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Knowledge Base - How To:- Fit Rear Wide Arches

This guide will help those wanting to fit our wide arches. It will also help massively if you are using any other type of arch or bodykit. Mk1 rear arch rot is a big problem, so going for a fibreglass wide option can be a good way to repair and cure the rot problem for good...anyway I hope its useful to someone.

The car in question is a mk1 v6 we built last year, the owner wanted a pair of wide arches to the rear and also a way to make the factory sideskirt fit like it would have done had Toyota done a wide arch version.

Ok I started by making sure the rear wheels were aligned properly, this is VERY important! Both tracking AND camber angles have to be spot on.
I used my camber gauge to check it and I found the passenger wheel had too much negative camber, which would make the wheel arch about 20mm narrower on that side. So it's imperative that you get the wheel geometry perfect before even attempting this.
After adjusting the camber to get both wheels sitting as good as possible you then need to determine how wide you want to go. Some wheels have huge offsets and big dishes on them, so don't really need any spacers but these wheels although already dished did need a little spacing to make the arch look fuller. So before I went any further some longer wheel studs where added....

These allow a 25mm spacer,which will then make this particular wheel stick out this much....

We are not going wild width (well not wild for us anyway!) on this car due to the fronts staying standard so this will be plenty while still giving the wide arch look we love. The arch can be trimmed right down to be only 1" wide if need be.
The next job is to place masking tape on the body just around the arch line, this is to give us reference points for measuring where to cut the new arch and by how much....

Take some very rough measurements (within 20mm will do) of the needed arch width at 4 or 5 points around the circumference....
Then place a wide strip of masking tape on the new arch to "catch" the area we are about to cut.... if you mess this up just add more tape.

Now we are going to mark out some datum points, I start with one line drawn at 12 oclock and then make several at various points on the radius where I think the arch distance is changing..... make the same marks at approximately the same place on the new arch....

Now the method of measuring exactly how much arch to cut away from each datum point is as follows.... obtain a straight edge, about a meter long, I use a plank of wood but anything straight will do, place this on both edges of the tyre and then measure from your quarter panel on each datum point to the straight edge.....

 

Transfer this measurement to the new arch at each datum point and then join them up with a solid line, the more datum points you use the more accurate it will be, but I find 5 or 6 ample....

Then get the grinder out and cut along your line,stay on the inside egde if you are unsure.... you can always remove more!
What you end up with is this... I've taped it to the car to assess the fit...

It might take a few goes with a little more measuring and trimming but it will get there eventually, take your time!

Now we aren't going to talk about securing the arch to the car just yet, for now I have bigger fish to fry!
Making the bespoke sideskirt section.
What I've done here is cut the original triangle so that it is in two sections,one part sits just before the arch and the other bit sits around the arch lip....

Cover the arch in masking tape on the empty area between the two parts of skirt.
Then apply a good thick layer of fibral into this void joining both sections back together.... we are just going for structure here, it doesn't need to be particularly pretty at this stage.... this is going to be a detachable panel just like the original triangle with a rubber seal on it and everything.

After a few more skims of fibral and a bit of profiling we have this....

 

This section will now peel off the arch and can be hand finished later on, we think it should look almost OEM when done.
The rear part of the arch has also been trimmed and profiled to suit.

The next step is to mark a line where the arch meets the bodywork...

Then cut the outer arch lip away to just leave the slope... then make many slices in the slope right up to the line, we will then bend these tabs outward to give the arch a good surface to bond onto.....

There was quite a lot of filler in these arches so I had to grind that away.
Bonding of the arch will happen tomorrow, for now I did the other side as well,which is a lot easier becuase you dont need to repeat the whole process of doing the first, just mark out the measurements you cut on the first arch and mirror them onto the new arch, takes all of 20 mins to do the second one....

The arches have now been blended and several coats of spray can primer added just to keep an eye on how its progressing, its very hard to judge the blend when its all different colours so priming it as you go helps a lot....

The sideskirt triangles are now completed....

 

 

The arches themselves have now had a thick high build primer layer, just happens to be white which will help with coverage on the final top coat of paint....

 

 

 

 

Here are the new triangles trimmed with a rubber seal and fitted, now tell me that doesn't look like an OEM fitment....

 

 

New arch liners were made, these are just thin strips of aluminium that bridge the gap between the cut wheel arch inner and the new outer arch...

This is bonded into place with Polyurethane and allowed to cure forming a totally water tight seal under the arch lip.
And finally .......... the finished job....

 

 


Paul Woods
3/9/2009


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Created : 2011-06-18 14:57:48, Last Modified : 2011-06-18 14:57:48

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