XRAY - Model racing cars

It really depends on the drivers style, track grip and tire combination. But I believe most of the team drivers have faster overall race times because they can run more consistent lap times with the spool.

I've found this to be the case for medium to low grip tracks where I also use a spool. But for high grip tracks I prefer a one-way used in conjunction with a softer rear tire to balance the front/rear grip. Different front/rear tire compounds may not be available though in a lot of controlled tire races.

Hey TeamGP, I just picked up the multidiff for my FK'05. A couple of questions. Can you explain the diffrence between a spool and a oneway. And under what conditions would be better.

Also I read in the Faq's to put a rubber washer on each side of the multidiff so it doesn't separate. Is this really nessessary? Have you ever had any problems? Also have you had any problems with the black blades getting destroyed using the spool.

Thanks.

It makes it possible to effectivly use the brake on tracks where braking is required such as last years worlds track and also this years Euros track, both these tracks had hairpins and chicanes where braking is usually required. A lot of drivers is using it on all asphalt tracks today because it makes the car more consistent and easy to drive as mentioned by teamgp. Some guys even use it on carpet with rubber tires because it is so consistent and makes the car dead stable compared to one-way which can make the car too twitchy and hard to drive. Normally you need to change your setup a little if you were using oneway.

On the spool we should distinguish between the FK05 and previous models. With the previous models I have allways struggled to get enough steering when running a spool and whence preferred to run a one-way under most circumstances (rubber tyres). With the FK05 I don't have a significant loss of steering when I use a spool. In fact steering is the same as are the laptimes. The main advantage is in the consistency and the fact that I can use the brakes. Overtaking has become much easier, especially if the other guy is running a one-way. The only disadvantage is that I lose about 20 seconds of runtime which puts me on the edge of dumping with 3300s. With 3700s on the other hand......

Mario gives a good explanation of how the three different settings affect the rotation of the front wheels here:

http://www.teamxray.com/xforum/viewtopic.php?t=1054

With a full one-way, you will have the most efficient use of power from your motor since both of the front wheels, which pull the car out of the corners, will always have 100% of the power as oppossed to a standard limited slip diff like you have in the rear. But since both front wheels turn at their own rate, steering is increased significantly and the car can become twitchy and oversteer a lot if the setup is off slightly. Brakes are non-existent, or very light if you turn down the braking EPA to about 50% on your transmitter so the rear end doesn't slide around when you use them.

With a locked one-way, the turn-in steering becomes more manageable but the trade off is that the front tires will fight each other and scrub more cornering speed throughout the entire corner. You still have the problem with brakes here as well. More stress will be applied to the driveshafts, cups and plastic blades as the front tires fight each other under power. Runtime is sacrificed some since the tires are fighting each other on-power.

With the multi-diff fully locked as a spool, you now have brakes! You can use them to stay on the gas longer and dive underneath to make a pass. Turn-in steering is decreased the most with this setting and you may have to change your setup to compensate. Runtime is sacrificed the most with the tires fighting each other on-power and the motor braking using battery power as well. But consistency is increased. Especially in low to medium grip situations. Usually good grippy tires (RP30's are wonderful), more rear droop, a higher rear ride height, layed down front shocks or more front toe-out will give you enough turn-in steering if you need it.

Peter,

I believe according to Tony's response that most drivers use a spool due to the power in todays mod motors. It's just plain easier to drive and it does let you use brakes.

The main problem with a diff when used with rubber tires is it's lack of on power steering. The spool solves this since it locks the front wheels together which helps to "pull" the car out of the corner.

In general everyone uses a diff in the front when running foams, especially on carpet. Of course in that situation on power steering usually isn't an issue. In fact I'd imagine the car would become harder to drive with a spool in it since traction is so high on carpet. I've never tried a spool on carpet as we only run foams in my area. With rubber tires it might still work.

Roy is correct concerning the spool for mod/rubber/asphalt racing.

Not everyone runs a diff with foams on carpet though.

A one-way works great if your driving style consists of maintaining high corner speed and being on the gas earlier and all the way through the exit. But drivers who are used to drag braking, rotating more through the apex at neutral throttle, and then increasing the throttle after the car is pointed more towards the next corner, have a hard time with the high amount of corner exit steering that the one-way provides.

However, the spool on carpet with foams normally makes the inner front wheel fight the outer one, due to the combination of high grip and differing corner radiuses per tire. I tried the spool and found that the dog bone blades were chewed up quickly and the front tires would "skip" and wear more.