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Post by dandog on Nov 21, 2006 3:22:33 GMT -5
Currently running 44 tooth rear and 16 tooth frontwhich gives approx 4100 rpm at 100km [rev counter changes its mind a bit!]I feel its a tad low ratio .Can anyone tell me how a smaller rear and larger front cog would go and if so what would give me roughly 3500rpm at 100kmhr cheers Dandog
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Post by StewRoss on Nov 21, 2006 5:27:59 GMT -5
Hi, 17/44 gives you 4,000 @100kmh...so you'd need higher gearing than that...therefore you'd possibly be looking at something like 17/40 or so at a pinch...bit of a guess. 16/44 = 2.75 17/44 = 2.588 17/40 = 2.353 Only thing is that a standard SR may not pull this gearing very well...a modified one will. Such things as a decent pipe, larger bore, high comp piston, larger carby etc. may be needed. From memory (...and I'd have to check the gearing to be sure) my cafe racer has something like 17/38 with a 525 chain and it is doing about 185kmh at 6,500...87.5mm piston, 38mm carby, Tingate race pipe and it's a fair bit lighter than standard as well. Drops dead beyond this figure though and is probably a trifle overgeared. 17/38 = 2.235 SR  |
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Post by colinjay on Nov 21, 2006 16:40:18 GMT -5
Hi there,
I agree with Stew, on the fact that you can over-gear. I have run 17/38, which is as tall as you can go with out modifing the engine cases and rear hub (with a 38 rear the chain will scrape on the mounting bosses of the hub). This gearing was run on my cafe racer for a while but made the bike almost unridable around town. It required a olt of rev and clutch slipping to get of the line and lost the low rev pick up that SR are known for. Also rarely got above 3rd gear uless out on the open road. I eventually when back to lower gearing (I can't remember what, I will have to check what it fitted now, when I get home tonight).
I currently run 17/44 on my "stockie" which give a good compromise of bottom end pickup and slightly lower revs at cruising speed of 100-110kph.
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Post by StewRoss on Nov 22, 2006 1:11:12 GMT -5
Yes true...one thing I forgot to mention is that I run a TX750 rear wheel on that bike and the sprockets fits well. You could go smaller if you wanted to, but you'd need an injection of horsepower to pull it. Mine is fine around town or out on the road but then I run AVGAS and the bike isn't standard. On all of the others I too run 17/44 with no problems. SR |
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Post by colinjay on Nov 22, 2006 16:26:00 GMT -5
Hi again,
I crunched some numbers last night (proof that I have no life?)based on the dimensions from the 1/2 worn K81 rear tyre on my stockie. To get 100kph at 3500rpm you would need to run a final drive ratio of 2.172:1 the closest you can get to this with sprockets on a SR is 17/37 (2.176:1). To get 100kph at 4000prm you need 2.482:1 which can be achieced with 17/42 (2.471:1).
These figure are base on a formula using rear tyre circumfrence. A more accurate calculation would use the radius of the rear tyre (axle to road surface) when the bike is carring its normal load (ie rider plus any luggage)
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Post by wotavidone on Nov 22, 2006 20:08:10 GMT -5
I reckon that's about right.
I run 17/42, with a very high profile Dunlop K60 (or is that 61) 4.00 * 18 tyre.
I'm just cracking the 100 km/hr mark with 4000 on the tacho.
The comments about pulling the gearing are very apt.
Seems like as you gear the bike up, it runs lower revs at highway speed, but mine just doesn't have much grunt after 5 grand. It'll probably pull the same speeds, but just does it all at lower revs.
Mick
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Post by StewRoss on Nov 23, 2006 0:58:52 GMT -5
Hi, Yes it does depend on the rolling diameter as well. I run a 120/90 rear tyre and I get 100kph at 4,000 with 17/44. SR |
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Post by fenz on Dec 1, 2006 3:07:57 GMT -5
What is stock gearing for a SR as mine has a 45 on the back
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Post by StewRoss on Dec 1, 2006 5:16:21 GMT -5
Hi, 16/44 is the standard gearing for the Aus. ones and probably the rest as well. SR |
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Post by SRwillie on Dec 1, 2006 19:14:39 GMT -5
Hey Stew, The XT500 rear hub fits and is a lighter alternative to the TX650/750. You do give up braking by using the XT hub. Pictures of my "H" model are in the 650 gallery.
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Post by StewRoss on Dec 2, 2006 5:14:35 GMT -5
Hi, Thanks, but I chose the TX drum because it was the biggest Yam drum I could find that matched the equally heavy Suzy front drum...more of a styling thing. I'd have put a Yam TR drum on it if I could have found one. My new cafe racer is going for the light weight bit... SR  |
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