R34 Diff Ratio's

[GTSBoy]

6 minutes ago, Adz #24 said:

Thanks for the info.

The issue I’m having with my r34 gtt sedan that has no major engine mods that was converted to manual in Japan is that I’m losing traction way to easily in 1st and sometimes in 2nd, (powers just not making it to the ground properly). I’m moving to a wider wheel setup so hopefully this reduces the loss of traction a bit but if not I’m thinking the next option is changing/upgrading the diff.

It’s my daily driver so 1.5 way would be where I’d want to go. Would a vspec GTR diff be an option?

As you can probably tell I’m new to this so slowly learning my way around things.

I'm not going to go into the physics details, because it will start arguments, but wider tyres do not produce more grip on their own.  it comes down more to larger diameter wheels allowing lower profile tyres causing less distortion of the tyre carcass which causes less internal frictional heating which then allows the use of softer compounds.  And the softer compounds cause the coefficient of friction to increase, which is what gives more grip.

So, technically, even without a wider tyre you could have a tyre with a softer compound and pick up grip.

A good diff will help with launch traction, but it's not the only (or even the main) thing going on.  There's a lot of other factors that can be wrong or right, from wheel alignment (specifically camber and toe), to spring and damper rates.  I recently found that decreasing my rear ARB from 24mm to 22mm not only improved the grip in corners, but somewhat surprisingly improved launch traction.  I think this is because it changed the spring-damper coupling, allowing a bit more movement (twist, if you want to think of the way the car will move as the traction load gets applied around the tailshaft).  Not expected, but it's there.  After that there's all sorts of other shit, like the health of the diff and subframe bushes.

An no.  The Vspec diff is the very very worst thing that you could think of putting in there.  Have a read about them.  At least it is sufficiently close to impossible for you to actually put one in there that you won't make the actual mistake of trying.

 

[Adz #24]

So if you were going to attack this problem in steps, what would be your first 5 things that you would look at?

[V28VX37]

11 hours ago, Adz #24 said:

Thanks for the info.

The issue I’m having with my r34 gtt sedan that has no major engine mods that was converted to manual in Japan is that I’m losing traction way to easily in 1st and sometimes in 2nd, (powers just not making it to the ground properly). I’m moving to a wider wheel setup so hopefully this reduces the loss of traction a bit but if not I’m thinking the next option is changing/upgrading the diff.

It’s my daily driver so 1.5 way would be where I’d want to go. Would a vspec GTR diff be an option?

As you can probably tell I’m new to this so slowly learning my way around things.

It's curious that you're trying to address loss of traction with a diff. Some questions:

1. What tyres are you running? How much meat is left on them?
2. What suspension are you running, especially spring rates?
3. How's your ride height and wheel alignment?

Since your car was modified already in Japan perhaps it has touge-spec rock hard 12kg/mm spring rates? That could easily cause bad traction.

Also on the diff, I have a GTT sedan with a Nismo 1.5-way in it. It's a beautiful diff on the track and spirited driving, and absolute s__thouse in daily driving. Basically, you can't feather the clutch in tight corners/driveways/manoeuvring as it won't lock properly and gets hellishly skippy. I would never ever ever put such a thing in a daily driver. Make sure you take someone else's 1.5/2-way for a good varied drive before making the decision.

Also from my research the GTR diff requires too much mucking around with shafts etc. and is not really a viable option for the GTT.

Just my $0.02

[Adz #24]

5 hours ago, V28VX37 said:

It's curious that you're trying to address loss of traction with a diff. Some questions:

1. What tyres are you running? How much meat is left on them?
2. What suspension are you running, especially spring rates?
3. How's your ride height and wheel alignment?

Since your car was modified already in Japan perhaps it has touge-spec rock hard 12kg/mm spring rates? That could easily cause bad traction.

Also on the diff, I have a GTT sedan with a Nismo 1.5-way in it. It's a beautiful diff on the track and spirited driving, and absolute s__thouse in daily driving. Basically, you can't feather the clutch in tight corners/driveways/manoeuvring as it won't lock properly and gets hellishly skippy. I would never ever ever put such a thing in a daily driver. Make sure you take someone else's 1.5/2-way for a good varied drive before making the decision.

Also from my research the GTR diff requires too much mucking around with shafts etc. and is not really a viable option for the GTT.

Just my $0.02

1. Pretty much brand new Kumho 245/35/20 +35 on lenso D1R’s

2. Blitz adjustable coilovers but don’t know the spring rate (how would I go about determining this?)

3. Ride is sitting fairly high so I have decent clearance so I can actually get in and out of driverways.

Im fairly new to a lot of this so it is a learning process for me. So it may not be the right thing to do changing to a LSD or I may be even wasting my time investigating this option but I’d rather use the knowledge of people that know and have possibly gone through similar issues. 

[admS15]

20 inch rim and 35 profile tyre is the problem there, not enough tyre wall, not to mention a good quality 20 inch tyre would be big $. An 18 inch wheel with 245/45/18 woul be heaps better.

[V28VX37]

^ What Bill said, try a 17 or 18 inch rim with a good tyre and it's likely to help.

Re spring rates, you can measure the length of the spring and the number of coils and run it through an online calculator. Generally high rate springs tend to look really dense so that can be a bit of a giveaway sign.

If your ride is harsh, crashy or sharp over uneven surfaces that could indicate hard suspension... but then again too large a rim with not enough tyre sidewall can show similar symptoms.

[Adz #24]

13 hours ago, V28VX37 said:

^ What Bill said, try a 17 or 18 inch rim with a good tyre and it's likely to help.

Re spring rates, you can measure the length of the spring and the number of coils and run it through an online calculator. Generally high rate springs tend to look really dense so that can be a bit of a giveaway sign.

If your ride is harsh, crashy or sharp over uneven surfaces that could indicate hard suspension... but then again too large a rim with not enough tyre sidewall can show similar symptoms.

Already had a decent set of 245/45/18 wrapped on Rays and was facing this problem plus the added fact that my clearance was horrible and I ruined my front bumper therefore the move to the larger wheel and higher ride height is the more practical option and not something that I want to move back from for my daily driving purposes so if this is the only way I can resolve the issue then I’ll have to live with it.

Ride is actually fairly smooth (other than the fact I’m driving on the sh1thouse roads of Sydney) with the adjustable blitz coilovers and also feels better with the larger wheel setup I now have.

Ill have a look and try and calculate my spring rate and also look into the setup of my ARB and the quality of the subframe bushes.

[niZmO_Man]

You want to avoid V-Spec diffs

[Kinkstaah]

Width and Brand of tyres is not the only thing. If you somehow do not have grip you have chosen very badly when it comes to tyres and perhaps the rims that said tyres sit on (limiting choices of good tyre)

No major engine mods means maximum 180kw. You should be able to maintain the car hooking up to the ground under full noise at nearly double that power. That's how far away from a "good" tractive setup your setup currently is. When people recommend sticky tyres and 18's or 17's the difference would be astronomical. You shouldn't be able to do a power skid on a stock power R34 pretty much ever.

[Adz #24]

45 minutes ago, Kinkstaah said:

Width and Brand of tyres is not the only thing. If you somehow do not have grip you have chosen very badly when it comes to tyres and perhaps the rims that said tyres sit on (limiting choices of good tyre)

No major engine mods means maximum 180kw. You should be able to maintain the car hooking up to the ground under full noise at nearly double that power. That's how far away from a "good" tractive setup your setup currently is. When people recommend sticky tyres and 18's or 17's the difference would be astronomical. You shouldn't be able to do a power skid on a stock power R34 pretty much ever.

Aw well guess $1k in performance tyres isn’t good enough I’ll just have to live with this problem.

[admS15]

So what brand and model are the tyres?

[Adz #24]

Kumho Escta 4X

[GTSBoy]

The KU22 (the real code for the Ecsta 4X) is hardly a performance tyre.  It's literally labelled as a "comfort tyre" by Kumho.  The KU36 was a performance tyre, though now replaced by the V720.

I will confess that my car (R32 with 25Neo) will easily light up the rears on a launch, unless the tyres (V720s) are really warm.  R32s are, however, renowned for not having as good rear geometry as they put onto the 33s onwards.  And the car is also >100kg lighter than a 33 or 34, which doesn't help with weight transfer on launch.  And it is set up for corners. </excuses>

 

[V28VX37]

I have half worn KU36 in 235/45R17, not overly hard suspension and the said Nismo 1.5-way. They're 'ok' warm/hot but spin city for the first couple of gears when cold. In the wet, forget about it.

To OP, I reckon the most cost effective test you could do is borrow a pair of 17" stockies from someone, pretty much with any tyre, and drop pressures to high 20's. Go do a couple of launches and report back. If traction improves you might need to downsize your current wheel setup – if not you could start looking at your suspension setup.

Sidenote – The R chassis can't really be dropped much without throwing in a full set of adjustable arms as well. Do you have adjustable rear camber arms and traction rods, and a good alignment from someone knowledgeable?

[Adz #24]

5 hours ago, V28VX37 said:

I have half worn KU36 in 235/45R17, not overly hard suspension and the said Nismo 1.5-way. They're 'ok' warm/hot but spin city for the first couple of gears when cold. In the wet, forget about it.

To OP, I reckon the most cost effective test you could do is borrow a pair of 17" stockies from someone, pretty much with any tyre, and drop pressures to high 20's. Go do a couple of launches and report back. If traction improves you might need to downsize your current wheel setup – if not you could start looking at your suspension setup.

Sidenote – The R chassis can't really be dropped much without throwing in a full set of adjustable arms as well. Do you have adjustable rear camber arms and traction rods, and a good alignment from someone knowledgeable?

Maybe that’s my next option to look into adjustable rear camber arms and traction rods, anyone in Sydney you’d suggest I could go and see?

[V28VX37]

Sorry mate not sure, I'm based in Melbourne. Just Jap can supply the arms, they are pretty easy to install Diy, then you'll just need someone to do the alignment.

[GTSBoy]

Actually, adjustable arms are not trivial.  It's easy to set the camber arm to get the camber you desire.  It is much harder to set the traction arm length to minimise bump steer.  Almost no-one ever does it, and almost all installations are probably worse than the stock arms because of it.

It's a circular process.  Set the camber arm length to get camber right.  This requires that you take a stab at changing the traction arm length also.  Then you have to take it off the wheel aligner (probably), jack it up off the ground, set up your bump steer gauge, fiddle with the traction arm length until you have minimal bump steer, then put it back on the wheel aligner and check and correct the camber, then probably back to the bump steer gauge to make sure that you haven't spoiled it.  Rinse and repeat until no changes are required.  Might take one back and forth, or might take 6.

If you take it to a wheel aligner to do the whole process, it would want to be an expert at setting up this stuff, not your local Bob Jane, etc.  And it will cost a lot more for the labour/service than for the arms.

[Adz #24]

Sounds good I’ll speak to Darron at JustJap maybe he can point me in the right direction for alignment.

Or Maybe not lol I’ll just have to live with this for the time being I don’t mind being slightly sideways when I give it a full snoot. (At least it’ll make me behave myself a bit more)

Edited August 21, 2018 by Adz #24
A

[niZmO_Man]

21 hours ago, Adz #24 said:

Kumho Escta 4X

Dude, those are all-season tyres, for snow/freezing weather. Whoever sold them to you, never go back to them.

They came on my Liberty wagon, noisy and trash in wet and dry because it's made for alpine conditions. Replaced them with Hankook K120 (sold out on tyresales), which are an excellent street tyre. What are your tyre size(s)? You could replace the rear pair with something good (then replace the fronts afterwards).

[Adz #24]

2 hours ago, niZmO_Man said:

Dude, those are all-season tyres, for snow/freezing weather. Whoever sold them to you, never go back to them.

They came on my Liberty wagon, noisy and trash in wet and dry because it's made for alpine conditions. Replaced them with Hankook K120 (sold out on tyresales), which are an excellent street tyre. What are your tyre size(s)? You could replace the rear pair with something good (then replace the fronts afterwards).

They are not winter tyres buddy, they are all season, surprisingly winter tyres are called ‘winter tyres’ having lived in Calgary, Canada I know what winter tyres are. I didn’t buy them from shop mate so don’t worry about that.