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4 Wheel Drive Rally Cars - Printable Version

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4 Wheel Drive Rally Cars - BAracer - 21st-Jul-21

Looking ahead to some rally driving over the winter, I have acquired a couple of 4WD rally cars. So primary drive to the rear wheels, belt drive to the front. 

Any tips for setting up the tyres, e.g. balancing the grip levels front vs rear? Or is it simply a case of max grip all round? 

Any tips for initial weight balance front to rear? 

Any argument for removing the belt and just running 2WD at the rear? 

Thanks in advance...

RE: 4 Wheel Drive Rally Cars - chrisguyw - 21st-Jul-21

Largely depends on the track surface !!.................if the tracks have anything added to the surface to replicate snowy/muddy/loose conditions, there is an argument for 4WD.

If the tracks are "clean" and consistent, I would favour rear wheel drive every time

Cheers
Chris Walker

PS if employing 4WD, different tyre compounds, different ratios, and different tyre diameters (all of these front to rear) are commonly utilized.

RE: 4 Wheel Drive Rally Cars - Scuderia_Turini - 21st-Jul-21

The belt drive to the other axle is just extra friction to consume motor power. Where there is a long motor shaft to one axle, that will sap motor power unless the shaft is perfectly true and has a locating bearing at the end beside the pinion.
So, as Chris says, unless the track surface is raid-type or has some form of coating then removing the secondary drive kit will mean that all available motor power and torque goes to the primary drive.
However, some events require the all-wheel-drive to be retained.

Leo

RE: 4 Wheel Drive Rally Cars - rallyhub - 22nd-Jul-21

As already mentioned here, testing is most important.
A 4WD car with a dual shaft motor can be easily converted for testing to 2WD by removing the front pinion. Then lap times can be compared.
The same can be done with a belt drive car by removing the belt, or even experiment with different belt lenghts and diameters.
About that theme I wrote an article in the October 2007 issue of the NSCC Journal page 15 till 18 for Scalextric belt drive front motor cars:
http://www.nscc.co.uk/pdf/journal_2007/October%202007.pdf
Maybe the upcoming September issue of Slot Car Magazine will be useful:

It will contain an article about the testing of the whole SRC rally tyre range with all different sizes, materials and compounds.

rallyhub Thumbup

RE: 4 Wheel Drive Rally Cars - BAracer - 22nd-Jul-21

(22nd-Jul-21, 09:32 AM)rallyhub Wrote:  Maybe the upcoming September issue of Slot Car Magazine will be useful:

It will contain an article about the testing of the whole SRC rally tyre range with all different sizes, materials and compounds.

rallyhub Thumbup

Any excuse to show off my SRC tyre chart...

[attachment=16463]

RE: 4 Wheel Drive Rally Cars - rallyhub - 22nd-Jul-21

Hi Jeremy,

You have put a lot of work into your enlightening tyre chart.
It wouldn't be nice if I appropriated your work for publication in the magazine.
I did make a table of the test results.

Hub Thumbup

RE: 4 Wheel Drive Rally Cars - OXO cube - 22nd-Jul-21

recently entered a 4wd SCX seat Cordoba into the wye summer rally as a proxy entry 
i used the TecniToys Pro Turbo 4x4 motor 
changed the gearing so the fronts wheels were faster , thinking they would in effect pull the car around corners and left the original rear gearing 
supported the long motor shaft to remove play and keep the gears in mesh  
fixed the braids to get maximum guide depth 
used a nice average weight with a 40/60 balance 
lexan interior and glazing 

was hoping for great ( or atleast decent ) things , but alas disappointment was on the horizon   

it came 2nd last !?!?!?!?
my 2wd Scally TR7 rebuild performed better!?!?!?

however upon return i noticed one of the rear bushings had popped out ( i had forgotten to fix in place )
not sure if this happened in the return post or not ?
after repositioning and gluing the bushings it runs great now and beats the pants off the TR7 hands down so maybe it went un-noticed 
but either way it was a lesson learnt ( glue/fix  bushings every time )

having said that i would agree with both Leo and Chris , rear 2wd is the best route 
the Cordoba will now have to wait for a 4wd only class me thinks 
but i must say i really enjoyed the 4x4 build  Bigsmile

Kev

RE: 4 Wheel Drive Rally Cars - rallyhub - 22nd-Jul-21

(22nd-Jul-21, 01:25 PM)OXO cube Wrote:  changed the gearing so the fronts wheels were faster , thinking they would in effect pull the car around corners
That increased understeer. The car wants to go staight out of the bends into the bushes. Wavegreen


The advantage of a belt drive is you can regulate under- or oversteer by chosing the right belt dimensions.
Another advantage of a belt drive to the front wheels is its self regulating effect:
When entering a bend, the resistance on the front wheels increases (inner wheel wants to go straight). The belt will smoothly start to slip over the pulley(s).
Now the drive forces will go more and more to the rear axle, causing more oversteer, that turns the car into the bend.
At the end of the bend the resistant at the rear wheels increases, lifting the front of the car, which results in less slipping of the belt and more power to the front axle, which decreases oversteer.
That's exactly what you need to get out of the corner quickly.
I tested this many times on my Ninco belt drive cars. With the belt mounted (4WD) the car was faster and very smooth.
Maybe on a track with very, very long straights, the belt will create resistant and make the car slower than a 2WD setup.

Hub Thumbup

RE: 4 Wheel Drive Rally Cars - Kevan - 19th-Oct-23

A timely revisit to 4WD with Slot Rally UK visiting clubs next April.

4WD is only competitive in a 4WD class (or Raid) 2WD wins our Rally events every time. 

My most competitive...SCX pro Citroën Xsara WRC, yes it has a slightly modified chassis with floating brass side pans but the rest apart from NSR rear tyres is out of the box.

RE: 4 Wheel Drive Rally Cars - BAracer - 19th-Oct-23

Cards on the table...I've invested in a 4WD SRC Delta S4 to bolster my entry into the UK Slot Rally next year. I'm putting my faith in 4WD and taking up the challenge of trying to harness the additional grip that four driven wheels must give. 

I just re-checked the Abergavenny Summer Stages results. My 4WD 205 and 2WD 208 both ran well, but the 205 just came out on top.