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DRz-400 Wide Range Gearbox

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Using the Suzuki DRz-400 as an Adventure bike has one major frustration for me and that is the five-speed gearbox. Well, not the gearbox as such, but the closeness of the ratios. If the bike is geared for tight or difficult terrain then a comfortable touring speed in open going sees the engine revving harder than I like for longevity. Conversely, if it’s geared for cruising at moderate revs, then first gear is too high for easy riding in tricky terrain and the clutch risks being punished..

The standard Suzuki ratios are: 1st gear = 14:32 (0.44), 2nd gear = 15:26 (0.58), 3rd gear = 16:22 (0.73), 4th gear = 22:24 (0.92), and 5th gear = 22:19 (1.16). A calculation shows that the steps between the ratios is (approximately) 24%, 20%, 20%, 20%, which are unusual spacings – generally the gaps are closer in the higher gears, due to the importance of maintaining revs nearer the bike’s peak torque because of increasing drag . While it is true that wind resistance increases with the square of increasing speed, the power needed to overcome that resistance increases with the cube. The new ratios that I have had made, installed and tested are: 1st gear = 14:32 (0.44), 2nd gear = 19:29 (0.66), 3rd gear = 23:24 (0.96), 4th gear = 29:24 (1.21), and 5th gear = 28:20 (1.40). They have much more useable steps of (approximately) 33%, 31%, 23%, 13%.

Its first outing on a steeply rutted clay track proved that the wide ratio gearbox feels normal in its operation, allowing the 400 to climb rough hills without distress, lugging, or clutch slipping to maintain revs. Later, on the sealed country roads the DRz cruised along at relaxed revs in top gear yet still had sufficient torque on hand for decent acceleration. So a great result and a transformed bike for ADVriding!!

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keep going... sounds very interesting as few have toyed with the idea in the past. so what are the costs involved and so on???

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My 9 (original shaft with first gear and 9 new gears were made. 8 as 2nd to 5th sets and one first gear as the dogs on this gear also had to be changed) new gears were designed and manufactured in the UK by Novaracing.com . This project took along time to get right with most of the time in the design stage, The gear ratios were modeled on a STD Honda XR650 which has about the widest ratio of any Dual Sport bike. For the Suzuki the torque of the DRz engine, crankcase clearance, dog requirements, pitting considerations and what the bike will be used for all came into play. 1st and 2nd need to be a reason space but not to much otherwise when going up a steep climb and wanting to go from 1st the 2nd the jump is not to much for the engine to take it. The same from 4th to 5th, if you are on the road with a head wind or up hill or both these gears have to be a reasonable jump so the engine does not die. So the extra space is between 2nd to 3rd to 4th. When the gears had been made I went to the factory and tested by hand that all gears were selectable and no clearance issues, of course the real test is on the road which fortunately all went very well.

Iam now running 13/43, in first gear at 3,000RPM I am doing 10.5 MPH (17KPH) at 6,000RPM in 5th I am running at 70MPH (110KPH).

With regards to cost for this one of project I paid for the design and production. The total cost was 1250GBP in the UK. I was told further gear sets would be in the order of 800GBP per set.

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Hi, I did take pictures but dont know how to post them here. If you have an email address I can send them. Nova have been making gears for 20 years and for some of the top race teams in Europe, obviously time will tell but they have a very good reputation for quality.

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Very nice.. Pardon me if I sound stupid but what's 800gpb work out to be in American dollars?

So your saying it still has grunt for low end torque and wheelies and up hills in dirt and tight areas but also revs less on highway then a stock drz would?

If that's true then these should sell themselves correct?

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That is a great idea. I wish my bike has the transmission you now have. I have always been a fan of the old trail bikes with the dual range transmission.

Would you be so kind as to post or PM me the specs of the gears you made? I am hoping I could have a local machine shop duplicate your project.

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800 UK Pounds (GPB) is about 1250USD.

Yes correct depending on what you want to use the bike for the gear ratios are great and cover most situations but not racing as the original 'close ratio' box is better.

The ratios are in the original posting above that’s all I have the UK designer has the drawings and dimensions.

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I looked at the LTZ but it is a completly different gearbox with reverse! The crankcase is also different so it wont fit straight in to bike frame.

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800 UK Pounds (GPB) is about 1250USD.

Yes correct depending on what you want to use the bike for the gear ratios are great and cover most situations but not racing as the original 'close ratio' box is better.

The ratios are in the original posting above that’s all I have the UK designer has the drawings and dimensions.

Bob

What model DRZ do you have and have you done any mods to the bore/cams/carb/pipe etc.

Just wondering how much hp you're producing since the ratios you copied came from a bike(XR650) with ~45hp out of the box.

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The Bike I use is a E24 which is an Australian version, this is a full E version which is road legal. The engine I used to make wide range was an SM which I built up then switched with the original. As far as I know all the DR-z400 crankcases and transmissions are the same (this does not include the LRZ quad). It was necessary to lightly relieve the casting for the shift fork boss in the right crankcase and a radius was ground into two of the shift forks, to allow clearance for the new gears. No other mods necessary.

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Hopefully here are 7 pictures of the gearbox.

http://photobucket.com/DRz400WR

The first 2 pictures (1-2) are the new gears in one side of the the case.

GB6.jpg

GB5.jpg

The second 2 pictures (3-4) show the small amount of metal removed from one seletor post mount to clear the bigger gear.

GB4.jpg

GB3.jpg

The third 2 pictures 5-6) are the shafts with old and new gears.

GB2.jpg

GB1.jpg

Last picture is an example of one selector that was ground to clear the bigger gear.

GB7.jpg

Edited by Bobwest
added pics

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The Bike I use is a E24 which is an Australian version, this is a full E version which is road legal. The engine I used to make wide range was an SM which I built up then switched with the original. As far as I know all the DR-z400 crankcases and transmissions are the same (this does not include the LRZ quad). It was necessary to lightly relieve the casting for the shift fork boss in the right crankcase and a radius was ground into two of the shift forks, to allow clearance for the new gears. No other mods necessary.

Ok, sounds good

Did you use the E cams in the SM motor ?

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