SX REAR MOUNTED SHOCK MOD

[stegger]

In jimmy's report (and what a great report) there's photo's of si moss's car with the rear shocks mounted behind the rear shock tower.
1/ What benefit does this have ?
2/ Is it only for certain tracks ?
3/ Do you run different oil's, pistons, spring with the mod ?
Thanks in advance

[Chrislong]

Hey Ste, There is an easy way of doing this mod, all you need are four long screws, 2x M3 locknuts and something to shim the tower back further. If you remove the wishbones from the gearbox sides, and literally put them on the other side of the car (but remember to get toe in right).... this achieves rear mounting positions on the wishbone, while wheelbase being marginally shorter (2mm). Then mount the tower on the rear of the tower mount, but with some spacing (I used about 6-7mm by using 4x Losi pistons I had lay around) and use longer screws here. Then using long screws to mount the shocks, followed by 2x lock nuts (so the shocks are behind the tower and nut under it as with the std shock screws). The only thing to modify is the rear bumper, which needs to be cut narrow as the blocks now hang further back than they did. You may need more antisquat, as the wishbone on LWB binds on the blocks otherwise.

I have seen two other ways of doing this. One involves swapping wishbone but not blocks, and then modifying the wishbone - this acheives a very short wheelbase. The other way is leaving the wishbones alone and redrilling them - so nothing else on the car changes - just the shocks.

The benefit, is when the wishbone flex's, because the shock is on the rear it is now the front of the wishbone which flex's and this helps the car drive very bumpy tracks such as Talywain - this is where it was tried and was found to be good.

It was done for a certain track, but this mod will give benefits on all tracks... as it also moves weight rearwards which I believe the car needs. it also does other things (depending on which way you do the mod, there are 3 ways of achieving the rear mounted shock). but the way most have done this, makes the car shorter, and the angle of the driveshafts creates better forward traction.

I would not change the setup for the initial try. Shouldn't need to be any different.

Ste, PM me your email address, I will email you some photos tomorrow of how mine looks.

[jimmy]

Good stuff Chris - I was just told 'its better over the bumps boss' - but you actually explained it all!

[restimax]

any images?

[Losi_110]

hi chris, a quick question. Do you not run the roll bar on the back of your car? I'm assuming that with the wishbones turned round you can't use it any more.

[tony12795]

Mossy tried what Chris has said and yes the idea was to make the car better over bumpy sections. But at Ozfest he put the whish bones the correct way and just left the shocks at the back, The Team are just testing little tweaks here and there to fine tune the rear end a little. So Mossy did run the rear roll bar at Ozfest.

You will also notice that that he is running the car a little harder too (Grey springs)

Tony

[Chrislong]

Yeh to mount the rear roll bar, you will need to drill holes in wishbone for the way I have explained.

Some people have only swapped wishbones, not the blocks, but then file 3-4mm off the back otherwise the car is mega_short.com.

I think Mossy has left wishbones alone but then drilled new holes for the shocks on rear of wishbone, so nothing other than shocks has changed. Apparently the method above gives better forward traction than this due to swept forward driveshaft angle.

The way I have done it is somewhere between these two. Will be giving it a thrashing on Saturday. I haven't seen anyone achieve rear shocks with my method yet either.

An unmodified car is still excellent. For example Grant Williams was in the A-final at Oswestry with his car unmodified. So its all down to personal taste. Don't just follow a trend like a mindless sheep thinking it is necessary, as it isn't always.

[PaulUpton]

To try and help you guys doing the mod, I found that with the suspention on the rear this gave the car alot more weight transfer, and with the long ball joints on the shocks this made the rear loose on entry into the corner and the front push out the corner, now having gone back to the short the ball joints this has stopped both these problems, hope this helps!

[bender]

Now that there are a few of us running the SX at my local low-grip dirt track, we are finally starting to improve the car for Aussie conditions. My car was handling and jumping very well, with the rear shock mod fitted for the first time.

However, I'm still not convinced that its effect is that great, and I believe that the mods greatest grip improvement comes from the sweep of the drive shafts, rather than the ballast difference by having the shocks out the back.

I've done a few calculations and discovered that moving the shocks to the back is only moving around 2.5% of the mass back approx 6.7% and moves the wing back only 3.2%. How much this contributes to improving grip is debatable, especially as my own car was never really lacking in grip to start with.

The biggest improvement in my car has been the fitting of Tamiya shocks from the 501x, which certainly improved the cars handling over the bumps.

Next meeting I will be trying something else, running the shocks at the front of the arm again, but modifying the arms so that the wheelbase is reduced a further 2-3mm from the kit "short" position. This should result in a similar wheelbase and driveshaft sweep compared to reversing the arms, but still allows the shocks to be in their original locations.

The next step is to try and get the motor as far back as possible. I'm switching to the 80t spur for the next meeting but it would be better if Schumacher made down to a 75t spur I think, though perhaps it would be difficult to get the right ratios with some of the hotter mod motors.

[Chrislong]

Im using a 78tooth Losi spur on mine - for motor position. Any smaller and I can't mesh the pinion.

Im on 78/23 on a 5.5 Speed Passion.

I am using the car as standard, I felt the driveshaft angle locked the shocks on power not allowing them to absorb bumps - felt very skitty to me... I tried several ways of doing it, and it was at no point better than the std mounting position.

[B&H Racing]

Chris - Any mods to fit a on a Losi Spur Gear ?

[Chrislong]

Originally Posted by B&H Racing

Chris - Any mods to fit a on a Losi Spur Gear ?

Yeh, I reemed out the hole to match the layshaft bushing. be careful to get it bang on central.

Ideally, we need layshafts turned down to suit the spur - know anybody with a lathe?

Chris

[bender]

Originally Posted by Chrislong

Im using a 78tooth Losi spur on mine - for motor position. Any smaller and I can't mesh the pinion.

Yep, unfortunately I've just discovered that - with the 80t spur I can't go smaller than a 21 or 22 pinion by the looks of it
I probably should've checked a bit more thoroughly before buying the gear

[Chrislong]

Originally Posted by bender

Yep, unfortunately I've just discovered that - with the 80t spur I can't go smaller than a 21 or 22 pinion by the looks of it
I probably should've checked a bit more thoroughly before buying the gear

What motor are you using, you may be undergeared? I wouldn't gear even my fastest 5.5 motor that low. Im gearing it on 78/23. but don't forget - we can change the idler gears and thats what I will do if I need to.

[discostu]

Originally Posted by bender

Now that there are a few of us running the SX at my local low-grip dirt track, we are finally starting to improve the car for Aussie conditions. My car was handling and jumping very well, with the rear shock mod fitted for the first time.

However, I'm still not convinced that its effect is that great, and I believe that the mods greatest grip improvement comes from the sweep of the drive shafts, rather than the ballast difference by having the shocks out the back.

I've done a few calculations and discovered that moving the shocks to the back is only moving around 2.5% of the mass back approx 6.7% and moves the wing back only 3.2%. How much this contributes to improving grip is debatable, especially as my own car was never really lacking in grip to start with.

The biggest improvement in my car has been the fitting of Tamiya shocks from the 501x, which certainly improved the cars handling over the bumps.

Next meeting I will be trying something else, running the shocks at the front of the arm again, but modifying the arms so that the wheelbase is reduced a further 2-3mm from the kit "short" position. This should result in a similar wheelbase and driveshaft sweep compared to reversing the arms, but still allows the shocks to be in their original locations.

The next step is to try and get the motor as far back as possible. I'm switching to the 80t spur for the next meeting but it would be better if Schumacher made down to a 75t spur I think, though perhaps it would be difficult to get the right ratios with some of the hotter mod motors.

i can see were your coming from with the percentages moving the shocks behind, have you calculated the diffrence in force that loads up the rear shocks under acceleration having extra mass at the rear when the car accelerates it should create more rear load thus better rear traction assuming the shocks are setup correctly and anti squat plus every thing else that contributes to setup but as like for like test it should genarate more rear traction.

stu rand