DRz-400 wide range gearbox

[Westy123]

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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!!
Pictures here -
http://s1224.photobucket.com/albums/...nge%20gearbox/

[topo]

Fantastic mod!

Can i ask how much this has set you back? would love to do this myself, or even just throw a new 5th gear in as an overdrive.

[buggsubique]

Mate, we need more of a write up! And you should consider posting this on ThumperTalk in the DRZ400 forum. I dare say if you put together a kitset option you would sell a few of these around the globe...

Really interested in how you made em.

Again, awesome!

[Padmei]

If you started a business with exchange gearboxes you'd make a fortune. As you know this is the biggest problem with them.
Well done

[timmehpwr]

very interested in finding out more/how much! I spend far too much time in 5th gear even off road

[Westy123]

Mate, we need more of a write up! And you should consider posting this on ThumperTalk in the DRZ400 forum. I dare say if you put together a kitset option you would sell a few of these around the globe...

Really interested in how you made em.

Again, awesome!

Hi already on ThumperTalk for sometime now.

The Bike I use is a E24 which is an Australian version E which is road legal. The engine I used to make wide range was an SM which I built up then switched with the original. I used HC1 cams, SM base gaskets and SM exhaust. I find for Adventure riding this gives me the performance and reliability I need for long distance trips. 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.

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 (I did try to find a local NZ Company but could not find anyone who had the experience or really wanted to do the job) by Novaracing.com . This project took along time to get right with most of the time in the design stage, The overall 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 (this is why just changing top gear for overdrive will not work well). So the extra space is between 2nd to 3rd to 4th. When the gears had been made I went to the factory in the UK 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.

Now at 3,000 RPM in 1st I am doing about 17kph (10.5mph), 6,000 RPM in 5th I am doing about 110kph
(about 70mph).
I paid 1250 GBP pounds (about $NZ2500) as I had to pay for the design (which was the crucial stage) now any further 'one off' sets will be in the region of 960 GBP pounds You might say that is alot of cash but for Adventure riding it really does make the difference to a bike that can now tackle any terrain.

Regards Rob

[Transalper]

Found the Thumpertalk thread.... here