'95 Sierra: setting up suspension to clear 31's

[gwagensteve]

Yes Dave, I'll be at Bill's block. I'll bring the bits with me.

I'll PM you the details of how to get there.

Steve.

[davidsuzuki]

Jonfromhamilton: I hope so, look forward to meeting everyone and having a good look at the cars. I'll need plenty of tips for the mods I'm planning.
Steve: thanks, I got your message. Which day(s) will you be attending?? I was thinking to just come up for a daytrip.

[gwagensteve]

I'll be there from Friday night through to Sunday arvo. Saturday would be the best day v

Steve.

[davidsuzuki]

So I had a look at some other rigs on the weekend and decided I want to go for Maxxis 31 x 10.50 R15 (265 x 75 x R15) Trepador Radials on Mickey Thompson 15X8 BCD 5x139.7 Backspace 3-5/8" Offset -22mm Classic Alloy Rims.

According to a tyre calculator app I've been using if I go from my current tyres, which are 205 x 70 x R15 to 265 x 75 x R15 I will be increasing the total tyre height by 16.5%.
So this would follow that 4.9:1 (16% reduction in high range / 115% low range )transfer gears would be the best match for on-road? Have I done my calculations right??

I'm also wondering about the best rim offest and backspace specs to go for. Anyone know off-hand what might be a good choice to stop the tyres from sticking out beyond the stock flares, but then also not rubbing on the springs?? Will the Mickey Thompson rims I've specified be suitable to achieve this??

[gwagensteve]

Sorry for the late reply David.

4.9's will be fine. The result in a crawl ratio of 66:1 which is the right side of 60:1 - the ratio I think is an ideal starting point for gearing a sierra on 31's.

I'm sure you'll be happy with treps, butI'm not so sure about the wheel choice. I wouldn't run 8" rims with a 31"X10.5 tyre. They add excessively to overall width, and the tyres aren't as happy staying on the beads at low pressure with the wider rim. My preference is for a 7" rim with a 10.5" tyre.

As for the backspacing, I'm not 100% sure about that solution. I ran your figures on a calculator (http://www.1010tires.com/Tools/Wheel-Offset-Calculator) and I reckon that's going to make your car 62mm wider per side just from the rims. That's making for a pretty wide car. Whilst a wide car is stable and looks cool, it's not necessarily an advantage.

Maybe someone can chime in with their experience with 31's on a WT in relation to backspacing?

Steve

[lbzook]

I think that your going to struggle to find a rim that will have your tyres inside the stock flares AND not hitting the springs.
I'm running 31x10.5's on 7" rims with 0 offset or 3.5" BS, that put the outer edge of the tyre in line with the edge of the stock flares, but they hit the springs on full lock.
So to try to get the tyres off the springs, I was running 30mm wheel spacers for a while. That pulled the tyres away from the springs by about 5mm on full lock, but then the outer edge of my tyres where WAY outside the stock flares.
I've now ditched the spacers and just deal with hitting the springs occasionally, I could solve this by spacing the steering stops out a bit, but it doesn't bother me too much as its just a weekend car.
Hope that some of this might help

Leigh

[jonfromhamilton]

You're not cool unless your tyres hit your springs anyway, especially when you transfer weight quickly while rolling and it's really loud.

[gwagensteve]

It's no being deal to run a longer steering stop - It's just a 6mm bolt adjusted to suit. It's a big deal to run lots of flare/have the tyres hanging out/get a defect

Just my 2C though. I'm not always the best judge.

Steve.

[davidsuzuki]

Thanks for the input. If the steering stops are easy to adjust I I'd rather get the 31's have a reduced turning circle. I wonder how drastic the effect might be? Would it even be noticeable when performing a U turn?

[gwagensteve]

Sorry, have you confused tyre diameter with rim width?

In any case, if you adjust your steering stops accurately, you won't really notice the drop in steering lock with 31's

I'd still advise against 8" rims though.

Steve.