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Author: Subject: Raw striker scrub radius
martinnitram

posted on 5/8/18 at 10:01 PM Reply With Quote
Raw striker scrub radius

Does anyone know what the ideal scrub radius should be on a IRS striker.

Mine has around 85-90mm of positive scrub, I ran a straight edge along the upper and lower ball joints and marked the floor before putting wheel back on and measuring to centre of tyre.

Its running escort uprights with alloy hubs which are +10mm wider than standard and wheels are ET24 offset.

Reason for asking is the rough road handling is twitchy and nervous and running out of ideas.

Regards
Martin

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adithorp

posted on 6/8/18 at 12:27 PM Reply With Quote
Have you checked the bump steer? There's a thread somewhere on the JPSC club forum where someone altered the rack position and cured it.

Here it is...
https://jpsc.org.uk/forum/viewtopic.php?f=4&t=307&p=1773#p1773

[Edited on 6/8/18 by adithorp]





"A witty saying proves nothing" Voltaire

http://jpsc.org.uk/forum/

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martinnitram

posted on 6/8/18 at 05:29 PM Reply With Quote
Interesting link thanks.

No not tested bump steer properly. I'm having the alignment and corner weights checked in a just over a week so ill ask them to check it properly then.

Looking at the arms they appear spot on straight with each other.

But going back to the scrub radius, im wondering how much difference the 10mm extended hubs make to the handling, I cant compare before and after as it was such a pig before I changed to the current escort uprights and hubs it's actually an improvement from what it was.

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phelpsa

posted on 6/8/18 at 07:10 PM Reply With Quote
90mm is quite a lot but not excessive (our locost had a lot more). More likely to be bump steer.
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martinnitram

posted on 7/8/18 at 08:25 PM Reply With Quote
I contacted Raw today and had a helpful chat with Martin and he gave me some pointers with the geo and general settings and spring rates that they recommend for a road going striker.
Recommended spring rates are 180lb all round
and frame alignment no more than 5mm out.


So this afternoon ive been checking a few more areas to see whats going on
Had the springs out and checked the poundage, they have 180 just visible written on them, checked on scales and they are round about that rate.

While springs were off checked for bump steer and found no more that 10ths of a mm over the full droop to full compression.


Strung car out again checked frame alignment and toe front and rear again and seems fine, i set it to 1mm toe in all round and 1 deg of camber all round. Raw recommend a different setting of 1mm toe out front, 2-5mm toe in rear.


Ride height is close to what Raw recommend

Castor is recommended 5 deg, this i cant check with much accuracy other than eyeball it and there is some there.

Ill just have to wait until i get the geo set to the Raw settings, if that makes no difference then it can only be the scrub causing the wandering.

Open to all suggestions

Regards.

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martinnitram

posted on 3/9/18 at 03:28 PM Reply With Quote
More improvement made

Had the RAW alignment settings done properly and has made noticeable difference to handling on uneven roads and particularly at high speed.

But still not as good as i hoped, so went back to the king pin inclination / scrub radius idea, a friend of mine has the same wheels on his RS turbo 195/50/15, and being a front wheel drive has more positive offset, about 13mm difference, these immediatly made the steering lighter and tracked even better at speed.
Bumpy road handling also improved again, wouldn't describe it as great, but these cars can't be expected to cover ground in the same way as a Subaru or fast hatch would so not sure how much more i can expect.

So now ive proved my idea the plan is to get new front wheels with more positive offset than i think i need and then space it, and remove spacers until no more improvement can be gained.


Always open to other suggestions.

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martinnitram

posted on 15/9/18 at 07:39 PM Reply With Quote
Result.

Finally got some new wheels on the front
Went for ET40 in the end which gives me about 40/45mm of scrub, and has worked a treat, really calmed the twitchy front end down and seems to suit the escort uprights.
I am on the limit now of clearance on full lock, mudguards to side panel but nothing touching.

So as simple as that in the end.

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AdamR20

posted on 16/9/18 at 07:42 AM Reply With Quote
Interesting to hear your results, thanks for sharing!
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