Triumphrat

Shorty · 07-17-2006

It' actually pretty easy Kevin. Takes about 30 minutes or less. Dinqua has the procedures and pics available on a link in a step-by-step format (maybe someone out there has the link available for posting?).

Shorty

dazco · 07-17-2006

Quote:

On 2006-07-17 05:16, lunus wrote:
It has to be a ratio guys, not a fixed number of RPM.

This is my understanding

If you replace a 17 with an 18 then, for any given RPM in any given gear, you're gonna go 18/17 times as fast. For example with a 17 tooth on my 2003 Bonnie I'm doing around 83mph at 5000 rpm. If I fit an 18 then I'll be doing 83 * 18/17 = 88mph approx.

Conversely at a given speed I'll be doing less revs, so again if I'm doing 5000 rpm at 83mph wth a 17, I'll be doing 5000 * 17/18 = 4720rpm at 83mph with an 18. In other words around 280rpm less.

However at 41mph with a 17 I've got about 2500rpm and if I fitted an 18 I'd be spinning at 41 * 17/18 = 2360rpm, or about 140rpm less.

So very roughly speaking you "gain" 1mph per 1000 rpm if you move from a 17 to an 18, or putting it another way, you're doing about 50 rpm per thousand less at any given road speed.

Mind you, as I've said before elsewhere, these engines rev very happily and will cruise all day at 85-90mph with the standard gearing. 5000-6000 rpm may seem high if you've come from a push-rod twin or a 45deg V (I presume, never having ridden one) but not if you look at what the triples and fours are doing.

Depends on your style and location whether it's a good idea to change.

Cheers

Good someone here has some math skills. Mine are non-existant. In fact, my brain just shuts down if i even try and figure things like this out. But i'm glad you did. It's kinda odd tho that i feel more of a difference on the street than i do on the freeway because your calculations show there is a bigger difference in RPM between 2 sprockets that are one tooth apar at freeway speeds than there is at slower street speeds. Just the opposite of what i feel, but i'll take your word. But one thing that does jive is my accessment of 200 RPMs difference because while i didn't mention it, it was at 70mph that i checked that. So given 83mph gives you 280 RPM's diff, then i would figure at 70mph, 200 RPM's diff would be about right. One thing tho......the same numbers would not applyu to all the twins would they? I mean, they are not all internally geared the same.

sweatmachine · 07-17-2006

Just to add my $0.02, everyone seems to like the 18t and 19t, but I went from the 18t (stock on T100) to the 19t and didn't like it one bit. I tried to stick with it, and did for maybe 1000 miles. I put the 18t back on and haven't missted the 19t.

Just one Bonnie rider's opinion. The 19t felt like I was in the wrong gear all the time. My iridium spark plugs did more to stop vibrations at highway speed than did the 19t.

Ronnierockster · 07-17-2006

I have just fitted an 18 tooth sprocket.. Makes a real difference to the ride, more relaxed . The performance seems the same, in fact you seem to be able to rev for longer through the gears giving an impression of more performance.. A superb modification. I can only think that the 17 sprocket is fitted to ease the emissions test for Triumph.. RR :hammer: :hammer:

TheLiveEye · 07-17-2006

Sweetmachine

Quote:

Just to add my $0.02, everyone seems to like the 18t and 19t, but I went from the 18t (stock on T100) to the 19t and didn't like it one bit. I tried to stick with it, and did for maybe 1000 miles. I put the 18t back on and haven't missted the 19t.

Just one Bonnie rider's opinion. The 19t felt like I was in the wrong gear all the time. My iridium spark plugs did more to stop vibrations at highway speed than did the 19t.

Hey, Sweetmachine that was exactly my assesment of the 19t, felt like it turned into a tractor. Chug, chug, lug lug,(Different strokes for different folks)

But when I went back to my 17t is when I really noticed the difference.

You might want to try the 17t.

I think its great. Did 1200 miles over July 9th weekend through the hills of Pennsylvania, going to and from Pocono RAT Raid. Don't know how hilly it is in Austin area, but the 17t rocks on the hills and twisties..... :wink:

sweatmachine · 07-17-2006

TheLiveEye,

I've been thinking about getting a 17t, I may have to try it. Austin is very hilly. The area just west of Austin is called the "Texas Hill Country."

lunus · 07-19-2006

Quote:

On 2006-07-17 07:58, dazco wrote:
Good someone here has some math skills. Mine are non-existant. In fact, my brain just shuts down if i even try and figure things like this out. But i'm glad you did. It's kinda odd tho that i feel more of a difference on the street than i do on the freeway because your calculations show there is a bigger difference in RPM between 2 sprockets that are one tooth apar at freeway speeds than there is at slower street speeds. Just the opposite of what i feel, but i'll take your word. But one thing that does jive is my accessment of 200 RPMs difference because while i didn't mention it, it was at 70mph that i checked that. So given 83mph gives you 280 RPM's diff, then i would figure at 70mph, 200 RPM's diff would be about right. One thing tho......the same numbers would not applyu to all the twins would they? I mean, they are not all internally geared the same.

You're right dazco, at 70 you save a little more than 200rpm.

Also I see no reason why what you say about "feel" shouldn't be true. It might be that the difference (in torque/"feel"/vibration/whatever) between say 2000 and 2100 RPM is greater than that between say 4000 and 4200 RPM.

As for the "rule" working for all the twins, well it does in the sense that the ratio 17/18 always applies if you change the front final drive sprocket (on any bike).

However that would give different results in terms of RPM depending on what the bike was - if you had for example a 50cc racer that revved at 22000 RPM at 80 then changing from a 17 to an 18 would change the rpm from 22000 to 22000 * 17/18 which is approx 20800 -a difference of 1200 RPM at 80, not 280 RPM as you'd get on a Bonnie. And of course the feel would be very different.

I understand as well that the cruiser engines are tuned more for torque and so the effect of dropping revs on those may be different to a Bonnie and a Bonnie may be different from a T100 and a Speedy different from an America. You'll get a very similar result in the number of rev's dropped but it may have a very different "feel" - and that feel miught be different again at 40mph as at 80mph

Phew !

DrEnglish · 07-19-2006

I'm just gonna fit a 38 to the front and then the bike will hit like what, 240 MPH at redline in fifth?

wenzel850 · 07-19-2006

As I have said before I put a 19t on my T100 and just love the difference it made in my bike. I live in the Pocono's and ride alot of those twisty and mountainous roads that where mentioned, and the 19t makes no difference. In fact I feel it gives me more drive coming out of a long sweeping corner.

Well as was also said "to each his own".

lunus · 07-20-2006

Quote:

On 2006-07-19 11:16, DrEnglish wrote:
I'm just gonna fit a 38 to the front and then the bike will hit like what, 240 MPH at redline in fifth?

yep, right after you bore out the engine to 7 litres.