Tuning Spring Rates...discuss.

[Eoin611]

I'm looking for advice or opinion on suitable spring rates for a motorsport destined X1/9. I've gone through any existing threads, some of which include input from myself several years ago regarding my last VTEC X1/9 and trawled through various other sites but can't seem to find information regarding standard production spring rates or suggestions for what might work best for racing. My last X1/9 ran with 160lb in front and 350lb at the rear and handled reasonably well, (felt a little soft in front though) I'm now using a Punto 1242 16valve engine and plan to install 250lb at the rear and 160lb again in front. My logic is that the reduced speed and weight of the 1242 engine compared to the 2.2 Honda will result in less stress under braking and so I conclude that the 160lb springs should be sufficient this time around. Trial and error will no doubt play a part so I'm hoping to use the Forum as a sounding board and hope somebody out there has ideas or suggestions that could help. Using X1/9 Konis in front and Group 4 Bilsteins at the rear, simply because they were in the shed and could be made to fit.

 

[jimbro1000]

The spring rates depend as much upon the surface your racing on as the car itself.

The sig pic looks like your doing your thing on a loose surface in which case overly hard springs aren't going to help. We also need to know what your available damping rates are.

160lb springs on the front are fairly soft as you've pointed out and not far off what you'd use on the road but the 350lb springs on the rear are fairly stiff. The FIRE engine would give a weight distribution edging more towards 50:50 than a standard car but in a stripped out racer this is very hard to judge without putting it on some scales. Switch to 250lb springs would balance the car out more but gut feeling says it might still be too stiff in terms of simple balance, in terms of what you need though I would be looking to push the front rate up a bit.

 

[Eoin611]

Thanks for the response. The track is a smooth asphalt clockwise oval, there is a neglible left hander that is flat out and not a concern, turning right is the priority. The class I'll be running in is limited to 7inch slicks. The car in the sig pic looked fairly dirty that day, (long since written off) and was parked in the Pit Area, hence the gravel surface. I was concerned that I was simply replacing a standard front spring with a 160lb spring without knowing how much of a change there is between them, if any. The Konis i'm using in front are the Red Koni road-going ones that were in the last car I raced, they are still in perfect condition thankfully. I've adjusted them to full stiffness and then back half a turn, this was done on a trial & error basis over several races and seemed to work well. I've raced the FIRE engine in the front of a Cinq and a Toyota Starlet using 250lb springs up front which both handled incredibly well,this is my reason for thinking it might work in the back of an X1/9 with same engine weight. It's been over five years since I did anything with an X1/9 so I'm open to all ideas. I've seen a few USA sites stating they run much stiffer in front than at the rear, huge rates in their springs,400-500 in some cases, this just doesn't seem right at all. Do you have any set-up recommendations for keeping the inside rear wheel on the ground when exiting a corner? I can put the car on scales and get the corner weights sorted but I've never done it on a mid-engined car before, only FWD or National Hot Rod cars, with an X1/9 I'm not sure what I should be aiming for balance wise. As i've said,any suggestions or ideas you have would be great, changing springs takes minutes so i'm prepared to spend my first few days swapping them around, what I need is a good starting point

 

[jimbro1000]

The problem is that without knowing your corner weights you are only ever going to be guessing.

If you're on asphalt and using slicks you need to keep the spring rates pretty high. With the suspension lowered the roll centres should be low enough that it corners flat as you like. Just making the suspension stiff isn't going to stop the roll though, you need to keep the CoG low (as I'm sure you already know). The trick is get the suspension working rather than just so stiff it is basically just locked up.

I ran a fair bit of camber on the back of mine with a variety of spring rates - I have a box full of different rates. I confess that I never quite got mine where I wanted it to be but it was a great compromise between wet and dry setups (possibly better in the wet than it should have been on the balance of that equation).

The thing with the front is that you also have the extra thrust bar and this adds to the effective spring rate even if only by a a little. There is no easy way to alter the spring rate on these unless you find some stiffer rubber bushes.

 

[Eoin611]

Thanks for the feedback, decided to go with the 250lb at the back and going to go with my gut feeling and try 180lb in front. It'll be a start if nothing else, should be on the track in a few weeks. Adaptor plate to make first. Will post how it works out, might be of use to someone else.

 

[Eoin611]

Have raced the car a few times now and seem to have found the spring rates that work. 220lb in the front and 400lb at the back seems to tick all the boxes for the track I'm racing on. Restrictions on standard gearboxes mean no LSD but have had no issues with inside rear wheel lifting and spinning. I did encounter this when using a 160lb spring in front. Front end remains perfectly level when cornering, the 250lb was a tad stiff and led to slight understeer at times. Softening it by 30lb now means the front of the car does exactly what's needed, tucks in nicely and stays there.
Two adjustable AVO shocks in front and two Konis at the back have also helped.

 

[jimbro1000]

Have you considered using a viscous coupling off a coupe instead of an LSD?
It gives a similar effect, if not quite as dramatic - or are these precluded as well?

Nice job on the spring rates - I'll bookmark this thread and if I ever get mine back on the track I'll let you know how it compares.

The problem is the labels for my different spring pairs I have seem to have gone missing at some point so I need to get them measured - oh the joys...

 

[Eoin611]

I had measured all the springs at home and carefully labelled them all. By the time I came back to use them they were all mixed up in a box and there wasn't a label to be found. Used a hydraulic press, a bathroom scales and a ruler to fix it. Compressed each spring an inch and checked to see what reading appeared on the scales.
Have thought of using the Coupe 'box, might try it and wait for a scrutineer to realise what I'm doing. If any other tips for racing one of these cars comes to mind keep me posted, next step is tune the Punto 1242 16v engine. Thanks again for the feedback.