[alchemysa]

My daughter has on old SJ410 1 litre narrow wheelbase farm bomb on her hobby farm. It goes OK and is a handy ute but the block is mostly steep so she always feel that its tippy, or it wants to go downhill too fast even in low gear.

I'm wondering if replacing the old 15'' rims and the tall skinny light truck tyres with something lower might improve it in a number of areas. Smaller height tyres would lower the centre of gravity, help the engine braking and slow it down going down hill, and probably help it climb. (First gear is too high in these things!) The block is steep but its mostly smooth so ground clearance is not a problem.

So, does anyone know if there are any small diameter 5 stud wheels that would fit on this? They would need to have room for the brake drums. Maybe I could even reverse them to give a bit of extra wheelbase? I guess I'm picturing something that would look more like a Gator than a Sierra!

I saw a very small 4x4 'mini' truck the other day that had rims that were probably only 12 or 13 inches. I wish I had paid more attention to what model it was.

Any suggestions appreciated.

[Gwagensteve]

14" is the smallest that will clear the brakes, but 14" wheels in a 5x5.5" PCD would need to be custom made, and 14" tyres with an appropriate tread pattern and size won't be easy to find. You can swap to 15" rims and run tyres down to about 26" diameter, but that will only make a tiny difference to your gearing. Going to crazy rim offset has disadvantages too.

The better solution is to lower the gearing. In your model this can be done by replacing the diff ratios with 4.56 (lj80) or 4.88 (lj50) or lowering transfer case gearing. If your car has a 4wd light you can replace the transfer gear ratios quite easily to more than double your low range reduction.

[AckerDackerly]

If the truck's suspension is not lifted in any way, the problem may be pshycological than real.

That said, a better idea might be to purchase lower-profile (60-series?) 15 inch tyres which would actually lower the vehicle in a safer manner without the hassle - that GwagenSteve rightly pointed out - of going through the purchase of custom wheels.

Also, you can control the speed of decent on a steep hill by selecting a lower gear. This will provide engine braking - assuming the engine has sufficient compression.

I was amazed with the things my SJ413 could do in stock condition by using engine braking and careful steering to avoid driving down a hill sideways - or "off-camber".

I hope that this helps!

[Gwagensteve]

SJ410's first gear is 20% taller than an sj413, the track width is substantially narrower even before this installation of 16x4.5" rims. The op's model may also have drum brakes all round, which aren't self adjusting.

Add the high COG of a flatbed and the feeling of instability is far from psychological. They aren't stable and have terrible brakes and engine braking.

[alchemysa]

Gwagensteve wrote:

even before this installation of 16x4.5" rims.

Are they 16s"? I should have checked, but its 60 kms away. All the spec sheets and WSM's I looked at listed 15's even on the early Sierras so I just assumed these were 15's as well, although they always looked bloody tall.

Anyway thats good news as I can get some cheap 15" Sierra rims (the ones with the round holes) with stock radial tyres. They should lower the thing noticably. They might even widen the track a smidgen.

Yes Gwagen the brakes are all drum and the gearing is too high. (Its ALWAYS in low range). Its not the transfer box with the light so cheap crawler gear mod is not an option I guess. Handbrake is pretty crap too, and its too narrow, so all up its not ideal for this situation but as long as she only drives straight up and straight down the hills it does an OK job.

Thanks for the help.

[Reubs]

Secondhand 205/65R15 Commodore tyres are pretty cheap and reasonably small and will fit on stock 15" rims. If you need traction then Trepadors used to come in 205/70R15 - not sure if they are still available.

Secondhand wheel spacers can be had cheaply from time to time as well.

[Jezza86]

drive it with the seat belt on. roll it. put it back on its wheels. repeat.
isn't that what all serious sierra owners dream of?

could ballast it too, down nice and low. fill wheels with water, or bolt a heap of 1" plate to the chassis rails. just trying to think of cheap options being a paddock basher

obviously wont fix the whole 'no breaks issue', but, sometimes you just have to fix the breaks...

[alchemysa]

Picked up some cheap Sierra 15" rims with 205/70 tyres today. Fitting these instead of the existing skinny 16'' light truck tyres will lower the ute by about 3 cm, increase wheelbase width (tyre footprint) by about 6cm total, and reduce tyre circumference from about 222 to 210 cms. Individually tats nothing significant but collectively it might provide just that extra little bit of stability. Unfortunately I can't get to the car and actually fit them for a a weeks but when I do I shall let you know.

[alchemysa]

I guess not many of you guys are interested in fitting smaller wheels to your Sierras, but I said I'd give a follow up to this so here it is. Changing from 16" skinny light truck wheels on the little 1 litre SJ410 pickup to 15" Sierra rims with lower profile 205/70 tyres made a huge difference in my opinion. I also fitted a spare wheel under the tray to add a little bit more weight down low. The car just feels so much steadier, better balanced and safer now. Excessive wheel spin has also disappeared because its easier to get the revs right. Its quite amazing what just an extra 2 inches of width, 2 inches less height, and 5 inches less tyre circumference makes. A steep gravel driveway on her block that previously required 4wd can now easily be climbed in 2wd. And in 4wd it crawls up, down, and around her hills so comfortably now that its hard top believe it was previously nerve wrackingly tippy.

All up, $50 for 5 old 15" rims and tyres was a good investment.