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Dveitch8

Bigger front, smaller rear! Sprockets?

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Ive got the stock 13 and a 48 rear my top speeds a little better but 1st sucks will going up a tooth in the front increase the top speed while keeping first closer to stock?(14/50) I want a good combo for tight single track and open fire roads.

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07 with a stock 19" and iam going to replace the chain at the same time, thanks for the answer with the e axle also gray.

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the 48 is a smaller back but now 1st is too high, it seemed that a tooth in the front would make less of a change down low but a bigger difference in say 5th thus widdening the gears but iam not sure, just speculation

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Ive got the stock 13 and a 48 rear my top speeds a little better but 1st sucks will going up a tooth in the front increase the top speed while keeping first closer to stock?(14/50) I want a good combo for tight single track and open fire roads.

The only way to get low gearing for tight single track and still have the bike be very fast on open fire roads would be to get a WR450F with the wide ratio tranny. Since that's not really an option here you will need to compromise a little. If you want to lower your gearing for tight single track then you would need to go with a smaller front or larger rear sprocket. This with increase your secondary reduction ratio. If you want higher gearing for open fire roads you would need to go with a larger front or smaller rear sprocket. This would decrease your secondary ratio. Adding 1 tooth to the front sprocket is about the same as going 3 teeth smaller in the rear. Stock 13/49=3.77 ratio and your current setup 13/48=3.69 ratio.

Gear Ratio Chart

-----12---13--14---15---16---17

40- 3.33 3.08 2.86 2.67 2.50 2.35

41- 3.42 3.15 2.93 2.73 2.56 2.41

42- 3.50 3.23 3.00 2.80 2.63 2.47

43- 3.58 3.31 3.07 2.87 2.69 2.53

44- 3.67 3.38 3.14 2.93 2.75 2.59

45- 3.75 3.46 3.21 3.00 2.81 2.65

46- 3.83 3.54 3.29 3.07 2.88 2.71

47- 3.92 3.62 3.36 3.13 2.94 2.76

48- 4.00 3.69 3.43 3.20 3.00 2.82

49- 4.08 3.77 3.50 3.27 3.06 2.88

50- 4.17 3.85 3.57 3.33 3.13 2.94

51- 4.25 3.92 3.64 3.40 3.19 3.00

52- 4.33 4.00 3.71 3.47 3.25 3.06

53- 4.42 4.08 3.79 3.53 3.31 3.12

2007 YZ450F Gearbox Ratios

Primary Reduction Ratio (2.652)

Secondary Reduction Ratio (3.769) ***with stock 49/13 sprockets

Gear Ratio - 1st Gear (1.929)

Gear Ratio - 2nd Gear (1.533)

Gear Ratio - 3rd Gear (1.278)

Gear Ratio - 4th Gear (1.091)

Gear Ratio - 5th Gear (0.952)

Motorcycle Gearing Worksheet

www.4strokes.com/tech/gearing_calc.xls

You will need Microsoft Excel. Just replace all the numbers in the pink column with the ratios in your bike.

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When you say first is too high, do you mean that it is too much like second or third?

First is a "low" gear, and 5th is a "high" gear. Adding a tooth in the front is like taking 3 off of the back, and makes all of the gears "higher".

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1st is to fast and its more like second and I end up having to clutch it a lot in some of the trails I've been riding lately, but like you said the only real way to solve that would be a wr gearbox, guess I'll just suck it up and deal with having to just kick it down a notch on the fire roads, guess I was just hoping for a magical response that would feed my denial of the situation at hand ( the need for a wide ratio gerabox) :thumbsup: anyone have some recomendations of a happy medium or is the stock ratio the best all around?

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OK, now we're on the same page at least. Your error was in thinking that increasing the front sprocket size would lower the gearing; it would raise it.

You can go to a 52 or 53 on the rear, but it will shorten up 5th gear a little as well. It comes out to about 6 mph less on top to be able to go 0.6 mph slower at 2000 in first. But you might find that it works. Then too, there's nothing wrong with using the clutch.

Another cure for this could be an auto clutch like the Rekluse.

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yeah I was thinking about the autoclutch or maybe even a flywheel weight. I was aware that going bigger in the front would raise the gearing, my idea was instead of going with a smaller rear (48) using a 50 or bigger and then take the front up to say a 14 if this would act like widening the gears but I guess a 13/48 would be the same as a 14/51. just dumb thinking on my part:bonk:

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You should get a heavier flywheel or a weight regardless of what you do with gearing or the clutch. I use the GYT-R offroad (+9 oz) flywheel. makes the engine noticeably smoother at low speeds.

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I want to gear down with and x-ring chain (wider than stock). Any problems going to 12/48 instead of 13/52? In particular, are there any interference problems (x-chain hitting the case) with the 12?

Thanks

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I want to gear down with and x-ring chain (wider than stock). Any problems going to 12/48 instead of 13/52? In particular, are there any interference problems (x-chain hitting the case) with the 12?

Thanks

The 12/48 or 13/52 combo would give you the same 4.0 ratio. I would recommend not running a 12 tooth front sprocket because it will accelerate chain wear and also wear out the swingarm slider faster.

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I would recommend not running a 12 tooth front sprocket because it will accelerate chain wear and also wear out the swingarm slider faster.
...to say nothing of the fact that the 12 tooth sprocket will itself wear faster.

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