Slimy38
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| posted on 5/2/26 at 04:31 PM |
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Changing design weights
After my IVA fail, I've got the mechanical bits scheduled for the next couple of weekends. But I wanted to make a swift start on one issue, which
is the design weights. I put 361Kg for axle 1 and 409Kg for axle 2, for a combined gross weight of 770Kg. They calculated it at 331Kg axle 1 and 430Kg
axle 2, 762Kg combined. To be honest I'm impressed how close I was, but obviously having my design weight lower than actual is the kicker
here.
How do I change the design weights? One thing I was looking at said put the new weights on the manufacturer plate, does that override the values on
the application form? I did the form electronically so I am expecting to have to make the change either by email or by snail mail.
I've sent an email to approvals@dvsa.gov.uk who were looking after my initial application, is that a reasonable place to start?
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Slimy38
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| posted on 6/2/26 at 07:57 AM |
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Well, I started this morning with an email in my inbox saying that they've made the changes. There was me thinking it was going to be an uphill
battle with all sorts of evidence and letters to submit, and instead it was 'yep, all done, fix the other defects and submit it for a
retest'.
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JAG
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| posted on 6/2/26 at 08:00 AM |
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Hmm DVSA being helpful, it sounds like a trap to me 
...but if it's fixed then that's good news, probably 
Justin
Who is this super hero? Sarge? ...No.
Rosemary, the telephone operator? ...No.
Penry, the mild-mannered janitor? ...Could be!
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Slimy38
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| posted on 6/2/26 at 09:23 AM |
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quote:
Originally posted by JAG
Hmm DVSA being helpful, it sounds like a trap to me
...but if it's fixed then that's good news, probably
LOL, it's not just me with that mindset then, I'm now worried that it was far too simple and it'll fail the retest on a technicality! I
have the email though so I'll print it and take it with me.
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gremlin1234
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| posted on 6/2/26 at 09:52 AM |
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that is good,
I thought most people put weights as 450/450/900 to give flexibility.
weights are used for tyre suitability, braking performance,
and I can't think of anything else
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JAG
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| posted on 6/2/26 at 11:19 AM |
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quote:
I have the email though so I'll print it and take it with me
A very wise move IMHO
Justin
Who is this super hero? Sarge? ...No.
Rosemary, the telephone operator? ...No.
Penry, the mild-mannered janitor? ...Could be!
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russbost
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| posted on 6/2/26 at 11:27 AM |
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What have you changed it too? In your other message you mentioned weights in the low 400's (Kg), the design weight (Max DGW) is the total weight
of car full of fuel luggage & passengers & should then have a bit more added to give "headroom", but you don't want to go too
high or it will fail on brake test!
I would get advice from the actual manufacturer HTH
I no longer run Furore Products or Furore Cars Ltd, but would still highly recommend them for Acewell dashes, projector headlights, dominator
headlights, indicators, mirrors etc, best prices in the UK! Take a look at http://www.furoreproducts.co.uk/ or find more parts on Ebay, user names
furoreltd & furoreproducts, discounts available for LCB users.
Don't forget Stainless Steel Braided brake hoses, made to your exact requirements in any of around 16 colours.
http://shop.ebay.co.uk/furoreproducts/m.html?_dmd=1&_ipg=50&_sop=12&_rdc=1
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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Slimy38
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| posted on 6/2/26 at 02:40 PM |
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quote:
Originally posted by russbost
What have you changed it too? In your other message you mentioned weights in the low 400's (Kg), the design weight (Max DGW) is the total weight
of car full of fuel luggage & passengers & should then have a bit more added to give "headroom", but you don't want to go too
high or it will fail on brake test!
I would get advice from the actual manufacturer HTH
I'm classed as the manufacturer on this one 
I've put it as 400Kg for the front and 500Kg for the rear. That's what the examiner suggested, I asked whether the brake test would need to
be redone and he said no.
I think that 'not wanting to go too high' was what scuppered me, I was trying to be decently accurate but without having decently accurate
scales.
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gremlin1234
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| posted on 6/2/26 at 02:57 PM |
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quote:
Originally posted by Slimy38
I've put it as 400Kg for the front and 500Kg for the rear. That's what the examiner suggested,
yep sensible figures ;-)
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Slimy38
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| posted on 7/2/26 at 03:03 PM |
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OK, I think I've made another cock up on numbers...
My braking effort with the current DGW of 770Kg is 66.88% and a pass. If I understand that percentage, it means I have a braking force of 515Kg.
I've changed the design weights to 400/500, for a total of 900Kg. If I work out the braking efficiency, assuming the same braking force of 515Kg,
I end up with an efficiency of 57%. That's lower than the 60% threshold.
However the form also includes the fact that both front wheels locked, so in theory the braking effort is then more about tyre traction rather than
actual braking effort.
The IVA says 'The service brake performance must be at least 60%, (of the CLW or DGW as determined to be the highest) or more than half the
road wheels lock.'.
Do I need to reduce the design weight to get to 60%, or will the wheels locking be the deciding factor here?
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russbost
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| posted on 7/2/26 at 04:16 PM |
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If you achieve lockup on an axle you've effectively reached max brake force on that axle, the limit being made by tyre adhesion NOT brake
efficiency, so you don't need to worry about brake efficiency (which I think you said they weren't retesting anyway?)
Good luck with the retest
I no longer run Furore Products or Furore Cars Ltd, but would still highly recommend them for Acewell dashes, projector headlights, dominator
headlights, indicators, mirrors etc, best prices in the UK! Take a look at http://www.furoreproducts.co.uk/ or find more parts on Ebay, user names
furoreltd & furoreproducts, discounts available for LCB users.
Don't forget Stainless Steel Braided brake hoses, made to your exact requirements in any of around 16 colours.
http://shop.ebay.co.uk/furoreproducts/m.html?_dmd=1&_ipg=50&_sop=12&_rdc=1
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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Slimy38
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| posted on 7/2/26 at 04:23 PM |
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quote:
Originally posted by russbost
If you achieve lockup on an axle you've effectively reached max brake force on that axle, the limit being made by tyre adhesion NOT brake
efficiency, so you don't need to worry about brake efficiency (which I think you said they weren't retesting anyway?)
Good luck with the retest
Ah awesome, that's what I was hoping for And yeah he did say he wouldn't repeat the brake testing.
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Mr Whippy
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| posted on 7/2/26 at 04:51 PM |
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quote:
Originally posted by russbost
If you achieve lockup on an axle you've effectively reached max brake force on that axle, the limit being made by tyre adhesion NOT brake
efficiency, so you don't need to worry about brake efficiency (which I think you said they weren't retesting anyway?)
Good luck with the retest
When I originally built my beach buggy I had a hell of a time passing the brake test as it was just too light at the front, even with him sitting on
the front bumper bar it kept just locking up, I could actually lift the front off the ground. In the end he just took it for a test drive with a
portable brake tester in the footwell, said it was a death trap but still passed it.
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gremlin1234
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| posted on 7/2/26 at 06:07 PM |
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don't change it again,
it's now what they recommended, (and quite normal) and they said the break test does not need to be repeated.
no need to change.
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