25,977	125 Pit Bike Wheel Upgrade My son was quickly outgrowing his 125, so I picked up a set of larger wheels that took him from a 12 / 14 combo to 14 / 17. I found a really aggressive rear tire for the new 14" rim (haven't bothered with something better for the front yet). I also took the opportunity to change the gear ratio from the pathetic 37 / 14 setup (2.64:1). Some searching on the JT website revealed that the bolt pattern on the rear wheel matches the early eighties Suzuki RM50. The only drawback is that the RM50 used a 420 chain instead of a 428, but the new RK 420 chain I installed is not likely to break. Some more searching found a Honda front sprocket that fit the countershaft and converted it to 420 to match the new rear. He now has a 45 / 12 setup (3.75:1), and it will climb anything! That little 125 is unstoppable. There was a trade-off in top end speed, but I don't want my fearless 14 year old rocketing through the trails anyway. Hill climbing power is way more important. The 45 tooth rear sprocket is the absolute outer limit within the design of the chain guide. We're leaving it alone now. I had to trim off the stud that locates the rear brake caliper and weld a new one in that allows the wheel to be adjusted further back. The new aggressive knobby barely clears the swingarm. This photo shows the new wheels; the larger front rim is the most obvious difference. The only other mod that was needed was to trim 1/2" from the lip of the skidplate and bend it slightly up towards the valve cap for front tire clearance. This photo doesn't show the modified skidplate. __________________ Weldangrind "I figure I'm well-prepared for coping with a bike that comes from the factory with unresolved issues and that rewards the self-reliant owner." - Buccaneer
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06-24-2009, 12:54 AM	#2
Weldangrind Join Date: Mar 2009 Location: Sardis, BC, Canada Posts: 25,977	Hey NoName, This is what the crummy number plate used to look like. The new Konker plate you have now is alot cooler. Cheers! __________________ Weldangrind "I figure I'm well-prepared for coping with a bike that comes from the factory with unresolved issues and that rewards the self-reliant owner." - Buccaneer
	0

06-24-2009, 10:23 AM	#4
Weldangrind Join Date: Mar 2009 Location: Sardis, BC, Canada Posts: 25,977	For awhile he'll ride my old PE175 Suzuki. He's light enough (even at 6') that the PE will haul him up any hill he wants to climb. He has a little cash, and he's trying to decide if he wants a better bike or a pick-up. __________________ Weldangrind "I figure I'm well-prepared for coping with a bike that comes from the factory with unresolved issues and that rewards the self-reliant owner." - Buccaneer
	0

06-24-2009, 03:32 AM	#3
TurboT Join Date: Sep 2008 Location: Surrey, B.C., Canada Posts: 2,185	Gio does make a nice looking MX bike. Good job! What does your boy have now, Weldandgrind?
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