XRAY - Model racing cars

For the 1st time ever I have had a go at taking the weights at the individual wheels. A bit Heath Robinson as I only have two digital scales of usable size. I made sure they were level with each other and I put a couple of books behind them (centred)which after plenty of trial and error were level with the scales (almost).

I placed the rear wheels on the books and then lowered the front onto the scales and noted the readings. Then I reversed the process and measured the rear wheels, remembering that what was right was now left.

We are not talking clinical accuracy here, there was an 8gm difference between the scales in just weighing the total car, but....

Front vs rear was 660 vs 700 Easily fixed as I added some weight for the BTCC and stuck it on the rear which was easier in the rush.

Right vs left was 656 vs 704. Nothing I can do about that really without adding 50gm weight to the left. I could move the transponder over.

But what I am not sure how to interpret is individual wheel weights. “Looking “ at the car from the rear they were

250 410 front

454 246 rear

Left right

I guess I expected more equality. Car was setup on the Hudy station and has zero tweak.

Without having 4 decent scales under each wheel there is a lot of room for inaccuracy here but I would have thought the relative left and right readings for the individual axles would have been reasonable and the total weight from the 4 figures is within 10 gms of the total car weight given by the scales.
Any views on whether I should be concerned about what I am seeing here or whether the method used just invalidates it all.?

sorry to avoid confusion that should have said "..... without adding 50gm to the RIGHT"

Hi

I use 4 small digital scales to check corner weights (T3'11). Your method sounds like it should work (I think 4 scales are easier, and they are cheap on a well-known auction site)

Some thoughts.....

1. It is important to have the measuring surface as flat as possible - I use a spirit level.
2. Keep the wheel/tyre weights out of the equation, use aluminium setup wheels or the Hudy camber supports (check weigh them first).
3. It is quite common to have two heavy corners on a diagonal - "tweak" in my book- when you say you have zero tweak, how did you assess this? Surprisingly small linear movements on the spring seats give big differences in weight. Think of a 4 legged chair - if 2 legs on a diagonal are slightly longer than the others, the majority of your weight is taken on the 2 long ones.
4. I would loosen off the topdeck screws, give the whole chassis a few twists and "jiggles" to settle it, put it down on a level surface and retighten the screws evenly, across diagonal points.
5. Disconnect the roll bars, re-set the static ride height and re-weigh. re-connect the roll bars and check that they are not introducing uneven corner weights. Adjust the mounting turnbuckles in the right direction if they are.
6. Even out the weights using the spring seat screws, if you go down on the left by 1/2 turn, go up 1/2 turn on the right - this keeps the centreline ride height roughly the same. I would not adjust by more than 1-2 turns though.
7. Move your balance weights around to see where the optimum position is.
8. I have on occasion introduced a certain amount of "reverse tweak" by loosening the top deck screws, twist the chassis in the opposite direction and re-tighten.
9. The 50g overall L-R is quite high - can you move the battery to compensate? My balance weights (20g) generally go front-left to counter the motor weight - your results seem to indicate this could also be the best spot.
10. On my T3'11, it is possible to get all 4 corners within 10g of each other (not worth the hassle to chase it any further!)
11. It is more important to have even corner weights than ride height, I find about 0.2mm differences in ride with even weights (e.g. 5.0mm front left and 5.2mm front right)


HTH

Yes thanks for that CMFORSE, some really useful bits there . Your point no 10, getting everything within 10gm says it all really!

I didn’t think about point 1!
I didn’t think about point 2 either and I have a set of Hudy setup wheels, doh

Yup, moving the battery out will help the left/right balance I am sure. Unlike the T3 my 009 contains the battery within the perimeter of the bottom deck so a fair adjustment is possible.

I assess my tweak as follows
- I put it on the Hudy tweak station to get a feel for anything major. IE if it were out by one mark or more at both ends, I would stop there and hit the top deck screws or the top & bottom deck screws

- Assuming not I set the droop and then use the smooth ride height gauge at an end of the chassis to raise the chassis and check that the two Hudy wheels leave the floor at the same time. Repeat for the other end.

- Then I set the ride height and go though the same process to check that the wheels with the springs attached leave the floor at the same time. Using a digital calliper I check that the spring seat screws are in the same position relative to the bottom of the shock body and that the lengths of the exposed pistons are the same.

- Then I fit the the Hudy camber supports, check the camber and then put the car on the Hudy tweak station and check both ends.

Having just typed the above I don’t see how I can be showing such a major difference on an axle and nothing on the Hudy tweak station, which is based on the balance of the weight on the opposite axle!!!!

So I guess I need to take the Sorex wheels out the equation and be more careful on setting up the weighing system (including getting 4 mini scales ).

Personally I think my process for checking tweak is pretty thorough but I welcome any comment on something I am overlooking!!

Hi

I don't have any experience with the Hudy tweak station, so can't add much value there I'm afraid. From the description, I assume it is the "Pro" tweak station? Maybe someone else can comment.

Your method sounds pretty thorough. I'd vote that the discrepancies are more likely to be on the scale method at the mo! BTW, the spring rates are typically 300g/mm, so a 30g difference is only 0.1mm in height


For info - on the '009, you have to hang the Lipo out over the edge of the chassis to get the L-R balance correct (The T3's have the motor mounted further inboard to help the balance). I made up some carbon fibre "L" shaped mounts from a scrap chassis for the outboard mounts, and made inboard mounts from some PVC angle, was pretty secure.

I don't generally do the full-blown corner weighing all the time, at the track, I'll re-check corner weights with wheels and tyres fitted (since we race on them, not on setup stations ), and then do a "lift the chassis and see if the wheels lift off evenly" check between heats.

Cheers

Charles

Those weight or really out. Try this and re-weigh the car to see if it changes much as your corner weights should be a lot closer to each other.

Use your setup standoffs in place of your wheels and take your shocks off, make fixed equal length linkage to replace the shocks and see if it get closer left to right. I usually see the left rear just slightly heavier due to the motor, but nothing like those spreads.

Hows the ride height from left to right? This could really throw the readings off too, thats why the fixed link in place of the shock can help. If your running shocks with negative rebound it can mess up those readings too.

With high C lipos getting heaver & heavier, is the issue of balance changing -again
my new lipo is approx 300g, a Speed passion BL motor weighs 160g.
So if anything the lipo needs to come more inboard & the motor more outboard to balance things up ??