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Makotosun

More straight line speed

  • AnthandEmma
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More straight line speed was created by AnthandEmma

I need to change worn sprockets and chain on my Yamaha LT2 1972 and looking for more straight-line speed. Currently in top gear & looking for more gears at 40mph!
currently fitted is 14 teeth front sprocket and 49 teeth on rear with a 112 link chain.
what would be best to achieve more speed but not create a problem pulling away.
I am looking at JT sprockets so have options but also looking at a kit that has +2 teeth on front but-4 teeth on rear. Will this achieve my goal or is there a better configuration?
thanks in advance
18 Jun 2021 00:35 #1

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Replied by RT325 on topic More straight line speed

+2 front & -4 rear sounds radical but pulling away from a standstill will never be a problem no mater what--within reason. Main thing is to 'not' overdo it or it'll go slower. Trial & error if not too expensive for what you have planned. Does sound very undergeared though if ya looking for another gear. I'd do it. Worst case is it'll go faster in 4th, but be great on downhills or tail wind.
There's an RX115 piston available @54mm, two mm bigger than yours. I've often wondered if they'd fit but realy need one to compare gudgeon height & stuff. I have an LS3 which is pretty much the road version of an LT2 so i might experiment oneday. They have a good center plug head too, so easy to spin in the lathe to up the compression a bit. Here's a random pic of one.
www.aliexpress.com/item/32600417585.html
 
Last edit: 18 Jun 2021 02:14 by RT325.
18 Jun 2021 02:11 #2

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Replied by Swoop56 on topic More straight line speed

Yamaha produced 15 T and 16 T front sprockets . I'd be tempted to try 15 on the front first .
It's not going to be a " night and day " difference , but there is a limit to how much you
can raise the gearing before you start actually going slower .
The following user(s) Liked this Post: MarkT
18 Jun 2021 04:55 #3

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Replied by MarkT on topic More straight line speed

That's stock gearing and Yamaha rates that model to have an (optimistic) 58 mph top speed. 

So something isn't right.  Speedos get gummed up and read low sometimes.  There are apps you can use with a cell phone to use it as a GPS speedometer to verify your speed.

Or it's a small engine and maybe you're just not used to winding it out?  They don't have a lot of power so if you just don't like cruising with the revs up you might just need to get used to it?  Going to taller gearing might be a mistake as you might find yourself downshifting at every little rise in the road and not being able to reach top speed anymore.
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
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18 Jun 2021 05:50 #4

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Replied by apex on topic More straight line speed

+1 on Mark T's comment. I went a little to far in gearing trying to get a higher cruising speed for my kid's AT2 125, and ended up spending too much time in 4th anyway due to wind & any slight road rise. 
Allrighty Then
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18 Jun 2021 11:39 #5

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