Was wondering if someone can help me get a better understanding of how changing the height of your diff can influence the handling of your car?

Is it related to the the change of the drive shaft angles?

I'm not familiar with any cars that have this adjustment...is this something specific to the Type R? (I ask because I see it in your sig)

-rocky b

05 Xrays had that option too. Good point though, maybe not many cars have that option.

the tc5 also has cams to adjust the hieght as well

maybe something to do with chassis roll and roll center but i dunno either

maybe COG?

The cams on the Xray are for adjusting belt tension, my FK04 has them as well as every other XRay TC that I am aware of. The OP had mentioned changing driveshaft angle, but I'm not aware of any shaft drive cars that have the cams.

-rocky b

the FK05 has oval shaped pieces that the diff cam slides into. You could get these oval pieces in different offsets.

I once read that it had something to do with plunge angle of the driveshafts, but that was a long time ago.

Hmm that sounds plausible...maybe for raising the diff when running ultra-low carpet ride heights to keep the dogbones from binding...or maybe for raising the diff when running different sized diff pulleys to keep them from protruding below the chassis? I know XRay offers different tooth layshaft pulleys (for changing internal drive ratio) and I think they have different diff pulley sizes as well.

-rocky b

is there even such thing of different diff pully sizes?!?

i know for the old rs4's there were different pully sizes that ride off the layshats or something like that

Just checked, XRay offers 32T and 34T diff pulleys, as well as 16T, 18T, and I believe 20T layshaft pulleys.

-rocky b

i see said the blind man

TA05 and derivatives have the same adjustment but I am not sure what it's for. Apart from a marginal drop in COG (and really mean marginal) it can be used to tension the belts to the nth degree as well as allow for the use of different size diff and center pulleys (and Tamiya has everything (or nearly) from 32 teeth to 37 for diffs and center I think you can have 16, 17, 18. Some belts need to be mixed and matched though as pulleys change size significantly, but there you go, you can get any internal ratio you want.

The LOSI chassis has optional 41 tooth diff pulleys (on top of the original 42) and so do the TC5 and I think the Corally RDX versions.

My JRX-S also has adjustable diff heights. Info straight from the manual:

Diff Height: Caution! When adjusting the differential heights, rotate the acentrics as to loosen the belts, rotating in the opposite direction, with the belts installed can severely damage the belts. Diff heights in the JRX-S are also adjustable by rotating the acentrics that positions them. The diffs can be adjusted from a full low position to a full high position. The low position will allow the car to roll more and keep the car in a turn longer, increasing on-power steering. The high diff position will give the car a flatter and more responsive feel. It is also possible to change the balance of the car quite drastically by offsetting the height of the diffs from front to rear. Testing has shown that maximum total steering can be obtained by running the front diff low and the rear diff high. For less total steering do the opposite. For less overall traction run the front and rear diffs in the low position. For more overall traction, do the opposite

JRX-S Type R

Diff Height: Caution! When adjusting the differential heights, rotate the eccentrics as to loosen the belts, rotating the belts in the opposite direction, with the belts installed can severely damage the belts. Diff heights in the Type R are also adjustable by rotating the eccentrics that position them. The diffs can be adjusted from a full low position to a full high position. The low position will allow the car to roll more and keep the car in the turn longer, increasing on-power steering. The high position will give the car a flatter and more responsive feel. It is also possible to change the balance of the car quite drastically by offsetting the heights of the diffs from front to rear. On asphalt tracks with rubber tires, testing has shown the best results with the rear diff in the low position and the front diff in the high position. On carpet with foam tires running the diffs in the low position has yielded the best results.

thanks kcunamay.

There is a bit more info in the older jrxs manual than the type r manual. The info in the Type r manual just gave me more questions than answers.

I would still like to know how changing the diff height causes these effects.

The effects are because of the geometry(sp?) change of the driveshafts. It's not a weight thing.

This is something that was posted by Levanen from AE a while ago when some one asked about diff heights:
Raising the diff will result in more onpower traction in the end you raised the diff. For example, putting the front diff to
the highest position and rear diff to the lowest position will give you the most onpower steering and vice versa. I normally
run mine mid low both ends, sometimes mid high in the front. If the driveshafts are straight your car will the more neutral
on and off power. The driveshafts try to straighten out when accelerating which causes the handling effects.

The center of gravitys effect is minimal. The diffs weigh less than 10g. Try taping a 10g lead weight on the topdeck and see
if it makes a difference That is 10x bigger change on the center of gravity than the diffheight and you probably wont be
able to tell a difference.



Hope that helps.

Thankyou Scottmisfits!

Thats the answer I was hoping for. Make sense to me. I thought it was to do with the driveshafts wanting to be straight, but now I know!