Close-ratio gearboxes

[Boston Fit]

I've heard the gearbox in my car described as having a "close ratio." What is a close-ratio gearbox, and how is it different, performance-wise, from the alternative?

[ClutchDisc]

As far as I know, that means that the difference in gear ratios are closer together than other transmissions.

[theholycow]

You know how the 1->2 shift can be difficult to do smoothly because there's such a big difference between those two gears? And how other gears are easier because there's less difference? You can describe 1 and 2 as being a relatively wider ratio difference than 3 and 4 are.

In a close-ratio gearbox, the gears are all closer together than in a wide-ratio gearbox.

That's what close vs. wide ratios are. Here's why:

Close ratios are good if you race or if you generally like to operate at high RPM. You can complete the shifts faster and, most importantly, stay in the best part of your engine's powerband, keeping it at the RPM that makes the most power. They're also good if you don't drive at a variety of speeds; if you mostly drive between 20 and 40mph, close ratios allow you to have a best gear for every 5mph.

If you regularly drive at a wide range of speeds, like if you spend 50% of your driving on the interstate at 65mph and the other 50% on surface streets at 20-45mph, and especially if you also have a low-revving engine, wide ratios will be better. Wide ratios allow you to have both lower and higher gears than a close-ratio gearbox. You use the lower gears for better acceleration, and the higher gears to keep your RPM down and your fuel economy up.

I don't dislike close ratios, but I dislike the lack of total range that comes with them because I drive 40% 65mph interstate and 60% 20-50mph surface streets and my engine prefers to rev low (as do I). Besides wide ratios, another solution would be more gears...close ratios would work great for me if there were 15 of them instead of 5.

[rml605]

My car is close ratio aside from 1-2. I can close to dump the clutch on every other shift and get it smooth. The bad thing however IMO with such close ratios, is if im 6th or 5th..DS from 6th to 5th or 5th to 4th..does not really do anything. So sometimes it's kind of confusing for me and has me wondering if I should shift two gears down, but then if I do, i'll be at kind of high RPM.

What cars have a close 1-2? Doesn't the GTO? I would love that.

[ClutchFork]

LINK for further information

[Boston Fit]

Great info here, guys. Thanks. I have zero mechanical knowledge, so I am trying to understand the concept of close vs. wide ratios by way of an everyday analogy.

Say you have a steep incline to climb (on foot), and you can use five stairs to climb it. You are free to position each stair wherever you want along the length of the incline. If you put the first four close together, those will be easy to climb, but the last one will be hard. If you instead space them equally, the last one becomes easier to reach but the first four will be harder. And so on.

Is that kind of how gear ratios work?

[theholycow]

Yes, that's a pretty good analogy.

[Boston Fit]

Yes, that's a pretty good analogy.

Thanks!

[ClutchFork]

It is an excellent analogy. If we dig deeper though we will see that while a stairway is linear, the gear ratios would be more of a geometric relationship. You could perhaps look at it as cumulative steps. I am not sure I understand it even, but when you do an all our run through the gears, pedal to the metal, you'll notice that you spend the least time in first and that you spend more time in each successive gear. That is what I am getting at here, but for simplicity's sake, the stairway analogy is perfect!

[theholycow]

I am not sure I understand it even, but when you do an all our run through the gears, pedal to the metal, you'll notice that you spend the least time in first and that you spend more time in each successive gear.

I was thinking about that sort of thing but I decided that the analogy worked as a simplified explanation, not directly applicable but providing the general idea.

To take the analogy into that territory, imagine you can change the slope and there's a lot more stairs. Instead of being a straight line up the hill, it starts almost level with 5 tiny steps, then the grade increases and there's 5 small steps, then the grade increases and there's 5 normal steps, then the grade increases and there's 5 large steps, then the grade increases and there's 5 huge steps. With a close ratio transmission the grade doesn't increase as much, the step size doesn't increase as much, and you don't end up at the same altitude (or you had to start from a higher altitude) compared to a wide ratio transmission.

[daleadbull]

Close ratio means lot of shifting but it also give you better control of your power band. You can be in the right gear to get the maximum performance out of your engine. The downside is fuel economy, most close ratio gear boxes usually tend to rev higher at highway speeds but some manufacturers are putting long final gears to compensate for that.

IMO if you have a forced induction engine, close gear ratios are essential. You don't want to shift and fall out of the boost region and have to build up boost again. That is bad for performance and fuel efficiency. On the other hand, big naturally aspirated engines would be fine with wider ratios.

I love shifting so close ratio boxes are great for me. In a wide ratio, you can rev out a gear then when you shift to the next gear you can be out of the powerband which hurts acceleration. My perfect gear box would would be close ratio with a tall final gear for highway cruising.

[ClutchFork]

My Ranger is not close ratio, but I would not mind widening it a bit with deeper first and second gears for better get out. It would be great if the New Venture 1500 gearbox would mate to my Ranger engine. ClutchDisc has the exact ratios that I would like in my first and second gear.

Ranger M5ODR1: 3.72, 2.20, 1.50, 1.00, 0.79

S-10 NV-1500: 3.94, 2.37, 1.49, 1.00, 0.83

Not only would I have quicker launch and go, but also I would have more power in OD.

The best part though is I would get that Muncie-Rock-Crusher-like gear whine that I love so much.

Project Tranny Swap! Is it feasible? Is it low cost assuming I can sell the M5ODR1? Do I have time to mess with it (NO, but it's fun to dream).

Hey ClutchDisc? Wanna swap trannies?

[theholycow]

I think the NV1500 has an integrated bellhousing, which would make it a terrible candidate for the job. I bet it'd be pretty easy to find a T5 with the ratios you want. Besides sourcing one from a Mustang, GM T5's should be easy enough too; the transmission has a bellhousing mounting pattern compatible with Ford, as I understand.

However, it sounds like what you really want is a shorter rear end. I think that would be easier to find, easier to do, and less expensive.

[ClutchFork]

I think the NV1500 has an integrated bellhousing, which would make it a terrible candidate for the job. I bet it'd be pretty easy to find a T5 with the ratios you want. Besides sourcing one from a Mustang, GM T5's should be easy enough too; the transmission has a bellhousing mounting pattern compatible with Ford, as I understand.

However, it sounds like what you really want is a shorter rear end. I think that would be easier to find, easier to do, and less expensive.

I think the Mazda tranny also has an intregal bell housing but not sure. Well, you are right, a different rear end is a simpler solution but then one has to go to the dealer for the computer to be adjusted to the new gear ratio which is affected by any changes behind the transmission but I suppose that would be a lot easier and cheaper. I have a 3.73 rear. 10 percent would put me about 4:10 and around 2900 rpm on the freeway at 70. That is where just changing the first two gears is nice.

[LHOswald]

theres a reason transmissions are developed for an engine, and not the other way around. a 1.6 liter 4 cylinder and a 5.7 liter v8 are going to need completely different combinations of space between gearing, number of gears, and final drive ratios. on a torque-ier, lower revolution engine, having wider gears isn't just practical, its sorta necessary. (especially for highway speeds) and since the engine is putting out more torque anyway, the the wider gears won't affect acceleration so much. on the other side of the coin, a high revving, not so torquey engine is going to need a closer-ratio gearbox to put the power down effectively, although then you can end up with an engine thats turning over 3k at highway speeds (my car). although i feel like we've had that discussion on this forum many a times...