Unsprung masses for Prado 120

[Whitey Shockie Maker of the Month Award Find all posts View Profile Close Whitey]

Hi everyone,

I'm hoping someone might have accurate figures for the unsprung masses front and rear.

I used the old fashioned technique and weighed each corner on the scales after jacking the car up.

I have 45kg for the front per corner, and 144kg per corner on the rear.

I did these measurements with my BFG A/T 275/65 tyres (tyre + 17" alloy rim = 34kg), so keep in mind the factory grandtreks will be lower in weight.

These measurements suggest the rear solid axle, drive axles, gears, trailing arms etc. all add up to about 220kg.

I've chased Toyota up today to try and get accurate figures, but they couldn't find anything.

Best

Mark

[mjrandom Out of control poster! Find all posts View Profile Close mjrandom]

45kg sounds too light at the front. BFGs and wheels will be about that much. Plus hub and rotor and caliper etc. Then add 50% of the UCAS and lower arms, strut and some part of the sway bar. Probably more like 100+kg each end. 220kg sounds a bit light at the back too. All the live axle, brakes etc and half the driveshaft, trailing arms etc.

Question is why do you want to know?

[Whitey Shockie Maker of the Month Award Find all posts View Profile Close Whitey]

Hey,

I'm trying to get the suspension frequencies as accurate as possible.

The measurements using scales are off centre, you have mass hanging off everywhere to the sides at different angles, so the numbers will be on the low side.

Regarding the front, my bfg+rim = 34kg, which leaves 11kg for rotor/hub/cv/arms etc, which definitely seems too low.

I doubt Toyota will be able to get me anything, so hopefully someone has actually measured everything when they've been changing suspension??


Best

Mark

[mjrandom Out of control poster! Find all posts View Profile Close mjrandom]

Fair enough. Can't help you though. amts did some weights of wheels and tyres and I thought the BFG and alloy rim was close to 40kg. Might be worth a call to John at Zordo's, he might have some information to help you out.

[Guest Close Guest]

That rim and tyre weight data is here http://www.pradopoint.com/showthread...tyres-and-rims

[mjrandom Out of control poster! Find all posts View Profile Close mjrandom]

I'm wrong! 34kg is on the money. Forgot you will need to add a CV and half a driveshaft at the fronts.

[craigm Addicted PP Member Find all posts View Profile Close craigm]

I'm wrong!.

Don't let SWMBO see that statement mjr!!!

[AJ120 Out of control poster! Find all posts View Profile Close AJ120]

I thought 34kg sounded a bit heavy, when I weighed mine they were 31kg with the alloy rim and 265/70's, that seems spot on with AMTS thread.

Cheers Andrew

[Whitey Shockie Maker of the Month Award Find all posts View Profile Close Whitey]

Hey,

I double checked, I got 34.3kg a few times, could be my digital crappy scales are rubbo, but I have 275/65 BFG A/T tyres, which aren't in amts thread, and could be a bit heavier than 265/70??

Best

Mark

[photoprado Avid PP Poster! Find all posts View Profile Close photoprado]

Hey,

I'm trying to get the suspension frequencies as accurate as possible.

Ok, that sounds interesting, how does it work and what are the benefits?

I've heard of and seen people corner weighting on racecars, but this sounds different?

[mjrandom Out of control poster! Find all posts View Profile Close mjrandom]

Don't let SWMBO see that statement mjr!!!

I'm always wrong, it's only the degree of difficulty that varies.

[Whitey Shockie Maker of the Month Award Find all posts View Profile Close Whitey]

Hey photoprado,

The point of this exercise for me is to calculate the minimum rear coil spring rate to avoid pitching in a heavily loaded Prado. Last time I was in the desert, minor shallow dips in between dunes, 1m wide x 10cm deep would set off a very strong pitching motion. The pitch was so strong the shocks could not dampen it out even after several cycles, and I had to brake to stop it. This is in most part due to a mismatch in suspension frequency between front and rear, in this case the rear being lower than the front. The pitch will depend strongly on your wheelbase and speed, in this case about 20km/h in the Simpson. Note this is nothing to do with anti-squat geometry, as there isn't any huge acceleration involved.

When this happened, my front spring was 617lb/in, and rear was 212lb/in, giving with my vehicle weights around 1.22Hz front and 1.03Hz rear, which is a huge 18% mismatch the wrong way!

The solution of course is quite simple, just use a stiffer spring in the rear, eg, using a 285lb/in will give you 1.22Hz front and 1.20Hz rear (loaded 300kg extra), a difference of only a couple of percent. This should drastically reduce and potentially eliminate the pitch, usually a difference of 1% is used to minimise/kill pitch.

I was thinking about a progressive spring in the 250-350lb/in range to get around this problem, but it's too hard getting them custom made.

I'm just going to run C59-327 (232lb/in) around town, and swap in a C59-329 (285lb/in) when I load the Prado up a lot.

It's good fun figuring out how the suspension works and making sure your Prado doesn't turn into a boat!

Regarding the unsprung masses, changing from 45kg to 65kg on the front increases the frequency from 1.22 to 1.25Hz, increasing the front:rear mismatch by 2%.

So if you have the unsprung masses incorrect as I likely do at the moment, they can make quite big changes in the frequencies.

Best

Mark

[photoprado Avid PP Poster! Find all posts View Profile Close photoprado]

Very interesting stuff. That probably explains some of my pogo!

[Whitey Shockie Maker of the Month Award Find all posts View Profile Close Whitey]

Hey photoprado,

If you're running the setup I think you are BE5-A712/ZC7300 (385mm free 617lb/in) front and BE5-A713/ZC7325 (420mm free 212lb/in) rear, if you've got even a moderate 100kg load in the back, this is around an 8% mismatch, and will definitely pitch at low speeds (20-30km/h) over >1m wide 10cm deep divots (with smooth graded entry and exit, not a sudden edge).

See if you can find a widely corrugated track and test your pitching Prado out on it at 20-30km/h! Throw some weights in the cargo area if you need to.

Best

Mark

[photoprado Avid PP Poster! Find all posts View Profile Close photoprado]

Almost.

Also have the Polyairs in the back.