new here

[Moto63]

Nice collection of bikes you have wart, the XBR with the 650 motor looks nice. Regards Michael

[Propellor]

Yes, we all seem to experience trouble with photos. I wonder if there's any way that could be changed? The site is a pretty popular one.

I'm no expert but this is how I usually do it.

If it's an online image - on google images or similar -
Left click on the thumbnail - when it bring it up right click on 'copy image location' then in the reply box on this sight select the image button ( below underscore) [img] [img] and left click between the 2 image boxes and select paste. The code should end in .jpg.

If the image is on your computer you will need to upload it onto something like Picasa, Photobox, Google + photos. Then click on the thubnail - when it brings the image up right click and select 'copy image location' then paste it into the reply box as before. You can't paste an image straight from your desktop ( at least I haven't found a way yet.)

Cheers Steve.

Sorry to burst that particular bubble, but I never turn the computer on. Strictly i pad or kindle fire.

Like I say, the procedure on here is straightforward, it just won't accept anything over 250kb. I finally managed to find a way to convert a photo to less than 250kb. Only for this system to scupper me by then saying it only takes .jpg. Mine was .jpeg.

 

I gave up trying.

[guest1230]

"Xbr 44hp @ 7000 rpm
Dommi. 45hp @ 6000rpm

There's the problem. The difference is 1.17. "


Gear ratios are to do with the diference in turning speed, cog to cog or sprocket to sprocket, or so I thought!

Will have an influence on HP at back wheel (maybe) but can't use the above formula surely.

[Propellor]

"Xbr 44hp @ 7000 rpm
Dommi. 45hp @ 6000rpm

There's the problem. The difference is 1.17. "


Gear ratios are to do with the diference in turning speed, cog to cog or sprocket to sprocket, or so I thought!

Will have an influence on HP at back wheel (maybe) but can't use the above formula surely.

Power is a constant value from crank to rear wheel, minus mechanical losses. So the gears affect hp at rear wheel only by how many gear pairs are involved, plus of course other mechanical losses; chain, Oilseals etc.

Where gear or chain ratios reduce speed they also multiply torque by that same ratio. The ratio of the number of teeth. If gears increase speed (as the xbr top gear does) then torque is divideo by that same ratio. Some torque is lost by mechanical losses.

If you're in doubt that I speak the truth, then apply the horsepower formula and you'll see it works that way.

[Propellor]

"Xbr 44hp @ 7000 rpm
Dommi. 45hp @ 6000rpm

There's the problem. The difference is 1.17. "


Gear ratios are to do with the diference in turning speed, cog to cog or sprocket to sprocket, or so I thought!

Will have an influence on HP at back wheel (maybe) but can't use the above formula surely.

In the context of the thread, namely matching overall ratio to engine speed versus rear wheel speed, my comment meant that the power is the same, so is the desired rear wheel speed. The difference in engine speed is 1.17, so that is the amount we need to change the overall ratio found in the xbr, to achieve the same rear wheel speed.

Seems straightforward to me.

[JOOLZ]

I see you are still interested in the gearing problem, actual data taken from my speedo and rev counter memory is @100mph the engine was at 6128 rpm, thats a standard XBR 500 clutch and gear box with a 15 tooth sprocket but with an 80 profile rear tire

[Propellor]

I see you are still interested in the gearing problem, actual data taken from my speedo and rev counter memory is @100mph the engine was at 6128 rpm, thats a standard XBR 500 clutch and gear box with a 15 tooth sprocket but with an 80 profile rear tire

So it seems to be geared for 115mph? A touch more with the stock tyre?

Seems a tad overgeared for stock power?

[JOOLZ]

My bike hasnt got "stock power" 600cc, flowed head, special cam, big bore exhaust amongst other mods

[Propellor]

My bike hasnt got "stock power" ........

Ah. What power has it got? 

[JOOLZ]

Around 40 ft lbs of torque and 50hp

[blew]

I've been reading this topic with great interest.I have no idea what revs an xbr 500 normally pulls,since mine had a knackered piston when I bought it.I have run my xbr for a few years now with an xl 600 barrel and piston,compression ratio unknown but pretty high.It is reluctant to rev over 6000,although it will do so in the lower gears if I insist.It pulls like a train in top,and if I want it will sit effortlessly at 80 - 85 for as long as I want.Top speed is about 95-98 sitting normally,just over 6000 rpms,which it reaches without too much effort.Question for the cognoscenti-has my 600 got a lower powerband/rev range due to having a 600 piston?The 600s have a power band about 1000 rpms lower than the 500,all else being equal.Should I fit a 16 tooth gearbox sprocket?

[Propellor]

Putting down the basics:

Std xbr setup.
Primary 2.482
Top gear 0.875
Secondary (36/15) 2.4

2.482x0.875x2.4=5.21

7000/5.21 =1343 rear wheel rpm

Wart set up.
Primary 2.482
Top gear 0.875
Secondary (34/16) 2.125

2.482x0.875x2.125=4.61

6000/4.61=1303 rear wheel rpm.

(Please feel free to correct any mistakes!)

What that rear wheel rpm equates to, we can calculate later, but it's obvious there shouldn't be much difference in top speed. This doesn't stack up against what wart tells us, but they appear to be the facts?

It looks like the dommi primary set would help raise the gearing a bit more, bringing it somewhere like a stock xbr overall ratio.

Bit of a mystery chaps. Steve has reached a similar conclusion. It's over to you wart.....

Blimey. This was a while ago now and we covered some ground (Ho Ho). There's a few ways to approach this, but the above post I made seems reasonably appropriate to your question. Seems that you need to be aiming for around 1300 to 1340 rpm at the rear wheel coinciding with max power engine rpm. Divide down from the engine rpm as I've done above.

How does this pan out with what you actually have?

Aiming for this rear wheel rpm is basically copying what Honda seems to have aimed for on the stock xbr500. So if we assume that they were right and that your engine power is about the same (albeit at lower revs), then aiming for the same rear wheel rpm should yield a good result for the road.

Cheers.

[timbo]

Alison's XBR has a XL600 barrel and piston, gas flowed head, and bespoke exhaust. No idea of figures, but it goes like Sh1t of a Shovel, and sounds raucous 

[deleted to save space]

[blew]

Does the standard 500 really rev to 7,800?? Mine goes off the boil over 7,000.

[Propellor]

Does the standard 500 really rev to 7,800?? Mine goes off the boil over 7,000.

I stand a chance of helping work out the gearing and the various torque figures. But others on here will be better able to advise on what the engines can and can't do. What I can say is that the specs for the stock 600 have it making max power at 6000rpm. That's where the data in my post above came from. So it doesn't surprise me in the slightest to hear that yours runs out of puff at 7000rpm. I wonder what the safe max operating rpm is? Before it "lets go".