Spring Rate And Wheel/tyre Setup For Tarmac Rally.

[sweefu]

Hi everyone,

I'm looking for some advice about wheels/tyres, spring rates and general setup for my first go at a Tarmac Rally (sort of, just the 'touring' class).

My car is an S14 Silvia but I find much better advice on this forum - I hope that's ok. The car is my daily driver and I use it for drifting too. I don't have the funds to set the car up for a proper racing class at the moment so I am going to have a go with the touring class.

The car has the following work done to it:

HSD HR coilovers 8kg/mm front 7kg/mm rear.

R33 front calipers, DBA 4000 rotors, A1RM pads, Nulon fluid (rear brakes are standard S14 with A1RM pads).

AGI 4 point bolt-in roll cage

Firstly I am seeking advice about what spring rates would be appropriate. I know my current combo is too stiff and it also has very little droop, the car balances on 3 wheels when I go in/out of my driveway. Whatever spring rates I decide I plan to add a helper spring to the front and rear to have a little more droop - would this be a good idea?

Should I use something like 7kg/mm front and 5kg/mm rear? Or even 6/4? Or another combo? Any advice here would be greatly appreciated.

Secondly, wheels/tyres. I have the choice of either 17x8 +32 or 17x9 +13, I have a set of each.

I have a tiny budget for tyres, around $800 for the set. This is only the touring class so hopefully these tyres will be adequate. I see my choices as RSR or KU36, possibly Kumho V70A too.
Can anyone recommend a good size to start with? And which wheel size would be best? 235/45r17 is common and readily available, perhaps a 245 width would be available with the V70A - I'm not sure yet.
In the US I see Silvia guys running 255/40r17 all round but to me this sounds massive - can anyone comment on this sort of setup?

Any other advice relating to my first road rally experience would be great too.

Thanks very much,

Anthony.

[sweefu]

I already have some 7kg/mm springs, so I might use those in the front and buy 5kg/mm for the rear - can anyone suggest if this might be OK or still too stiff? I know it depends on each individual setup and HSD really aren't designed for this sort of thing, but I just need to work with what I have. I'm unsure if I should add a helper spring to rear only, or front and rear?

Also wheels/tyres - I don't want to use the 17x9 set as I need to run spacers for them (real offset is +38, I use a 25mm spacer).

To keep things simple I want to use my 17x8 +32 set with 235/45r17 (maybe 245 if it comes up cheap) or my 16x9 +22 set with a 225/45 or 225/50 tyre - would the extra sidewall height with a 225/50 have any benefit?

Thanks.

[Dale FZ1]

Firstly find out what wheel/tyre limits/constraints are placed on entries for touring events. Presumably there are some events you particularly want to enter, so speak to people from the organising club(s) and clarify. Nothing inherently wrong with KU36 rubber, or Achilles 123S for that matter, you aren't on special stages.

6&4 kg springs should offer some hope of working. Spend time and if needed, money, to ensure you have decent droop travel with those shocks. And that both ends don't have silly bump steer issues. Then if the car goes off the road it's because of driver/navigator error.

Some of the things you're asking aren't going to be best resolved on a forum - get involved with people doing what you're wanting to do and see what works (or not).

[Bazil_1]

Not sure about spring rate as my car is a lot heavier however can tell you that we went softer once getting the car setup and sorted. Make sure you have a decent amount of ground clearance as the roads can be quite rough. Softer suspension with more wheel droop will be faster through rough corners as the tyre can keep on the ground for longer. Have you had your car weighed recently?

At touring speeds you won't get to the limit of most decent street tyres. KU36's would be a good choice and will have enough in them for several track days after. What size tyres are you running at the moment? My street setup on the 33 is 255/40 R17 RE002s which offer plenty of grip for a tour. In a lighter car you won't need quite the same width, just keep close to your current overall circumference if you like the current gear ratio. 245 on a 9" rim will have a slightly stretched tread while 235 would be better off on a 8".

[Bazil_1]

**Double Post**

[sweefu]

Firstly find out what wheel/tyre limits/constraints are placed on entries for touring events. Presumably there are some events you particularly want to enter, so speak to people from the organising club(s) and clarify. Nothing inherently wrong with KU36 rubber, or Achilles 123S for that matter, you aren't on special stages.

6&4 kg springs should offer some hope of working. Spend time and if needed, money, to ensure you have decent droop travel with those shocks. And that both ends don't have silly bump steer issues. Then if the car goes off the road it's because of driver/navigator error.

Some of the things you're asking aren't going to be best resolved on a forum - get involved with people doing what you're wanting to do and see what works (or not).

Thanks for the help here mate.

The tyre just needs to be approved for road use, a friend of mine enters the proper modern class and uses Dunlop D03G for example.

I'm just sticking with the RSR/KU36 type of tyre because of a) my budget and b) not entering the proper modern class.

For springs, not a lot of money will be spent, I'm really doing this to have a bit of fun and try a tarmac event with the setup I have, I just want to tweak it to work as best as it can. I've lined up some helper springs (front and rear) so this should help to give me enough droop.

I also understand everything won't be resolved on a forum, I have time put aside for testing and alignment before the event, I'm just trying to rough out some of the broader ideas first

Thanks again for the help mate.

Not sure about spring rate as my car is a lot heavier however can tell you that we went softer once getting the car setup and sorted. Make sure you have a decent amount of ground clearance as the roads can be quite rough. Softer suspension with more wheel droop will be faster through rough corners as the tyre can keep on the ground for longer. Have you had your car weighed recently?

At touring speeds you won't get to the limit of most decent street tyres. KU36's would be a good choice and will have enough in them for several track days after. What size tyres are you running at the moment? My street setup on the 33 is 255/40 R17 RE002s which offer plenty of grip for a tour. In a lighter car you won't need quite the same width, just keep close to your current overall circumference if you like the current gear ratio. 245 on a 9" rim will have a slightly stretched tread while 235 would be better off on a 8".

Cheers for the help mate. I have been using my car for drifting lately and it's definitely too low, I will raise it up when I install the new springs. I haven't ever had my car weighed.

I haven't run a matched set of wheels/tyres for ages, my last matched set was 16x9 +22 with 205/50r16 tyres. Since then I've just run whatever combination of wheels/tyres I have spare.

KU36 are available for $800/set in 235/45r17, those with my 17x8 +32 wheels would have to be a good bet. RSR are also available for that price/size.

Thanks for the help, I'll keep checking out tyre options. I think V70A will be way too far out of my budget unfortunately.

[hrd-hr30]

Helper springs won't give you more droop, they're just to keep springs captive at full shock extension. You need longer shocks to get more droop.

I wouldn't worry too much about it for the touring event. Like you say work with what you've got, 7/5kg will be fine.

[sweefu]

Helper springs won't give you more droop, they're just to keep springs captive at full shock extension. You need longer shocks to get more droop.

I wouldn't worry too much about it for the touring event. Like you say work with what you've got, 7/5kg will be fine.

Maybe I have the terminology mixed up. I thought a helper spring would stop the wheel lifting by giving it more extension before it lifts off the road.

For example, at the moment when I turn into my driveway one of the rear wheels lifts, there is only a small amount of droop before the shock is at full extension so the wheel lifts up

With a helper spring the wheel could continue to droop down and stay in contact with the road.

I know a helper spring won't make my shock stroke longer but I thought it might change the section of shock travel I use. Right now only the first ~40mm of travel is being used, with a helper spring I would have ~40mm more 'usable travel' if that makes sense, 80mm total for example.

Cheers.

[Dale FZ1]

Drift boy and street-cool culture has people thinking the fast way to good setup and handling is drop the ride height really low.

With help from a very experienced suspension engineer, I have learned that there is a window within which you can get decent handling without making it ridiculously low.

Any tarmac event is going to require an amount of bump and droop travel so that the wheel stays in contact with the ground. Traction under all conditions rules. Hopefully you've got something more like 100-120mm total travel, and a good 60mm of bump.

Harry is right in suggesting not spending too much or changing too much. Run what ya brung but try to get setup within a happy window so it has a chance of working but not throwing you off the road. Eg slightly too stiff springs won't be great but a bump steering pig will make the event a whole lot less fun. Another recent thread in this section has addressed that issue for a track Skyline.

Helper springs only compensate for shock and spring length settings at full extension so the spring doesn't rattle on/off its seat.

You'd expect a touring category isn't too serious and gives you a "come and try" taste for this style of event.

[260DET]

Proper shocks like Bilstein or Koni are worth the money, HSD sounds like the 'put your own brand on them' type but anyway those like the brands mentioned are the real deal, not some Asian pretender.

[sweefu]

Drift boy and street-cool culture has people thinking the fast way to good setup and handling is drop the ride height really low.

With help from a very experienced suspension engineer, I have learned that there is a window within which you can get decent handling without making it ridiculously low.

Any tarmac event is going to require an amount of bump and droop travel so that the wheel stays in contact with the ground. Traction under all conditions rules. Hopefully you've got something more like 100-120mm total travel, and a good 60mm of bump.

Harry is right in suggesting not spending too much or changing too much. Run what ya brung but try to get setup within a happy window so it has a chance of working but not throwing you off the road. Eg slightly too stiff springs won't be great but a bump steering pig will make the event a whole lot less fun. Another recent thread in this section has addressed that issue for a track Skyline.

Helper springs only compensate for shock and spring length settings at full extension so the spring doesn't rattle on/off its seat.

You'd expect a touring category isn't too serious and gives you a "come and try" taste for this style of event.

Thanks again for the help - no need to assume my car is swaybar-smashing low! haha

The reason why I'm looking at tweaking my setup is to maintain traction everywhere I can and keep all 4 wheels safely planted on the tarmac. I know my setup won't ever be up to a competition level car but I just want to make it a bit of fun (and safe too).

Proper shocks like Bilstein or Koni are worth the money, HSD sounds like the 'put your own brand on them' type but anyway those like the brands mentioned are the real deal, not some Asian pretender.

Cheers for the suggestion but I'm not looking to buy anything new, just tweak the setup I have. I've used Bilstein before and they were awesome, no questions there! HSD are good in their own right too, considering the price.

Thanks again.

[hrd-hr30]

Maybe I have the terminology mixed up. I thought a helper spring would stop the wheel lifting by giving it more extension before it lifts off the road.

For example, at the moment when I turn into my driveway one of the rear wheels lifts, there is only a small amount of droop before the shock is at full extension so the wheel lifts up

With a helper spring the wheel could continue to droop down and stay in contact with the road.

I know a helper spring won't make my shock stroke longer but I thought it might change the section of shock travel I use. Right now only the first ~40mm of travel is being used, with a helper spring I would have ~40mm more 'usable travel' if that makes sense, 80mm total for example.

Cheers.

It's quite normal for any coilover setup to lift wheels going over driveways. Even the Bilstein spring and shock combo I had on my aristo lifted a rear wheel on some driveways. Don't be too worried about it. My GTR on BuddyClub coilovers did it, Supra on Tein Flex did it, 180sx on Teins did it, Soarer on BC's does it. I wouldn't be worried about using any of them on a tarmac rally, and I did drive the GTR (harder than I should) on a couple of closed stages of the SunCoast rally in 07 and it was great. Perks of being a SSO

The amount of droop you have is set by the shock length. If the springs are captive at full droop, a helper spring is not needed and will not change anything - not the amount of droop, or the part of the shock travel you are using unless you don't set the ride height back to where it was. But if you don't reset the ride height, it will raise the vehicle by the thickness of the compressed helper spring, and raising the vehicle will leave you with less available droop travel. Even if the springs aren't captive at full droop, helpers won't give you any more droop travel, they just hold the springs captive.

But like I said before, I wouldn't be too worried about your droop travel. Change your spring rates to 7/5, run it at a sensible height and enjoy.

Edited August 6, 2014 by hrd-hr30