Changing Final Drive any downsides?
Discussion
Thinking of changing the final drive in my Clio 172 tack\race car. Gearbox is coming out (for a leak) so fitting an LSD and maybe a shorter FD while it's out.
Looking at a Bacci 12\58 which will give a top speed of 131 in 5th (only ever reached 115 top speed in any race).
Any downsides that I won't be aware off?
Not too experienced , started 18 mths ago (couple of kart\car track days before this) with a std 172 cup (now stripped and race prepared) and have completed 3 races this year, Brands, Mallory & Donington.
Thanks....
Looking at a Bacci 12\58 which will give a top speed of 131 in 5th (only ever reached 115 top speed in any race).
Any downsides that I won't be aware off?
Not too experienced , started 18 mths ago (couple of kart\car track days before this) with a std 172 cup (now stripped and race prepared) and have completed 3 races this year, Brands, Mallory & Donington.
Thanks....
How do you find your current gear ratios, particularly in the lower gears out of slow corners. If you fit a shorter final drive you might find that 1st is now too short to comfortably shift down to, or that you find yourself awkwardly in between gears at certain positions on a race track. If you're happy with your current ratios in the lower gears, I'd be inclined to leave them alone because if you end up short shifting or 1st gear becomes less usable, it could actually cost you lap times.
I don't know the renault's gear ratios but I know that in my car I'd like a longer 1st, and a shorter 5th...
I don't know the renault's gear ratios but I know that in my car I'd like a longer 1st, and a shorter 5th...
Here are my proposed changes -
and this is the std FD ratio
At the moment I've never used 1st (apart from the start) 2nd - most hairpins (Mallory), never at brands or Donington.
A lap of brand is 4th for paddock - 3rd for druids - fourth along Copper straight, 3rd goind into clear ways and the 4th just after the exit and 5th just passed the start finish line....
All fairly comfortable I'd say myself.
300bhp/ton said:
You might want to check terminal speeds in gear and see how it affects it. Overall I'd have thought it'd be good, but you might create a few flat spots. It will mean more gear changes and you need a driving style to suit i.e. spending more time in the higher revs.
Terminal speed seem to be ok --130 as at the moment I've never got much past 115 - maybe 120 on the back straight at Snetterton..Trying to work out my Brands gear changes now...will have to watch a lap and note the revs speed of each change and & adjust with the ne FD ratio - crude but should give an idea.
Toastfrenzy said:
Well, I would be expecting some improvement - can you expand, after all I'm not wanting too waste 5-£700 fitting a different FD if the results don't warrant the outlay.
A lot of people seem to get suckered into the marketing with shorter gears, the sales pitch along the lines of "20% more torque to the wheels" is technically correct, but also misleading. If it were 20% more torque at the same speeds then yes it would be significantly quicker, but gearing just scales the engine output, so what you actually get is 20% more torque at 20% less speed. If you did that on the engine's torque curve, the power output would remain unchanged.The net outcome is that while the peak acceleration in each gear is higher, it's delivered at proportionally lower speeds and the overall acceleration of the car is not altered greatly. It will have a slight improvement, but if the change in ratio suggests that you'll gain 20%, it will nowhere near modifying the engine to deliver 20% more torque.
If you are looking to improve laptimes, I'm not sure it represents a good value modification over engine tuning. The LSD however, definitely does.
Krikkit said:
Also worth thinking about what kind of diff you're using if it's getting pulled to bits - a plate is a significant upgrade from an ATB/Quaife type.
The only thing putting me off the plate diff is the maintenance - I can't get the box out myself (would have to pay to get it removed) and not too sure of the cost of the yearly strip & re-plating. Guessing that would be at least 2-£300 plus the £150 to remove - refit the box.Not sold on the ATB - yet, though I've got an option on a 1 year old one, been used in 4 races, in the pipe line. This may be the deciding factor (cost and maintenance) for an LSD...It'll be an improvement over the open STD one fitted at the moment.
Kozy said:
A lot of people seem to get suckered into the marketing with shorter gears, the sales pitch along the lines of "20% more torque to the wheels" is technically correct, but also misleading. If it were 20% more torque at the same speeds then yes it would be significantly quicker, but gearing just scales the engine output, so what you actually get is 20% more torque at 20% less speed. If you did that on the engine's torque curve, the power output would remain unchanged.
The net outcome is that while the peak acceleration in each gear is higher, it's delivered at proportionally lower speeds and the overall acceleration of the car is not altered greatly. It will have a slight improvement, but if the change in ratio suggests that you'll gain 20%, it will nowhere near modifying the engine to deliver 20% more torque.
If you are looking to improve laptimes, I'm not sure it represents a good value modification over engine tuning. The LSD however, definitely does.
Good point....The net outcome is that while the peak acceleration in each gear is higher, it's delivered at proportionally lower speeds and the overall acceleration of the car is not altered greatly. It will have a slight improvement, but if the change in ratio suggests that you'll gain 20%, it will nowhere near modifying the engine to deliver 20% more torque.
If you are looking to improve laptimes, I'm not sure it represents a good value modification over engine tuning. The LSD however, definitely does.
Will have to get my lap of Brands and work out the where the "new" gear changes will be, I'll do that for Mallory and Donington too.. theoretically - I'm thinking 3rd would be 4th...maybe not as easy as that....as I won't know where the 7400 rev limit will be with a shorter FD.
How can I get time distance on the two rpm - speed graphs I posted above?
Yes this is the trouble, you may improve the gearing for one track and make it worse for another. The more you can research and find out the effects in advance, you more you can avoid doing things which become more of a hindrance than an advantage.
If you've got this data, I can probably help you in figuring out speed at various points as I've written a spreadsheet taking all these variables into account to model acceleration distance and time.
Toastfrenzy said:
How can I get time distance on the two rpm - speed graphs I posted above?
Not sure exactly what you mean but that, but I don't think you'll be doing that without engine torque curves, weight and aero data. All of these will affect how quickly you can accelerate, and thus how much distance you can cover.If you've got this data, I can probably help you in figuring out speed at various points as I've written a spreadsheet taking all these variables into account to model acceleration distance and time.
Edited by Kozy on Tuesday 6th November 17:18
Actually thinking about it, the gearing could be related to the distance without all the other stuff, so you could probably figure out shift points around a track, however I should imagine this would end up being incredibly complex and time consuming for little real benefit.
How much does the FD cost, and how much could you do to the engine for the same money?
How much does the FD cost, and how much could you do to the engine for the same money?
Going down a wheel size would have similar effects yes. The effects on RPM and acceleration are probably not as pronounced as a ratio change, but there are more benefits, less unsprung and rotating mass (by far and away the best place to lose weight), smaller, lighter, cheaper tyres etc.
My point is though that personally I would not spend money on gearing that could be spent on improving the engines output unless the car was significantly over or undergeared, which I don't believe a Clio is. Mods like this are great at making the car feel faster, but it's largely placebo with a near stock engine.
My point is though that personally I would not spend money on gearing that could be spent on improving the engines output unless the car was significantly over or undergeared, which I don't believe a Clio is. Mods like this are great at making the car feel faster, but it's largely placebo with a near stock engine.
Kozy said:
Actually thinking about it, the gearing could be related to the distance without all the other stuff, so you could probably figure out shift points around a track, however I should imagine this would end up being incredibly complex and time consuming for little real benefit.
How much does the FD cost, and how much could you do to the engine for the same money?
Around £650, thinking of using Bacci...How much does the FD cost, and how much could you do to the engine for the same money?
http://www.bacciromano.com/index.php?p=prodotti&am...
Euro 1.24 for a £1...
The Clio F4R is and expensive lump to get any worth while gains out off....ITB's are around 2.8K with full management & fitted - for 20-25BHP.....
Any idea how to estimate how quicker the 7400 limit would be reached with a shorter FD..
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