Triumphrat

MorganB · 09-09-2008, 06:31 PM

Why don't manufacturers of 5-speed motorcycles make the top gear just as tall as the sixth gear on a 6-speed transmission, and make each gear have a larger "step"?

In other words, first gear would be just as short as the first gear on a 6-speed transmission, 5th gear would be just as tall as a 6th gear, and the graduations between gears would be slightly wider to compensate for the lack of six gears.

????

ggRAT · 09-10-2008, 11:07 AM

Good question. Why can't we have a top gear that would allow the bike to "cruise" at 75 mph (120 kph) and 3000 rpms or less. Today, my Bonneville with a 19t & 43t sprockets is going 75 mph at 4,000 RPMs. Wouldn't that cut gas consumption by about 25% on the highway?

TennesseeDon · 09-10-2008, 01:58 PM

I had a T-Bird Sport with the 6 speed transmission, and the top gear was the same as the top gear on the Bonneville 5 speed, 3500 RPM = approx. 55 mph.
I remember reading an article about the development of the new Bonneville which stated that the transmission was the same as the T-Bird Sport, minus 5th gear. That seems about right.

Don
2001 Bonneville

justbrian · 09-10-2008, 07:29 PM

Yep - a lot of six speeds are just close ratio transmissions. Some of the touring style bikes have overdrive gears up top, but anything "sporty" is probably gonna be closer to the range on our Twins.

Gas mileage may suffer (not that ~50mpg sucks), but at least it keeps you in the power band.

ohiorider · 09-10-2008, 07:45 PM

Quote:

Originally Posted by ggRAT

Good question. Why can't we have a top gear that would allow the bike to "cruise" at 75 mph (120 kph) and 3000 rpms or less. Today, my Bonneville with a 19t & 43t sprockets is going 75 mph at 4,000 RPMs. Wouldn't that cut gas consumption by about 25% on the highway?

Sorry, no it won't. It still takes a given amount of hp to push the bike down the highway, to overcome weight, and at higher speed, wind resistance plays a major role in fuel consumption. And our Bonnies (plus rider), pretty though they may be, are about as streamlined as a barn door. Even though the rpms may be lower, you'll probably have to give the bike a bit more throttle to generate the hp required to overcome wind, weight, rolling resistance, etc. Unfortunately, there isn't any free ride.

Bob

RedBird · 09-10-2008, 09:28 PM

If you took either 4th or 5th gears out of the Tiger 1050, it would feel about like the Bonnie transmission. On the Tiger 1050, the 4th and 5th gears are very close together--too close IMHO. At 75 mph on the Tiger in 6th gear, I am taching very close to the same rpm at 75 on the Bonnie in 5th. The Tiger will just keep going up in rpm a lot further.

MorganB · 09-10-2008, 09:32 PM

Quote:

Originally Posted by ohiorider

Sorry, no it won't. It still takes a given amount of hp to push the bike down the highway, to overcome weight, and at higher speed, wind resistance plays a major role in fuel consumption. And our Bonnies (plus rider), pretty though they may be, are about as streamlined as a barn door. Even though the rpms may be lower, you'll probably have to give the bike a bit more throttle to generate the hp required to overcome wind, weight, rolling resistance, etc. Unfortunately, there isn't any free ride.

Bob

I haven't pushed it that hard yet, but I think my stock Bonnie is capable of running out of RPMs in top gear before wind resistance overcomes the available horsepower. My old bike was an SV650, which makes almost exactly the same horsepower as the Bonneville, and it was capable of much higher speeds in top gear - even taking into account the difference in engine redline speeds.

IF my assumption is correct, a taller top gear would probably give better gas mileage at highway speed.

mikeinva · 09-10-2008, 10:57 PM

its more about ft/lbs then hp and bonnies have good ft/lbs at lower rpms you dont need to have much of ether to cruse down the road at 70 to 75 mph.the gear ratios are to tight to make a good cruser.There geared more like a drag bike and once you get them making poweronce they hit top rpms in 1st gear and you shift fast you will never see tach drop more then 1000 rpms all the way through the gear box.

ivar · 09-11-2008, 08:21 AM

Quote:

Originally Posted by MorganB

My old bike was an SV650, which makes almost exactly the same horsepower as the Bonneville, and it was capable of much higher speeds in top gear - even taking into account the difference in engine redline speeds.

Stock for stock, my 05 SV is alot stronger than my 02 Bonnie - and ratings are 72HP vs 61HP. (But still I ride the Bonnie much more)

I beilieve the SV peaks at 9000 and redlines at over 11000, vs 7400 for the Bonnie.

Phil-1100 · 09-11-2008, 10:28 AM

The bonneville gearbox is 1,2,3,4,6 - it has 5th gear missing, one of the reasons it behaves different to a six speed box is the primary gearing is so different.
A six speed on the outside of five speed - note 5th gear missing