new gearing possible or not

Well over my time of riding this XJ of mine i come to know that cursing along at 65 is easy. But it saddens me that i haf to be just shy of 5,000RPM's to do it. i know not all bikes do this my dad's harley runs about 2k rpms and my last yamaha also ran about 4k rpm's


I mean are we stuck running thease high rpm's i know that we are getting good gasmilage and it makes quick acceleration. but who can auchely say that with their 750 theay haf to use the throttel to get up to 25mph or even 65mph

so to make this short is their a way to make my bike run lower rpm's at 65mph in 5th gear.



a littel deaper i know that if i can lower the gearing then i will loose acceleration but i cant use all my throttel now on take off or the bike will flip or break loose. i also know that the spedo is run off the front tire so i wouldent haf to change the gearing in the spedo.

 

That is what this bike was designed to do... and honestly I don't find the throttle position changes the gas mileage all that much.

I've run my bike on the highway at much higher RPMs for hours straight. Put it to you this way. I did 1300km in 12 hours requiring 9 gas stops. The bike burned a tiny bit of oil and made it happily. I certainly was above 65mph for almost all of that trip.

I think you can do it - but you're talking about splitting the case and swapping gear pairs... this isn't a nice easy project like on the cassette type transmissions on the newer bikes.

So, while you can do it, I'd be surprised if it was worth it in terms of time and money... if you are interested in doing it then we'd be interested in hearing about it. Maybe someone later can learn from your work and do it faster and more cheapily.

My vote is 'bad idea'...

 

myvote is good idea!

only because i am right t here with you! matter of fact i would even be alright with an entire less agressively geared transmission, (not toomuch mind you) perhaps iwill tackle this next year during my transmissions class.

 

Actually I have been contemplating this same subject. I too, would like to change 5th gear to bring the RPM's down to about 2500 in top gear when I'm running at 65 mph. I know that the bike would suffer on acceleration for passing, but I could just drop a gear, make the pass, then back up to the taller gear for cruising. Not only would the gear increase the economy of the machine, but it would also increase the top-end speed. Am I totally off my rocker here? Or is this possible?

 

My vote also: bad idea

My problem with it is that the bike will probably not have the power to accelerate AT ALL if you change 5th gear that much. Understand that the gears in the transmission are torque multipliers. For example, if first gear is 4:1, then you're multiplying the torque applied by 4. To get to the RPM you want, you'll have to overdrive 5th gear thereby lowering the applied torque. My guess is unless you have one monster of a motor, it won't have enough power to accelerate at all in 5th gear. Doesn't sound like a problem? Think about having to drop a gear everytime you pull up a slight hill. Doesn't sound like fun to me.

Also, the powerband of a Harley is much different than ours, so it's really hard to compare the two. Harley's make most of their power before 4500 rpms, and fall flat on their face by 5700. Our bikes are just STARTING to make good power at 4500. When you have a redline of 9500, a cruise speed of 5k really isn't that bad.

 

Good concept but bad idea. If it were as easy as changing sprockets then I would have done it already but it would be way too much work to do it right. If you are going to try it I would look for a different rear end. You may be able to find another model that has a smaller rear gear. As for top speed, the bike can already go over 100mph so I don’t see the need for a much faster bike.

Let’s remember that our bikes are not V-Twins which are designed to run at a low RPM. I just finished a 1,100 miles long weekend in which 700 of the miles were at 65-75 mph and the bike had no problems. At that speed you can barely hear the engine because of the wind anyways.

 

I'm casting in on both sides. I have done gear swaps on water-cooled VW's but they are setup in a cassett type stack, easy day. The gear box in my 81 650 is stacked as well but there is no support for gear changes other than stock so far as I have found. One could spring the cash for custom gears (technology has come a long way in the past twenty years, anything can be made one-off fairly easily and cheaply, relativily speaking). The problem lies in that the gear swap wouldn't be just one or two gears, you would also have to have the carrier gear on the recieving shaft changed as well since it is shared between two input gears. So three gears would need to be made, expensive and you have to either be an engineer and design your patterns or pay someone to do it for you (more expense). I am unaware of any gears that are a direct swap, but they might just be out there if you are willing to sit down and do the footwork. I would love to drop my rpms in the top end but the close ratio in the lower end is great. Apparently, this split ratio arrangement never crossed anyones mind previously in the design department. They aim at the greatest bulk of the market which is the about town fellow. XJ's really aren't intended to be used for long distance trips but, if you really want to travel with your toy, you take the good with the bad. I used my XJ to run from San Diego to Sacramento and hated the trip, it hurt, and I even had a custom seat and pegs. This is an adventure I hope that someone (not me, I'm too bloody busy right now) will visit and spend some time on to pull out an answer.

 

XJ900 rear end might have slightly taller gearing, but probably not enough to make the swap worthwhile. Considering their low-rev nature, a Virago rear end might be even better for gearing, if they fit.

 

The Virago is set up for the torque of the the V motor and could be a solution. A taller output gear in the rear would make the entire gear box taller gears (which may or may not be desirable). I just don't know enough about the Virago to know if it would fit (got rid of the '83 550 with the ex-wife, whew, glad of it too).

 

Looks like it's a common rear end on the 650/750/900 @ 32/11 ratio.

 

Don't know if it's worth it myself. As stated previously, these bikes are built to work this way.

Changing one thing usually just puts strain on another. Eg Change sprocket sizes puts more strain on clutch at take off.

One thing I've been wondering is whether the XJ550 gearing would drop into a 650 or 750. The 550 has a six speed box but don't know whether the final drive ratio would be that much different in top gear.

Wouldn't mind getting hold of an empty 650/750 case to see if my spare set of 550 gears would fit in.

The pic below shows the stats and gear ratio's of my XJ550. If anyone has the gear ratio's for their bike I'd be interested to see them.

 

Most Virago's I've seen redline close to 9k also...

 

Pity you’re as far away as you are Goon, I'd gladly pull the innards out of my spare 650 (it needs to come apart anyway) to accommodate your whim. I'm curious too; a 550 shouldn't be that hard to find for cheap. I wouldn't mind it if the 6th gear was steeper than the 650/750's 5th but it would be meaningless if the final outputs were the same. I found that in my VW experiences. The water cooled 4 speed had the same final output as the 5 speed, so I stuck with the 4 speed. Fewer shifts (I'm lazy by nature) and less wear on the clutch, better gas mileage too. Back to the topic, I'm curious as well and I'll bet if it is possible, who ever finds out it is possible will be adored for years to come. Any takers?

 

I wonder if one could rebuild the rear hub assemblies internals... a few teeth would make a world of difference.

 

Yeah, I thought about the rear-end too. But I decided that I didn't want to change all of the ratios. Just 5th gear. And I've also decided that if I could get the rpm's down to 3500 at 65 mph, that would probably be close enough. Still working on a possible solution.

 

Changing the gearing to obtain 65mph @3500 RPM IMO would be impossible unless it could be done at the rear end.

I have done some stats on the gear ratio's of a 650 and the only possibility of obtaining that spped at those revs would be to use a reverse of the first gear cogs. Of course, This is impossible as the driven gear of first gear is part of the shaft itself.

Reversing the drive/driven gear of second (given the sprockets would engage with the existing fourth) would only give a speed of 56 mph@3500rpm.

The attached pic shows standard 650 gearing which matches toads claim to 65mph @5000rpm.

 

Given the second gears could be reversed and would mesh with fourth properly the 3500rpm would obtain 56.033mph as shown.

 

And finally. if second cogs (given they meshed)were reversed then to obtain 65mph, 4000rpm would be required.

Now if anybody has looked at the cogs in detail then the chances of any changes would be virtually non existant. Drive and driven gear splines would have to be the same and selector linkage locators would have to be the same.

My guess is the cogs would have to be specially machined to make it work.

Now if someone has that kind of machining experience/contact to trust with their gearbox then they would be everybody' friend. :wink:

Just my opinion but trying to bring some fact into the discussion.

Comments?

 

Completely agree...

If you had to make an rpm change, do a less drastic change to the rear end - each gear will be slightly taller but that won't change the bike much at all - just change the speeds at which you are in the fun part of the engine.

IMHO - Live with it as is - if the cruising RPM in unbearable then save the money you would have spend on this mod, sell the bike, and get something more geared for your taste (pun intended )

 

Hey Goon, do you have one of those calculators for a shaft driven bike? That looks like a pretty cool tool there. Is it available online somewhere?

 

DC,
It's just a program I wrote myself to work out the speed differences when changing sprockets and tyre sizes.

As with the 650 pic above all you have to do is substitute sprockets for number of teeth on the crown and pinion of the shaft drive.

The hardest part is finding the info on the gears in the gearbox. Most of the info I have found was taken from the teeth count on online parts diagrams.

I do have a copy for download if your interested.
http://mop_one.tripod.com/SpeedCalc

 

Thanks Goon,

I download the file, although it doesn't look like it will work for our shafties. Not only do you need to figure the gear ratio of the rearend (32/11),2.909, but then there is the ratio of the:

transmission output (49/36), 1.361 and
middle gear case (19/18 ), 1.055

Maybe if I knew how to write the program, I could modify it. Oh well, I guess I'll have to go "Old School" and write up a program in GWBasic. :lol: Now where on earth did I put basic at on this puter. :?

 

Thanks DC, If I didn't know better I'd think that was a hint. I have been working on incorporating shafty's into the program and now you've provided me with some figures I may get it finished soon.

The figures I used earlier for the 650 should still be accurate as the final ratios have been "tricked" into shaft drive ratios.

But making it work properly can (and will) be done.

Just need to remember how to incorporate those new values into the calculation.

Cheers
HG

 

i was not thinking of changing 5th gear because that would be way to pain staking all thought if properly tuned would be nice to just change 5th i was just wondering if one could change the rear gear off the shaft to what ever gear in the back end to make every gearn run lower rpm's because i dono about your bike's because mine isent stock in 5th gear i can go up a 45 digree incline and not haf to use more than 1/8 of the trhottel there with out leaving 5th gear if i put it in 5th at 25mph and roll to 65 in less than 5 seckonds id say so it's not like my bike dosen't have the power at the lower end



now to a sad not for all you that dont know i got picked up operating my xj with out a licnce or endorsment and got ticketed now i haf to sell my xj to pay off the fines no biggy i guess because ill get the back in 2 months and i can get my drea bike (Buell X-1) any who i will no longer be posting on here due to some well reputated people relly not thinking before they speek or well type if you want to know the hole story here is the link to the full story enjoy Riding hope you all get your dream bike l8er


http://xjbikes.com/Forums/viewtopic/t=798.html

 

Thinking before you speak... sounds like good advice. I "assume" you were doing a functional test of your bike when you were picked up and not out joy riding. Of course this begs the question, what where you thinking riding without the required licence or endorsements? Bad risk management, poor judgement? Murphy (who never sleeps by the way) was bound to catch you. If you cannot endure the scrutiny of your peers, don't broadcast the dirt my friend. I once said that I would miss your input on the forum, and I will, but I will not miss the whiney boo-hoo just because some of our members decided to question a call with thought-out statements. Your argument is decidedly poor and I'm all for calling a spade a spade. If the performance of our forum (and I read your link) is all it takes for you to run away, you have a rough road ahead of you in life. Get a grip on this issue or you will be running the rest of your days (even Ted Kazinski(?) tried to hide and look what happened to him). I don't wish this upon anyone, even you. I know what it is to face unpleasant things, I've been chewed out, ridiculed, disgraced, it hurts. But a fellow doesn't get by on looks alone. You have to take your knocks, builds character and you walk taller after you take it on the chin. I appreciate your parting wish for us all and thank you for it, it was thoughtful. Fairwell Toad, you opened some good discussions.

 

Snosherrif,
Wait till I've modified it for shaft drives. Should only be a week or so away.

Cheers
HG

 

82 xj750 j ratios are as follows.
1ST gear 2.187
2nd gear 1.500
3rd gear 1.153
4th gear .933
5th gear .812

That is what is in my owners manual anyway

 

just a question here, But are the foreign bikes the same gear ratios as the US versions?

 

according to samsr 4th & 5th are already overdriven gears. wouldn't changing the final drive ratio screw everything up?

 

Gear ratios appear to be the same regardless of the market a bike was released in.


Robby, The gearing is still related to the final drive ratio so IF you could change that then you would notice a differece in performance. Of course you would have to find and overdrive replacement of .7 to make a difference.

The only real way to make a difference is to change the final drive ratio much the same as changing sprockets on a chain drive.

I don't think anyone has found a replacement that will work on an XJ though.

 

YEP , buy a harley or equivelent........

 

I have a friend with a virago up the street from me. I am going to see if the ratio by spinnig the tire and counting revolutions of the shaft. Also going to see if the rear end would work on an xj. Will let you know what happens. Should be a couple of days. By the way those numbers came right out of my owners manual. They were under the specs in the back.

 

Finally got up close and personal with the virago. Appear to be the same gearing in the rear. May have to look at different avenuues of approach. Maybe a slightly larger rear tire when my wears out.

 

You don't want a larger rear tire, it will just be wider. What you want is a TALLER rear tire, with a different aspect ratio so it will be taller. It's hard to find them by diameter though since there's no specification for outside diameter. Take a look at the Harley brand Dunlop tires, they are a lot bigger in diameter by several inches than a regular model Dunlop marked the same size. Check some side by side at some bike stores and you'll see what I mean.

 

Just to clear up some misconceptions-

XJ650, 750, and XJ900s all have the same transmission gearing. In addition to a beefed-up clutch, the 900 and the 650 Seca had different, ie: better heat-treating for some of the gears, but the gearbox components will all physically interchange.

Final drive ratio is the same for all 3 size XJ engines.

The overall gearing change for the 900 is accomplished in the secondary reduction gear pair....it's a slightly taller 49/36 versus the 650 & 750's 48/37tooth gearset.

This results in about a 5% change, or about a 300 rpm reduction at 60 mph.

I've got a 750 Seca engine installed in a 650 Seca chassis, and will be doing this gearing change when I pull the engine to fix the starter clutch.

 

Just a thought,but how about raising the overall gearing by swapping to 750 Seca rear rim. The Seca rim is a larger diameter,and should interchange with the stock Maxim 16" rear rim. Keep in mind that your stock tire won't fit the larger Seca rim,but it seems that replacing the wheel would be easier (and cheaper) than re-inventing it. Best of luck, Dan.

 

Measure the OD of both mounted tires. The 16" cruiser-style tire is pretty fat and tall, and I don't know which one is actually bigger in diameter.

The difference in circumference will be the change in effective gearing. Think of the tire as being the last gear in your bike's drivetrain.


The wheel swap itself should be a bolt-on.

 

How right you are! I am on a mission to find out which WOULD have the larger circumference.... Thank you for pointing that out. Regards; Dan.

 

Here's a quick look, courtesy of Metzler's Tire fitment chart.

A 130/90/16" ME880 is 657mm in height when mounted on a 3.00" rim.
A 120/90/18" Lazertech rear is 675mm when mounted on a 2.75" rim.

Both of the rear wheels on our bikes are significantly narrower than the measuring rim spec Metzler references, so both tires will stand a bit taller than the chart's numbers indicate. I think the 18" Seca wheel is more underwidth than the other, so it should gain a bit more in height.


That's not a huge significant for the better: only a hair more than a 1% reduction in overall gearing. It should get a little better with the tire-squeeze factored in, but I doubt you'll get to 2%.

In case you're wondering, a 130/80/18" is even shorter, and needs a wider wheel than the skinny 2.15" hoop the Seca has.

 

Easy gearing change, using Yamaha parts:

Here is what will be going into the mongrel-bikes' engine...

XJ900 middle drive gears.

I'll slip them in when the cases are split this coming weekend...the starter clutch was starting to make rude noises, so my scooter was parked until the parts arrived.

 

Without seeing a BSFC (brake specific fuel consumption) curve and overlaying the hp and torque curve, I wouldn't try to change the gearing. I remember I had an old Yamaha 360 enduro that we swapped the rear sprocket so it would wheelie easier, but then it only ran 52 mph.

I've found that when I try to outsmart something, I usually outsmart myself.

But if you do work it out, I'll be in line to buy!

 

This will only be an overall gearing change of about 5%, the combined final drive changing from 4.18 to 3.98, or much less than the jump from 4th to 5th. If you insist on using chain driven sprockets for reference, that's like taking two teeth off a 40 tooth rear sprocket. Noticeable, but not dramatic. It's not Daytona gearing.


In motorcycle terms, BSFC is of no concern for a trivial change like this.

 

Has anyone ever thought of the vmax rear gear ring? I looked at the parts blow up and they use a lot of similar parts. Would it fit into our rear case? It has 9 teeth to our 11. I'm not sure of the final ratio from this? I think it could work!
VMAX parts diagram

 

I found this website for virago setup. It says it will work on a virago and I know that Viragos are the same as XJ's because I have one on mine. I have a 1981 XV920, but this one is on a '84 700. it has the same gear setup as ours (32/11 teeth). So, I think we have a possibility? Check it out!

virago rear gear website

 

So, nobody has an opinion on this? I thought this would be of interest to many?

 

looks good, wonder what the tooth count is on the other gear, and how much it will drop the rpm? perhaps too much?

 

It is the same 32 teeth on the virago, but the vmax & venture have 33