Triumphrat

dazco · 04-28-2006, 10:30 AM

This is something i think needs to be said because it's apparently something few if any realized about the greaing of the twins and thier differences. I suspected this for a long time but didn't realize it was to such a degree. Talking to CarlS at another forum, he quoted his bonnie with stock sprocket (tho he's now using an extra tooth) as turning 4800 RPM's at 70, quite a bit higher than a speedmaster which stock is at about 4200 at 70. I hear bonnie owners saying things about the speedmaster like "how can you live with a 16 tooth sprocket" and such. they also are the ones who rave the most fanatical about the benefits of larger sprockets. They als often go up 2 teeth and don't find that as being too much. So simply put, larger sprockets on a bonnie are necassary because the bike's internal gearing is lower.

So it all makes total sense now. An extra tooth drops RPM's by about 2-300, so TWO extra teeth on a bonnie with give it about the same RPM's as a stock speedy !!! So now we know why bonnie owners are ravenous about sprockets, and it's no wonder ! I thought my speedy revved rather high with the stock 16, but by comparison it was barely breathing ! Why they would gear the bonneville so low os beyond me. (unless the toque is much less, but i doubt that) But if i had one i'd definatly go up a minimum of 2 teeth. According to CarlS's estimation of 4800 at 70, 3 extra teeth would put it about where my speedy is now with 1 extra tooth. So those with a bonnie and 2 extra teeth are NOT feeling legs as long as mine with one extra !

Hope this will help end some of the confusion about sprockets because the opinions that deviate from the popular may now have a logical reason, IE: a SM owner who goes up 2 may find it too high while bonnie owners are always happy with it. Now you know why and can more easily evaluate rider opinions on this awesome mod. Did i mention i'm still thrilled about the 17? :-D :-D :-D

[ This message was edited by: dazco on 2006-04-28 08:30 ]

Normandy · 04-28-2006, 11:20 AM

You mention it so much (thanks) that I ordered a 17 T from Brent 2 days ago. I went to the dealer to get one and they don't stock it ? Being standard on America, figured they would have stock. Anyway, I'm waiting anxiously for my little package to arrive.

Panthermark · 04-28-2006, 11:31 AM

Yeah, my stock 18T isn't bad, but I will probably go to a 19T pretty soon.

MES · 04-28-2006, 02:36 PM

I have been wondering about the same thing since day one.
I have looked (admittedly not that hard) for the internal gearing specs for the different Triumph models. Triumphs site does not list them in the tech specs.
I ride a stock Bonnie.
When I first got it, it was quite apparent that it was on a very tight leash. The poor little thing wanted to go but it just couldn't.
Waited until the 500 service and put on the 18t front. What a difference. At least this configuration is reasonable.
I have a19t but have never used it because of the following.
With an 18t front, in heavy non stop-and-go traffic 1st is a little big and I find that I have to feather the clutch. A 19t front will just exacerbated the problem.
Yes, One could switch out the rear sprocket for an intermediate configuration.
I believe that the real "problem" ( if it is a problem) is in the internal configuration.
Ideally I would like to see something along these lines.
1st & 2nd kept as
3rd slightly taller (as with a 18t front)
4th & 5th being much taller ( as with a 19t)
Either that or just go with a 6sp.
An extra 10ft.lbs of torque would help.
Meh, can't have it all

going up to northern Idaho in July. I'll put the 19 on for the trip up and and then switch back to 17 once I'm there.

dazco · 04-28-2006, 02:51 PM

Quote:

On 2006-04-28 09:20, Normandy wrote:
You mention it so much (thanks) that I ordered a 17 T from Brent 2 days ago. I went to the dealer to get one and they don't stock it ? Being standard on America, figured they would have stock. Anyway, I'm waiting anxiously for my little package to arrive.

You have a speedmaster so i can say with confidence that you're gonna love it.

MES's post suggests a bonnie may be different in the way it takes to the higher gearing. But on the other hand most seem to feel good about even 2 teeth on the bonnie. 3 will bring them to where mine is now, but maybe the bonnie's torque just isn't quite enough. Condiser that mine is geared to the equivilent of 3 more teeth on a bonnie, and i find zero lack of power on take off. I don't have to feather the clutch at all. Then again, the 05 and above SM's ARE designed for low end torque with a cam grind that's tweaked for that, so maybe an equivilent gearing would indeed be a bit much on a bonnie. All i know is i find it a huge improvment. This certainly explains why bonnie owners talk so much about high RPM's at cruising speeds tho. I never realized just how low the internal gearing was till CarlS told me his hit 4800 at 70 MPH.

Sheepdog · 04-28-2006, 07:35 PM

Not to be argumentative and maybe it's a misprint, but my Triumph Service Manual states that the internal gear ratios are identical for the T100, America, and Speedmaster (in all gears. In fifth the ratio is 1.07:1). The difference between the T100 and the Speedy is in rim and sprocket size. The diameter of the Speedmaster wheel and tire is 25.7 inches (based on a tire size of 170-80-15) as compared to the T100, which is 25.2 (based on a tire size of 130-80-17). The Speedy uses a 16-42 final drive, the T100 a 17-43. Thus, the gear inches (the distance in inches a wheel travels in one revolution) in fifth gear are:

Speedy: 212"
T100: 200"

Therefore, the Speedy is geared about 6% taller than the T100. It makes sense that the T100 can deal with a two tooth C/S increase better than the Speedmaster, but not because of internal gear ratios. Wheel and sprocket sizes are what make the diff.

dazco · 04-28-2006, 08:10 PM

You're right i'm sure. But i didn't mean to make a point of the internal gearing being taller, but i just assumed that was the reason for the RPM differences. But the point was whatever the reason, the bonnie runs about 600 RPM's higher at 70mph. So 6 of one, half dozen of the other if you know what i mean. But the main point aside, interesting about the wheels, sprocket and tires, and it certainly makes sense since as you say the internal gearing is the same.

Quote:

On 2006-04-28 17:35, Sheepdog wrote:
Not to be argumentative and maybe it's a misprint, but my Triumph Service Manual states that the internal gear ratios are identical for the T100, America, and Speedmaster (in all gears. In fifth the ratio is 1.07:1). The difference between the T100 and the Speedy is in rim and sprocket size. The diameter of the Speedmaster wheel and tire is 25.7 inches (based on a tire size of 170-80-15) as compared to the T100, which is 25.2 (based on a tire size of 130-80-17). The Speedy uses a 16-42 final drive, the T100 a 17-43. Thus, the gear inches (the distance in inches a wheel travels in one revolution) in fifth gear are:

Speedy: 212"
T100: 200"

Therefore, the Speedy is geared about 6% taller than the T100. It makes sense that the T100 can deal with a two tooth C/S increase better than the Speedmaster, but not because of internal gear ratios. Wheel and sprocket sizes are what make the diff.

MES · 04-28-2006, 11:41 PM

Quote:

Not to be argumentative ...

Your not being argumentative at all. In fact, it was a big help.
When I was talking about the internal gearing I was talking specifically about the Bonnie. With (a whole)44ft.lb of torque though, there isn't a lot of room for creativity. An extra 10ft.lbs of torque would help.15ft.lbs lower down would be better.

Guess they made the internals all the same to cut costs

Quote:

Why they would gear the Bonneville so low os beyond me. (unless the toque is much less, but i doubt that)

Bonneville:62ps (61 bhp)@7,300 rpm 60Nm (44ft.lbs.)@7,200rpm

T100:67ps (66 bhp)@7,200 rpm 70.5Nm(52ft.lbs.)@6,000rpm

Thruxton:70ps (69 bhp)@7,200 rpm 72 Nm (53 ft.lbs.)@6,400rpm

Speedmaster:55 ps(54 bhp)@6,750 rpm 69 Nm (51 ft.lbs.)@ 4,800 rpm.

Daz, as you can see your speedy got some fat on the low end. That is probably why you can pull higher gears.
I would like to see the torque curves for the 4 (stock). It would be interesting.

I think you will find most of the Bonnie and T100 guys using a 18T c/s, unless the vast majority of their miles are on the highway. I could be wrong about this though.

dazco · 04-29-2006, 01:30 AM

Quote:

Daz, as you can see your speedy got some fat on the low end. That is probably why you can pull higher gears.
I would like to see the torque curves for the 4 (stock). It would be interesting.

Yea, i didn't even think about the curve, and i always forget how low the torque is developed when comparing my bike with others. They really did do a good job of developing low RPM torque with those cams, tho it does cost you in the upper ranges. Also, i wasn't condisering the fact that some of the opinions i've read were by those with unmodified bikes. i don't know what my torque is now with the mods, but it's easily discernable as more. So i could have closer to 60 than 50 in the low end, which would be huge compared to a stock bonnie. I still think the bonnies would do well to add at least one tooth tho. Right now i'm sitting here with fingers crossed for tomorrows weather because it's supposed to be nice and i haven't yet had a chance to ride with the new sprocket for more than 1/2 hour at a time. Wether permitting i'm hoping to get about 125 miles in tomorrow on one of my favorite twistie routes.

peterbear · 04-29-2006, 09:02 AM

one of the first things was when i got my t100 was to go up to a 19 tooth on the front and it makes really nice to ride,but you have to slip the clutch from the lights .