Does a short ratio gearbox really make a car faster?
Discussion
I have been pondering this a lot recently, does a close ratio gearbox really make a car faster, assuming the stock car is not significantly over geared to be begin with?
The overriding factors have surely got to be power and weight, you cannot conjure up power out of nowhere with a gearbox though admittedly ripping through each gear quicker will certainly give the illusion of speed that people crave.
The overriding factors have surely got to be power and weight, you cannot conjure up power out of nowhere with a gearbox though admittedly ripping through each gear quicker will certainly give the illusion of speed that people crave.
What is "faster"?
Many cars with a quick 0-60 ststistic are specifically geared to just hit 60 in second gear, meaning only one gear-change. Doesn't mean the car is quick to 70 though!
Lower gearing = faster "in gear" acceleration, but more gear changes. Swings and roundabouts.
Also, the "width" of a gear depends on the engine's rev range and its usefulness depends on the torque curve. In other words there are many variables.
Many cars with a quick 0-60 ststistic are specifically geared to just hit 60 in second gear, meaning only one gear-change. Doesn't mean the car is quick to 70 though!
Lower gearing = faster "in gear" acceleration, but more gear changes. Swings and roundabouts.
Also, the "width" of a gear depends on the engine's rev range and its usefulness depends on the torque curve. In other words there are many variables.
By faster, I mean will cover more ground in an elapsed time, say a standing start 1/4 or 1/2 mile sprint.
Obviously, certain points can be improved, say 0-60, 40-80, or anything that would really hinge on the number of shifts required, but over distance and up to high speeds using every gear, can a car be made significantly faster just with ratio changes? Assuming the stock car has a set of ratios that match the powerband, and the car is not significantly overgeared (i.e. geared for 180mph when it can only push 130mph).
Obviously, certain points can be improved, say 0-60, 40-80, or anything that would really hinge on the number of shifts required, but over distance and up to high speeds using every gear, can a car be made significantly faster just with ratio changes? Assuming the stock car has a set of ratios that match the powerband, and the car is not significantly overgeared (i.e. geared for 180mph when it can only push 130mph).
Mainly depends on the power curve of the engine. You want to keep the engine producing as much HP as possible, a shorter ratio box can allow for this.
For example if you change from 2nd to 3rd and the revs go from 7000 to 5000rpm, the engine may produce 150hp@5000rpm, a shorter box would allow the car to drop to 5500rpm where it could be producing 170hp. So you have more HP for more of the time. Its not really important for cars with a horizontal power curve, as it'd produce similar HP at 5000 and 5500rpm.
Edit: This is proven by a friend having a VTS with a VTR box (longer ratios) his VTS is slower than a standard one, although it can do ~100 in third
For example if you change from 2nd to 3rd and the revs go from 7000 to 5000rpm, the engine may produce 150hp@5000rpm, a shorter box would allow the car to drop to 5500rpm where it could be producing 170hp. So you have more HP for more of the time. Its not really important for cars with a horizontal power curve, as it'd produce similar HP at 5000 and 5500rpm.
Edit: This is proven by a friend having a VTS with a VTR box (longer ratios) his VTS is slower than a standard one, although it can do ~100 in third
Depends. Faster where?
Don't the F1 teams spend ages optimising gear ratios for each track? There will be a "best set" for qually, an "best set" for the race and a "best set" for the race laps without DRS. Lower gear ratios than those will make the car slower.
My Elise has the close ratio box, but I've not driven one like it with the standard box, so I can't tell.
I assume there will be a set of circumstances under which my car would be faster than one with a normal gearbox, and a set of circumstances under which mine will be slower. Certainly I wouldn't bugger about with changing the ratios unless I had a particular goal in mind.
Don't the F1 teams spend ages optimising gear ratios for each track? There will be a "best set" for qually, an "best set" for the race and a "best set" for the race laps without DRS. Lower gear ratios than those will make the car slower.
My Elise has the close ratio box, but I've not driven one like it with the standard box, so I can't tell.
I assume there will be a set of circumstances under which my car would be faster than one with a normal gearbox, and a set of circumstances under which mine will be slower. Certainly I wouldn't bugger about with changing the ratios unless I had a particular goal in mind.
StottyZr said:
Mainly depends on the power curve of the engine. You want to keep the engine producing as much HP as possible, a shorter ratio box can allow for this.
For example if you change from 2nd to 3rd and the revs go from 7000 to 5000rpm, the engine may produce 150hp@5000rpm, a shorter box would allow the car to drop to 5500rpm where it could be producing 170hp. So you have more HP for more of the time. Its not really important for cars with a horizontal power curve, as it'd produce similar HP at 5000 and 5500rpm.
Does the power really matter though? What the car reacts to is the force at the contact patch, i.e. the wheel torque. If you shorten a gear, you increase the torque at the wheels but also reduce the speed it is made at. Is there a gain? For example if you change from 2nd to 3rd and the revs go from 7000 to 5000rpm, the engine may produce 150hp@5000rpm, a shorter box would allow the car to drop to 5500rpm where it could be producing 170hp. So you have more HP for more of the time. Its not really important for cars with a horizontal power curve, as it'd produce similar HP at 5000 and 5500rpm.
Obviously power does matter as it dictates how long you can hold each gear. More power is effectively the ability to maintain a high torque multiplication (lower gear) for longer meaning more average acceleration. If you're stepping down the torque multiplier more often, surely it all averages out?
I guess this can be divided into two scenarios:
Final drive change, the car is optimally geared as standard, both aero and gear limited to 150mph.
Does a shorter final drive improve acceleration from 0-vmax?
Ratio changes. The car is optimally geared so that shifting at peak power means it will drop to peak torque in the next gear. Will closing the gap between gears net a gain?
Edited because I mis-spelt 'shifting' and got censored.
Edited by Kozy on Monday 17th December 14:16
It is absolutely about dialing the gearbox into the engine's useful power, most of which will be between a mid range RPM figure and somewhere up near the rev limiter. if each upchange places you at the point where you are just into that useful range then the whole thing works much better. I have built quite a few peugeot BE3 boxes with a lower third/fourth/fifth, and the transformation is huge. as the revvy little Mi16 then doesn't die on its feet when you change second-to third and so on. But without a sixth gear you then have to live with a rapid accelerating car that cruises at 5000 rpm at 88 or so.
A cammy screamer will have very different characteristics from a V8, and a high boosting turbo is different again.
For the rear drive stuff, ZF and Getrag both made dogleg close ratio direct-drive-in-fifth (rather than overdrive fifth) gearboxes for exactly the purpose of making the same engine and car combination quicker, at the expense of cruising comfort.
A cammy screamer will have very different characteristics from a V8, and a high boosting turbo is different again.
For the rear drive stuff, ZF and Getrag both made dogleg close ratio direct-drive-in-fifth (rather than overdrive fifth) gearboxes for exactly the purpose of making the same engine and car combination quicker, at the expense of cruising comfort.
Flatinfourth said:
It is absolutely about dialing the gearbox into the engine's useful power, most of which will be between a mid range RPM figure and somewhere up near the rev limiter. if each upchange places you at the point where you are just into that useful range then the whole thing works much better.
That sums it so nicely, one of the most obvious examples of this I experienced was in a 106 Rallye (the early 1.3 version). The whole character of the car meant you were whipping through the gears, keeping in the power band thanks to its close ratio box. The big downside was that at motorway speed you really needed 6th or 7th gear, which was unfortunate as it only had 5!Most pro racing cars are geared to suit which ever circuit there on, there's quite a big difference between Monoca gearing and Monza!
Ozzie Osmond said:
What is "faster"?
Many cars with a quick 0-60 ststistic are specifically geared to just hit 60 in second gear, meaning only one gear-change. Doesn't mean the car is quick to 70 though!
Lower gearing = faster "in gear" acceleration, but more gear changes. Swings and roundabouts.
Also, the "width" of a gear depends on the engine's rev range and its usefulness depends on the torque curve. In other words there are many variables.
I suspect there have been more than a few gearbox ratios specifically chosen to hit the magic 0-60 or 62 in just before the change up to third. Marketing chosen over engineering.Many cars with a quick 0-60 ststistic are specifically geared to just hit 60 in second gear, meaning only one gear-change. Doesn't mean the car is quick to 70 though!
Lower gearing = faster "in gear" acceleration, but more gear changes. Swings and roundabouts.
Also, the "width" of a gear depends on the engine's rev range and its usefulness depends on the torque curve. In other words there are many variables.
Dave Hedgehog said:
quiraing said:
What's definition of "tractive force"?
whats the definition of "of?" Now is that a simple enough question and is the grammar and spelling correct? Even if it's not, do you understand the question?
You'll find most cars are over geared for economy or pleasant cruising down the motorway. However your 200bhp hatch etc will only get you to about 140 if you have an Autobahn at your disposal, it's probably got the gear ratios to do 155, so if you never see an Autobhan and do like to boot it down a B road or a tight track (not even that tight - I could only just hit 133 down Lavant straight at Goodwood with 265bhp in a 900kg car gear limited to 135) then you may as well knock the whole lot down with a lower ratio final drive, top end down to a gear limited 120, you will get there a fair bit quicker.
I got caught out once by gearing, never riden a proper motoX bike 450cc, was riding a 100bhp 600cc daily got on motoX bike and gave it a handful and promptly flew off the back, bike geared to do 70 flat out with 60bhp would ruin the 100bhp one off the line geared to do 140.
I got caught out once by gearing, never riden a proper motoX bike 450cc, was riding a 100bhp 600cc daily got on motoX bike and gave it a handful and promptly flew off the back, bike geared to do 70 flat out with 60bhp would ruin the 100bhp one off the line geared to do 140.
quiraing said:
Dave Hedgehog said:
quiraing said:
What's definition of "tractive force"?
whats the definition of "of?" Now is that a simple enough question and is the grammar and spelling correct? Even if it's not, do you understand the question?
Captain Muppet said:
Don't the F1 teams spend ages optimising gear ratios for each track? There will be a "best set" for qually, an "best set" for the race and a "best set" for the race laps without DRS. Lower gear ratios than those will make the car slower.
You are right, there are three best sets - but F1 rules only allow you to choose one. The rules mean the same gear ratios are required from qualifying onwards. Generally the gear set is chosen via simulation prior to the race, using tractive effort, and also balancing cornering and top speed for the lowest lap time. Previously this simply meant taking into account the car's predicted drag, wind speed and direction, engine power and the length of the straight.
DRS then forces you to choose between those three sets you mentioned. Longer ratios avoid lengthy periods sitting in the rev limiter with DRS active, particularly when qualifying, but then the gears can be too long for the optimum race lap time when DRS is not active. So you need to weigh up whether you will be using DRS lots (following other cars), and go for longer gears in the race, or whether you will be in front not using DRS, so can gear shorter for the better non-DRS lap time, hoping that your better lap time is sufficient to keep you ahead. The latter is what Red Bull like to do, hence the abysmal top speed at most races.
I believe next year the 'free' use of DRS in practice and qualifying will be gone, which will reduce the difference between the optimum qualifying ratios and race ratios.
But having done all this, the driver might find (s)he's between gears in a certain corner, or for a particular corner, one gear is too low, but the next too high, and resolving this might make the car more drivable and so give better lap times.
andy43 said:
quiraing said:
Dave Hedgehog said:
quiraing said:
What's definition of "tractive force"?
whats the definition of "of?" Now is that a simple enough question and is the grammar and spelling correct? Even if it's not, do you understand the question?
BACK TO OP:
The problem with shortening your gearing is that you are fooled in to believing the car is faster simply because you're going through the gears faster. You need to actually have data to check if there's a real benefit. You might not be fully utilising your cars torque band or getting too much wheel slip. You will notice the biggest difference on a car that has a 'peaky' torque delivery.
GroundEffect said:
andy43 said:
quiraing said:
Dave Hedgehog said:
quiraing said:
What's definition of "tractive force"?
whats the definition of "of?" Now is that a simple enough question and is the grammar and spelling correct? Even if it's not, do you understand the question?
BACK TO OP:
The problem with shortening your gearing is that you are fooled in to believing the car is faster simply because you're going through the gears faster. You need to actually have data to check if there's a real benefit. You might not be fully utilising your cars torque band or getting too much wheel slip. You will notice the biggest difference on a car that has a 'peaky' torque delivery.
Depends on whether you ideally need torque or max power and depends on the event. Lower final drive = lower top speed, but the car is more flexible with the power you have. Wheel slip factor is always interesting and changes by the minute, have to drive accordingly, and must always remember to look up the charts half way round the corner.
But, when it comes down to it, you just get in the fkn car and go!!
Short ratio gearbox is fine but only when matched to suitable final-drive ratio.
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