XRAY - Model racing cars

XRAY Oil Conversion Table




The links below reference to other charts & conversion sites





(Asc vs. Losi vs. Old XRAY vs. New cSt XRAY)

The compact allows you to quickly and easily balance car tires by identifying the heaviest part of the wheel so that proper balancing aids can be applied. This also helps to identify improperly glued rubber tires or differences in inserts. Precision-balanced tires will improve your car's traction and stability, and also give improved shock absorber action.



Wheel adapters are available optionally for different scale wheels:

Diff shimming quick tip


1) Build the drive shaft, pinion & bearing assembly as normal into the bulkhead.
2) Build diff case, gasket & bevel gear with two screws only just to hold together.
3) Now the bearings can be loosely attached with shims to the diff & whole assembly into bulkhead assembly.
4) Make sure the F & R bulkhead cases sits square against each other, or if needed use the wood screws & front wishbone mount to achieve this.

Picture shows holding the drive shaft in the palm of ones hand pulling slightly whilst checking play on the diff gear.

This method just allows for quick shimming prior to fitting outdrive & filling with oil.

FAQ on the 41 Tooth Overdrive Gear

Principals on when & how to use it for its best results.

This gear when used will physically overdrive the front & basically make the front wheels turn faster than the rear. It will work at its best on hairpin style tracks or when you are pushing past the apex on a tight turn.

How it works is when your off power & slowing or breaking into a corner the weight of the car transfers forward & so loads the front wheels. The loading of the front wheels now means the front wheels are traveling at the speed of the car & by them being overdriven means they are turning faster than the rears. What this does is makes the rear wheels act like a break & in a way skid the rear of the car around but under control, giving the better turn in.

When you exit the turn on power the weight transfer is towards the rear now & the rear wheels take up the load & speed of wheels turning. The front now being unloaded & overdriven means by it turning faster pulls the front out of the turn giving more steering pull but greater stability over bumps as again it is being pulled.

The 41t gear is a tunning aid & for the std diff the oils remains the same & does not need altering.

FAQ on the Front active Diff

The active diff works like a conventional diff in how it turns through a corner & so can be adjusted with oil to slow or speed this action. The difference is when power is applied, as when a wheel off loads or diffs out normally on a conventional diff power takes the easy route & away from the load wheel & will unsettle the car. The active however locks at this point via the internal mechanism re applying the power to the loaded wheel bringing back stability & drive..

The speed it locks is adjusted by the v shaped cams or segments which come in a 90 deg or 120 deg pair. How these are used is down to driver preference & has no real golden rule, other than
90 deg for slow or smooth lock
120 deg for fast & aggressive lock

Oils to use

Again is down to driver preference but would advice when swapping from your std diff to the active run the same oil first, from here you can then adjust to get your desired balance but normally from experience you will end up going down in oil for greater turn in.
From experince 5k for a std diff & 3k for the active on dirt when uing the 808.
The XT8 find 5k is a good start point for the active.
Some of you will think i use this or that but this is a guide only or start point.

Where to use

It seems to give its best advantage on fast smooth flowing tracks with fast sweepers, in these areas will give better pull & balance over a std diff.
If you are still needing more turn in on the slow turns use the 41t specific overdrive gear.

Where not to use which i hate to say.

Undulating low grip tracks seem to cause a confussion in the diff as it senses or reacts to the continual change in loss of traction. It seems to pull unpredictably at the steering. An example of this is harper adams or better known the Neo track in th UK. For here the traction is always low & has many adverse cambers & undulating sections requiring the use of soft tyres. This combination for some reason just causes problems.


The Front Active is a great tunning aid & again just needs you to practice with it to see what suits you in how you drive.

XRAY XB808 Diff Bearing Tech Tip

It has been found that pinion bearings — if not maintained correctly and also when used in extremely dusty conditions — can in some circumstances have failures.

Please follow this tip and use HUDY Bearing Grease #106220 to increase the lifespan of the bearings considerably. The tip works for both the original 2-bearing & 3-bearing pinion designs.



With pinion assembly built, slide the driveshaft-side bearing on, and then apply grease to the face where the spacer sits.



Apply the spacer and then fill the remaining gaps with grease.



Now fit the 2nd bearing and remove any excess grease that is pushed out.

If you are using the new 3-bearing pinion, apply a small amount of grease on the 3rd bearing face, then fit and remove any excess grease.



Prior to fitting the pinion assembly to the diff bulkhead, apply grease to the drive shaftside bearing face. When assembled this acts as a seal to the bulkhead.

We recommend that this procedure is performed every 2-3 hours to dramatically increase the bearing lifespan and help to achieve a problem free drivetrain. If you are running in extremely dusty conditions, repeat this procedure more often .