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Tony
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2,834 Posts
Discussion Starter · #1 ·
I am sure that some of you here have built four wheel drive cars, I intend to build one using a Scaley Mini Clubmand shell. My question is, do you use the same gear ratio for front and back axles, I ask this because most real four wheel drives put more power to the front axle. Sense tells me that they should be the same but I felt it better to ask. I will be using a JK Hawk motor which has a shaft long enough to power both axles. Thanks in advance

Tony
 

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Horlicks Hero
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1,940 Posts
QUOTE (Bigtone @ 18 Jun 2012, 11:48) <{POST_SNAPBACK}>I ask this because most real four wheel drives put more power to the front axle.
Real as in 1:1 cars ? Then I would have to disagree with you. As examples, my old Subaru Impreza 2.5RS had a VLSD that nominally split the torque 50:50 until something started to slip, my current Subaru Impreza RA has an adjustable center diff that when open has a 65:35 split in favour of the rear, but can be electronically adjusted until it achieves a 50:50 split with no slip allowed, a Nissan GTR sends most of its torque to the rear, with just a small amount sent to the front and the MazdaSpeed is predominantly a front wheel drive car until the computer deigns to send a bit of torque to the rear in the faintest of nods to allwheeldriviness.

However, in answer to your question, my recently purchased SCX Pro Citroen Xsara has different sized crowns front and rear. I haven't had a chance to run it yet, so I don't know how well this makes it behave, but the precedent is certainly there for choosing different ratios front and rear on an AWD slot car.
 

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I've got 20-odd SCX 4WDs and they all have the same gears and tyres front and rear. I've read that the SCX pro cars (as mentioned by Stuart, above) have a smaller crown on the front axle. Apparently(sp?) this is supposed to help pull the car through corners but I can't comment on that never having had or seen one. Fitting smaller tyres on the front has the same effect.

I also have a fair few band-driven 4WDs, of various manufacturers, and they all have the same pulleys front and rear.

Personally I can't see any advantage in having front and rear tyres turning at different speeds. The majority of my slot cars are 4wd and they are all 50/50.

HTH
 

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Most 4x4 slot cars are set up with the same geraing at both ends, but they run better when the front wheels don't touch the track, so the gearing makes little difference.
 

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Rich Dumas
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3,546 Posts
Several years ago a member of my club built a 4WD car for a proxy series that was quite sucessful. The car used a Slot.it HRS chassis and a sidewinder motor pod. Drive to the front wheels was via pulleys and a belt. He got the best results if the front wheels were turning a little faster than the rear wheels.
 

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Eddie Grice
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2,295 Posts
QUOTE (RichD @ 18 Jun 2012, 13:29) <{POST_SNAPBACK}>He got the best results if the front wheels were turning a little faster than the rear wheels.
I agree, as a general rule it's better to have a 4wd slotcar's front wheels running slightly faster than the rear.
Eddie
 

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Premium Member
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The daddy of them all, the MRRC 4WD Merc, used a smaller bevel gear at the front, and smaller wheels/tyres at the front.

Partly the reason for this was that the real Merc has smaller fronts, and also if the gear at the front was larger it would have sawn the guide in half.

Legend has it that they were quicker with a 0/100 torque split - front drive disconnected!

In the mid-80s Ian Fisher built a 4WD Galaxie with twin inline 16Ds in a simple piano wire and brass chassis to get more grip and therefore speed on the slippery Quorn track. It was good there, and average to good elsewhere.

Gary Cannell had a beautifully-built brass and wire Front wheel drive car which was interesting and quite exciting when it came off the track as it had no motor and rolling resistance to slow it down, but that's another story.

Hope this helps

Rob
 

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Circuit Owner
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5,892 Posts
QUOTE (StuBeeDoo @ 18 Jun 2012, 13:09) <{POST_SNAPBACK}>I've got 20-odd SCX 4WDs and they all have the same gears and tyres front and rear. I've read that the SCX pro cars (as mentioned by Stuart, above) have a smaller crown on the front axle. Apparently(sp?) this is supposed to help pull the car through corners but I can't comment on that never having had or seen one. Fitting smaller tyres on the front has the same effect.

I also have a fair few band-driven 4WDs, of various manufacturers, and they all have the same pulleys front and rear.

Personally I can't see any advantage in having front and rear tyres turning at different speeds. The majority of my slot cars are 4wd and they are all 50/50.

HTH

Please don't interpret this as nit picking - no offence intended, I am just saying this in case somebody reads this and takes the advice given - fitting LARGER tyres (not smaller tyres) to the front wheels would have the same effect as fitting a smaller gear.

StuBeeDoo is absolutely right - a smaller gear has less teeth and so will turn more times for any given number of motor rotations. This means the road speed of the tyres would be faster at the front than the rear when identical wheels and tyres are used front and rear.

If the gears are the same front and rear then the way to increase the road speed of the front wheels would be to increase their diameter (whatever combination of tyre and wheel that made the overall diameter larger than the rear). This way - for an identical number of axle rotations the front wheels would travel further.

I believe some recent SCX cars have a smaller front gear - this is because the overall diameter of the front wheel/tyre combination is also a bit smaller than the rear (as the 1:1 car) - so the overall effect of smaller gear and wheel/tyre at the front delivers the same distance travelled per motor rotation as the rear drive - an attempt to keep it 50:50.

I agree completely with StuBeeDoo on the 50:50 thing - same drive speed front and rear.

The problem with trying to have different drive speeds front and rear is that you will inevitably increase wear into the drivetrain - with belt drive this would cause belt slippage and make the car less smooth to drive. With direct drive it will make the tyres turn at different speeds and cause lack of grip (like having permanent wheelspin on two of your wheels). Splitting torque in 1:1 cars does not force the wheels to turn at different speeds - it is designed to put more power where it will do most good and that is when all wheels are driving and not slipping. You balance torque because it takes more effort at one end of the car to turn the wheels at the same speed as the other end.

Ask any driver of a LandRover who locks the diff on tarmac - the transmission winds itself up into knots that let go with alarming unpredictability with wheel spin (or a broken transmission). I used to have one so I have experienced it (the wheel spin not the broken transmission fortunately). On some early military versions the diffs were permanently locked and drivers were taught to bump over kerbs every now and again to allow the transmission to unwind itself! (my stepdad was one of those military drivers).

I imagine that forcing slot car wheels to turn at different drive speeds would be the same as locking the diff on a high grip surface. I imagine that would cause significant extra tyre wear and make the car slide more through lack of grip. I haven't tried it myself - does anybody out there have the answer?
 

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Nobby Berkshire
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2,015 Posts
Slotcars do not behave as real 1:1 cars as the mechanics are completely different, so there's no point comparing like with like. Fit hubs and gears that you can refit and experiement with different gear ratios to find what gets you the best results.

But I doubt if having one motor driving two axles with the same rpm in different ways caused by a competing gear ratio combination will only prove detrimental to smooth racing in a toy car.
 

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Alexis Gaitanis
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2,398 Posts
QUOTE (Mr Modifier @ 18 Jun 2012, 21:50) <{POST_SNAPBACK}>I believe some recent SCX cars have a smaller front gear - this is because the overall diameter of the front wheel/tyre combination is also a bit smaller than the rear (as the 1:1 car) - so the overall effect of smaller gear and wheel/tyre at the front delivers the same distance travelled per motor rotation as the rear drive - an attempt to keep it 50:50.
Only the SCX Pro Xsaras have a smaller front gear out of the box .The above comment is allways valid when smaller front tires are used.It seem that it has to do with the grip though.I've been testing a Delta Integrale with different wheel dias front and rear and different ratios,started with 9/29 rear 9/26 front then changed rear to 9/28 and the car improved.I have to find the reason for the car beeing tail happy on clean track,gears or tires?On the other hand tested on a stage with cocoa left over from the last championship race it seems that you get better pull exiting corners as it is.
 

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Circuit Owner
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OK now that's interesting - I'm referring to the cocoa scenario.

Do you think it's because the front is always trying to "get away" from the rear (because the front wheels are rotating faster)? On a power slide/drift where all 4 wheels are sliding I guess this would tend to pull the rear back into line providing front and rear have the same levels of grip.

Oh for a high speed video camera so we could look in detail at what the wheels are doing relative to the track surface!
 

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Johnny Fuglestad
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417 Posts
at our tracks wood and sport the fastest setup with equal tyres front and rear, is with frontwheels overdriven 1 or 2 tooth crown smaller in front. When car lean over in curves the frontwheel get grip and drag the rear of the car after it resulting in less rear slide/faster cornering.
 

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Avant slot rally cars have a smaller front puller as do prorace ninco's
MSC Gp B cars are equal front to rear but the Suby has more drive to the front
With the amount of slip and wheelspin you get in slots windup is a not issue - just look at a std front axle
Which works better - I'm not sure - I do know that 4wd is the faster way around MY rally track - I did blind tests with my son removing the drive belt in his Avant slot EvoX
Cheers
 

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QUOTE (RSCLIO @ 19 Jun 2012, 07:14) <{POST_SNAPBACK}>Which works better - I'm not sure - I do know that 4wd is the faster way around MY rally track - I did blind tests with my son removing the drive belt in his Avant slot EvoX
It's horses for courses. I wasn't convinced of the benefit/necessity of a 4WD slot car, so the first couple I bought, I disabled the drive to the front. I haven't done any back-to-back RWD/4WD lap time comparisons on individual cars, but all my 4WDs are now 4WD and on my track (44mtrs) they are at least 2sec a lap quicker than any of my RWD cars.

So I agree with RSClio.
 

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Tony
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2,834 Posts
Discussion Starter · #17 ·
Hi John
I like a challenge and the Hawk 6 is small and powerful and can be tamed with an electronic controller and I am going to use Voki gears. I am already building a front wheel drive anglewinder mini clubman. It has 5/8ths wide sponge tyres and the rear wheels can revolve independently and the motor is a hawk with an Proslot Puppy Dog armamture.
Tony
 

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It must be horses for courses.
I remember the best 4WD car I'd ever seen suddenly started going better than ever. On careful inspection the reason for the extra speed became obvious - the front pinion had come unsoldered so it had converted itself to RWD.
I think 4WD has the best chance of being competitive in relatively low grip situations - rather like it is in full size.
 

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Alexis Gaitanis
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2,398 Posts
I just checked ratios of the Integrale.
Previous setup
Rear 9/27 with wheel dia 19.5 or 20,41 mm/rotation
Front 9/26 with wheel dia 16.8 or 18,260308 mm/rotation.
The reason for using so small tires in front is that the car has to deal with several jumps so i want to give the guide maximum vertical travel.
The car was tail happy.
I switched to 9/23 in front or 20,642087 mm/rotation.
At home it looks good,but will have to chek on cocoa at the club,next week.Will post results.
I will also try is 9/24 in front or 19,782 mm/rotation
 

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QUOTE (pasiro @ 19 Jun 2012, 16:38) <{POST_SNAPBACK}>Both my prorace ninco's have had the same all round


That'll teach me to make a genralisation we have a Ninco Colberg C4 that is geared taller at the front
 
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