TTI five speed box question...

TTI road going five speed box, my low gears are 29 and 16 which gives me 1.812. I find
this to be a tad high for low speed work. I'm getting 3750 at 70 mph and changing the
box sprocket a tooth down will make low gear better but then raise the rpm for
dual carriage work which I want to avoid.
Anybody know what other ratios are available?

Have you checked with Bruce at TTI? He does mention on his web site that alternative first gear ratios are available for the standard AMC 5-speed box.

Ken

If you are using separate exhausts, you might consider fitting a 2 into 1 to get more bottom end power. If the gearing is too high, tractability can be a problem. I'd also be looking at carburation at low throttle openings - slide cutaways.

I have a 2.75 low in my TTI box

1st Gear 2.75
2nd Gear 1.85
3rd Gear 1.46
4th Gear 1.21
5th Gear Direct

AMC 6 SPEED

Standard: 1st: 2.294, 2nd 1.755, 3rd 1.418, 4th 1.243, 5th: 1.1, 6th: direct
Low: 1st: 2.438, 2nd: 1.755, 3rd: 1.418, 4th: 1.243, 5th: 1.1, 6th: direct
Close: 1st: 2.169, 2ND: 1.69, 3RD: 1.418, 4th: 1.243, 5th: 1.1, 6th: direct

AMC XHD 5 SPEED

Standard: 1st: 2.438, 2nd: 1.75, 3rd: 1.379, 4th: 1.144, 5th: direct
Close: 1st: 2.209, 2nd: 1.661, 3rd: 1.379, 4th: 1.144, 5th: direct

AMC 5 SPEED

Standard: 1st: 2.294, 2nd: 1.69, 3rd: 1.356, 4th: 1.144, 5th: direct
Alternative low and close ratio: Available for 1st gear please ask

Thanks to all. Im in UK and looks like TTI goes through Minnovation so I shall ring them after the holiday. The bike will pull the first gear I have now
but in traffic or green lane it is just too high to putter along with out constant clutching. Suspect it will come down to pricing in the end.

Onder said:

Thanks to all. Im in UK and looks like TTI goes through Minnovation so I shall ring them after the holiday. The bike will pull the first gear I have now
but in traffic or green lane it is just too high to putter along with out constant clutching. Suspect it will come down to pricing in the end.

Click to expand...

If you contact Bruce at TTi with the gearbox serial number he will check with the build sheet what ratios are in it. Unless it was purchased via Minnovation I doubt they have that data.

I seriously doubt you have a 1.812 first gear. For a start Bruce does not make a 5 speed with that high a ratio and the highest he does on a 4 speed is 1.89:1.

1.8 ish was about the ratio of first in a Manx 4 Speed, and indeed it would be a pain in the arse on the road in any circumstance. I had that ratio in my Rickman 850 with a Quaife 4 Speed with Manx ratios back in the '70s, I used to bump start it in first, whilst those with Quaife 5 speeds used second! Because it was the same 1.8 ish ratio!

Have you physically pulled the cassette and counted teeth? Are you sure you have counted the right gears? Or have you counted 1st gear pair? I think that is what you may have done and seen 29 and divided by 16 to get your 1.812, but this is not your 1st gear ratio.

My guess is you have the 2.3 or 2.4.

In the workshop manual and parts schematic the gear pairs are called, 1st gear pair, 2nd gear pair, 3rd gear pair, 4th gear pair (and 5th gear pair)........but the 'pairs' aren't the only gears that transmit drive in each gear. You might think of the gear pairs as a useful reference for assembly, being the order in which each gear pair is placed on to the shafts, rather than being related to the actual gearing ratios for each gear.

There is an explanation of how the 4sp Norton box works here, and it correctly identifies which gears are used for which ratio: https://www.oldbritts.com/gearbox_info.html

There is a set of diagrams with the box in each gear and a coloured trace showing the drive path somewhere, but at the moment I can't find it.

I would suggest before getting too deep here you check the primary ratio and the final drive ratio. Do you have a belt drive with a higher ratio? Do you have a large gearbox sprocket?

Going down a tooth on the gearbox sprocket may be all you need to do. Yes I did read you don't want to do that, but it is a realistic first action and much cheaper, and if you are seriously green laning then maybe you should come down more!

SteveA said:

There is a set of diagrams with the box in each gear and a coloured trace showing the drive path somewhere, but at the moment I can't find it.

Click to expand...

Is this what you are referring to?
https://www.rgmnorton.co.uk/csi/1245184/f/pdf/nortonamcgearbox..pdf

comnoz said:

I have a 2.75 low in my TTI box

1st Gear 2.75
2nd Gear 1.85
3rd Gear 1.46
4th Gear 1.21
5th Gear Direct

Click to expand...

That is an interesting spread. How do you like it? What front sprocket are you using?

I counted the pairs of gears and went with that for the ratios so clearly, according to you, Im off base!
Therefore here are the counts maybe you can sort me out.

starting from the timing side moving to the drive side
29/16
24/23
25/22
26/20
26/20
Im running a BNR belt. 22 teeth on the box.
As stated previously 3750 rpm @ 70mph indicated
No Im not seriously green laning, but its Kernow and that is what you have to deal with in order to get around. Still dont want to lose the top end for when I need to hit the dual.

Onder said:

I counted the pairs of gears and went with that for the ratios so clearly, according to you, Im off base!

Click to expand...

The gear ratio is calculated from 2 ratios, the set of gears for the gear you are in and the common set of gears that all drive runs through. So 29/16 is one half of the story, you need to identify the common gears and apply that ratio to the other 4 gears sets, on a 4 speed box the common gears are the set nearest the clutch wrongly called the 4th gear set (as 4th is just the mainshaft locked to the sleeve gear, so no gears are actually used) , for a TTI box it may not be those.

gortnipper said:

Is this what you are referring to?
https://www.rgmnorton.co.uk/csi/1245184/f/pdf/nortonamcgearbox..pdf

Click to expand...

No it isn't but I suspect this is an interpretation of the earlier sketch based representation I am refering to. It definitely carries the same message and is a bit easier to understand than the oldbritts cutaway box, which however must be grat in a classroom demo.

The RGM chart for first gear clearly shows that to calculate first gear ratio you will need a formula involving both first gear pair and top gear pair.

Since it pretty much doesn't involve the intermediate gears I think this would apply directly to a 5 speed, and most likely a 6 speed.

Onder said:

I counted the pairs of gears and went with that for the ratios so clearly, according to you, Im off base!
Therefore here are the counts maybe you can sort me out.

starting from the timing side moving to the drive side
29/16
24/23
25/22
26/20
26/20
Im running a BNR belt. 22 teeth on the box.
As stated previously 3750 rpm @ 70mph indicated
No Im not seriously green laning, but its Kernow and that is what you have to deal with in order to get around. Still dont want to lose the top end for when I need to hit the dual.

Click to expand...

No, not according to me, according to the data I looked up.

Knowing that it is a BNR belt drive does not indicate the ratio? The standard primary ratio is 2.192 (57/26) Most likely the ratio you have will be between 1.7 and 1.9, as most belt drives are.

With a 22 gearbox sprocket that is a pretty tall overall ratio, I think it is higher than a standard primary with a 24!

Why not try a 21 gearbox sprocket and see how that works overall? You will have lost absolutely nothing, and I suspect you will still run around 4000 at 70mph indicated.

I had no idea where 'Kernow' is, but I see now that it is Cornwall, which means you must do much more riding on tight narrow lanes, so in truth setting it up for dual carriageways doesn't seem the most useful solution, most of the time.....

It does look as if you may have been better offf if you had specced a super low first like Comnoz says he has.....and surely you must also be able to change your to...as per your original post.....but my guess is still that will be rather more than the cost of a final drive sprocket.

I also wonder if it the lower first gives a bigger gap between ratios, which may be desirable or not. TTi, fits a lower second gear ratio with their lower first in their AMC XHD 5 Speed standard gear set, as compared to their close ratio gear set in the same box. (see above).

Standard Commando is 2.556, so 2.75 is pretty low......I suspect it works for Comnoz due to a larger capacity engine, fuel injection and riding on different types of roads, in the US including mountains, few of those roads are I suspect as tight as Cornish ones. I am also guessing his belt drive ratio is way from anything fitted as standard to a Commando. And his choice will also take into account the weight of his machine complete with the gear he needs to carry for his trips. You should observe that all of Comnoz's ratios are different to any of the boxes TTi list, and has a fairly large gap between 4th and top, so probably he uses top as an 'overdrive' for the highway!

kommando said:

The gear ratio is calculated from 2 ratios, the set of gears for the gear you are in and the common set of gears that all drive runs through. So 29/16 is one half of the story, you need to identify the common gears and apply that ratio to the other 4 gears sets, on a 4 speed box the common gears are the set nearest the clutch wrongly called the 4th gear set (as 4th is just the mainshaft locked to the sleeve gear, so no gears are actually used) , for a TTI box it may not be those.

Click to expand...

I think the set up for top and first are the same in pretty much all AMC style boxes, and a few others, only the intermediates change when there are more of them.

Onder said:

I counted the pairs of gears and went with that for the ratios so clearly, according to you, Im off base!
Therefore here are the counts maybe you can sort me out.

starting from the timing side moving to the drive side
29/16
24/23
25/22
26/20
26/20
Im running a BNR belt. 22 teeth on the box.
As stated previously 3750 rpm @ 70mph indicated
No Im not seriously green laning, but its Kernow and that is what you have to deal with in order to get around. Still dont want to lose the top end for when I need to hit the dual.

Click to expand...

So, with 26/20 as the common multiplier, assuming the order of the gear pairs is first, third, fourth, second, and "fifth", your overall gearbox ratios are:

First gear - 2.356
Second gear - 1.690
Third gear - 1.356
Fourth gear - 1.144
Fifth gear - 1.000

As already pointed out, the "fifth" gear pair isn't fifth gear, but the ratio of the splined layshaft gear to the sleeve (output to sprocket) gear, and so is the common multiplier for the other gear pairs.

Except for first gear, those ratios match the numbers on the TTI web site for his "AMC 5 SPEED". He mentions that alternative first gear pairs are available, so I assume you have one of those.

The BNR belt drives I run are a 1.75 ratio. If you're running a 22T countershaft, you must have a different primary drive ratio than mine, because that combo would give you a 3.341 final drive ratio (primary drive ratio times final (chain) drive ratio), way too tall gearing. With that sort of gearing and normal 19" rear tire, you would be seeing almost 160 mph at 7000 rpm, and about 85 mph at 3750 rpm. For reference, that is the gearing combo I once used for a race at Daytona with a 920 Commando and 17" rear tire. Not what you'd pick for normal riding anywhere. If your speedo and tach are accurate, to run 70 mph at 3750 rpm, you would have to have a primary drive ratio closer to 2.1 to 2.2, or pretty much the same as a stock Commando.

If your problem is that first gear is still too high a ratio for low speed riding in your local roads, but you don't want to be buzzing it higher on the highways, about the only option left is to get a lower alternative first gear pair from Bruce at TTI. Either that or go back to a stock 4-speed gearbox, which has a lower first gear.

If convenient, you might let us know what ratio your BNR drive is, and what size rear tire you are using. With that, we could give you some better numbers for comparison.

Ken

<If your problem is that first gear is still too high a ratio for low speed riding in your local roads, but you don't want to be buzzing it higher on the highways, about the only option left is to get a lower alternative first gear pair from Bruce at TTI.>

This is pretty much where I came in. How accurate the tach and speedo are Im unsure which is why I said "indicated". Rear wheel is 19". I shall go
measure the front and rear pulley diameters after supper and post.

There really is a wide spread of road speeds out here and it is common for me to be on the dual where most travel close to 80mph and it really
helps to be able to keep rpm down. After all with a five speed you can go to fourth for the hills. And not uncommon to go directly off the dual on
to a single lane with a nice spread of gravel and manure!

OK the pulley and clutch housing look to be 2:1.

Onder said:

<If your problem is that first gear is still too high a ratio for low speed riding in your local roads, but you don't want to be buzzing it higher on the highways, about the only option left is to get a lower alternative first gear pair from Bruce at TTI.>

This is pretty much where I came in. How accurate the tach and speedo are Im unsure which is why I said "indicated". Rear wheel is 19". I shall go
measure the front and rear pulley diameters after supper and post.

There really is a wide spread of road speeds out here and it is common for me to be on the dual where most travel close to 80mph and it really
helps to be able to keep rpm down. After all with a five speed you can go to fourth for the hills. And not uncommon to go directly off the dual on
to a single lane with a nice spread of gravel and manure!

Click to expand...

Changing down for the hills is a good idea.

Onder said:

OK the pulley and clutch housing look to be 2:1.

Click to expand...

That fits "reasonably" well with your indicated 3750 rpm at 70 mph. By my calcs, with 2:1 primary, 22T sprocket, and 100/90-19 rear tire, you would get something like 77 mph at 3750 rpm. FWIW, with a stock Commando with 22T countershaft and stock 2.19 primary ratio, 3750 rpm produces right at 70 mph.

If you calculated the ratio using pulley diameters, you might find it doesn't give the same answer as counting the teeth, unless you are careful to measure actual pitch diameters at the teeth.

In any case, that's more just for interest than anything else. As you have already concluded, your only option for reducing rpm at high speed that won't affect first gear performance is to go to a larger countershaft and fit a lower first gear.

Ken

Usually lowering first gear only involves changing a pair of gears, which in the case of a TTI box, Bruce Verdon could supply very easily. If the primary drive ratio is too high because of belt pullies, that is a good thing, because then you can either go down a tooth on the countershaft sprocket or up two or three on the rear. That way the box internals spin faster and the loads on the gears inside are lower.
With a 4 speed Commando box, most AMC first gears will fit and there are plenty of low first gear pairs around. Lowering first gear give a bigger gap between first and second, which most riders would not notice unless they were racing. When I bought my 6 speed TTI box, I was not thinking clearly. My 4 speed close box was perfect everywhere except during a clutch start to a race. Once the bike was rolling, I never went below 2nd gear. So I could have simply fitted a better ratio 1st gear pair and lived with the gap between 1st and 2nd. I'd have saved myself $5000. I recently spoke to one of the old A-grade riders - he said he has three first gears for his Manx - for different circuits..