Curing understeer !!?

[AlistairCoker]

Hi chaps,
I've had an SR3 for 3 yrs and the car never suffered from understeer. However, I was going through splitters so quickly I increased the ride hide slightly (about 3 turns) and at the same time went from avons to dunlops. The car is horrible now, massive understeer. The front splitter now rides a little higher but I've already scraped the lip away. I can't believe it's an aero thing though and I can't really lower the car any more as or I will completely ruin the splitter.

I don't know much about setting the car up regarding toe-in/out, etc but I haven't touched any of those settings anyway so I am a bit confused.

Can anyone suggest what I can try to cure understeer ?

Cheers
Ali

[splitpin]

Were the Avons radials or crossplies?

Either way, sounds like you may well be way way overdue on flat patching, camber & toe and indeed, damper condition checks; also perhaps bushes and rod ends?

[ScottHughes]

When you raised the front you should have also raised the rear at the same time otherwise you would have sent weight to the back and off the front wheels reducing grip and hence promoted understeer. The back should ride higher then the front slightly about 5mm.

[lanan]

Ali,
I have sent you an email which bounced back saying that you were away untill Feb 8th....!!.....That's a hell of a holiday..!!

Graham

[AlistairCoker]

Thanks for all your feedback. I didn't think about raising the rear too and the understeer coincides with raising the front last summer. I will raise the rear and see if that helps before changing camber settings, etc, cheers guys.

[splitpin]

Sounds like that was a good bit of 2 + 2 = 4 work from our Scott

When you check the ride height, do it on a nice flat surface (like a pit garage), driver seated (or both seats occupied if you normally run two up) and about three gallons of fuel on board. Get the checker to bounce on front and rear to fully settle it back down if it's been up on a quick lift to adjust. Some shocks also need to be centred back into their retainer seats as they can drop out of line when the wheels have dangled - watch your fingers!

PS Like Graham, I got on holiday auto-reply; like he said, darn good holiday that one ........... have fun

Edited by splitpin on Friday 19th March 21:08

[Simon T]

You cant change the weight distribution from side to side or front to rear by changing the ride height, you have to phsically move weight around to do that. You can only effect the cross weights by adjusting the spring platform height or pushrod length, if this moves the cross weight away from 50/50 you will notice more understeer in one direction than the other

your understeer may be caused by a change in airflow under the car but is most likely that the Dunlops need more negative camber and toe out than the Avons to get them working properly, what is your front camber/ Toe set to?

Simon

Edited by Simon T on Saturday 20th March 11:20

Edited by Simon T on Saturday 20th March 11:23

[splitpin]

Absolutely Simon, totally spot on, but I do think that by raising the ride height appreciably (as it sounds) just on the front, compared to the rear springs, Ali may well have compressed his front springs quite a fair amount and introduced the front and rear seriously imbalanced effect, whereby the front feels hard, skippy and edgy i.e. the dreaded 'can't feel what's happening' front end pogo stick effect?

With the amazing braking performance a Radical can achieve, we can all agree that a nose high attitude is not a nice place to be?

[Simon T]

depends if its on pushrods or not and if there was any droop in the front before adjustment... Three turns on the spring colars is about 5-6mm ride height increase if there was any droop, if not its about the right level of preload for a diffuser clad car. My bet would be the switch to the Dunlops had much more impact than the ride height adjustment.

Easy to check. Return ride height to original first and see if it goes back to original performance.

Simon

(BTW. Not sure what the braking force has to do with the front being highter?)

[AlistairCoker]

Not sure how to measure toe settings but just had a look and there is a fair degree of negative camber and the tyres are certainly wearing a lot faster on the inside and there seems to be almost no wear on the outside, could too much negative cambergive understeer ?? Even then I haven't messed withe the camber settings so that doesn't make sense. Can't really redcue ride height to check cos it knackers the splitter, having real trouble with the riveted prongs that the bonnet slots onto, the rivets keep coming lose and then the whole bonnet droops.

[SportsLibre]

Simon T said:

My bet would be the switch to the Dunlops had much more impact than the ride height adjustment.

Can't comment on the tyres, but raising the front without a corresponding rear increase would definitely induce understeer on a clubsport.

Also, due to the nature of the Nik Link there is no droop on the front as each side seams to hold up the other on the preload, or at least that is how it appeared when I jacked up mine the other day.

Edited by SportsLibre on Saturday 20th March 20:32

[lanan]

Simon T said:

You cant change the weight distribution from side to side or front to rear by changing the ride height, ...... You can only effect the cross weights by adjusting the spring platform height or pushrod length,]

Sorry Simon, But yes you can..............and as you say, you do it by raising the spring platform or pushrod, which raises the ride height and hence redistributes the weuight.

[LCM]

lanan said:

Simon T said:

You cant change the weight distribution from side to side or front to rear by changing the ride height, ...... You can only effect the cross weights by adjusting the spring platform height or pushrod length,]

Sorry Simon, But yes you can..............and as you say, you do it by raising the spring platform or pushrod, which raises the ride height and hence redistributes the weuight.

Sorry to be pedantic, but Simon's right. You can't change the static weight distribution simply by changing overall ride height BUT you can by changing relative ride height - either at one end (rake) or one side (cant) [ps, that's cant not can't or even Kant] or indeed both.

There again, considering the ontological implications of this discussion, perhaps it is Kant

pps It's good to see you considering the metaphysics of the Niklink by means of empirical exploration, Angus. I am sure that you will be more fulfilled when next our cosmic paths intersect

[BertBert]

lanan said:

Simon T said:

You cant change the weight distribution from side to side or front to rear by changing the ride height, ...... You can only effect the cross weights by adjusting the spring platform height or pushrod length,]

Sorry Simon, But yes you can..............and as you say, you do it by raising the spring platform or pushrod, which raises the ride height and hence redistributes the weuight.

I'm with Simon on this one. I think the effect that the ride height change has is akin to changing weight distribution which is why grizzled old race engineers talk about it in those terms. However simple physics shows that a raise of the front only has a miniscule effect on the actual distribution of weight.

Bert

BTW just to be clear before I get a load of GBH from Graham, by grizzled I of course mean highly experienced.

[LCM]

BertBert said:

lanan said:

Simon T said:

You cant change the weight distribution from side to side or front to rear by changing the ride height, ...... You can only effect the cross weights by adjusting the spring platform height or pushrod length,]

Sorry Simon, But yes you can..............and as you say, you do it by raising the spring platform or pushrod, which raises the ride height and hence redistributes the weuight.

I'm with Simon on this one. I think the effect that the ride height change has is akin to changing weight distribution which is why grizzled old race engineers talk about it in those terms. However simple physics shows that a raise of the front only has a miniscule effect on the actual distribution of weight.

Bert

BTW just to be clear before I get a load of GBH from Graham, by grizzled I of course mean highly experienced.

One man's miniscule is another man's minuscule is another man's larva: http://www.youtube.com/watch?v=MleXPVxLGX0&fea... .................

Roll centres anyone?

[Martin B]

LCM said:

Roll centres anyone?

Go on then, I haven't got round to plotting this out yet but I'm sure you have, what height and how static are they throughout the suspension travel?

Thanks

Martin

[AlistairCoker]

Just checkesd ride height and it is 5 turns from the bottom on the front and 14 turns on the back so it already seems the front is far lower than the back. I guess its not a ride height issue. Seems strange that the avons were fine, it seems to be since I changed to dunlops. Also forgot to mention, it is much worse in slower speed corners ??

[lanan]

LCM said:

lanan said:

Simon T said:

You cant change the weight distribution from side to side or front to rear by changing the ride height, ...... You can only effect the cross weights by adjusting the spring platform height or pushrod length,]

Sorry Simon, But yes you can..............and as you say, you do it by raising the spring platform or pushrod, which raises the ride height and hence redistributes the weuight.

Sorry to be pedantic, but Simon's right. You can't change the static weight distribution simply by changing overall ride height BUT you can by changing relative ride height - either at one end (rake) or one side (cant) [ps, that's cant not can't or even Kant] or indeed both.

Sorry LCM but Simon didn't say " You can't change the static weight distribution simply by changing overall ride height"....He said You cant change the weight distribution from side to side or front to rear by changing the ride height"...Which is as you agree not the case.....

[Martin B]

Are you talking about static or dynamic weight distribution? From the way I see it, static weight distribution has nothing to do with ride height, whereas dynamic weight distribution is another matter and will take into account roll centres, CofG height, spring rates, roll bar stiffness, anti dive/squat geometry, tyre pressures/loading etc.

Or have I got it wrong (it wouldn't surprise me)?

Also, I thought that lengthening or shortening the wheelbase was the way to alter front/rear weight distribution (other than moving the weight around the car of course)

Martin

Edited by Martin B on Sunday 21st March 10:34

Edited by Martin B on Sunday 21st March 11:32

[lanan]

Maybe I didn't explain myself correctly. Never was my strong point..
What I was clarifying was.
Eg.
If you raise the RR spring platform 2mm.
You have raised the rear ride height, mostly the RR and you have moved weight.Increase LF & RR and decrease RF & LR.

Therefore you can alter weight distribution by raising ride height.

I didn't mean raise the car equaly, which would probably require a 1m rear ride height to see a difference..