INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Jobs

Increasing Comfort

Increasing Comfort

(OP)
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.

RE: Increasing Comfort

I would expect that change in tyre size to make no discernible difference, at least no more than a change in tyre construction even at the same size.

At a wild guess I would say you are American as Americans and Europeans tend to have different expectations regards ride and handling, so buying a European car would probably be disjointing unless you where prepared to accept the firm feel. Buying a car without a real good test drive on various surfaces is just plain nuts, but I guess you already know that. Personally I like to find a similar car a year or so old if possible to really test. it how it will be for most of its life, but I guess you already know that now.

Within reason your best result will come from lowering tyre pressure and or using a soft sidewall tyre and a rib tread rather than a block tread design with lots of little cuts in the tread ribs to let them flex, and using a rim tyre combo where the tyres are not undersized for the rim or stretched, ie the tread should be a little wider than the bead of the rim.

Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
http://eng-tips.com/market.cfm
for site rules
 

RE: Increasing Comfort

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

I'm a bit surprised, typically French cars have rather plush suspensions.

I really would try dropping the tire pressure. Changing tire sizes is a step in the right direction, but you've only gained half an inch in sidewall height, not really a huge difference in stiffness, given that most of the vertical spring rate is supplied by the air.

When you hit a small bump is it the sound or the feeling through the seat or what exactly are you objecting to? Is it worse when the back wheel hits?


 

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies  http://eng-tips.com/market.cfm?

RE: Increasing Comfort

(OP)
Thank you for your answers...

As same of you may know I'm a member of an LPG association, so I confess I was more focused on the engine, because I wanted to test how the new downsized and turbocharged European engines behave on LPG.

patprimmer,

the idea of decreasing wheels diameter and increasing tire height was precisely to have more "air and rubber" between the wheels and the road. Decreasing tire contact area with the road should help minimize the chance of finding small irregularities on the road(at least that was my reasoning).

No I'm not an American, I'm European, but I have some of the Americans likes, like more comfort than handling, and more torque than power.

Greg Locock,

You are at least as surprised as I am, but believe me this car hasn't a typical French suspension, I think this could be the result of an attempt to avoid the moose test Class A syndrome, since this car has similar shape and size as the Mercedes.

I only gained half an inch in sidewall height, but I have legal limitations to the size of tires I can use, so I can't go further than that.

I'm thinking in changing suspension, so if you could help me with my initial question that would be appreciated...  

Thank you,

John     

RE: Increasing Comfort

until you tell me what the actual problem is I can't really advise you

When you hit a small bump is it the sound or the feeling through the seat or what exactly are you objecting to? Is it worse when the back wheel hits?
 

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies  http://eng-tips.com/market.cfm?

RE: Increasing Comfort

Hi John,

What make, model, and size tire in on there now?

And I'm interested in what Greg L has to say too.

Dan T

RE: Increasing Comfort

(OP)
Sorry,

GregLocock, I missed that one...

What I feel is vertical movements, on good roads, where there isn't any visible irregularity...

They are random, and happened with the old wheels and tires too, so I don't believe it is a malfunction, I think it's a hard suspension design problem.

Strangely it behaves rather well in bad roads, that is not so harsh as you could expect from its behavior on good roads.

You "feel" to much the road in good roads


Tmoose, the tires are Michelin Energy Saver 175/65/R15 88H  

RE: Increasing Comfort

Odd, but I'm not finding that size in either A/S of LX4 through Tire Rack.  But it's likely that European size availability differs a bit.

The thing that does catch my eye is the 88 vs 84 load index.  That suggests that you have a reinforced tire capable of carrying greater loads and possibly higher inflation pressures.  Such tires would tend to ride a bit more harshly than the same size in a standard load configuration.

Why wouldn't you have gone to a 185/65-15 (for a little more sidewall height and width/sidewall bulge for slightly more vertical compliance)?


Norm

RE: Increasing Comfort

(OP)
NormPeterson, you wrote: "Why wouldn't you have gone to a 185/65-15"

That would change tire diameter and I can't legally do it...

Besides this is the second set of wheels/tires and I don't think I can solve this only changing tires.  

RE: Increasing Comfort

I seem to have lost the plot here. Well is not my area anyway so my knowledge is more casual observer obtained, but I initially thought the complaint was low amplitude high frequency intermittent, like joints in a concrete surface road.

Now I am feeling it is long term undulation or low frequency high amplitude or like a boat in a swell rather than a boat in a short sharp chop.

If the former, I see tyres playing a large part, especially tread and sidewall hardness and maybe it is also rubber bush dependent to some extent.

If the latter I see it as being almost tyre irrelevant and heavily shock absorber dependent and at a SWAG, I would think, soft compression and firm rebound, but like I say, not my area and personally I like relatively short firm ride with moderately firm compression and really firm rebound control and that always sways my thinking toward what I like.

Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
http://eng-tips.com/market.cfm
for site rules
 

RE: Increasing Comfort

(OP)

Greg Locock, I'm thinking in a shock retune or in buying a frequency selective damping shock absorver. However, I thought it should be wise to change both, shocks and springs. That is in changing spings and tune shocks.

patprimmer, low amplitude high frequency intermittent is a good way to describe it, only you don't need a concrete road to feel it.

Greg, so should I try a shock retune without changing springs?

RE: Increasing Comfort

Well to be honest I don't think the problem is well enough described for me to make any hard and fast recommendations, but my gut feel is that you don't have a primary ride issue so spring changes are unlikely to be helpful. If you change springs you'll need to change shocks anyway so you might as well buy some adjustable shocks and have done with it.

You might try removing the sta bar as well, it could be that you have excessive roll stiffness. The car will be very rolly on corners, be careful.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376 http://eng-tips.com/market.cfm?

RE: Increasing Comfort

To be honest to me it still sounds like softer tyre tread and sidewall and softer bushes, rubber spring seats or whatever will filter out low amplitude before it transmits to the spring The closer it is to the impact, the quicker the reaction time to the impact, but once again, not my area so I am shooting wildly in the dark.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
http://eng-tips.com/market.cfm
for site rules

RE: Increasing Comfort

Incidentally the actual underlying problem may not be shocks or springs or even tires.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376 http://eng-tips.com/market.cfm?

RE: Increasing Comfort

Could it be seats?

Could it be static friction in bushes or shocker shafts?

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
http://eng-tips.com/market.cfm
for site rules

RE: Increasing Comfort

Could it be unsprung weight to high for the weight of the car. ie light car, heavy wheels?

I am curious about Gregs question about front to rear influence.Is that suspicions about resonance in the chassis?

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
http://eng-tips.com/market.cfm
for site rules

RE: Increasing Comfort

No, typically the two suspensions are quite different in architecture and tune and it is common for one end or the other to be the main source of trouble.

It could be seats. It could be lots of things. It certainly sounds expensive.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376 http://eng-tips.com/market.cfm?

RE: Increasing Comfort

It certainly sounds like a full development program to sort out. It might be cheaper to change cars rather than try to fix it.

Letting air out of the tyres sounds the easiest if somewat basic solution.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
http://eng-tips.com/market.cfm
for site rules

RE: Increasing Comfort

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.

RE: Increasing Comfort

(OP)
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

RE: Increasing Comfort

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
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
http://eng-tips.com/market.cfm
for site rules

RE: Increasing Comfort

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

RE: Increasing Comfort

(OP)
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

RE: Increasing Comfort

I would try about 2.0 bar and 1.8 bar

Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
http://eng-tips.com/market.cfm
for site rules

RE: Increasing Comfort

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


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Increasing Comfort

(OP)
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?

RE: Increasing Comfort

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

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Increasing Comfort

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
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
http://eng-tips.com/market.cfm
for site rules

RE: Increasing Comfort

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.

RE: Increasing Comfort

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
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
http://eng-tips.com/market.cfm
for site rules

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close