Increasing Comfort

[rdd48856]

I bought a Renault GrandModus without doing a test drive and I’m very unpleased with its comfort in good roads.

I'm talking about feeling all the small bumps and holes, which could be very annoying in Highway driving.

I already changed my wheels from 16” to 15”, and my tires from 185/55 R16 to 175/65 R15. It improved a little, but not significantly.

Now I'm thinking in changing my springs for softer ones and adjust my shock absorbers.

On the safe side how much can I decrease my springs K?

Thank you.

 

[Tmoose]

For my last millenium old tech vehicles an extra 2 or 3 psi sometimes brings a noticeable increase in harshness. (I'm still confused about the ride quality complaint). Before buying more parts I'd Maybe test drive a few other examples and subject my tire pressure gauge to a grand jury investigation. I do remember my Renault 16 fondly, in no small part for the way it dispatched twisted frost heaved New England secondary roads.

 

[rdd48856]

O.K., Thanks,

I must confess I never thought tuning suspension could be so difficult...

I tuned all my previous cars, but mostly engine and electronics, never suspension...but I'm not ready to give up so easily.

But for now let's talk about tire pressure...I don't have a recommended pressure for this size of tires, only for the old ones. (It's funny this size of tires is permitted by Renault, but not even Renault itself can give me the recommended pressure).

I'm using the recommended pressure for the 185/60 R15 tires. Is there a pressure conversion formula when you change tire profile?

Thanks again.

Tmoose I'm ready to give you all the input you need, just ask...

John

 

[patprimmer]

What pressure are you using.

Once again selecting pressure is a black art and varies according t0:-

Tyre size.
Tyre construction.
Rim size.
Weight on wheel.
Operating speed.
Manner of operation.
Road surface.
Suspension geometry
Drivers preference re comfort, traction, handling, durability, fuel economy trade-offs.

You need them hard enough so they won't pull off the rim bead or overheat.

If you go soft for comfort you will sacrifice precise handling and stability, tyre life (maybe, depending on actual pressure) and fuel economy


Regards
Pat
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[rdd48856]

Recommended pressure for 185/55 R16 - In Highroads 2.5bar - Front; 2.0bar - Rear;

 

[rdd48856]

Sorry,

Renault recommended pressure for 185/55 R16 - In Highroads 2.5bar - Front, 2.0bar - Rear; Outside Highroads 2.4bar - Front, 2.0bar - Rear.

I'm using, with 175/65 R15, 2.4 bar - Front; 1.9 bar - Rear;

I never thought this could involve so much "black art"...

Thank you,

John

 

[patprimmer]

I would try about 2.0 bar and 1.8 bar

Regards
Pat
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[GregLocock]

Strictly speaking it isn't a black art for the most part, but proper ride work needs instrumentation and experience. The alternative, bunging new bits on and seeing what seems to help, is expensive, if educational. Where it gets interesting is that inevitably things you'd like to do to improve the ride degrade the handling, so managing that tradeoff is tricky.

Cheers

Greg Locock


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[rdd48856]

Greg Locock, that leads us to my first question: how far can I go without compromising safety too much...

By the way: is there a simple way to convert recommended tire pressure when changing tire profile...can I simple use P = A/F?

 

[GregLocock]

Impossible to say without driving the car. For pressures, take a peek at a T&RA book.

Cheers

Greg Locock


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[patprimmer]

I would let them down a little at a time and see how it feels.

Find a corner where a total loss of control will give a soft landing and then lean on it real hard then inspect the sidewalls for scuffing. If they scuff up half way up the sidewall you are probably to soft for safety.

Regards
Pat
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[gt6racer2]

Guys, don't forget that the pressure also has a primary role in keeping the tire on the rim, as well as keeping tire temps at workable levels at highway speeds. Bad things can happen at low pressures.
Shocks are probably the best fix, but what to do ? In many cases smooth road/small input annoyance can be caused by too little damping allowing run on shake of the unsprung mass, and more damping in compression will actually improve the ride. Sure, the initial impact will be harder, but a single thump is less annoying. Best bet would be to get some adjustables and set them how you like.

 

[patprimmer]

They have to be really soft before you pull them off the bead.

They get to hot if to soft and close to their maximum load. It is really unusual for a car with reasonable profile height to be close to maximum tyre load rating. They will need to be really soft to overheat.



Regards
Pat
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